Radiocesium migration in the litter layer of different forest types in Fukushima, Japan.

PubMed

Kurihara, Momo; Onda, Yuichi; Kato, Hiroaki; Loffredo, Nicolas; Yasutaka, Tetsuo; Coppin, Frederic

2018-07-01

Cesium-137 ( 137 Cs) migration in the litter layer consists of various processes, such as input via throughfall, output via litter decomposition, and input from deeper layers via soil organism activity. We conducted litter bag experiments over 2 years (December 2014-November 2016) to quantify the inputs and outputs of 137 Cs in the litter layer in a Japanese cedar plantation (Cryptomeria japonica) and a mixed broadleaf forest dominated by Quercus serrata located 40 km northwest of the Fukushima Dai-ichi Nuclear Power Plant. The experiments included four conditions, combining contaminated and non-contaminated litter and deeper layer material, and the inputs and outputs were estimated from the combination of 137 Cs increases and decreases in the litter layer under each condition. The 137 Cs dynamics differed between the two forests. In the C. japonica forest, some 137 Cs input via throughfall remained in the litter layer, and downward 137 Cs flux passed through the litter layer was 0.42 (/year).Upward flux of 137 Cs from the deeper layer was very restricted, < 0.017 (/year). In the broadleaf forest, migration of 137 Cs in throughfall into deeper layers was restricted, downward 137 Cs flux was less than 0.003 (/year).Upward input of 137 Cs from the deeper layer was prominent, 0.037 (/year). 137 Cs output via litter decomposition was observed in both forests. The flux in the C. japonica forest was slower than that in the broadleaf forest, 0.12 and 0.15 (/year), respectively. Copyright © 2018 Elsevier Ltd. All rights reserved.

Simultaneous effects of leaf irradiance and soil moisture on growth and root system architecture of novel wheat genotypes: implications for phenotyping.

PubMed

Nagel, Kerstin A; Bonnett, David; Furbank, Robert; Walter, Achim; Schurr, Ulrich; Watt, Michelle

2015-09-01

Plants in the field are exposed to varying light and moisture. Agronomic improvement requires knowledge of whole-plant phenotypes expressed in response to simultaneous variation in these essential resources. Most phenotypes, however, have been described from experiments where resources are varied singularly. To test the importance of varying shoot and root resources for phenotyping studies, sister pre-breeding lines of wheat were phenotyped in response to independent or simultaneous exposure to two light levels and soil moisture profiles. The distribution and architecture of the root systems depended strongly on the moisture of the deeper soil layer. For one genotype, roots, specifically lateral roots, were stimulated to grow into moist soil when the upper zone was well-watered and were inhibited by drier deep zones. In contrast, the other genotype showed much less plasticity and responsiveness to upper moist soil, but maintained deeper penetration of roots into the dry layer. The sum of shoot and root responses was greater when treated simultaneously to low light and low soil water, compared to each treatment alone, suggesting the value of whole plant phenotyping in response to multiple conditions for agronomic improvement. The results suggest that canopy management for increased irradiation of leaves would encourage root growth into deeper drier soil, and that genetic variation within closely related breeding lines may exist to favour surface root growth in response to irrigation or in-season rainfall. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Hydraulic redistribution by two semi-arid shrub species: implications for Sahelian agro-ecosystems

Treesearch

F. Kizito; M.I. Dragila; M. Sene; J.R. Brooks; F.C. Meinzer; I. Diedhiou; M. Diouf; A. Lufafa; R.P. Dick; J. Selker; R. Cuenca

2012-01-01

Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in...

Recovery of Escherichia coli from Soil after Addition of Sterile Organic Wastes

PubMed Central

Unc, Adrian; Gardner, Julie; Springthorpe, Susan

2006-01-01

Laboratory batch tests indicate that addition of sterile municipal sewage biosolids to clay soil from four depths increases the numbers of Escherichia coli isolates recoverable in EC-MUG broth (EC broth with 4-methylumbelliferyl-β-glucuronide). This effect was most marked for the deeper soil layers, with increases of about 2.6 orders of magnitude in E. coli most probable number. PMID:16517690

Characterization of magnetically enhanced buried soil layer in arid environment

NASA Astrophysics Data System (ADS)

Petrovsky, E.; Grison, H.; Kapicka, A.; Silva, P. F.; Font, E.

2011-12-01

Magnetic susceptibility (MS) of soils, reflecting the presence of magnetite/maghemite, can be used in several environmental applications. Magnetic topsoil mapping is often used to outline areas polluted by atmospherically deposited dust. However, in these studies, the magnetically enhanced layer is usually shallow, some 5-6 cm under the surface. In our contribution, we present the case when the magnetic susceptibility is enhanced in deeper soil layers. Investigated soils are mostly sandy soils, from several localities in Portugal, in a zone with arid climate. Sample profiles were collected always in forests or forest stands with pines, cork oaks or eucalyptus trees in two areas: around the city of Sines (on the coast south of Lisbon) and around the city of Abrantes (inland, north-east of Lisbon). Both areas are presumably affected by one major source of pollution - power plant. Surface magnetic susceptibility measurements were performed by Bartington MS2D loop; values vary from 10 to 300 x 10-5 SI units. Vertical distribution of magnetic susceptibility was measured already in situ using the SM400 (ZHInstruments) on profiles about 40cm in length. Mass-specific MS was determined using Bartington MS2B dual frequency meter and Agico MFK1. Nine vertical profiles were selected for detailed analyses including the ARM, IRM and hysteresis measurements. Distinctly enhanced magnetic layers were detected in deeper horizons. This enhancement can be ascribed to several mechanisms. Migration of magnetic particles seems to be probable, as observed in our model experiments with sand columns. In coastal areas, the enhanced layer could be due to tsunami deposits, as described in other areas. Finally, in particular at sites close to power plants, the construction works followed by surface remediation have to be also considered as one of the possible mechanisms.

Impact of Native and Invasive Earthworm Activity on Forest Soil Organic Matter Dynamics

NASA Astrophysics Data System (ADS)

Top, Sara; Filley, Timothy

2010-05-01

Many northern North American forests are experiencing the introduction of exotic European lumbricid species earthworms with documented losses in litter layers, expansion of A-horizons, loss of the organic horizon, changes in fine root density, and shifts in microbial populations as a result. Some of these forests were previously devoid of these ecosystem engineers. We compare the soil isotope and molecular chemistry from two free air CO2 enrichment (FACE) forest experiments (aspen FACE at Rhinelander, Wisconsin and sweet gum FACE at Oak Ridge National Lab, Tennessee) that lie within the zones of earthworm invasion. These sites exhibit differences in amounts of exotic and native species as well as endogeic (predominantly mineral soil dwelling) and epigeic (litter and organic matter horizon dwelling) types. We investigated the impact of earthworm activity by tracking the relative abundance and stable carbon isotope compositions of lignin and substituted fatty acids extracted from isolated earthworms and their fecal pellets and from host soils. Additionally, 15N-labeled additions to the soil provide additional methods for tracking earthworm impacts. Indications of root vs leaf input to earthworm casts and fecal matter were derived from differences in the chemical composition of cutin, suberin, and lignin. The isotopically depleted CO2 used in FACE and the resulting isotopically depleted plant organic matter afford an excellent opportunity to assess biopolymer-specific turnover dynamics. We find that endogeic species are proportionately more responsible for fine root cycling while some epigeic species are responsible for microaggregation of foliar cutin. CSIA of fecal pellet lignin and SFA indicate how these biopolymer pools can be derived from variable sources, roots, background soil, foliar tissue within one earthworm. Additionally, CSIA indicates the distinct roles that different earthworm types have in "aging" surface soil biopolymer pools through encapsulation and upward transport of deeper soil carbon, and "freshening" deeper soil biopolymer pools through downward transport of surface carbon to deeper layers. Although, endogeic species burrow down below 30 cm in these systems, comparison of 13C and 15N in soil layers and fecal matter indicate their greatest impact is restricted to the upper 5 cm. As earthworm species abundance and activity are not is steady state in these forests, the role of these important invertebrates should be more considered when assessing the ability of forest soils to accumulate new plant input.

Geogrid reinforced road subgrade influence on the pavement evenness

NASA Astrophysics Data System (ADS)

Šiukščius, A.; Vorobjovas, V.; Vaitkus, A.

2018-05-01

As a result of increasing geogrid reinforcement applications in the road subgrade, there are number of projects where geogrid reinforcement is used to control road pavement evenness when there are small layers of peat or mud deeper under road construction. For this task geogrid reinforcement application is not documented but widely used in Lithuania for over a decade. This paper evaluates the long term influence of the geogrid reinforced soil influence on the road surface evenness, when the organic soils stratify in the deeper layers of the subgrade. The geological conditions of the investigated sections are reviewed. The experiment methodology and test results are described, which leads to the conclusions and insights how the pavement evenness depend on the geological conditions and its enhancement. The question is raised about the need for including this geogrid application to the normative documentation. Explanation of the problems that are encountered and the need for further research is given.

Modeling the effects of fire severity and climate warming on active layer thickness and soil carbon storage of black spruce forests across the landscape in interior Alaska

Treesearch

H. Genet; A. D. McGuire; K. Barrett.; A. Breen; E. S. Euskirchen; J. F. Johnstone; E. S. Kasischke; A. M. Melvin; A. Bennett; M. C. Mack; T. S. Rupp; A. E. G. Schuur; M. R. M. R. Turetsky; F. Yuan

2013-01-01

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw,...

Effects of different regulatory methods on improvement of greenhouse saline soils, tomato quality, and yield.

PubMed

Maomao, Hou; Xiaohou, Shao; Yaming, Zhai

2014-01-01

To identify effective regulatory methods scheduling with the compromise between the soil desalination and the improvement of tomato quality and yield, a 3-year field experiment was conducted to evaluate and compare the effect of straw mulching and soil structure conditioner and water-retaining agent on greenhouse saline soils, tomato quality, and yield. A higher salt removing rate of 80.72% in plough layer with straw mulching was obtained based on the observation of salt mass fraction in 0 ~ 20 cm soil layer before and after the experiment. Salts were also found to move gradually to the deeper soil layer with time. Straw mulching enhanced the content of soil organic matter significantly and was conductive to reserve soil available N, P, and K, while available P and K in soils of plough layer with soil structure conditioner decreased obviously; thus a greater usage of P fertilizer and K fertilizer was needed when applying soil structure conditioner. Considering the evaluation indexes including tomato quality, yield, and desalination effects of different regulatory methods, straw mulching was recommended as the main regulatory method to improve greenhouse saline soils in south China. Soil structure conditioner was the suboptimal method, which could be applied in concert with straw mulching.

Plant inputs, microbial carbon use in soil and decomposition under warming: effects of warming are depth dependent

NASA Astrophysics Data System (ADS)

Pendall, E.; Carrillo, Y.; Dijkstra, F. A.

2017-12-01

Future climate will include warmer conditions but impacts on soil C cycling remain uncertain and so are the potential warming-driven feedbacks. Net impacts will depend on the balance of effects on microbial activity and plant inputs. Soil depth is likely to be a critical factor driving this balance as it integrates gradients in belowground biomass, microbial activity and environmental variables. Most empirical studies focus on one soil layer and soil C forecasting relies on broad assumptions about effects of depth. Our limited understanding of the use of available C by soil microbes under climate change across depths is a critical source of uncertainty. Long-term labelling of plant biomass with C isotopic tracers in intact systems allows us to follow the dynamics of different soil C pools including the net accumulation of newly fixed C and the net loss of native C. These can be combined with concurrent observations of microbial use of C pools to explore the impacts of depth on the relationships between plant inputs and microbial C use. We evaluated belowground biomass, in-situ root decomposition and incorporation of plant-derived C into soil C and microbial C at 0-5 cm and 5-15 cmover 7 years at the Prairie Heating And CO2 Enrichment experiment. PHACE was a factorial manipulation of CO2 and warming in a native mixed grass prairie in Wyoming, USA. We used the continuous fumigation with labelled CO2 in the elevated CO2 treatments to study the C dynamics under unwarmed and warmed conditions. Shallower soils had three times the density of biomass as deeper soils. Warming increased biomass in both depths but this effect was weaker in deeper soils. Root litter mass loss in deeper soil was one third that of the shallow and was not affected by warming. Consistent with biomass distribution, incorporation of plant-derived C into soil and microbial C was lower in deeper soils and higher with warming. However, in contrast to the effect of warming on biomass, the effect of warming on incorporation of plant derived C into microbes was stronger in deeper soils. Thus, warming made microbes incorporate relatively more plant inputs in deeper soils, where biomass was less stimulated. This dependency on depth of impacts of warming on microbial C cycling should have important implications for forecasting potential feedbacks of soil C to climate change.

[On the effect of partial flooding on 137Cs and 90Sr in forest biogeocenosis].

PubMed

Perevolotskaia, T V; Bulavik, I M; Perevolotskiĭ, A N

2009-01-01

The analysis was made on 137Cs and 90Sr distribution oak, pine and hornbeam plantations depending on different under soil water levels. Intensity of 137Cs and of 90Sr migration along the vertical layers of soils is determined by under soil water level at a specific sampling site. The closer under soil water to the surface of the soil, the lowest radionuclide contamination is in the upper soil levels and the highest radionuclide contamination is in the deeper layers. The "fast" and "slow" quasi diffusion coefficients for 137Cs and for 90Sr and their contribution to the total migration of radionuclide through vertical soil levels were determined. A decrease in 137Cs and increase in 90Sr transfer factors to the elements of overground phytomass as a result of under soil water level lowering was established.

Leaching behavior of veterinary antibiotics in animal manure-applied soils.

PubMed

Pan, Min; Chu, L M

2017-02-01

Agricultural fields worldwide are being contaminated by the escalating application of veterinary antibiotics (VAs) via animal manure and biosolids applied as fertilizers or of wastewater for irrigation, resulting in soil degradation and damage to the health of terrestrial environments. This paper describes a series of column studies investigating the leaching behavior of five VAs, tetracycline (TC), sulfamethazine (SMZ), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), under different simulated rainfall conditions that could occur in agricultural environments. Our aim was to explore the effects of acid rain and torrential rain on the leaching of different VAs and to determine their leaching behaviors along the soil profile. The results showed that acid rain accelerated the accumulation of VAs from animal manure in surface soil while long rainfall durations promoted the downward migration of VAs in soil. Under acid rain conditions, a higher concentration of VAs remained in the animal manure. More VAs were eluted to deeper soil layers and the leachate under extreme rainfall conditions. The leachability of VAs was higher in sandy soil than in clay or loamy soil. SMZ and ERY posed a higher risk to deeper soil layers and groundwater, while NOR and TC tended to persist in surface soil, which can be explained by their different physicochemical properties in soil. Moreover, the general trends from two model assessments and soil column measurements appeared to be in agreement. SMZ had a high leachability, while NOR tended to accumulate in soils. This study provided vital insight into the persistence mechanisms of VAs in terrestrial environments and their potential risks to soils and groundwater. Copyright © 2016 Elsevier B.V. All rights reserved.

Soil organic carbon sequestration potential of conservation vs. conventional tillage

NASA Astrophysics Data System (ADS)

Meurer, Katharina H. E.; Ghafoor, Abdul; Haddaway, Neal R.; Bolinder, Martin A.; Kätterer, Thomas

2017-04-01

Soil tillage has been associated with many negative impacts on soil quality, especially a reduction in soil organic carbon (SOC). The benefits of no tillage (NT) on topsoil SOC concentrations have been demonstrated in several reviews, but the effect of reduced tillage (RT) compared to conventional tillage (CT) that usually involves soil inversion through moldboard ploughing is still unclear. Moreover, the effect of tillage on total SOC stocks including deeper layers is still a matter of considerable debate, because the assessment depends on many factors such as depth and method of measurement, cropping systems, soil type, climatic conditions, and length of the experiments used for the analysis. From a recently published systematic map database consisting of 735 long-term field experiments (≥ 10 years) within the boreal and temperate climate zones (Haddaway et al. 2015; Environmental Evidence 4:23), we selected all tillage studies (about 80) reporting SOC concentrations along with dry soil bulk density and conducted a systematic review. SOC stocks were calculated considering both fixed soil depths and by using the concept of equivalent soil mass. A meta-analysis was used to determine the influence of environmental, management, and soil-related factors regarding their prediction potential on SOC stock changes between the tillage categories NT, RT, and CT. C concentrations and stocks to a certain depth were generally highest under NT, intermediate under RT, and lowest under CT. However, this effect was mainly limited to the first 15 cm and disappeared or was even reversed in deeper layers, especially when adjusting soil depth according to the equivalent soil mineral mass. Our study highlights the impact of tillage-induced changes in soil bulk density between treatments and shows that neglecting the principles of equivalent soil mass leads to overestimation of SOC stocks for by conservation tillage practices.

Spatial 2D distribution of the proportion of soil phosphorus uptake by maize and soybean caused by tillage and fertilization

NASA Astrophysics Data System (ADS)

Li, Haixiao; Mollier, Alain; Ziadi, Noura; Messiga, Aimé Jean; Parent, Leon-Étienne; Morel, Christian

2017-04-01

Plant-available soil phosphorus (P) accumulates primarily in the topsoil due to P fertilization and P released from crop residues. In contrast with conventional tillage (moldboard plough, MP), conservation tillage [e.g. no-till, (NT)] often leads to higher P concentrations in the topsoil mainly due to the absence of mixing between soil, fertilizer, and crop residues. Our objective was to estimate the proportion of P uptake from a given soil mass across the soil profile under maize and soybean as the product of root surface density proportions and local plant-available soil P. This study was conducted on a long-term field experiment initiated in 1992 in southern Quebec, Canada, and established on a clay-loam soil under MP and NT systems. The experiment was factorially treated with three P doses (0, 17.5 and 35 kg P ha-1 applied as triple superphosphate on maize at 5 cm depth and at 5 cm on one side of the crop row). Soil was sampled at flowering stage at five depths (0-5, 5-10, 10-20, 20-30 and 30-40 cm) and three horizontal distances perpendicular to the crop row (5, 15 and 25 cm) in 2014 and 2015 to map a grid soil P availability to plants, e.g. phosphate ion concentrations in solution and the time-dependent amount of phosphate ions that can equilibrate- solution by diffusion, root distribution, and consequently crop P uptake, which was calculated as the fraction of plant-available soil P intercepted by surface roots. In general, NT tended to have higher soil P status in the upper soil layer and lower soil P status in the deeper soil layer compared to MP ; confirming previous results obtained from the same experimental site. This variation along the soil profile was significantly affected by sampling distance to crop row with higher concentration observed at 5-cm distance mainly because of the placement of P fertilizers. The 2D distribution of P uptake depended on tillage practice and P fertilization. There was higher proportions of P uptake from the 0-10 and 0-20 cm layers in NT (46% and 79%, respectively) compared to MP (25% and 68%, respectively). On average 8% of P uptake originated from the 30-40 cm layer irrespective of tillage, indicating that plant P uptake from deeper soil layers also influenced the P cycling in agroecosystems.

Polycyclic aromatic hydrocarbons in soils from the Tibetan Plateau, China: distribution and influence of environmental factors.

PubMed

Wang, Shuang; Ni, Hong-Gang; Sun, Jian-Lin; Jing, Xin; He, Jin-Sheng; Zeng, Hui

2013-03-01

Thirty four sampling sites along an elevation transect in the Tibetan Plateau region were chosen. Soil cores were divided into several layers and a total of 175 horizon soil samples were collected from July to September 2011, for determination of polycyclic aromatic hydrocarbons (PAHs). The measured PAHs concentration in surface soils was 56.26 ± 45.84 ng g(-1), and the low molecular weight PAHs (2-3 rings) predominated, accounting for 48% and 35%. We analyzed the spatial (altitudinal and vertical) distribution of PAHs in soil, and explored the influence of related environmental factors. Total organic carbon (TOC) showed a controlling influence on the distribution of PAHs. PAH concentrations declined with soil depth, and the composition patterns of PAHs along soil depth indicated that the heavy PAHs tended to remain in the upper layers (0-10 cm), while the light fractions were transported downward more easily. PAHs inventories (8.77-57.92 mg m(-2)) for soil cores increased with mean annual precipitation, while the topsoil concentrations decreased with it. This implies that an increase in precipitation could transfer more PAHs from the atmosphere to the soil and further transport PAHs from the topsoil to deeper layers.

Microbial Community and Functional Structure Significantly Varied among Distinct Types of Paddy Soils But Responded Differently along Gradients of Soil Depth Layers

PubMed Central

Bai, Ren; Wang, Jun-Tao; Deng, Ye; He, Ji-Zheng; Feng, Kai; Zhang, Li-Mei

2017-01-01

Paddy rice fields occupy broad agricultural area in China and cover diverse soil types. Microbial community in paddy soils is of great interest since many microorganisms are involved in soil functional processes. In the present study, Illumina Mi-Seq sequencing and functional gene array (GeoChip 4.2) techniques were combined to investigate soil microbial communities and functional gene patterns across the three soil types including an Inceptisol (Binhai), an Oxisol (Leizhou), and an Ultisol (Taoyuan) along four profile depths (up to 70 cm in depth) in mesocosm incubation columns. Detrended correspondence analysis revealed that distinctly differentiation in microbial community existed among soil types and profile depths, while the manifest variance in functional structure was only observed among soil types and two rice growth stages, but not across profile depths. Along the profile depth within each soil type, Acidobacteria, Chloroflexi, and Firmicutes increased whereas Cyanobacteria, β-proteobacteria, and Verrucomicrobia declined, suggesting their specific ecophysiological properties. Compared to bacterial community, the archaeal community showed a more contrasting pattern with the predominant groups within phyla Euryarchaeota, Thaumarchaeota, and Crenarchaeota largely varying among soil types and depths. Phylogenetic molecular ecological network (pMEN) analysis further indicated that the pattern of bacterial and archaeal communities interactions changed with soil depth and the highest modularity of microbial community occurred in top soils, implying a relatively higher system resistance to environmental change compared to communities in deeper soil layers. Meanwhile, microbial communities had higher connectivity in deeper soils in comparison with upper soils, suggesting less microbial interaction in surface soils. Structure equation models were developed and the models indicated that pH was the most representative characteristics of soil type and identified as the key driver in shaping both bacterial and archaeal community structure, but did not directly affect microbial functional structure. The distinctive pattern of microbial taxonomic and functional composition along soil profiles implied functional redundancy within these paddy soils. PMID:28611747

Microbial Community and Functional Structure Significantly Varied among Distinct Types of Paddy Soils But Responded Differently along Gradients of Soil Depth Layers.

PubMed

Bai, Ren; Wang, Jun-Tao; Deng, Ye; He, Ji-Zheng; Feng, Kai; Zhang, Li-Mei

2017-01-01

Paddy rice fields occupy broad agricultural area in China and cover diverse soil types. Microbial community in paddy soils is of great interest since many microorganisms are involved in soil functional processes. In the present study, Illumina Mi-Seq sequencing and functional gene array (GeoChip 4.2) techniques were combined to investigate soil microbial communities and functional gene patterns across the three soil types including an Inceptisol (Binhai), an Oxisol (Leizhou), and an Ultisol (Taoyuan) along four profile depths (up to 70 cm in depth) in mesocosm incubation columns. Detrended correspondence analysis revealed that distinctly differentiation in microbial community existed among soil types and profile depths, while the manifest variance in functional structure was only observed among soil types and two rice growth stages, but not across profile depths. Along the profile depth within each soil type, Acidobacteria , Chloroflexi , and Firmicutes increased whereas Cyanobacteria , β -proteobacteria , and Verrucomicrobia declined, suggesting their specific ecophysiological properties. Compared to bacterial community, the archaeal community showed a more contrasting pattern with the predominant groups within phyla Euryarchaeota , Thaumarchaeota , and Crenarchaeota largely varying among soil types and depths. Phylogenetic molecular ecological network (pMEN) analysis further indicated that the pattern of bacterial and archaeal communities interactions changed with soil depth and the highest modularity of microbial community occurred in top soils, implying a relatively higher system resistance to environmental change compared to communities in deeper soil layers. Meanwhile, microbial communities had higher connectivity in deeper soils in comparison with upper soils, suggesting less microbial interaction in surface soils. Structure equation models were developed and the models indicated that pH was the most representative characteristics of soil type and identified as the key driver in shaping both bacterial and archaeal community structure, but did not directly affect microbial functional structure. The distinctive pattern of microbial taxonomic and functional composition along soil profiles implied functional redundancy within these paddy soils.

Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest

USGS Publications Warehouse

Melvin, April M.; Celis, Gerardo; Johnstone, Jill F.; McGuire, A. David; Genet, Helene; Schuur, Edward A.G.; Rupp, T. Scott; Mack, Michelle C.

2018-01-01

Increasing wildfire activity in Alaska's boreal forests has led to greater fuel-reduction management. Management has been implemented to reduce wildfire spread, but the ecological impacts of these practices are poorly known. We quantified the effects of hand-thinning and shearblading on above- and belowground stand characteristics, plant species composition, carbon (C) and nitrogen (N) pools, and soil thaw across 19 black spruce (Picea mariana) dominated sites in interior Alaska treated 2-12 years prior to sampling. The density of deciduous tree seedlings was significantly higher in shearbladed areas compared to unmanaged forest (6.4 vs. 0.1 stems m−2), and unmanaged stands exhibited the highest mean density of conifer seedlings and layers (1.4 stems m−2). Understory plant community composition was most similar between unmanaged and thinned stands. Shearblading resulted in a near complete loss of aboveground tree biomass C pools while thinning approximately halved the C pool size (1.2 kg C m−2 compared to 3.1 kg C m−2 in unmanaged forest). Significantly smaller soil organic layer (SOL) C and N pools were observed in shearbladed stands (3.2 kg C m−2 and 116.8 g N m−2) relative to thinned (6.0 kg C m−2 and 192.2 g N m−2) and unmanaged (5.9 kg C m−2 and 178.7 g N m−2) stands. No difference in C and N pool sizes in the uppermost 10 cm of mineral soil was observed among stand types. Total C stocks for measured pools was 2.6 kg C m−2 smaller in thinned stands and 5.8 kg C m−2smaller in shearbladed stands when compared to unmanaged forest. Soil thaw depth averaged 13 cm deeper in thinned areas and 46 cm deeper in shearbladed areas relative to adjacent unmanaged stands, although variability was high across sites. Deeper soil thaw was linked to shallower SOL depth for unmanaged stands and both management types, however for any given SOL depth, thaw tended to be deeper in shearbladed areas compared to unmanaged forest. These findings indicate that fuel-reduction management alters plant community composition, C and N pools, and soil thaw depth, with consequences for ecosystem structure and function beyond those intended for fire management.

[The concentration and distribution of 137Cs in soils of forest and agricultural ecosystems of Tula Region].

PubMed

Lipatov, D N; Shcheglov, A I; Tsvetnova, O B

2007-01-01

The paper deals with a comparative study of 137Cs contamination in forest, old arable and cultivated soils of Tula Region. Initial interception of Chernobyl derived 137Cs is higher in forest ecosystems: oak-forest > birch-forest > pine-forest > agricultural ecosystems. Vertical migration of 137Cs in deeper layers of soils was intensive in agricultural ecosystems: cultivated soils > old arable soils > birch-forest soils > oak-forest soils > pine-forest soils. In study have been evaluated spatial variability of 137Cs in soil and asymmetrical distribution, that is a skew to the right. Spatial heterogeneity of 137Cs in agricultural soils is much lower than in forest soils. For cultivated soil are determined the rate of resuspension, which equal to 6.1 x 10(-4) day(-1). For forest soils are described the 137Cs concentration in litter of different ecosystems. The role of main accumulation and barrier of 137Cs retain higher layers of soils (horizon A1(A1E) in forest, horizon Ap in agricultural ecosystems) in long-term forecast after Chernobyl accident.

Effects of nitrogen and biochar amendment on soil methane concentration profiles and diffusion in a rice-wheat annual rotation system

NASA Astrophysics Data System (ADS)

Xu, Xin; Wu, Zhen; Dong, Yubing; Zhou, Ziqiang; Xiong, Zhengqin

2016-12-01

The CH4 emissions from soil were influenced by the changeable CH4 concentrations and diffusions in soil profiles, but that have been subjected to nitrogen (N) and biochar amendment over seasonal and annual time frames. Accordingly, a two-year field experiment was conducted in southeastern China to determine the amendment effects on CH4 concentrations and diffusive effluxes as measured by a multilevel sampling probe in paddy soil during two cycles of rice-wheat rotations. The results showed that the top 7-cm soil layers were the primary CH4 production sites during the rice-growing seasons. This layer acted as the source of CH4 generation and diffusion, and the deeper soil layers and the wheat season soil acted as the sink. N fertilization significantly increased the CH4 concentration and diffusive effluxes in the top 7-cm layers during the 2013 and 2014 rice seasons. Following biochar amendment, the soil CH4 concentrations significantly decreased during the rice season in 2014, relative to the single N treatment. Moreover, 40 t ha-1 biochar significantly decreased the diffusive effluxes during the rice seasons in both years. Therefore, our results showed that biochar amendment is a good strategy for reducing the soil profile CH4 concentrations and diffusive effluxes induced by N in paddy fields.

Effects of nitrogen and biochar amendment on soil methane concentration profiles and diffusion in a rice-wheat annual rotation system.

PubMed

Xu, Xin; Wu, Zhen; Dong, Yubing; Zhou, Ziqiang; Xiong, Zhengqin

2016-12-08

The CH 4 emissions from soil were influenced by the changeable CH 4 concentrations and diffusions in soil profiles, but that have been subjected to nitrogen (N) and biochar amendment over seasonal and annual time frames. Accordingly, a two-year field experiment was conducted in southeastern China to determine the amendment effects on CH 4 concentrations and diffusive effluxes as measured by a multilevel sampling probe in paddy soil during two cycles of rice-wheat rotations. The results showed that the top 7-cm soil layers were the primary CH 4 production sites during the rice-growing seasons. This layer acted as the source of CH 4 generation and diffusion, and the deeper soil layers and the wheat season soil acted as the sink. N fertilization significantly increased the CH 4 concentration and diffusive effluxes in the top 7-cm layers during the 2013 and 2014 rice seasons. Following biochar amendment, the soil CH 4 concentrations significantly decreased during the rice season in 2014, relative to the single N treatment. Moreover, 40 t ha -1 biochar significantly decreased the diffusive effluxes during the rice seasons in both years. Therefore, our results showed that biochar amendment is a good strategy for reducing the soil profile CH 4 concentrations and diffusive effluxes induced by N in paddy fields.

Desert shrub responses to experimental modification of precipitation seasonality and soil depth: relationship to the two-layer model and ecohydrological niche

USGS Publications Warehouse

Germino, Matthew J.; Reinhardt, Keith

2013-01-01

1. Ecohydrological niches are important for understanding plant community responses to climate shifts, particularly in dry lands. According to the two-layer hypothesis, selective use of deep-soil water increases growth or persistence of woody species during warm and dry summer periods and thereby contributes to their coexistence with shallow-rooted herbs in dry ecosystems. The resource-pool hypothesis further suggests that shallow-soil water benefits growth of all plants while deep-soil water primarily enhances physiological maintenance and survival of woody species. Few studies have directly tested these by manipulating deep-soil water availability and observing the long-term outcomes. 2. We predicted that factors promoting infiltration and storage of water in deep soils, specifically greater winter precipitation and soil depth, would enhance Artemisia tridentata (big sagebrush) in cold, winter-wet/summer-dry desert. Sagebrush responses to 20 years of winter irrigation were compared to summer- or no irrigation, on plots having relatively deep or shallow soils (2 m vs. 1 m depths). 3. Winter irrigation increased sagebrush cover, and crown and canopy volumes, but not density (individuals/plot) compared to summer or no irrigation, on deep-soil plots. On shallow-soil plots, winter irrigation surprisingly decreased shrub cover and size, and summer irrigation had no effect. Furthermore, multiple regression suggested that the variations in growth were related (i) firstly to water in shallow soils (0-0.2 m) and secondly to deeper soils (> 1 m deep) and (ii) more by springtime than by midsummer soil water. Water-use efficiency increased considerably on shallow soils without irrigation and was lowest with winter irrigation. 4. Synthesis. Sagebrush was more responsive to the seasonal timing of precipitation than to total annual precipitation. Factors that enhanced deep-water storage (deeper soils plus more winter precipitation) led to increases in Artemisia tridentata that were consistent with the two-layer hypothesis, and the contribution of shallow water to growth on these plots was consistent with the resource-pool hypothesis. However, shallow-soil water also had negative effects on sagebrush, suggesting an ecohydrological trade-off not considered in these or related theories. The interaction between precipitation timing and soil depth indicates that increased winter precipitation could lead to a mosaic of increases and decreases in A. tridentata across landscapes having variable soil depth.

Prediction of the P-leaching potential of arable soils in areas with high livestock densities*

PubMed Central

Werner, Wilfried; Trimborn, Manfred; Pihl, Uwe

2006-01-01

Due to long-term positive P-balances many surface soils in areas with high livestock density in Germany are oversupplied with available P, creating a potential for vertical P losses by leaching. In extensive studies to characterize the endangering of ground water to P pollution by chemical soil parameters it is shown that the available P content and the P concentration of the soil solution in the deeper soil layers, as indicators of the P-leaching potential, cannot be satisfactorily predicted from the available P content of the topsoils. The P equilibrium concentration in the soil solution directly above ground water table or the pipe drainage system highly depends on the relative saturation of the P-sorption capacity in this layer. A saturation index of <20% normally corresponds with P equilibrium concentrations of <0.2 mg P/L. Phytoremediation may reduce the P leaching potential of P-enriched soils only over a very long period. PMID:16773724

Distribution and significance of dissolved organic carbon under three land-use systems, NSW, Australia

NASA Astrophysics Data System (ADS)

Fancy, Rubeca; Wilson, Brian R.; Daniel, Heiko; Osanai, Yui

2017-04-01

Carbon accumulation in surface soils is well documented but very little is known about the mechanisms and processes that result in carbon accumulation and long-term storage in the deeper soil profile. Understanding soil carbon storage and distribution mechanisms is critical to evaluate the sequestration potential of the soils of different land uses. Recent investigations have demonstrated that the movement of dissolved organic carbon (DOC) in the soil profile could contribute significantly to the carbon balance of terrestrial ecosystems. However, very little is known regarding the importance of DOC to vertical distribution of soil organic carbon (SOC) pool through the soil profile in different land-use systems, management practices and conditions prevalent in Australia. We investigated the quantity and distribution of SOC and DOC through the profile under three different land-use systems in northern NSW, Australia. A series of site clusters containing a representative range of land-uses (cultivated, improved pasture and woodland) were selected across the region. Within each land use, we determined SOC and DOC concentration and quantity down the soil profile to a depth of 0-100 cm using six soil depth increments. Here we discuss the distribution and relative importance of DOC down the soil profile to the storage and distribution of carbon. We compare and contrast the patterns associated with the different land use systems and explore potential mechanisms of carbon cycling in these soils. Near to the soil surface, SOC had larger concentrations in the order woodland>improved pasture>cropping at all sites studied. However, DOC was found in significantly larger concentrations in the woodland soils at all soil depths. The larger DOC:TOC ratio in woodland and improved pasture soils suggests a direct relationship between TOC and DOC but increased DOC:TOC ratio in deeper soil layers suggests an increasing importance of DOC in soil carbon cycling in these deeper soils under Australian conditions.

Fate and transport of carbamazepine in soil aquifer treatment (SAT) infiltration basin soils.

PubMed

Arye, Gilboa; Dror, Ishai; Berkowitz, Brian

2011-01-01

The transport and fate of the pharmaceutical carbamazepine (CBZ) were investigated in the Dan Region Reclamation Project (SHAFDAN), Tel-Aviv, Israel. Soil samples were taken from seven subsections of soil profiles (150 cm) in infiltration basins of a soil aquifer treatment (SAT) system. The transport characteristics were studied from the release dynamics of soil-resident CBZ and, subsequently, from applying a pulse input of wastewater containing CBZ. In addition, a monitoring study was performed to evaluate the fate of CBZ after the SAT. Results of this study indicate adsorption, and consequently retardation, in CBZ transport through the top soil layer (0-5 cm) and to a lesser extent in the second layer (5-25 cm), but not in deeper soil layers (25-150 cm). The soluble and adsorbed fractions of CBZ obtained from the two upper soil layers comprised 45% of the total CBZ content in the entire soil profile. This behavior correlated to the higher organic matter content observed in the upper soil layers (0-25 cm). It is therefore deduced that when accounting for the full flow path of CBZ through the vadose zone to the groundwater region, the overall transport of CBZ in the SAT system is essentially conservative. The monitoring study revealed that the average concentration of CBZ decreased from 1094 ± 166 ng L⁻¹ in the recharged wastewater to 560 ± 175 ng L⁻¹ after the SAT. This reduction is explained by dilution of the recharged wastewater with resident groundwater, which may occur as it flows to active reclamation wells. Copyright © 2010 Elsevier Ltd. All rights reserved.

Study of the water transportation characteristics of marsh saline soil in the Yellow River Delta.

PubMed

He, Fuhong; Pan, Yinghua; Tan, Lili; Zhang, Zhenhua; Li, Peng; Liu, Jia; Ji, Shuxin; Qin, Zhaohua; Shao, Hongbo; Song, Xueyan

2017-01-01

One-dimensional soil column water infiltration and capillary adsorption water tests were conducted in the laboratory to study the water transportation characteristics of marsh saline soil in the Yellow River Delta, providing a theoretical basis for the improvement, utilization and conservation of marsh saline soil. The results indicated the following: (1) For soils with different vegetation covers, the cumulative infiltration capacity increased with the depth of the soil layers. The initial infiltration rate of soils covered by Suaeda and Tamarix chinensis increased with depth of the soil layers, but that of bare soil decreased with soil depth. (2) The initial rate of capillary rise of soils with different vegetation covers showed an increasing trend from the surface toward the deeper layers, but this pattern with respect to soil depth was relatively weak. (3) The initial rates of capillary rise were lower than the initial infiltration rates, but infiltration rate decreased more rapidly than capillary water adsorption rate. (4) The two-parameter Kostiakov model can very well-simulate the changes in the infiltration and capillary rise rates of wetland saline soil. The model simulated the capillary rise rate better than it simulated the infiltration rate. (5) There were strong linear relationships between accumulative infiltration capacity, wetting front, accumulative capillary adsorbed water volume and capillary height. Copyright © 2016 Elsevier B.V. All rights reserved.

[Effects of precipitation intensity on soil organic carbon fractions and their distribution under subtropical forests of South China].

PubMed

Chen, Xiao-mei; Liu, Ju-xiu; Deng, Qi; Chu, Guo-wei; Zhou, Guo-yi; Zhang, De-qiang

2010-05-01

From December 2006 to June 2008, a field experiment was conducted to study the effects of natural precipitation, doubled precipitation, and no precipitation on the soil organic carbon fractions and their distribution under a successional series of monsoon evergreen broad-leaf forest, pine and broad-leaf mixed forest, and pine forest in Dinghushan Mountain of Southern China. Different precipitation treatments had no significant effects on the total organic carbon (TOC) concentration in the same soil layer under the same forest type (P > 0.05). In treatment no precipitation, particulate organic carbon (POC) and light fraction organic carbon (LFOC) were mainly accumulated in surface soil layer (0-10 cm); but in treatments natural precipitation and doubled precipitation, the two fractions were infiltrated to deeper soil layers. Under pine forest, soil readily oxidizable organic carbon (ROC) was significantly higher in treatment no precipitation than in treatments natural precipitation and doubled precipitation (P < 0.05). The percentage of soil POC, ROC, and LFOC to soil TOC was much greater under the forests at early successional stage than at climax stage, suggesting that the forest at early successional stage might not be an ideal place for soil organic carbon storage. Precipitation intensity less affected TOC, but had greater effects on the labile components POC, ROC, and LFOC.

Soil organic matter decomposition and temperature sensitivity after forest fire in permafrost regions in Canada

NASA Astrophysics Data System (ADS)

Aaltonen, Heidi; Palviainen, Marjo; Köster, Kajar; Berninger, Frank; Pumpanen, Jukka

2017-04-01

On the Northern Hemisphere, 24% of soils are underlain by permafrost. These soils contain 50% of the global soil carbon pool. The Northern Hemisphere is also the region which is predicted to be most affected by climate warming and this causes uncertainties over the future of the permafrost. It has been estimated that 25% of permafrost might thaw by 2100, exposing previously frozen carbon pools to decomposition. In addition, global warming is expected to cause increase in the frequency of wild fires, which further increase permafrost melting by removing the insulating organic surface layer. The amount of released soil carbon from permafrost soils after forest fire is affected by degradability and temperature sensitivity of the soil organic matter, as well as soil depth and the stage of succession. Yet the common effect of these factors remains unclear. We studied how soil respiration and its temperature sensitivity (Q10) vary in different depths and within time by taking soil samples from different fire chronosequence areas (burned 3, 25, 46 and 100 years ago) from permafrost region in Northern Canada (Yukon and Northwest Territories, along Dempster Highway). The samples from three different depths (5, 10 and 30 cm) were incubated in four different temperatures (1, 7, 13 and 19°C) over 24h. Our results showed that the CO2 fluxes followed the stages of succession, with recently burned sites having lowest rates. The organic matter at 5 cm depth proved to be more labile and temperature sensitive than in deeper depths. The Q10 values, however, did not differ between sites, excluding 30 cm at the most recently burned site that had a significantly higher Q10 value than the other sites. The results implicate that heterotrophic soil respiration decreases on permafrost regions during the first stages after forest fire. At the same time the temperature sensitivity in deeper soil layers may increase.

Boreal Forest Permafrost Sensitivity Ecotypes to changes in Snow Depth and Soil Moisture

NASA Astrophysics Data System (ADS)

Dabbs, A.; Romanovsky, V. E.; Kholodov, A. L.

2017-12-01

Changes in the global climate, pronounced especially in polar regions due to their accelerated warming, are expected by many global climate models to have large impacts on the moisture budget throughout the world. Permafrost extent and the soil temperature regime are both strongly dependent on soil moisture and snow depth because of their immense effects on the thermal properties of the soil column and surface energy balance respectively. To assess how the ground thermal regime at various ecotypes may react to a change in the moisture budget, we performed a sensitivity analysis using the Geophysical Institute Permafrost Laboratory model, which simulates subsurface temperature dynamics by solving a one-dimensional nonlinear heat equation with phase change. We used snow depth and air temperature data from the Fairbanks International Airport meteorological station as forcing for this sensitivity analysis. We looked at five different ecotypes within the boreal forest region of Alaska: mixed, deciduous and black forests, willow shrubs and tundra. As a result of this analysis, we found that ecotypes with higher soil moisture contents, such as willow shrubs, are most sensitive to changes in snow depth due to the larger amount of latent heat trapped underneath the snow during the freeze up of active layer. In addition, soil within these ecotypes has higher thermal conductivity due to high saturation degree allowing for deeper seasonal freezing. Also, we found that permafrost temperatures were most sensitive to changes in soil moisture in ecotypes that were not completely saturated such as boreal forest. These ecotypes lacked complete saturation because of thick organic layers that have very high porosities or partially drained mineral soils. Contrarily, tundra had very little response to changes in soil moisture due to its thin organic layer and almost completely saturated soil column. This difference arises due to the disparity between the frozen and unfrozen thermal conductivities of the soil. In highly saturated soils, the frozen thermal conductivity of the soil can be more than double that of the unfrozen thermal conductivity while in dryer soils that ratio reduces down to less than 1.5. This difference allows the seasonal freezing to penetrate quicker and deeper causing even more latent heat to be released and trapped.

Comparison of rainfall and stemflow peak intensities and infiltration patterns for a mature coastal forest in British Columbia, Canada

NASA Astrophysics Data System (ADS)

van Meerveld, Ilja; Spencer, Sheena

2017-04-01

Most studies on stemflow have focused on the amount of stemflow in different forests or for different rainfall events. So far, few studies have looked at how stemflow intensity varies during rainfall events and how peak stemflow intensities compare to peak rainfall intensities. High stemflow intensities at the base of the tree, where roots and other preferential flow pathways are prevalent, may lead to faster and deeper infiltration of stemflow than rainfall and thus affect soil moisture dynamics and potentially also subsurface stormflow generation. We measured stemflow intensities for three Western hemlock, two Western red cedar, two Douglas-fir and one Birch tree in a mature coniferous forest in coastal British Columbia to determine how stemflow intensities were related to rainfall intensity. We sprayed a blue dye tracer on two Western hemlock trees (29 and 52 cm diameter at breast height (DBH)) to determine how stemflow water flows through the soil and to what depth it infiltrates. We also applied the blue dye tracer to an area between the trees to compare infiltration of stemflow with rainfall. Stemflow increased linearly with event total precipitation for all trees. The larger trees almost exclusively had funneling ratios (i.e. the volume of stemflow per unit basal area divided by the rainfall) smaller than one, regardless of species and event size. The funneling ratios for the small trees were generally larger for larger events (up to a funneling ratio of 20) but there was considerable scatter in this relation. Trees with a DBH <35 cm, which represent 24% of the total basal area of the study site, contributed 72% of the estimated total stemflow amount. Stemflow intensities (volume of stemflow per unit basal area per hour) often increased in a stepwise manner. When there were two precipitation bursts, stemflow intensity was usually highest during the second precipitation burst. However, when there were several hours of very low rainfall intensity between consecutive precipitation bursts, stemflow intensity was lower during the first burst after the break in rainfall. Peak stemflow intensities were higher than the maximum precipitation intensity. The blue dye that was applied to the tree stems was found more frequently at depth than near the soil surface. Stemflow flowed primarily through the 10 cm organic rich upper layer of the soil around the tree before flowing between or along live and dead roots, inside dead roots, around rocks and boulders deeper into the soil. Lateral flow was observed above a dense clay layer but where roots were able to penetrate the clay layer, the infiltrating water flowed deeper into the soil and (almost) reached the soil-bedrock interface. Stemflow appeared to infiltrate deeper (122 cm) than rainfall (85 cm) but this difference was in part due to variations in maximum soil depth. These results suggest that even though stemflow is only a minor component of the water balance, the double funnelling of stemflow may significantly affect soil moisture, recharge and runoff generation.

Vertical profile of 137Cs in soil.

PubMed

Krstić, D; Nikezić, D; Stevanović, N; Jelić, M

2004-12-01

In this paper, a vertical distribution of 137Cs in undisturbed soil was investigated experimentally and theoretically. Soil samples were taken from the surroundings of the city of Kragujevac in central Serbia during spring-summer of 2001. The sampling locations were chosen in such a way that the influence of soil characteristics on depth distribution of 137Cs in soil could be investigated. Activity of 137Cs in soil samples was measured using a HpGe detector and multi-channel analyzer. Based on vertical distribution of 137Cs in soil which was measured for each of 10 locations, the diffusion coefficient of 137Cs in soil was determined. In the next half-century, 137Cs will remain as the source of the exposure. Fifteen years after the Chernobyl accident, and more than 30 years after nuclear probes, the largest activity of 137Cs is still within 10 cm of the upper layer of the soil. This result confirms that the penetration of 137Cs in soil is a very slow process. Experimental results were compared with two different Green functions and no major differences were found between them. While both functions fit experimental data well in the upper layer of soil, the fitting is not so good in deeper layers. Although the curves obtained by these two functions are very close to each other, there are some differences in the values of parameters acquired by them.

Experimental warming increased soil nitrogen sink in the Tibetan permafrost

NASA Astrophysics Data System (ADS)

Chang, Ruiying; Wang, Genxu; Yang, Yuanhe; Chen, Xiaopeng

2017-07-01

In permafrost soil, warming regulates the nitrogen (N) cycle either by stimulating N transformation or by enhancing cryoturbation, the mixture of soil layers due to repeated freeze thaw. Here N isotopic values (δ15N) of plants and the soil were investigated in a 7 year warming experiment in a permafrost-affected alpine meadow on the Qinghai-Tibetan Plateau. The results revealed that warming significantly decreased the δ15N in the plant (aboveground and belowground parts) and different soil fractions (clay and silt fraction, aggregate, and bulk soil). The decreased soil δ15N was associated with an increase in soil N stock due to greater N fixation. The incremental N retention in plants and soil mineral-associated fractions from warming resulted in a decrease in soil inorganic N, which constrains the role of nitrification/denitrification in soil δ15N, suggesting a restrained rather than an open N cycle. Furthermore, enhanced cryoturbation under warming, identified by a downward redistribution of 137Cs into deeper layers, promoted N protection from transformation. Overall, the decrease in soil δ15N indicated higher rates of N input through fixation relative to N loss through nitrification and denitrification in permafrost-affected ecosystems under warming conditions.

Root growth dynamics linked to above-ground growth in walnut (Juglans regia).

PubMed

Contador, Maria Loreto; Comas, Louise H; Metcalf, Samuel G; Stewart, William L; Porris Gomez, Ignacio; Negron, Claudia; Lampinen, Bruce D

2015-07-01

Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature. Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia 'Chandler') using minirhizotron techniques. Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production. The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Nitrogen acquisition by plants and microorganisms in a temperate grassland

PubMed Central

Liu, Qianyuan; Qiao, Na; Xu, Xingliang; Xin, Xiaoping; Han, Jessie Yc; Tian, Yuqiang; Ouyang, Hua; Kuzyakov, Yakov

2016-01-01

Nitrogen (N) limitation is common in most terrestrial ecosystems, often leading to strong competition between microorganisms and plants. The mechanisms of niche differentiation to reduce this competition remain unclear. Short-term 15N experiments with NH4+, NO3−, and glycine were conducted in July, August and September in a temperate grassland to evaluate the chemical, spatial and temporal niche differentiation by competition between plants and microorganisms for N. Microorganisms preferred NH4+ and NO3−, while plants preferred NO3−. Both plants and microorganisms acquired more N in August and September than in July. The soil depth had no significant effects on microbial uptake, but significantly affected plant N uptake. Plants acquired 67% of their N from the 0–5 cm soil layer and 33% from the 5–15 cm layer. The amount of N taken up by microorganisms was at least seven times than plants. Although microorganisms efficiently compete for N with plants, the competition is alleviated through chemical partitioning mainly in deeper soil layer. In the upper soil layer, neither chemical nor temporal niche separation is realized leading to strong competition between plants and microorganisms that modifies N dynamics in grasslands. PMID:26961252

Nitrogen acquisition by plants and microorganisms in a temperate grassland.

PubMed

Liu, Qianyuan; Qiao, Na; Xu, Xingliang; Xin, Xiaoping; Han, Jessie Yc; Tian, Yuqiang; Ouyang, Hua; Kuzyakov, Yakov

2016-03-10

Nitrogen (N) limitation is common in most terrestrial ecosystems, often leading to strong competition between microorganisms and plants. The mechanisms of niche differentiation to reduce this competition remain unclear. Short-term (15)N experiments with NH4(+), NO3(-), and glycine were conducted in July, August and September in a temperate grassland to evaluate the chemical, spatial and temporal niche differentiation by competition between plants and microorganisms for N. Microorganisms preferred NH4(+) and NO3(-), while plants preferred NO3(-). Both plants and microorganisms acquired more N in August and September than in July. The soil depth had no significant effects on microbial uptake, but significantly affected plant N uptake. Plants acquired 67% of their N from the 0-5 cm soil layer and 33% from the 5-15 cm layer. The amount of N taken up by microorganisms was at least seven times than plants. Although microorganisms efficiently compete for N with plants, the competition is alleviated through chemical partitioning mainly in deeper soil layer. In the upper soil layer, neither chemical nor temporal niche separation is realized leading to strong competition between plants and microorganisms that modifies N dynamics in grasslands.

Role of Native and Exotic Earthworms in Plant Biopolymer Dynamics in Forest Soil

NASA Astrophysics Data System (ADS)

Filley, Timothy

2010-05-01

Many forests within northern North America are experiencing the introduction of earthworms for the first time, presumably since before the last major glaciation. Forest dynamics are undergoing substantial changes because of the activity of the mainly European lumbricid species. Documented losses in litter layers, expansion of A-horizons, loss of the organic horizon, changes in fine root density, and shifts in microbial populations have all been documented in invaded zones. Two free air CO2 enrichment (FACE) forest experiments (aspen FACE at Rhinelander, Wisconsin and sweet gum FACE at Oak Ridge National Lab, Tennessee) lie within the zones of invasion and exhibit differences in amounts of exotic and native species as well as endogeic (predominantly mineral soil dwelling) and epigeic (litter and organic matter horizon dwelling) types. Considerations of carbon accrual dynamics and relative input of above vs. below ground plant input in these young successional systems do not consider the potential impact of these ecosystem engineers. We investigated the impact of earthworm activity by tracking the relative abundance and stable carbon isotope compositions of lignin and substituted fatty acids extracted from isolated earthworms and their fecal pellets and from host soils. Indications of root vs leaf input to earthworm casts and fecal matter were derived from differences in the chemical composition of cutin, suberin, and lignin. The isotopically depleted CO2 used in FACE and the resulting isotopically depleted plant organic matter afford an excellent opportunity to assess biopolymer-specific turnover dynamics. We find that endogeic species are proportionately more responsible for fine root cycling while some epigeic species are responsible for microaggregation of foliar cutin. CSIA of fecal pellet lignin and SFA indicates how these biopolymer pools can be derived from variable sources, roots, background soil, foliar tissue within one earthworm. Additionally, CSIA indicates the distinct roles that different earthworm types have in "aging" surface soil biopolymer pools through encapsulation and upward transport of deeper soil carbon, and "freshening" deeper soil biopolymer pools through downward transport of surface carbon to deeper layers,. As earthworm species abundance and activity are not is steady state in many forests, the role of these important invertebrates should be more considered when assessing the changing soil state.

Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

USGS Publications Warehouse

Bullen, Thomas D.; Chadwick, Oliver A.

2016-01-01

Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as litterfall. This observation implicates an uptake flux from an additional source which we attribute to biolifting. We view the heavy exchangeable Ba relative to soil parent values in deeper soils at sites where P is enriched in surface soils, and indeed at all but the wettest site across the climosequence, to represent the complement of an isotopically light Ba fraction removed from these soils by plant roots consistent with the biolifting hypothesis. We further suggest that decreasing heaviness of depth-integrated exchangeable Ba in deeper soils with increasing median annual precipitation across the climosequence reflects greater reliance on shallow nutrient sources as site water balance increases. While the Ca, Sr and Ba isotopes considered together were useful in confirming an important role for nutrient biolifting across the climosequence, the Ba isotopes provided the most robust tracer of biolifting and have the greatest potential to find application as an isotopic proxy for P dynamics in soils.

Landscape and hydrologic changes in the permafrost regions of the Western Canadian Arctic

NASA Astrophysics Data System (ADS)

Marsh, P.

2012-12-01

The Western Canadian Arctic, in the vicinity of the Mackenzie River Delta, is characterized by long cold winters, short summers, low precipitation, thin organic soils, and ice-rich continuous permafrost. Over the last few decades, this region has undergone dramatic changes in climate, with warming air temperature and decreasing winter and summer precipitation. This has resulted in various landscape changes, including the warming of the upper layers of the permafrost, deepening of the active layer, drainage of permafrost affected lakes, an ongoing change from tundra to shrub tundra, and earlier spring breakup of streams, rivers and lakes. However, interactions between climate, hydrology, snow, and vegetation greatly affect both the spatial and temporal changes to the permafrost and hydrology of this region. Knowledge of these changes is important to the understanding of methane dynamics in this permafrost landscape, and for predicting future changes. Two examples of observed landscape change will be discussed. First, ground based observations and analysis of air photo images has demonstrated that shrub expansion is not uniform across the landscape, but instead is characterized by shrub patches of varying size. This patchiness is likely related to existing variations in soil temperature and moisture, active layer depth, snowcover, and tundra fires. As shrub patches further develop, they impact soil temperature and active layer depth. For example, small patches of shrubs typically have snow depths that are deeper than surrounding tundra areas due to the accumulation of blowing snow, and as a result have much warmer soil temperatures and deeper active layers. In contrast to these small shrub patches, large shrub patches have snow depths only slightly larger than found in the surrounding tundra and therefore only slightly warmer winter soil temperatures. However, shading of the surface during the summer may result in cooler summer soil temperatures. The overall effect of large shrub patches may be either deeper or shallower active layer depths than the surrounding tundra areas, depending on the leaf area index, the degree of shrub bending during the winter, and snow accumulation. Second, in contrast to many areas in Alaska and Siberia where increased rates of lake drainage have been reported, the rate of lake drainage in the Western Canadian Arctic has been decreasing over the past 50 years. The primary factors causing lake drainage in this region are high lake levels and winter cracking of ice wedges in the area immediately around the lake. Hydrologic modelling has suggested that summer lake levels have not changed significantly over the last 50 years, and therefore are not responsible for the decrease in drainage. However, the role of factors such as snow dams at lake outlets that result in high spring water levels, or the offsetting factors of warmer, but less snowy winters on ice wedge cracking are not well understood. As a result, further research is required to better understand how these lakes will respond to future changes in climate. Given the potential changes to methane dynamics in areas of changing permafrost, there is an urgent need to better understand ongoing, and future, changes in the landscape of these permafrost regions.

Using a hybrid model to predict solute transfer from initially saturated soil into surface runoff with controlled drainage water.

PubMed

Tong, Juxiu; Hu, Bill X; Yang, Jinzhong; Zhu, Yan

2016-06-01

The mixing layer theory is not suitable for predicting solute transfer from initially saturated soil to surface runoff water under controlled drainage conditions. By coupling the mixing layer theory model with the numerical model Hydrus-1D, a hybrid solute transfer model has been proposed to predict soil solute transfer from an initially saturated soil into surface water, under controlled drainage water conditions. The model can also consider the increasing ponding water conditions on soil surface before surface runoff. The data of solute concentration in surface runoff and drainage water from a sand experiment is used as the reference experiment. The parameters for the water flow and solute transfer model and mixing layer depth under controlled drainage water condition are identified. Based on these identified parameters, the model is applied to another initially saturated sand experiment with constant and time-increasing mixing layer depth after surface runoff, under the controlled drainage water condition with lower drainage height at the bottom. The simulation results agree well with the observed data. Study results suggest that the hybrid model can accurately simulate the solute transfer from initially saturated soil into surface runoff under controlled drainage water condition. And it has been found that the prediction with increasing mixing layer depth is better than that with the constant one in the experiment with lower drainage condition. Since lower drainage condition and deeper ponded water depth result in later runoff start time, more solute sources in the mixing layer are needed for the surface water, and larger change rate results in the increasing mixing layer depth.

Seasonal reversal of temperature-moisture response of net carbon exchange of biocrusted soils in a cool desert ecosystem.

NASA Astrophysics Data System (ADS)

Tucker, C.; Reed, S.; Howell, A.

2017-12-01

Carbon cycling associated with biological soil crusts, which occur in interspaces between vascular plants in drylands globally, may be an important part of the coupled climate-carbon cycle of the Earth system. A major challenge to understanding CO2 fluxes in these systems is that much of the biotic and biogeochemical activity occurs in the upper few mm of the soil surface layer (i.e., the `mantle of fertility'), which exhibits highly dynamic and difficult to measure temperature and moisture fluctuations. Here, we report data collected in a cool desert ecosystem over one year using a multi-sensor approach to simultaneously measuring temperature and moisture of the biocrust surface layer (0-2 mm), and the deeper soil profile (5-20 cm), concurrent with automated measurement of surface soil CO2 effluxes. Our results illuminate robust relationships between microclimate and field CO2 pulses that have previously been difficult to detect and explain. The temperature of the biocrust surface layer was highly variable, ranging from minimum of -9 °C in winter to maximum of 77 °C in summer with a maximum diurnal range of 61 °C. Temperature cycles were muted deeper in the soil profile. During summer, biocrust and soils were usually hot and dry and CO2 fluxes were tightly coupled to pulse wetting events experienced at the biocrust surface, which consistently resulted in net CO2 efflux (i.e., respiration). In contrast, during the winter, biocrust and soils were usually cold and moist, and there was sustained net CO2 uptake via photosynthesis by biocrust organisms, although during cold dry periods CO2 fluxes were minimal. During the milder spring and fall seasons, short wetting events drove CO2 loss, while sustained wetting events resulted in net CO2 uptake. Thus, the upper and lower bounds of net CO2 exchange at a point in time were functions of the seasonal temperature regime, while the actual flux within those bounds was determined by the magnitude and duration of biocrust and soil wetting events. These patterns reflect both the low temperature sensitivity and slow initiation in response to wetting of photosynthesis compared to respiration by biocrust organisms. Our study highlights the importance of cool and cold periods for C uptake in biocrusted soils of the Colorado Plateau.

Understanding the hydrologic and geochemical control of regolith formation on shale in a hilly landscape

NASA Astrophysics Data System (ADS)

Xiao, D.; Brantley, S.; Li, L.

2017-12-01

Chemical weathering transforms rock to soil and determine soil texture, bedrock depth, and soil hydrological properties. At the Shale Hills watershed in central Pennsylvania, field evidence indicated that the regolith depth, hydrologic processes, and chemical depletion are different at the two aspects. Current regolith formation models considering reactive transport processes have a limitation in coupling complex and evolving hydrodynamic conditions. We hypothesize that deeper regolith forms when more water flushes dissolved mass out of the system. The hypothesis is tested by developing a two-dimensional regolith formation model at the hillslope scale using measured mineral composition and hydrologic properties at Shale Hills using CrunchFlow. A 2-D hillslope domain was setup to simulate hydrogeochemical processes at north and south aspects and to understand the evolution of hydrodynamics, rock properties, and extent of chemical reactions. The bedrock has the primary minerals of quartz, illite, chlorite, calcite, and pyrite; goethite and kaolinite precipitated as secondary minerals. The permeability, mass transfer, and groundwater table depth were constrained by field measurement. We implemented different recharge rates on north and south aspects based on the annually averaged fluxes from a current reanalysis using a hydrologic model. The simulation started from a homogeneous bedrock composition at 10,000 years ago. After 10,000 years' weathering, the south facing aspect with small recharge rate has a shallower soil and regolith. The simulation output indicates the formation of a shallow and a deep groundwater, based on the formation of lateral flow that connects to the stream. One is at the interface between high permeability soil zone and low permeability regolith zone, forming a relatively high-velocity perched groundwater layer. The remnant water infiltrates into the deeper low permeability zone and forms the regional groundwater layer. Because of high permeability in perched layer on north facing aspect, the remnant water in regional groundwater layer leads to shallower water table depth on north facing aspect. The model will be used to understand the role fractures, climate, and mineral compositions in affecting regolith formation.

Modelling the Impact of Climate Change on Soil Water Availability and Plant Community Shifts in the Colorado Plateau

NASA Astrophysics Data System (ADS)

Thomas, A.; Gill, R. A.

2016-12-01

Climate change with an accompanying decrease in soil moisture is expected to have a significant impact on the sensitive, water-limited ecosystems of America's southwestern deserts. Already, studies have documented shifts in the distributions of competing grasses and shrubs in this region, potentially altering ecosystem function. Of particular interest is the loss of desert grasses and the expansion of desert shrubs over the past three decades. The objective of this work is to use a process-based hydrological model to extrapolate site-level measurements to assess trends in soil moisture availability that may impact plant communities in the Colorado Plateau and surrounding regions. The model, SOILWAT, simulates the daily movement of water through plant and soil layers, incorporating precipitation, interception, evaporation, infiltration between soil layers, and absorption and transpiration by plants, as well as physical site characteristics. We applied SOILWAT to 50 sites that were stratified through the northern, central, and southern regions of Ephedra viridis. We focused on E. viridis because it has displaced desert grasses in plot-scale studies. The model was driven using spatially interpolated daily weather data from the PRISM climate model over a 34-year period. We found that across all years, average soil water content in the sandy soil of the region was higher in soil layers 40-60 cm deep than in the top 20 cm, and highest in the deepest layers down to 100 cm. The consistently higher margin of water in deeper layers may indicate the vulnerability of shallow-rooted grass to increasing evaporation and an advantage to deeply-rooted shrubs such as Ephedra.

Forest soil carbon is threatened by intensive biomass harvesting.

PubMed

Achat, David L; Fortin, Mathieu; Landmann, Guy; Ringeval, Bruno; Augusto, Laurent

2015-11-04

Forests play a key role in the carbon cycle as they store huge quantities of organic carbon, most of which is stored in soils, with a smaller part being held in vegetation. While the carbon storage capacity of forests is influenced by forestry, the long-term impacts of forest managers' decisions on soil organic carbon (SOC) remain unclear. Using a meta-analysis approach, we showed that conventional biomass harvests preserved the SOC of forests, unlike intensive harvests where logging residues were harvested to produce fuelwood. Conventional harvests caused a decrease in carbon storage in the forest floor, but when the whole soil profile was taken into account, we found that this loss in the forest floor was compensated by an accumulation of SOC in deeper soil layers. Conversely, we found that intensive harvests led to SOC losses in all layers of forest soils. We assessed the potential impact of intensive harvests on the carbon budget, focusing on managed European forests. Estimated carbon losses from forest soils suggested that intensive biomass harvests could constitute an important source of carbon transfer from forests to the atmosphere (142-497 Tg-C), partly neutralizing the role of a carbon sink played by forest soils.

[Runoff loss of soil mineral nitrogen and its relationship with grass coverage on Loess slope land].

PubMed

Zhang, Yali; Li, Huai'en; Zhang, Xingchang; Xiao, Bo

2006-12-01

In a simulated rainfall experiment on Loess slope land, this paper determined the rainfall, surface runoff and the effective depth of interaction (EDI) between rainfall and soil mineral nitrogen, and studied the effects of grass coverage on the EDI and the runoff loss of soil mineral nitrogen. The results showed that with the increase of EDI, soil nitrogen in deeper layers could be released into surface runoff through dissolution and desorption. The higher the grass coverage, the deeper the EDI was. Grass coverage promoted the interaction between surface runoff and surface soil. On the slope land with 60%, 80% and 100% of grass coverage, the mean content of runoff mineral nitrogen increased by 34.52%, 32.67% and 6.00%, while surface runoff decreased by 4.72%, 9.84% and 12.89%, and eroded sediment decreased by 83.55%, 87.11% and 89.01%, respectively, compared with bare slope land. The total runoff loss of soil mineral nitrogen on the lands with 60%, 80%, and 100% of grass coverage was 95.73%, 109.04%, and 84.05% of that on bare land, respectively. Grass cover had dual effects on the surface runoff of soil mineral nitrogen. On one hand, it enhanced the influx of soil mineral nitrogen to surface runoff, and on the other hand, it markedly decreased the runoff, resulting in the decrease of soil mineral nitrogen loss through runoff and sediment. These two distinct factors codetermined the total runoff loss of soil mineral nitrogen.

Modeling Feedbacks Between Water and Vegetation in the Climate System

NASA Technical Reports Server (NTRS)

Miller, James R.; Russell, Gary L.; Hansen, James E. (Technical Monitor)

2001-01-01

Not only is water essential for life on earth, but life itself affects the global hydrologic cycle and consequently the climate of the planet. Whether the global feedbacks between life and the hydrologic cycle tend to stabilize the climate system about some equilibrium level is difficult to assess. We use a global climate model to examine how the presence of vegetation can affect the hydrologic cycle in a particular region. A control for the present climate is compared with a model experiment in which the Sahara Desert is replaced by vegetation in the form of trees and shrubs common to the Sahel region. A second model experiment is designed to identify the separate roles of two different effects of vegetation, namely the modified albedo and the presence of roots that can extract moisture from deeper soil layers. The results show that the presence of vegetation leads to increases in precipitation and soil moisture in western Sahara. In eastern Sahara, the changes are less clear. The increase in soil moisture is greater when the desert albedo is replaced by the vegetation albedo than when both the vegetation albedo and roots are added. The effect of roots is to withdraw water from deeper layers during the dry season. One implication of this study is that the insertion of vegetation into the Sahara modifies the hydrologic cycle so that the vegetation is more likely to persist than initially.

Response of deep soil moisture to land use and afforestation in the semi-arid Loess Plateau, China

NASA Astrophysics Data System (ADS)

Yang, Lei; Wei, Wei; Chen, Liding; Mo, Baoru

2012-12-01

SummarySoil moisture is an effective water source for plant growth in the semi-arid Loess Plateau of China. Characterizing the response of deep soil moisture to land use and afforestation is important for the sustainability of vegetation restoration in this region. In this paper, the dynamics of soil moisture were quantified to evaluate the effect of land use on soil moisture at a depth of 2 m. Specifically, the gravimetric soil moisture content was measured in the soil layer between 0 and 8 m for five land use types in the Longtan catchment of the western Loess Plateau. The land use types included traditional farmland, native grassland, and lands converted from traditional farmland (pasture grassland, shrubland and forestland). Results indicate that the deep soil moisture content decreased more than 35% after land use conversion, and a soil moisture deficit appeared in all types of land with introduced vegetation. The introduced vegetation decreased the soil moisture content to levels lower than the reference value representing no human impact in the entire 0-8 m soil profile. No significant differences appeared between different land use types and introduced vegetation covers, especially in deeper soil layers, regardless of which plant species were introduced. High planting density was found to be the main reason for the severe deficit of soil moisture. Landscape management activities such as tillage activities, micro-topography reconstruction, and fallowed farmland affected soil moisture in both shallow and deep soil layers. Tillage and micro-topography reconstruction can be used as effective countermeasures to reduce the soil moisture deficit due to their ability to increase soil moisture content. For sustainable vegetation restoration in a vulnerable semi-arid region, the plant density should be optimized with local soil moisture conditions and appropriate landscape management practices.

Circular linkages between soil biodiversity, fertility and plant productivity are limited to topsoil at the continental scale.

PubMed

Delgado-Baquerizo, Manuel; Powell, Jeff R; Hamonts, Kelly; Reith, Frank; Mele, Pauline; Brown, Mark V; Dennis, Paul G; Ferrari, Belinda C; Fitzgerald, Anna; Young, Andrew; Singh, Brajesh K; Bissett, Andrew

2017-08-01

The current theoretical framework suggests that tripartite positive feedback relationships between soil biodiversity, fertility and plant productivity are universal. However, empirical evidence for these relationships at the continental scale and across different soil depths is lacking. We investigate the continental-scale relationships between the diversity of microbial and invertebrate-based soil food webs, fertility and above-ground plant productivity at 289 sites and two soil depths, that is 0-10 and 20-30 cm, across Australia. Soil biodiversity, fertility and plant productivity are strongly positively related in surface soils. Conversely, in the deeper soil layer, the relationships between soil biodiversity, fertility and plant productivity weaken considerably, probably as a result of a reduction in biodiversity and fertility with depth. Further modeling suggested that strong positive associations among soil biodiversity-fertility and fertility-plant productivity are limited to the upper soil layer (0-10 cm), after accounting for key factors, such as distance from the equator, altitude, climate and physicochemical soil properties. These findings highlight the importance of surface soil biodiversity for soil fertility, and suggest that any loss of surface soil could potentially break the links between soil biodiversity-fertility and/or fertility-plant productivity, which can negatively impact nutrient cycling and food production, upon which future generations depend. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Magnetic Measurements of Atmospheric Dust Deposition in Soils

NASA Astrophysics Data System (ADS)

Kapička, Aleš; Petrovský, Eduard; Grison, Hana; Podrázský, Vilém; Křížek, Pavel

2010-05-01

Atmospheric dust of anthropogenic origin contains significant portion of minerals characterized by ferrimagnetic properties [1,2]. These minerals, mostly iron oxides, can serve as tracers of industrial pollutants in soil layers. Moreover, recent results, e.g., [3,4] show significant correlation between concentration-dependent magnetic parameters (e.g., low-field magnetic susceptibility) and concentration of heavy metals (e.g., Pb, Zn, Cd). In our paper we have investigated magnetic properties of depth soil profiles from Krušné hory Mountains (Czech Republic), which belong to a highly contaminated, so-called Black Triangle in central Europe. Emissions are determined by considerable concentration of big sources of pollution (power plants burning fossil fuel, metallurgical and chemical industry). Increased values of magnetic susceptibility (25 - 200 × 10-5 SI) were clearly identified in the top-soil layers. Thermomagnetic analyses and SEM observation indicate that the accumulated anthropogenic ferrimagnetics dominate these layers. Magnetic enhancement is limited to depths of 4-7 cm below the soil surface, usually in F-H or top of Ah soil horizons; deeper soil horizons contain mainly magnetically weak materials and are characterized by much lower values of susceptibility (up to 30 × 10-5 SI). Significant magnetic parameters (e.g., Curie temperature Tc) and SEM results of contaminated topsoils are comparable with magnetic parameters of atmospheric dust, collected (using high-volume samplers) at the same localities.

Increased precipitation accelerates soil organic matter turnover associated with microbial community composition in topsoil of alpine grassland on the eastern Tibetan Plateau.

PubMed

Han, Conghai; Wang, Zongli; Si, Guicai; Lei, Tianzhu; Yuan, Yanli; Zhang, Gengxin

2017-10-01

Large quantities of carbon are stored in alpine grassland of the Tibetan Plateau, which is extremely sensitive to climate change. However, it remains unclear whether soil organic matter (SOM) in different layers responds to climate change analogously, and whether microbial communities play vital roles in SOM turnover of topsoil. In this study we measured and collected SOM turnover by the 14 C method in alpine grassland to test climatic effects on SOM turnover in soil profiles. Edaphic properties and microbial communities in the northwestern Qinghai Lake were investigated to explore microbial influence on SOM turnover. SOM turnover in surface soil (0-10 cm) was more sensitive to precipitation than that in subsurface layers (10-40 cm). Precipitation also imposed stronger effects on the composition of microbial communities in the surface layer than that in deeper soil. At the 5-10 cm depth, the SOM turnover rate was positively associated with the bacteria/fungi biomass ratio and the relative abundance of Acidobacteria, both of which are related to precipitation. Partial correlation analysis suggested that increased precipitation could accelerate the SOM turnover rate in topsoil by structuring soil microbial communities. Conversely, carbon stored in deep soil would be barely affected by climate change. Our results provide valuable insights into the dynamics and storage of SOM in alpine grasslands under future climate scenarios.

The impact of a shallow biobarrier on water recharge patterns in a semi-arid environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laundre, J.W.

1997-12-31

This study attempted to measure the effect of a shallow biobarrier of gravel and cobble on water flow patterns during spring snow melt and recharge. The design consisted of 30 metal culverts 3 m in diameter and 1.6 m long, positioned on end. Test culverts contained 50-cm biobarrier of gravel or cobble and then an additional 50 cm of soil placed above the barrier layer. A neutron probe was used to measure soil moisture above and below the barrier. Measurements were made in the fall and again immediately after snow melt in the spring. During recharge, the biobarriers provided amore » capillary break which resulted in a pooling of water above the barrier layer. With sufficient snowmelt, the water can penetrate the break and possibly penetrate deeper than in the absence of the barrier layer.« less

Estimating soil organic and aboveground woody carbon stock in a protected dry Miombo ecosystem, Zimbabwe: Landsat 8 OLI data applications

NASA Astrophysics Data System (ADS)

Dube, Timothy; Muchena, Richard; Masocha, Mhosisi; Shoko, Cletah

2018-06-01

Accurate and reliable soil organic carbon stock estimation is critical in understanding forest role to regional carbon cycles. So far, the total carbon pool in dry Miombo ecosystems is often under-estimated. In that regard this study sought to model the relationship between the aboveground woody carbon pool and the soil carbon pool, using both ground-based and remote sensing methods. To achieve this objective, the Ratio Vegetation Index (RVI), Normalized Difference Vegetation Index (NDVI), and the Soil Adjusted Vegetation Index (SAVI) computed from the newly launched Landsat 8 OLI satellite data were used. Correlation and regression analysis were used to relate Soil Organic Carbon (S.O.C), aboveground woody carbon and remotely sensed vegetation indices. Results showed a soil organic carbon in the upper soil layer (0-15 cm) was positively correlated with aboveground woody carbon and this relationship was significant (r = 0.678; P < 0.05) aboveground carbon. However, there were no significant correlations (r = -0.11, P > 0.05) between SOC in the deeper soil layer (15-30 cm) and aboveground woody carbon. These findings imply that (relationship between aboveground woody carbon and S.O.C) aboveground woody carbon stocks can be used as a proxy to estimate S.O.C in the top soil layer (0-15 cm) in dry Miombo ecosystems. Overall, these findings underscore the potential and significance of remote sensing data in understanding savanna ecosystems contribution to the global carbon cycle.

Spatial and vertical distribution of short chain chlorinated paraffins in soils from wastewater irrigated farmlands.

PubMed

Zeng, Lixi; Wang, Thanh; Han, Wenya; Yuan, Bo; Liu, Qian; Wang, Yawei; Jiang, Guibin

2011-03-15

Chlorinated paraffins (CPs) are one of the most complex groups of halogenated contaminants in the environment. However, studies of short chain CPs (SCCPs) in China are very scarce. In this study, the concentrations and distribution of SCCPs in farm soils from a wastewater irrigated area in China were investigated. SCCPs were detected in all topsoil samples, with the sum of the concentrations (ΣSCCPs) in the range of 159.9-1450 ng/g (dry weight, dw). A noticeable spatial trend and specific congener distribution were observed in the wastewater irrigated farmland. Soil vertical profiles showed that ΣSCCP concentrations below the plowed layer decreased exponentially and had a significant positive relationship (R(2) > 0.83) with total organic carbon in soil cores. Furthermore, soil vertical distributions indicated that lower chlorinated (Cl(5-6)) and shorter chain (C(10-12)) congeners are more prone to migrate to deeper soil layers compared to highly chlorinated and longer chain congeners. This work demonstrated that effluents from sewage treatment plants (STPs) could be a significant source of SCCPs to the ambient environment and wastewater irrigation can lead to higher accumulation of SCCPs in farm soils.

Manipulative lowering of the water table during summer does not affect CO2 emissions and uptake in a fen in Germany.

PubMed

Muhr, Jan; Höhle, Juliane; Otieno, Dennis O; Borken, Werner

2011-03-01

We simulated the effect of prolonged dry summer periods by lowering the water table on three manipulation plots (D(1-3)) in a minerotrophic fen in southeastern Germany in three years (2006-2008). The water table at this site was lowered by drainage and by excluding precipitation; three nonmanipulated control plots (C(1-3)) served as a reference. We found no significant differences in soil respiration (R(Soil)), gross primary production (GPP), or aboveground respiration (R(AG)) between the C(1-3) and D(1-3) plots in any of the measurement years. The water table on the control plots was naturally low, with a median water table (2006-2008) of 8 cm below the surface, and even lower during summer when respiratory activity was highest, with median values (C(1-3)) between 11 and 19 cm below the surface. If it is assumed that oxygen availability in the uppermost 10 cm was not limited by the location of the water table, manipulative lowering of the water table most likely increased oxygen availability only in deeper peat layers where we expect R(Soil) to be limited by poor substrate quality rather than anoxia. This could explain the lack of a manipulation effect. In a second approach, we estimated the influence of the water table on R(Soil) irrespective of treatment. The results showed a significant correlation between R(Soil) and water table, but with R(Soil) decreasing at lower water tables rather than increasing. We thus conclude that decomposition in the litter layer is not limited by waterlogging in summer, and deeper peat layers bear no significant decomposition potential due to poor substrate quality. Consequently, we do not expect enhanced C losses from this site due to increasing frequency of dry summers. Assimilation and respiration of aboveground vegetation were not affected by water table fluctuations between 10 and >60 cm depth, indicating the lack of stress resulting from either anoxia (high water table) or drought (low water table).

Occurrence of 1,1'-dimethyl-4,4'-bipyridinium (Paraquat) in irrigated soil of the Lake Chad Basin, Niger.

PubMed

Crampon, Marc; Copard, Yoann; Favreau, Guillaume; Raux, Julie; Merlet-Machour, Nadine; Le Coz, Mathieu; Ibrahim, Maïmouna; Peulon-Agasse, Valérie; Portet-Koltalo, Florence

2014-09-01

Increased use of agrochemical products to improve yields for irrigated crops in sub-Saharan Africa has been accompanied by a significant increase in the risk of environmental contamination. Detailed examples of the fate of pesticides after initial spreading on crop fields are scarce in tropical regions, where safe practices and related health risks are poorly understood by smallholder farmers. In the semi-arid environment of the Lake Chad Basin, SE Niger, both intrinsic properties of pesticides and extrinsic factors such as soil and climate helped to characterize processes leading to an accumulation of pesticides in soils. Analysis by HPLC-UV of a 6 m deep soil profile showed the presence of Paraquat at concentrations from 953 ± 102 μg kg(-1) to 3083 ± 175 μg kg(-1) at depths between 0.80 and 2.75 m below the land surface. Soil analysis revealed that up to approximately 15 % of the total soil matrix consists of smectites, a clay mineral capable of retaining cationic pesticides such as Paraquat, and a very low content of organic matter (<0.15 wt.% TOC). Paraquat could be stored and not bioavailable in a clayey barrier at approximately 2-m depth and therefore does not represent an immediate risk for populations or environment in this form. However, if the Paraquat application rate remains constant, the clayey barrier could reach a saturation limit within 150-200 years and 180-220 years if we consider a DT50 in soil of ~1,000 days (FAO). Consequently, it could lead to a deeper infiltration and so a pollution of groundwater. Such a scenario can represent a health risk for drinking water and for the Lake Chad, which is a major resource for this densely populated region of semi-arid Africa. Further analyses should focus on deeper layers and groundwater Paraquat contents to validate or invalidate the hypothesis of storage in this clay-rich layer.

Lack of bedrock grain size influence on the soil production rate

NASA Astrophysics Data System (ADS)

Gontier, Adrien; Rihs, Sophie; Chabaux, Francois; Lemarchand, Damien; Pelt, Eric; Turpault, Marie-Pierre

2015-10-01

Our study deals with the part played by bedrock grain size on soil formation rates. U- and Th-series disequilibria were measured in two soil profiles developed from two different facies of the same bedrock, i.e., fine and coarse grain size granites, in the geomorphically flat landscape of the experimental Breuil-Chenue forest site, Morvan, France. The U- and Th-series disequilibria of soil layers and the inferred soil formation rate (1-2 mm ky-1) are nearly identical along the two profiles despite differences in bedrock grain size, variable weathering states and a significant redistribution of U and Th from the uppermost soil layers. This indicates that the soil production rate is more affected by regional geomorphology than by the underlying bedrock texture. Such a production rate inferred from residual soil minerals integrated over the age of the soil is consistent with the flat and slowly eroding geomorphic landscape of the study site. It also compares well to the rate inferred from dissolved solutes integrated over the shorter time scale of solute transport from granitic and basaltic watersheds under similar climates. However, it is significantly lower than the denudation or soil formation rates previously reported from either cosmogenic isotope or U-series measurements from similar climates and lithologies. Our results highlight the particularly low soil production rates of flat terrains in temperate climates. Moreover, they provide evidence that the reactions of mineral weathering actually take place in horizons deeper than 1 m, while a chemical steady state of both concentrations and U-series disequilibria is established in the upper most soil layers, i.e., above ∼70 cm depth. In such cases, the use of soil surface horizons for determining weathering rates is precluded and illustrates the need to focus instead on the deepest soil horizons.

[Deuterium isotope characteristics of precipitation infiltrated in the West Ordos Desert of Inner Mongolia, China].

PubMed

Chen, Jie; Xu, Qing; Gao, De Qiang; Ma, Ying Bin; Zhang, Bei Bei; Hao, Yu Guang

2017-07-18

Understanding the soil-profile temporal and spatial distribution of rainwater in arid and semiarid regions provides a scientific basis for the restoration and maintenance of degraded desert ecosystems in the West Ordos Desert of Inner Mongolia, China. In this study, the deuterium isotope (δD) value of rainwater, soil water, and groundwater were examined in the West Ordos Desert. The contribution of precipitation to soil water in each layer of the soil profile was calculated with two-end linear mixed model. In addition, the temporal and spatial distribution of δD of soil water in the soil profile was analyzed under different-intensity precipitation. The results showed that small rainfall events (0-10 mm) affected the soil moisture and the δD value of soil water in surface soil (0-10 cm). About 30.3% to 87.9% of rainwater was kept in surface soil for nine days following the rainfall event. Medium rainfall events (10-20 mm) influenced the soil moisture and the δD value of soil water at soil depth of 0-40 cm. About 28.2% to 80.8% of rainwater was kept in soil layer of 0-40 cm for nine days following the medium rainfall event. Large (20-30 mm) and extremely large (＞30 mm) rainfall events considerably influenced the soil moisture and δD value of soil water in each of the soil layers, except for the 100-150 cm layer. The δD value of soil water was between those δD values of rainwater and groundwater, which suggested that precipitation and groundwater were the sources of soil water in the West Ordos Desert. Under the same intensity rainfall, the δD value of surface soil water (0-10 cm) was directly affected by δD of rainwater. With increasing soil depth, the variation of soil water δD decreased, and the soil water of 100-150 cm kept stable. With increasing intensity of precipitation, the influence of precipitation on soil water δD lasted for a longer duration and occurred at a deeper soil depth.

Spatial variability of soil salinity in coastal saline soil at different scales in the Yellow River Delta, China.

PubMed

Wang, Zhuoran; Zhao, Gengxing; Gao, Mingxiu; Chang, Chunyan

2017-02-01

The objectives of this study were to explore the spatial variability of soil salinity in coastal saline soil at macro, meso and micro scales in the Yellow River delta, China. Soil electrical conductivities (ECs) were measured at 0-15, 15-30, 30-45 and 45-60 cm soil depths at 49 sampling sites during November 9 to 11, 2013. Soil salinity was converted from soil ECs based on laboratory analyses. Our results indicated that at the macro scale, soil salinity was high with strong variability in each soil layer, and the content increased and the variability weakened with increasing soil depth. From east to west in the region, the farther away from the sea, the lower the soil salinity was. The degrees of soil salinization in three deeper soil layers are 1.14, 1.24 and 1.40 times higher than that in the surface soil. At the meso scale, the sequence of soil salinity in different topographies, soil texture and vegetation decreased, respectively, as follows: depression >flatland >hillock >batture; sandy loam >light loam >medium loam >heavy loam >clay; bare land >suaeda salsa >reed >cogongrass >cotton >paddy >winter wheat. At the micro scale, soil salinity changed with elevation in natural micro-topography and with anthropogenic activities in cultivated land. As the study area narrowed down to different scales, the spatial variability of soil salinity weakened gradually in cultivated land and salt wasteland except the bare land.

Quantitative study on the fate of residual soil nitrate in winter wheat based on a 15N-labeling method.

PubMed

Zhang, Jing-Ting; Wang, Zhi-Min; Liang, Shuang-Bo; Zhang, Ying-Hua; Zhou, Shun-Li; Lu, Lai-Qing; Wang, Run-Zheng

2017-01-01

A considerable amount of surplus nitrogen (N), which primarily takes the form of nitrate, accumulates in the soil profile after harvesting crops from an intensive production system in the North China Plain. The residual soil nitrate (RSN) is a key factor that is included in the N recommendation algorithm. Quantifying the utilization and losses of RSN is a fundamental necessity for optimizing crop N management, improving N use efficiency, and reducing the impact derived from farmland N losses on the environment. In this study, a 15N-labeling method was introduced to study the fate of the RSN quantitatively during the winter wheat growing season by 15N tracer technique combined with a soil column study. A soil column with a 2 m height was vertically divided into 10 20-cm layers, and the RSN in each layer was individually labeled with a 15N tracer before the wheat was sown. The results indicated that approximately 17.68% of the crop N derived from RSN was located in the 0-2 m soil profile prior to wheat sowing. The wheat recovery proportions of RSN at various layers ranged from 0.21% to 33.46%. The percentages that still remained in the soil profile after the wheat harvest ranged from 47.08% to 75.44%, and 19.46-32.64% of the RSN was unaccounted for. Upward and downward movements in the RSN were observed, and the maximum upward and downward distances were 40 cm and 100 cm, respectively. In general, the 15N-labeling method contributes to a deeper understanding of the fates of the RSN. Considering the low crop recovery of the RSN from deep soil layers, water and N saving practices should be adopted during crop production.

No shift to a deeper water uptake depth in response to summer drought of two lowland and sub-alpine C₃-grasslands in Switzerland.

PubMed

Prechsl, Ulrich E; Burri, Susanne; Gilgen, Anna K; Kahmen, Ansgar; Buchmann, Nina

2015-01-01

Temperate C3-grasslands are of high agricultural and ecological importance in Central Europe. Plant growth and consequently grassland yields depend strongly on water supply during the growing season, which is projected to change in the future. We therefore investigated the effect of summer drought on the water uptake of an intensively managed lowland and an extensively managed sub-alpine grassland in Switzerland. Summer drought was simulated by using transparent shelters. Standing above- and belowground biomass was sampled during three growing seasons. Soil and plant xylem waters were analyzed for oxygen (and hydrogen) stable isotope ratios, and the depths of plant water uptake were estimated by two different approaches: (1) linear interpolation method and (2) Bayesian calibrated mixing model. Relative to the control, aboveground biomass was reduced under drought conditions. In contrast to our expectations, lowland grassland plants subjected to summer drought were more likely (43-68%) to rely on water in the topsoil (0-10 cm), whereas control plants relied less on the topsoil (4-37%) and shifted to deeper soil layers (20-35 cm) during the drought period (29-48%). Sub-alpine grassland plants did not differ significantly in uptake depth between drought and control plots during the drought period. Both approaches yielded similar results and showed that the drought treatment in the two grasslands did not induce a shift to deeper uptake depths, but rather continued or shifted water uptake to even more shallower soil depths. These findings illustrate the importance of shallow soil depths for plant performance under drought conditions.

Study of the degradation of the herbicides 2,4-D and MCPA at different depths in contaminated agricultural soil.

PubMed

Crespin, M A; Gallego, M; Valcárcel, M; González, J L

2001-11-01

Two phenoxyacid herbicides (2,4-D and MCPA) and their six corresponding phenols were determined in soil by using gas chomatography with electron impact mass spectrometry (GC/MS) for confirmation/quantitation. An automatic extraction (leaching), preconcentration, and cleanup (sorption) module was developed to extract the eight compounds from soil. The average recovery of all species, spiked to soil at microg/kg-mg/kg levels, was 95% (average standard deviation +/- 5%). A plot of agricultural clayey soil (approximately 12 m2) was contaminated with both herbicides (approximately 96 g/m3, depth 10 cm, density 1.23 g/cm3) and irrigated with (17 mm) at variable time intervals. Both herbicides and their corresponding phenol compounds were monitored at different soil depths over a 50 day period. The degradation of both herbicides in the surface layer (t(1/2) approximately 5 days) is a result of photodecomposition and microbial action; in the deeper layers, the degradation products occur in lower proportions by effect of leaching and are also the result of microbial action. The six phenol metabolites are only detected in the surface layer as they form preferentially by photodecomposition. The main metabolites (viz. 2,4-DCP for 2,4-D and 4-C-2-MP for MCPA) are formed within 24 h after the soil is contaminated; their concentration peaks are at day 8 in the absence of irrigation.

Coupled long-term summer warming and deeper snow alters species composition and stimulates gross primary productivity in tussock tundra.

PubMed

Leffler, A Joshua; Klein, Eric S; Oberbauer, Steven F; Welker, Jeffrey M

2016-05-01

Climate change is expected to increase summer temperature and winter precipitation throughout the Arctic. The long-term implications of these changes for plant species composition, plant function, and ecosystem processes are difficult to predict. We report on the influence of enhanced snow depth and warmer summer temperature following 20 years of an ITEX experimental manipulation at Toolik Lake, Alaska. Winter snow depth was increased using snow fences and warming was accomplished during summer using passive open-top chambers. One of the most important consequences of these experimental treatments was an increase in active layer depth and rate of thaw, which has led to deeper drainage and lower soil moisture content. Vegetation concomitantly shifted from a relatively wet system with high cover of the sedge Eriophorum vaginatum to a drier system, dominated by deciduous shrubs including Betula nana and Salix pulchra. At the individual plant level, we observed higher leaf nitrogen concentration associated with warmer temperatures and increased snow in S. pulchra and B. nana, but high leaf nitrogen concentration did not lead to higher rates of net photosynthesis. At the ecosystem level, we observed higher GPP and NEE in response to summer warming. Our results suggest that deeper snow has a cascading set of biophysical consequences that include a deeper active layer that leads to altered species composition, greater leaf nitrogen concentration, and higher ecosystem-level carbon uptake.

Can the soil fauna of boreal forests recover from lead-derived stress in a shooting range area?

PubMed

Selonen, Salla; Liiri, Mira; Setälä, Heikki

2014-04-01

The responses of soil faunal communities to lead (Pb) contamination in a shooting range area and the recovery of these fauna after range abandonment were studied by comparing the communities at an active shotgun shooting range, an abandoned shooting range, and a control site, locating in the same forest. Despite the similar overall Pb pellet load at the shooting ranges, reaching up to 4 kg m(-2), Pb concentrations in the top soil of the abandoned range has decreased due to the accumulation of detritus on the soil surface. As a consequence, soil animal communities were shown to recover from Pb-related disturbances by utilizing the less contaminated soil layer. Microarthropods showed the clearest signs of recovery, their numbers and community composition being close to those detected at the control site. However, in the deepest organic soil layer, the negative effects of Pb were more pronounced at the abandoned than at the active shooting range, which was detected as altered microarthropod and nematode community structures, reduced abundances of several microarthropod taxa, and the total absence of enchytraeid worms. Thus, although the accumulation of fresh litter on soil surface can promote the recovery of decomposer communities in the top soil, the gradual release of Pb from corroding pellets may pose a long-lasting risk for decomposer taxa deeper in the soil.

Ecohydrology of dry regions: storage versus pulse soil water dynamics

USGS Publications Warehouse

Lauenroth, William K.; Schlaepfer, Daniel R.; Bradford, John B.

2014-01-01

Although arid and semiarid regions are defined by low precipitation, the seasonal timing of temperature and precipitation can influence net primary production and plant functional type composition. The importance of precipitation seasonality is evident in semiarid areas of the western U.S., which comprise the Intermountain (IM) zone, a region that receives important winter precipitation and is dominated by woody plants and the Great Plains (GP), a region that receives primarily summer precipitation and is dominated by perennial grasses. Although these general relationships are well recognized, specific differences in water cycling between these regions have not been well characterized. We used a daily time step soil water simulation model and twenty sites from each region to analyze differences in soil water dynamics and ecosystem water balance. IM soil water patterns are characterized by storage of water during fall, winter, and spring resulting in relatively reliable available water during spring and early summer, particularly in deep soil layers. By contrast, GP soil water patterns are driven by pulse precipitation events during the warm season, resulting in fluctuating water availability in all soil layers. These contrasting patterns of soil water—storage versus pulse dynamics—explain important differences between the two regions. Notably, the storage dynamics of the IN sites increases water availability in deep soil layers, favoring the deeper rooted woody plants in that region, whereas the pulse dynamics of the Great Plains sites provide water primarily in surface layers, favoring the shallow-rooted grasses in that region. In addition, because water received when plants are either not active or only partially so is more vulnerable to evaporation and sublimation than water delivered during the growing season, IM ecosystems use a smaller fraction of precipitation for transpiration (47%) than GP ecosystems (49%). Recognizing the pulse-storage dichotomy in soil water regimes between the IM and GP regions may be useful for understanding the potential influence of climate changes on soil water patterns and resulting dominant plant functional groups in both regions.

Rapid runoff via shallow throughflow and deeper preferential flow in a boreal catchment underlain by frozen silt (Alaska, USA)

USGS Publications Warehouse

Koch, Joshua C.; Ewing, Stephanie A.; Striegl, Robert G.; McKnight, Diane M.

2013-01-01

In high-latitude catchments where permafrost is present, runoff dynamics are complicated by seasonal active-layer thaw, which may cause a change in the dominant flowpaths as water increasingly contacts mineral soils of low hydraulic conductivity. A 2-year study, conducted in an upland catchment in Alaska (USA) underlain by frozen, well-sorted eolian silt, examined changes in infiltration and runoff with thaw. It was hypothesized that rapid runoff would be maintained by flow through shallow soils during the early summer and deeper preferential flow later in the summer. Seasonal changes in soil moisture, infiltration, and runoff magnitude, location, and chemistry suggest that transport is rapid, even when soils are thawed to their maximum extent. Between June and September, a shift occurred in the location of runoff, consistent with subsurface preferential flow in steep and wet areas. Uranium isotopes suggest that late summer runoff erodes permafrost, indicating that substantial rapid flow may occur along the frozen boundary. Together, throughflow and deep preferential flow may limit upland boreal catchment water and solute storage, and subsequently biogeochemical cycling on seasonal to annual timescales. Deep preferential flow may be important for stream incision, network drainage development, and the release of ancient carbon to ecosystems

Microbial functional diversity responses to 2 years since biochar application in silt-loam soils on the Loess Plateau.

PubMed

Zhu, Li-Xia; Xiao, Qian; Shen, Yu-Fang; Li, Shi-Qing

2017-10-01

The structure and function of soil microbial communities have been widely used as indicators of soil quality and fertility. The effect of biochar application on carbon sequestration has been studied, but the effect on soil microbial functional diversity has received little attention. We evaluated effects of biochar application on the functional diversities of microbes in a loam soil. The effects of biochar on microbial activities and related processes in the 0-10 and 10-20cm soil layers were determined in a two-year experiment in maize field on the Loess Plateau in China. Low-pyrolysis biochar produced from maize straw was applied into soils at rates of 0 (BC0), 10 (BC10) and 30 (BC30)tha -1 . Chemical analysis indicated that the biochar did not change the pH, significantly increased the amounts of organic carbon and nitrogen, and decreased the amount of mineral nitrogen and the microbial quotient. The biochar significantly decreased average well colour development (AWCD) values in Biolog EcoPlates™ for both layers, particularly for the rate of 10tha -1 . Biochar addition significantly decreased substrate richness (S) except for BC30 in the 0-10cm layer. Effects of biochar on the Shannon-Wiener index (H) and Simpson's dominance (D) were not significant, except for a significant increase in evenness index (E) in BC10 in the 10-20cm layer. A principal component analysis clearly differentiated the treatments, and microbial use of six categories of substrates significantly decreased in both layers after biochar addition, although the use of amines and amides did not differ amongst the three treatments in the deeper layer. Maize above ground dry biomass and height did not differ significantly amongst the treatments, and biochar had no significant effect on nitrogen uptake by maize seedlings. H was positively correlated with AWCD, and negatively with pH. AWCD was positively correlated with mineral N and negatively with pH. Our results indicated that shifts in soil microbial functional diversity affected by biochar were not effective indicators of soil quality in earlier maize growth periods in this region. Copyright © 2017. Published by Elsevier Inc.

Plant nutrient acquisition strategies in tundra species: at which soil depth do species take up their nitrogen?

NASA Astrophysics Data System (ADS)

Limpens, Juul; Heijmans, Monique; Nauta, Ake; van Huissteden, Corine; van Rijssel, Sophie

2016-04-01

The Arctic is warming at unprecedented rates. Increased thawing of permafrost releases nutrients locked up in the previously frozen soils layers, which may initiate shifts in vegetation composition. The direction in which the vegetation shifts will co-determine whether Arctic warming is mitigated or accelerated, making understanding successional trajectories urgent. One of the key factors influencing the competitive relationships between plant species is their access to nutrients, in particularly nitrogen (N). We assessed the depth at which plant species took up N by performing a 15N tracer study, injecting 15(NH4)2SO4 at three depths (5, 15, 20 cm) into the soil in arctic tundra in north-eastern Siberia in July. In addition we explored plant nutrient acquisition strategy by analyzing natural abundances of 15N in leaves. We found that vascular plants took up 15N at all injection depths, irrespective of species, but also that species showed a clear preference for specific soil layers that coincided with their functional group (graminoids, dwarf shrubs, cryptogams). Graminoids took up most 15N at 20 cm depth nearest to the thaw front, with grasses showing a more pronounced preference than sedges. Dwarf shrubs took up most 15N at 5 cm depth, with deciduous shrubs displaying more preference than evergreens. Cryptogams did not take up any of the supplied 15N . The natural 15N abundances confirmed the pattern of nutrient acquisition from deeper soil layers in graminoids and from shallow soil layers in both deciduous and evergreen dwarf shrubs. Our results prove that graminoids and shrubs differ in their N uptake strategies, with graminoids profiting from nutrients released at the thaw front, whereas shrubs forage in the upper soil layers. The above implies that graminoids, grasses in particular, will have a competitive advantage over shrubs as the thaw front proceeds and/or superficial soil layers dry out. Our results suggest that the vertical distribution of nutrients over the soil will play an important role in vegetation succession as permafrost thaw progresses.

[Effects of mulching management of Phyllostachys heterocycla forests on the characteristics of soil infiltration and biometrics in southwest Zhejiang Province, China].

PubMed

Wang, Yi Kun; Jin, Ai Wu; Fang, Sheng Zuo

2017-05-18

Soil infiltration, soil physical and chemical properties, root length density and soil fauna diversity were studied in Phyllostachys heterocycla forests with different mulching times in southwest Zhejiang Province, China. Significant differences of soil infiltration capability were found among the forests with different mulching times and among soil layers. Soil infiltration capability generally declined in the deeper soil layers. With mulching management, soil infiltration capability increased under the first mulching, and then declined with the increase of mulching times. The Kostiakov model was suitable for simulating soil infiltration process. With the extending of mulching times (4 to 6 years), soil pH and total/non-capillary porosity decreased, while soil bulk density, soil orga-nic matter and total nitrogen contents increased significantly. Soil initial, steady, and average infiltration rates as well as the cumulative infiltration amount correlated closely with the length density of roots with diameter from 0.5 mm to 5.0 mm, showing a decreasing tendency with the decrease in root length density. Soil fauna density was highest in the forest under the first mulching, and was lowest after third mulching. The decreased numbers of large and meso-arthropods, including Symphyla, Chilopoda, Diplopoda, Hymenoptera and pseudoscorpions, and the micro-arthropods, including Oribatida, Mesostigmata, Onychiuridae, Neanuridae, Cyphoderidae, and Entomobryidae, showed negative effects on soil infiltration. In conclusion, long-term mulching changed soil physical and chemical properties, decreased soil infiltration capability, and suppressed the development of soil fauna, which might cause the decline ofP. heterocycla forests.

Downward migration of radiocesium in an abandoned paddy soil after the Fukushima Dai-ichi Nuclear Power Plant accident.

PubMed

Takahashi, Junko; Wakabayashi, Shokichi; Tamura, Kenji; Onda, Yuichi

2018-02-01

After the Fukushima Dai-ichi Nuclear Power Plant accident on March 2011, continuous monitoring of the detailed vertical distribution of radiocesium in soil is required to evaluate the fate of radiocesium and establish strategies for remediation and management of the contaminated land. It is especially important to investigate paddy soil because little knowledge has been accumulated for paddy soil and wetland rice is a major staple in Japan. Therefore, we monitored the vertical distribution of 137 Cs in abandoned paddy soil in a planned evacuation zone from June 2011 to March 2016. The decontamination works (i.e., 5 cm of surface soil removal and re-covering with uncontaminated soil) were conducted by the government in 2015. As a result of monitoring, the 137 Cs gradually migrated downward with time and the 137 Cs concentration in the 0-10 cm soil was almost homogenous in October 2014, although it was non-cultivated. The liner relationship was obtained between the median depth, which is the thickness of a soil layer containing half of the total 137 Cs inventory, and the time after the accident, indicating the migration rate was constant (1.3 cm y -1 ) before the decontamination works. After the decontamination works, the 137 Cs concentration in the uppermost surface layer was reduced by 90%, however the total 137 Cs inventory was reduced by only 50-70%. It was shown that the efficiency of 137 Cs removal by the decontamination works decrease linearly over time in fields like the studied paddy, in which the homogenization of 137 Cs concentration occurred. Conversely, the downward migration of 137 Cs to subsurface layers deeper than 10 cm (i.e., plowpan layer) with low permeability rarely occurred. It is expected that these unique trends in distribution and migration of 137 Cs would be found in abandoned paddy soils with properties similar to the studied soil, sandy loam but poorly drained because of the low permeable plowpan layer, although further validation is necessary. Copyright © 2017 Elsevier Ltd. All rights reserved.

Using atmospheric fallout to date organic horizon layers and quantify metal dynamics during decomposition

NASA Astrophysics Data System (ADS)

Kaste, James M.; Bostick, Benjamin C.; Heimsath, Arjun M.; Steinnes, Eiliv; Friedland, Andrew J.

2011-03-01

High concentrations of metals in organic matter can inhibit decomposition and limit nutrient availability in ecosystems, but the long-term fate of metals bound to forest litter is poorly understood. Controlled experiments indicate that during the first few years of litter decay, Al, Fe, Pb, and other metals that form stable complexes with organic matter are naturally enriched by several hundred percent as carbon is oxidized. The transformation of fresh litter to humus takes decades, however, such that current datasets describing the accumulation and release of metals in decomposing organic matter are timescale limited. Here we use atmospheric 210Pb to quantify the fate of metals in canopy-derived litter during burial and decay in coniferous forests in New England and Norway where decomposition rates are slow and physical soil mixing is minimal. We measure 210Pb inventories in the O horizon and mineral soil and calculate a 60-630 year timescale for the production of mobile organo-metallic colloids from the decomposition of fresh forest detritus. This production rate is slowest at our highest elevation (˜1000 m) and highest latitude sites (>63°N) where decomposition rates are expected to be low. We calculate soil layer ages by assuming a constant supply of atmospheric 210Pb and find that they are consistent with the distribution of geochemical tracers from weapons fallout, air pollution, and a direct 207Pb application at one site. By quantifying a gradient of organic matter ages with depth in the O horizon, we describe the accumulation and loss of metals in the soil profile as organic matter transforms from fresh litter to humus. While decomposition experiments predict that Al and Fe concentrations increase during the initial few years of decay, we show here that these metals continue to accumulate in humus for decades, and that enrichment occurs at a rate higher than can be explained by quantitative retention during decomposition alone. Acid extractable Al and Fe concentrations are higher in the humus layer of the O horizon than in the mineral soil immediately beneath this layer: it is therefore unlikely that physical soil mixing introduces significant Al and Fe to humus. This continuous enrichment of Al and Fe over time may best be explained by the recent suggestion that metals are mined from deeper horizons and brought into the O horizon via mycorrhizal plants. In sharp contrast to Al and Fe, we find that Mn concentrations in decomposing litter layers decrease exponentially with age, presumably because of leaching or rapid uptake, which may explain the low levels of acid extractable Mn in the mineral soil. This study quantifies how metals are enriched and lost in decomposing organic matter over a longer timescale than previous studies have been able to characterize. We also put new limits on the rate at which metals in litter become mobile organo-metallic complexes that can migrate to deeper soil horizons or surface waters.

Vertical characterization of soil contamination using multi-way modeling--a case study.

PubMed

Singh, Kunwar P; Malik, Amrita; Basant, Ankita; Ojha, Priyanka

2008-11-01

This study describes application of chemometric multi-way modeling approach to analyze the dataset pertaining to soils of industrial area with a view to assess the soil/sub-soil contamination, accumulation pathways and mobility of contaminants in the soil profiles. The three-way (sampling depths, chemical variables, sampling sites) dataset on heavy metals in soil samples collected from three different sites in an industrial area, up to a depth of 60 m each was analyzed using three-way Tucker3 model validated for stability and goodness of fit. A two component Tucker3 model, explaining 66.6% of data variance, allowed interpretation of the data information in all the three modes. The interpretation of core elements revealing interactions among the components of different modes (depth, variables, sites) allowed inferring more realistic information about the contamination pattern of soils both along the horizontal and vertical coordinates, contamination pathways, and mobility of contaminants through soil profiles, as compared to the traditional data analysis techniques. It concluded that soils at site-1 and site-2 are relatively more contaminated with heavy metals of both the natural as well as anthropogenic origins, as compared to the soil of site-3. Moreover, the accumulation pathways of metals for upper shallow layers and deeper layers of soils in the area were differentiated. The information generated would be helpful in developing strategies for remediation of the contaminated soils for reducing the subsequent risk of ground-water contamination in the study region.

Contribution of the biological crust to the soil CO2 efflux in a Mediterranean ecosystem

NASA Astrophysics Data System (ADS)

Morillas, Lourdes; Bellucco, Veronica; Lo Cascio, Mauro; Marras, Serena; Spano, Donatella; Mereu, Simone

2016-04-01

Lately, the important role of the soil biological crust (hereafter biocrust) in Mediterranean ecosystems is emerging from a multitude of articles. It is becoming apparent that the biocrust has an important role in regulating ecosystem functions and that it interacts with the woody and herbaceous vegetation to a degree depending on the availability of water among other factors. Here we present the first results of a wider project and focus on the contribution of the biocrust to soil CO2 efflux, and on how the respiration of the biocrust responds to soil water content and temperature. A manipulative experiment was performed in a Mediterranean shrubland ecosystem in Sardinia (Italy) to assess the contribution of the bicocrust to soil CO2 efflux and to identify the main environmental drivers of the CO2 efflux in this ecosystem. For 19 months,in situ soil CO2 efflux was measured over three different surfaces: soil deprived of biocrust (hereafter Soil), biocrust (hereafter BC) and intact soil (hereafter Soil+BC). For these surfaces, three different approaches were used to investigate the dependency of CO2 efflux on soil temperature and soil water content, e.g. a simple linear regression, a multi-linear equation, and a modified version of the most common used Lloyd and Taylor model (Lloyd and Taylor, 1994). Results showed that CO2 effluxes emitted by Soil, BC and Soil+BC were differently driven by soil moisture and temperature: BC respiration was mainly controlled by soil moisture at 5 cm depth, whereas both soil temperature and water content at 20 cm depth determined Soil CO2 efflux. Soil temperature and water content at 5 cm depth drove Soil+BC respiration. We also found that biocrust can contribute substantially (up to 60%) to the total soil respiration depending on its moisture content. This contribution persists even in periods in which deeper soil layers are inactive, as small water pulses can activate lichens, mosses and cyanobacteria associated to the biocrust as well as the metabolism of carbon in soils, while deeper soil layers remain dormant. The important differences observed in CO2 efflux between Soil and Soil+BC suggest that projections on carbon budgets may underestimate soil CO2 efflux in spatially heterogeneous Mediterranean areas. Thus, our results highlight the relevance of accounting for the biocrust contribution to soil respiration and its responses to environmental drivers. The ongoing and planned activities to understand the full complexity of all factors determining respiration in water limited environments are briefly discussed. Lloyd, J., Taylor, J. A., 1994. On the temperature dependence of soil respiration. Funct. Ecol. 8, 315-323.

The effect of break of runoff connectivity on SOC concentration in loess catchment of the Lublin Upland (Poland)

NASA Astrophysics Data System (ADS)

Rejman, Jerzy; Rafalska-Przysucha, Anna; Paluszek, Jan

2014-05-01

Soil erosion processes lead to redistribution of soils and soil organic carbon (SOC) in the landscape. In this study, we aimed to evaluate the effect of runoff connectivity on horizontal and vertical SOC concentration in the catchment. SOC concentration was examined in a small agricultural catchment located in deep loess area of the Lublin Upland, Poland (51019'55"N, 22023'16"E). The catchment area of 5.6 ha is divided into 11 parcels. Conventional tillage is performed on each of the parcel and plow includes of 1-2 moldboard and 1 cultivator operations per year. Tillage is performed along the longest side of parcels. Crop rotation includes wheat, barley, sugar beets, potatoes and maize. Connectivity of temporal overland flow in the catchment is disturbed by grassed borders of the parcels. SOC concentration was studied in 151 sampling points in a grid 20 by 20 m. Structure of soil profile was studied in each of the sampling points, and soil cores were taken from two soil layers of 0-25 and 25-50 cm, and from 7 profiles located within the closed depression and the areas where line of temporary overland flow cross the grassed parcel borders. SOC concentration in soil samples was determined by wet combustion with dichromate solution. Depositional soils represented 57 profiles in the catchment. The thickness of accumulated soil layer varied from 20 to 151 cm with a mean of 55 cm. SOC concentration ranged from 8.4 to 15.0 g kg-1 (with a mean of 11.0 g kg-1) in the upper and from 2.9 to 14.5 g kg-1 (7.5) in the deeper soil layer. Coefficient of variation was 12.9% in the layer 0-25 cm, and 44.5% in the layer 25-50 cm. To find the reasons of high variability of SOC concentration in deeper soil layer, the location of depositional soils in the catchment was analyzed. The analysis enabled to distinguish two groups of depositional soils of different SOC concentration at the depth of 25-50 cm. Depositional soils located in the zones of temporal stagnation of overland flow (i.e. closed depressions and the areas where the lines of concentrated flow cross the parcel borders) characterized higher SOC concentration with a mean of 10.10 g kg-1, and depositional soils located on slopes - lower (4.10 g kg-1). The first group represented 33 profiles, the second 24. Coefficient of variation in each group of soil was 19%. Vertical SOC concentration showed a large variation in profiles of depositional soils, with layers of higher and smaller SOC concentration at different depth. Soils located in the zones where lines of concentrated temporary flow cross the field borders showed a high SOC enrichment in buried Ab horizons (at the depth >80 cm) in comparison to soils located in closed depressions. The difference could be a result of larger area that contributes to overland flow in the case of sites located at lines of flow in comparison to the contribution area of closed depressions. The exception is a profile SP6, where the SOC concentration in Ab is similar to the Ab horizon in depressions. The SP6 profile is located in the lower part of the catchment at the end of a parcel of the length of 110 m. The other profiles (SP2, and SP5) are in the areas were distance between the parcel borders is 40-60 m, and SP7 is at the catchment outlet. It seems that the difference in SOC concentration in Ab between SP6 and SP2-SP5 is a result of more effective decrease of velocity of overland flow by closely located grassed borders of the parcels. The studies showed that grassed parcel borders fill an effective role in an increase of soil carbon stock in the areas where lines of temporary overland flow cross the parcel border. The effectiveness of SOC accumulation was larger in the past, as it is proved by high SOC concentration in buried Ab horizon, and was dependent on the distance between the grassed borders.

Facilitated transport in European soils from the Euro-soil project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolfing, J.; Scheltens, S.D.

1999-07-01

The authors studied the response of five reference soils from the European Union (a vertic cambisol, rendzina, dystric cambisol, orthic luvisol, and orthic podzol, also known as Euro-soils 1 to 5) to the addition of HCl and NaOH. For all soils, which were incubated as soil slurries, the amount of organic carbon in solution remained essentially constant upon addition of HCl but increased upon addition of NaOH; that is, it was not the pH of the soil that determined changes in the solubilization of dissolved organic carbon but {Delta}pH. This observation has implications for the design of active soil managementmore » strategies, because increased amounts of dissolved organic carbon in the soil solution pose a risk for leaching of contaminants to deeper soil layers and eventually to the groundwater. In the past, much attention has been paid to the reaction of soils to acidification and changing land use as practiced when agricultural land is taken out of production. The observations reported here indicate that soil alkalization is not necessarily without environmental and toxicological risks.« less

Modeling the effects of fire severity and climate warming on active layer and soil carbon dynamics of black spruce forests across the landscape in interior Alaska

USGS Publications Warehouse

Genet, H.; McGuire, Anthony David; Barrett, K.; Breen, A.; Euskirchen, E.S.; Johnstone, J.F.; Kasischke, E.S.; Melvin, A.M.; Bennett, A.; Mack, M.C.; Rupp, T.S.; Schuur, A.E.G.; Turetsky, M.R.; Yuan, F.

2013-01-01

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layer caused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness of 1.1 m on average by 2100. The combination of warming and fire led to a simulated cumulative loss of 9.6 kgC m−2 on average by 2100. Our analysis suggests that ecosystem carbon storage in boreal forests in interior Alaska is particularly vulnerable, primarily due to the combustion of organic layer thickness in fire and the related increase in active layer thickness that exposes previously protected permafrost soil carbon to decomposition.

Can Earthworm "mix up" Soil Carbon Budgets in Temperate Forests Under Elevated Carbon Dioxide?

NASA Astrophysics Data System (ADS)

Sánchez-de León, Y.; González-Meler, M.; Sturchio, N. C.; Wise, D. H.; Norby, R. J.

2008-12-01

The effects of global change on earthworms and their associated feedbacks on soil and ecosystem processes have been largely overlooked. We studied how the responses of a temperate deciduous forest to elevated carbon dioxide atmospheric concentrations (e[CO2]) influence earthworms and the soil processes affected by them. Our objectives were to: i) identify soil layers of active soil mixing under e[CO2] and current carbon dioxide atmospheric concentrations (c[CO2]) using fallout cesium (137Cs), ii) study how e[CO2] affects earthworm populations, iii) understand the relationship between soil mixing and earthworms at our study site, and iv) identify the implications of earthworm-mediated soil mixing for the carbon budget of a temperate forest. To study soil mixing, we measured vertical 137Cs activity in soil cores (0-24 cm depth) collected in replicated e[CO2] and c[CO2] sweetgum (Liquidambar styraciflua) plots (n = 2) in a Free Air CO2 Enrichment (FACE) ecosystem experiment at Oak Ridge National Laboratory. We measured earthworm density and fresh weight in the plots in areas adjacent to where soil cores were taken. Preliminary results on the vertical distribution of 137Cs in the c[CO2] treatments showed that higher 137Cs activity was located from 8-16 cm depth and no 137Cs activity was measured below 20 cm. In contrast, in the e[CO2] treatment, peak 137Cs activity was slightly deeper (10-18 cm), and 137Cs activity was still measured below 22 cm. Mean earthworm density was higher in e[CO2] than c[CO2] treatments (168 m-2 and 87 m-2, respectively; p = 0.046); earthworm fresh weights, however, did not differ significantly between treatments (32 g m-2 and 18 g m-2, respectively; p = 0.182). The 137Cs vertical distribution suggest that soil mixing occurs deeper in e[CO2] than in c[CO2] treatments, which is consistent with higher earthworm densities in e[CO2] than in c[CO2] treatments. Mixing deeper low carbon content soil with shallower high carbon soil may result in a dilution of net carbon inputs in forest soils exposed to e[CO2]. Vertical dilution of new carbon may explain why carbon accrual is detected only near the surface at this FACE site. By identifying the depths of active soil mixing and possible soil mixing mechanisms (e.g. earthworms), accounting of new organic carbon accrual could be more reliably determined for forest soils in response to e[CO2] conditions.

The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.

PubMed

Fisher, James P; Estop-Aragonés, Cristian; Thierry, Aaron; Charman, Dan J; Wolfe, Stephen A; Hartley, Iain P; Murton, Julian B; Williams, Mathew; Phoenix, Gareth K

2016-09-01

Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate. © 2016 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

Soil Tillage Management Affects Maize Grain Yield by Regulating Spatial Distribution Coordination of Roots, Soil Moisture and Nitrogen Status.

PubMed

Wang, Xinbing; Zhou, Baoyuan; Sun, Xuefang; Yue, Yang; Ma, Wei; Zhao, Ming

2015-01-01

The spatial distribution of the root system through the soil profile has an impact on moisture and nutrient uptake by plants, affecting growth and productivity. The spatial distribution of the roots, soil moisture, and fertility are affected by tillage practices. The combination of high soil density and the presence of a soil plow pan typically impede the growth of maize (Zea mays L.).We investigated the spatial distribution coordination of the root system, soil moisture, and N status in response to different soil tillage treatments (NT: no-tillage, RT: rotary-tillage, SS: subsoiling) and the subsequent impact on maize yield, and identify yield-increasing mechanisms and optimal soil tillage management practices. Field experiments were conducted on the Huang-Huai-Hai plain in China during 2011 and 2012. The SS and RT treatments significantly reduced soil bulk density in the top 0-20 cm layer of the soil profile, while SS significantly decreased soil bulk density in the 20-30 cm layer. Soil moisture in the 20-50 cm profile layer was significantly higher for the SS treatment compared to the RT and NT treatment. In the 0-20 cm topsoil layer, the NT treatment had higher soil moisture than the SS and RT treatments. Root length density of the SS treatment was significantly greater than density of the RT and NT treatments, as soil depth increased. Soil moisture was reduced in the soil profile where root concentration was high. SS had greater soil moisture depletion and a more concentration root system than RT and NT in deep soil. Our results suggest that the SS treatment improved the spatial distribution of root density, soil moisture and N states, thereby promoting the absorption of soil moisture and reducing N leaching via the root system in the 20-50 cm layer of the profile. Within the context of the SS treatment, a root architecture densely distributed deep into the soil profile, played a pivotal role in plants' ability to access nutrients and water. An optimal combination of deeper deployment of roots and resource (water and N) availability was realized where the soil was prone to leaching. The correlation between the depletion of resources and distribution of patchy roots endorsed the SS tillage practice. It resulted in significantly greater post-silking biomass and grain yield compared to the RT and NT treatments, for summer maize on the Huang-Huai-Hai plain.

Soil Tillage Management Affects Maize Grain Yield by Regulating Spatial Distribution Coordination of Roots, Soil Moisture and Nitrogen Status

PubMed Central

Wang, Xinbing; Zhou, Baoyuan; Sun, Xuefang; Yue, Yang; Ma, Wei; Zhao, Ming

2015-01-01

The spatial distribution of the root system through the soil profile has an impact on moisture and nutrient uptake by plants, affecting growth and productivity. The spatial distribution of the roots, soil moisture, and fertility are affected by tillage practices. The combination of high soil density and the presence of a soil plow pan typically impede the growth of maize (Zea mays L.).We investigated the spatial distribution coordination of the root system, soil moisture, and N status in response to different soil tillage treatments (NT: no-tillage, RT: rotary-tillage, SS: subsoiling) and the subsequent impact on maize yield, and identify yield-increasing mechanisms and optimal soil tillage management practices. Field experiments were conducted on the Huang-Huai-Hai plain in China during 2011 and 2012. The SS and RT treatments significantly reduced soil bulk density in the top 0–20 cm layer of the soil profile, while SS significantly decreased soil bulk density in the 20–30 cm layer. Soil moisture in the 20–50 cm profile layer was significantly higher for the SS treatment compared to the RT and NT treatment. In the 0-20 cm topsoil layer, the NT treatment had higher soil moisture than the SS and RT treatments. Root length density of the SS treatment was significantly greater than density of the RT and NT treatments, as soil depth increased. Soil moisture was reduced in the soil profile where root concentration was high. SS had greater soil moisture depletion and a more concentration root system than RT and NT in deep soil. Our results suggest that the SS treatment improved the spatial distribution of root density, soil moisture and N states, thereby promoting the absorption of soil moisture and reducing N leaching via the root system in the 20–50 cm layer of the profile. Within the context of the SS treatment, a root architecture densely distributed deep into the soil profile, played a pivotal role in plants’ ability to access nutrients and water. An optimal combination of deeper deployment of roots and resource (water and N) availability was realized where the soil was prone to leaching. The correlation between the depletion of resources and distribution of patchy roots endorsed the SS tillage practice. It resulted in significantly greater post-silking biomass and grain yield compared to the RT and NT treatments, for summer maize on the Huang-Huai-Hai plain. PMID:26098548

Impacts of different types of measurements on estimating unsaturated flow parameters

NASA Astrophysics Data System (ADS)

Shi, Liangsheng; Song, Xuehang; Tong, Juxiu; Zhu, Yan; Zhang, Qiuru

2015-05-01

This paper assesses the value of different types of measurements for estimating soil hydraulic parameters. A numerical method based on ensemble Kalman filter (EnKF) is presented to solely or jointly assimilate point-scale soil water head data, point-scale soil water content data, surface soil water content data and groundwater level data. This study investigates the performance of EnKF under different types of data, the potential worth contained in these data, and the factors that may affect estimation accuracy. Results show that for all types of data, smaller measurements errors lead to faster convergence to the true values. Higher accuracy measurements are required to improve the parameter estimation if a large number of unknown parameters need to be identified simultaneously. The data worth implied by the surface soil water content data and groundwater level data is prone to corruption by a deviated initial guess. Surface soil moisture data are capable of identifying soil hydraulic parameters for the top layers, but exert less or no influence on deeper layers especially when estimating multiple parameters simultaneously. Groundwater level is one type of valuable information to infer the soil hydraulic parameters. However, based on the approach used in this study, the estimates from groundwater level data may suffer severe degradation if a large number of parameters must be identified. Combined use of two or more types of data is helpful to improve the parameter estimation.

Impacts of Different Types of Measurements on Estimating Unsaturatedflow Parameters

NASA Astrophysics Data System (ADS)

Shi, L.

2015-12-01

This study evaluates the value of different types of measurements for estimating soil hydraulic parameters. A numerical method based on ensemble Kalman filter (EnKF) is presented to solely or jointly assimilate point-scale soil water head data, point-scale soil water content data, surface soil water content data and groundwater level data. This study investigates the performance of EnKF under different types of data, the potential worth contained in these data, and the factors that may affect estimation accuracy. Results show that for all types of data, smaller measurements errors lead to faster convergence to the true values. Higher accuracy measurements are required to improve the parameter estimation if a large number of unknown parameters need to be identified simultaneously. The data worth implied by the surface soil water content data and groundwater level data is prone to corruption by a deviated initial guess. Surface soil moisture data are capable of identifying soil hydraulic parameters for the top layers, but exert less or no influence on deeper layers especially when estimating multiple parameters simultaneously. Groundwater level is one type of valuable information to infer the soil hydraulic parameters. However, based on the approach used in this study, the estimates from groundwater level data may suffer severe degradation if a large number of parameters must be identified. Combined use of two or more types of data is helpful to improve the parameter estimation.

Learning from soil gas change and isotopic signatures during 2012 Emilia seismic sequence.

PubMed

Sciarra, Alessandra; Cantucci, Barbara; Coltorti, Massimo

2017-10-27

Soil surveys were performed in Medolla (Italy), a peculiar area characterized by spotty high soil temperature, gas vent, and lack of vegetation, to determine the migration mechanisms and spatial behavior of gas species. Hereby we present soil gas measurements and their isotopic ratios measured between 2008 and 2015, including the 2012 Emilia-Romagna seismic sequence. We found that soil gas concentrations markedly changed during the main shocks of May 20 and 29, 2012 (Mw 6.1 and 6.0, respectively), highlighting the presence of a buried fault intersecting the gas vents. We suggest that crustal dilation associated with seismic activity favored the uprising of geogas towards the surface. Changes in the isotopic signature highlight the contribution of two distinct sources, one deeper, thermogenic and another superficial related to organic-rich layer, whose relative contribution varied before, during and after the earthquake. We suppose an increase of microbial component likely due to the ground shaking of shallower layers linked to seismic sequence, which masks the thermogenic contribution. Although the changes we detect are specific for an alluvial plain, we deduce that analogous processes may be active elsewhere, and that soil gas geochemistry represents an useful tool to discriminate the gas migration related to seismic activity.

Simulation of Long-term Yield and Soil Water Consumption in Apple Orchards on the Loess Plateau, China, in Response to Fertilization.

PubMed

Peng, Xingxing; Guo, Zheng; Zhang, Yujiao; Li, Jun

2017-07-14

The Loess Plateau, China, is the world's largest apple-producing region, and over 80% of the orchards are in rainfed (dryland) areas. Desiccation of the deep soil layer under dryland apple orchards is the main stressor of apple production in this region. Fertilization is a factor that causes soil desiccation in dryland apple orchards. Given its applicability and precision validations, the Environmental Policy Integrated Climate (EPIC) model was used to simulate the dynamics of fruit yield and deep soil desiccation in apple orchards under six fertilization treatments. During the 45 years of study, the annual fruit yield under the fertilization treatments initially increased and then decreased in a fluctuating manner, and the average fruit yields were 24.42, 27.27, 28.69, 29.63, 30.49 and 29.43 t/ha in these respective fertilization treatments. As fertilization increased, yield of the apple orchards increased first and then declined,desiccation of the soil layers occurred earlier and extended deeper, and the average annual water consumption, over-consumption and water use efficiency increased as fertilization increased. In terms of apple yields, sustainable soil water use, and economic benefits, the most appropriate fertilization rate for drylands in Luochuan is 360-480 kg/ha N and 180-240 kg/ha P.

Spatiotemporal analysis of black spruce forest soils and implications for the fate of C

USGS Publications Warehouse

Harden, Jennifer W.; Manies, Kristen L.; O'Donnell, Jonathan; Johnson, Kristofer; Frolking, Steve; Fan, Zhaosheng

2012-01-01

Post-fire storage of carbon (C) in organic-soil horizons was measured in one Canadian and three Alaskan chronosequences in black spruce forests, together spanning stand ages of nearly 200 yrs. We used a simple mass balance model to derive estimates of inputs, losses, and accumulation rates of C on timescales of years to centuries. The model performed well for the surface and total organic soil layers and presented questions for resolving the dynamics of deeper organic soils. C accumulation in all study areas is on the order of 20–40 gC/m2/yr for stand ages up to ∼200 yrs. Much larger fluxes, both positive and negative, are detected using incremental changes in soil C stocks and by other studies using eddy covariance methods for CO2. This difference suggests that over the course of stand replacement, about 80% of all net primary production (NPP) is returned to the atmosphere within a fire cycle, while about 20% of NPP enters the organic soil layers and becomes available for stabilization or loss via decomposition, leaching, or combustion. Shifts toward more frequent and more severe burning and degradation of deep organic horizons would likely result in an acceleration of the carbon cycle, with greater CO2 emissions from these systems overall.

Soil Carbon Cycling - More than Changes in Soil Organic Carbon Stocks

NASA Astrophysics Data System (ADS)

Lorenz, K.

2015-12-01

Discussions about soil carbon (C) sequestration generally focus on changes in soil organic carbon (SOC) stocks. Global SOC mass in the top 1 m was estimated at about 1325 Pg C, and at about 3000 Pg C when deeper soil layers were included. However, both inorganically and organically bound carbon forms are found in soil but estimates on global soil inorganic carbon (SIC) mass are even more uncertain than those for SOC. Globally, about 947 Pg SIC may be stored in the top 1 m, and especially in arid and semi-arid regions SIC stocks can be many times great than SOC stocks. Both SIC and SOC stocks are vulnerable to management practices, and stocks may be enhanced, for example, by optimizing net primary production (NPP) by fertilization and irrigation (especially optimizing belowground NPP for enhancing SOC stocks), adding organic matter (including black C for enhancing SOC stocks), and reducing soil disturbance. Thus, studies on soil C stocks, fluxes, and vulnerability must look at both SIC and SOC stocks in soil profiles to address large scale soil C cycling.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Genet, Helene; McGuire, A. David; Barrett, K.

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and testedmore » a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layercaused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness of 1.1 m on average by 2100. The combination of warming and fire led to a simulated cumulative loss of 9.6 kgC m 2 on average by 2100. Our analysis suggests that ecosystem carbon storage in boreal forests in interior Alaska is particularly vulnerable, primarily due to the combustion of organic layer thickness in fire and the related increase in active layer thickness that exposes previously protected permafrost soil carbon to decomposition.« less

Influence of a compost layer on the attenuation of 28 selected organic micropollutants under realistic soil aquifer treatment conditions: insights from a large scale column experiment.

PubMed

Schaffer, Mario; Kröger, Kerrin Franziska; Nödler, Karsten; Ayora, Carlos; Carrera, Jesús; Hernández, Marta; Licha, Tobias

2015-05-01

Soil aquifer treatment is widely applied to improve the quality of treated wastewater in its reuse as alternative source of water. To gain a deeper understanding of the fate of thereby introduced organic micropollutants, the attenuation of 28 compounds was investigated in column experiments using two large scale column systems in duplicate. The influence of increasing proportions of solid organic matter (0.04% vs. 0.17%) and decreasing redox potentials (denitrification vs. iron reduction) was studied by introducing a layer of compost. Secondary effluent from a wastewater treatment plant was used as water matrix for simulating soil aquifer treatment. For neutral and anionic compounds, sorption generally increases with the compound hydrophobicity and the solid organic matter in the column system. Organic cations showed the highest attenuation. Among them, breakthroughs were only registered for the cationic beta-blockers atenolol and metoprolol. An enhanced degradation in the columns with organic infiltration layer was observed for the majority of the compounds, suggesting an improved degradation for higher levels of biodegradable dissolved organic carbon. Solely the degradation of sulfamethoxazole could clearly be attributed to redox effects (when reaching iron reducing conditions). The study provides valuable insights into the attenuation potential for a wide spectrum of organic micropollutants under realistic soil aquifer treatment conditions. Furthermore, the introduction of the compost layer generally showed positive effects on the removal of compounds preferentially degraded under reducing conditions and also increases the residence times in the soil aquifer treatment system via sorption. Copyright © 2015 Elsevier Ltd. All rights reserved.

Below-ground attributes on reclaimed surface minelands over a 40-year chronosequence

NASA Astrophysics Data System (ADS)

Limb, Ryan; Bohrer, Stefanie; Volk, Jay

2017-04-01

Reclamation following mining activities often aims to restore stable soils that support productive and diverse native plant communities. The soil re-spread process increases soil compaction, which may alter soil water, plant composition, rooting depths and soil organic matter. This may have a direct impact on vegetation establishment and species recruitment. Seasonal wet/dry and freeze/thaw patterns are thought to alleviate soil compaction over time. However, this has not been formally evaluated on reclaimed landscapes at large scales. Our objectives were to (1) determine soil compaction alleviation, (2) rooting depth and (3) spatial patterns of soil water content over a time-since-reclamation gradient. Soil resistance to penetration varied by depth, with shallow compaction remaining unchanged, but deeper compaction increased over time rather than being alleviated. Root biomass and depth did not increase with time and was consistently less than reference locations. Plant communities initially had a strong native component, but quickly became dominated by invasive species following reclamation and soil water content became increasingly homogeneous over the 40-year chronosequence. Seasonal weather patterns and soil organic matter additions can reduce soil compaction if water infiltration is not limited. Shallow and strongly fibrous-rooted grasses present in reclaimed sites added organic matter to shallow soil layers, but did not penetrate the compacted layers and allow water infiltration. Strong linkages between land management strategies, soil properties and vegetation composition can advance reclamation efforts and promote heterogeneous landscapes. However, current post-reclamation management strategies are not facilitating natural seasonal weather patterns to reducing soil compaction.

Comparing soil moisture memory in satellite observations and models

NASA Astrophysics Data System (ADS)

Stacke, Tobias; Hagemann, Stefan; Loew, Alexander

2013-04-01

A major obstacle to a correct parametrization of soil processes in large scale global land surface models is the lack of long term soil moisture observations for large parts of the globe. Currently, a compilation of soil moisture data derived from a range of satellites is released by the ESA Climate Change Initiative (ECV_SM). Comprising the period from 1978 until 2010, it provides the opportunity to compute climatological relevant statistics on a quasi-global scale and to compare these to the output of climate models. Our study is focused on the investigation of soil moisture memory in satellite observations and models. As a proxy for memory we compute the autocorrelation length (ACL) of the available satellite data and the uppermost soil layer of the models. Additional to the ECV_SM data, AMSR-E soil moisture is used as observational estimate. Simulated soil moisture fields are taken from ERA-Interim reanalysis and generated with the land surface model JSBACH, which was driven with quasi-observational meteorological forcing data. The satellite data show ACLs between one week and one month for the greater part of the land surface while the models simulate a longer memory of up to two months. Some pattern are similar in models and observations, e.g. a longer memory in the Sahel Zone and the Arabian Peninsula, but the models are not able to reproduce regions with a very short ACL of just a few days. If the long term seasonality is subtracted from the data the memory is strongly shortened, indicating the importance of seasonal variations for the memory in most regions. Furthermore, we analyze the change of soil moisture memory in the different soil layers of the models to investigate to which extent the surface soil moisture includes information about the whole soil column. A first analysis reveals that the ACL is increasing for deeper layers. However, its increase is stronger in the soil moisture anomaly than in its absolute values and the first even exceeds the latter in the deepest layer. From this we conclude that the seasonal soil moisture variations dominate the memory close to the surface but these are dampened in lower layers where the memory is mainly affected by longer term variations.

Irrigation and Nitrogen Regimes Promote the Use of Soil Water and Nitrate Nitrogen from Deep Soil Layers by Regulating Root Growth in Wheat.

PubMed

Liu, Weixing; Ma, Geng; Wang, Chenyang; Wang, Jiarui; Lu, Hongfang; Li, Shasha; Feng, Wei; Xie, Yingxin; Ma, Dongyun; Kang, Guozhang

2018-01-01

Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6-45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1-45.3% compared to the W1 treatments during the drier growing seasons (2010-2011, 2012-2013, and 2015-2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011-2012, 2013-2014, and 2014-2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO 3 -N from the deep soil layers. N applications increased yield by 19.1-64.5%, with a corresponding increase in WUE of 66.9-83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha -1 , respectively. A N application rate of 240 kg ha -1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO 3 -N and also in reducing the residual NO 3 -N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180-240 kg ha -1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical.

Soil organic components distribution in a podzol and the possible relations with the biological soil activities

NASA Astrophysics Data System (ADS)

Alvarez-Romero, Marta; Papa, Stefania; Verstraeten, Arne; Curcio, Elena; Cools, Nathalie; Lozano-Garcia, Beatriz; Parras-Alcántara, Luis; Coppola, Elio

2016-04-01

This research reports the preliminary results of a study based on the SOC (Soil Organic Carbon) fractionation in a pine forest soil (Pinus nigra). Hyperskeletic Albic Podzol soil (P113005, World Reference Base, 2014), described by the following sequence O-Ah-E-Bh-Bs-Cg, was investigated at Zoniën, Belgium. Total (TOC) and extractable (TEC) soil contents were determined by Italian official method of soil analysis. Different soil C fractions were also determined: Humic Acid Carbon (HAC) and Fulvic Acid Carbon (FAC). Not Humic Carbon (NHC) and Humin Carbon (Huc) fractions were obtained by difference. Along the mineral soil profile, therefore, were also tested some enzymatic activities, such as cellulase, xylanase, laccase and peroxidase, involved in the degradation of the main organic substance components, and dehydrogenase activity, like soil microbial biomass index. The results shows a differential TEC fractions distribution in the soil profile along three fronts of progress: (i) An E leaching horizon of TEC; Bh horizon (humic) of humic acids preferential accumulation, morphologically and analytically recognizable, in which humic are more insoluble that fulvic acids, and predominate over the latter; (ii) horizon Bs (spodic) in which fulvic acids are more soluble that humic acid, and predominate in their turn. All enzyme activities appear to be highest in the most superficial part of the mineral profile and decrease towards the deeper layers with different patterns. It is known that the enzymes production in a soil profile reflects the organic substrates availability, which in turn influences the density and the composition of the microbial population. The deeper soil horizons contain microbial communities adapted and specialized to their environment and, therefore, different from those present on the surface The results suggest that the fractionation technique of TEC is appropriate to interpret the podsolisation phenomenon that is the preferential distribution of the different fractions of the SOC. It can form the base study for evaluation of changes in some biological activity along soil profile.

Post-fire recovery of soil organic matter in a Cambisol from typical Mediterranean forest in Southwestern Spain.

PubMed

Jiménez-González, Marco A; De la Rosa, José María; Jiménez-Morillo, Nicasio T; Almendros, Gonzalo; González-Pérez, José Antonio; Knicker, Heike

2016-12-01

Wildfire is a recurrent phenomenon in Mediterranean ecosystems and contributes to soil degradation and desertification, which are partially caused by alterations to soil organic matter (SOM). The SOM composition from a Cambisol under a Mediterranean forest affected by a wildfire is studied in detail in order to assess soil health status and better understand of soil recovery after the fire event. The soil was sampled one month and twenty-five months after the wildfire. A nearby unburnt site was taken as control soil. Soil rehabilitation actions involving heavy machinery to remove burnt vegetation were conducted sixteen months after the wildfire. Immediately after fire the SOM increased in topsoil due to inputs from charred vegetation, whereas a decrease was observed in the underlying soil layer. Twenty-five months after fire soil-pH increased in fire-affected topsoil due to the presence of ashes, a decrease in SOM content was recorded for the burnt topsoil and similar trend was observed for the water holding capacity. The pyro-chromatograms of burned soils revealed the formation of additional aromatic compounds. The thermal cracking of long-chain n-alkanes was also detected. Solid-state 13 C NMR spectroscopy supported the increase of aromatic compounds in the fire-affected topsoil due to the accumulation of charcoal, whereas the deeper soil sections were not affected by the fire. Two years later, soil parameters for the unburnt and burnt sites showed comparable values. The reduction of the relative intensity in the aromatic C region of the NMR spectra indicated a decrease in the charcoal content of the topsoil. Due to the negligible slope in the sampling site, the loss of charcoal was explained by the post-fire restoration activity, degradation, leaching of pyrogenic SOM into deeper soil horizons or wind erosion. Our results support that in the Mediterranean region, fire-induced alteration of the SOM is not lasting in the long-term. Copyright © 2016 Elsevier B.V. All rights reserved.

Impact of interspecific interactions on the soil water uptake depth in a young temperate mixed species plantation

NASA Astrophysics Data System (ADS)

Grossiord, Charlotte; Gessler, Arthur; Granier, André; Berger, Sigrid; Bréchet, Claude; Hentschel, Rainer; Hommel, Robert; Scherer-Lorenzen, Michael; Bonal, Damien

2014-11-01

Interactions between tree species in forests can be beneficial to ecosystem functions and services related to the carbon and water cycles by improving for example transpiration and productivity. However, little is known on below- and above-ground processes leading to these positive effects. We tested whether stratification in soil water uptake depth occurred between four tree species in a 10-year-old temperate mixed species plantation during a dry summer. We selected dominant and co-dominant trees of European beech, Sessile oak, Douglas fir and Norway spruce in areas with varying species diversity, competition intensity, and where different plant functional types (broadleaf vs. conifer) were present. We applied a deuterium labelling approach that consisted of spraying labelled water to the soil surface to create a strong vertical gradient of the deuterium isotope composition in the soil water. The deuterium isotope composition of both the xylem sap and the soil water was measured before labelling, and then again three days after labelling, to estimate the soil water uptake depth using a simple modelling approach. We also sampled leaves and needles from selected trees to measure their carbon isotope composition (a proxy for water use efficiency) and total nitrogen content. At the end of the summer, we found differences in the soil water uptake depth between plant functional types but not within types: on average, coniferous species extracted water from deeper layers than did broadleaved species. Neither species diversity nor competition intensity had a detectable influence on soil water uptake depth, foliar water use efficiency or foliar nitrogen concentration in the species studied. However, when coexisting with an increasing proportion of conifers, beech extracted water from progressively deeper soil layers. We conclude that complementarity for water uptake could occur in this 10-year-old plantation because of inherent differences among functional groups (conifers and broadleaves). Furthermore, water uptake depth of beech was already influenced at this young development stage by interspecific interactions whereas no clear niche differentiation occurred for the other species. This finding does not preclude that plasticity-mediated responses to species interactions could increase as the plantation ages, leading to the coexistence of these species in adult forest stands.

Characterizing soil moisture and snow cover effects on boreal-arctic soil freeze/thaw dynamics and cold-season carbon emissions

NASA Astrophysics Data System (ADS)

Yi, Y.; Kimball, J. S.; Moghaddam, M.; Chen, R. H.; Reichle, R. H.; Oechel, W. C.; Zona, D.

2017-12-01

The contribution of cold season respiration to boreal-arctic carbon cycle and its potential feedbacks to climate change remain poorly quantified. Here, we developed an integrated modeling framework combining airborne low frequency (L+P-band) airborne radar retrievals and landscape level (≥1km) environmental observations from satellite optical and microwave sensors with a detailed permafrost carbon model to investigate underlying processes controlling soil freeze/thaw (FT) dynamics and cold season carbon emissions. The permafrost carbon model simulates the snow and soil thermal dynamics with soil water phase change included and accounts for soil carbon decomposition up to 3m below surface. Local-scale ( 50m) radar retrievals of active layer thickness (ALT), soil moisture and freeze/thaw (FT) status from NASA airborne UAVSAR and AirMOSS sensors are used to inform the model parameterizations of soil moisture effects on soil FT dynamics, and scaling properties of active layer processes. Both tower observed land-atmosphere fluxes and atmospheric CO2 measurements are used to evaluate the model processes controlling cold season carbon respiration, particularly the effects of snow cover and soil moisture on deep soil carbon emissions during the early cold season. Initial comparisons showed that the model can well capture the seasonality of cold season respiration in both tundra and boreal forest areas, with large emissions in late fall and early winter and gradually diminishing throughout the winter. Model sensitivity analyses are used to clarify how changes in soil thermodynamics at depth control the magnitude and seasonality of cold season respiration, and how a deeper unfrozen active layer with warming may contribute to changes in cold season respiration. Model outputs include ALT and regional carbon fluxes at 1-km resolution spanning recent satellite era (2001-present) across Alaska. These results will be used to quantify cold season respiration contributions to the annual carbon cycle and help close the boreal-arctic annual carbon budget.

[Effects of field border length for irrigation on the water consumption characteristics and grain yield of wheat].

PubMed

Ma, Shang-Yu; Yu, Zhen-Wen; Wang, Dong; Zhang, Yong-Li; Shi, Yu

2012-09-01

In the wheat growth seasons of 2009 -2010 and 2010-2011, six border lengths of 10, 20, 40, 60, 80 and 100 m were installed in a wheat field to study the effects of different border lengths for irrigation on the water consumption characteristics and grain yield of wheat. The results showed that with the increasing border length from 10 to 80 m, the irrigation amount and the proportion of irrigation amount to total water consumption amount, the water content in 0-200 cm soil layers and the soil water supply capacity at anthesis stage, as well as the wheat grain yield and water use efficiency increased, while the soil water consumption amount and the water consumption amount of wheat from jointing to anthesis stages as well as the total water consumption amount decreased. At the border length of <80 m, the irrigation amount was smaller, and the water content in upper soil layers was lower, as compared with those at the border length of 80 m, which led to the wheat to absorb more water from deeper soil layers, and thus, the total water consumption increased. At the border length of 100 m, the irrigation amount, soil water consumption amount, and total water consumption amount all increased, and, due to the excessive irrigation amount and the uneven distribution of irrigation water when irrigated once, the 1000-grain mass, grain yield, and water use efficiency decreased significantly, which was not conductive to the water-saving and high-yield cultivation.

Assessment of metal retention in newly constructed highway embankments.

PubMed

Werkenthin, Moritz; Kluge, Björn; Wessolek, Gerd

2016-12-01

Newly constructed embankments should provide both a specific bearing capacity to enable trafficability in emergency cases and a sufficient pollutant retention capacity to protect the groundwater. A number of lysimeters were installed along the A115 highway to determine total and dissolved metal concentrations in road runoff and in the soil solution of newly constructed embankments. Dissolved concentrations in soil solution of the embankments did not exceed the trigger values of the German legislation. Depending on the metal, total concentrations in soil solution were more than twice as high as dissolved concentrations. The high infiltration rates lead to increased groundwater recharge beneath the embankments (up to 4100 mm a -1 ). Although metal concentrations were not problematic from the legislators' point of view, the elevated infiltration rates beside the road facilitated the transfer of high metal loads into deeper soil layers and potentially into the groundwater as well.

Concentration and spatial distribution of lead in soil used for ammunition destruction.

PubMed

do Nascimento Guedes, Jair; do Amaral Sobrinho, Nelson Moura Brasil; Ceddia, Marcos Bacis; Vilella, André Luis Oliveira; Tolón-Becerra, Alfredo; Lastra-Bravo, Xavier Bolívar

2012-10-01

Studies on heavy metal contamination in soils used for ammunition disposal and destruction are still emerging. The present study aimed to evaluate the contamination level and spatial distribution of lead in disposal and destruction areas. This site was used for ammunition disposal and destruction activities for 20 years. The ammunition destruction site (1,296 ha), a sampling system that followed a sampling grid (5 m × 5 m) with 30 points was adopted and samples were collected at the following five depths with a total of 150 samples. During the collection procedure, each sampling grid point was georeferenced using a topographic global positioning system. Data were validated through semivariogram and kriging models using Geostat software. The results demonstrated that the average lead value was 163 mg kg(-1), which was close to the investigation limit and the contamination levels were higher downstream than upstream. The results showed that there was lead contamination at the destruction site and that the contamination existed mainly at the surface layer depth. However, high lead concentrations were also found at deeper soil depths in the destruction area due to frequent detonations. According to the planimetry data, the areas that require intervention significantly decreased with increasing depths in the following order: 582.7 m(2) in the 0-20 cm layer; 194.6 m(2) in the 20-40 cm layer; 101.6 m(2) in the 40-60 cm layer; and 45.3 m(2) in the 60-80 cm layer.

Metagenomics Reveals Microbial Community Composition And Function With Depth In Arctic Permafrost Cores

NASA Astrophysics Data System (ADS)

Jansson, J.; Tas, N.; Wu, Y.; Ulrich, C.; Kneafsey, T. J.; Torn, M. S.; Hubbard, S. S.; Chakraborty, R.; Graham, D. E.; Wullschleger, S. D.

2013-12-01

The Arctic is one of the most climatically sensitive regions on Earth and current surveys show that permafrost degradation is widespread in arctic soils. Biogeochemical feedbacks of permafrost thaw are expected to be dominated by the release of currently stored carbon back into the atmosphere as CO2 and CH4. Understanding the dynamics of C release from permafrost requires assessment of microbial functions from different soil compartments. To this end, as part of the Next Generation Ecosystem Experiment in the Arctic, we collected two replicate permafrost cores (1m and 3m deep) from a transitional polygon near Barrow, AK. At this location, permafrost starts from 0.5m in depth and is characterized by variable ice content and higher pH than surface soils. Prior to sectioning, the cores were CT-scanned to determine the physical heterogeneity throughout the cores. In addition to detailed geochemical characterization, we used Illumina MiSeq technology to sequence 16SrRNA genes throughout the depths of the cores at 1 cm intervals. Selected depths were also chosen for metagenome sequencing of total DNA (including phylogenetic and functional genes) using the Illumina HiSeq platform. The 16S rRNA gene sequence data revealed that the microbial community composition and diversity changed dramatically with depth. The microbial diversity decreased sharply below the first few centimeters of the permafrost and then gradually increased in deeper layers. Based on the metagenome sequence data, the permafrost microbial communities were found to contain members with a large metabolic potential for carbon processing, including pathways for fermentation and methanogenesis. The surface active layers had more representatives of Verrucomicrobia (potential methane oxidizers) whereas the deep permafrost layers were dominated by several different species of Actinobacteria. The latter are known to have a diverse metabolic capability and are able to adapt to stress by entering a dormant yet viable state. In addition, several isolates were obtained from different depths throughout the cores, including methanogens from some of the deeper layers. Together these data present a new view of potential geochemical cycles carried out by microorganisms in permafrost and reveal how community members and functions are distributed with depth.

Feedbacks between soil penetration resistance, root architecture and water uptake limit water accessibility and crop growth - A vicious circle.

PubMed

Colombi, Tino; Torres, Lorena Chagas; Walter, Achim; Keller, Thomas

2018-06-01

Water is the most limiting resource for global crop production. The projected increase of dry spells due to climate change will further increase the problem of water limited crop yields. Besides low water abundance and availability, water limitations also occur due to restricted water accessibility. Soil penetration resistance, which is largely influenced by soil moisture, is the major soil property regulating root elongation and water accessibility. Until now the interactions between soil penetration resistance, root system properties, water uptake and crop productivity are rarely investigated. In the current study we quantified how interactive effects between soil penetration resistance, root architecture and water uptake affect water accessibility and crop productivity in the field. Maize was grown on compacted and uncompacted soil that was either tilled or remained untilled after compaction, which resulted in four treatments with different topsoil penetration resistance. Higher topsoil penetration resistance caused root systems to be shallower. This resulted in increased water uptake from the topsoil and hence topsoil drying, which further increased the penetration resistance in the uppermost soil layer. As a consequence of this feedback, root growth into deeper soil layers, where water would have been available, was reduced and plant growth decreased. Our results demonstrate that soil penetration resistance, root architecture and water uptake are closely interrelated and thereby determine the potential of plants to access soil water pools. Hence, these interactions and their feedbacks on water accessibility and crop productivity have to be accounted for when developing strategies to alleviate water limitations in cropping systems. Copyright © 2018 Elsevier B.V. All rights reserved.

Localization of 15N uptake in a Tibetan alpine Kobresia pasture

NASA Astrophysics Data System (ADS)

Schleuß, Per-Marten; Kuzyakov, Yakov

2014-05-01

The Kobresia Pygmea ecotone covers approximately 450.000 km2 and is of large global and regional importance due several socio-ecological aspects. For instance Kobresia pastures store high amounts of carbon, nitrogen and other nutrients, represent large grazing areas for herbivores, provide a fast regrowth after grazing events and protect against mechanical degradation and soil erosion. However, Kobresia pastures are assumed to be a grazing induced and are accompanied with distinct root mats varying in thickness between 5-30 cm. Yet, less is known about the morphology and the functions of this root mats, especially in the background of a progressing degradation due to changes of climate and management. Thus we aimed to identify the importance of single soil layers for plant nutrition. Accordingly, nitrogen uptake from different soil depths and its remain in above-ground biomass (AGB), belowground biomass (BGB) and soil were determined by using a 15N pulse labeling approach during the vegetation period in summer 2012. 15N urea was injected into six different soil depths (0.5 cm, 2.5 cm, 7.5 cm, 12.5 cm, 17.5 cm, 22.5 cm / for each 4 replicates) and plots were sampled 45 days after the labeling. For soil and BGB samples were taken in strict sample intervals of 0-1 cm, 1-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm. Results indicate that total recovery (including AGB, BGB and soil) was highest, if tracer was injected into the top 5 cm and subsequently decreased with decreasing injection depth. This is especially the case for the 15N recovery of BGB, which is clearly attributed to the root density and strongly decreased with soil depth. In contrast, the root activity derived from the 15N content of roots increased with soil depth, which is primary associated to a proportionate increase of living roots related to dead roots. However, most 15N was captured in plant biomass (67.5-85.3 % of total recovery), indicating high 15N uptake efficiency possibly due to N limitation of Kobresia ecosystems. Considering only the nitrogen uptake of AGB hardly any differences appeared between the six injection depths. Nevertheless, it could be shown, that 50.4 % percent of total variance of AGB nitrogen uptake could be explained by combining root density and root activity. Concluding, from the upper root mat horizons highest amounts of nitrogen were taken up by plants, because root densities are correspondingly high. However, in deeper root mat layers the root activity increases and accordingly plays a key role for plant nitrogen supply in this depth. Underlying causes for increasing root activities may be better soil moisture conditions, lower variation of soil temperature and/or a higher access to plant available nitrogen in deeper soil layers.Please fill in your abstract text.

Radioisotopes (137Cs, 40K, 210Pb) indicate that cryoturbation processes in Alaskan tussock tundra are accelerated under deeper winter snow: results from short and long-term winter snow depth experiments

NASA Astrophysics Data System (ADS)

Blanc-Betes, E.; Sturchio, N. C.; Taneva, L.; Welker, J. M.; Guilderson, T. P.; Poghosyan, A.; Gonzalez-Meler, M. A.

2010-12-01

Permafrost soils cover 8.6% of the Earth land area and contain up to 50% of the global soil organic carbon (SOC) pool. Amplified warming in northern latitudes has resulted directly and/or indirectly in multiple structural and functional changes in arctic ecosystems which may lead to strong forcing feedbacks on the climate system. Cryoturbation is a dominant soil forming process in permafrost regions that results to the mixing of soil layers during freeze-thaw cycles, and may increase in rates following global warming. As a result, the active layer of cryoturbated soils can average 62% larger C stocks than those from non-cryoturbated ones. Cryoturbation is a critical overlooked driver of C dynamics in permafrost soils that will likely play a pivotal role in the fate of Arctic soil C under climate change conditions. However, cryoturbation phenomena is difficult to quantify. We measured cryoturbation rates using a multiple isotope approach at Toolik Lake, Alaska, in moist acidic tundra soils from short- and long-term snow addition experiments. Shifts in cryoturbation rates as affected by these manipulations were measured by the relative activity of natural and weapon-derived radioisotopes (e.g. 137Cs, 40K, 210Pb). By tracking the vertical distribution of these fallout and natural radioisotopes in soils and calculating soil diffusion coefficients, we were able to quantify cryoturbation mixing rates and sediment transport mechanisms that operate at multiannual time scales. Our results show an apparent uplift of buried organic matter to the surface as a result of soil thermal insulation and subsequent deepening of the active layer. These results sharply contrast with current notions that cryoturbation in Arctic systems results in net burial of organic matter, resulting in increased C storage at depth. Mechanisms of this mechanical mixing and its effects on C redistribution and storage of organic matter will be presented to shed light on this apparent contradiction.

Effect of land use change on the carbon cycle in Amazon soils

NASA Technical Reports Server (NTRS)

Trumbore, Susan E.; Davidson, Eric A.

1994-01-01

The overall goal of this study was to provide a quantitative understanding of the cycling of carbon in the soils associated with deep-rooting Amazon forests. In particular, we wished to apply the understanding gained by answering two questions: (1) what changes will accompany the major land use change in this region, the conversion of forest to pasture? and (2) what is the role of carbon stored deeper than one meter in depth in these soils? To construct carbon budgets for pasture and forest soils we combined the following: measurements of carbon stocks in above-ground vegetation, root biomass, detritus, and soil organic matter; rates of carbon inputs to soil and detrital layers using litterfall collection and sequential coring to estimate fine root turnover; C-14 analyses of fractionated SOM and soil CO2 to estimate residence times; C-13 analyses to estimate C inputs to pasture soils from C-4 grasses; soil pCO2, volumetric water content, and radon gradients to estimate CO2 production as a function of soil depth; soil respiration to estimate total C outputs; and a model of soil C dynamics that defines SOM fractions cycling on annual, decadal, and millennial time scales.

Fire effects on soil organic matter content, composition, and nutrients in boreal interior Alaska

USGS Publications Warehouse

Neff, J.C.; Harden, J.W.; Gleixner, G.

2005-01-01

Boreal ecosystems contain a substantial fraction of the earth's soil carbon stores and are prone to frequent and severe wildfires. In this study, we examine changes in element and organic matter stocks due to a 1999 wildfire in Alaska. One year after the wildfire, burned soils contained between 1071 and 1420 g/m2 less carbon than unburned soils. Burned soils had lower nitrogen than unburned soils, higher calcium, and nearly unchanged potassium, magnesium, and phosphorus stocks. Burned surface soils tended to have higher concentrations of noncombustible elements such as calcium, potassium, magnesium, and phosphorus compared with unburned soils. Combustion losses of carbon were mostly limited to surface dead moss and fibric horizons, with no change in the underlying mineral horizons. Burning caused significant changes in soil organic matter structure, with a 12% higher ratio of carbon to combustible organic matter in surface burned horizons compared with unburned horizons. Pyrolysis gas chromatography - mass spectroscopy also shows preferential volatilization of polysaccharide-derived organic matter and enrichment of lignin-and lipid-derived compounds in surface soils. The chemistry of deeper soil layers in burned and unburned sites was similar, suggesting that immediate fire impacts were restricted to the surface soil horizon. ?? 2005 NRC.

Improving Land-Surface Model Hydrology: Is an Explicit Aquifer Model Better than a Deeper Soil Profile?

NASA Technical Reports Server (NTRS)

Gulden, L. E.; Rosero, E.; Yang, Z.-L.; Rodell, Matthew; Jackson, C. S.; Niu, G.-Y.; Yeh, P. J.-F.; Famiglietti, J. S.

2007-01-01

Land surface models (LSMs) are computer programs, similar to weather and climate prediction models, which simulate the storage and movement of water (including soil moisture, snow, evaporation, and runoff) after it falls to the ground as precipitation. It is not currently possible to measure all of the variables of interest everywhere on Earth with sufficient accuracy. Hence LSMs have been developed to integrate the available information, including satellite observations, using powerful computers, in order to track water storage and redistribution. The maps are used to improve weather forecasts, support water resources and agricultural applications, and study the Earth's water cycle and climate variability. Recently, the models have begun to simulate groundwater storage. In this paper, we compare several possible approaches, and examine the pitfalls associated with trying to estimate aquifer parameters (such as porosity) that are required by the models. We find that explicit representation of groundwater, as opposed to the addition of deeper soil layers, considerably decreases the sensitivity of modeled terrestrial water storage to aquifer parameter choices. We also show that approximate knowledge of parameter values is not sufficient to guarantee realistic model performance: because interaction among parameters is significant, they must be prescribed as a harmonious set.

Closing the water balance with cosmic-ray soil moisture measurements and assessing their relation to evapotranspiration in two semiarid watersheds

NASA Astrophysics Data System (ADS)

Schreiner-McGraw, A. P.; Vivoni, E. R.; Mascaro, G.; Franz, T. E.

2016-01-01

Soil moisture dynamics reflect the complex interactions of meteorological conditions with soil, vegetation and terrain properties. In this study, intermediate-scale soil moisture estimates from the cosmic-ray neutron sensing (CRNS) method are evaluated for two semiarid ecosystems in the southwestern United States: a mesquite savanna at the Santa Rita Experimental Range (SRER) and a mixed shrubland at the Jornada Experimental Range (JER). Evaluations of the CRNS method are performed for small watersheds instrumented with a distributed sensor network consisting of soil moisture sensor profiles, an eddy covariance tower, and runoff flumes used to close the water balance. We found a very good agreement between the CRNS method and the distributed sensor network (root mean square error (RMSE) of 0.009 and 0.013 m3 m-3 at SRER and JER, respectively) at the hourly timescale over the 19-month study period, primarily due to the inclusion of 5 cm observations of shallow soil moisture. Good agreement was also obtained in soil moisture changes estimated from the CRNS and watershed water balance methods (RMSE of 0.001 and 0.082 m3 m-3 at SRER and JER, respectively), with deviations due to bypassing of the CRNS measurement depth during large rainfall events. Once validated, the CRNS soil moisture estimates were used to investigate hydrological processes at the footprint scale at each site. Through the computation of the water balance, we showed that drier-than-average conditions at SRER promoted plant water uptake from deeper soil layers, while the wetter-than-average period at JER resulted in percolation towards deeper soils. The CRNS measurements were then used to quantify the link between evapotranspiration and soil moisture at a commensurate scale, finding similar predictive relations at both sites that are applicable to other semiarid ecosystems in the southwestern US.

Closing the water balance with cosmic-ray soil moisture measurements and assessing their spatial variability within two semiarid watersheds

NASA Astrophysics Data System (ADS)

Schreiner-McGraw, A. P.; Vivoni, E. R.; Mascaro, G.; Franz, T. E.

2015-06-01

Soil moisture dynamics reflect the complex interactions of meteorological conditions with soil, vegetation and terrain properties. In this study, intermediate scale soil moisture estimates from the cosmic-ray sensing (CRS) method are evaluated for two semiarid ecosystems in the southwestern United States: a mesquite savanna at the Santa Rita Experimental Range (SRER) and a mixed shrubland at the Jornada Experimental Range (JER). Evaluations of the CRS method are performed for small watersheds instrumented with a distributed sensor network consisting of soil moisture sensor profiles, an eddy covariance tower and runoff flumes used to close the water balance. We found an excellent agreement between the CRS method and the distributed sensor network (RMSE of 0.009 and 0.013 m3 m-3 at SRER and JER) at the hourly time scale over the 19-month study period, primarily due to the inclusion of 5 cm observations of shallow soil moisture. Good agreement was obtained in soil moisture changes estimated from the CRS and watershed water balance methods (RMSE = 0.001 and 0.038 m3 m-3 at SRER and JER), with deviations due to bypassing of the CRS measurement depth during large rainfall events. This limitation, however, was used to show that drier-than-average conditions at SRER promoted plant water uptake from deeper layers, while the wetter-than-average period at JER resulted in leakage towards deeper soils. Using the distributed sensor network, we quantified the spatial variability of soil moisture in the CRS footprint and the relation between evapotranspiration and soil moisture, in both cases finding similar predictive relations at both sites that are applicable to other semiarid ecosystems in the southwestern US. Furthermore, soil moisture spatial variability was related to evapotranspiration in a manner consistent with analytical relations derived using the CRS method, opening up new possibilities for understanding land-atmosphere interactions.

The Influence of Tree Species on Subsurface Stormflow at the Hillslope Scale

NASA Astrophysics Data System (ADS)

Jost, G.; Weiler, M.

2006-12-01

This study investigates the effect of Norway spruce (Picea abies (L.) Karst) and European beech (Fagus sylvatica L.), two very common tree species in Central Europe, on soil water storage and runoff response to precipitation. We postulate that on the same type of soil, spruce with its shallow rooting system leads to different soil water storage and runoff responses than the deep rooting beech. To test this hypothesis, we chose a beech and a spruce stand with comparable soil type, a stagnic cambisol with a stagnic layer in about 50 cm soil depth. In each of the two stands we sprinkled a hillslope of 6 m by 10 m with intensities of 100 mm/h and 60 mm/h for one hour each. Surface and shallow interflow as well as interflow in different soil depths was collected by inserted sheet metals and gutters in 10 cm, 30 cm and 60 cm soil depth. Soil water storage responses were measured by 48 multiplexed TDR sensors at each hillslope. TDR wave-guides (20 cm long) were installed in a 45° angle in 10 cm, 30 cm, 50 cm and 70 cm soil depth. Volumetric water content was measured in 6 minute intervals. Sprinkling experiments show that even at intensities of 100 mm/h all the applied water infiltrates, independent of the vegetation cover. The deeper soil horizons respond immediately to the applied precipitation. This vertical water flux response is larger under beech. Under spruce most of the water transport happens in the topsoil layers (upper 40 cm), whereas under beech the entire soil profile down to 80 cm soil depth reacts to sprinkling. Under spruce at intensities of 100 mm/h the whole pore space is almost filled. The larger pores in the topsoil under beech stemming from higher biogenic activity and in the subsoil from more intense rooting are still far from reaching their maximum capacity. High antecedent soil water content (around field capacity) still doesn't cause infiltration excess overland flow but the time that it takes for the soil water storage to drain to its initial value is less than one hour. The hillslope at the spruce stand produces between 23% and 28% runoff. However, the beech hillslope produces roughly twice as much. These experiments show that the interactions between tree species and soil in the vadose zone lead to different pore systems and thus different responses to subsurface stormflow. Beech with its deeper rooting systems and its higher biogenic activity (lower C/N ratio) creates a very effective preferential flow path system that leads to greater amounts of subsurface stormflow. Under high antecedent soil water storage, saturation excess overland flow is more likely to occur in soils under spruce with its smaller preferential flow system.

Dissecting the variable source area concept - Flow paths and water mixing processes

NASA Astrophysics Data System (ADS)

Dahlke, H. E.; Easton, Z. M.; Lyon, S. W.; Brown, L. D.; Walter, M. T.; Steenhuis, T.

2010-12-01

Variable source areas (VSAs) are hot spots of hydrological (saturation excess runoff) and biogeochemical processes (e.g. nitrogen, phosphorus, organic carbon cycling) in the landscapes of the northeastern U.S. The prevalence of shallow, highly transmissive soils, steep topography, and impeding layers in the soil (i.e. fragipan) have long been recognized as first-order controls on VSA formation. Nevertheless, there is still understanding to be gained by studying subsurface flow processes in VSAs. Thus, we instrumented (trenched) a 0.5 ha hillslope in the southern tier of New York State, U.S.A. and measured water fluxes in the trench, upslope water table dynamics, surface and bedrock topography in conjunction with isotopic and geochemical tracers in order to four-dimensionally characterize (XYZ and Time) subsurface storm flow response within the VSA for five storm events. We used tracer-based hydrograph separation models and physically measured flow components to separate temporally (i.e. event and pre-event) and spatially shallow water from above the fragipan layer (including both surface runoff and shallow interflow) and deeper water from below the fragipan layer. Shallow water (event/pre-event) contributions were greatest during storms with wet antecedent conditions and large rainfall amounts (> 15 mm), when soils above the fragipan were saturated, prohibiting deep percolation through cracks in the fragipan. Shallow water contributions were well correlated to the saturated contributing area. During these events, the pre-event shallow water peaked on the rising and falling limb, which can be explained by flushing of pre-event water from macropores on the rising limb and subsequent drainage of pre-event water from micropores into macropores on the falling limb. During events with dry antecedent conditions, greater amounts of event water (24 - 28 %) are proportionally contributed by surface runoff in the top 10 cm of the soil through macropores than by shallow interflow from the soil-fragipan interface. Pre-event deeper water contributions to total trench discharge varied between 15 and 65% but were independent of total rainfall amounts, rainfall intensities, and water table dynamics. Our results have important implication for the protection of streams from dissolved pollutant transport and recommend that preference be given to variable-width buffers over fixed-width stream buffers.

Mobility of selected trace elements in Mediterranean red soil amended with phosphogypsum: experimental study.

PubMed

Kassir, Lina Nafeh; Darwish, Talal; Shaban, Amin; Ouaini, Naim

2012-07-01

Soil amendment by phosphogypsum (PG) application becomes of increasing importance in agriculture. This may lead, however, to soil, plant, and groundwater contamination with trace elements (TEs) inherently present in PG. Monitoring of selected TEs (Pb, Zn, Cu, and Cd) distribution and mobility in a Mediterranean red soil profile has been performed in soil parcels applied with PG over a 16-month period. Concentrations were measured in soil and plant samples collected from various depth intervals at different points in time. TEs sequential extraction was performed on soil and PG samples. Results showed soil profile enrichment peaked 5 months after PG application for Cd, and 12 months for Pb, Zn, and Cu. Rainwater, pH, total organic carbon, and cationic exchange capacity were the main controlling factors in TEs accumulation in soils. Cd was transferred to a soil depth of about 20 cm. Zn exhibited mobility towards deeper layers. Pb and Cu were accumulated in around 20-55-cm-deep layers. PG increased the solubility of the studied TEs; PG-applied soils contained TEs bound to exchangeable and acid-soluble fractions in higher percentages than reference soil. Pb, Zn, and Cu were sorbed into mineral soil phases, while Cd was mainly found in the exchangeable (bio-available) form. The order of TEs decreasing mobility was Zn > Cd > Pb > Cu. Roots and leaves of existed plants, Cichorium intybus L., accumulated high concentrations of Cd (1-2.4 mg/kg), exceeding recommended tolerable levels, and thus signifying potential health threats through contaminated crops. It was therefore recommended that PG should be applied in carefully established, monitored, and controlled quantities to agricultural soils.

Effects of Conversion from Boreal Forest to Arctic Steppe on Soil Communities and Ecosystem Carbon Pools

NASA Astrophysics Data System (ADS)

Han, P. D.; Natali, S.; Schade, J. D.; Zimov, N.; Zimov, S. A.

2014-12-01

The end of the Pleistocene marked the extinction of a great variety of arctic megafauna, which, in part, led to the conversion of arctic grasslands to modern Siberian larch forest. This shift may have increased the vulnerability of permafrost to thawing because of changes driven by the vegetation shift; the higher albedo of grassland and low insulation of snow trampled by animals may have decreased soil temperatures and reduced ground thaw in the grassland ecosystem, resulting in protection of organic carbon in thawed soil and permafrost. To test these hypothesized impacts of arctic megafauna, we examined an experimental reintroduction of large mammals in northeast Siberia, initiated in 1988. Pleistocene Park now contains 23 horses, three musk ox, one bison, and several moose in addition to the native fauna. The park is 16 square km with a smaller enclosure (< 1 km) where animals spend most of their time and our study was focused. We measured carbon-pools in forested sites (where scat surveys showed low animal use), and grassy sites (which showed higher use), within the park boundaries. We also measured thaw depth and documented the soil invertebrate communities in each ecosystem. There was a substantial difference in number of invertebrates per kg of organic soil between the forest (600 ± 250) and grassland (300 ± 250), though these differences were not statistically significant they suggest faster nutrient turnover in the forest or a greater proportion of decomposition by invertebrates than other decomposers. While thaw depth was deeper in the grassland (60 ± 4 cm) than in the forest (40 ± 6 cm), we did not detect differences in organic layer depth or percent organic matter between grassland and forest. However, soil in the grassland had higher bulk density, and higher carbon stocks in the organic and mineral soil layers. Although deeper thaw depth in the grassland suggests that more carbon is available to microbial decomposers, ongoing temperature monitoring will help determine whether or not differences detected in summer continue throughout the year. This study provides a preliminary understanding of the role megafauna play in carbon emissions from the arctic, and suggests that animals play a critical role in regulating permafrost thaw and the fate of carbon stored in Arctic soils.

Land cover effects on thresholds for surface runoff generation in Eastern Madagascar

NASA Astrophysics Data System (ADS)

van Meerveld, Ilja H. J.; Prasad Ghimire, Chandra; Zwartendijk, Bob W.; Ravelona, Maafaka; Lahitiana, Jaona; Bruijnzeel, L. Adrian

2016-04-01

Reforestation and natural regrowth in the tropics are promoted for a wide range of benefits, including carbon sequestration, land rehabilitation and streamflow regulation. However, their effects on runoff generation mechanisms and streamflow are still poorly understood. Evaporative losses (transpiration and interception) likely increase with forest regrowth, while infiltration rates are expected to increase and surface runoff occurrence is, therefore, expected to decrease. As part of a larger project investigating the effects of land use on hydrological processes in upland Eastern Madagascar, this presentation reports on a comparison of the thresholds for surface runoff generation at a degraded grassland site, a young secondary forest site (5-7 years; LAI 1.83) and a mature secondary forest site (ca. 20 years; LAI 3.39). Surface runoff was measured on two (young and mature secondary forest) or three (degraded site) 3 m by 10 m plots over a one-year period (October 2014-September 2015). Soil moisture was measured at four (degraded site) to six depths (both forests), while perched groundwater levels were measured in piezometers installed at 30 cm below the soil surface. Soil hydraulic conductivity was measured in situ at the surface and at 10-20 and 20-30 cm depths at three locations in each plot. Porosity, moisture content at field capacity and bulk density were determined from soil cores taken at 2.5-7.5, 12.5-17.5 and 22.5-27.5 cm depth. The porosity and texture of the different plots were comparable. The hydraulic conductivity of the soil differed between the different land uses and declined sharply at 20-30 cm below the soil surface. Total surface runoff during the study period was 11% of incident rainfall at the degraded site vs. 2% for the two secondary forest sites. Maximum monthly runoff coefficients were 22%, 3.5% and 2.7% for the degraded site, the young forest site and the mature forest site, respectively, but individual event runoff coefficients could be as high as 45%, 12%, and 10%, respectively. Initial analyses indicate that a threshold rainfall amount was required before surface runoff occurs. Comparison of surface runoff occurrence with perched groundwater levels and soil moisture data showed that surface runoff was generated once the top-soil (0-20 cm) became saturated because of impeded drainage to the low hydraulic conductivity deeper layers. Thresholds for saturation overland flow generation were higher at the two forested sites compared to the degraded grassland due to their greater percolation to deeper layers, faster shallow lateral flow, and larger available storage in the top layers. The detailed analyses of the soil moisture and rainfall thresholds for surface runoff generation and their temporal variation will be used to develop a bucket-based conceptual model for runoff generation at these upland tropical sites. Key words: Runoff plot, rainfall threshold, soil moisture, saturation overland flow, secondary forest, soil hydraulic conductivity, Madagascar, p4ges project

Interaction of Solar-Flare-Accelerated Nuclei with the Solar Photosphere and the Isotopic Composition of the Solar Wind

NASA Astrophysics Data System (ADS)

Vasil'ev, G. I.; Ostryakov, V. M.; Pavlov, A. K.; Chakchurina, M. E.

2017-12-01

The nuclear interactions of solar-flare-accelerated protons and ions with the solar atmosphere and the deeper layers of the Sun lead to the formation of several stable and radioactive isotopes. This article examines the GEANT4 depth profiles of 2H, 3H, 3He, 6Li, 7Li, 10Be, and 14C. When accelerated particles pass through a layer of 0.1-2 g cm-2, 6Li, 7Li, 10Be, and 14C isotopes form in sufficient amounts to explain their anomalous abundances in lunar soil samples. It is assumed that they escape into interplanetary space with coronal mass ejections immediately after the flare.

[Influencing factors of soil organic carbon in deeper soil layers at a small watershed on tableland region of the Loess Plateau, China].

PubMed

Che, Sheng-guo; Guo, Sheng-li

2010-05-01

Analyzing and estimating soil organic carbon (SOC) storage and changes in deep layers under different land uses and landforms may play a pivotal role in comprehending the balance and cycle mechanisms of C cycling, and comprehending the capacity of C sequestration in the terrestrial ecosystem. The study mainly emphasized on effects of landforms and land uses on vertical distribution characteristic of SOC sampled to a depth of 200 cm at the Wangdonggou watershed on the tableland region of Loess Plateau, China. For the top soil of 0-20 cm, the order of SOC contents was gully (10.0 g x kg(-1)) > tableland (7.8 g x kg(-1)) and slopeland (8.2 g x kg(-1)). For the subsoil, SOC in tableland was higher than that in gully and slopeland. For slopeland and gully, SOC decreased with increasing depth, while for tableland, SOC decreased initially, then increased, lastly decreased. Meanwhile, for tableland, the order of SOC appeared approximately manmade grassland > cropland > orchard with the effecting depth of land uses for 40 cm, and for slopeland the order was native grassland (4.3 g x kg(-1)) > manmade woodland (3.8 g x kg(-1)) > manmade grassland (3.3 g x kg(-1)) > orchard (3.3 g x kg(-1)) with the depth for 100 cm, while for gully, there was no significantly difference (p > 0.05) among different land uses. SOC storage in the profile of 20-200 cm accounted for 67.6% sampled to a depth of 100 cm, while for 100-200cm, SOC storage accounted 37.3% in 0-200 cm equaled to 63.8% of the SOC storage in 0-100 cm. The results revealed that landforms and land uses highly significantly (p < 0.05) affected the vertical distribution of SOC at a small watershed scale and considerable amounts of C were stored at deeper depths.

Field versus laboratory experiments to evaluate the fate of azoxystrobin in an amended vineyard soil.

PubMed

Herrero-Hernández, E; Marín-Benito, J M; Andrades, M S; Sánchez-Martín, M J; Rodríguez-Cruz, M S

2015-11-01

This study reports the effect that adding spent mushroom substrate (SMS) to a representative vineyard soil from La Rioja region (Spain) has on the behaviour of azoxystrobin in two different environmental scenarios. Field dissipation experiments were conducted on experimental plots amended at rates of 50 and 150 t ha(-1), and similar dissipation experiments were simultaneously conducted in the laboratory to identify differences under controlled conditions. Azoxystrobin dissipation followed biphasic kinetics in both scenarios, although the initial dissipation phase was much faster in the field than in the laboratory experiments, and the half-life (DT50) values obtained in the two experiments were 0.34-46.3 days and 89.2-148 days, respectively. Fungicide residues in the soil profile increased in the SMS amended soil and they were much higher in the top two layers (0-20 cm) than in deeper layers. The persistence of fungicide in the soil profile is consistent with changes in azoxystrobin adsorption by unamended and amended soils over time. Changes in the dehydrogenase activity (DHA) of soils under different treatments assayed in the field and in the laboratory indicated that SMS and the fungicide had a stimulatory effect on soil DHA. The results reveal that the laboratory studies usually reported in the literature to explain the fate of pesticides in amended soils are insufficient to explain azoxystrobin behaviour under real conditions. Field studies are necessary to set up efficient applications of SMS and fungicide, with a view to preventing the possible risk of water contamination. Copyright © 2015 Elsevier Ltd. All rights reserved.

Irrigation and Nitrogen Regimes Promote the Use of Soil Water and Nitrate Nitrogen from Deep Soil Layers by Regulating Root Growth in Wheat

PubMed Central

Liu, Weixing; Ma, Geng; Wang, Chenyang; Wang, Jiarui; Lu, Hongfang; Li, Shasha; Feng, Wei; Xie, Yingxin; Ma, Dongyun; Kang, Guozhang

2018-01-01

Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6–45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1–45.3% compared to the W1 treatments during the drier growing seasons (2010–2011, 2012–2013, and 2015–2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011–2012, 2013–2014, and 2014–2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO3-N from the deep soil layers. N applications increased yield by 19.1–64.5%, with a corresponding increase in WUE of 66.9–83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha−1, respectively. A N application rate of 240 kg ha−1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO3-N and also in reducing the residual NO3-N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180–240 kg ha−1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical. PMID:29449850

Fostering Deeper Critical Inquiry with Causal Layered Analysis

ERIC Educational Resources Information Center

Haigh, Martin

2016-01-01

Causal layered analysis (CLA) is a technique that enables deeper critical inquiry through a structured exploration of four layers of causation. CLA's layers reach down from the surface litany of media understanding, through the layer of systemic causes identified by conventional research, to underpinning worldviews, ideologies and philosophies,…

Oxidized charcoal contribution to the humic material of deeper soil horizons in selected soils of the Doñana National Park, Spain

NASA Astrophysics Data System (ADS)

Knicker, Heike; González-Vila, Fransisco; Clemente-Salas, Luis

2017-04-01

The Doñana National Park is located at the mouth of the river Guadalquivir in Southern Spain and represents one of the largest marshlands reserves of Europe. Although vegetation fires are now prevented as far as possible, some of the areas were formerly subjected to frequent prescribed fires since 1628 (approximately every 25-30 years). The so formed pyrogenic organic matter (PyOM) is supposed to compose a major proportion of the slow-cycling carbon pools in soils and as such it is expected to affect quality and quantity of the soil organic matter (SOM) in the present reclaimed soils. In order to test this, the SOM of three profiles (Humaquepts) within the protected center region were analyzed by solid state 13C NMR spectroscopy. The respective pyrogenic organic carbon (PyOC) content was elucidated, using the chemical oxidation method. Two of the selected profiles had experienced no fire since installation of the park in 1969. Here, no major quantities of PyOC were recovered in the O layer, but an increase of aromaticity correlating with PyOC contents was revealed with soil depth. At both sites, PyOC accounted for more than 15% of the Ctot in the A/C horizon (> 50 cm). This clearly evidences a downward translocation of charcoal within the soil profile. The third profile suffered a severe fire in 1985. The fire combusted all of the O layer (0-20 cm), but after 19 years, it recovered to approximately 15 cm, although only minor contributions of PyOC were revealed. Whereas directly after the fire, the soil at a depths of 55 cm contained only 3 mg g-1 organic C without any evidence of PyOC, after 16 and 19 years a clear increase of Ctot (10-15 mg g-1) with a considerable contribution of PyOC (12% of Ctot) was revealed. Although the absolute concentration of PyOC did not decrease in the lower depths, its relative contribution to Ctot declined. This may be explained by the constant input of fresh litter l, which on a long term masks the presence of char. Alternatively, a more efficient downwards transport and subsequent stabilization of PyOC may have occurred. In summary, the studied profiles clearly demonstrate that not only in tropical soils but also in fire-affected soils of the temperate climatic zones, PyOC has an important contribution to the chemical composition of humic material in deeper horizons.

Do Forest Age and Soil Depth Affect Carbon and Nitrogen Adsorption in Mineral Horizons?

NASA Astrophysics Data System (ADS)

Spina, P. G.; Lovett, G. M.; Fuss, C. B.; Goodale, C. L.; Lang, A.; Fahey, T.

2015-12-01

Mineral soils retain large amounts of organic matter through sorption on the surfaces of mineral soils, the largest pools of carbon (C) and nitrogen (N) in the forests of the northeastern U.S. In addition to determining organic matter storage, adsorption and desorption processes are important controllers of runoff chemistry. We are studying adsorption dynamics of mineral soils collected from a chronosequence of hardwood forest sites in the White Mountains, NH to determine how soils vary in their DOM adsorption capacities as a function of effective C and N saturation. We hypothesize that forest age determines proximity to saturation because young forests may need to mine soil organic matter (SOM) in mineral soils to obtain nitrogen to meet growth demands, while the soils of older forests have had time to reaccumulate SOM, eventually reaching C and N saturation. Consequently, we expect adsorption capacities to first increase with forest age in young forests, as the trees mine C and N from mineral surfaces. They will then decrease with forest age in older forests as mining slows and C and N begin to re-accumulate. Batch experiments were conducted with mineral soil samples and dilutions of forest floor leachate. However, preliminary results from a mature forest site (about 100 years old), which we predicted to be a low point of C and N saturation from decades of mining, contradict expectations. Dissolved organic carbon (DOC) adsorption in its shallow mineral soil layers (0-3 cm below E or A horizons) are lower than younger sites ranging from 20 to about 40 years old. In addition to forest age, soil depths also affect N retention dynamics in forest soils. We hypothesized that deeper mineral soils might have greater adsorption capacities due to the fact that they are exposed to less DOC and DON leaching from organic layers and therefore less saturated. Results from the same mature forest site confirm this. Soils from 3-10 cm depth have more potential to adsorb DOC and DON than soils from 0-3 cm depth. For example, at 80 mg/L DOC, the >3-10 layer adsorbed 11.37 mg total N (TN)/g dry soil whereas the 0-3 layer adsorbed 2.13 mg TN/g dry soil. This project will also consider the effects of soil texture, soil C and N content, and Al and Fe oxide and hydroxide content.

Pendimethalin and oxyfluorfen degradation under two irrigation conditions over four years application.

PubMed

Alister, Claudio A; Gomez, Patricio A; Rojas, Sandra; Kogan, Marcelo

2009-05-01

A four-year field study was conducted to determine the effect of pluviometric conditions on pendimethalin and oxyfluorfen soil dynamics. Adsorption, dissipation and soil movement were studied in a sandy loam soil from 2003 to 2007. Pendimethalin and oxyfluorfen were applied every year on August at 1.33 and 0.75 kg ha(-1), respectively. Herbicide soil concentrations were determined at 0, 10, 20, 40, 90 and 340 days after application (DAA), under two pluviometric regimens, natural rainfall and irrigated (30 mm every 15 days during the first 90 DAA). More than 74% of the herbicide applied was detected at the top 2.5 cm layer for both herbicides, and none was detected at 10 cm or deeper. Pendimethalin soil half-life ranged from 10.5 to 31.5 days, and was affected mainly by the time interval between application and the first rain event. Pendimethalin soil residues at 90 DAA fluctuated from 2.5 to 13.8% of the initial amount applied, and it decreased to 2.4 and 8.6% at 340 DAA. Oxyfluorfen was more persistent than pendimethalin as indicated by its soil half-life which ranged from 34.3 to 52.3 days, affected primarily by the rain amount at the first rainfall after application. Oxyfluorfen soil residues at 90 DAA ranged from 16.7 to 34.8% and it decreased to 3.3 and 17.9% at 340 DAA. Based on half-life values, herbicide soil residues after one year, and soil depth reached by the herbicides, we conclude that both herbicides should be considered as low risk to contaminate groundwater. However, herbicide concentration at the top 2.5 cm layer should be considered in cases where runoff or soil erosion could occur, because of the potential for surface water contamination.

Maize varieties released in different eras have similar root length density distributions in the soil, which are negatively correlated with local concentrations of soil mineral nitrogen.

PubMed

Ning, Peng; Li, Sa; White, Philip J; Li, Chunjian

2015-01-01

Larger, and deeper, root systems of new maize varieties, compared to older varieties, are thought to have enabled improved acquisition of soil resources and, consequently, greater grain yields. To compare the spatial distributions of the root systems of new and old maize varieties and their relationships with spatial variations in soil concentrations of available nitrogen (N), phosphorus (P) and potassium (K), two years of field experiments were performed using six Chinese maize varieties released in different eras. Vertical distributions of roots, and available N, P and K in the 0-60 cm soil profile were determined in excavated soil monoliths at silking and maturity. The results demonstrated that new maize varieties had larger root dry weight, higher grain yield and greater nutrient accumulation than older varieties. All varieties had similar total root length and vertical root distribution at silking, but newer varieties maintained greater total root length and had more roots in the 30-60 cm soil layers at maturity. The spatial variation of soil mineral N (Nmin) in each soil horizon was larger than that of Olsen-P and ammonium-acetate-extractable K, and was inversely correlated with root length density (RLD), especially in the 0-20 cm soil layer. It was concluded that greater acquisition of mineral nutrients and higher yields of newer varieties were associated with greater total root length at maturity. The negative relationship between RLD and soil Nmin at harvest for all varieties suggests the importance of the spatial distribution of the root system for N uptake by maize.

Maize Varieties Released in Different Eras Have Similar Root Length Density Distributions in the Soil, Which Are Negatively Correlated with Local Concentrations of Soil Mineral Nitrogen

PubMed Central

Ning, Peng; Li, Sa; White, Philip J.; Li, Chunjian

2015-01-01

Larger, and deeper, root systems of new maize varieties, compared to older varieties, are thought to have enabled improved acquisition of soil resources and, consequently, greater grain yields. To compare the spatial distributions of the root systems of new and old maize varieties and their relationships with spatial variations in soil concentrations of available nitrogen (N), phosphorus (P) and potassium (K), two years of field experiments were performed using six Chinese maize varieties released in different eras. Vertical distributions of roots, and available N, P and K in the 0–60 cm soil profile were determined in excavated soil monoliths at silking and maturity. The results demonstrated that new maize varieties had larger root dry weight, higher grain yield and greater nutrient accumulation than older varieties. All varieties had similar total root length and vertical root distribution at silking, but newer varieties maintained greater total root length and had more roots in the 30–60 cm soil layers at maturity. The spatial variation of soil mineral N (Nmin) in each soil horizon was larger than that of Olsen-P and ammonium-acetate-extractable K, and was inversely correlated with root length density (RLD), especially in the 0–20 cm soil layer. It was concluded that greater acquisition of mineral nutrients and higher yields of newer varieties were associated with greater total root length at maturity. The negative relationship between RLD and soil Nmin at harvest for all varieties suggests the importance of the spatial distribution of the root system for N uptake by maize. PMID:25799291

Co-transport of chlordecone and sulfadiazine in the presence of functionalized multi-walled carbon nanotubes in soils.

PubMed

Zhang, Miaoyue; Engelhardt, Irina; Šimůnek, Jirka; Bradford, Scott A; Kasel, Daniela; Berns, Anne E; Vereecken, Harry; Klumpp, Erwin

2017-02-01

Batch and saturated soil column experiments were conducted to investigate sorption and mobility of two 14 C-labeled contaminants, the hydrophobic chlordecone (CLD) and the sulfadiazine (SDZ), in the absence or presence of functionalized multi-walled carbon nanotubes (MWCNTs). The transport behaviors of CLD, SDZ, and MWCNTs were studied at environmentally relevant concentrations (0.1-10 mg L -1 ) and they were applied in the column studies at different times. The breakthrough curves and retention profiles were simulated using a numerical model that accounted for the advective-dispersive transport of all compounds, attachment/detachment of MWCNTs, equilibrium and kinetic sorption of contaminants, and co-transport of contaminants with MWCNTs. The experimental results indicated that the presence of mobile MWCNTs facilitated remobilization of previously deposited CLD and its co-transport into deeper soil layers, while retained MWCNTs enhanced SDZ deposition in the topsoil layers due to the increased adsorption capacity of the soil. The modeling results then demonstrated that the mobility of engineered nanoparticles (ENPs) in the environment and the high affinity and entrapment of contaminants to ENPs were the main reasons for ENP-facilitated contaminant transport. On the other hand, immobile MWCNTs had a less significant impact on the contaminant transport, even though they were still able to enhance the adsorption capacity of the soil. Copyright © 2016 Elsevier Ltd. All rights reserved.

Modeling thermal dynamics of active layer soils and near-surface permafrost using a fully coupled water and heat transport model

USGS Publications Warehouse

Jiang, Yueyang; Zhuang, Qianlai; O'Donnell, Jonathan A.

2012-01-01

Thawing and freezing processes are key components in permafrost dynamics, and these processes play an important role in regulating the hydrological and carbon cycles in the northern high latitudes. In the present study, we apply a well-developed soil thermal model that fully couples heat and water transport, to simulate the thawing and freezing processes at daily time steps across multiple sites that vary with vegetation cover, disturbance history, and climate. The model performance was evaluated by comparing modeled and measured soil temperatures at different depths. We use the model to explore the influence of climate, fire disturbance, and topography (north- and south-facing slopes) on soil thermal dynamics. Modeled soil temperatures agree well with measured values for both boreal forest and tundra ecosystems at the site level. Combustion of organic-soil horizons during wildfire alters the surface energy balance and increases the downward heat flux through the soil profile, resulting in the warming and thawing of near-surface permafrost. A projection of 21st century permafrost dynamics indicates that as the climate warms, active layer thickness will likely increase to more than 3 meters in the boreal forest site and deeper than one meter in the tundra site. Results from this coupled heat-water modeling approach represent faster thaw rates than previously simulated in other studies. We conclude that the discussed soil thermal model is able to well simulate the permafrost dynamics and could be used as a tool to analyze the influence of climate change and wildfire disturbance on permafrost thawing.

Enhancing Nitrogen Availability, Ammonium Adsorption-Desorption, and Soil pH Buffering Capacity using Composted Paddy Husk

NASA Astrophysics Data System (ADS)

Latifah, O.; Ahmed, O. H.; Abdul Majid, N. M.

2017-12-01

Form of nitrogen present in soils is one of the factors that affect nitrogen loss. Nitrate is mobile in soils because it does not absorb on soil colloids, thus, causing it to be leached by rainfall to deeper soil layers or into the ground water. On the other hand, temporary retention and timely release of ammonium in soils regulate nitrogen availability for crops. In this study, composted paddy husk was used in studies of soil leaching, buffering capacity, and ammonium adsorption and desorption to determine the: (i) availability of exchangeable ammonium, available nitrate, and total nitrogen in an acid soil after leaching the soil for 30 days, (ii) soil buffering capacity, and (iii) ability of the composted paddy husk to adsorb and desorb ammonium from urea. Leaching of ammonium and nitrate were lower in all treatments with urea and composted paddy husk compared with urea alone. Higher retention of soil exchangeable ammonium, available nitrate, and total nitrogen of the soils with composted paddy husk were due to the high buffering capacity and cation exchange capacity of the amendment to adsorb ammonium thus, improving nitrogen availability through temporary retention on the exchange sites of the humic acids of the composted paddy husk. Nitrogen availability can be enhanced if urea is amended with composted paddy husk.

Depth profiling of Pu, 241Am and 137Cs in soils from southern Belarus measured by ICP-MS and alpha and gamma spectrometry.

PubMed

Boulyga, Sergei F; Zoriy, Myroslav; Ketterer, Michael E; Becker, J Sabine

2003-08-01

The depth distribution of plutonium, americium, and 137Cs originating from the 1986 accident at the Chernobyl Nuclear Power Plant (NPP) was investigated in several soil profiles in the vicinity from Belarus. The vertical migration of transuranic elements in soils typical of the 30 km relocation area around Chernobyl NPP was studied using inductively coupled plasma mass spectrometry (ICP-MS), alpha spectrometry, and gamma spectrometry. Transuranic concentrations in upper soil layers ranged from 6 x 10(-12) g g(-1) to 6 x 10(-10) g g(-1) for plutonium and from 1.8 x 10(-13) g g(-1) to 1.6 x 10(-11) g g(-1) for americium. These concentrations correspond to specific activities of (239+240)Pu of 24-2400 Bq kg(-1) and specific activity of 241Am of 23-2000 Bq kg(-1), respectively. Transuranics in turf-podzol soil migrate slowly to the deeper soil layers, thus, 80-95%, of radionuclide inventories were present in the 0-3 cm intervals of turf-podzol soils collected in 1994. In peat-marsh soil migration processes occur more rapidly than in turf-podzol and the maximum concentrations are found beneath the soil surface (down to 3-6 cm). The depth distributions of Pu and Am are essentially identical for a given soil profile. (239+240)Pu/137Cs and 241Am/137Cs activity ratios vary by up to a factor of 5 at some sites while smaller variations in these ratios were observed at a site close to Chernobyl, suggesting that 137Cs is dominantly particle associated close to Chernobyl but volatile species of 137Cs are of relatively greater importance at the distant sites.

Global Soil Moisture Estimation through a Coupled CLM4-RTM-DART Land Data Assimilation System

NASA Astrophysics Data System (ADS)

Zhao, L.; Yang, Z. L.; Hoar, T. J.

2016-12-01

Very few frameworks exist that estimate global-scale soil moisture through microwave land data assimilation (DA). Toward this goal, we have developed such a framework by linking the Community Land Model version 4 (CLM4) and a microwave radiative transfer model (RTM) with the Data Assimilation Research Testbed (DART). The deterministic Ensemble Adjustment Kalman Filter (EAKF) within the DART is utilized to estimate global multi-layer soil moisture by assimilating brightness temperature observations from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E). A 40-member of Community Atmosphere Model version 4 (CAM4) reanalysis is adopted to drive CLM4 simulations. Spatial-specific time-invariant microwave parameters are pre-calibrated to minimize uncertainties in RTM. Besides, various methods are designed in consideration of computational efficiency. A series of experiments are conducted to quantify the DA sensitivity to microwave parameters, choice of assimilated observations, and different CLM4 updating schemes. Evaluation results indicate that the newly established CLM4-RTM-DART framework improves the open-loop CLM4 simulated soil moisture. Pre-calibrated microwave parameters, rather than their default values, can ensure a more robust global-scale performance. In addition, updating near-surface soil moisture is capable of improving soil moisture in deeper layers, while simultaneously updating multi-layer soil moisture fails to obtain intended improvements. We will show in this presentation the architecture of the CLM4-RTM-DART system and the evaluations on AMSR-E DA. Preliminary results on multi-sensor DA that integrates various satellite observations including GRACE, MODIS, and AMSR-E will also be presented. ReferenceZhao, L., Z.-L. Yang, and T. J. Hoar, 2016. Global Soil Moisture Estimation by Assimilating AMSR-E Brightness Temperatures in a Coupled CLM4-RTM-DART System. Journal of Hydrometeorology, DOI: 10.1175/JHM-D-15-0218.1.

Effects of field experimental warming on wheat root distribution under conventional tillage and no-tillage systems.

PubMed

Hou, Ruixing; Ouyang, Zhu; Han, Daorui; Wilson, Glenn V

2018-03-01

Despite the obvious importance of roots to agro-ecosystem functioning, few studies have attempted to examine the effects of warming on root biomass and distribution, especially under different tillage systems. In this study, we performed a field warming experiment using infrared heaters on winter wheat, in long-term conventional tillage and no-tillage plots, to determine the responses of root biomass and distribution to warming. Soil monoliths were collected from three soil depths (0-10, 10-20, and 20-30 cm). Results showed that root biomass was noticeably increased under both till and no-till tillage systems (12.1% and 12.9% in 2011, and 9.9% and 14.5% in 2013, in the two tillage systems, respectively) in the 0-30 cm depth, associated with a similar increase in shoot biomass. However, warming-induced root biomass increases occurred in the deeper soil layers (i.e., 10-20 and 20-30 cm) in till, while the increase in no-till was focused in the surface layer (0-10 cm). Differences in the warming-induced increases in root biomass between till and no-till were positively correlated with the differences in soil total nitrogen ( R 2  = .863, p  <   .001) and soil bulk density ( R 2  = .853, p  <   .001). Knowledge of the distribution of wheat root in response to warming should help manage nutrient application and cycling of soil C-N pools under anticipated climate change conditions.

Using soil seed banks to assess temporal patterns of genetic variation in invasive plant populations.

PubMed

Fennell, Mark; Gallagher, Tommy; Vintro, Luis Leon; Osborne, Bruce

2014-05-01

Most research on the genetics of invasive plant species has focused on analyzing spatial differences among existing populations. Using a long-established Gunnera tinctoria population from Ireland, we evaluated the potential of using plants derived from seeds associated with different soil layers to track genetic variation through time. This species and site were chosen because (1) G. tinctoria produces a large and persistent seed bank; (2) it has been present in this locality, Sraheens, for ∼90 years; (3) the soil is largely undisturbed; and (4) the soil's age can be reliably determined radiometrically at different depths. Amplified fragment length polymorphic markers (AFLPs) were used to assess differences in the genetic structure of 75 individuals sampled from both the standing population and from four soil layers, which spanned 18 cm (estimated at ∼90 years based on (210)Pb and (137)Cs dating). While there are difficulties in interpreting such data, including accounting for the effects of selection, seed loss, and seed migration, a clear pattern of lower total allele counts, percentage polymorphic loci, and genetic diversity was observed in deeper soils. The greatest percentage increase in the measured genetic variables occurred prior to the shift from the lag to the exponential range expansion phases and may be of adaptive significance. These findings highlight that seed banks in areas with long-established invasive populations can contain valuable genetic information relating to invasion processes and as such, should not be overlooked.

Using soil seed banks to assess temporal patterns of genetic variation in invasive plant populations

PubMed Central

Fennell, Mark; Gallagher, Tommy; Vintro, Luis Leon; Osborne, Bruce

2014-01-01

Most research on the genetics of invasive plant species has focused on analyzing spatial differences among existing populations. Using a long-established Gunnera tinctoria population from Ireland, we evaluated the potential of using plants derived from seeds associated with different soil layers to track genetic variation through time. This species and site were chosen because (1) G. tinctoria produces a large and persistent seed bank; (2) it has been present in this locality, Sraheens, for ∼90 years; (3) the soil is largely undisturbed; and (4) the soil's age can be reliably determined radiometrically at different depths. Amplified fragment length polymorphic markers (AFLPs) were used to assess differences in the genetic structure of 75 individuals sampled from both the standing population and from four soil layers, which spanned 18 cm (estimated at ∼90 years based on 210Pb and 137Cs dating). While there are difficulties in interpreting such data, including accounting for the effects of selection, seed loss, and seed migration, a clear pattern of lower total allele counts, percentage polymorphic loci, and genetic diversity was observed in deeper soils. The greatest percentage increase in the measured genetic variables occurred prior to the shift from the lag to the exponential range expansion phases and may be of adaptive significance. These findings highlight that seed banks in areas with long-established invasive populations can contain valuable genetic information relating to invasion processes and as such, should not be overlooked. PMID:24967082

Improving Soil Moisture and Temperature Profile and Surface Turbulent Fluxes Estimations in Irrigated Field by Assimilating Multi-source Data into Land Surface Model

NASA Astrophysics Data System (ADS)

Chen, Weijing; Huang, Chunlin; Shen, Huanfeng; Wang, Weizhen

2016-04-01

The optimal estimation of hydrothermal conditions in irrigation field is restricted by the deficiency of accurate irrigation information (when and how much to irrigate). However, the accurate estimation of soil moisture and temperature profile and surface turbulent fluxes are crucial to agriculture and water management in irrigated field. In the framework of land surface model, soil temperature is a function of soil moisture - subsurface moisture influences the heat conductivity at the interface of layers and the heat storage in different layers. In addition, soil temperature determines the phase of soil water content with the transformation between frozen and unfrozen. Furthermore, surface temperature affects the partitioning of incoming radiant energy into ground (sensible and latent heat flux), as a consequence changes the delivery of soil moisture and temperature. Given the internal positive interaction lying in these variables, we attempt to retrieve the accurate estimation of soil moisture and temperature profile via assimilating the observations from the surface under unknown irrigation. To resolve the input uncertainty of imprecise irrigation quantity, original EnKS is implemented with inflation and localization (referred to as ESIL) aiming at solving the underestimation of the background error matrix and the extension of observation information from the top soil to the bottom. EnKS applied in this study includes the states in different time points which tightly connect with adjacent ones. However, this kind of relationship gradually vanishes along with the increase of time interval. Thus, the localization is also employed to readjust temporal scale impact between states and filter out redundant or invalid correlation. Considering the parameter uncertainty which easily causes the systematic deviation of model states, two parallel filters are designed to recursively estimate both states and parameters. The study area consists of irrigated farmland and is located in an artificial oasis in the semi-arid region of northwestern China. Land surface temperature (LST) and soil volumetric water content (SVW) at first layer measured at Daman station are taken as observations in the framework of data assimilation. The study demonstrates the feasibility of ESIL in improving the soil moisture and temperature profile under unknown irrigation. ESIL promotes the coefficient correlation with in-situ measurements for soil moisture and temperature at first layer from 0.3421 and 0.7027 (ensemble simulation) to 0.8767 and 0.8304 meanwhile all the RMSE of soil moisture and temperature in deeper layers dramatically decrease more than 40 percent in different degree. To verify the reliability of ESIL in practical application, thereby promoting the utilization of satellite data, we test ESIL with varying observation internal interval and standard deviation. As a consequence, ESIL shows stabilized and promising effectiveness in soil moisture and soil temperature estimation.

Spread of Mycobacterium avium subsp. paratuberculosis through soil and grass on a mouflon (Ovis aries) pasture.

PubMed

Kaevska, Marija; Lvoncik, S; Lamka, J; Pavlik, I; Slana, I

2014-10-01

The aims of this study were to describe spatial contamination of the environment on a mouflon pasture, as well as to assess the contamination of grass and roots after surface contamination and in depth contamination with feces and buried tissues from animals infected with Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis). Samples of soil, roots, and aerial parts of plants were collected from different locations inside the mouflon pasture, and one control sample site was chosen outside the area where the animals are living. M. a. paratuberculosis DNA was present in all the examined sites and was more often detected in roots than in soil. DNA was detected at up to 80 cm of depth and was spatially more widespread than the initial hypothesis of M. a. paratuberculosis leaching vertically into deeper layers of soil. This study broadens our knowledge of the spread and persistence of M. a. paratuberculosis in an environment with highly infected animals.

Community structures and activity of denitrifying microbes in a forested catchment in central Japan: survey using nitrite reductase genes

NASA Astrophysics Data System (ADS)

Ohte, N.; Aoki, M.; Katsuyama, C.; Suwa, Y.; Tange, T.

2012-12-01

To elucidate the mechanisms of denitrification processes in the forested catchment, microbial ecological approaches have been applied in an experimental watershed that has previously investigated its hydrological processes. The study catchment is located in the Chiba prefecture in central Japan under the temperate Asian monsoon climate. Potential activities of denitrification of soil samples were measured by incubation experiments under anoxic condition associated with Na15NO3 addition. Existence and variety of microbes having nitrite reductase genes were investigated by PCR amplification, cloning and sequencings of nirK and nirS fragments after DNA extraction. Contrary to our early expectation that the potential denitrification activity was higher at deeper soil horizon with consistent groundwater residence than that in the surface soil, denitrification potential was higher in shallower soil horizons than deeper soils. This suggested that the deficiency of NO3- as a respiratory substrate for denitrifier occurred in deeper soils especially in the summer. However, high denitrification activity and presence of microbes having nirK and nirS in surface soils usually under aerobic condition was explainable by the fact that the majority of denitrifying bacteria have been recognized as a facultative anaerobic bacterium. This also suggests the possibility of that denitrification occurs even in the surface soils if the wet condition is provided by rainwater during and after a storm event. Community structures of microbes having nirK were different between near surface and deeper soil horizons, and ones having nirS was different between saturated zone (under groundwater table) and unsaturated soil horizons. These imply that microbial communities with nisK are sensitive to the concentration of soil organic matters and ones with nirS is sensitive to soil moisture contents.

Degradation and movement in soil of the herbicide isoproturon analyzed by a Photosystem II-based biosensor.

PubMed

Malý, J; Klem, K; Lukavská, A; Masojídek, J

2005-01-01

We have examined the persistence and movement of a urea-type herbicide, isoproturon [IPU; 3-(4-isopropylphenyl)-1,1'-dimethylurea], in soil using a novel herbicide-detection device, the prototype of a portable electrochemical biosensor based on Photosystem II particles immobilized on printed electrodes, and evaluated its results against two other methods: (i) chlorophyll-fluorescence bioassay based on polyphasic induction curves, and (ii) standard analysis represented by liquid chromatography. The data of the herbicide's content determined in soil extracts from field experiments correlated in all three methods. The biosensor assay was effective in determining the herbicide's concentration to as low as 10(-7) M. The results of our experiments also showed the kinetics of movement, degradation, and persistence of isoproturon in various depths of soil. After 6 to 9 wk, almost half of the isoproturon was still actively present in the upper soil layers (0-10 and 10-20 cm) and only 5 to 10% of biological activity was inhibited in the deeper soil layer tested (20-30 cm). Thus, inhibition within the limit of detection of both bioassays could be observed up to 9 wk after application in all profiles (0-30 cm), whereas inhibition persisted for up to 11 wk in the upper soil profile (0-10 cm). The use of the biosensor demonstrated its possibility for making rapid and cheap phytotoxicity tests. Our biosensor can give preliminary information about the biological activity of isoproturon in hours--much faster than growth biotests that may take several days or more.

Microbial community structure and diversity in the soil spatial profile of 5-year-old Robinia pseudoacacia 'Idaho,' determined by 454 sequencing of the 16S RNA gene.

PubMed

Chang, Yanping; Bu, Xiangpan; Niu, Weibo; Xiu, Yu; Wang, Huafang

2013-01-01

Relatively little information is available regarding the variability of microbial communities inhabiting deeper soil layers. We investigated the distribution of soil microbial communities down to 1.2 m in 5-year-old Robinia pseudoacacia 'Idaho' soil by 454 sequencing of the 16S RNA gene. The average number of sequences per sample was 12,802. The Shannon and Chao 1 indices revealed various relative microbial abundances and even distribution of microbial diversity for all evaluated sample depths. The predicted diversity in the topsoil exceeded that of the corresponding subsoil. The changes in the relative abundance of the major soil bacterial phyla showed decreasing, increasing, or no consistent trends with respect to sampling depth. Despite their novelty, members of the new candidate phyla OD1 and TM7 were widespread. Environmental variables affecting the bacterial community within the environment appeared to differ from those reported previously, especially the lack of detectable effect from pH. Overall, we found that the overall relative abundance fluctuated with the physical and chemical properties of the soil, root system, and sampling depth. Such information may facilitate forest soil management.

Coupling HYDRUS-1D Code with PA-DDS Algorithms for Inverse Calibration

NASA Astrophysics Data System (ADS)

Wang, Xiang; Asadzadeh, Masoud; Holländer, Hartmut

2017-04-01

Numerical modelling requires calibration to predict future stages. A standard method for calibration is inverse calibration where generally multi-objective optimization algorithms are used to find a solution, e.g. to find an optimal solution of the van Genuchten Mualem (VGM) parameters to predict water fluxes in the vadose zone. We coupled HYDRUS-1D with PA-DDS to add a new, robust function for inverse calibration to the model. The PA-DDS method is a recently developed multi-objective optimization algorithm, which combines Dynamically Dimensioned Search (DDS) and Pareto Archived Evolution Strategy (PAES). The results were compared to a standard method (Marquardt-Levenberg method) implemented in HYDRUS-1D. Calibration performance is evaluated using observed and simulated soil moisture at two soil layers in the Southern Abbotsford, British Columbia, Canada in the terms of the root mean squared error (RMSE) and the Nash-Sutcliffe Efficiency (NSE). Results showed low RMSE values of 0.014 and 0.017 and strong NSE values of 0.961 and 0.939. Compared to the results by the Marquardt-Levenberg method, we received better calibration results for deeper located soil sensors. However, VGM parameters were similar comparing with previous studies. Both methods are equally computational efficient. We claim that a direct implementation of PA-DDS into HYDRUS-1D should reduce the computation effort further. This, the PA-DDS method is efficient for calibrating recharge for complex vadose zone modelling with multiple soil layer and can be a potential tool for calibration of heat and solute transport. Future work should focus on the effectiveness of PA-DDS for calibrating more complex versions of the model with complex vadose zone settings, with more soil layers, and against measured heat and solute transport. Keywords: Recharge, Calibration, HYDRUS-1D, Multi-objective Optimization

Refine phosphorus stratification caused by long-term tillage and P fertilisation in maize -soybean rotation in eastern Canada

NASA Astrophysics Data System (ADS)

Ziadi, Noura; Morel, Christian

2017-04-01

The use of conservation tillage for crops production worldwide has increased markedly over recent years. Nutrient distributions under no-till (NT) compared with conventional moldboard tillage (CT) management in the cold, humid region of the eastern Canada need to be assessed for future placement, quantity, and type of fertilizers to efficiently match crop demands. We determined soil-profile distributions of soil total C (TC), total N (TN), and phosphate ions concentration (CP) in soil solution to a depth of 0.4 m after 23 years of continuous CT and NT management at different P fertilization rates on a clay loam soil in eastern Canada cropped with grain maize -soybean rotation. The experimental site was initiated in 1992 in southern Quebec, Canada. In August 2014, soil samples were collected at five profiles: 0 to 5, 5 to 10, 10 to 20, 20 to 30 and 30 to 40 cm under CT and NT fertilized at three P fertilizations (0 (P0), 17.5 (P0.5), and 35 (P1) kg P ha-1 applied as triple superphosphate on maize at 5 cm depth). To refine CNP stratification analysis for NT-P0 and NT-P1, supplemental soils of the 0-5 cm layer were sampled in P0 and P1 and then cutting into 5 layers of 1 cm. Different patterns for CP in relation to P fertilization under CT and NT were observed at the five profiles. The CP values did not differ significantly within ploughed layer but increased with P fertilization, e.g. 0.031, 0.066, and 0.075 mg P L-1 for P0, P0.5 and P1, respectively. Significant decline was observed in deeper depth beyond the plough. The Cp results in NT-P0 did not differ significantly to those of MP-P0. By contrast, highly significant P stratifications were observed in NT-P0.5 and NT-P1, especially marked in NT-P1 for which the CP value in 0-5 cm layer (0.35 mg P L-1) was 50 times greater than that in 30-40 cm layer (0.007 mg P L-1). To refine the C, N, and P stratifications, supplemental sampling was carried out in the 0-5 cm to cut this layer every 1 cm depth for P0 and P1. Most dramatic changes occurred within the 0-5 cm depth. The CP value in the first cm of soil (0.20 mg P L-1) was four times greater than that in the 4-5 cm layer (0.049 mg P L-1) of soil. The main reason for the large P accumulation in the first centimeter of soil is the annual return of plant residues to the soil surface. The stratification of TC and TN within the 0-5 cm layer showed similar trends irrespective of P fertilization. Under NT, the magnitude of CNP stratifications within the 0-1 cm layer to the 4-5 cm layer is equivalent to that observed in the 0-5 cm layer to the 30-40 cm layer.

Land-Use Conversion Changes the Multifractal Features of Particle-Size Distribution on the Loess Plateau of China

PubMed Central

Sun, Caili; Liu, Guobin; Xue, Sha

2016-01-01

Analyzing the dynamics of soil particle-size distributions (PSDs), soil nutrients, and erodibility are very important for understanding the changes of soil structure and quality after long-term land-use conversion. We applied multifractal Rényi spectra (Dq) and singularity spectra (f(α)) to characterize PSDs 35 years after conversions from cropland to shrubland with Caragana microphylla (shrubland I), shrubland with Hippophae rhamnoides (shrubland II), forested land, and grassland on the Loess Plateau of China. Multifractal parameters (capacity dimension (D0), entropy dimension (D1), D1/D0, correlation dimension (D2), and Hölder exponent of order zero (α0)) were used to analyze the changes of PSDs. Dq and f(α) characterized the PSDs well and sensitively represented the changes in PSDs after conversion. All types of land-use conversion significantly improved the properties of the topsoil (0–10 cm), but the effect of shrubland I and even forested land decreased with depth. All types of land-use conversion significantly increased D1 and D2 in the topsoil, and D1 and D2 in the 10–50 cm layers of shrubland II, forested land, and grassland and D1 in the 50–100 cm layers of shrubland II were significantly higher relative to the control. Both D1 and D2 were positively correlated with the contents of soil nutrients and fine particles and were negatively correlated with soil erosion, indicating that D1 and D2 were potential indices for quantifying changes in soil properties and erosion. In conclusion, all types of land-use conversion significantly improved the conditions of the topsoil, but conversion from cropland to shrubland II, forested land, and grassland, especially shrubland II and grassland, were more effective for improving soil conditions in deeper layers. PMID:27527201

Seasonal Dynamics of Water Use Strategy of Two Salix Shrubs in Alpine Sandy Land, Tibetan Plateau.

PubMed

Zhu, Yajuan; Wang, Guojie; Li, Renqiang

2016-01-01

Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ18O, and δ13C was used to determine main water source and long-term water use efficiency of Salix psammophila and S. cheilophila, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two Salix shrubs were investigated to determine their distribution pattern. The results showed that S. psammophila and S. cheilophila absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. Salix psammophila used ground water during the growing season and relied on shallow soil water recharged by rain in summer. Salix cheilophila used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in S. psammophila and longer fine roots in S. cheilophila facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two Salix shrubs increased during the dry season in spring. The long-term water use efficiency was higher in S. psammophila than in S. cheilophila, as the former species is better adapted to semiarid climate of alpine sandy land.

Seasonal Dynamics of Water Use Strategy of Two Salix Shrubs in Alpine Sandy Land, Tibetan Plateau

PubMed Central

Zhu, Yajuan; Wang, Guojie; Li, Renqiang

2016-01-01

Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ18O, and δ13C was used to determine main water source and long-term water use efficiency of Salix psammophila and S. cheilophila, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two Salix shrubs were investigated to determine their distribution pattern. The results showed that S. psammophila and S. cheilophila absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. Salix psammophila used ground water during the growing season and relied on shallow soil water recharged by rain in summer. Salix cheilophila used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in S. psammophila and longer fine roots in S. cheilophila facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two Salix shrubs increased during the dry season in spring. The long-term water use efficiency was higher in S. psammophila than in S. cheilophila, as the former species is better adapted to semiarid climate of alpine sandy land. PMID:27243772

Weathering behavior of REE-Y in a granitic soil profile (Case of Strengbach watershed)

NASA Astrophysics Data System (ADS)

Gangloff, Sophie; Stille, Peter; Chabaux, François

2017-04-01

Rare earth elements and yttrium (REE-Y) can be used as tracers of bedrock weathering and soil formation. One of the aims of this study is to better understand the different phenomena which impact the REE-Y mobilization and modify the REE-Y pattern along a soil profile. Our study has been performed on a granitic soil profile and soil solutions corresponding, sampled in a forest parcel covered with spruces from the Strengbach catchment. The behavior of the REE-Y pattern are compared with previously published results. The samples were collected from 2009 to 2013 and ultra-filtered to determine the spatial and temporal influence as well as that of the colloidal and dissolved fractions on the evolution of the REE-Y patterns. The EFTi of the soil indicates that during alteration process, phosphate minerals and zircon might be dissolved and induce the formation of secondary mineral phase like xenotime in the deeper soil horizons. The ultra-filtered soil solutions from humic horizon show that the REE-Y are principally enriched in the colloidal fraction controlling the REE-Y dynamic while in the deeper soil solutions colloidal and dissolved fractions influence the REE-Y. The mobility of REE-Y is controlled by the dissolution of the zircon and phosphate minerals, the precipitation of the REE-Y(PO4) and the evolution of OC with depth. The comparative study of the soil profile, soil water extracts and soil solutions show that (Eu*/Eu)DS anomaly reflects weathering of plagioclase in the micropores and the migration of the released Eu to the macropores, the (Ce*/Ce) anomaly, is stabilized by the electron shuttling of the humic acid (aromaticity) and provides information on the redox conditions only in the deeper soil horizons depleted in humic acid and finally the HREE enrichment in the deeper soil solutions results from the partial dissolution of secondary minerals in the upper soil horizons (above 30 cm depth).

Effect of soil disturbance on recharging fluxes: Case study on the Snake River Plain, Idaho National Laboratory, USA

USGS Publications Warehouse

Nimmo, J.R.; Perkins, K.S.

2008-01-01

Soil structural disturbance influences the downward flow of water that percolates deep enough to become aquifer recharge. Data from identical experiments in an undisturbed silt-loam soil and in an adjacent simulated waste trench composed of the same soil material, but disturbed, included (1) laboratory- and field-measured unsaturated hydraulic properties and (2) field-measured transient water content profiles through 24 h of ponded infiltration and 75 d of redistribution. In undisturbed soil, wetting fronts were highly diffuse above 2 m depth, and did not go much deeper than 2 m. Darcian analysis suggests an average recharge rate less than 2 mm/year. In disturbed soil, wetting fronts were sharp and initial infiltration slower; water moved slowly below 2 m without obvious impediment. Richards' equation simulations with realistic conditions predicted sharp wetting fronts, as observed for disturbed soil. Such simulations were adequate for undisturbed soil only if started from a post-initial moisture distribution that included about 3 h of infiltration. These late-started simulations remained good, however, through the 76 d of data. Overall results suggest the net effect of soil disturbance, although it reduces preferential flow, may be to increase recharge by disrupting layer contrasts. ?? Springer-Verlag 2007.

Effects of land preparation and artificial vegetation on soil moisture variation in a loess hilly catchment of China

NASA Astrophysics Data System (ADS)

Feng, Tianjiao; Wei, Wei; Chen, Liding; Yu, Yang

2017-04-01

In the dryland regions, soil moisture is the main factor to determine vegetation growth and ecosystem restoration. Land preparation and vegetation restoration are the principal means for improving soil water content(SWC). Thus, it is important to analyze the coupling role of these two means on soil moisture. In this study, soil moisture were monitored at a semi-arid loess hilly catchment of China, during the growing season of 2014 and 2015. Four different land preparation methods (level ditches, fish-scale pits, adverse grade tablelands and level benches)and vegetation types(Prunus armeniaca, Platycladus orientalis, Platycladus orientalis and Caragana microphylla) were included in the experimental design. Our results showed that: (1)Soil moisture content differed across land preparation types, which is higher for fish-scale pits and decreased in the order of level ditches and adverse grade tablelands.(2) Rainwater harvesting capacity of fish-scale pits is greater than adverse grade tablelands. However the water holding capacity is much higher at soils prepared with the adverse grade tablelands method than the ones prepared by fish-scale pits methods. (3) When land preparation method is similar, vegetation play a key role in soil moisture variation. For example, the mean soil moisture under a Platycladus orientalis field is 26.72% higher than a Pinus tabulaeformis field, with the same land preparation methods. (4)Soil moisture in deeper soil layers is more affected by changes in the vegetation cover while soil moisture in the shallower layers is more affected by the variation in the land preparation methods. Therefore, we suggest that vegetation types such as: Platycladus orientalisor as well as soil preparation methods such as level ditch and fish-scale pit are the most appropriate vegetation cover and land preparation methods for landscape restoration in semi-arid loess hilly area. This conclusion was made based on the vegetation type and land preparation with the best water-holding capacity.

Carbon turnover in topsoil and subsoil: The microbial response to root litter additions and different environmental conditions in a reciprocal soil translocation experiment

NASA Astrophysics Data System (ADS)

Preusser, Sebastian; Poll, Christian; Marhan, Sven; Kandeler, Ellen

2017-04-01

At the global scale, soil organic carbon (SOC) represents the largest active terrestrial organic carbon (OC) pool. Carbon dynamics in subsoil, however, vary from those in topsoil with much lower C concentrations in subsoil than in topsoil horizons, although more than 50 % of SOC is stored in subsoils below 30 cm soil depth. In addition, microorganisms in subsoil are less abundant, more heterogeneously distributed and the microbial communities have a lower diversity than those in topsoil. Especially in deeper soil, the impact of changes in habitat conditions on microorganisms involved in carbon cycling are largely unexplored and consequently the understanding of microbial functioning is limited. A reciprocal translocation experiment allowed us to investigate the complex interaction effects of altered environmental and substrate conditions on microbial decomposer communities in both topsoil and subsoil habitats under in situ conditions. We conducted this experiment with topsoil (5 cm soil depth) and subsoil (110 cm) samples of an acid and sandy Dystric Cambisol from a European beech (Fagus sylvatica L.) forest in Lower Saxony, Germany. In total 144 samples were buried into three depths (5 cm, 45 cm and 110 cm) and 13C-labelled root litter was added to expose the samples to different environmental conditions and to increase the substrate availability, respectively. Samples were taken in three month intervals up to a maximum exposure time of one year to follow the temporal development over the experimental period. Analyses included 13Cmic and 13C PLFA measurements to investigate the response of microbial abundance, community structure and 13C-root decomposition activity under the different treatments. Environmental conditions in the respective soil depths such as soil temperature and water content were recorded throughout the experimental period. All microbial groups (gram+ and gram- bacteria, fungi) showed highest relative 13C incorporation in 110 cm depth and samples with root addition had generally higher microbial abundances than those with no root addition. Here, especially fungi benefited from the additional carbon source with highly increased abundances in all incorporation depths. Also the altered environmental conditions in the different incorporation depths significantly influenced the different microbial groups. The steepest decrease with depth was detected in fungal abundance, while bacteria were less affected and increased in relative abundance in soil samples incorporated into subsoil layers. The highest seasonal variability in microbial abundance, however, was determined in 5 cm incorporation depth demonstrating the higher amplitude in micro-climatic and micro-environmental conditions in this near-surface soil habitat. In summary, this experiment demonstrated that carbon quality and quantity are the main factors restricting fungal abundance in deeper soil layers, while bacterial decomposer communities are adapted to a wider range of habitat conditions.

Compensatory Root Water Uptake of Overlapping Root Systems

NASA Astrophysics Data System (ADS)

Agee, E.; Ivanov, V. Y.; He, L.; Bisht, G.; Shahbaz, P.; Fatichi, S.; Gough, C. M.; Couvreur, V.; Matheny, A. M.; Bohrer, G.

2015-12-01

Land-surface models use simplified representations of root water uptake based on biomass distributions and empirical functions that constrain water uptake during unfavorable soil moisture conditions. These models fail to capture the observed hydraulic plasticity that allows plants to regulate root hydraulic conductivity and zones of active uptake based on local gradients. Recent developments in root water uptake modeling have sought to increase its mechanistic representation by bridging the gap between physically based microscopic models and computationally feasible macroscopic approaches. It remains to be demonstrated whether bulk parameterization of microscale characteristics (e.g., root system morphology and root conductivity) can improve process representation at the ecosystem scale. We employ the Couvreur method of microscopic uptake to yield macroscopic representation in a coupled soil-root model. Using a modified version of the PFLOTRAN model, which represents the 3-D physics of variably saturated soil, we model a one-hectare temperate forest stand under natural and synthetic climatic forcing. Our results show that as shallow soil layers dry, uptake at the tree and stand level shift to deeper soil layers, allowing the transpiration stream demanded by the atmosphere. We assess the potential capacity of the model to capture compensatory root water uptake. Further, the hydraulic plasticity of the root system is demonstrated by the quick response of uptake to rainfall pulses. These initial results indicate a promising direction for land surface models in which significant three-dimensional information from large root systems can be feasibly integrated into the forest scale simulations of root water uptake.

Modeling daily soil temperature over diverse climate conditions in Iran—a comparison of multiple linear regression and support vector regression techniques

NASA Astrophysics Data System (ADS)

Delbari, Masoomeh; Sharifazari, Salman; Mohammadi, Ehsan

2018-02-01

The knowledge of soil temperature at different depths is important for agricultural industry and for understanding climate change. The aim of this study is to evaluate the performance of a support vector regression (SVR)-based model in estimating daily soil temperature at 10, 30 and 100 cm depth at different climate conditions over Iran. The obtained results were compared to those obtained from a more classical multiple linear regression (MLR) model. The correlation sensitivity for the input combinations and periodicity effect were also investigated. Climatic data used as inputs to the models were minimum and maximum air temperature, solar radiation, relative humidity, dew point, and the atmospheric pressure (reduced to see level), collected from five synoptic stations Kerman, Ahvaz, Tabriz, Saghez, and Rasht located respectively in the hyper-arid, arid, semi-arid, Mediterranean, and hyper-humid climate conditions. According to the results, the performance of both MLR and SVR models was quite well at surface layer, i.e., 10-cm depth. However, SVR performed better than MLR in estimating soil temperature at deeper layers especially 100 cm depth. Moreover, both models performed better in humid climate condition than arid and hyper-arid areas. Further, adding a periodicity component into the modeling process considerably improved the models' performance especially in the case of SVR.

A 3-step framework for understanding the added value of surface soil moisture measurements for large-scale runoff prediction via data assimilation - a synthetic study in the Arkansas-Red River basin

NASA Astrophysics Data System (ADS)

Mao, Y.; Crow, W. T.; Nijssen, B.

2017-12-01

Soil moisture (SM) plays an important role in runoff generation both by partitioning infiltration and surface runoff during rainfall events and by controlling the rate of subsurface flow during inter-storm periods. Therefore, more accurate SM state estimation in hydrologic models is potentially beneficial for streamflow prediction. Various previous studies have explored the potential of assimilating SM data into hydrologic models for streamflow improvement. These studies have drawn inconsistent conclusions, ranging from significantly improved runoff via SM data assimilation (DA) to limited or degraded runoff. These studies commonly treat the whole assimilation procedure as a black box without separating the contribution of each step in the procedure, making it difficult to attribute the underlying causes of runoff improvement (or the lack thereof). In this study, we decompose the overall DA process into three steps by answering the following questions (3-step framework): 1) how much can assimilation of surface SM measurements improve surface SM state in a hydrologic model? 2) how much does surface SM improvement propagate to deeper layers? 3) How much does (surface and deeper-layer) SM improvement propagate into runoff improvement? A synthetic twin experiment is carried out in the Arkansas-Red River basin ( 600,000 km2) where a synthetic "truth" run, an open-loop run (without DA) and a DA run (where synthetic surface SM measurements are assimilated) are generated. All model runs are performed at 1/8 degree resolution and over a 10-year period using the Variable Infiltration Capacity (VIC) hydrologic model at a 3-hourly time step. For the DA run, the ensemble Kalman filter (EnKF) method is applied. The updated surface and deeper-layer SM states with DA are compared to the open-loop SM to quantitatively evaluate the first two steps in the framework. To quantify the third step, a set of perfect-state runs are generated where the "true" SM states are directly inserted in the model to assess the maximum possible runoff improvement that can be achieved by improving SM states alone. Our results show that the 3-step framework is able to effectively identify the potential as well as bottleneck of runoff improvement and point out the cases where runoff improvement via assimilation of surface SM is prone to failure.

Vertical nutrient and trace element migration in cambisoils after application of residues from anaerobic digestion of pig manure

NASA Astrophysics Data System (ADS)

Sager, Manfred; Unterfrauner, Hans

2013-04-01

Cambisols sampled in alpine pastures were packed into soil columns in order to monitor downward migration of nutrient and trace elements, applied within the residue from anaerobic digestion of a pig manure. 2 rain events per week were simulated. The manure added substantial amounts of K, ammonium, Na, Ca, P, S, Cl, B, Zn and Cu to the soil, whereas Mg, Mn, Ni, Cr, Pb, Cd and V were at the same level. In the eluates, total elemental composition as well as nitrate and ammonium were monitored. Addition of soluble Fe (at 1000 mg/l as FeCl3) decreased the release of soluble sulphate, but had no significant effect on the release of Fe and P. During subsequent rain events, exchangeable K remained enriched in the topsoil, wheras total sulfur moved to deeper layers. After 8 weeks, the columns were dismantled and analyzed for quasi-total and mobile fractions. Both in topsoils and subsoils, manure addition finally increased soil pH in case of low P soils, but decreased soil pH in case of high pH soils. Effects of manure applications on groundwater formation processes will be discussed.

Chinese Grain for Green Program led to highly increased soil organic carbon levels: A meta-analysis

PubMed Central

Song, Xinzhang; Peng, Changhui; Zhou, Guomo; Jiang, Hong; Wang, Weifeng

2014-01-01

The Grain for Green Program (GGP), initiated in 1999, is the largest ecological restoration project in central and western China. Here, for the first time, we performed a meta-analysis and found that the GGP largely increased the soil organic carbon (SOC). The SOC was increased by 48.1%, 25.4%, and 25.5% at soil depths of 0–20 cm, 20–40 cm, and 40–60 cm, respectively. Moreover, this carbon accumulation has significantly increased over time since GGP implementation. The carbon accumulation showed a significantly more active response to the GGP in the top 20 cm of soil than in the deeper soil layers. Conversion of cropland to forest could lead to significantly greater SOC accumulation than would the conversion of cropland to grassland. Conversion from cropland to woodland could lead to greater SOC accumulation than would the conversion to either shrubland or orchard. Our results suggest that the GGP implementation caused SOC to accumulate and that there remains a large potential for further accumulation of carbon in the soil, which will help to mitigate climate change in the near future. PMID:24675818

Seasonal Variability of Riverine Geochemistry (87Sr/86Sr, δ13CDIC, δ44/40Ca, and major ions) in Permafrost Watersheds on the North Slope of Alaska

NASA Astrophysics Data System (ADS)

Lehn, G. O.; Jacobson, A. D.; Douglas, T. A.; McClelland, J. W.; Khosh, M. S.; Barker, A. J.

2014-12-01

Global climate models predict amplified warming at high latitudes, where permafrost soils have historically acted as a carbon sink. As warming occurs, the seasonally thawed active layer will propagate downward into previously frozen mineral-rich soil, releasing carbon and introducing unique chemical weathering signatures into rivers. We use variations in the 87Sr/86Sr, δ13CDIC, δ44/40Ca, and major ion geochemistry of rivers to track seasonal active layer dynamics. We collected water from six streams on the North Slope of Alaska between May and October, 2009 and 2010. All rivers drain continuous permafrost but three drain tussock tundra-dominated watersheds and three drain steeper bedrock catchments with minor tundra coverage. In tundra streams, elevated 87Sr/86Sr ratios, low δ13CDIC values and major ions ([Na+]+[K+]/ [Ca+2]+[Mg+2]) in spring melt runoff suggest flushing of shallow soils with relatively low carbonate content. By July, 87Sr/86Sr ratios stabilize at relatively low values and δ13CDIC at relatively higher values, indicating the active layer thawed into deeper carbonate-rich soils. In bedrock streams, elevated 87Sr/86Sr ratios correlate with high discharge. By late fall, bedrock stream 87Sr/86Sr ratios decrease steadily, consistent with increased carbonate weathering. Nearly constant δ13CDIC values and high [SO4-2] for most of the melt season imply significant sulfuric acid-carbonate weathering in bedrock streams. δ13CDIC values suggest a shift to carbonic acid-carbonate weathering in late 2010, possibly due to limited oxygen for pyrite oxidation during freezing of the active layer. δ44/40Ca values in both tundra and bedrock streams increase during the seasons, suggesting increased uptake of 40Ca by plants. δ44/40Ca values of rivers are at least 0.1-0.2‰ higher than their watershed soils, rocks and sediments, suggesting significant plant uptake. Our findings show how seasonal changes in mineral weathering have potential for tracking active layer dynamics.

[Effects of rainfall intensity on rainfall infiltration and redistribution in soil on Loess slope land].

PubMed

Li, Yi; Shao, Ming'an

2006-12-01

With simulation test, this paper studied the patterns of rainfall infiltration and redistribution in soil on typical Loess slope land, and analyzed the quantitative relations between the infiltration and redistribution and the movement of soil water and mass, with rainfall intensity as the main affecting factor. The results showed that rainfall intensity had significant effects on the rainfall infiltration and water redistribution in soil, and the microcosmic movement of soil water. The larger the rainfall intensity, the deeper the wetting front of rainfall infiltration and redistribution was, and the wetting front of soil water redistribution had a slower increase velocity than that of rainfall infiltration. The power function of the wetting front with time, and also with rainfall intensity, was fitted well. There was also a quantitative relation between the wetting front of rainfall redistribution and the duration of rainfall. The larger the rainfall intensity, the higher the initial and steady infiltration rates were, and the cumulative infiltration increased faster with time. Moreover, the larger the rainfall intensity, the smaller the wetting front difference was at the top and the end of the slope. With the larger rainfall intensity, both the difference of soil water content and its descending trend between soil layers became more obvious during the redistribution process on slope land.

Constraining the 2012-2014 growing season Alaskan methane budget using CARVE aircraft measurements

NASA Astrophysics Data System (ADS)

Hartery, S.; Chang, R. Y. W.; Commane, R.; Lindaas, J.; Miller, S. M.; Wofsy, S. C.; Karion, A.; Sweeney, C.; Miller, C. E.; Dinardo, S. J.; Steiner, N.; McDonald, K. C.; Watts, J. D.; Zona, D.; Oechel, W. C.; Kimball, J. S.; Henderson, J.; Mountain, M. E.

2015-12-01

Soil in northen latitudes contains rich carbon stores which have been historically preserved via permafrost within the soil bed; however, recent surface warming in these regions is allowing deeper soil layers to thaw, influencing the net carbon exchange from these areas. Due to the extreme nature of its climate, these eco-regions remain poorly understood by most global models. In this study we analyze methane fluxes from Alaska using in situ aircraft observations from the 2012-2014 Carbon in Arctic Reservoir Vulnerability Experiment (CARVE). These observations are coupled with an atmospheric particle transport model which quantitatively links surface emissions to atmospheric observations to make regional methane emission estimates. The results of this study are two-fold. First, the inter-annual variability of the methane emissions was found to be <1 Tg over the area of interest and is largely influenced by the length of time the deep soil remains unfrozen. Second, the resulting methane flux estimates and mean soil parameters were used to develop an empirical emissions model to help spatially and temporally constrain the methane exchange at the Alaskan soil surface. The empirical emissions model will provide a basis for exploring the sensitivity of methane emissions to subsurface soil temperature, soil moisture, organic carbon content, and other parameters commonly used in process-based models.

Accumulation, availability, and uptake of heavy metals in a red soil after 22-year fertilization and cropping.

PubMed

Zhou, Shiwei; Liu, Jing; Xu, Minggang; Lv, Jialong; Sun, Nan

2015-10-01

Fertilization is important to increase crop yields, but long-term application of fertilizers probably aggravated the risk of heavy metals in acidic soils. In this study, the effect of 22-year fertilization and cropping on accumulation, availability, and uptake of heavy metals in red soil was investigated. The results showed that pig manure promoted significantly cadmium (Cd) accumulation (average 1.1 mg kg(-1)), nearly three times higher than national soil standards and, thus, increased metal availability. But the enrichment of heavy metals decreased remarkably by 50.5 % under manure fertilization, compared with CK (control without fertilization). On the contrary, chemical fertilizers increased greatly lead (Pb) availability and Cd activity; in particular, exceeding 85 % of soil Cd became available to plant under N (nitrogen) treatment during 9-16 years of fertilization, which correspondingly increased their enrichment by 29.5 %. Long-term application of chemical fertilizers caused soil acidification and manure fertilization led to the increase in soil pH, soil organic matter (SOM), and available phosphorus (Olsen P), which influenced strongly metal behavior in red soil, and their effect had extended to deeper soil layer (20∼40 cm). It is advisable to increase application of manure alone with low content of heavy metals or in combination with chemical fertilizers to acidic soils in order to reduce toxic metal risk.

Effects of disturbance and vegetation type on total and methylmercury in boreal peatland and forest soils.

PubMed

Braaten, Hans Fredrik Veiteberg; de Wit, Heleen A

2016-11-01

Mercury (Hg) concentrations in freshwater fish relates to aquatic Hg concentrations, which largely derives from soil stores of accumulated atmospheric deposition. Hg in catchment soils as a source for aquatic Hg is poorly studied. Here we test if i) peatland soils produce more methylmercury (MeHg) than forest soils; ii) total Hg (THg) concentrations in top soils are determined by atmospheric inputs, while MeHg is produced in the soils; and iii) soil disturbance promotes MeHg production. In two small boreal catchments, previously used in a paired-catchment forest harvest manipulation study, forest soils and peatlands were sampled and analysed for Hg species and additional soil chemistry. In the undisturbed reference catchment, soils were sampled in different vegetation types, of varying productivity as reflected in tree density, where historical data on precipitation and throughfall Hg and MeHg fluxes were available. Upper soil THg contents were significantly correlated to throughfall inputs of Hg, i.e. lowest in the tree-less peatland and highest in the dense spruce forest. For MeHg, top layer concentrations were similar in forest soils and peatlands, likely related to atmospheric input and local production, respectively. The local peatland MeHg production was documented through significantly higher MeHg-to-THg ratios in the deeper soil layer samples. In the disturbed catchment, soils were sampled in and just outside wheeltracks in an area impacted by forest machinery. Here, MeHg concentrations and the MeHg-to-THg ratios in the upper 5 cm were weakly significantly (p = 0.07) and significantly (p = 0.04) different in and outside of the wheeltracks, respectively, suggesting that soil disturbance promotes methylation. Differences in catchment Hg and MeHg streamwater concentrations were not explained by soil Hg and MeHg information, perhaps because hydrological pathways are a stronger determinant of streamwater chemistry than small variations in soil chemistry driven by disturbance and atmospheric inputs of Hg. Copyright © 2016 Elsevier Ltd. All rights reserved.

Soil organic matter mineralization of permafrost peat lands and sensitivity to temperature and lack of oxygen

NASA Astrophysics Data System (ADS)

Lamprecht, Richard E.; Diáková, Kateřina; Voigt, Carolina; Šantrůčková, Hana; Martikainen, Pertti; Biasi, Christina

2017-04-01

Globally, a significant pool of soil organic carbon (SOC) (Tarnocai et al. 2009) is stored in arctic peatlands where extensive permafrost prevents the decomposition of old soil organic matter (SOM). Vulnerability of ancient organic depositions in changing environment becomes a considerable issue in future climate models. Palsa mires, a typical cryogenic peatland type in subarctic tundra, are not only an important SOC pool but also have been reported as a source of nitrous oxide (N2O) (Marushchak et al. 2011). Microbial SOM mineralization and its sensitivity to changing environmental conditions are crucial to understand future C losses and greenhouse gas (GHG) fluxes in this abundant landform of subarctic region. The purpose of this experiment was to determine potential SOM mineralization in different layers of deep soil cores from an Arctic peatland. First, we aimed to define a response of C losses and GHG exchange rates to temperature and aerobic/anaerobic conditions in different peat layers down to the permafrost and beyond. Secondly, we sought for relations among SOM mineralization, nutrient availability and parameters of indigenous microbial community. Finally, we attempted to link the potential SOM mineralization of the different peat layers with surface GHG fluxes from a proceeding study conducted with the same, intact soil cores. Five deep peat soil cores were separated into five layers (0 20, 20 40, 40 60 cm, permafrost interface and permafrost layer). Homogenized peat was incubated in a factorial set-up of three temperatures (4, 10, and 16 °C) under aerobic and anaerobic conditions. At the beginning and the end of the total 5.5-months incubation period, we determined C and N availability, microbial biomass and potential activities of extracellular enzymes. Heterotrophic respiration (CO2), methane (CH4) and nitrous oxide (N2O) emissions were monitored weekly at the initial phase and biweekly later during the incubation. First results show that C-loss from aerobic decomposition dominated over C-loss from anaerobic decomposition with clear temperature sensitivities in different peat layers. Moreover, the peat layers showed definite patterns especially to N2O losses, less for CO2 losses. This study addresses the essential question to which extent deeper soil horizons of subarctic organic depositions contribute to the total soil GHG fluxes, and whether the nutrient availability, microbial community and environmental factors (i.e. temperature, O2 availability) constrain the SOM mineralization. REFERENCES Marushchak ME, Pitkämäki A, Koponen H, Biasi C, Seppälä M, Martikainen PJ (2011) Hot spots for nitrous oxide emissions found in different types of permafrost peatlands. Global Change Biol 17:2601-2614 Tarnocai C, Canadell JG, Schuur EAG, Kuhry P, Mazhitova G, Zimov S (2009) Soil organic carbon pools in the northern circumpolar permafrost region. Global Biogeochem Cycles 23

Deep rooting conferred by DEEPER ROOTING 1 enhances rice yield in paddy fields.

PubMed

Arai-Sanoh, Yumiko; Takai, Toshiyuki; Yoshinaga, Satoshi; Nakano, Hiroshi; Kojima, Mikiko; Sakakibara, Hitoshi; Kondo, Motohiko; Uga, Yusaku

2014-07-03

To clarify the effect of deep rooting on grain yield in rice (Oryza sativa L.) in an irrigated paddy field with or without fertilizer, we used the shallow-rooting IR64 and the deep-rooting Dro1-NIL (a near-isogenic line homozygous for the Kinandang Patong allele of DEEPER ROOTING 1 (DRO1) in the IR64 genetic background). Although total root length was similar in both lines, more roots were distributed within the lower soil layer of the paddy field in Dro1-NIL than in IR64, irrespective of fertilizer treatment. At maturity, Dro1-NIL showed approximately 10% higher grain yield than IR64, irrespective of fertilizer treatment. Higher grain yield of Dro1-NIL was mainly due to the increased 1000-kernel weight and increased percentage of ripened grains, which resulted in a higher harvest index. After heading, the uptake of nitrogen from soil and leaf nitrogen concentration were higher in Dro1-NIL than in IR64. At the mid-grain-filling stage, Dro1-NIL maintained higher cytokinin fluxes from roots to shoots than IR64. These results suggest that deep rooting by DRO1 enhances nitrogen uptake and cytokinin fluxes at late stages, resulting in better grain filling in Dro1-NIL in a paddy field in this study.

Magnetic properties of alluvial soils contaminated with lead, zinc and cadmium

NASA Astrophysics Data System (ADS)

Petrovský, E.; Kapička, A.; Jordanova, N.; Borůvka, L.

2001-09-01

Several proxy methods have been used recently to outline increased levels of pollution. One of them is based on measurements of the concentration of (ferri)magnetic minerals of anthropogenic origin. This method has been used recently in the mapping of both polluted and unpolluted areas. In order to validate this method, a more detailed study of links between magnetic parameters characterising the physical shape of magnetic minerals and concentrations of heavy metals is needed. In this study, we analysed the magnetic characteristics of alluvial soils, formed as a result of several breakdowns of wet deposit sink of ashes from a lead ore smelter. The soils were previously analysed for concentration of lead, zinc and cadmium. Our results show that in this case of a shared source of heavy metals and magnetic minerals, simple measurements of magnetic susceptibility discriminate well between polluted and clean areas. In addition, the concentration pattern agrees with the concentrations of the heavy metals studied in deeper soil layers that were not affected by post-depositional changes due to climate and remediation efforts.

SMAP Data Assimilation at the GMAO

NASA Technical Reports Server (NTRS)

Reichle, R.; De Lannoy, G.; Liu, Q.; Ardizzone, J.

2016-01-01

The NASA Soil Moisture Active Passive (SMAP) mission has been providing L-band (1.4 GHz) passive microwave brightness temperature (Tb) observations since April 2015. These observations are sensitive to surface(0-5 cm) soil moisture. Several of the key applications targeted by SMAP, however, require knowledge of deeper-layer, root zone (0-100 cm) soil moisture, which is not directly measured by SMAP. The NASA Global Modeling and Assimilation Office (GMAO) contributes to SMAP by providing Level 4 data, including the Level 4 Surface and Root Zone Soil Moisture(L4_SM) product, which is based on the assimilation of SMAP Tb observations in the ensemble-based NASA GEOS-5 land surface data assimilation system. The L4_SM product offers global data every three hours at 9 km resolution, thereby interpolating and extrapolating the coarser- scale (40 km) SMAP observations in time and in space (both horizontally and vertically). Since October 31, 2015, beta-version L4_SM data have been available to the public from the National Snow and Ice Data Center for the period March 31, 2015, to near present, with a mean latency of approx. 2.5 days.

90Sr and 137Cs in environmental samples from Dolon near the Semipalatinsk Nuclear Test Site.

PubMed

Gastberger, M; Steinhäusler, F; Gerzabek, M H; Hubmer, A; Lettner, H

2000-09-01

The (90)Sr and (137)Cs activities of soil, plant, and milk samples from the village of Dolon, located close to the Semipalatinsk Nuclear Test Site in Kazakhstan, were determined. The areal deposition at the nine sampling sites is in the range of <500 to 6,100 Bq m(-2) and 300 to 7,900 Bq m-2 for (90)Sr and (137)Cs, respectively. Similar values have been reported in the literature. At some of the sites both nuclides mainly have remained in the top 6 cm of the soil profiles; at others they were partly transported into deeper soil layers since the deposition. For most of the samples the (90)Sr yield after destruction of the soil matrix is significantly higher than after extracting with 6 M HCl indicating that (90)Sr is partly associated with fused silicates. The low mean (90)Sr activity concentrations of vegetation samples (14 Bq kg(-1) dw) and milk samples (0.05 Bq kg(-1) fw) suggest that this has favorable consequences in terms of limiting its bioavailability.

[Soil moisture estimation method based on both ground-based remote sensing data and air temperature in a summer maize ecosystem.

PubMed

Wang, Min Zheng; Zhou, Guang Sheng

2016-06-01

Soil moisture is an important component of the soil-vegetation-atmosphere continuum (SPAC). It is a key factor to determine the water status of terrestrial ecosystems, and is also the main source of water supply for crops. In order to estimate soil moisture at different soil depths at a station scale, based on the energy balance equation and the water deficit index (WDI), a soil moisture estimation model was established in terms of the remote sensing data (the normalized difference vegetation index and surface temperature) and air temperature. The soil moisture estimation model was validated based on the data from the drought process experiment of summer maize (Zea mays) responding to different irrigation treatments carried out during 2014 at Gucheng eco-agrometeorological experimental station of China Meteorological Administration. The results indicated that the soil moisture estimation model developed in this paper was able to evaluate soil relative humidity at different soil depths in the summer maize field, and the hypothesis was reasonable that evapotranspiration deficit ratio (i.e., WDI) linearly depended on soil relative humidity. It showed that the estimation accuracy of 0-10 cm surface soil moisture was the highest (R 2 =0.90). The RMAEs of the estimated and measured soil relative humidity in deeper soil layers (up to 50 cm) were less than 15% and the RMSEs were less than 20%. The research could provide reference for drought monitoring and irrigation management.

Vertical Distribution of Soil Denitrifying Communities in a Wet Sclerophyll Forest under Long-Term Repeated Burning.

PubMed

Liu, Xian; Chen, Chengrong; Wang, Weijin; Hughes, Jane M; Lewis, Tom; Hou, Enqing; Shen, Jupei

2015-11-01

Soil biogeochemical cycles are largely mediated by microorganisms, while fire significantly modifies biogeochemical cycles mainly via altering microbial community and substrate availability. Majority of studies on fire effects have focused on the surface soil; therefore, our understanding of the vertical distribution of microbial communities and the impacts of fire on nitrogen (N) dynamics in the soil profile is limited. Here, we examined the changes of soil denitrification capacity (DNC) and denitrifying communities with depth under different burning regimes, and their interaction with environmental gradients along the soil profile. Results showed that soil depth had a more pronounced impact than the burning treatment on the bacterial community size. The abundance of 16S rRNA and denitrification genes (narG, nirK, and nirS) declined exponentially with soil depth. Surprisingly, the nosZ-harboring denitrifiers were enriched in the deeper soil layers, which was likely to indicate that the nosZ-harboring denitrifiers could better adapt to the stress conditions (i.e., oxygen deficiency, nutrient limitation, etc.) than other denitrifiers. Soil nutrients, including dissolved organic carbon (DOC), total soluble N (TSN), ammonium (NH(4)(+)), and nitrate (NO(3)(-)), declined significantly with soil depth, which probably contributed to the vertical distribution of denitrifying communities. Soil DNC decreased significantly with soil depth, which was negligible in the depths below 20 cm. These findings have provided new insights into niche separation of the N-cycling functional guilds along the soil profile, under a varied fire disturbance regime.

[Simulation of CO2 exchange between forest canopy and atmosphere].

PubMed

Diao, Yiwei; Wang, Anzhi; Jin, Changjie; Guan, Dexin; Pei, Tiefan

2006-12-01

Estimating the scalar source/sink distribution of CO2 and its vertical fluxes within and above forest canopy continues to be a critical research problem in biosphere-atmosphere exchange processes and plant ecology. With broad-leaved Korean pine forest in Changbai Mountains as test object, and based on Raupach's localized near field theory, the source/sink and vertical flux distribution of CO2 within and above forest canopy were modeled through an inverse Lagrangian dispersion analysis. This model correctly predicted a strong positive CO2 source strength in the deeper layers of the canopy due to soil-plant respiration, and a strong CO2 sink in the upper layers of the canopy due to the assimilation by sunlit foliage. The foliage in the top layer of canopy changed from a CO2 source in the morning to a CO2 sink in the afternoon, while the soil constituted a strong CO2 source all the day. The simulation results accorded well with the eddy covariance CO2 flux measurements within and above the canopy, and the average precision was 89%. The CO2 exchange predicted by the analysis was averagely 15% higher than that of the eddy correlation, but exhibited identical temporal trend. Atmospheric stability remarkably affected the CO2 exchange between forest canopy and atmosphere.

Effects of agricultural practices and vadose zone stratigraphy on nitrate concentration in ground water in Kansas, USA

USGS Publications Warehouse

Townsend, M.A.; Sleezer, R.O.; Macko, S.A.; ,

1996-01-01

Differences in nitrate-N concentrations in,around water in Kansas can be explained by variations in agricultural practices and vadose-zone stratigraphy. In northwestern Kansas, past use of a local stream for tailwater runoff from irrigation and high fertilizer applications for sugar-beet farming resulted in high nitrate-N concentrations (12-60 mg L-1; in both soil and ground water. Nitrogen isotope values from the soil and ground water range from +4 to +8? which is typical for a fertilizer source. In parts of south-central Kansas, the use of crop rotation and the presence of both continuous fine-textured layers and a reducing ground-water chemistry resulted in ground-water nitrate-N values of 10 mg L-1; in both soil and grounwater. Nitrogen isotope values of +3 to +7? indicate a fertilizer source. Crop rotation decreased nitrate-N values in the shallow ground water (9 m). However, deeper ground water showed increasing nitrate-N concentrations as a result of past farming practices.

Uncertainty in Arctic hydrology projections and the permafrost-carbon feedback

NASA Astrophysics Data System (ADS)

Andresen, C. G.; Lawrence, D. M.; Wilson, C. J.; McGuire, D.

2017-12-01

Projected warming is expected to thaw permafrost soils and deepen the permafrost active layer. These changes will affect surface hydrological conditions. Since the soil hydrologic state exerts a strong influence on the rate and pathway of soil organic matter decomposition into CO2 or CH4, there is a strong need to examine and better understand model projections of hydrologic change and how differences in process representation affect projections of wetting and/or drying of changing permafrost landscapes. This study aims to advance understanding of where, when and why arctic will become wetter or drier. We assessed simulations from 8 "permafrost enabled" land models that were run in offline mode from 1960 to 2299 forced with the same projected climate for a high-emissions scenario. Climate models project increased precipitation (P) across most of the Arctic domain and the land models indicate that runoff and evapotranspiration (ET) will also both increase. In general, the water input to the soil (P-ET) also increases, but the models project a contradicting long-term drying of the surface soil. The surface drying in the models can generally be explained by filtration of moisture to deeper soil layers as the active layer deepens or by increased sub-surface drainage where permafrost in a grid cell thaws completely. Though, there is a qualitative agreement in this type of response across the models, the projections vary dramatically in magnitude. Variability among simulations is largely attributed to parameterization and structural differences across the participating models, particularly the diverse representations of evapotranspiration, water table and soil water storage and transmission. A limited set of results from single forcing experiments suggests that the warming effect in the sensitivity analysis was the principal driver of soil drying while CO2 and precipitation effects had a small wetting influence. When compared to observational data, simulations tend to underestimate discharge by a factor of 2 for the major arctic river basins. This analysis serves as a baseline to identify key process representation gaps and opportunities to improve representation of permafrost hydrology and associated projections of carbon and energy feedbacks in land models.

The Role of Disturbance in Arctic Ecosystem Response to a Changing Climate

NASA Astrophysics Data System (ADS)

Hinzman, L. D.

2014-12-01

Wildfires in the tundra regions and the boreal forest project an immediate effect upon the surface energy and water budget by drastically altering the surface albedo, roughness, infiltration rates, and moisture absorption capacity in organic soils. Although fires create a sudden and drastic change to the landcover, it is only the beginning of a long process of recovery and perhaps a shift to a different successional pathway. In permafrost regions, these effects become part of a process of long-term (20-50 years) cumulative impacts. Burn severity may largely determine immediate impacts and long-term disturbance trajectories. As transpiration decreases or ceases, soil moisture increases markedly, remaining quite wet throughout the year. Because the insulating quality of the organic layer is removed during fires, permafrost begins to thaw near the surface and warm to greater depths. Within a few years, it may thaw to the point where it can no longer completely refreeze every winter, creating a permanently thawed layer in the soil called a talik. After formation of a talik, soils can drain internally throughout the year. At this point, soils may become quite dry, as the total precipitation received annually in the Arctic is quite low. The local ecological community must continuously adapt to the changing soil thermal and moisture regimes. The wet soils found over shallow permafrost favor black spruce forests. After a fire creates a deeper permafrost table (thicker active layer) the invading tree species tend to be birch or alder. The hydrologic and thermal regime of the soil is the primary factor controlling these vegetation trajectories and the subsequent changes in surface mass and energy fluxes. The complexities of a changing climate accentuate these processes of change and complicate predictions of the resulting vegetation trajectories. Understanding these shifts in vegetative communities and quantifying the consequences of thawing permafrost can only be accomplished through complementary analyses of field research data and numerical simulations. The permafrost dramatically controls other landscape features and its dynamic response to thermal influences yield consequent effects on the surficial ecology, water and energy balances and regional climate.

Hydro-thermal processes and thermal offsets of peat soils in the active layer in an alpine permafrost region, NE Qinghai-Tibet plateau

NASA Astrophysics Data System (ADS)

Wang, Qingfeng; Jin, Huijun; Zhang, Tingjun; Cao, Bin; Peng, Xiaoqing; Wang, Kang; Xiao, Xiongxin; Guo, Hong; Mu, Cuicui; Li, Lili

2017-09-01

Observation data of the hydrothermal processes in the active layer are vital for the verification of permafrost formation and evolution, eco-hydrology, ground-atmosphere interactions, and climate models at various time and spatial scales. Based on measurements of ground temperatures in boreholes, of temperatures and moisture contents of soils in the active layer, and of the mean annual air temperatures at the Qilian, Yeniugou and Tuole meteorological stations in the upper Heihe River Basin (UHRB) and the adjacent areas, a series of observations were made concerning changes in the lower limit of permafrost (LLP) and the related hydrothermal dynamics of soils in the active layer. Because of the thermal diode effect of peat soils, the LLP (at 3600 m) was lower on the northern slope of the Eboling Mountains at the eastern branch of the UHRB than that (at 3650-3700 m) on the alluvial plain at the western branch of the UHRB. The mean temperature of soils at depths of 5 to 77 cm in the active layer on peatlands was higher during periods with subzero temperatures and lower during periods with above-zero temperatures in the vicinity of the LLP on the northern slope of the Eboling Mountains than those at the LLP at the western branch of the UHRB. The thawing and downward freezing rates of soils in the active layer near the LLP on the northern slope of the Eboling Mountains were 0.2 and 1.6 times those found at the LLP at the western branch of the UHRB. From early May to late August, the soil water contents at the depths of 20 to 60 cm in the active layer near the LLP on the northern slope of the Eboling Mountains were significantly lower than those found at the LLP at the western branch of the UHRB. The annual ranges of soil temperatures (ARSTs), mean annual soil temperatures (MASTs) in the active layer on peatlands, and the mean annual ground temperature (MAGT) at a depth of 14 m of the underlying permafrost were all significantly lower near the LLP on the northern slope of the Eboling Mountains. Moreover, the thermophysical properties of peat soils and high moisture contents in the active layer on peatlands resulted in the lower soil temperatures in the active layer close to the LLP on the northern slope of the Eboling Mountains than those found at the LLP at the western branch of the UHRB in the warm season, especially at the deeper depths (20-77 cm). They also resulted in the smaller freezing index (FI) and thawing index (TI) and larger FI/TI ratios of soils at the depths of 5 to 77 cm in the active layer near the LLP on the northern slope of the Eboling Mountains. In short, peatlands have unique thermophysical properties for reducing heat absorption in the warm season and for limiting heat release in the cold season as well. However, the permafrost zone has shrunk by 10-20 km along the major highways at the western branch of the UHRB since 1985, and a medium-scale retrogressive slump has occurred on the peatlands on the northern slope of the Eboling Mountains in recent decades. The results can provide basic data for further studies of the hydrological functions of different landscapes in alpine permafrost regions. Such studies can also enable evaluations and forecasts the hydrological impacts of changing frozen ground in the UHRB and of other alpine mountain regions in West China.

Water withdrawal in deep soil layers: a key strategy to cope with drought in tropical eucalypt plantations

NASA Astrophysics Data System (ADS)

Christina, M.; Laclau, J.; Nouvellon, Y.; Duursma, R. A.; Stape, J. L.; Lambais, G. R.; Le Maire, G.

2013-12-01

Little is known about the role of very deep roots to supply the water requirements of tropical forests. Clonal Eucalyptus plantations managed in short rotation on very deep Ferralsols are simple forest ecosystems (only 1 plant genotype growing on a relatively homogeneous soil) likely to provide an insight into tree water use strategies in tropical forests. Fine roots have been observed down to a depth of 6 m at age 1 year in Brazilian eucalypt plantations. However, the contribution of water stored in very deep soil layers to stand evapotranspiration over tree growth has been poorly quantified. An eco-physiological model, MAESPA, has been used to simulate half-hourly stand water balance over the first three years of growth in a clonal Eucalyptus grandis plantation in southern Brazil (Eucflux project, State of São Paulo). The water balance model in MAESPA is an equilibrium-type model between soil and leaf water potentials for individual trees aboveground, and at the stand scale belowground. The dynamics of the vertical fine root distribution have been taken into account empirically from linear interpolations between successive measurements. The simulations were compared to time series of soil water contents measured every meter down to 10m deep and to daily latent heat fluxes measured by eddy covariance. Simulations of volumetric soil water contents matched satisfactorily with measurements (RMSE = 0.01) over the three-year period. Good agreement was also observed between simulated and measured latent heat fluxes. In the rainy season, more than 75 % of tree transpiration was supplied by water withdrawn in the upper 1 m of soil, but water uptake progressed to deeper soil layers during dry periods, down to a depth of 6 m, 12 m and 15 m the first, second and third year after planting, respectively. During the second growing season, 15% of water was withdrawn below a depth of 6 m, and 5% below 10m. Most of the soil down to 12m deep was dried out the second year after planting and deep drainage was negligible after 2 years. As a consequence, during the third year after planting only 4% of water was taken up below 6m. However, during the dry season, this deep water still supplied 50% of water requirements. Our results show that deep fine roots of E. grandis play a major role in supplying tree water requirements during extended dry periods. Large amounts of water are stored in the whole soil profile after clear cutting and the fast exploration of deep soil layers by roots make it available for tree growth. After canopy closure, precipitation becomes the key limitation for the productivity of these plantations grown in deep sandy soils. Our results suggest that a territorial strategy leading to a fast exploration of very deep soil layers might provide a strong competitive advantage in regions prone to drought.

Soil carbon sequestration by three perennial legume pastures is greater in deeper soil layers than in the surface soil

NASA Astrophysics Data System (ADS)

Guan, X.-K.; Turner, N. C.; Song, L.; Gu, Y.-J.; Wang, T.-C.; Li, F.-M.

2016-01-01

Soil organic carbon (SOC) plays a vital role as both a sink for and source of atmospheric carbon. Revegetation of degraded arable land in China is expected to increase soil carbon sequestration, but the role of perennial legumes on soil carbon stocks in semiarid areas has not been quantified. In this study, we assessed the effect of alfalfa (Medicago sativa L.) and two locally adapted forage legumes, bush clover (Lespedeza davurica S.) and milk vetch (Astragalus adsurgens Pall.) on the SOC concentration and SOC stock accumulated annually over a 2 m soil profile. The results showed that the concentration of SOC in the bare soil decreased slightly over the 7 years, while 7 years of legume growth substantially increased the concentration of SOC over the 0-2.0 m soil depth. Over the 7-year growth period the SOC stocks increased by 24.1, 19.9 and 14.6 Mg C ha-1 under the alfalfa, bush clover and milk vetch stands, respectively, and decreased by 4.2 Mg C ha-1 in the bare soil. The sequestration of SOC in the 1-2 m depth of the soil accounted for 79, 68 and 74 % of the SOC sequestered in the 2 m deep soil profile under alfalfa, bush clover and milk vetch, respectively. Conversion of arable land to perennial legume pasture resulted in a significant increase in SOC, particularly at soil depths below 1 m.

Physically-based failure analysis of shallow layered soil deposits over large areas

NASA Astrophysics Data System (ADS)

Cuomo, Sabatino; Castorino, Giuseppe Claudio; Iervolino, Aniello

2014-05-01

In the last decades, the analysis of slope stability conditions over large areas has become popular among scientists and practitioners (Cascini et al., 2011; Cuomo and Della Sala, 2013). This is due to the availability of new computational tools (Baum et al., 2002; Godt et al., 2008; Baum and Godt, 2012; Salciarini et al., 2012) - implemented in GIS (Geographic Information System) platforms - which allow taking into account the major hydraulic and mechanical issues related to slope failure, even for unsaturated soils, as well as the spatial variability of both topography and soil properties. However, the effectiveness (Sorbino et al., 2010) of the above methods it is still controversial for landslides forecasting especially depending on the accuracy of DTM (Digital Terrain Model) and for the chance that distinct triggering mechanisms may occur over large area. Among the major uncertainties, layering of soil deposits is of primary importance due to soil layer conductivity contrast and differences in shear strength. This work deals with the hazard analysis of shallow landslides over large areas, considering two distinct schematizations of soil stratigraphy, i.e. homogeneous or layered. To this purpose, the physically-based model TRIGRS (Baum et al., 2002) is firstly used, then extended to the case of layered deposit: specifically, a unique set of hydraulic properties is assumed while distinct soil unit weight and shear strength are considered for each soil layer. Both models are applied to a significant study area of Southern Italy, about 4 km2 large, where shallow deposits of air-fall volcanic (pyroclastic) soils have been affected by several landslides, causing victims, damages and economic losses. The achieved results highlight that soil volume globally mobilized over the study area highly depends on local stratigraphy of shallow deposits. This relates to the depth of critical slip surface which rarely corresponds to the bedrock contact where cohesionless coarse materials lie on deeper soil layers with small effective cohesion. It is also shown that, due to a more realistic assessment of soil stratigraphy, the success of the model may increase when performing a back-analysis of a recent real event. References Baum, R. L., W. Z. Savage, and J. W. Godt (2002), TRIGRS-A Fortran program for transient rainfall infiltration and grid-based regional slope-stability analysis. U.S. Geological Survey, Open-file report 02-424, 35 p. Baum, R.L., Godt, J.W. (2012) Assessment of shallow landslide potential using 1-D and 3-D slope stability analysis Landslides and Engineered Slopes: Protecting Society through Improved Understanding - Eberhardt et al. (eds) 2012 Taylor & Francis Group, London, ISBN 978-0-415-62123-6, 1667-1672. Cascini L., Cuomo S., Della Sala M. (2011). Spatial and temporal occurrence of rainfall-induced shallow landslides of flow type: A case of Sarno-Quindici, Italy. Geomorphology, 126(1-2), 148-158. Cuomo S., Della Sala M. (2013). Spatially distributed analysis of shallow landslides and soil erosion induced by rainfall. (submitted to Natural Hazards). Godt, J.W., Baum, R.L., Savage, W.Z., Salciarini, D., Schulz, W.H., Harp, E.L. (2008). Transient deterministic shallow landslide modeling: requirements for susceptibility and hazard assessments in a GIS framework. Engineering Geology 102, 214-226. Salciarini, D., Tamagnini, C., Conversini, P., Rapinesi, S. (2012). Spatially distributed rainfall thresholds for the initiation of shallow landslides. Natural Hazards 61, 229-245. Sorbino G., Sica C., Cascini L. (2010). Susceptibility analysis of shallow landslides source areas using physically based models. Natural Hazards, 53(2), 313-332.

Storage and Bioavailability of Molybdenum in Soils Increased by Organic Matter Complexation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wichard, T.; Mishra, B; Myneni, S

2009-01-01

The micronutrient molybdenum is a necessary component of the nitrogen-fixing enzyme nitrogenase1, 2. Molybdenum is very rare in soils, and is usually present in a highly soluble form, making it susceptible to leaching3, 4. However, it is generally thought that molybdenum attaches to mineral surfaces in acidic soils; this would prevent its escape into the groundwater, but would also impede uptake by microbes3. Here we use X-ray spectroscopy to examine the chemical speciation of molybdenum in soil samples from forests in Arizona and New Jersey. We show that in the leaf litter layer, most of the molybdenum forms strong complexesmore » with plant-derived tannins and tannin-like compounds; molybdenum binds to these organic ligands across a wide pH range. In deeper soils, molybdenum binds to both iron oxides and natural organic matter. We suggest that the molybdenum bound to organic matter can be captured by small complexing agents that are released by nitrogen-fixing bacteria; the molybdenum can then be incorporated into nitrogenase. We conclude that the binding of molybdenum to natural organic matter helps prevent leaching of molybdenum, and is thus a critical step in securing new nitrogen in terrestrial ecosystems.« less

Role of Subsurface Physics in the Assimilation of Surface Soil Moisture Observations

NASA Technical Reports Server (NTRS)

Reichle, R. H.

2010-01-01

Root zone soil moisture controls the land-atmosphere exchange of water and energy and exhibits memory that may be useful for climate prediction at monthly scales. Assimilation of satellite-based surface soil moisture observations into a land surface model is an effective way to estimate large-scale root zone soil moisture. The propagation of surface information into deeper soil layers depends on the model-specific representation of subsurface physics that is used in the assimilation system. In a suite of experiments we assimilate synthetic surface soil moisture observations into four different models (Catchment, Mosaic, Noah and CLM) using the Ensemble Kalman Filter. We demonstrate that identical twin experiments significantly overestimate the information that can be obtained from the assimilation of surface soil moisture observations. The second key result indicates that the potential of surface soil moisture assimilation to improve root zone information is higher when the surface to root zone coupling is stronger. Our experiments also suggest that (faced with unknown true subsurface physics) overestimating surface to root zone coupling in the assimilation system provides more robust skill improvements in the root zone compared with underestimating the coupling. When CLM is excluded from the analysis, the skill improvements from using models with different vertical coupling strengths are comparable for different subsurface truths. Finally, the skill improvements through assimilation were found to be sensitive to the regional climate and soil types.

[Effects of tillage practices on root spatial distribution and yield of spring wheat and pea in the dry land farming areas of central Gansu, China].

PubMed

Zhang, Ming Jun; Li, Ling Ling; Xie, Jun Hong; Peng, Zheng Kai; Ren, Jin Hu

2017-12-01

A field experiment was conducted to explore the mechanism of cultivation measures in affecting crop yield by investigating root distribution in spring wheat-pea rotation based on a long-term conservation tillage practices in a farming region of Gansu. The results showed that with the develo-pment of growth period, the total root length, root surface area of spring wheat and pea showed a consistent trend of increase after initial decrease and reached the maximum at flowering stage. Higher root distribution was found in the 0-10 cm soil layer at seedling and 10-30 cm soil layer at flowering and maturity stages in spring wheat, while in the field pea, higher root distribution was found in the 0-10 cm soil layer at seedling and maturity, and in the 10-30 cm soil layer at flowering stages. No tillage with straw mulching and plastic mulching increased the root length and root surface area. Compared with conventional tillage in spring wheat and field pea, root length increased by 35.9% to 92.6%, and root surface area increased by 43.2% to 162.4%, respectively. No tillage with straw mulching and plastic mulching optimized spring wheat and pea root system distribution, compared with conventional tillage, increased spring wheat and field pea root length and root surface area ratio at 0-10 cm depths at the seedling stage, the root distribution at deeper depths increased significantly at flowering and maturity stages, and no tillage with straw mulching increased root length and root surface area ratio by 3.3% and 9.7% respectively, in 30-80 cm soil layer at the flowering stage. The total root length, root surface area and yield had significantly positive correlation for spring wheat in each growth period, and the total root length and pea yield also had significant positive correlation. No tillage with straw mulching and plastic mulching boosted yield of spring wheat and pea by 23.4%-38.7% compared with the conventional tillage, and the water use efficiency was increased by 13.7%-28.5%. It was concluded that no-till farming and straw mulching (plastic) could increase crop root length and root surface area, optimize the spatial distribution of roots in the soil, enhance crop root layer absorption ability, so as to improve crop yield and water utilization.

Potential of native shrubs Haloxylon salicornicum and Calligonum Polygonoides for restoration of degraded lands in Arid Western Rajasthan, India.

PubMed

Rathore, V S; Singh, J P; Bhardwaj, S; Nathawat, N S; Kumar, Mahesh; Roy, M M

2015-01-01

Shrub-induced soil property spatial heterogeneity is common in arid and semi-arid ecosystems and aids desertified land restoration. However, the effectiveness of this technique may rely on the plant species used and the habitat conditions present. To assess the degree to which planting two native species, Haloxylon salicornicum and Calligonum polygonoides, facilitates degraded land restoration, soil and herbaceous plant community properties were measured 7 years after planting. Soil samples were extracted at two depths (0-5 and 5-20 cm) from three sub-habitats, i.e., under the shrub canopy, from alleys between shrubs and from the open area. Shrub planting increased the quantity of silt + clay content (30-39 %); enhanced water holding capacities (24-30 %); increased the levels of organic carbon (48-69 %), available nitrogen (31-47 %), available phosphorus (32-41 %), and electrical conductivity (21-33 %); and decreased the pH (7-12 %) and bulk density levels (5-6 %) in the surface layer of soils beneath the canopy. Soil property changes were more significant at the surface (0-5 cm) than in the deeper layer (5-20 cm), and were more pronounced under H. salicornicum than under C. polygonoides. Furthermore, the density and biomass levels of herbaceous plants were 1.1 to 1.2 and 1.4 to 1.6 times greater, respectively, in the shrub alleys than in open area. H. salicornicum induced more robust soil amelioration and herbaceous plant facilitative properties than did C. polygonoides. Artificially planting these shrubs may thus be employed to restore degraded areas of arid regions.

Soil Salt Distribution and Tomato Response to Saline Water Irrigation under Straw Mulching

PubMed Central

Zhai, Yaming; Yang, Qian; Wu, Yunyu

2016-01-01

To investigate better saline water irrigation scheme for tomatoes that scheduling with the compromise among yield (Yt), quality, irrigation water use efficiency (IWUE) and soil salt residual, an experiment with three irrigation quotas and three salinities of irrigation water was conducted under straw mulching in northern China. The irrigation quota levels were 280 mm (W1), 320 mm (W2) and 360 mm (W3), and the salinity levels were 1.0 dS/m (F), 3.0 dS/m (S1) and 5.0 dS/m (S2). Compared to freshwater, saline water irrigations decreased the maximum leaf area index (LAIm) of tomatoes, and the LAIm presented a decline tendency with higher salinity and lower irrigation quota. The best overall quality of tomato was obtained by S2W1, with the comprehensive quality index of 3.61. A higher salinity and lower irrigation quota resulted in a decrease of individual fruit weight and an increase of the blossom-end rot incidence, finally led to a reduction in the tomato Yt and marketable yield (Ym). After one growth season of tomato, the mass fraction of soil salt in plough layer under S2W1 treatment was the highest, and which presented a decline trend with an increasing irrigation quota. Moreover, compared to W1, soil salts had a tendency to move to the deeper soil layer when using W2 and W3 irrigation quota. According to the calculation results of projection pursuit model, S1W3 was the optimal treatment that possessed the best comprehensive benefit (tomato overall quality, Yt, Ym, IWUE and soil salt residual), and was recommended as the saline water irrigation scheme for tomatoes in northern China. PMID:27806098

Soil Salt Distribution and Tomato Response to Saline Water Irrigation under Straw Mulching.

PubMed

Zhai, Yaming; Yang, Qian; Wu, Yunyu

2016-01-01

To investigate better saline water irrigation scheme for tomatoes that scheduling with the compromise among yield (Yt), quality, irrigation water use efficiency (IWUE) and soil salt residual, an experiment with three irrigation quotas and three salinities of irrigation water was conducted under straw mulching in northern China. The irrigation quota levels were 280 mm (W1), 320 mm (W2) and 360 mm (W3), and the salinity levels were 1.0 dS/m (F), 3.0 dS/m (S1) and 5.0 dS/m (S2). Compared to freshwater, saline water irrigations decreased the maximum leaf area index (LAIm) of tomatoes, and the LAIm presented a decline tendency with higher salinity and lower irrigation quota. The best overall quality of tomato was obtained by S2W1, with the comprehensive quality index of 3.61. A higher salinity and lower irrigation quota resulted in a decrease of individual fruit weight and an increase of the blossom-end rot incidence, finally led to a reduction in the tomato Yt and marketable yield (Ym). After one growth season of tomato, the mass fraction of soil salt in plough layer under S2W1 treatment was the highest, and which presented a decline trend with an increasing irrigation quota. Moreover, compared to W1, soil salts had a tendency to move to the deeper soil layer when using W2 and W3 irrigation quota. According to the calculation results of projection pursuit model, S1W3 was the optimal treatment that possessed the best comprehensive benefit (tomato overall quality, Yt, Ym, IWUE and soil salt residual), and was recommended as the saline water irrigation scheme for tomatoes in northern China.

Insights into the effects of patchy ice layers on water balance heterogeneity in peatlands

NASA Astrophysics Data System (ADS)

Dixon, Simon; Kettridge, Nicholas; Devito, Kevin; Petrone, Rich; Mendoza, Carl; Waddington, Mike

2017-04-01

Peatlands in boreal and sub-arctic settings are characterised by a high degree of seasonality. During winter soils are frozen and snow covers the surface preventing peat moss growth. Conversely, in summer, soils unfreeze and rain and evapotranspiration drive moss productivity. Although advances have been made in understanding growing season water balance and moss dynamics in northern peatlands, there remains a gap in knowledge of inter-seasonal water balance as layers of ice break up during the spring thaw. Understanding the effects of ice layers on spring water balance is important as this coincides with periods of high wildfire risk, such as the devastating Fort McMurrary wildfire of May, 2016. We hypothesise that shallow layers of ice disconnect the growing surface of moss from a falling water table, and prevent water from being supplied from depth. A disconnect between the evaporating surface and deeper water storage will lead to the drying out of the surface layer of moss and a greater risk of severe spring wildfires. We utilise the unsaturated flow model Hydrus 2D to explore water balance in peat layers with an impermeable layer representing ice. Additionally we create models to represent the heterogeneous break up of ice layers observed in Canadian boreal peatlands; these models explore the ability of breaks in an ice layer to connect the evaporating surface to a deeper water table. Results show that peatlands with slower rates of moss growth respond to dry periods by limiting evapotranspiration and thus maintain moist conditions in the sub-surface and a water table above the ice layer. Peatlands which are more productive continue to grow moss and evaporate during dry periods; this results in the near surface mosses drying out and the water table dropping below the level of the ice. Where there are breaks in the ice layer the evaporating surface is able to maintain contact with a falling water table, but connectivity is limited to above the breaks, with limited lateral transfer of water above the ice. Conceptually this means that peatlands which tend to have lower rates of growth are largely unaffected by the presence of a shallow ice layer in the early growing season, and are able to maintain moist sub-surface conditions in the absence of precipitation. They will thus be more resistant to severe wildfire. Conversely, peatlands which tend towards higher levels of moss productivity are able to maintain moss growth during dry periods. In the presence of an ice layer this greater productivity leads to a disconnection from deep water sources, extensive drying out of moss above the ice, and a greater susceptibility to severe wildfires. Our study gives important insights into the mechanisms behind heterogeneity in burning and depth of burn in northern peatland wildfires, as well as into burn heterogeneity within peatland microtopography.

Shifted energy fluxes, increased Bowen ratios, and reduced thaw depths linked with drainage-induced changes in permafrost ecosystem structure

NASA Astrophysics Data System (ADS)

Göckede, Mathias; Kittler, Fanny; Kwon, Min Jung; Burjack, Ina; Heimann, Martin; Kolle, Olaf; Zimov, Nikita; Zimov, Sergey

2017-12-01

Hydrologic conditions are a key factor in Arctic ecosystems, with strong influences on ecosystem structure and related effects on biogeophysical and biogeochemical processes. With systematic changes in water availability expected for large parts of the northern high-latitude region in the coming centuries, knowledge on shifts in ecosystem functionality triggered by altered water levels is crucial for reducing uncertainties in climate change predictions. Here, we present findings from paired ecosystem observations in northeast Siberia comprising a drained and a control site. At the drainage site, the water table has been artificially lowered by up to 30 cm in summer for more than a decade. This sustained primary disturbance in hydrologic conditions has triggered a suite of secondary shifts in ecosystem properties, including vegetation community structure, snow cover dynamics, and radiation budget, all of which influence the net effects of drainage. Reduced thermal conductivity in dry organic soils was identified as the dominating drainage effect on energy budget and soil thermal regime. Through this effect, reduced heat transfer into deeper soil layers leads to shallower thaw depths, initially leading to a stabilization of organic permafrost soils, while the long-term effects on permafrost temperature trends still need to be assessed. At the same time, more energy is transferred back into the atmosphere as sensible heat in the drained area, which may trigger a warming of the lower atmospheric surface layer.

Fate of leaf-litter N in forest and grassland along a pedo-climatic gradient in south-western Siberia: an in situ 15N-labelling experiment

NASA Astrophysics Data System (ADS)

Brédoire, Félix; Zeller, Bernd; Nikitich, Polina; Barsukov, Pavel A.; Rusalimova, Olga; Bakker, Mark R.; Legout, Arnaud; Bashuk, Alexander; Kayler, Zachary E.; Derrien, Delphine

2017-04-01

The suitability of Siberia for agriculture is expected to increase in the next decades due to strong and rapid climatic changes, but little is known on the environmental drivers of soil fertility there, especially nitrogen (N). Plant-available N is mainly derived from litter decomposition. South-western (SW) Siberia is located on the transition between several bioclimatic zones that are predicted to shift and extend along with climate change (steppe, forest-steppe, sub-taiga). The soils of this region are formed on a common loess deposit but they are submitted to different climatic conditions and vegetation cover. In the south of the region, typically in steppe/forest-steppe, soil freezes over winter because of a relatively shallow snow-pack, and water shortages are frequent in summer. In the north, typically in sub-taiga, the soil is barely frozen in winter due to a thick snow-pack and sufficient soil moisture in summer. In this study, we characterized the dynamics of leaf litter decomposition and the transfer of N from leaf litter to the soil and back to plants. Four sites were chosen along a climate gradient (temperature, precipitation and snow depth). At each site, we applied 15N-labelled leaf litter on the soil surface in experimental plots in an aspen (Populus tremula L.) forest and in a grassland. Twice a year during three years, we tracked the 15N derived from the decomposing labelled-litter in the organic layers, in the first 15 cm of the soil, and in above-ground vegetation. Soil temperature and moisture were monitored at a daily timestep over three years and soil water budgets were simulated (BILJOU model, Granier et al. 1999). We observed contrasting patterns in the fate of litter-derived 15N between bioclimatic zones. Over three years, along with faster decay rates, the release of leaf litter-N was faster in sub-taiga than in forest-steppe. As such, higher quantities of 15N were transferred into the soil in sub-taiga. The transfer was also deeper there, which might be related to a more intense drainage because of higher snow levels, as inferred from soil water budget modelling. Interestingly, this higher drainage seems to induce only a small loss of N from the system. Such retention could result from soil physico-chemical properties (higher fine silt and oxides contents) enhancing soil organic matter stabilization, and/or by the immobilization of N in microbial metabolites. We observed differing N dynamics between forest and grassland that can be related to the different chemical composition of initial litter (tree leaves vs. grasses) and plant-soil interactions. In general, N was retained in the first centimeters of the mineral soil in grassland while the transfer was deeper in the forest soils. As fine root exploration is denser in grassland topsoil than in forest topsoil, we infer that an efficient uptake of N by grasses in the first soil layers limits N migration down the profile. It is also possible that grasses are active earlier in the season than trees and understorey species, i.e. at snow-melt when drainage is the most intense.

Impact of absorption in the top layer of a two layer sample on spectroscopic spectral domain interferometry of the bottom layer

NASA Astrophysics Data System (ADS)

Fleischhauer, F.; Feuchter, T.; Leick, L.; Rajendram, R.; Podoleanu, A.

2018-03-01

Spectroscopic spectral domain interferometry and spectroscopic optical coherence tomography combine depth information with spectrally-resolved localised absorption data. These additional data can improve diagnostics by giving access to functional information of the investigated sample. One possible application is measuring oxygenation levels at the retina for earlier detection of several eye diseases. Here measurements with different hollow glass tube phantoms are shown to measure the impact of a superficial absorbing layer on the precision of reconstructed attenuation spectra of a deeper layer. Measurements show that a superficial absorber has no impact on the reconstructed absorption spectrum of the deeper absorber. Even when diluting the concentration of the deeper absorber so far that an incorrect absorption maximum is obtained, still no influence of the superficially placed absorber is identified.

Temporal and Spatial Separation of Water Use Averts Competition for Soil Water Resources in a Sahelian Agroforestry System

NASA Astrophysics Data System (ADS)

Bogie, N. A.; Bayala, R.; Diedhiou, I.; Dick, R.; Ghezzehei, T. A.

2016-12-01

A changing climate along with human and animal population pressure can have a devastating effect on crop yields and food security in the Sudano-Sahel. Agricultural solutions to address soil degradation and crop water stress are needed to combat this increasingly difficult situation. Large differences in crop success have been observed even during drough stress in peanut and millet grown in association with two native evergreen shrubs, Piliostigma reticulatum, and Guiera senegalensis at the sites of Nioro du Rip and Keur Matar, respectively. We investigate how farmers can increase crop productivity by capitalizing on the evolutionary adaptation of native shrubs to the harsh Sudano-Sahelian environment as well as the physical mechanisms at work in the system that can lead to more robust yields. Research plots at Keur Matar Arame and Nioro du Rip with no fertilizer added were monitored from 2012-2015 using two soil moisture sensor networks at depths of 10, 20, 40, 60, 100, 200, and 300cm. Our data show that there is more water available to crops in the shallow soil layers as a result of a temporal and spatial shift of shrub soil moisture use to deeper layers and the presence of hydraulic redistribution. At the beginning of the dry season just after the crop harvest, maximum weekly transpirational water use descends from 100 to 300cm over the course of one to two months. We hypothesize that after early February, 2-3 months into the dry season, the majority of water use by shrubs comes from below 3m depth. As the first rains come in June-July, the shrubs continue to use deep soil moisture until a significant portion of the soil profile undergoes infiltration. It is during this time that a large difference in hydraulic head can drive hydraulic redistribution, which, in addition to surface shading by the shrub canopy, can help to maintain higher soil moisture in the shallow soil layers near the shrubs. This builds on previous work at the site investigating growing season water balance, transfer of hydraulic lift water between crops and shrubs, and the alteration of soil physical properties by shrubs. Using even the limited resources that farmers possess, this agroforestry technique can be expanded over wide swaths of the Sahel.

Importance of rodents for hydrology: lessons learnt from various field experiments

NASA Astrophysics Data System (ADS)

van Schaik, Loes; Zangerlé, Anne; Schneider, Anne-Kathrin; Schröder, Boris; Eccard, Jana

2017-04-01

organisms are known to create soil macropores of different sizes and with varying extent and orientation: most commonly earthworms, rodents, moles and roots. Preferential flow through macropore networks is dynamic and typically occurs when short individual macropores become connected at the hillslope scale as the nodes between the macropores become wet. Large lateral macropores may contribute to rapid subsurface stormflow of water and solutes at hillslope scale and supply a significant part of the catchment scale discharge during high intensity rainfall events even under relatively dry catchment state. Outflow from soil pipes, especially in the valley bottom or along the banking near to streams, is frequently observed, however, it remains a challenge to measure the spatial distribution, extent and connectivity of macropores at hill slope scales. We hypothesize that local information on organism abundances may be used as an indicator for spatial variability in infiltration, water storage and fluxes at the small scale and that knowledge on the landscape scale spatial distribution of organisms can provide information on connectivity of macropores at hillslope scale. Here we summarize the lessons learnt during three years of measurements aimed at determining the influence of rodent burrows on soil hydrology in a meso-scale catchment. Within the Attert Catchment (297 km2) in Luxembourg we performed sprinkling experiments with a brilliant blue tracer on twelve plots, of which six directly above rodent burrow openings and six on a surface without a rodent burrow opening, in order to examine the influence of the burrow openings on the infiltration pattern. Then we tested the extent of flow through mice burrows in different forest types, with varying geology and slope, by supplying 5 Liters of water with brilliant blue tracer directly to 24 burrow openings at soil surface. We excavated the burrows to measure how far the water was transported laterally in the burrow. Though we have serendipitous evidence of lateral water flow through large macropores in deeper soil layers from other projects, with the experiments we performed with the purpose to characterize this, the water did not seem to infiltrate into the burrow openings at the soil surface at all and the infiltration pattern under burrows was not different from that in soils without these openings. The five liter of brilliant blue dyed water which we poured into burrow openings did not flow far into the burrows, it generally infiltrated straight away into the surrounding soil. These results seem to show that the infiltration of water to rodent macropores during high intensity events does not take place at the soil surface but rather through other macropores, e.g. earthworm channels, which connect to deeper lateral channels. Also the lateral flow of water through the rodent burrows is apparently more effective in the deeper soils, where we occasionally saw a burrow with completely blue walls but little infiltration into the surrounding matrix.

Tsunami Evidence in South Coast Java, Case Study: Tsunami Deposit along South Coast of Cilacap

NASA Astrophysics Data System (ADS)

Rizal, Yan; Aswan; Zaim, Yahdi; Dwijo Santoso, Wahyu; Rochim, Nur; Daryono; Dewi Anugrah, Suci; Wijayanto; Gunawan, Indra; Yatimantoro, Tatok; Hidayanti; Herdiyani Rahayu, Resti; Priyobudi

2017-06-01

Cilacap Area is situated in coastal area of Southern Java and directly affected by tsunami hazard in 2006. This event was triggered by active subduction in Java Trench which active since long time ago. To detect tsunami and active tectonic in Southern Java, paleo-tsunami study is performed which is targeted paleo-tsunami deposit older than fifty years ago. During 2011 - 2016, 16 locations which suspected as paleo-tsunami location were visited and the test-pits were performed to obtain characteristic and stratigraphy of paleo-tsunami layers. Paleo-tsunami layer was identified by the presence of light-sand in the upper part of paleo-soil, liquefaction fine grain sandstone, and many rip-up clast of mudstone. The systematic samples were taken and analysis (micro-fauna, grainsize and dating analysis). Micro-fauna result shows that paleo-tsunami layer consist of benthonic foraminifera assemblages from different bathymetry and mixing in one layer. Moreover, grainsize shows random grain distribution which characterized as turbulence and strong wave deposit. Paleo-tsunami layers in Cilacap area are correlated using paleo-soil as marker. There are three paleo-tsunami layers and the distribution can be identified as PS-A, PS-B and PS-C. The samples which were taken in Glempang Pasir layer are being dated using Pb - Zn (Lead-Zinc) method. The result of Pb - Zn (Lead-Zinc) dating shows that PS-A was deposited in 139 years ago, PS-B in 21 years ago, and PS C in 10 years ago. This result indicates that PS -1 occurred in 1883 earthquake activity while PS B formed in 1982 earthquake and PS-C was formed by 2006 earthquake. For ongoing research, the older paleo-tsunami layers were determined in the Gua Nagaraja, close to Selok location and 6 layers of Paleo-tsunami suspect found which shown a similar characteristic with the layers from another location. The three layers deeper approximately have an older age than another location in Cilacap.

Total Storage and Landscape Partitioning of Soil Organic Carbon and Phytomass Carbon in Siberia

NASA Astrophysics Data System (ADS)

Siewert, M. B.; Hanisch, J.; Weiss, N.; Kuhry, P.; Hugelius, G.

2014-12-01

We present results of detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) from two study sites in Siberia. The study sites in the Tundra (Kytalyk) and the Taiga (Spasskaya Pad) reflect two contrasting environments in the continuous permafrost zone. In total 57 individual field sites (24 and 33 per study site respectively) have have been sampled for SOC and PC along transects cutting across different land covers. In Kytalyk the sampling depth for the soil pedons was 1 m depth. In Spasskaya Pad where the active layer was significantly deeper, we aimed for 2 m depth or tried to include at least the top of the permafrost. Here the average depth of soil profiles was 152 cm. PC was sampled from 1x1 m ground coverage plots. In Spasskaya Pad tree phytomass was also estimated on a 5x5 m plot. The SOC storage was calculated separately for the intervals 0-30 cm, 30-100 cm and 100-200 cm (the latter only for Spasskaya Pad), as well as for organic layer vs. mineral soil, active layer vs. permafrost and for cryoturbated soil horizons. Landscape partitioning was performed by thematic up-scaling using a vegetation based land cover classification of very high resolution (2x2 m) satellite imagery. Non-Metric Multidimensional Scaling (NMDS) was used to explore the relationship of SOC with PC and different soil and permafrost related variables. The results show that the different land cover classes can be considered distinct storages of SOC, but that PC is not significantly related to total SOC storage. At both study sites the 30-100 cm SOC storage is more important for the total SOC storage than the 0-30 cm interval, and large portions of the total SOC are stored in the permafrost. The largest contribution comes from wetland pedons, but highly cryoturbated individual non-wetland pedons can match these. In Kytalyk the landscape partitioning of SOC mostly follows large scale geomorphological features, while in Spasskaya pad forest type also has a large influence.

An alternative methodology for the analysis of electrical resistivity data from a soil gas study

NASA Astrophysics Data System (ADS)

Johansson, Sara; Rosqvist, Hâkan; Svensson, Mats; Dahlin, Torleif; Leroux, Virginie

2011-08-01

The aim of this paper is to present an alternative method for the analysis of resistivity data. The methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills. The main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores. Field measurements of electrical resistivity, static chamber gas flux and weather data were collected at a landfill in Helsingborg, Sweden. The resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 ×20 m. The ABEM Lund Imaging System provided vertical and horizontal resistivity profiles every second hour. The data were inverted in Res3Dinv using L1-norm-based optimization method with a standard least-squares formulation. Each horizontal soil layer was then represented as a linear interpolated raster model. Different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer, and the vertical extension of the zones could be followed at greater depths in deeper layer models. The average resistivity values of the defined areas were calculated and plotted on a time axis, to provide graphs of the variation in resistivity with time in a specific section of the ground. Residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data. The resulting residual resistivity graphs were compared with field data of soil moisture, precipitation, soil temperature and methane flux. The results of the study were qualitative, but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found. Even though more research and better data quality is necessary for verification of the results presented here, we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application.

Propagation of hydroclimatic variability through the critical zone

NASA Astrophysics Data System (ADS)

Porporato, A. M.; Calabrese, S.; Parolari, A.

2016-12-01

The interaction between soil moisture dynamics and mineral-weathering reactions (e.g., ion exchange, precipitation-dissolution) affects the availability of nutrients to plants, composition of soils, soil acidification, as well as CO2 sequestration. Across the critical zone (CZ), this interaction is responsible for propagating hydroclimatic fluctuations to deeper soil layers, controlling weathering rates via leaching events which intermittently alter the alkalinity levels. In this contribution, we analyze these dynamics using a stochastic modeling approach based on spatially lumped description of soil hydrology and chemical weathering reactions forced by multi-scale temporal hydrologic variability. We quantify the role of soil moisture dynamics in filtering the rainfall fluctuations through its impacts on soil water chemistry, described by a system of ordinary differential equations (and algebraic equations, for the equilibrium reactions), driving the evolution of alkalinity, pH, the chemical species of the soil solution, and the mineral-weathering rate. A probabilistic description of the evolution of the critical zone is thus obtained, allowing us to describe the CZ response to long-term climate fluctuations, ecosystem and land-use conditions, in terms of key variables groups. The model is applied to the weathering rate of albite in the Calhoun CZ observatory and then extended to explore similarities and differences across other CZs. Typical time scales of response and degrees of sensitivities of CZ to hydroclimatic fluctuations and human forcing are also explored.

[Effects of different amounts of phosphate fertilizers on copper, zinc transfer in red soil under the application of KH2PO4].

PubMed

Guo, Liang; Li, Zhong-wu; Huang, Bin; Wang, Yan; Zhang, Yan

2014-09-01

In order to study the effects of different phosphate addition amounts on migration and transformation of heavy metals (Cu, Zn) in soil, an indoor leaching experiment using soil columns was carry out to study the leaching behavior of Cu and Zn. The KH2PO4 was chosen as the fertilizer application at the doses of 5 mg.kg-1, 15 mg.kg-1 and 25 mg.kg-1. The results showed that KH2PO4, could reduce the leachate pH, but different phosphate amounts had little effect on leachate pH, pH in leachate kept rising in the whole leaching process. With the application of KH2PO4, Cu migration was mainly in the surface layer while Zn migrated into deeper soil. Concentrations of Cu, Zn in deep soil leachate were low indicating that it was harmless to the shallow groundwater. After leaching, heavy metals mainly existed in the residual form in soil, the proportion of residual form of Cu was around 60% and the proportion of residual form of Zn was around 40%. High concentration of KH2PO4 helps the transformation of Zn from residual organic combination state to exchange state.

Measuring and modeling three-dimensional water uptake of a growing faba bean (Vicia faba) within a soil column

NASA Astrophysics Data System (ADS)

Huber, Katrin; Koebernick, Nicolai; Kerkhofs, Elien; Vanderborght, Jan; Javaux, Mathieu; Vetterlein, Doris; Vereecken, Harry

2014-05-01

A faba bean was grown in a column filled with a sandy soil, which was initially close to saturation and then subjected to a single drying cycle of 30 days. The column was divided in four hydraulically separated compartments using horizontal paraffin layers. Paraffin is impermeable to water but penetrable by roots. Thus by growing deeper, the roots can reach compartments that still contain water. The root architecture was measured every second day by X-ray CT. Transpiration rate, soil matric potential in four different depths, and leaf area were measured continously during the experiment. To investigate the influence of the partitioning of available soil water in the soil column on water uptake, we used R-SWMS, a fully coupled root and soil water model [1]. We compared a scenario with and without the split layers and investigated the influence on root xylem pressure. The detailed three-dimensional root architecture was obtained by reconstructing binarized root images manually with a virtual reality system, located at the Juelich Supercomputing Centre [2]. To verify the properties of the root system, we compared total root lengths, root length density distributions and root surface with estimations derived from Minkowski functionals [3]. In a next step, knowing the change of root architecture in time, we could allocate an age to each root segment and use this information to define age dependent root hydraulic properties that are required to simulate water uptake for the growing root system. The scenario with the split layers showed locally much lower pressures than the scenario without splits. Redistribution of water within the unrestricted soil column led to a more uniform distribution of water uptake and lowers the water stress in the plant. However, comparison of simulated and measured pressure heads with tensiometers suggested that the paraffin layers were not perfectly hydraulically isolating the different soil layers. We could show compensation efficiency of water uptake by the roots in the lower and wetter compartments. By comparing transpiration rates of experiments with and without additional paraffin layers, we were able to quantify restrictions of plant growth to available soil water. [1] Javaux, M., T. Schröder, J. Vanderborght, and H. Vereecken (2008), Use of a Three-Dimensional Detailed Modeling Approach for Predicting Root Water Uptake, Vadose Zone Journal, 7(3), 1079-1079. [2] Stingaciu, L., H. Schulz, A. Pohlmeier, S. Behnke, H. Zilken, M. Javaux, H. Vereecken (2013), In Situ Root System Architecture Extraction from Magnetic Resonance Imaging for Water Uptake Modeling, Vadose Zone Journal, 12(1). [3] Koebernick, N., U. Weller, K. Huber, S. Schlüter, H.-J. Vogel, R. Jahn; H. Vereecken, D. Vetterlein, In situ visualisation and quantification of root-system architecture and growth with X-ray CT, Manuscript submitted for publication.

Subsurface profiling using integrated geophysical methods for 2D site response analysis in Bangalore city, India: a new approach

NASA Astrophysics Data System (ADS)

Chandran, Deepu; Anbazhagan, P.

2017-10-01

Recently, site response analysis has become a mandatory step for the design of important structures. Subsurface investigation is an essential step, from where the input parameters for the site response study like density, shear wave velocity (Vs), thickness and damping characteristics, etc, are obtained. Most site response studies at shallow bedrock sites are one-dimensional (1D) and are usually carried out by using Vs from multi-channel analysis of surface waves (MASW) or a standard penetration test (SPT) for N values with assumptions that soil layers are horizontal, uniform and homogeneous. These assumptions are not completely true in shallow bedrock regions as soil deposits are heterogeneous. The objective of this study is to generate the actual subsurface profiles in two-dimensions at shallow bedrock regions using integrated subsurface investigation testing. The study area selected for this work is Bangalore, India. Three survey lines were selected in Bangalore at two different locations; one at the Indian Institute of Science (IISc) Campus and the other at Whitefield. Geophysical surveys like ground penetrating radar (GPR) and 2D MASW were carried out at these survey lines. Geophysical test results are compared and validated with a conventional geotechnical SPT. At the IISc site, the soil profile is obtained from a trench excavated for a proposed pipeline used to compare the geophysical test results. Test results show that GPR is very useful to delineate subsurface layers, especially for shallow depths at both sites (IISc Campus and Whitefield). MASW survey results show variation of Vs values and layer thickness comparatively at deeper depths for both sites. They also show higher density soil strata with high Vs value obtained at the IISc Campus site, whereas at the Whitefield site weaker soil with low shear velocity is observed. Combining these two geophysical methods helped to generate representative 2D subsurface profiles. These subsurface profiles can be further used to understand the difference between 1D and 2D site response.

Understory vegetation mediates permafrost active layer dynamics and carbon dioxide fluxes in open-canopy larch forests of northeastern Siberia.

PubMed

Loranty, Michael M; Berner, Logan T; Taber, Eric D; Kropp, Heather; Natali, Susan M; Alexander, Heather D; Davydov, Sergey P; Zimov, Nikita S

2018-01-01

Arctic ecosystems are characterized by a broad range of plant functional types that are highly heterogeneous at small (~1-2 m) spatial scales. Climatic changes can impact vegetation distribution directly, and also indirectly via impacts on disturbance regimes. Consequent changes in vegetation structure and function have implications for surface energy dynamics that may alter permafrost thermal dynamics, and are therefore of interest in the context of permafrost related climate feedbacks. In this study we examine small-scale heterogeneity in soil thermal properties and ecosystem carbon and water fluxes associated with varying understory vegetation in open-canopy larch forests in northeastern Siberia. We found that lichen mats comprise 16% of understory vegetation cover on average in open canopy larch forests, and lichen abundance was inversely related to canopy cover. Relative to adjacent areas dominated by shrubs and moss, lichen mats had 2-3 times deeper permafrost thaw depths and surface soils warmer by 1-2°C in summer and less than 1°C in autumn. Despite deeper thaw depths, ecosystem respiration did not differ across vegetation types, indicating that autotrophic respiration likely dominates areas with shrubs and moss. Summertime net ecosystem exchange of CO2 was negative (i.e. net uptake) in areas with high shrub cover, while positive (i.e. net loss) in lichen mats and areas with less shrub cover. Our results highlight relationships between vegetation and soil thermal dynamics in permafrost ecosystems, and underscore the necessity of considering both vegetation and permafrost dynamics in shaping carbon cycling in permafrost ecosystems.

Surveyor 3 Preliminary Science Results

NASA Technical Reports Server (NTRS)

1967-01-01

Surveyor III soft-landed on the Moon at 00:04 GMT on April 20, 1967. Data obtained have significantly increased our knowledge of the Moon. The Surveyor III spacecraft was similar to Surveyor I; the only major change in scientific instrumentation was the addition of a soil mechanics surface sampler. Surveyor III results at this preliminary evaluation of data give valuable information about the relation between the surface skin of under-dense material responsible for the photometric properties and the deeper layers of material whose properties resemble those of ordinary terrestrial soils. In addition, they provide new insight into the relation between the general lunar surface as seen by Surveyor I and the interior of a large subdued crater. The new results have also contributed to our understanding of the mechanism of downhill transport. Many critical questions cannot, however, be answered until final reduction of experimental data.

Soil carbon sequestration by three perennial legume pastures is greater in deeper soil layers than in the surface soil

NASA Astrophysics Data System (ADS)

Guan, X.-K.; Turner, N. C.; Song, L.; Gu, Y.-J.; Wang, T.-C.; Li, F.-M.

2015-07-01

Soil organic carbon (SOC) plays a vital role as both a sink for and source of atmospheric carbon. Revegetation of degraded arable land in China is expected to increase soil carbon sequestration, but the role of perennial legumes on soil carbon stocks in semiarid areas has not been quantified. In this study, we assessed the effect of alfalfa (Medicago sativa L.) and two locally adapted forage legumes, bush clover (Lespedeza davurica S.) and milk vetch (Astragalus adsurgens Pall.) on the SOC concentration and SOC stock accumulated annually over a 2 m soil profile, and to estimate the long-term potential for SOC sequestration in the soil under the three forage legumes. The results showed that the concentration of SOC of the bare soil decreased slightly over the 7 years, while 7 years of legume growth substantially increased the concentration of SOC over the 0-2.0 m soil depth measured. Over the 7 year growth period the SOC stocks increased by 24.1, 19.9 and 14.6 Mg C ha-1 under the alfalfa, bush clover and milk vetch stands, respectively, and decreased by 4.2 Mg C ha-1 under bare soil. The sequestration of SOC in the 1-2 m depth of soil accounted for 79, 68 and 74 % of SOC sequestered through the upper 2 m of soil under alfalfa, bush clover and milk vetch, respectively. Conversion of arable land to perennial legume pasture resulted in a significant increase in SOC, particularly at soil depths below 1 m.

Persistence of culturable Escherichia coli fecal contaminants in dairy alpine grassland soils.

PubMed

Texier, Stéphanie; Prigent-Combaret, Claire; Gourdon, Marie Hélène; Poirier, Marie Andrée; Faivre, Pierre; Dorioz, Jean Marcel; Poulenard, Jérome; Jocteur-Monrozier, Lucile; Moënne-Loccoz, Yvan; Trevisan, Dominique

2008-01-01

Our knowledge of Escherichia coli (E. coli) ecology in the field is very limited in the case of dairy alpine grassland soils. Here, our objective was to monitor field survival of E. coli in cow pats and underlying soils in four different alpine pasture units, and to determine whether the soil could constitute an environmental reservoir. E. coli was enumerated by MPN using a selective medium. E. coli survived well in cow pats (10(7) to 10(8) cells g(-1) dry pat), but cow pats disappeared within about 2 mo. In each pasture unit, constant levels of E. coli (10(3) to 10(4) cells g(-1) dry soil) were recovered from all topsoil (0-5 cm) samples regardless of the sampling date, that is, under the snow cover, immediately after snow melting, or during the pasture season (during and after the decomposition of pats). In deeper soil layers below the root zone (5-25 cm), E. coli persistence varied according to soil type, with higher numbers recovered in poorly-drained soils (10(3) to 10(4) cells g(-1) dry soil) than in well-drained soils (< 10(2) cells g(-1) dry soil). A preliminary analysis of 38 partial uidA sequences of E. coli from pat and soils highlighted a cluster containing sequences only found in this work. Overall, this study raises the possibility that fecal E. coli could have formed a naturalized (sub)population, which is now part of the indigenous soil community of alpine pasture grasslands, the soil thus representing an environmental reservoir of E. coli.

Impacts of Soil-aquifer Heat and Water Fluxes on Simulated Global Climate

NASA Technical Reports Server (NTRS)

Krakauer, N.Y.; Puma, Michael J.; Cook, B. I.

2013-01-01

Climate models have traditionally only represented heat and water fluxes within relatively shallow soil layers, but there is increasing interest in the possible role of heat and water exchanges with the deeper subsurface. Here, we integrate an idealized 50m deep aquifer into the land surface module of the GISS ModelE general circulation model to test the influence of aquifer-soil moisture and heat exchanges on climate variables. We evaluate the impact on the modeled climate of aquifer-soil heat and water fluxes separately, as well as in combination. The addition of the aquifer to ModelE has limited impact on annual-mean climate, with little change in global mean land temperature, precipitation, or evaporation. The seasonal amplitude of deep soil temperature is strongly damped by the soil-aquifer heat flux. This not only improves the model representation of permafrost area but propagates to the surface, resulting in an increase in the seasonal amplitude of surface air temperature of >1K in the Arctic. The soil-aquifer water and heat fluxes both slightly decrease interannual variability in soil moisture and in landsurface temperature, and decrease the soil moisture memory of the land surface on seasonal to annual timescales. The results of this experiment suggest that deepening the modeled land surface, compared to modeling only a shallower soil column with a no-flux bottom boundary condition, has limited impact on mean climate but does affect seasonality and interannual persistence.

The Impact of Solar Arrays on Arid Soil Hydrology: Some Numerical Simulations

NASA Astrophysics Data System (ADS)

Luo, Y.; Berli, M.; Koonce, J.; Shillito, R.; Dijkema, J.; Ghezzehei, T. A.; Yu, Z.

2016-12-01

Hot deserts are prime locations for solar energy generation but also recognized as particularly fragile environments. Minimizing the impact of facility-scale solar installations on desert environments is therefore of increasing concern. This study focuses on the impact of photovoltaic solar arrays on the water balance of arid soil underneath the array. The goal was to explore whether concentrated rainwater infiltration along the solar panel drip lines would lead to deeper infiltration and an increase in soil water storage in the long term. A two-dimensional HYDRUS model was developed to simulate rainwater infiltration into the soil within a photovoltaic solar array. Results indicate that rainwater infiltrates deeper below the drip lines compared to the areas between solar panels but only for coarse textured soil. Finer-textured soils redistribute soil moisture horizontally and the concentrating effect of solar panels on rainwater infiltration appears to be small.

From bulk soil to intracrystalline investigation of plant-mineral interaction

NASA Astrophysics Data System (ADS)

Lemarchand, D.; Voinot, A.; Chabaux, F.; Turpault, M.

2011-12-01

Understanding the controls and feedbacks regulating the flux of matter between bio-geochemical reservoirs in forest ecosystems receives a fast growing interest for the last decades. A complex question is to understand how minerals and vegetation interact in soils to sustain life and, to a broader scope, how forest ecosystems may respond to human activity (acid rain, harvesting,...) and climate perturbations (temperature, precipitation,...). Many mineralogical and biogeochemical approaches have longtime been developed, and occasionally coupled, in order to investigate the mechanisms by which chemical elements either are exchanged between soil particles and solutions, or are transferred to plants or to deeper soil layers and finally leave the system. But the characterization of particular processes like the contribution of minor reactive minerals to plant nutrition and global fluxes or the mechanisms by which biology can modify reaction rates and balance the bioavailability of nutrients in response to environmental perturbation sometimes fails because of the lack of suitable tracers. Recent analytical and conceptual advances have opened new perspectives for the use of light "non traditional" stable isotopes. Showing a wild range of concentrations and isotopic compositions between biogeochemical reservoirs in forest ecosystem, boron has physico-chemical properties particularly relevant to the investigation of water/rock interactions even when evolving biologically-mediated reactions. In this study, we focused on the distribution of boron isotopes from intracrystalline to bulk soil scales. An overview of the boron distribution and annual fluxes in the soil-plant system clearly indicates that the vegetation cycling largely controls the mobility of boron. We also observe that the mineral and biological B pools have drastically different isotopic signature that makes the transfer of B between them very easy to follow. In particular, the podzol soil we analyzed shows a clear contribution of vegetation-recycled B to neoformed mineral phases, whereas B in minerals from the brown acidic soil rather indicates predominant mineral dissolution with little or even no B supply from the soil solution. If B isotopes thus proved their sensitivity to the soil forming conditions, a simple isotopic budget also demonstrates that the isotopic signature shown by the vegetation cannot result from fractionation during boron absorption. Analyses of B isotopes within intracrystalline phyllosilicate minerals further identify the interfoliar layers as the major source of B during plant nutrition. Additionally, weathering experiments placing phyllosilicates in contact with various alteration agents (protons, organic acid or siderophore) point to the role of the latters as likely responsible for the boron liberation from the phyllosilicate interfoliar layers. This scenario gives the phyllosilicate interfoliar layers a central function in the plant nutrition in context studied here of soils developed on granitic bedrocks. It also implies a very dynamic system in which plants and minerals can exchange matter over very short periods of time.

Distribution and mobility of lead (Pb), copper (Cu), zinc (Zn), and antimony (Sb) from ammunition residues on shooting ranges for small arms located on mires.

PubMed

Mariussen, Espen; Johnsen, Ida Vaa; Strømseng, Arnljot Einride

2017-04-01

An environmental survey was performed on shooting ranges for small arms located on minerotrophic mires. The highest mean concentrations of Pb (13 g/kg), Cu (5.2 g/kg), Zn (1.1 g/kg), and Sb (0.83 g/kg) in the top soil were from a range located on a poor minerotrophic and acidic mire. This range had also the highest concentrations of Pb, Cu, Zn, and Sb in discharge water (0.18 mg/L Pb, 0.42 mg/L Cu, 0.63 mg/L Zn, and 65 μg/L Sb) and subsurface soil water (2.5 mg/L Pb, 0.9 mg/L Cu, 1.6 mg/L Zn, and 0.15 mg/L Sb). No clear differences in the discharge of ammunition residues between the mires were observed based on the characteristics of the mires. In surface water with high pH (pH ~7), there was a trend with high concentrations of Sb and lower relative concentrations of Cu and Pb. The relatively low concentrations of ammunition residues both in the soil and soil water, 20 cm below the top soil, indicates limited vertical migration in the soil. Channels in the mires, made by plant roots or soil layer of less decomposed materials, may increase the rate of transport of contaminated surface water into deeper soil layers and ground water. A large portion of both Cu and Sb were associated to the oxidizable components in the peat, which may imply that these elements form inner-sphere complexes with organic matter. The largest portion of Pb and Zn were associated with the exchangeable and pH-sensitive components in the peat, which may imply that these elements form outer-sphere complexes with the peat.

Input of easily available organic C and N stimulates microbial decomposition of soil organic matter in arctic permafrost soil

PubMed Central

Wild, Birgit; Schnecker, Jörg; Alves, Ricardo J. Eloy; Barsukov, Pavel; Bárta, Jiří; Čapek, Petr; Gentsch, Norman; Gittel, Antje; Guggenberger, Georg; Lashchinskiy, Nikolay; Mikutta, Robert; Rusalimova, Olga; Šantrůčková, Hana; Shibistova, Olga; Urich, Tim; Watzka, Margarete; Zrazhevskaya, Galina; Richter, Andreas

2014-01-01

Rising temperatures in the Arctic can affect soil organic matter (SOM) decomposition directly and indirectly, by increasing plant primary production and thus the allocation of plant-derived organic compounds into the soil. Such compounds, for example root exudates or decaying fine roots, are easily available for microorganisms, and can alter the decomposition of older SOM (“priming effect”). We here report on a SOM priming experiment in the active layer of a permafrost soil from the central Siberian Arctic, comparing responses of organic topsoil, mineral subsoil, and cryoturbated subsoil material (i.e., poorly decomposed topsoil material subducted into the subsoil by freeze–thaw processes) to additions of 13C-labeled glucose, cellulose, a mixture of amino acids, and protein (added at levels corresponding to approximately 1% of soil organic carbon). SOM decomposition in the topsoil was barely affected by higher availability of organic compounds, whereas SOM decomposition in both subsoil horizons responded strongly. In the mineral subsoil, SOM decomposition increased by a factor of two to three after any substrate addition (glucose, cellulose, amino acids, protein), suggesting that the microbial decomposer community was limited in energy to break down more complex components of SOM. In the cryoturbated horizon, SOM decomposition increased by a factor of two after addition of amino acids or protein, but was not significantly affected by glucose or cellulose, indicating nitrogen rather than energy limitation. Since the stimulation of SOM decomposition in cryoturbated material was not connected to microbial growth or to a change in microbial community composition, the additional nitrogen was likely invested in the production of extracellular enzymes required for SOM decomposition. Our findings provide a first mechanistic understanding of priming in permafrost soils and suggest that an increase in the availability of organic carbon or nitrogen, e.g., by increased plant productivity, can change the decomposition of SOM stored in deeper layers of permafrost soils, with possible repercussions on the global climate. PMID:25089062

Geophysical evidence for non-uniform permafrost degradation after fire across boreal landscapes

NASA Astrophysics Data System (ADS)

Minsley, B. J.; Pastick, N. J.; Wylie, B. K.; Brown, D. N.; Kass, A.

2015-12-01

Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. We present a combination of multi-scale remote sensing, geophysical, and field observations that reveal details of both near-surface (<1 m) and deeper impacts of fire on permafrost. Along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska, subsurface imaging indicates locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be most vulnerable to future change, and also where permafrost has thawed. High-resolution geophysical data corroborate remote sensing interpretations of near-surface permafrost, and also add new high-fidelity details of spatial heterogeneity that extend from the shallow subsurface to depths of about 10 m. Data collected along each transect include observations of active layer thickness (ALT), organic layer thickness (OLT), plant species cover, electrical resistivity tomography (ERT), and downhole Nuclear Magnetic Resonance (NMR) measurements. Results show that post-fire impacts on permafrost can be variable, and depend on multiple factors such as fire severity, soil texture, and soil moisture.

Soil hydrology of agroforestry systems: Competition for water or positive tree-crops interactions?

NASA Astrophysics Data System (ADS)

Gerjets, Rowena; Richter, Falk; Jansen, Martin; Carminati, Andrea

2017-04-01

In dry periods during the growing season crops may suffer from severe water stress. The question arises whether the alternation of crop and tree strips might enhance and sustain soil water resources available for crops during drought events. Trees reduce wind exposure, decreasing the potential evapotranspiration of crops and soils; additionally hydraulic lift from the deep roots of trees to the drier top soil might provide additional water for shallow-rooted crops. To understand the above and belowground water relations of agroforestry systems, we measured soil moisture and soil water potential in crop strips as a function of distance to the trees at varying depth as well as meteorological parameters. At the agroforestry site Reiffenhausen, Lower Saxony, Germany, two different tree species are planted, each in one separated tree strip: willow breed Tordis ((Salix viminalis x Salix Schwerinii) x Salix viminalis) and poplar clone Max 1 (Populus nigra x Populus maximowiczii). In between the tree strips a crop strip of 24 m width was established with annual crop rotation, managed the same way as the reference site. During a drought period in May 2016 with less than 2 mm rain in four weeks, an overall positive effect on hydrological conditions of the agroforestry system was observed. The results show that trees shaded the soil surface, lowering the air temperature and further increasing the soil moisture in the crop strips compared to the reference site, which was located far from the trees. At the reference site the crops took up water in the upper soil (<20 cm depth); after the soil reached water potentials below -100 kPa, root water uptake moved to deeper soil layers (<40 cm). Because of the higher wind and solar radiation exposure the reference soil profile was severely dried out. Also in the crop strips of the agroforestry system, crops took up water in the upper soil. However, the lower soil layers remained wet for an extended period of time. The tree strips reduced the wind speed, hence lowering evapotranspiration in the crop strip. The plot was not aligned directly to North and we observed steeper soil water potential gradients in the part of the crop strip more exposed to sunlight. The two tree species behaved differently. The poplar strips showed more marked diurnal changes in soil water potential, with fast drying during daytime and rewetting during nighttime. We suppose that the rewetting during nighttime was caused by hydraulic lift, which supports passively the drier upper soil with water from the wetter, lower soil layers. This experimental study shows the importance of above- and belowground tree-crop interactions and demonstrate the positive effect of tree strips in reducing drought stress in crops.

Paired tree and soil instrumentation: what can we learn from two instrumented sites across various gradients in a forested catchment

NASA Astrophysics Data System (ADS)

Hartsough, P. C.; Roudneva, E.; Malazian, A. I.; Meadows, M. W.; Bales, R. C.; Hopmans, J. W.

2012-12-01

Extensive instrumentation both below and above ground across a forested catchment in the Southern Sierra Critical Zone Observatory (SSCZO) within the Kings River Experimental Watershed (KREW) begins to untangle the complex relationship between precipitation, water storage and transpiration as it relates to water availability from deeper sources. The first instrumented site (CZT-1) includes a White Fir (Abies concolor) situated on a flat ridge with access to deep soil moisture. Monitoring and modeling of shallow and deep soil regions confirm that there is significant soil water available from 100-400cm as the tree exhausts water from shallower depths. A root excavation and limited drilling show roots distributed from 30-150cm with limited roots available to access deeper soil water and water stored in the saprolite. At a second instrumented site, CZT-2, a Ponderosa Pine (Pinus ponderosa) was instrumented with a similar suite of sap flow and soil sensors. The CZT-2 site is on a slight slope and is characterized by shallow soils (<90cm) with extensive cobbles and bedrock outcrops with limited access to deeper soil or saprolite water. The second site also sits in the open while the first site is more protected in a closed forest. The two sites show different responses to changes in rain and snow loading from above as well as soil drainage and water depletion from below across a wet to dry transition. They also have different thresholds for transpiration shut down both due to late season water deficit and also during winter periods where air temperatures are high enough to permit photosynthesis. Sap flux and extensive soil water content and water potential measurements around both trees as well as evapotranspiration measurements from a 50m flux tower located adjacent to the two instrumented trees, show little water limitation during wet years and only moderate water limitation during a drought year. Access to deeper water storage pools is confirmed by modeling results across the soil/tree/atmosphere continuum.

Short-term changes of metal availability in soil. Part I: comparing sludge-amended with metal-spiked soils.

PubMed

Natal-da-Luz, T; Ojeda, G; Costa, M; Pratas, J; Lanno, R P; Van Gestel, C A M; Sousa, J P

2012-08-01

Sewage sludge application to soils is regulated by its total metal content. However, the real risk of metals is determined by the fraction that is biologically available. The available fraction is highly related to the strength of metal binding by the matrix, which is a dynamic process. The evaluation of the fate of metals in time can contribute increased accuracy of ecological risk assessment. Aiming to evaluate short-term changes in metal availability when metals were applied to soil directly (metal-spiked) or by way of an organic matrix (sludge-amended), a laboratory experiment was performed using open microcosms filled with agricultural soil. A concentration gradient of industrial sludge (11, 15, 55, and 75 t/ha) that was contaminated predominantly with chromium, copper, nickel, and zinc, or soil freshly spiked with the same concentrations of these metals, were applied on top of the agricultural soil. After 0, 3, 6, and 12 weeks, total (HNO(3) 69 %) and 0.01 M CaCl(2)-extractable metal concentrations in soil and metal content in the percolates were measured. Results demonstrated that comparison between sludge-amended and metal-spiked soils may give important information about the role of sludge matrix on metal mobility and availability in soil. In sludge-amended soils, extractable-metal concentrations were independent of the sludge concentration and did not change over time. In metal-spiked soils, metal extractability decreased with time due to ageing and transport of metals to deeper layers. In general, the sludge matrix increased the adsorption of metals, thus decreasing their mobility in soils.

Wet deposition and soil content of Beryllium - 7 in a micro-watershed of Minas Gerais (Brazil).

PubMed

Esquivel L, Alexander D; Moreira, Rubens M; Monteiro, Roberto Pellacani G; Dos Santos, Anômora A Rochido; Juri Ayub, Jimena; Valladares, Diego L

2017-04-01

Beryllium-7 ( 7 Be) is a natural radionuclide of cosmogenic origin, normally used as a tracer for several environmental processes; such as soil redistribution, sediment source discrimination, atmospheric mass transport, and trace metal scavenging from the atmosphere. In this research the content of 7 Be in soil, its seasonal variation throughout the year and its relationship with the rainfall regime in the Mato Frio creek micro-watershed was investigated, to assess its potential use in estimating soil erosion. The 7 Be content in soil shows a marked variation throughout the year. Minimum 7 Be values were observed in the dry season (from April to September) and were between 7 and 14 times higher in the rainy season (from October to March). The seasonal oscillations in 7 Be soil content could be explained by the asymmetric rainfall regime. A highly linear relationship between rainfall amount and 7 Be deposition was observed in rain water. A good agreement between 7 Be soil content and 7 Be atmospheric deposition was noticed, mainly in wet months. 7 Be penetration in soil reaches a 5 cm depth, this could be explained by the soil type in the region. The soils are Acrisol type, characterized by low pH values and clay illuviation in deeper layers of the soil. In some regions of Brazil special attention should be paid if this radionuclide will be used as soil erosion tracer, taking into account the soil origin and its particular properties. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Molecular Investigation of Soil Organic Carbon Composition, Variability, and Spatial Distribution Across an Alpine Catchment

NASA Astrophysics Data System (ADS)

Hsu, H. T.; Lawrence, C. R.; Winnick, M.; Druhan, J. L.; Williams, K. H.; Maher, K.; Rainaldi, G. R.; McCormick, M. E.

2016-12-01

The cycling of carbon through soils is one of the least understood aspects of the global carbon cycle and represents a key uncertainty in the prediction of land-surface response to global warming. Thus, there is an urgent need for advanced characterization of soil organic carbon (SOC) to develop and evaluate a new generation of soil carbon models. We hypothesize that shifts in SOC composition and spatial distribution as a function of soil depth can be used to constrain rates of transformation between the litter layer and the deeper subsoil (extending to a depth of approximately 1 m). To evaluate the composition and distribution of SOC, we collected soil samples from East River, a shale-dominated watershed near Crested Butte, CO, and characterized relative changes in SOC species as a function of depth using elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR) and bulk C X-ray absorption spectroscopy (XAS). Our results show that total organic carbon (TOC) decreases with depth, and high total inorganic carbon (TIC) content was found in deeper soils (after 75 cm), a characteristic of the bedrock (shale). The distribution of aliphatic C relative to the parent material generally decreases with depth and that polysaccharide can be a substantial component of SOC at various depths. On the other hand, the relative distribution of aromatic C, traditionally viewed as recalcitrant, only makes up a very small part of SOC regardless of depth. These observations confirm that molecular structure is not the only determinant of SOC turnover rate. To study other contributors to SOC decomposition, we studied changes in the spatial correlation of SOC and minerals using X-ray fluorescence spectroscopy (XRF) and scanning transmission X-ray microscopy (STXM). We found that aromatics mostly locate on the surface of small soil aggregates (1-10 μm). Polysaccharides and proteins, both viewed as labile traditionally, are more evenly distributed over the interior of the particles, which could limit microbial access and thus decrease decomposition rate. The speciation and spatial distribution results can be compared to field-measured CO2-fluxes, soil moisture, and radiocarbon data to assess the factors that control SOC turnover rates in different environments across the catchment and enhance the development of SOC models.

Hydrogeological and geophysical investigations to evaluate groundwater influences on GHG emissions at the national research site Skogaryd

NASA Astrophysics Data System (ADS)

Banzhaf, Stefan; Klemedtsson, Leif; Sturkell, Erik; Nyström, Elin; Barthel, Roland

2015-04-01

The overall objective of the presented study is to explore the impact of groundwater fluctuations on greenhouse gas (GHG) emissions from peatlands and in particular from drained organic soils. The hypothesis is that drained organic soils react sensitively to changing water content, i.e. that frequent changes of groundwater level enhance the emissions of GHG from these soils and thus contribute significantly to global warming. The area under investigation is based at the Skogaryd Research Catchment (within Swedish Infrastructure for Ecosystem Sciences, SITES) in western Sweden (Meyer, et al., 2013), which was recently assigned the status of a national research site by the Swedish research council (www.vr.se). Skogaryd is a unique place in Sweden for doing research on organic soils as the area was simultaneously afforested in the 1960s and the drained fertile soils have a different land-use history. The ditching for drainage purposes throughout the entire area has had and still has a huge influence on groundwater level, which in turn is assumed to trigger GHG emissions from the organic soils at Skogaryd. To address the influence of groundwater dynamics on GHG emissions in this system, a characterisation of the subsurface using electrical resistivity and Ground Penetrating Radar (GPR) measurements was carried out. These geophysical measurements were combined with drilling along them to allow for ground truthing. An average peat thickness of around 3 m was estimated for the field site. Below the peat follows a fine sand layer, which reaches a maximum thickness of around 1.0 m right at the valley borders and thins out significantly towards the middle of the valley. Below the fine sand layer follows a layer of marine clay, which extends down to the bedrock at depths between 12 and 15 m below ground surface. The results show that the peat layer in Skogaryd forms an isolated hydraulic system without interaction with deeper or regional groundwater systems. The continuously extending clay layer hinders water moving downward or upward crossing the border of peat and clay. The peat layer is a fast reacting hydraulic system that shows immediate reaction to precipitation or drought and is independent from regional groundwater levels. The study of groundwater controls on the GHG from the drained organic soils at Skogaryd can thus focus on the fast reacting peat layer. Future investigations will show if this conclusion can be generalized for similar situations in Sweden. Geophysical measurements have proved to be a valuable method for estimating the peat thickness over a large area. Meyer A, Tarvainen L, Nousratpour A, Björk RG, Ernfors M, Grelle A, Kasimir Klemedtsson Å, Lindroth A, Räntfors M, Rütting T, Wallin G, Weslien P, Klemedtsson L (2013) A fertile peatland forest does not constitute a major greenhouse gas sink. Biogeosciences 10: 7739-7758 DOI 10.5194/bg-10-7739-2013

Seasonal Variability of Major Ions and δ13CDIC in Permafrost Watersheds of Arctic Alaska

NASA Astrophysics Data System (ADS)

Lehn, G. O.; Jacobson, A. D.; Douglas, T. A.; McClelland, J. W.; Khosh, M. S.; Barker, A. J.

2011-12-01

Models and observations predict that climate change will have more severe effects at higher latitudes. Many effects may already be underway. Increasing temperatures are expected to thaw permafrost soils, changing the hydrology and biogeochemistry of Arctic watersheds. These changes are particularly important because permafrost thaw could destabilize a large carbon reservoir, potentially leading to sizable greenhouse gas emissions. Tracking soil thaw and concomitant changes in carbon export are therefore critical to predicting feedbacks between Arctic climate change and global warming. As the climate warms, the seasonally thawed active layer will extend into deeper, previously frozen, mineral-rich soils, increasing the signal of chemical weathering in streams. Historical methods of monitoring active layer thaw depth are labor intensive and may not capture the heterogeneity of Arctic soils, whereas stream geochemistry provides a unique opportunity to integrate signals across vast spatial distances. We present major ion geochemistry and δ13C of dissolved inorganic carbon (DIC) variations that relate to seasonal changes in permafrost thaw depths. Samples were collected from six watersheds on the North Slope of Alaska. All rivers drain continuous permafrost but three drain tussock tundra-dominated watersheds and three drain bare bedrock catchments with minor tundra influences. Water samples were collected from April until October in 2009 and 2010. The major ion and δ13CDIC trends of tundra streams suggest that silicate weathering dominates during the spring melt while carbonate weathering dominates as the active layer deepens in the summer. In tundra streams, early season δ13CDIC values indicate carbonic acid-silicate weathering. Summer δ13CDIC values indicate carbonic acid-carbonate weathering. In both cases, carbonic acid forms from CO2 produced by the microbial decomposition of C3 organic matter. Bedrock streams have nearly constant δ13CDIC values and high dissolved sulfate concentrations through the year, indicating sulfuric acid-carbonate weathering. In late fall of 2010, δ13CDIC decreases in all streams suggest increased CO2 from a source with relatively negative δ13C values, possibly methane oxidation in soils. The difference between the tundra and bedrock streams allows us to clearly isolate the effect of soil thaw on stream geochemistry. Our initial findings illustrate how seasonal changes in mineral weathering have potential for tracking active layer dynamics.

Modeling hydrological controls on vegetation distribution across topography in Seward Peninsula, Alaska

NASA Astrophysics Data System (ADS)

Mekonnen, Z. A.; Riley, W. J.; Grant, R. F.; Salmon, V. G.; Iversen, C. M.; Biraud, S.; Breen, A. L.

2017-12-01

Observed changes in vegetation affect carbon and nutrient cycles in diverse landscapes of northern ecosystems. These changes can be affected by topography and landscape hydrology. We applied a coupled transect version of the ecosystem model ecosys in a landscape underlain by impermeable permafrost at Kougarok, Alaska to examine hydrological controls on watershed-scale vegetation distributions. Our preliminary results indicate strong relationships between vegetation distribution and soil physical and hydraulic properties that control water, nutrients, and energy flows across the hillslope. Modeled differences in aboveground biomass across the Kougarok hillslope had a good agreement (R2 0.80) with preliminary biomass measurements from the NGEE-Arctic project in summer 2016. Low soil water content from shallower soil depth and lateral flow of water and nutrients in the upper slope position of the hillslope resulted in water stress and low N mineralization for plants with deeper roots. The middle slope position had intermediate soil moisture from deeper soil and higher N mineralization that favoured fast-growing and deep-rooted plants. The gentle slope and deeper soil in the lower slope position resulted in saturated soil, thus reduced O2 for microbes, hence favouring plants with higher root porosity. Earth system models that do not account for the underlying mechanisms of surface and sub-surface flows of water, nutrients, and energy may not predict these types of dynamics in Arctic ecosystems.

[Effects of ridge-cultivation and plastic film mulching on root distribution and yield of spring maize in hilly area of central Sichuan basin, China.

PubMed

Zha, Li; Xie, Meng Lin; Zhu, Min; Dou, Pan; Cheng, Qiu Bo; Wang, Xing Long; Yuan, Ji Chao; Kong, Fan Lei

2016-03-01

A field experiment was conducted to study the effects of planting pattern (ridge culture, flatten culture, furrow culture) and film mulching on the distribution of spring maize root system and their influence on the yield of spring maize in the hilly area of central Sichuan basin. The results showed that ridge and film mulching had great influence on root morphology and root distribution of maize. The root length, root surface area and root volume of film mulching was 42.3%, 50.0%, 57.4% higher than those of no film mulching at jointing stage. The film mulching significantly increased the dry mass of root in vertical and horizontal distribution, and increased the root allocation ratio in deeper soil layer (20-40 cm) and the allocation ratio of wide row (0-20 cm) in horizontal direction. The effects of planting pattern on root growth and root distribution differed by film mulching. With film mulching, the ridge culture significantly increased the root dry mass in each soil layer and enlarged the distribution percentage of wide row (20-40 cm) in horizontal direction, as well as the dry mass of root in horizontal distribution and the root allocation ratio of wide row. The root mass under film mulching was in the order of ridge culture>flatten culture>furrow culture. Without film mulching, the furrow culture significantly increased root dry mass of narrow row (0-40 cm), and the root mass under no film mulching was in the order of furrow culture > ridge culture >flatten culture. As for the spike characteristics and maize yield, the filming mulching mea-sures reduced the corn bald length while increased the spike length, grain number, 1000-grain mass and yield. The yield under film mulching was in the order of ridge culture>flatten culture> furrow culture, while it was furrow culture > flatten culture > ridge culture under no film mulching. The reason for yield increase under ridge culture with film mulching was that it increased root weight especially in deep soil, and promoted the root allocation ratio in deeper soil and wide row (20-40 cm) in horizontal direction. The ridge-furrow culture without film mulching was helpful to root growth and increased the maize yield.

Magnetic mapping of distribution of wood ash used for fertilization of forest soil.

PubMed

Petrovský, Eduard; Remeš, Jiří; Kapička, Aleš; Podrázský, Vilém; Grison, Hana; Borůvka, Luboš

2018-06-01

The effect of wood-ash fertilization on forest soils has been assessed mainly through geochemical methods (e.g., content of soil organic matter or nutrients). However, a simple and fast method of determining the distribution of the ash and the extent of affected soil is missing. In this study we present the use of magnetic susceptibility, which is controlled by Fe-oxides, in comparing the fertilized soil in the forest plantation of pine and oak with intact forest soil. Spatial and vertical distribution of magnetic susceptibility was measured in an oak and pine plantation next to stems of young plants, where wood ash was applied as fertilizer. Pattern of the susceptibility distribution was compared with that in non-fertilized part of the plantation as well as with a spot of intact natural forest soil nearby. Our results show that the wood-ash samples contain significant amount of ferrimagnetic magnetite with susceptibility higher than that of typical forest soil. Clear differences were observed between magnetic susceptibility of furrows and ridges. Moreover, the dispersed ash remains practically on the surface, does not penetrate to deeper layers. Finally, our data suggest significant differences in surface values between the pine and oak plants. Based on this study we may conclude that magnetic susceptibility may represent a simple and approximate method of assessing the extent of soil affected by wood-ash. Copyright © 2018 Elsevier B.V. All rights reserved.

Effects of Pisha sandstone content on solute transport in a sandy soil.

PubMed

Zhen, Qing; Zheng, Jiyong; He, Honghua; Han, Fengpeng; Zhang, Xingchang

2016-02-01

In sandy soil, water, nutrients and even pollutants are easily leaching to deeper layers. The objective of this study was to assess the effects of Pisha sandstone on soil solute transport in a sandy soil. The miscible displacement technique was used to obtain breakthrough curves (BTCs) of Br(-) as an inert non-adsorbed tracer and Na(+) as an adsorbed tracer. The incorporation of Pisha sandstone into sandy soil was able to prevent the early breakthrough of both tracers by decreasing the saturated hydraulic conductivity compared to the controlled sandy soil column, and the impeding effects increased with Pisha sandstone content. The BTCs of Br(-) were accurately described by both the convection-dispersion equation (CDE) and the two-region model (T-R), and the T-R model fitted the experimental data slightly better than the CDE. The two-site nonequilibrium model (T-S) accurately fit the Na(+) transport data. Pisha sandstone impeded the breakthrough of Na(+) not only by decreasing the saturated hydraulic conductivity but also by increasing the adsorption capacity of the soil. The measured CEC values of Pisha sandstone were up to 11 times larger than those of the sandy soil. The retardation factors (R) determined by the T-S model increased with increasing Pisha sandstone content, and the partition coefficient (K(d)) showed a similar trend to R. According to the results of this study, Pisha sandstone can successfully impede solute transport in a sandy soil column. Copyright © 2015 Elsevier Ltd. All rights reserved.

Mapping Spatial Variability of Soil Salinity in a Coastal Paddy Field Based on Electromagnetic Sensors

PubMed Central

Guo, Yan; Huang, Jingyi; Shi, Zhou; Li, Hongyi

2015-01-01

In coastal China, there is an urgent need to increase land area for agricultural production and urban development, where there is a rapid growing population. One solution is land reclamation from coastal tidelands, but soil salinization is problematic. As such, it is very important to characterize and map the within-field variability of soil salinity in space and time. Conventional methods are often time-consuming, expensive, labor-intensive, and unpractical. Fortunately, proximal sensing has become an important technology in characterizing within-field spatial variability. In this study, we employed the EM38 to study spatial variability of soil salinity in a coastal paddy field. Significant correlation relationship between ECa and EC1:5 (i.e. r >0.9) allowed us to use EM38 data to characterize the spatial variability of soil salinity. Geostatistical methods were used to determine the horizontal spatio-temporal variability of soil salinity over three consecutive years. The study found that the distribution of salinity was heterogeneous and the leaching of salts was more significant in the edges of the study field. By inverting the EM38 data using a Quasi-3D inversion algorithm, the vertical spatio-temporal variability of soil salinity was determined and the leaching of salts over time was easily identified. The methodology of this study can be used as guidance for researchers interested in understanding soil salinity development as well as land managers aiming for effective soil salinity monitoring and management practices. In order to better characterize the variations in soil salinity to a deeper soil profile, the deeper mode of EM38 (i.e., EM38v) as well as other EMI instruments (e.g. DUALEM-421) can be incorporated to conduct Quasi-3D inversions for deeper soil profiles. PMID:26020969

Mapping spatial variability of soil salinity in a coastal paddy field based on electromagnetic sensors.

PubMed

Guo, Yan; Huang, Jingyi; Shi, Zhou; Li, Hongyi

2015-01-01

In coastal China, there is an urgent need to increase land area for agricultural production and urban development, where there is a rapid growing population. One solution is land reclamation from coastal tidelands, but soil salinization is problematic. As such, it is very important to characterize and map the within-field variability of soil salinity in space and time. Conventional methods are often time-consuming, expensive, labor-intensive, and unpractical. Fortunately, proximal sensing has become an important technology in characterizing within-field spatial variability. In this study, we employed the EM38 to study spatial variability of soil salinity in a coastal paddy field. Significant correlation relationship between ECa and EC1:5 (i.e. r >0.9) allowed us to use EM38 data to characterize the spatial variability of soil salinity. Geostatistical methods were used to determine the horizontal spatio-temporal variability of soil salinity over three consecutive years. The study found that the distribution of salinity was heterogeneous and the leaching of salts was more significant in the edges of the study field. By inverting the EM38 data using a Quasi-3D inversion algorithm, the vertical spatio-temporal variability of soil salinity was determined and the leaching of salts over time was easily identified. The methodology of this study can be used as guidance for researchers interested in understanding soil salinity development as well as land managers aiming for effective soil salinity monitoring and management practices. In order to better characterize the variations in soil salinity to a deeper soil profile, the deeper mode of EM38 (i.e., EM38v) as well as other EMI instruments (e.g. DUALEM-421) can be incorporated to conduct Quasi-3D inversions for deeper soil profiles.

Runoff sources and flowpaths in a partially burned, upland boreal catchment underlain by permafrost

USGS Publications Warehouse

Koch, Joshua C.; Kikuchi, Colin P.; Wickland, Kimberly P.; Schuster, Paul

2014-01-01

Boreal soils in permafrost regions contain vast quantities of frozen organic material that is released to terrestrial and aquatic environments via subsurface flowpaths as permafrost thaws. Longer flowpaths may allow chemical reduction of solutes, nutrients, and contaminants, with implications for greenhouse gas emissions and aqueous export. Predicting boreal catchment runoff is complicated by soil heterogeneities related to variability in active layer thickness, soil type, fire history, and preferential flow potential. By coupling measurements of permeability, infiltration potential, and water chemistry with a stream chemistry end member mixing model, we tested the hypothesis that organic soils and burned slopes are the primary sources of runoff, and that runoff from burned soils is greater due to increased hydraulic connectivity. Organic soils were more permeable than mineral soils, and 25% of infiltration moved laterally upon reaching the organic-mineral soil boundary on unburned hillslopes. A large portion of the remaining water infiltrated into deeper, less permeable soils. In contrast, burned hillslopes displayed poorly defined soil horizons, allowing rapid, mineral-rich runoff through preferential pathways at various depths. On the catchment scale, mineral/organic runoff ratios averaged 1.6 and were as high as 5.2 for an individual storm. Our results suggest that burned soils are the dominant source of water and solutes reaching the stream in summer, whereas unburned soils may provide longer term storage and residence times necessary for production of anaerobic compounds. These results are relevant to predicting how boreal catchment drainage networks and stream export will evolve given continued warming and altered fire regimes.

Ulex europaeus I and glycine max bind to the human olfactory bulb.

PubMed

Nagao, M; Oka, N; Kamo, H; Akiguchi, I; Kimura, J

1993-12-24

The distribution of binding sites for the fucose-selective lectin Ulex europaeus I and the terminal N-acetylgalactosamine-selective lectin glycine max in the human olfactory bulb were studied. These lectins bound to primary olfactory axons in the olfactory nerve layer and the glomerular layer. They also bound to fibers located in the deeper layers such as the external plexiform layer and the granular layer. Furthermore they projected to the olfactory stalk but not in the cerebrum. The deeper projections of the lectin binding fibers may affect the function of the olfactory bulb in humans.

Regional estimation of catchment-scale soil properties by means of streamflow recession analysis for use in distributed hydrological models

NASA Astrophysics Data System (ADS)

Vannier, Olivier; Braud, Isabelle; Anquetin, Sandrine

2013-04-01

The estimation of catchment-scale soil properties, such as water storage capacity and hydraulic conductivity, is of primary interest for the implementation of distributed hydrological models at the regional scale. This estimation is generally done on the basis of information provided by soil databases. However, such databases are often established for agronomic uses and generally do not document deep weathered rock horizons (i.e. pedologic horizons of type C and deeper), which can play a major role in water transfer and storages. Here we define the Drainable Storage Capacity Index (DSCI), an indicator that relies on the comparison of cumulated streamflow and precipitation to assess catchment-scale storage capacities. The DSCI is found to be reliable to detect underestimation of soil storage capacities in soil databases. We also use the streamflow recession analysis methodology defined by Brutsaert and Nieber (Water Resources Research 13(3), 1977) to estimate water storage capacities and lateral saturated hydraulic conductivities of the non-documented deep horizons. The analysis is applied to a sample of twenty-three catchments (0.2 km² - 291 km²) located in the Cévennes-Vivarais region (south of France). In a regionalisation purpose, the obtained results are compared to the dominant catchments geology. This highlights a clear hierarchy between the different geologies present in the area. Hard crystalline rocks are found to be associated to the thickest and less conductive deep soil horizons. Schist rocks present intermediate values of thickness and of saturated hydraulic conductivity, whereas sedimentary rocks and alluvium are found to be the less thick and the most conductive. Consequently, deep soil layers with thicknesses and hydraulic conductivities differing with the geology were added to a distributed hydrological model implemented over the Cévennes-Vivarais region. Preliminary simulations show a major improvement in terms of simulated discharge when compared to simulations done without deep soil layers. KEY WORDS: hydraulic soil properties, streamflow recession, deep soil horizons, soil databases, Boussinesq equation, storage capacity, regionalisation

The relative importance of decomposition and transport mechanisms in accounting for C profiles

NASA Astrophysics Data System (ADS)

Guenet, B.; Eglin, T.; Vasilyeva, N.; Peylin, P.; Ciais, P.; Chenu, C.

2012-10-01

Soil is the major terrestrial reservoirs of carbon, and a substantial part of this carbon is stored in deep layers, typically deeper than 50 cm below the surface. Several studies underlined the quantitative importance of this deep Soil Organic Carbon (SOC) pool and models are needed to better understand this stock and its evolution under climate and land-uses changes. In this study, we test and compare 3 simple theoretical models of vertical transport for SOC against SOC profiles measurements from a long-term bare fallow experiment carried out by the Central-Chernozem State Natural Biosphere Reserve named after V.V. Alekhin, in the Kursk Region of Russia. The transport schemes tested are diffusion, advection or both diffusion and advection. They are coupled to two different formulations of soil carbon decomposition kinetics. The first formulation is a first order kinetics widely used in global SOC decomposition models; the second one links SOC decomposition rate to the amount of fresh organic matter, representing a "priming effect". Field data are from a set of three bare fallow plots where soil received no input during the past 20, 26 and 58 yr respectively. Parameters of the models were optimized using a Bayesian method. The best results are obtained when SOC decomposition is assumed to be controlled by fresh organic matter. In comparison to the first-order kinetic model, the "priming" model reduces the underestimation of SOC decomposition in the top layers and the over estimation in the deep layers. We also observe that the transport scheme that improved the fit with the data depends on the soil carbon mineralization formulation chosen. When soil carbon decomposition is modelled to depend on the fresh organic matter amount, the transport mechanisms which improves best the fit to the SOC profile data is the model representing both advection and diffusion. Interestingly, the older the bare fallow is, the lesser the need for diffusion is. This suggests that stabilized carbon may not be transported within the profile by the same mechanisms than more labile carbon.

Global distribution of soil organic carbon, based on the Harmonized World Soil Database - Part 1: Masses and frequency distribution of SOC stocks for the tropics, permafrost regions, wetlands, and the world

NASA Astrophysics Data System (ADS)

Köchy, M.; Hiederer, R.; Freibauer, A.

2014-09-01

The global soil organic carbon (SOC) mass is relevant for the carbon cycle budget. We review current estimates of soil organic carbon stocks (mass/area) and mass (stock × area) in wetlands, permafrost and tropical regions and the world in the upper 1 m of soil. The Harmonized World Soil Database (HWSD) v.1.2 provides one of the most recent and coherent global data sets of SOC, giving a total mass of 2476 Pg. Correcting the HWSD's bulk density of organic soils, especially Histosols, results in a mass of 1062 Pg. The uncertainty of bulk density of Histosols alone introduces a range of -56 to +180 Pg for the estimate of global SOC in the top 1 m, larger than estimates of global soil respiration. We report the spatial distribution of SOC stocks per 0.5 arc minutes, the areal masses of SOC and the quantiles of SOC stocks by continents, wetland types, and permafrost types. Depending on the definition of "wetland", wetland soils contain between 82 and 158 Pg SOC. Incorporating more detailed estimates for permafrost from the Northern Circumpolar Soil Carbon Data Base (496 Pg SOC) and tropical peatland carbon, global soils contain 1324 Pg SOC in the upper 1 m including 421 Pg in tropical soils, whereof 40 Pg occur in tropical wetlands. Global SOC amounts to just under 3000 Pg when estimates for deeper soil layers are included. Variability in estimates is due to variation in definitions of soil units, differences in soil property databases, scarcity of information about soil carbon at depths > 1 m in peatlands, and variation in definitions of "peatland".

Accumulation of free amino acids during exposure to drought in three springtail species.

PubMed

Holmstrup, Martin; Slotsbo, Stine; Rozsypal, Jan; Henriksen, Per G; Bayley, Mark

2015-11-01

Springtails are closely related to insects, but they differ from these with respect to water balance, in particular because springtails are small and have high integumental permeability to water. Here we report a series of experiments addressing the dynamics of osmoregulation, water content and accumulation of free amino acids (FAAs) in three springtail species during exposure to a gradually increasing environmental desiccation simulating conditions in drought exposed soil. Folsomia candida and Protaphorura fimata (both living in the deeper soil layers; euedaphic species) were active throughout the 3week exposure, with the developing drought regime ending at -3.56MPa (the soil water activity at the permanent wilting point of plants is -1.5MPa) and remained hyperosmotic (having an body fluid osmolality higher than the corresponding environment) to their surrounding air. Sinella curviseta (living in upper soil/litter layers; hemiedaphic species) also survived this exposure, but remained hypoosmotic throughout (i.e. with lower osmolality than the environment). The body content of most FAAs increased in response to drought in all three species. Alanine, proline and arginine were the most significantly upregulated FAAs. By combining our results with data in the literature, we could account for 82% of the observed osmolality at -3.56MPa in F. candida and 92% in P. fimata. The osmolality of S. curviseta was only slightly increased under drought, but here FAAs were considerably more important as osmolytes than in the two other species. We propose that FAAs probably have general importance in drought tolerance of springtails. Copyright © 2015 Elsevier Ltd. All rights reserved.

A model of the CO2 exchanges between biosphere and atmosphere in the tundra

NASA Technical Reports Server (NTRS)

Labgaa, Rachid R.; Gautier, Catherine

1992-01-01

A physical model of the soil thermal regime in a permafrost terrain has been developed and validated with soil temperature measurements at Barrow, Alaska. The model calculates daily soil temperatures as a function of depth and average moisture contents of the organic and mineral layers using a set of five climatic variables, i.e., air temperature, precipitation, cloudiness, wind speed, and relative humidity. The model is not only designed to study the impact of climate change on the soil temperature and moisture regime, but also to provide the input to a decomposition and net primary production model. In this context, it is well known that CO2 exchanges between the terrestrial biosphere and the atmosphere are driven by soil temperature through decomposition of soil organic matter and root respiration. However, in tundra ecosystems, net CO2 exchange is extremely sensitive to soil moisture content; therefore it is necessary to predict variations in soil moisture in order to assess the impact of climate change on carbon fluxes. To this end, the present model includes the representation of the soil moisture response to changes in climatic conditions. The results presented in the foregoing demonstrate that large errors in soil temperature and permafrost depth estimates arise from neglecting the dependence of the soil thermal regime on soil moisture contents. Permafrost terrain is an example of a situation where soil moisture and temperature are particularly interrelated: drainage conditions improve when the depth of the permafrost increases; a decrease in soil moisture content leads to a decrease in the latent heat required for the phase transition so that the heat penetrates faster and deeper, and the maximum depth of thaw increases; and as excepted, soil thermal coefficients increase with moisture.

Urban soils as hotspots of anthropogenic carbon accumulation: Review of stocks, mechanisms and factors

NASA Astrophysics Data System (ADS)

Vasenev, Viacheslav; Kuzyakov, Yakov

2017-04-01

Urban soils and cultural layers accumulate carbon (C) over centuries and consequently large C stocks are sequestered below the cities. These C stocks as well as the full range of processes and mechanisms leading to high C accumulation in urban soils remain unknown. We collected data on organic (SOC), inorganic (SOC) and black (pyrogenic) (BC) C content in urban and natural soils from 100 papers based on Scopus and Web-of-Knowledge databases. The yielded database includes 770 values on SOC, SIC and BC stocks from 118 cities worldwide. The collected data were analyzed considering the effects of climatic conditions and urban-specific factors: city size, age and functional zoning. For the whole range of climatic conditions, the C contents in urban soils were 1.5-3 times higher than in respective natural soils. This higher C content and much deeper C accumulation in urban soils resulted in 3 to 5 times higher C stocks compared to natural soils. Urban SOC stocks were positively correlated with latitude, whereas SIC stocks were less affected by climate. The city size and age were the main factors controlling intra-city variability of C stocks with higher stocks in small cities compared to megapolises and in medieval compared to new cities. The inter-city variability of C stocks was dominated by functional zoning: large SOC and N stocks in residential areas and large SIC and BC stocks in industrial zones and roadsides were similar for all climates and for cities of different size and age. Substantial stocks of SOC, SIC and N were sequestered for long-term in the subsoils and cultural layers of the sealed soils, which underline the importance of these 'hidden' stocks for C assessments. Typical and specific for urban soils is that the anthropogenic factor overshadows the other five factors of soil formation. Substantial C stocks in urban soils and cultural layers result from specific mechanisms of C accumulation in cities: i) large and long-term C inputs from outside the city (e.g. suburban, agricultural and forest areas), and ii) C accumulation in parallel with upward soil growing without complete mineralization (common in natural soils). These mechanisms result over long period in gradual growing-up of urban soils and C accumulation. The average rate of urban soils' uprising growth of 50 cm per century and the average SOC contents of 3-5% led conclude that urban soils accumulate 15-30 kg C m-2 per century without steady state (common for all natural soils). These factors lead to high potential of urban soils for long-term C sequestration. We conclude that despite small area under the cities, urban soils are hotspots of belowground long-term C sequestration worldwide and the importance of urban soils will increase in future with global urbanization.

Preservation of Lipid Biomarkers Under Prolonged and Extreme Hyperaridity in Atacama Desert Soils

NASA Technical Reports Server (NTRS)

Wilhelm, Mary Beth

2015-01-01

Molecular biomarkers are the most direct biosignatures of life on early Earth and a key target in the search for life on Mars. Lipid biomarkers are of particular interest given their ability to survive oxidative degradation and record microbial presence and activity of microorganisms that occurred billions of years ago (Eigenbrode, 2008). Environmental conditions that suspend biotic and abiotic degradative processes prior to lithification can lead to enhanced biomolecular preservation over geological time-scales. The hyperarid core of the Atacama Desert in northern Chile offers a unique environment to investigate lipid biomarker taphonomy under extreme and prolonged dryness. We investigated the accumulation and degree of preservation of lipid biomarkers in million-year-old hyperarid soils where primarily abiotic conditions influence their taphonomy. Soils were extracted and free and membrane bound lipids were analyzed across a vertical profile of 2.5 meters in the Yungay hyper-arid core of the Atacama Desert. Due to the extremely low inventory of biomass in Atacama soils, samples were collected by scientists wearing cleanroom suits to minimize anthropogenic contamination during sampling. Fatty acids were found to be well preserved in Yungay soils, and were most abundant in the clay-rich soils at approx.2 m depth (approx.750 ng of fatty acid methyl ester/g of soil). These buried clays layers were fluvially deposited approximately 2 million years ago, and have been excluded from exposure to rainwater and modern surficial processes since their emplacement (Ewing et al., 2008). Monocarboxylic fatty acid, monohydroxy fatty acid, glycerol tetraether, and n-alkane hydrocarbon content was found to change with depth. Lipid biomarker content in deeper soil layers is suggestive of soils having been formed at a time when environmental conditions were capable of supporting active microbial communities and plants. In short, total lipid extracts reveal a remarkable degree of lipid biomarker preservation even in the oldest soils analyzed (ca. 2 Myr) indicating that typical diagenetic processes of lipid destruction are arrested under extreme dryness. This result has implications for the search for molecular biomarkers on Mars, which could have experienced millions to billions of years of extreme hyperaridity.

Preservation of Lipid Biomarkers Under Prolonged and Extreme Hyperaridity in Atacama Desert Soils

NASA Astrophysics Data System (ADS)

Wilhelm, M. B.; Davila, A. F.; Eigenbrode, J. L.; Parenteau, M. N.; Jahnke, L. L.; Summons, R. E.; Liu, X.; Wray, J. J.; Stamos, B.; O'Reilly, S. S.; Williams, A. J.

2015-12-01

Molecular biomarkers are the most direct biosignatures of life on early Earth and a key target in the search for life on Mars. Lipid biomarkers are of particular interest given their ability to survive oxidative degradation and record microbial presence and activity of microorganisms that occurred billions of years ago (Eigenbrode, 2008). Environmental conditions that suspend biotic and abiotic degradative processes prior to lithification can lead to enhanced biomolecular preservation over geological time-scales. The hyperarid core of the Atacama Desert in northern Chile offers a unique environment to investigate lipid biomarker taphonomy under extreme and prolonged dryness. We investigated the accumulation and degree of preservation of lipid biomarkers in million-year-old hyperarid soils where primarily abiotic conditions influence their taphonomy. Soils were extracted and free and membrane bound lipids were analyzed across a vertical profile of 2.5 meters in the Yungay hyper-arid core of the Atacama Desert. Due to the extremely low inventory of biomass in Atacama soils, samples were collected by scientists wearing cleanroom suits to minimize anthropogenic contamination during sampling. Fatty acids were found to be well preserved in Yungay soils, and were most abundant in the clay-rich soils at ~2 m depth (~750 ng of fatty acid methyl ester/g of soil). These buried clays layers were fluvially deposited approximately 2 million years ago, and have been excluded from exposure to rainwater and modern surficial processes since their emplacement (Ewing et al., 2008). Monocarboxylic fatty acid, monohydroxy fatty acid, glycerol tetraether, and n-alkane hydrocarbon content was found to change with depth. Lipid biomarker content in deeper soil layers is suggestive of soils having been formed at a time when environmental conditions were capable of supporting active microbial communities and plants. In short, total lipid extracts reveal a remarkable degree of lipid biomarker preservation even in the oldest soils analyzed (ca. 2 Myr) indicating that typical diagenetic processes of lipid destruction are arrested under extreme dryness. This result has implications for the search for molecular biomarkers on Mars, which could have experienced millions to billions of years of extreme hyperaridity.

Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps

DOE PAGES

Hugelius, Gustaf; Strauss, J.; Zubrzycki, S.; ...

2014-12-01

Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but SOC stock estimates were poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of permafrost SOC stocks, including quantitative uncertainty estimates, in the 0–3 m depth range in soils as well as for sediments deeper than 3 m in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. Revised estimates are based on significantly larger databases compared tomore » previous studies. Despite this there is evidence of significant remaining regional data gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for deposits below 3 m depth in deltas and the Yedoma region. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are substantial differences in other components, including the fraction of perennially frozen SOC. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 ± 12 and 472 ± 27 Pg for the 0–0.3 and 0–1 m soil depths, respectively (±95% confidence intervals). Storage of SOC in 0–3 m of soils is estimated to 1035 ± 150 Pg. Of this, 34 ± 16 Pg C is stored in poorly developed soils of the High Arctic. Based on generalized calculations, storage of SOC below 3 m of surface soils in deltaic alluvium of major Arctic rivers is estimated as 91 ± 52 Pg. In the Yedoma region, estimated SOC stocks below 3 m depth are 181 ± 54 Pg, of which 74 ± 20 Pg is stored in intact Yedoma (late Pleistocene ice- and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits. Total estimated SOC storage for the permafrost region is ∼1300 Pg with an uncertainty range of ∼1100 to 1500 Pg. Of this, ∼500 Pg is in non-permafrost soils, seasonally thawed in the active layer or in deeper taliks, while ∼800 Pg is perennially frozen. In conclusion, this represents a substantial ∼300 Pg lowering of the estimated perennially frozen SOC stock compared to previous estimates.« less

Limitations for phytoextraction management on metal-polluted soils with poplar short rotation coppice-evidence from a 6-year field trial.

PubMed

Michels, E; Annicaerta, B; De Moor, S; Van Nevel, L; De Fraeye, M; Meiresonne, L; Vangronsveld, J; Tack, F M G; Ok, Y S; Meers, Erik

2018-01-02

Poplar clones were studied for their phytoextraction capacity in the second growth cycle (6-year growth) on a site in the Belgian Campine region, which is contaminated with Cd and Zn via historic atmospheric deposition of nearby zinc smelter activities. The field trial revealed regrowth problems for some clones that could not be predicted in the first growth cycle. Four allometric relations were assessed for their capacity to predict biomass yield in the second growth cycle. A power function based on the shoot diameter best estimates the biomass production of poplar with R 2 values between 0.94 and 0.98. The woody biomass yield ranged from 2.1 to 4.8 ton woody Dry Mass (DM) ha -1 y -1 . The primary goal was to reduce soil concentrations of metals caused by phytoextraction. Nevertheless, increased metal concentrations were determined in the topsoil. This increase can partially be explained by the input of metals from deeper soil layers in the top soil through litterfall. The phytoextraction option with poplar short rotation coppice in this setup did not lead to the intended soil remediation in a reasonable time span. Therefore, harvest of the leaf biomass is put forward as a crucial part of the strategy for soil remediation through Cd/Zn phytoextraction.

Dro1, a major QTL involved in deep rooting of rice under upland field conditions.

PubMed

Uga, Yusaku; Okuno, Kazutoshi; Yano, Masahiro

2011-05-01

Developing a deep root system is an important strategy for avoiding drought stress in rice. Using the 'basket' method, the ratio of deep rooting (RDR; the proportion of total roots that elongated through the basket bottom) was calculated to evaluate deep rooting. A new major quantitative trait locus (QTL) controlling RDR was detected on chromosome 9 by using 117 recombinant inbred lines (RILs) derived from a cross between the lowland cultivar IR64, with shallow rooting, and the upland cultivar Kinandang Patong (KP), with deep rooting. This QTL explained 66.6% of the total phenotypic variance in RDR in the RILs. A BC(2)F(3) line homozygous for the KP allele of the QTL had an RDR of 40.4%, compared with 2.6% for the homozygous IR64 allele. Fine mapping of this QTL was undertaken using eight BC(2)F(3) recombinant lines. The RDR QTL Dro1 (Deeper rooting 1) was mapped between the markers RM24393 and RM7424, which delimit a 608.4 kb interval in the reference cultivar Nipponbare. To clarify the influence of Dro1 in an upland field, the root distribution in different soil layers was quantified by means of core sampling. A line homozygous for the KP allele of Dro1 (Dro1-KP) and IR64 did not differ in root dry weight in the shallow soil layers (0-25 cm), but root dry weight of Dro1-KP in deep soil layers (25-50 cm) was significantly greater than that of IR64, suggesting that Dro1 plays a crucial role in increased deep rooting under upland field conditions.

Improving Simulated Soil Moisture Fields Through Assimilation of AMSR-E Soil Moisture Retrievals with an Ensemble Kalman Filter and a Mass Conservation Constraint

NASA Technical Reports Server (NTRS)

Li, Bailing; Toll, David; Zhan, Xiwu; Cosgrove, Brian

2011-01-01

Model simulated soil moisture fields are often biased due to errors in input parameters and deficiencies in model physics. Satellite derived soil moisture estimates, if retrieved appropriately, represent the spatial mean of soil moisture in a footprint area, and can be used to reduce model bias (at locations near the surface) through data assimilation techniques. While assimilating the retrievals can reduce model bias, it can also destroy the mass balance enforced by the model governing equation because water is removed from or added to the soil by the assimilation algorithm. In addition, studies have shown that assimilation of surface observations can adversely impact soil moisture estimates in the lower soil layers due to imperfect model physics, even though the bias near the surface is decreased. In this study, an ensemble Kalman filter (EnKF) with a mass conservation updating scheme was developed to assimilate the actual value of Advanced Microwave Scanning Radiometer (AMSR-E) soil moisture retrievals to improve the mean of simulated soil moisture fields by the Noah land surface model. Assimilation results using the conventional and the mass conservation updating scheme in the Little Washita watershed of Oklahoma showed that, while both updating schemes reduced the bias in the shallow root zone, the mass conservation scheme provided better estimates in the deeper profile. The mass conservation scheme also yielded physically consistent estimates of fluxes and maintained the water budget. Impacts of model physics on the assimilation results are discussed.

The influence of land use on the concentration and vertical distribution of PBDEs in soils of an e-waste recycling region of South China.

PubMed

Cheng, Zhineng; Wang, Yan; Wang, Shaorui; Luo, Chunling; Li, Jun; Chaemfa, Chakra; Jiang, Haoyu; Zhang, Gan

2014-08-01

The vertical distribution of polybrominated diphenyl ethers (PBDEs) in soil at four sites within an e-waste recycling region of South China was investigated. PBDE concentrations in soil ranged from 1.38 to 765 ng/g. There was a trend of decreasing PBDE concentration with soil depth, especially in the paddy field. However, high concentrations of BDE-209 were found in deeper soils indicating a highly preferential migration. There was a stronger correlation between PBDEs and total organic carbon (TOC), compared to dissolved organic carbon (DOC), which suggests that the association between non-dissolved organic carbon (NDOC) and PBDEs is stronger than for DOC. Different land use types, in particular differences in farming activities, significantly influenced the vertical distribution of PBDEs in soils. PBDEs displayed a higher leaching tendency in moist paddy soil than in drier soils. The frequent flooding condition in paddy field may facilitate the vertical transfer of PBDEs to the deeper soils. Copyright © 2014 Elsevier Ltd. All rights reserved.

Impacts of hydraulic redistribution on overstory-understory interactions in a semiarid savanna

NASA Astrophysics Data System (ADS)

Barron-Gafford, G.; Minor, R. L.; Hendryx, S.; Lee, E.; Sutter, L., Jr.; Colella, A.; Murphy, P.; Sanchez-Canete, E. P.; Hamerlynck, E. P.; Kumar, P.; Scott, R. L.

2016-12-01

Hydraulic redistribution (HR) is an important ecohydrological process in dryland environments by which plants preferentially move water from wet to dry soil layers. How does this water movement by the overstory influence physiological activity in the understory? Are there periods of facilitation when the tree is lifting water and periods of competition when the water is being moved deeper in the profile? We combined trunk, lateral root, and taproot sap flow data, and linked these measures with shallow and deep soil moisture data to show that soil moisture gradients control hydraulic redistribution in overstory mesquite trees. During prolonged inter-rain periods of drought and in response to periods of high vapor pressure deficits, mesquites drew upon this deeper, stored water to meet biological demands. We created plots under mesquite that experienced HR and plots where HR was physically prohibited to quantify the impacts of HR on understory performance. We measured carbon and water exchange at the leaf-level on mesquite and understory grass and for entire understory ecosystem using a large, portable chamber. We found that HR provided a drought-buffering capacity for the overstory mesquite and a significant decrease in mesquite photosynthesis in trees where the capacity for HR was reduced. While we had hypothesized that water lifted by the mesquite in periods of drought would facilitate understory grass function, we found no evidence for this. In fact, we found that grasses actually conducted higher rates of photosynthesis in plots where HR was eliminated. Ultimately, we found that HR in upland savannas, where there is little to no access to deep water, yields a competitive interaction between overstory mesquites and understory grasses at the scale of individual precipitation pulse events and across entire growing seasons.

Archaeal diversity and the extent of iron and manganese pyritization in sediments from a tropical mangrove creek (Cardoso Island, Brazil)

NASA Astrophysics Data System (ADS)

Otero, X. L.; Lucheta, A. R.; Ferreira, T. O.; Huerta-Díaz, M. A.; Lambais, M. R.

2014-06-01

Even though several studies on the geochemical processes occurring in mangrove soils and sediments have been performed, information on the diversity of Archaea and their functional roles in these ecosystems, especially in subsurface environments, is scarce. In this study, we have analyzed the depth distribution of Archaea and their possible relationships with the geochemical transformations of Fe and Mn in a sediment core from a tropical mangrove creek, using 16S rRNA gene profiling and sequential extraction of different forms of Fe and Mn. A significant shift in the archaeal community structure was observed in the lower layers (90-100 cm), coinciding with a clear decrease in total organic carbon (TOC) content and an increase in the percentage of sand. The comparison of the archaeal communities showed a dominance of methanogenic Euryarchaeota in the upper layers (0-20 cm), whereas Crenarchaeota was the most abundant taxon in the lower layers. The dominance of methanogenic Euryarchaeota in the upper layer of the sediment suggests the occurrence of methanogenesis in anoxic microenvironments. The concentrations of Fe-oxyhydroxides in the profile were very low, and showed positive correlation with the concentrations of pyrite and degrees of Fe and Mn pyritization. Additionally, a partial decoupling of pyrite formation from organic matter concentration was observed, suggesting excessive Fe pyritization. This overpyritization of Fe can be explained either by the anoxic oxidation of methane by sulfate and/or by detrital pyrite tidal transportation from the surrounding mangrove soils. The higher pyritization levels observed in deeper layers of the creek sediment were also in agreement with its Pleistocenic origin.

Pleistocene permafrost features in soils in the South-western Italian Alps

NASA Astrophysics Data System (ADS)

D'Amico, Michele; Catoni, Marcella; Bonifacio, Eleonora; Zanini, Ermanno

2015-04-01

Because of extensive Pleistocenic glaciations which erased most of the previously existing soils, slope steepness and climatic conditions favoring soil erosion, most soils observed on the Alps (and in other mid-latitude mountain ranges) developed only during the Holocene. However, in few sites, particularly in the outermost sections of the Alpine range, Pleistocene glaciers covered only small and scattered surfaces because of the low altitude reached in the basins, and ancient soils could be preserved for long periods of time on particularly stable surfaces. In some cases, these soils retain good memories of past periglacial activity. We described and sampled soils on stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern Piemonte, Italy). The sampling sites were between 600 to 1600 m of altitude, under present day lower montane Castanea sativa/Ostrya carpinifolia forests, montane Fagus sylvatica and Pinus uncinata forests or montane heath/grazed grassland, on different quartzitic substrata. The surface morphology often showed strongly developed, fossil periglacial patterned ground forms, such as coarse stone circles on flat surfaces, or stone stripes on steeper slopes. The stone circles could be up to 5 m wide, while the sorted stripes could be as wide as 12-15 m. A strong lateral cryogenic textural sorting characterized the fine fraction too, with sand dominating close to the stone rims of the patterned ground features and silt and clay the central parts. The surface 60-120 cm of the soils were podzolized during the Holocene; as a result of the textural lateral sorting, the thickness of the podzolic E and Bs horizons varied widely across the patterns. The lower boundary of the Holocene Podzols was abrupt, and corresponded with dense layers with thick coarse laminar structure and illuvial silt accumulation (Cjj horizons). Dense Cjj diapiric inclusions were sometimes preserved in the central parts of the patterns. Where cover beds were developed, more superimposed podzol cycles were observed: the deeper podzols, included in the dense layer, were strongly cryoturbated and showed convoluted horizons and buried organic horizons. The presence of the dense Cjj horizons also influenced surface soil hydrology, which in turn influenced the expression of E and Bs horizons, in addition to textural lateral variability. In conclusion, surface morphology and soil properties evidence the presence of permafrost during cold Pleistocene phases, with an active layer 60-120 cm thick, associated with a particularly strong cryoturbation. However, all the permafrost features were not necessarily formed during the same periods, and dating of different materials would be necessary in order to obtain precise paleoenvironmental reconstructions of cold Quaternary phases in the Alps.

Soil carbon fractions and biological activity based indices can be used to study the impact of land management and ecological successions

DOE PAGES

de Moraes Sa, Joao Carlos; Potma Goncalves, Daniel Ruiz; Ferreira, Lucimara Aparecida; ...

2017-08-31

Soil organic carbon (SOC) is a strong indicator of soil health. Development of efficient soil quality indicators is crucial to better understand the impact of land management strategies on the recovery of degraded ecosystems. We hypothesized that SOC fractions and biological attributes can compose strong soil quality indicators to assess an ecosystem recovery following disturbance. Thus, the objective of this study was to evaluate the use of soil biological activity and SOC fractions to study the impact of different land use systems and ecological successions in ecosystem recovery. We selected six land use systems: tobacco (Nicotiana tabacum) cultivation; pastureland; reforestedmore » land with Eucalyptus sp.; and natural ecological successions with 10, 20 and 35 years of vegetation regeneration, respectively. We collected disturbed and undisturbed soil samples in triplicate at 0–5, 5–10, 10–20 and 20–40 cm depth intervals. Several fractionation approaches were used to determine SOC pools: hot water extractable organic carbon, permanganate oxidized organic carbon, particulate organic carbon, mineral associated organic carbon and total SOC. The activity of the enzyme arylsulfatase was used to represent soil biological attributes. We calculated three indices to represent the soil quality: carbon management index, soil resilience index and biological activity index. Our results suggest that the SOC fractions and the enzyme activity followed the increase of vegetation complexity of the ecological succession stages. The labile SOC pool, in addition to enzyme activity, was the most sensitive variable to assess land use changes. The biomass-C input was considered to be the main reason of SOC increase, and the gains of labile SOC fractions were directly related to the increase of SOC stocks. Both, biological and carbon management indices were efficient tools to characterize the impact of studied management systems. Also, we found that assessment of deeper soil layers (20–40 cm) was extremely important as incomplete inferences might be reached while evaluating only surface soil layers (0–20 cm). Here, we conclude that the carbon management and biological indices captured the stage of soil degradation and the influence of vegetation diversity in the soil resilience restoration, providing an advance in monitoring strategies that can be reproducible in any environment.« less

Soil carbon fractions and biological activity based indices can be used to study the impact of land management and ecological successions

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Moraes Sa, Joao Carlos; Potma Goncalves, Daniel Ruiz; Ferreira, Lucimara Aparecida

Soil organic carbon (SOC) is a strong indicator of soil health. Development of efficient soil quality indicators is crucial to better understand the impact of land management strategies on the recovery of degraded ecosystems. We hypothesized that SOC fractions and biological attributes can compose strong soil quality indicators to assess an ecosystem recovery following disturbance. Thus, the objective of this study was to evaluate the use of soil biological activity and SOC fractions to study the impact of different land use systems and ecological successions in ecosystem recovery. We selected six land use systems: tobacco (Nicotiana tabacum) cultivation; pastureland; reforestedmore » land with Eucalyptus sp.; and natural ecological successions with 10, 20 and 35 years of vegetation regeneration, respectively. We collected disturbed and undisturbed soil samples in triplicate at 0–5, 5–10, 10–20 and 20–40 cm depth intervals. Several fractionation approaches were used to determine SOC pools: hot water extractable organic carbon, permanganate oxidized organic carbon, particulate organic carbon, mineral associated organic carbon and total SOC. The activity of the enzyme arylsulfatase was used to represent soil biological attributes. We calculated three indices to represent the soil quality: carbon management index, soil resilience index and biological activity index. Our results suggest that the SOC fractions and the enzyme activity followed the increase of vegetation complexity of the ecological succession stages. The labile SOC pool, in addition to enzyme activity, was the most sensitive variable to assess land use changes. The biomass-C input was considered to be the main reason of SOC increase, and the gains of labile SOC fractions were directly related to the increase of SOC stocks. Both, biological and carbon management indices were efficient tools to characterize the impact of studied management systems. Also, we found that assessment of deeper soil layers (20–40 cm) was extremely important as incomplete inferences might be reached while evaluating only surface soil layers (0–20 cm). Here, we conclude that the carbon management and biological indices captured the stage of soil degradation and the influence of vegetation diversity in the soil resilience restoration, providing an advance in monitoring strategies that can be reproducible in any environment.« less

Fast simulated annealing inversion of surface waves on pavement using phase-velocity spectra

USGS Publications Warehouse

Ryden, N.; Park, C.B.

2006-01-01

The conventional inversion of surface waves depends on modal identification of measured dispersion curves, which can be ambiguous. It is possible to avoid mode-number identification and extraction by inverting the complete phase-velocity spectrum obtained from a multichannel record. We use the fast simulated annealing (FSA) global search algorithm to minimize the difference between the measured phase-velocity spectrum and that calculated from a theoretical layer model, including the field setup geometry. Results show that this algorithm can help one avoid getting trapped in local minima while searching for the best-matching layer model. The entire procedure is demonstrated on synthetic and field data for asphalt pavement. The viscoelastic properties of the top asphalt layer are taken into account, and the inverted asphalt stiffness as a function of frequency compares well with laboratory tests on core samples. The thickness and shear-wave velocity of the deeper embedded layers are resolved within 10% deviation from those values measured separately during pavement construction. The proposed method may be equally applicable to normal soil site investigation and in the field of ultrasonic testing of materials. ?? 2006 Society of Exploration Geophysicists.

Bacteria-to-Archaea ratio depending on soil depth and agrogenic impact

NASA Astrophysics Data System (ADS)

Semenov, Mikhail; Manucharova, Natalia; Kuzyakov, Yakov

2014-05-01

Archaeal communities and their potential roles in the soil ecosystem are affected by a number of soil proprerties and environmental factors. Competitive interactions between Archaea and Bacteria play a particular role in spread and abundance of these two domains. Therefore, the goal of the study was to evaluate the Bacteria-to-Archaea ratio in different soils. The research was carried out at field and natural ecosystems of European part of Russia. Samples were collected within the soil profiles (3-6 horizons) of chernozem and kastanozem with distinctly different agrogenic impact. In situ hybridization with fluorescently labeled rRNA-targeted oligonucleotide probes (FISH) was used to determine the abundance of metabolically active cells of Archaea and Bacteria. The Cmic, Corg, C/N, DNA content and growth characteristics have been analyzed as well. Determination of number of metabolically active cells in chernozem under arable land and forest revealed that abundance of Archaea in topsoil under forest was higher more than 2 times comparing with arable land, but leveled off in the deeper horizons. Plowing of Chernozem decreased amount of archaeal and bacterial active cells simultaneously, however, Bacteria were more resistant to agrogenic impact than Archaea. Determination of the taxonomic composition within Bacteria domain showed a significant decrease in the abundance of phylogenetic groups Firmicutes and Actinobacteria in the topsoil under arable land comparing to the forest, which is the main reason for the declining of the total amount of prokaryotic cells. In kastanozem significant change in the number of metabolically active cells due to plowing was detected only within 40 cm soil layer, and this effect disappeared in lower horizons. The number of Archaea was higher in the upper horizons of arable as compared to virgin soil. Conversely, the number of Bacteria in the upper layers of the soil after plowing kastanozem decreased. Relationship between soil organic carbon content and the amount of soil metabolically active Bacteria and Archaea cells revealed that distribution of both Bacteria and Archaea throughout the soil profile was governed by organic matter content. Thus, the organic matter content seemed to be the main factor of declining Bacteria-to- Archaea ratio down the profile (from 7.1 to 4.2 for virgin soil and from 5 to 3.9 for arable soil). In conclusion, Archaea out-compete Bacteria under conditions of reduced energy supply.

Depth profile of 236U/238U in soil samples in La Palma, Canary Islands

PubMed Central

Srncik, M.; Steier, P.; Wallner, G.

2011-01-01

The vertical distribution of the 236U/238U isotopic ratio was investigated in soil samples from three different locations on La Palma (one of the seven Canary Islands, Spain). Additionally the 240Pu/239Pu atomic ratio, as it is a well establish tool for the source identification, was determined. The radiochemical procedure consisted of a U separation step by extraction chromatography using UTEVA® Resin (Eichrom Technologies, Inc.). Afterwards Pu was separated from Th and Np by anion exchange using Dowex 1x2 (Dow Chemical Co.). Furthermore a new chemical procedure with tandem columns to separate Pu and U from the matrix was tested. For the determination of the uranium and plutonium isotopes by alpha spectrometry thin sources were prepared by microprecipitation techniques. Additionally these fractions separated from the soil samples were measured by Accelerator Mass Spectrometry (AMS) to get information on the isotopic ratios 236U/238U, 240Pu/239Pu and 236U/239Pu, respectively. The 236U concentrations [atoms/g] in each surface layer (∼2 cm) were surprisingly high compared to deeper layers where values around two orders of magnitude smaller were found. Since the isotopic ratio 240Pu/239Pu indicated a global fallout signature we assume the same origin as the probable source for 236U. Our measured 236U/239Pu value of around 0.2 is within the expected range for this contamination source. PMID:21481502

Natural remediation of an unremediated soil twelve years after a mine accident: trace element mobility and plant composition.

PubMed

Burgos, Pilar; Madejón, Paula; Madejón, Engracia; Girón, Ignacio; Cabrera, Francisco; Murillo, José Manuel

2013-01-15

The long-term influence of a mine spill in soil was studied 12 years after the Aznalcóllar accident. Soils where the pyritic sludge was not removed, a fenced plot established for research purposes (2000 m(2)) and soils where the process of remediation was accomplished successfully were sampled and studied in detail. Soils were characterized at different depths, down to 100 cm depth, determining chemical parameters and total concentrations of major and trace elements. Moreover plants colonizing remediated (RE) and non remediated (NRE) soils were also analysed attending their potential risk for herbivores. Strong acidification was observed in the NRE soil except in surface (0-10 cm). The progressive colonization of natural vegetation, more than 90% of the fenced plot covered by plants, could facilitate this increased pH values in the top soil (pH 6). In the NRE soil, the successive oxidation and hydrolysis of sulphide in the deposited sludge on the surface after the accident resulted in a re-dissolution of the most mobile element (Cd, Cu and Zn) and a penetration to deeper layers. Trace element concentrations in plants growing in the NRE soil showed normal contents for higher plants and tolerable for livestock. Nitrogen and mineral nutrients were of the same order in both soils, and also normal for high plants and adequate for animal nutrition. Despite of the natural remediation of the NRE soil, results demonstrate that the remediation tasks carried out in all the area, the Guadiamar Green Corridor at present, were necessary to avoid the leaching of the most mobile elements and minimize the risk of contamination of groundwater sources, many of them close to the Doñana National Park. Copyright © 2012 Elsevier Ltd. All rights reserved.

Comparison of sap flux data from two instrumented tree species in a forested catchment with different levels of water stress

NASA Astrophysics Data System (ADS)

Hartsough, P. C.; Roudneva, E.; Malazian, A. I.; Meadows, M. W.; Kelly, A. E.; Bales, R. C.; Goulden, M.; Hopmans, J. W.

2011-12-01

Two trees were instrumented with heat pulse sapflux sensors in the Southern Sierra Critical Zone Observatory (SSCZO) within the Kings River Experimental Watershed (KREW) to better understand transpiration as it relates to water availability from deeper sources. At the first instrumented site, CZT-1, a White Fir (Abies concolor) was instrumented on a flat ridge with access to deep soil moisture. Extensive monitoring of shallow and deep soil regions confirm that there is significant soil water available from 100-400cm as the tree exhausts water from shallower depths. A root excavation of an adjacent tree shows the roots distributed from 30-150cm with limited roots available to access deeper soil water and water stored in the saprolite. At the second instrumented site, CZT-2, a Ponderosa Pine (Pinus Ponderosa) was instrumented with a similar suite of sap flow and soil sensors. The CZT-2 site is on a slight slope and is characterized by shallow soils (<90cm) with extensive cobbles and bedrock outcrops with limited access to deeper soil or saprolite water. The second site also sits in the open while the first site is more protected in a closed forest. The two sites show different responses to changes in rain and snow loading from above as well as soil drainage and water depletion from below. They also have different thresholds for transpiration shut down both due to late season water deficit and also during winter periods where air temperatures are high enough to permit photosynthesis. Sap flux data are supplemented by extensive soil water content and potential measurements around both trees as well as evapotranspiration measurements from a 50m flux tower located between the two instrumented trees.

Frontolysis by surface heat flux in the Agulhas Return Current region with a focus on mixed layer processes: observation and a high-resolution CGCM

NASA Astrophysics Data System (ADS)

Ohishi, Shun; Tozuka, Tomoki; Komori, Nobumasa

2016-12-01

Detailed mechanisms for frontogenesis/frontolysis of the Agulhas Return Current (ARC) Front, defined as the maximum of the meridional sea surface temperature (SST) gradient at each longitude within the ARC region (40°-50°E, 55°-35°S), are investigated using observational datasets. Due to larger (smaller) latent heat release to the atmosphere on the northern (southern) side of the front, the meridional gradient of surface net heat flux (NHF) is found throughout the year. In austral summer, surface warming is weaker (stronger) on the northern (southern) side, and thus the NHF tends to relax the SST front. The weaker (stronger) surface warming, at the same time, leads to the deeper (shallower) mixed layer on the northern (southern) side. This enhances the frontolysis, because deeper (shallower) mixed layer is less (more) sensitive to surface warming. In austral winter, stronger (weaker) surface cooling on the northern (southern) side contributes to the frontolysis. However, deeper (shallower) mixed layer is induced by stronger (weaker) surface cooling on the northern (southern) side and suppresses the frontolysis, because the deeper (shallower) mixed layer is less (more) sensitive to surface cooling. Therefore, the frontolysis by the NHF becomes stronger (weaker) through the mixed layer processes in austral summer (winter). The cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the Monin-Obukhov depth. Furthermore, the above mechanisms obtained from the observation are confirmed using outputs from a high-resolution coupled general circulation model. Causes of model biases are also discussed.

Role of plant-mediated gas transport in CH4 emissions from Phragmites-dominated peatlands

NASA Astrophysics Data System (ADS)

van den Berg, Merit; Ingwersen, Joachim; van den Elzen, Eva; Lamers, Leon P. M.; Streck, Thilo

2016-04-01

A large part of the methane (CH4) produced in peatlands is directly oxidized and the extent of its oxidation depends on the gas transport pathway. In wetland ecosystems, CH4 can be transported from the soil to the atmosphere via diffusion, ebullition and via aerenchyma of roots and stems of vascular plants. Compared to other wetland plants, the very common species Phragmites australis (Common reed) appears to have a high ability to transport gases between the soil and atmosphere. The gas exchange within Phragmites plants takes place via convective flow through the culm, which is believed to be achieved by a humidity-induced pressure gradient and is more than 5-times as efficient as diffusion. By this mechanism, CH4 surpasses the upper (oxic) soil layers and therefore oxidation of CH4 may well be reduced. On the other hand, transport of oxygen in Phragmites plants tends to enhance O2concentration in the rhizosphere, which will foster CH4oxidation in deeper soil layers. It is therefore unknown whether humidity-induced convection leads to higher or lower overall CH4 emission in Phragmites, which is essential to understand their role in the emissions from these very common peatland types. To investigate whether this internal gas transport mechanism of reed promotes or reduces CH4 fluxes to the atmosphere, we conducted manipulative field experiments in a large Phragmites peatland in South-West Germany in October 2014 and July 2015. Using large chambers, we compared CH4 fluxes from intact plots, plots with cut reed, and plots with cut + sealed reed to exclude gas transport through the plants. Additionally, pore water samples from the plots were analyzed for possible changes in soil chemistry due to the change of oxygen transport into the soil by the treatments. Based on our results, we will explain the potential role of rhizosphere oxygenation and convective flow on CH4 emissions from Phragmites-dominated peatlands in relation to other environmental condition.

Experimental Investigation of Space Radiation Processing in Lunar Soil Ilmenite: Combining Perspectives from Surface Science and Transmission Electron Microscopy

NASA Technical Reports Server (NTRS)

Christoffersen, R.; Keller, L. P.; Rahman, Z.; Baragiola, R.

2010-01-01

Energetic ions mostly from the solar wind play a major role in lunar space weathering because they contribute structural and chemical changes to the space-exposed surfaces of lunar regolith grains. In mature mare soils, ilmenite (FeTiO3) grains in the finest size fraction have been shown in transmission electron microscope (TEM) studies to exhibit key differences in their response to space radiation processing relative to silicates [1,2,3]. In ilmenite, solar ion radiation alters host grain outer margins to produce 10-100 nm thick layers that are microstructurally complex, but dominantly crystalline compared to the amorphous radiation-processed rims on silicates [1,2,3]. Spatially well-resolved analytical TEM measurements also show nm-scale compositional and chemical state changes in these layers [1,3]. These include shifts in Fe/Ti ratio from strong surface Fe-enrichment (Fe/Ti >> 1), to Fe depletion (Fe/Ti < 1) at 40-50 nm below the grain surface [1,3]. These compositional changes are not observed in the radiation-processed rims on silicates [4]. Several mechanism(s) to explain the overall relations in the ilmenite grain rims by radiation processing and/or additional space weathering processes were proposed by [1], and remain under current consideration [3]. A key issue has concerned the ability of ion radiation processing alone to produce some of the deeper- penetrating compositional changes. In order to provide some experimental constraints on these questions, we have performed a combined X-ray photoelectron spectroscopy (XPS) and field-emission scanning transmission electron (FE-STEM) study of experimentally ion-irradiated ilmenite. A key feature of this work is the combination of analytical techniques sensitive to changes in the irradiated samples at depth scales going from the immediate surface (approx.5 nm; XPS), to deeper in the grain interior (5-100 nm; FE-STEM).

Winter precipitation and snow accumulation drive the methane sink or source strength of Arctic tussock tundra.

PubMed

Blanc-Betes, Elena; Welker, Jeffrey M; Sturchio, Neil C; Chanton, Jeffrey P; Gonzalez-Meler, Miquel A

2016-08-01

Arctic winter precipitation is projected to increase with global warming, but some areas will experience decreases in snow accumulation. Although Arctic CH4 emissions may represent a significant climate forcing feedback, long-term impacts of changes in snow accumulation on CH4 fluxes remain uncertain. We measured ecosystem CH4 fluxes and soil CH4 and CO2 concentrations and (13) C composition to investigate the metabolic pathways and transport mechanisms driving moist acidic tundra CH4 flux over the growing season (Jun-Aug) after 18 years of experimental snow depth increases and decreases. Deeper snow increased soil wetness and warming, reducing soil %O2 levels and increasing thaw depth. Soil moisture, through changes in soil %O2 saturation, determined predominance of methanotrophy or methanogenesis, with soil temperature regulating the ecosystem CH4 sink or source strength. Reduced snow (RS) increased the fraction of oxidized CH4 (Fox) by 75-120% compared to Ambient, switching the system from a small source to a net CH4 sink (21 ± 2 and -31 ± 1 mg CH4  m(-2)  season(-1) at Ambient and RS). Deeper snow reduced Fox by 35-40% and 90-100% in medium- (MS) and high- (HS) snow additions relative to Ambient, contributing to increasing the CH4 source strength of moist acidic tundra (464 ± 15 and 3561 ± 97 mg CH4  m(-2)  season(-1) at MS and HS). Decreases in Fox with deeper snow were partly due to increases in plant-mediated CH4 transport associated with the expansion of tall graminoids. Deeper snow enhanced CH4 production within newly thawed soils, responding mainly to soil warming rather than to increases in acetate fermentation expected from thaw-induced increases in SOC availability. Our results suggest that increased winter precipitation will increase the CH4 source strength of Arctic tundra, but the resulting positive feedback on climate change will depend on the balance between areas with more or less snow accumulation than they are currently facing. © 2016 John Wiley & Sons Ltd.

Digging Movie from Phoenix's Sol 18

NASA Technical Reports Server (NTRS)

2008-01-01

The Surface Stereo Imager on NASA's Phoenix Mars Lander recorded the images combined into this movie of the lander's Robotic Arm enlarging and combining the two trenches informally named 'Dodo' (left) and 'Goldilocks.'

The 21 images in this sequence were taken over a period of about 2 hours during Phoenix's Sol 18 (June 13, 2008), or the 18th Martian day since landing.

The main purpose of the Sol 18 dig was to dig deeper for learning the depth of a hard underlying layer. A bright layer, possibly ice, was increasingly exposed as the digging progressed. Further digging and scraping in the combined Dodo-Goldilocks trench was planned for subsequent sols.

The combined trench is about 20 centimeters (about 8 inches) wide. The depth at the end of the Sol 18 digging is 5 to 6 centimeters (about 2 inches).

The Goldilocks trench was the source of soil samples 'Baby Bear' and 'Mama Bear,' which were collected on earlier sols and delivered to instruments on the lander deck. The Dodo trench was originally dug for practice in collecting and depositing soil samples.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

[Characteristics of soil water infiltration in sub-alpine dark coniferous ecosystem of upper reaches of Yangtze River].

PubMed

Yu, Xinxiao; Zhao, Yutao; Zhang, Zhiqiang; Cheng, Genwei

2003-01-01

Dark coniferous forest is the predominant type of vegetation in the upper reaches of Yangtze River. Difference among different types of soil exists. The sand content of soil is higher and the soil texture is coarser in the early stage of forest succession. The sand content of soil decreases with the advancement of the forest succession while that of soil in Abies fabri over-mature forest is the lowest. In slope wash soil, the sand content of soil decreases with the increasing soil depth. The soil porosity and soil water-holding capacity increases and soil bulk density decreases with the advancement of forest succession and decrease of soil depth. The deeper soil depth or the smaller soil water content are, the smaller the unsaturated hydraulic conductivity of soil measured by CGA method. Moreover, the correlation of soil water content with unsaturated hydraulic conductivity of soil can be simulated by an exponential function. The saturated hydraulic conductivity of soil decreases exponentially with the increasing soil depth. The time to attain the stable infiltration rate is different among different soil depth, while the deeper the soil depth is, the longer the time needs. The variation in soil texture, soil physical properties and the high infiltration rate of soil there implicated that there are scarce surface runoff, but abundant in subsurface flow, return flow and seepage, which is the result of regulation by dark coniferous forest on hydrological processes.

{sup 40}K, {sup 115}Cs and {sup 226}Ra Soil and Plant Content in Seminatural Grasslands of Central Argentina

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayub, J. Juri; Velasco, R. H.; Rizzotto, M.

2008-08-07

Activity concentrations of {sup 40}K, {sup 226}Ra and {sup 137}Cs have been analyzed in soil and plant samples, collected in permanent grassland in central Argentina. Two near areas (A1 and A2) under field conditions with soil undisturbed at least in the last four decades were selected. For each of the three studied radionuclides we do not find differences in the inventories between both areas. The inventories range from 143 kBq m{sup -2} to 197 kBq m{sup -2} for {sup 40}K and from 13 kBq m{sup -2} to 18 kBq m{sup -2} for {sup 226}Ra. The vertical distributions of {sup 40}Kmore » and {sup 226}Ra are uniform through de soil profile. For {sup 137}Cs the inventories range from 0.33 kBq m{sup -2} to 0.73 kBq m{sup -2}. In spite of {sup 137}Cs inventories are similar in both areas the distribution through vertical profile is different. {sup 137}Cs activity concentration has a maximum for layers 5-10 cm depth in A1 and 10-15 cm depth in A2. For deeper layers both areas show similar activity concentrations. The diffusion coefficient (D{sub s}) and convection velocity (v{sub s}) are estimated with a convection-diffusion model. D{sub s} values are in the range reported in the bibliography, while v{sub s} values are one order of magnitude higher. After 40 years most {sup 137}Cs fallout is still in the layer 10-15 cm depth. The great penetration of {sup 137}Cs (25 cm) in these soils may be the result of a high sand and low fine materials content. {sup 137}Cs and {sup 226}Ra were not detected in grass samples. Activity concentration of {sup 40}K in vegetal samples ranges from 116 Bq kg{sup -1} to 613 Bq kg{sup -1}. The TF values obtained for {sup 40}K show a lognormal distribution and ranges from 0.05 to 0.42.« less

Distribution of black carbon in ponderosa pine forest floor and soils following the High Park wildfire

NASA Astrophysics Data System (ADS)

Boot, C. M.; Haddix, M.; Paustian, K.; Cotrufo, M. F.

2015-05-01

Biomass burning produces black carbon (BC), effectively transferring a fraction of the biomass C from an actively cycling pool to a passive C pool, which may be stored in the soil. Yet the timescales and mechanisms for incorporation of BC into the soil profile are not well understood. The High Park fire (HPF), which occurred in northwestern Colorado in the summer of 2012, provided an opportunity to study the effects of both fire severity and geomorphology on properties of carbon (C), nitrogen (N) and BC in the Cache La Poudre River drainage. We sampled montane ponderosa pine forest floor (litter plus O-horizon) and soils at 0-5 and 5-15 cm depth 4 months post-fire in order to examine the effects of slope and burn severity on %C, C stocks, %N and BC. We used the benzene polycarboxylic acid (BPCA) method for quantifying BC. With regard to slope, we found that steeper slopes had higher C : N than shallow slopes but that there was no difference in BPCA-C content or stocks. BC content was greatest in the forest floor at burned sites (19 g BPCA-C kg-1 C), while BC stocks were greatest in the 5-15 cm subsurface soils (23 g BPCA-C m-2). At the time of sampling, unburned and burned soils had equivalent BC content, indicating none of the BC deposited on the land surface post-fire had been incorporated into either the 0-5 or 5-15 cm soil layers. The ratio of B6CA : total BPCAs, an index of the degree of aromatic C condensation, suggested that BC in the 5-15 cm soil layer may have been formed at higher temperatures or experienced selective degradation relative to the forest floor and 0-5 cm soils. Total BC soil stocks were relatively low compared to other fire-prone grassland and boreal forest systems, indicating most of the BC produced in this system is likely lost, either through erosion events, degradation or translocation to deeper soils. Future work examining mechanisms for BC losses from forest soils will be required for understanding the role BC plays in the global carbon cycle.

Different Behavior of Enteric Bacteria and Viruses in Clay and Sandy Soils after Biofertilization with Swine Digestate

PubMed Central

Fongaro, Gislaine; García-González, María C.; Hernández, Marta; Kunz, Airton; Barardi, Célia R. M.; Rodríguez-Lázaro, David

2017-01-01

Enteric pathogens from biofertilizer can accumulate in the soil, subsequently contaminating water and crops. We evaluated the survival, percolation and leaching of model enteric pathogens in clay and sandy soils after biofertilization with swine digestate: PhiX-174, mengovirus (vMC0), Salmonella enterica Typhimurium and Escherichia coli O157:H7 were used as biomarkers. The survival of vMC0 and PhiX-174 in clay soil was significantly lower than in sandy soil (iT90 values of 10.520 ± 0.600 vs. 21.270 ± 1.100 and 12.040 ± 0.010 vs. 43.470 ± 1.300, respectively) and PhiX-174 showed faster percolation and leaching in sandy soil than clay soil (iT90 values of 0.46 and 2.43, respectively). S. enterica Typhimurium was percolated and inactivated more slowly than E. coli O157:H7 (iT90 values of 9.340 ± 0.200 vs. 6.620 ± 0.500 and 11.900 ± 0.900 vs. 10.750 ± 0.900 in clay and sandy soils, respectively), such that E. coli O157:H7 was transferred more quickly to the deeper layers of both soils evaluated (percolation). Our findings suggest that E. coli O157:H7 may serve as a useful microbial biomarker of depth contamination and leaching in clay and sandy soil and that bacteriophage could be used as an indicator of enteric pathogen persistence. Our study contributes to development of predictive models for enteric pathogen behavior in soils, and for potential water and food contamination associated with biofertilization, useful for risk management and mitigation in swine digestate recycling. PMID:28197137

Complete and Partial Photo-oxidation of Dissolved Organic Matter Draining Permafrost Soils.

PubMed

Ward, Collin P; Cory, Rose M

2016-04-05

Photochemical degradation of dissolved organic matter (DOM) to carbon dioxide (CO2) and partially oxidized compounds is an important component of the carbon cycle in the Arctic. Thawing permafrost soils will change the chemical composition of DOM exported to arctic surface waters, but the molecular controls on DOM photodegradation remain poorly understood, making it difficult to predict how inputs of thawing permafrost DOM may alter its photodegradation. To address this knowledge gap, we quantified the susceptibility of DOM draining the shallow organic mat and the deeper permafrost layer of arctic soils to complete and partial photo-oxidation and investigated changes in the chemical composition of each DOM source following sunlight exposure. Permafrost and organic mat DOM had similar lability to photomineralization despite substantial differences in initial chemical composition. Concurrent losses of carboxyl moieties and shifts in chemical composition during photodegradation indicated that photodecarboxylation could account for 40-90% of DOM photomineralized to CO2. Permafrost DOM had a higher susceptibility to partial photo-oxidation compared to organic mat DOM, potentially due to a lower abundance of phenolic moieties with antioxidant properties. These results suggest that photodegradation will likely continue to be an important control on DOM fate in arctic freshwaters as the climate warms and permafrost soils thaw.

Quantifying shallow and deep permafrost changes using radar remote sensing

NASA Astrophysics Data System (ADS)

Teshebaeva, K.; van Huissteden, K. J.

2017-12-01

Widespread thawing of permafrost in the northern Eurasian continent cause severe problems for infrastructure and global climate. Permafrost thaw by climate warming creates land surface instability, resulting in severe problems for infrastructure, and release of organic matter to the atmosphere as CO2 and CH4. Recent discoveries of CH4 seeps in lakes, in the Arctic Ocean, and CH4 emitting craters in the permafrost. These features indicate that permafrost destabilization might no longer be a surface feature only, but that also deeper layers of the permafrost, up to tens of meters, may be affected by warming. We study two potential areas in Siberian arctic; one of the test site is the Kytalyk research station near Chokurdagh town affected with a recent inundation of the Indigirka river in July 2017, which resulted in standing surface water for the period over a month. The wet soil and standing water may cause changes in active layer thickness and influence the thermal regime of the permafrost for the next decades in the region. The second test site is Yamal peninsula with recently CH4 emitting craters, which may start to contribute to emission hotspots. We hypothesize that these deeper subsurface processes also can be detected by mapping surface elevation changes using advanced SAR techniques. We test the potential of SAR imagery to enhance detection of these features, including surface movement related to permafrost active layer changes using InSAR time-series analysis. We also apply radar backscatter signal to detect seasonal changes related to the freeze-thaw cycles. The PRISM elevation data are used to estimate elevation changes in the region along with ground-based geophysical and geodetical fieldwork.

[Effects of the grain size and thickness of dust deposits on soil water and salt movement in the hinterland of the Taklimakan Desert].

PubMed

Sun, Yan-Wei; Li, Sheng-Yu; Xu, Xin-Wen; Zhang, Jian-Guo; Li, Ying

2009-08-01

By using mcirolysimeter, a laboratory simulation experiment was conducted to study the effects of the grain size and thickness of dust deposits on the soil water evaporation and salt movement in the hinterland of the Taklimakan Desert. Under the same initial soil water content and deposition thickness condition, finer-textured (<0.063 mm) deposits promoted soil water evaporation, deeper soil desiccation, and surface soil salt accumulation, while coarse-textured (0.063-2 mm) deposits inhibited soil water evaporation and decreased deeper soil water loss and surface soil salt accumulation. The inhibition effect of the grain size of dust deposits on soil water evaporation had an inflection point at the grain size 0.20 mm, i. e., increased with increasing grain size when the grain size was 0.063-0.20 mm but decreased with increasing grain size when the grain size was > 0.20 mm. With the increasing thickness of dust deposits, its inhibition effect on soil water evaporation increased, and there existed a logarithmic relationship between the dust deposits thickness and water evaporation. Surface soil salt accumulation had a negative correlation with dust deposits thickness. In sum, the dust deposits in study area could affect the stability of arid desert ecosystem.

The potential of organic substrates based on mushroom substrate and straw to dissipate fungicides contained in effluents from the fruit-packaging industry - Is there a role for Pleurotus ostreatus?

PubMed

Karas, Panagiotis A; Makri, Sotirina; Papadopoulou, Evangelia S; Ehaliotis, Constantinos; Menkissoglu-Spiroudi, Urania; Karpouzas, Dimitrios G

2016-02-01

Citrus fruit-packaging plants (FPP) produce large wastewater volumes with high loads of fungicides like ortho-phenylphenol (OPP) and imazalil (IMZ). No methods are in place for the treatment of those effluents and biobeds appear as a viable alternative. We employed a column study to investigate the potential of spent mushroom substrate (SMS) of Pleurotus ostreatus, either alone or in mixture with straw and soil plus a mixture of straw /soil to retain and dissipate IMZ and OPP. The role of P. ostreatus on fungicides dissipation was also investigated by studying in parallel the performance of fresh mushroom substrate of P. ostreatus (FMS) and measuring lignolytic enzymatic activity in the leachates. All substrates effectively reduced the leaching of OPP and IMZ which corresponded to 0.014-1.1% and 0.120-0.420% of their initial amounts respectively. Mass balance analysis revealed that FMS and SMS/Straw/Soil (50/25/25 by vol) offered the most efficient removal of OPP and IMZ from wastewaters respectively. Regardless of the substrate, OPP was restricted in the top 0-20cm of the columns and was bioavailable (extractable with water), compared to IMZ which was less bioavailable (extractable with acetonitrile) but diffused at deeper layers (20-50, 50-80cm) in the SMS- and Straw/Soil-columns. PLFAs showed that fungal abundance was significantly lower in the top layer of all substrates from where the highest pesticide amounts were recovered suggesting an inhibitory effect of fungicides on total fungi in the substrates tested. Our data suggest that biobeds packed with SMS-rich substrates could ensure the efficient removal of IMZ and OPP from wastewaters of citrus FPP. Copyright © 2015 Elsevier Inc. All rights reserved.

Combined deep sampling and mass-based approaches to assess soil carbon and nitrogen losses due to land-use changes in karst area of southwestern China

NASA Astrophysics Data System (ADS)

Hu, Yecui; Du, Zhangliu; Wang, Qibing; Li, Guichun

2016-07-01

The conversion of natural vegetation to human-managed ecosystems, especially the agricultural systems, may decrease soil organic carbon (SOC) and total nitrogen (TN) stocks. The objective of present study was to assess SOC and TN stocks losses by combining deep sampling with mass-based calculations upon land-use changes in a typical karst area of southwestern China. We quantified the changes from native forest to grassland, secondary shrub, eucalyptus plantation, sugarcane and corn fields (both defined as croplands), on the SOC and TN stocks down to 100 cm depth using fixed-depth (FD) and equivalent soil mass (ESM) approaches. The results showed that converting forest to cropland and other types significantly led to SOC and TN losses, but the extent depended on both sampling depths and calculation methods selected (i.e., FD or ESM). On average, the shifting from native forest to cropland led to SOC losses by 19.1, 25.1, 30.6, 36.8 and 37.9 % for the soil depths of 0-10, 0-20, 0-40, 0-60 and 0-100 cm, respectively, which highlighted that shallow sampling underestimated SOC losses. Moreover, the FD method underestimated SOC and TN losses for the upper 40 cm layer, but overestimated the losses in the deeper layers. We suggest that the ESM together with deep sampling should be encouraged to detect the differences in SOC stocks. In conclusion, the conversion of forest to managed systems, in particular croplands significantly decreased in SOC and TN stocks, although the effect magnitude to some extent depended on sampling depth and calculation approach selected.

Is soil dressing a way once and for all in remediation of arsenic contaminated soils? A case study of arsenic re-accumulation in soils remediated by soil dressing in Hunan Province, China.

PubMed

Su, Shiming; Bai, Lingyu; Wei, Caibing; Gao, Xiang; Zhang, Tuo; Wang, Yanan; Li, Lianfang; Wang, Jinjin; Wu, Cuixia; Zeng, Xibai

2015-07-01

The investigation of arsenic (As) re-accumulation in an area previously remediated by soil dressing will help in sustainable controlling the risks of As to local ecosystems and should influence management decisions about remediation strategies. In this study, As content in an area remediated by soil dressing and the possible As accumulation risk in agricultural products were investigated. The results indicated that after 7 years of agricultural activities, the average As content (24.6 mg kg(-1)) in surface soil of the investigated area increased by 83.6% compared with that (13.4 mg kg(-1)) in clean soil. Of the surface soil samples (n = 88), 21.6% had As levels that exceeded the limits of the Environmental Quality Standard for Soils of China (GB 15618-1995) and 98.9% of the surface soil samples with As contents exceeding that in clean soil was observed. Soil dressing might be not a remediation method once and for all in some contaminated areas, even though no significant difference in available As content was found between clean (0.18 mg kg(-1)) and surface (0.22 mg kg(-1)) soils. The foreign As in surface soil of the investigated area mainly specifically sorbed with soil colloid or associated with hydrous oxides of Fe and Al, or existed in residual fraction. The upward movement of contaminated soil from the deeper layers and the atmospheric deposition of slag particles might be responsible for the re-accumulation of As in the investigated area. Decreases in soil pH in the investigated soils and the fact that no plant samples had As levels exceeding the limits of the National Food Safety Standards for Contaminants of China (GB 2762-2012) were also observed.

Three-dimensional spatial patterns of soil carbon storage are altered by woody encroachment into grasslands

NASA Astrophysics Data System (ADS)

Zhou, Y.; Boutton, T. W.; Wu, X. B.

2016-12-01

Recent global trends of increasing woody plant abundance in grass-dominated ecosystems may substantially enhance soil organic carbon (SOC) storage and could represent an important carbon (C) sink in the terrestrial environment. However, most studies assessing SOC response to woody encroachment only consider surface soils, and have not explicitly assessed the extent to which deeper portions of the profile may be affected by this phenomenon. Consequently, little is known about the direction, magnitude, and spatial heterogeneity of SOC throughout the soil profile following woody encroachment. These factors were quantified via spatially-specific intensive soil sampling to a depth 1.2 m across a subtropical savanna landscape that has undergone woody proliferation during the past century in southern Texas, USA. Increased SOC sequestration following woody encroachment was observed throughout the profile, albeit at reduced magnitudes at deeper depths. Overall, soils beneath small woody clusters and larger groves accumulated 12.87 and 18.67 Mg C ha-1 more SOC, respectively, to a depth of 1. 2 m compared to grasslands. Recent woody encroachment during the past 100 y significantly altered the spatial pattern and amplified the spatial heterogeneity of SOC at the 0-5 cm depth, with marginal effects at 5-15 cm and no distinct impact on soils below 15 cm. Fine root density explained much of the variation in SOC in the upper 15 cm, while a combination of fine root density and soil clay content accounted for more of the variation in SOC in soils below 15 cm. These findings emphasize the existence of substantial SOC sequestration in deeper portions of the soil profile following woody encroachment. Given the geographical extent of woody encroachment on a global scale, this largely undocumented deep soil C sequestration suggests woody encroachment may play a more significant role in regional and global C sequestration than previously thought.

Deforestation impacts on soil organic carbon stocks in the Semiarid Chaco Region, Argentina.

PubMed

Villarino, Sebastián Horacio; Studdert, Guillermo Alberto; Baldassini, Pablo; Cendoya, María Gabriela; Ciuffoli, Lucía; Mastrángelo, Matias; Piñeiro, Gervasio

2017-01-01

Land use change affects soil organic carbon (SOC) and generates CO 2 emissions. Moreover, SOC depletion entails degradation of soil functions that support ecosystem services. Large areas covered by dry forests have been cleared in the Semiarid Chaco Region of Argentina for cropping expansion. However, deforestation impacts on the SOC stock and its distribution in the soil profile have been scarcely reported. We assessed these impacts based on the analysis of field data along a time-since-deforestation-for-cropping chronosequence, and remote sensing indices. Soil organic C was determined up to 100cm depth and physically fractionated into mineral associated organic carbon (MAOC) and particulate organic C (POC). Models describing vertical distribution of SOC were fitted. Total SOC, POC and MAOC stocks decreased markedly with increasing cropping age. Particulate organic C was the most sensitive fraction to cultivation. After 10yr of cropping SOC loss was around 30%, with greater POC loss (near 60%) and smaller MAOC loss (near 15%), at 0-30cm depth. Similar relative SOC losses were observed in deeper soil layers (30-60 and 60-100cm). Deforestation and subsequent cropping also modified SOC vertical distribution. Soil organic C loss was negatively associated with the proportion of maize in the rotation and total crop biomass inputs, but positively associated with the proportion of soybean in the rotation. Without effective land use polices, deforestation and agricultural expansion can lead to rapid soil degradation and reductions in the provision of important ecosystem services. Copyright © 2016 Elsevier B.V. All rights reserved.

Biogeochemistry of the Amazon River Basin: the role of aquatic ecosystems in the Amazon functioning

NASA Astrophysics Data System (ADS)

Victoria, R. L.; Ballester, V. R.; Krushe, A. V.; Richey, J. E.; Aufdenkampe, A. K.; Kavaguishi, N. L.; Gomes, B. M.; Victoria, D. D.; Montebello, A. A.; Niell, C.; Deegan, L.

2004-12-01

In this study we present the results of an integrated analysis of physical and anthropogenic controls of river biogeochemistry in Amazônia. At the meso-scale level, our results show that both soil properties and land use are the main drivers of river biogeochemistry and metabolism, with pasture cover and soil exchange cation capacity explaining 99% (p < 0.01) of the variability observed in surface water ions and nutrients concentrations. In small rivers, forest clearing can increase cations, P and C inputs. P and light are the main PPL limiting factors in forested streams, while in pasture streams N becomes limiting. P export to streams may increase or remain nearly undetectable after forest-to-pasture conversion, depending on soil type. Pasture streams on Oxisols have very low P export, while on Ultisols P export is increased. Conversions of forest to pasture leads to extensive growth of in channel Paspalum resulting in higher DOC concentrations and respiration rates. Pasture streams have higher DOC fluxes when compared to the forest ones. In pasture areas the soil are compacted, there is less infiltration and higher surface run off, leaching soil superficial layers and caring more DOC to the streams. In forest areas infiltration is deeper into the soils and canopy interaction is higher. Mineralogy and soil properties are key factors determining exports of nutrients to streams. Therefore, land use change effects on nutrient export from terrestrial to aquatic ecosystems and the atmosphere must be understood within the context of varying soil properties across the Amazon Basin.

Perturbations in the initial soil moisture conditions: Impacts on hydrologic simulation in a large river basin

NASA Astrophysics Data System (ADS)

Niroula, Sundar; Halder, Subhadeep; Ghosh, Subimal

2018-06-01

Real time hydrologic forecasting requires near accurate initial condition of soil moisture; however, continuous monitoring of soil moisture is not operational in many regions, such as, in Ganga basin, extended in Nepal, India and Bangladesh. Here, we examine the impacts of perturbation/error in the initial soil moisture conditions on simulated soil moisture and streamflow in Ganga basin and its propagation, during the summer monsoon season (June to September). This provides information regarding the required minimum duration of model simulation for attaining the model stability. We use the Variable Infiltration Capacity model for hydrological simulations after validation. Multiple hydrologic simulations are performed, each of 21 days, initialized on every 5th day of the monsoon season for deficit, surplus and normal monsoon years. Each of these simulations is performed with the initial soil moisture condition obtained from long term runs along with positive and negative perturbations. The time required for the convergence of initial errors is obtained for all the cases. We find a quick convergence for the year with high rainfall as well as for the wet spells within a season. We further find high spatial variations in the time required for convergence; the region with high precipitation such as Lower Ganga basin attains convergence at a faster rate. Furthermore, deeper soil layers need more time for convergence. Our analysis is the first attempt on understanding the sensitivity of hydrological simulations of Ganga basin on initial soil moisture conditions. The results obtained here may be useful in understanding the spin-up requirements for operational hydrologic forecasts.

The utilisation of municipal waste compost for the reclamation of anthropogenic soils: implications on C dynamics.

NASA Astrophysics Data System (ADS)

Said-Pullicino, D.; Bol, R.; Gigliotti, G.

2009-04-01

The application of municipal waste compost (MWC) and other organic materials may serve to enhance soil fertility and increase C stocks of earthen materials and mine spoils used in land reclamation activities, particularly in the recovery of degraded areas left by exhausted quarries, mines, abandoned industrial zones, degraded natural areas and exhausted landfill sites. Such land management options may serve as a precondition for landscaping and reclamation of degraded areas, reforestation or agriculture. In fact, previous results have shown that compost application to the capping layer of a landfill covering soil significantly enhanced the fertility, evidenced by an improvement in soil structure, porosity and water holding capacity, an increase in the relative proportion of recalcitrant C pools and an increase in soil nutrient content, microbial activity and soil microbial biomass. Proper management of MWC requires a capacity to understand and predict their impacts on C dynamics in the field subsequent to application. Although numerous works deal with the effects of compost application in agricultural systems, little is known on how land rehabilitation practices effect C dynamics in such relatively young soil systems. The estimation of SOC pools and their potential turnover rates in land reclamation activities is fundamental to our understanding of terrestrial C dynamics. In the framework of a long-term field experiment, the objective of this work was to evaluate the temporal and spatial dynamics of compost-derived organic matter with respect to the major processes involved in organic matter cycling in an anthropogenic landfill covering soil originally amended with a single dose of MWC. We investigated long-term organic C dynamics in such systems by collecting samples at different depths over a 10 year chronosequence subsequent to compost application to the top layer of the landfill covering soil. Variations in the stable isotope composition (delta 13C) of the soil samples show that even after 10 years, amended topsoils were significantly enriched in compost-derived organic matter, confirming that the utilisation of such organic inputs in land reclamation activities has the potential to enhance the C stocks of degraded areas. The addition of compost to the superficial layer also resulted in a significant input of soluble organic compounds subject to leaching along the soil profile. Sorption isotherms for compost-derived water-extractable organic matter onto mineral materials used for landfill covering suggest that sorptive preservation was primarily responsible for the increase in C content and the shift in the C isotopic signature to values similar to that of the applied compost, in the deeper soil horizons over the 10 year experimental period. This was also confirmed by the accumulation of lignin-derived phenolic compounds. Nevertheless, analysis for non-cellulosic carbohydrates in soils samples and their respective water-extractable fractions suggest that a proportion of compost-derived, labile organic matter fraction is leached through the soil profile and potentially lost from the soil system, particularly in the years immediately after compost application.

Opposing effects of fire severity on climate feedbacks in Siberian larch forests

NASA Astrophysics Data System (ADS)

Loranty, M. M.; Alexander, H. D.; Natali, S.; Kropp, H.; Mack, M. C.; Bunn, A. G.; Davydov, S. P.; Erb, A.; Kholodov, A. L.; Schaaf, C.; Wang, Z.; Zimov, N.; Zimov, S. A.

2017-12-01

Boreal larch forests in northeastern Siberia comprise nearly 25% of the continuous permafrost zone. Structural and functional changes in these ecosystems will have important climate feedbacks at regional and global scales. Like boreal ecosystems in North America, fire is an important determinant of landscape scale forest distribution, and fire regimes are intensifying as climate warms. In Siberian larch forests are dominated by a single tree species, and there is evidence that fire severity influences post-fire forest density via impacts on seedling establishment. The extent to which these effects occur, or persist, and the associated climate feedbacks are not well quantified. In this study we use forest stand inventories, in situ observations, and satellite remote sensing to examine: 1) variation in forest density within and between fire scars, and 2) changes in land surface albedo and active layer dynamics associated with forest density variation. At the landscape scale we observed declines in Landsat derived albedo as forests recovered in the first several decades after fire, though canopy cover varied widely within and between individual fire scars. Within an individual mid-successional fire scar ( 75 years) we observed canopy cover ranging from 15-90% with correspondingly large ranges of albedo during periods of snow cover, and relatively small differences in albedo during the growing season. We found an inverse relationship between canopy density and soil temperature within this fire scar; high-density low-albedo stands had cooler soils and shallower active layers, while low-density stands had warmer soils and deeper active layers. Intensive energy balance measurements at a high- and low- density site show that canopy cover alters the magnitude and timing of ground heat fluxes that affect active layer properties. Our results show that fire impacts on stand structure in Siberian larch forests affect land surface albedo and active layer dynamics in ways that may lead to opposing climate feedbacks. At effectively large scales these changes constitute positive and negative climate feedbacks, respectively. Accurate predictive understanding of terrestrial Arctic climate feedbacks requires improved knowledge regarding the ecological consequences of changing fire regimes in Siberian boreal forests.

Effects of Successive Harvests on Soil Nutrient Stocks in Established Tropical Plantation Forests

NASA Astrophysics Data System (ADS)

Mendoza, L.; McMahon, D.; Jackson, R. B.

2017-12-01

Large-scale plantation forests in tropical regions alter biogeochemical processes, raising concerns about the long-term sustainability of this land use. Current commercial practices result in nutrient export with removed biomass that may not be balanced by fertilizer application. Consequent changes in a landscape's nutrient distributions can affect the growth of future plantations or other vegetation. Prior studies have reported changes in soil chemical and physical properties when plantation forests replace pastures or native vegetation, but few have examined the impacts of multiple harvest cycles following plantation establishment. This study analyzed macronutrient and carbon content of soil samples from the world's most productive plantation forests, in southeastern Brazil, to understand the long-term effects of plantation forests on soil nutrient stocks and soil fertility. Soil was collected from Eucalyptus plantation sites and adjacent vegetation in 2004 and again in 2016, after at least one full cycle of harvesting and replanting. We found that within surface soil (0-10 cm) Mg and N did not change significantly and C, P, K and Ca concentrations generally increased, but to varying extents within individual management units. This trend of increasing nutrient concentrations suggests that additional harvests do not result in cumulative nutrient depletion. However, large changes in Ca and K concentrations in individual plantation units indicate that added fertilizer does not consistently accumulate in the surface soil. Analysis of deeper soil layers and comparison to unfertilized vegetation will help to determine the fate of fertilizers and native soil nutrients in repeatedly harvested plantations. These results address the necessity of long-term investigation of nutrient changes to better understand and determine the impacts of different types of land use in the tropics.

Ecohydrologic separation of water between trees and streams in a Mediterranean climate

EPA Science Inventory

Water movement in upland humid watersheds from the soil surface to the stream is often described using the concept of translatory flow, which assumes that water entering the soil as precipitation displaces the water that was present previously, pushing it deeper into the soil and...

Sampling depth confounds soil acidification outcomes

USDA-ARS?s Scientific Manuscript database

In the northern Great Plains (NGP) of North America, surface sampling depths of 0-15 or 0-20 cm are suggested for testing soil characteristics such as pH. However, acidification is often most pronounced near the soil surface. Thus, sampling deeper can potentially dilute (increase) pH measurements an...

Event Water Balance and Recharge at the Panola Mountain Research Watershed, Georgia, U.S.A.

NASA Astrophysics Data System (ADS)

Riley, J. W.; Aulenbach, B. T.

2016-12-01

Investigating catchment storage and runoff pathways allows a better mechanistic understanding of stream flow generation processes. This information can be used to elucidate processes such as those influencing baseflow that support human consumption and ecological needs. Here we describe storm runoff water budgets from 483 rain events to determine the conditions under which precipitation infiltrates to deeper storage that supports baseflow. Further, we examine the storage and recharge behavior of different storm characteristics and antecedent conditions. We use a simple water budget approach to achieve this in which Deep Recharge = (Precipitation) - (Storm Runoff) - (Event Change in Soil Storage). Hydrograph separation was used to determine the storm periods and split storm runoff into baseflow and quickflow. Quickflow was assumed to account for the event water lost to the stream. Data from volumetric water content sensors were used to calculate the soil profile water storage and the change in water storage over the course of an event. The remaining water after these two components was assumed to represent water available for deeper recharge. The median event quickflow:precipitation ratio was 11.8%. Event soil moisture recharge in the top one meter of soil accounted for a median of 65.3% of precipitation. Quickflow and shallow soil moisture recharge accounted for a median of 77.1% of the precipitation delivered to the watershed. Water budgets indicated that 43% of the events provided water for deeper recharge. Of these events, however, only 28% provided 50 mm or more of deep recharge. Because the focus was on events, when humidity was high and the vapor pressure deficit (VPD) was low, we ignored the role of evapotranspiration. However, interception, which was not accounted for, would have resulted in less storm precipitation than was measured at the watershed rain gage. Furthermore, transpiration may have altered the post-storm water balance when VPD increased and before excess water was able to infiltrate to deeper storage. While uncertainty remains, this study provided insight into the partitioning of incoming precipitation and the conditions under which water was likely available for deeper recharge.

Snow and Frost Depths on North and South Slopes

Treesearch

Richard S. Sartz

1973-01-01

Aspect affects soil frost depth by influencing the amount of solar radiation received at the ground or snow surface. Depending on the conditions, frost can be of equal depth on north and south slopes, deeper on north slopes, or deeper on south slopes. Data illustrate all three conditions

Rapid Turnover and Minimal Accretion of Mineral Soil Carbon During 60-Years of Pine Forest Growth on Previously Cultivated Land

NASA Astrophysics Data System (ADS)

Richter, D., Jr.; Mobley, M. L.; Billings, S. A.; Markewitz, D.

2016-12-01

At the Calhoun Long-Term Soil-Ecosystem field experiment (1957-present), reforestation of previously cultivated land over fifty years nearly doubled soil organic carbon (SOC) in surface soils (0 to 7.5-cm) but these gains were offset by significant SOC losses in subsoils (35 to 60-cm). Nearly all of the accretions in surface soils amounted to gains in light fraction SOC, whereas losses at depth were associated with silt and clay-sized particles. These changes are documented in the Calhoun Long-Term Soil-Ecosystem (LTSE) study that resampled soil from 16 plots about every five years and archived all soil samples from four soil layers within the upper 60-cm of mineral soil. We combined soil bulk density, density fractionation, stable isotopes, and radioisotopes to explore changes in SOC and soil organic nitrogen (SON) associated with five decades of the growth of a loblolly pine secondary forest. Isotopic signatures showed relatively large accumulations of contemporary forest-derived carbon in surface soils, and no accumulation of forest-derived carbon in subsoils. We interpret results to indicate that land-use change from cotton fields to secondary pine forests drove soil biogeochemical and hydrological changes that enhanced root and microbial activity and SOM decomposition in subsoils. As pine stands matured and are now transitioning to mixed pines and hardwoods, demands on soil organic matter for nutrients to support aboveground growth has eased due to pine mortality, and bulk SOM and SON and their isotopes in subsoils have stabilized. We anticipate major changes in the next fifty years as 1957 pine trees transition to hardwoods. This study emphasizes the importance of long-term experiments and deep soil measurements when characterizing SOC and SON responses to land use change. There is a remarkable paucity of E long-term soil data deeper than 30 cm.

Dynamics of water mass in the Central Siberia permafrost zone based on gravity survey from the grace satellites

NASA Astrophysics Data System (ADS)

Im, S. T.; Kharuk, V. I.

2015-12-01

The GRACE gravimetric survey is applied to analyze the equivalent water mass anomalies (EWMAs) in the permafrost zone of Central Siberia. Variations in EWMAs are related to precipitation, air temperature, potential evapotranspiration, and soil composition (drainage conditions). The EWMA dynamics demonstrates two periods. The period of 2003-2008 is characterized by a positive trend. The one of 2008-2012 shows a decrease in the trend with a simultaneous increase by 30-70% of EWMA dispersion in the background of growth (up to 40%) of precipitation variability. The rate of water mass increment demonstrates a positive correlation with the sand and gravel contents in soil ( r = 0.72) and a negative one with clay content ( r =-0.69 to-0.77). For Taimyr Peninsula, there is a deficit of residual water mass (~250 mm for the period of 2012-2013) indicating the deeper thawing of permafrost soils. In the Central Siberian Plateau, the indicator of more intensive permafrost thawing (and that of an increase in active layer thickness) is a considerable trend of water mass increase (2003-2008). The increasing trend of the largest Siberian rivers (Yenisei and Lena) is revealed in the period of 2003-2012.

Nutrients in groundwaters of the conterminous United States, 1992-1995

USGS Publications Warehouse

Nolan, B.T.; Stoner, J.D.

2000-01-01

Results of a national water quality assessment indicate that nitrate is detected in 71% of groundwater samples, more than 13 times as often as ammonia, nitrite, organic nitrogen, and orthophosphate, based on a common detection threshold of 0.2 mg/L. Shallow groundwater (typically 5 m deep or less) beneath agricultural land has the highest median nitrate concentration (3.4 mg/L), followed by shallow groundwater beneath urban land (1.6 mg/L) and deeper groundwater in major aquifers (0.48 mg/L). Nitrate exceeds the maximum contaminant level, 10 mg/L as nitrogen, in more than 15% of groundwater samples from 4 of 33 major aquifers commonly used as a source of drinking water. Nitrate concentration in groundwater is variable and depends on interactions among several factors, including nitrogen loading, soil type, aquifer permeability, recharge rate, and climate. For a given nitrogen loading, factors that generally increase nitrate concentration in groundwater include well-drained soils, fractured bedrock, and irrigation. Factors that mitigate nitrate contamination of groundwater include poorly drained soils, greater depth to groundwater, artificial drainage systems, intervening layers of unfractured bedrock, a low rate of groundwater recharge, and anaerobic conditions in aquifers.

Carbon and 14C distribution in tropical and subtropical agricultural soils

NASA Astrophysics Data System (ADS)

Prastowo, Erwin; Grootes, Pieter; Nadeau, Marie

2016-04-01

Paddy soil management affects, through the alternating anoxic and oxic conditions it creates, the transport and stabilisation of soil organic matter (SOM). Irrigation water may percolate more organic materials - dissolved (DOM) and colloidal - into the subsoil during anoxic conditions. Yet a developed ploughpan tends to prevent C from going deeper in the subsoil and partly decouple C distribution in top and sub soil. We investigate the influence of different soil type and environment. We observed the C and 14C distribution in paddy and non-paddy soil profiles in three different soil types from four different climatic regions of tropical Indonesia, and subtropical China. Locations were Sukabumi (Andosol, ca. 850 m a.s.l), Bogor (clayey Alisol, ca. 240 m a.s.l), and Ngawi (Vertisol, ca. 70 m a.s.l) in Jawa, Indonesia, and Cixi (Alisol(sandy), ca. 4 - 6 m a.s.l) in Zhejiang Province, China. We compared rice paddies with selected neighbouring non-paddy fields and employed AMS 14C as a tool to study C dynamics from bulk, alkali soluble-humic, and insoluble humin samples, and macrofossils (plant remains, charcoal). Our data suggest that vegetation type determines the quantity and quality of biomass introduced as litter and root material in top and subsoil, and thus contributes to the soil C content and profile, which fits the 14C signal distribution, as well as 13C in Ngawi with C4 sugar cane as upland crop. 14C concentrations for the mobile humic acid fraction were generally higher than for bulk samples from the same depth, except when recent plant and root debris led to high 14C levels in near-surface samples. The difference in sampling, - averaged layer for bulk sample and 1-cm layer thickness for point sample - shows gradients in C and 14C across the layers, which could be a reason for discrepancies between the two. High 14C concentrations - in Andosol Sukabumi up to 111 pMC - exceed the atmospheric 14CO2concentration in the sampling year in 2012 (˜ 103 pMC) and reflect stored organic material from earlier years with a higher atmospheric bomb 14C content. Direct inputs of plant material into the subsoil is indicated by young organic remains with more than 103 pMC below 0.8 m depth. In combination with 13C observation, it is quite obvious that introduction of young C took place in both paddy and non-paddy.

Effects of Pedogenic Fe Oxides on Soil Aggregate-Associated Carbon

NASA Astrophysics Data System (ADS)

Asefaw Berhe, A.; Jin, L.

2017-12-01

Carbon sequestration is intimately related to the soil structure, mainly soil aggregate dynamics. Carbon storage in soil aggregates has been recognized as an important carbon stabilization mechanism in soils. Organic matter and pedogenic Fe oxides are major binding agents that facilitate soil aggregate formation and stability. However, few studies have investigated how different forms of pedogenic Fe oxides can affect soil carbon distribution in different aggregate-size fractions. We investigated sequentially extracted pedogenic Fe oxides (in the order of organically complexed Fe extracted with sodium pyrophosphate, poorly-crystalline Fe oxides extracted with hydroxylamine hydrochloride, and crystalline Fe oxides extracted with dithionite hydrochloride) and determined the amount and nature of C in macroaggregates (2-0.25mm), microaggregates (0.25-0.053mm), and two silt and clay fractions (0.053-0.02mm, and <0.02mm) in Musick soil from Sierra Nevada mountain in California. We also determined how pedogenic Fe oxides affect soil carbon distribution along soil depth gradients. Findings of our study revealed that the proportion of organic matter complexed Fe decreased, but the proportion of crystalline Fe increased with increasing soil depths. Poorly crystalline Fe oxides (e.g. ferrihydrite) was identified as a major Fe oxide in surface soil, whereas crystalline Fe oxides (e.g. goethite) were found in deeper soil layers. These results suggest that high concentration of organic matter in surface soil suppressed Fe crystallization. Calcium cation was closely related to the pyrophosphate extractable Fe and C, which indicates that calcium may be a major cation that contribute to the organic matter complexed Fe and C pool. Increasing concentrations of extractable Fe and C with decreasing aggregate size fractions also suggests that Fe oxides play an important role in formation and stability of silt and clay fractions, and leading to further stabilization of carbon in soil. Our findings provide mechanistic understanding of how pedogenic Fe oxides play important role in carbon stabilization in different aggregate-size fractions in soil.

Changes in Soil Carbon and Nitrogen following Land Abandonment of Farmland on the Loess Plateau, China

PubMed Central

Deng, Lei; Shangguan, Zhou-Ping; Sweeney, Sandra

2013-01-01

The revegetation of abandoned farmland significantly influences soil organic C (SOC) and total N (TN). However, the dynamics of both soil OC and N storage following the abandonment of farmland are not well understood. To learn more about soil C and N storages dynamics 30 years after the conversion of farmland to grassland, we measured SOC and TN content in paired grassland and farmland sites in the Zhifanggou watershed on the Loess Plateau, China. The grassland sites were established on farmland abandoned for 1, 7, 13, 20, and 30 years. Top soil OC and TN were higher in older grassland, especially in the 0–5 cm soil depths; deeper soil OC and TN was lower in younger grasslands (<20 yr), and higher in older grasslands (30 yr). Soil OC and N storage (0–100 cm) was significantly lower in the younger grasslands (<20 yr), had increased in the older grasslands (30 yr), and at 30 years SOC had increased to pre-abandonment levels. For a thirty year period following abandonment the soil C/N value remained at 10. Our results indicate that soil C and TN were significantly and positively correlated, indicating that studies on the storage of soil OC and TN needs to focus on deeper soil and not be restricted to the uppermost (0–30 cm) soil levels. PMID:23940793

Improving Soil Moisture Estimation through the Joint Assimilation of SMOS and GRACE Satellite Observations

NASA Technical Reports Server (NTRS)

Girotto, Manuela

2018-01-01

Observations from recent soil moisture dedicated missions (e.g. SMOS or SMAP) have been used in innovative data assimilation studies to provide global high spatial (i.e., approximately10-40 km) and temporal resolution (i.e., daily) soil moisture profile estimates from microwave brightness temperature observations. These missions are only sensitive to near-surface soil moisture 0-5 cm). In contrast, the Gravity Recovery and Climate Experiment (GRACE) mission provides accurate measurements of the entire vertically integrated terrestrial water storage (TWS) column but, it is characterized by low spatial (i.e., 150,000 km2) and temporal (i.e., monthly) resolutions. Data assimilation studies have shown that GRACE-TWS primarily affects (in absolute terms) deeper moisture storages (i.e., groundwater). In this presentation I will review benefits and drawbacks associated to the assimilation of both types of observations. In particular, I will illustrate the benefits and drawbacks of their joint assimilation for the purpose of improving the entire profile of soil moisture (i.e., surface and deeper water storages).

Density and community structure of soil- and bark-dwelling microarthropods along an altitudinal gradient in a tropical montane rainforest.

PubMed

Illig, Jens; Norton, Roy A; Scheu, Stefan; Maraun, Mark

2010-09-01

Microarthropod communities in the soil and on the bark of trees were investigated along an elevation gradient (1,850, 2,000, 2,150, 2,300 m) in a tropical montane rain forest in southern Ecuador. We hypothesised that the density of microarthropods declines with depth in soil and increases with increasing altitude mainly due to the availability of resources, i.e. organic matter. In addition, we expected bark and soil communities to differ strongly, since the bark of trees is more exposed to harsher factors. In contrast to our hypothesis, the density of major microarthropod groups (Collembola, Oribatida, Gamasina, Uropodina) was generally low and decreased with altitude. However, as we predicted the density of each of the groups decreased with soil depth. Density of microarthropods on tree bark was lower than in soil. Overall, 43 species of oribatid mites were found, with the most abundant higher taxa being Poronota, pycnonotic Apheredermata, Mixonomata and Eupheredermata. The oribatid mite community on bark did not differ significantly from that in soil. The number of oribatid mite species declined with altitude (24, 23, 17 and 13 species at 1,850, 2,000, 2,150 and 2,300 m, respectively). Rarefaction curves indicate that overall about 50 oribatid mite species are to be expected along the studied altitudinal gradient. Results of this study indicate (1) that microarthropods may be limited by the quality of resources at high altitudes and by the amount of resources at deeper soil layers, and (2) that the bark of trees and the soil are habitats of similar quality for oribatid mites.

The effect of modifying rooting depths and nitrification inhibitors on nutrient uptake from organic biogas residues in maize

NASA Astrophysics Data System (ADS)

Dietrich, Charlotte C.; Koller, Robert; Nagel, Kerstin A.; Schickling, Anke; Schrey, Silvia D.; Jablonowski, Nicolai D.

2017-04-01

Optimizing the application of and nutrient uptake from organic nutrient sources, such as the nutrient-rich residues ("digestates") from the biogas industry, is becoming a viable option in remediating fertility on previously unsuitable soils for agricultural utilization. Proposedly, concurrent changes in root system architecture and functioning could also serve as the basis of future phytomining approaches. Herein, we evaluate the effect of spatial nutrient availability and nitrification on maize root architecture and nutrient uptake. We test these effects by applying maize-based digestate at a rate of 170 kg/ha in layers of varying depths (10, 25 and 40 cm) and through either the presence or absence of nitrification inhibitors. In order to regularly monitor above- and below-ground plant biomass production, we used the noninvasive phenotyping platform, GROWSCREEN-Rhizo at the Forschungszentrum Jülich, using rhizotrons (Nagel et al., 2012). Measured parameters included projected plant height and leaf area, as well as root length and spatial distribution. Additionally, root diameters were quantified after the destructive harvest, 21 days after sowing (DAS). Spatial nutrient availability significantly affected root system architecture, as for example root system size -the area occupied by roots- increased alongside nutrient layer depths. Fertilization also positively affected root length density (RLD). Within fertilized layers, the presence of nitrification inhibitors increased RLD by up to 30% and was most pronounced in the fine root biomass fraction (0.1 to 0.5mm). Generally, nitrification inhibitors promoted early plant growth by up to 45% across treatments. However, their effect varied in dependence of layer depths, leading to a time-delayed response in deeper layers, accounting for plants having to grow significantly longer roots in order to reach fertilized substrate. Nitrification inhibitors also initiated the comparatively early on-set of growth differences in shallower layers, where their effect on plant growth was temporarily most pronounced. At final harvest (21 DAS) however, effects of nitrification inhibitors on plant height were visible only in deeper layers. Furthermore, the statistically significant interaction between the factors time x layer depths x nitrification inhibitors underlined the dynamic influence of nitrification inhibitors on plant growth over time and across rooting depths. This study offers insights into optimizing nutrient uptake and plant productivity by (re-) using residues from the biogas industry. It is among the first to monitor and try to explain the dynamics of nitrification inhibitors on root system architecture over time. A modified N-fertilization application scheme might also serve as a promising tool in optimizing phytoremediation and phytomining techniques through predictably altering root structure in fertilized layers. References: Nagel, K. A. ; Putz, A. ; Gilmer, F. ; Heinz, K. ; Fischbach, A. ; Pfeifer, J. ; Faget, M. ; Blossfeld, S. ; Ernst, M. ; Dimaki, C. ; Kastenholz, B. ; Kleinert, A.-K. ; Galinski, A. ; Scharr, H. ; Fiorani, F. ; Schurr, U. (2012): GROWSCREEN-Rhizo is a novel phenotyping robot enabling simultaneous measurements of root and shoot growth for plants grown in soil-filled rhizotrons.
Functional plant biology 39(11), 891-904.

Global distribution of soil organic carbon - Part 1: Masses and frequency distributions of SOC stocks for the tropics, permafrost regions, wetlands, and the world

NASA Astrophysics Data System (ADS)

Köchy, M.; Hiederer, R.; Freibauer, A.

2015-04-01

The global soil organic carbon (SOC) mass is relevant for the carbon cycle budget and thus atmospheric carbon concentrations. We review current estimates of SOC stocks and mass (stock × area) in wetlands, permafrost and tropical regions and the world in the upper 1 m of soil. The Harmonized World Soil Database (HWSD) v.1.2 provides one of the most recent and coherent global data sets of SOC, giving a total mass of 2476 Pg when using the original values for bulk density. Adjusting the HWSD's bulk density (BD) of soil high in organic carbon results in a mass of 1230 Pg, and additionally setting the BD of Histosols to 0.1 g cm-3 (typical of peat soils), results in a mass of 1062 Pg. The uncertainty in BD of Histosols alone introduces a range of -56 to +180 Pg C into the estimate of global SOC mass in the top 1 m, larger than estimates of global soil respiration. We report the spatial distribution of SOC stocks per 0.5 arcminutes; the areal masses of SOC; and the quantiles of SOC stocks by continents, wetland types, and permafrost types. Depending on the definition of "wetland", wetland soils contain between 82 and 158 Pg SOC. With more detailed estimates for permafrost from the Northern Circumpolar Soil Carbon Database (496 Pg SOC) and tropical peatland carbon incorporated, global soils contain 1325 Pg SOC in the upper 1 m, including 421 Pg in tropical soils, whereof 40 Pg occurs in tropical wetlands. Global SOC amounts to just under 3000 Pg when estimates for deeper soil layers are included. Variability in estimates is due to variation in definitions of soil units, differences in soil property databases, scarcity of information about soil carbon at depths > 1 m in peatlands, and variation in definitions of "peatland".

The relative importance of decomposition and transport mechanisms in accounting for soil organic carbon profiles

NASA Astrophysics Data System (ADS)

Guenet, B.; Eglin, T.; Vasilyeva, N.; Peylin, P.; Ciais, P.; Chenu, C.

2013-04-01

Soil is the major terrestrial reservoir of carbon and a substantial part of this carbon is stored in deep layers, typically deeper than 50 cm below the surface. Several studies underlined the quantitative importance of this deep soil organic carbon (SOC) pool and models are needed to better understand this stock and its evolution under climate and land-uses changes. In this study, we tested and compared three simple theoretical models of vertical transport for SOC against SOC profiles measurements from a long-term bare fallow experiment carried out by the Central-Chernozem State Natural Biosphere Reserve in the Kursk Region of Russia. The transport schemes tested are diffusion, advection and both diffusion and advection. They are coupled to three different formulations of soil carbon decomposition kinetics. The first formulation is a first order kinetics widely used in global SOC decomposition models; the second one, so-called "priming" model, links SOC decomposition rate to the amount of fresh organic matter, representing the substrate interactions. The last one is also a first order kinetics, but SOC is split into two pools. Field data are from a set of three bare fallow plots where soil received no input during the past 20, 26 and 58 yr, respectively. Parameters of the models were optimised using a Bayesian method. The best results are obtained when SOC decomposition is assumed to be controlled by fresh organic matter (i.e., the priming model). In comparison to the first-order kinetic model, the priming model reduces the overestimation in the deep layers. We also observed that the transport scheme that improved the fit with the data depended on the soil carbon mineralisation formulation chosen. When soil carbon decomposition was modelled to depend on the fresh organic matter amount, the transport mechanism which improved best the fit to the SOC profile data was the model representing both advection and diffusion. Interestingly, the older the bare fallow is, the lesser the need for diffusion is, suggesting that stabilised carbon may not be transported within the profile by the same mechanisms than more labile carbon.

Modeling Water and Nutrient Transport through the Soil-Root-Canopy Continuum: Explicitly Linking the Below- and Above-Ground Processes

NASA Astrophysics Data System (ADS)

Kumar, P.; Quijano, J. C.; Drewry, D.

2010-12-01

Vegetation roots provide a fundamental link between the below ground water and nutrient dynamics and above ground canopy processes such as photosynthesis, evapotranspiration and energy balance. The “hydraulic architecture” of roots, consisting of the structural organization of the root system and the flow properties of the conduits (xylem) as well as interfaces with the soil and the above ground canopy, affect stomatal conductance thereby directly linking them to the transpiration. Roots serve as preferential pathways for the movement of moisture from wet to dry soil layers during the night, both from upper soil layer to deeper layers during the wet season (‘hydraulic descent’) and vice-versa (‘hydraulic lift’) as determined by the moisture gradients. The conductivities of transport through the root system are significantly, often orders of magnitude, larger than that of the surrounding soil resulting in movement of soil-moisture at rates that are substantially larger than that through the soil. This phenomenon is called hydraulic redistribution (HR). The ability of the deep-rooted vegetation to “bank” the water through hydraulic descent during wet periods for utilization during dry periods provides them with a competitive advantage. However, during periods of hydraulic lift these deep-rooted trees may facilitate the growth of understory vegetation where the understory scavenges the hydraulically lifted soil water. In other words, understory vegetation with relatively shallow root systems have access to the banked deep-water reservoir. These inter-dependent root systems have a significant influence on water cycle and ecosystem productivity. HR induced available moisture may support rhizosphere microbial and mycorrhizal fungi activities and enable utilization of heterogeneously distributed water and nutrient resources To capture this complex inter-dependent nutrient and water transport through the soil-root-canopy continuum we present modeling results using coupled partial differential equations of transport in soils and roots along with that for nutrient dynamics. We study the feedbkack of HR on the dynamics of water and nitrogen cycling in the soil and how these dynamics influence root water and nitrogen uptake and consequently carbon assimilation by the canopy. The forcing data is obtained from the Ameriflux Tower located in Blodgett Forest, Sierra Nevada, California. We consider single-species (Ponderosa Pine) and multi-species (overstory Ponderosa Pine and understory shrubs) interaction. When single species is considered, the near surface soil-moisture available from HR during dry summer season is an important source of evaporation and contributes significantly to the total ET flux. However, when multi-species interactions are taken into account, the soil-water from the HR becomes an important source of transpiration from the understory. The results also show that passive plant nitrogen uptake is higher when HR is present and it is critical for sustaining expected rates of carbon assimilation.

The combined effects of a long-term experimental drought and an extreme drought on the use of plant-water sources in a Mediterranean forest.

PubMed

Barbeta, Adrià; Mejía-Chang, Monica; Ogaya, Romà; Voltas, Jordi; Dawson, Todd E; Peñuelas, Josep

2015-03-01

Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. This study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions. © 2014 John Wiley & Sons Ltd.

Characteristics of Eurasian snowmelt and its impacts on the land surface and surface climate

NASA Astrophysics Data System (ADS)

Ye, Kunhui; Lau, Ngar-Cheung

2018-03-01

The local hydrological and climatic impacts of Eurasian snowmelt are studied using advanced land surface and atmospheric data. It is found that intense melting of snow is located at mid-high latitudes in April and May. Snowmelt plays an important role in determining the seasonal cycles of surface runoff and soil moisture (SM). Specifically, melting is accompanied by sharp responses in surface runoff and surface SM while the impacts are delayed for deeper-layer of soil. This is particularly significant in the western sector of Eurasia. On interannual timescales, the responses of various surface parameters to snowmelt in the same month are rather significant. However, the persistence of surface SM anomalies is weak due to the strong soil evaporation anomalies and surplus of surface energy for evaporation. Strong impacts on the sensible heat flux, planetary boundary layer height and precipitation in the next month following the melting of snow are identified in west Russia and Siberia. Downward propagation of surface SM anomalies is observed and a positive evaporation-convection feedback is identified in west Russia. However, the subsequent impacts on the local convective precipitation in late spring-summer and its contribution to the total precipitation are seemingly weak. The atmospheric water vapor convergence has strong control over the total precipitation anomalies. Overall, snowmelt-produced SM anomalies are not found to significantly impact the late spring-summer local climate anomalies in Northern Eurasia. Therefore, the delayed remote-responses of atmospheric circulation and climate to the melting of Eurasian snow may be only possible near the melting period.

Concentrations and flux measurements of volatile organic compounds (VOC) in boreal forest soil

NASA Astrophysics Data System (ADS)

Mäki, Mari; Aaltonen, Hermanni; Heinonsalo, Jussi; Hellén, Heidi; Pumpanen, Jukka; Bäck, Jaana

2017-04-01

Volatile organic compounds (VOC) impact soil processes as VOCs transmit signals between roots and rhizosphere (Ditengou et al., 2015), VOCs can regulate microbial activity (Asensio et al., 2012), and VOCs can also promote root growth (Hung et al., 2012). Belowground concentrations of VOCs have not been measured in situ and for this reason, knowledge of how different soil organisms such as roots, rhizosphere and decomposers contribute to VOC production is limited. The aim of this study was to determine and quantify VOC fluxes and concentrations of different horizons from boreal forest soil. The VOC concentrations and fluxes were measured from Scots pine (Pinus sylvestris) forest soil at the SMEAR II station in southern Finland from 21th of April to 2nd of December in 2016. VOC fluxes were measured using dynamic (flow-through) chambers from five soil collars placed on five different locations. VOC concentrations were also measured in each location from four different soil horizons with the measurement depth 1-107 cm. VOCs were collected from underground gas collectors into the Tenax-Carbopack-B adsorbent tubes using portable pumps ( 100 ml min-1). The VOC concentrations and fluxes of isoprene, 11 monoterpenes, 13 sesquiterpenes and different oxygenated VOCs were measured. Sample tubes were analyzed using thermal desorption-gas chromatograph-mass spectrometry (TD-GC-MS). Soil temperature and soil water content were continuously monitored for each soil horizon. Our preliminary results show that the primary source of VOCs is organic soil layer and the contribution of mineral soil to the VOC formation is minor. VOC fluxes and concentrations were dominated by monoterpenes such as α-pinene, camphene, β-pinene, and Δ3-carene. Monoterpene concentration is almost 10-fold in organic soil compared to the deeper soil layers. However, the highest VOC fluxes on the soil surface were measured in October, whereas the monoterpene concentrations in organic soil were highest in July and August. Organic soil is formed by organic matter which contains energy rich compounds for microbial decomposition and fine root biomass is also highest in soil surface (Helmisaari et al., 2007). With these analyses, we aim at distinguishing the VOC sinks and sources in the soil layers and quantifying the potential role of VOC uptake by soil microbiota. Asensio, D., Yuste, J. C., Mattana, S., Ribas, À., Llusià, J., and Peñuelas, J.: Litter VOCs induce changes in soil microbial biomass C and N and largely increase soil CO2 efflux. Plant and soil, 360(1-2), 163-174, doi:10.1007/s11104-012-1220-9, 2012. Ditengou, F. A., Müller, A., Rosenkranz, M., Felten, J., Lasok, H., van Doorn, M. M., Legue, V., Palme, K., Schnitzler, J.-P., and Polle, A. Volatile signalling by sesquiterpenes from ectomycorrhizal fungi reprogrammes root architecture. Nature communications, 6:6279, doi:10.1038/ncomms7279, 2015. Helmisaari, H. S., Derome, J., Nöjd, P., & Kukkola, M.: Fine root biomass in relation to site and stand characteristics in Norway spruce and Scots pine stands. Tree Physiology, 27(10), 1493-1504, 2007. Hung, R., Lee, S., and Bennett, J. W.: Arabidopsis thaliana as a model system for testing the effect of Trichoderma volatile organic compounds. Fungal Ecology, 6(1), 19-26, doi:10.1016/j.funeco.2012.09.005, 2013.

Monitoring of the active layer at Kapp Linne', SVALBARD 1972-2002

NASA Astrophysics Data System (ADS)

Akerman, J.

2003-04-01

The active layer has been monitored at ten sites in the vicinity of Kapp Linné, (78o03'42" 13o37'07") Svalbard during the period 1972 - 2002. The ten sites differ in elevation, distance from the sea, vegetation cover, substrate and active periglacial processes. From 1994 the International permafrost Association "CALM" standard grids, with measurement within 100x100m squares, has been applied. Microclimate and soil temperatures have been monitored by data logger covering levels form 2 m above to 7m below the ground. The macroclimate is covered by complete data series from the nearby weather station at Kapp Linne’, covering the period 1912 to 2002. A number of periglacial processes, especially slope processes, are monitored parallel with the active layer. The mean active layer for the sites varies between 1,13m and 0,43m. The deepest active layer is found in the exposed, well drained raised beach ridges and the shallowest in the bogs. The interannual variability during the observation period do not correlate well with the MAAT but better with the summer climate, June - August mean or DDT. The data clearly illustrate colder summers during the period 1972 to 1983 and after that steadily increasing summer temperatures. The active layer follows the same general pattern with good correlations. There are several surface indications as a response to the deepening active layer especially in the bogs. Thermokarst scars appear frequently and a majority of the palsa like mounds and pounus have disappeared. A drastic change in the vegetation on the bogs has also occurred, from dry heath to wet Carex vegetation. In summary the observations from Kapp Linne’ are; 1. A clear trend towards milder summers, 2. A clear trend towards deeper active layers, 3. All sites show a similar pattern, 4. The bogs are getting strikingly wetter, 5. Mounds in the bog sites are disappearing, 6. The slow slope processes are getting accelerated, 7. Thermokarst depressions and scars are appearing in a small scale at all sites, 8. Soil temperatures are increasing at all levels down to 7 m.

Joint Multifractal Analysis of penetration resistance variability in an olive orchard.

NASA Astrophysics Data System (ADS)

Lopez-Herrera, Juan; Herrero-Tejedor, Tomas; Saa-Requejo, Antonio; Villeta, Maria; Tarquis, Ana M.

2016-04-01

Spatial variability of soil properties is relevant for identifying those zones with physical degradation. We used descriptive statistics and multifractal analysis for characterizing the spatial patterns of soil penetrometer resistance (PR) distributions and compare them at different soil depths and soil water content to investigate the tillage effect in soil compactation. The study was conducted on an Inceptisol dedicated to olive orchard for the last 70 years. Two parallel transects of 64 m were selected as different soil management plots, conventional tillage (CT) and no tillage (NT). Penetrometer resistance readings were carried out at 50 cm intervals within the first 20 cm of soil depth (López de Herrera et al., 2015a). Two way ANOVA highlighted that tillage system, soil depth and their interaction are statistically significant to explain the variance of PR data. The comparison of CT and NT results at different depths showed that there are significant differences deeper than 10 cm but not in the first two soil layers. The scaling properties of each PR profile was characterized by τ(q) function, calculated in the range of moment orders (q) between -5 and +5 taken at 0.5 lag increments. Several parameters were calculated from this to establish different comparisons (López de Herrera et al., 2015b). While the multifractal analysis characterizes the distribution of a single variable along its spatial support, the joint multifractal analysis can be used to characterize the joint distribution of two or more variables along a common spatial support (Kravchenko et al., 2000; Zeleke and Si, 2004). This type of analysis was performed to study the scaling properties of the joint distribution of PR at different depths. The results showed that this type of analysis added valuable information to describe the spatial arrangement of depth-dependent penetrometer data sets in all the soil layers. References Kravchenko AN, Bullock DG, Boast CW (2000) Joint multifractal analysis of crop yield and terrain slope. Agro. j. 92: 1279-1290. López de Herrera, J., Tomas Herrero Tejedor, Antonio Saa-Requejo and Ana M. Tarquis (2015a) Influence of tillage in soil penetration resistance variability in an olive orchard. Geophysical Research Abstracts, 17, EGU2015-15425. López de Herrera, J., Tomás Herrero Tejedor, Antonio Saa-Requejo, A.M. Tarquis. Influence of tillage in soil penetration resistance variability in an olive orchard. Soil Research, accepted, 2015b. doi: SR15046 Zeleke TB, Si BC (2004) Scaling properties of topographic indices and crop yield: Multifractal and joint multifractal approaches. Agro. j. 96: 1082-1090.

[Effect of long-term fertilization on microbial community functional diversity in black soil].

PubMed

Liu, Jing-xin; Chi, Feng-qin; Xu, Xiu-hong; Kuang, En-jun; Zhang, Jiu-ming; Su, Qing-rui; Zhou, Bao-ku

2015-10-01

In order to study the effects of long-term different fertilization on microbial community functional diversity in arable black. soil, we examined microbial metabolic activities in two soil la- yers (0-20 cm, 20-40 cm) under four treatments (CK, NPK, M, MNPK) from a 35-year continuous fertilization field at the Ministry of Agriculture Key Field Observation Station of Harbin Black Soil Ecology Environment using Biolog-ECO method. The results showed that: in the 0-20 cm soil layer, combined application of organic and inorganic fertilizer(MNPK) increased the rate of soil microbial carbon source utilization and community metabolism richness, diversity and dominance; In the 20-40 cm layer, these indices of the MNPK treatment was lower than that of the NPK treat- ment; while NPK treatment decreased soil microbial community metabolism evenness in both layers. Six groups of carbon sources used by soil microbes of all the treatments were different between the two soil layers, and the difference was significant among all treatments in each soil layer (P < 0.05) , while the variations among treatments were different in the two soil layers. Canonical correspondence analysis (CCA) showed that soil microbial community metabolic function of all the treatments was different between the two soil layers, and there was difference among all treatments in each soil layer, while the influences of soil nutrients on soil microbial community metabolic function of all treatments were similar in each soil layer. It was concluded that long-term different fertilization affected soil microbial community functional diversity in both tillage soil layer and down soil layers, and chemical fertilization alone had a larger influence on the microbial community functional diversity in the 20-40 cm layer.

Quasi 3D modelling of water flow in the sandy soil

NASA Astrophysics Data System (ADS)

Rezaei, Meisam; Seuntjens, Piet; Joris, Ingeborg; Boënne, Wesley; De Pue, Jan; Cornelis, Wim

2016-04-01

Monitoring and modeling tools may improve irrigation strategies in precision agriculture. Spatial interpolation is required for analyzing the effects of soil hydraulic parameters, soil layer thickness and groundwater level on irrigation management using hydrological models at field scale. We used non-invasive soil sensor, a crop growth (LINGRA-N) and a soil hydrological model (Hydrus-1D) to predict soil-water content fluctuations and crop yield in a heterogeneous sandy grassland soil under supplementary irrigation. In the first step, the sensitivity of the soil hydrological model to hydraulic parameters, water stress, crop yield and lower boundary conditions was assessed after integrating models at one soil column. Free drainage and incremental constant head conditions were implemented in a lower boundary sensitivity analysis. In the second step, to predict Ks over the whole field, the spatial distributions of Ks and its relationship between co-located soil ECa measured by a DUALEM-21S sensor were investigated. Measured groundwater levels and soil layer thickness were interpolated using ordinary point kriging (OK) to a 0.5 by 0.5 m in aim of digital elevation maps. In the third step, a quasi 3D modelling approach was conducted using interpolated data as input hydraulic parameter, geometric information and boundary conditions in the integrated model. In addition, three different irrigation scenarios namely current, no irrigation and optimized irrigations were carried out to find out the most efficient irrigation regime. In this approach, detailed field scale maps of soil water stress, water storage and crop yield were produced at each specific time interval to evaluate the best and most efficient distribution of water using standard gun sprinkler irrigation. The results show that the effect of the position of the groundwater level was dominant in soil-water content prediction and associated water stress. A time-dependent sensitivity analysis of the hydraulic parameters showed that changes in soil water content are mainly affected by the soil saturated hydraulic conductivity Ks in a two-layered soil. Results demonstrated the large spatial variability of Ks (CV = 86.21%). A significant negative correlation was found between ln Ks and ECa (r = 0.83; P≤0.01). This site-specific relation between ln Ks and ECa was used to predict Ks for the whole field after validation using an independent dataset of measured Ks. Result showed that this approach can accurately determine the field scale irrigation requirements, taking into account variations in boundary conditions and spatial variations of model parameters across the field. We found that uniform distribution of water using standard gun sprinkler irrigation is not an efficient approach since at locations with shallow groundwater, the amount of water applied will be excessive as compared to the crop requirements, while in locations with a deeper groundwater table, the crop irrigation requirements will not be met during crop water stress. Numerical results showed that optimal irrigation scheduling using the aforementioned water stress calculations can save up to ~25% irrigation water as compared to the current irrigation regime. This resulted in a yield increase of ~7%, simulated by the crop growth model.

Transport and degradation of perchlorate in deep vadose zone: implications from direct observations during bioremediation treatment

NASA Astrophysics Data System (ADS)

Dahan, Ofer; Katz, Idan; Avishai, Lior; Ronen, Zeev

2017-08-01

An in situ bioremediation experiment of a deep vadose zone ( ˜ 40 m) contaminated with a high concentration of perchlorate (> 25 000 mg L-1) was conducted through a full-scale field operation. Favourable environmental conditions for microbiological reduction of perchlorate were sought by infiltrating an electron donor-enriched water solution using drip irrigation underlying an airtight sealing liner. A vadose zone monitoring system (VMS) was used for real-time tracking of the percolation process, the penetration depth of dissolved organic carbon (DOC), and the variation in perchlorate concentration across the entire soil depth. The experimental conditions for each infiltration event were adjusted according to insight gained from data obtained by the VMS in previous stages. Continuous monitoring of the vadose zone indicated that in the top 13 m of the cross section, perchlorate concentration is dramatically reduced from thousands of milligrams per litre to near-detection limits with a concurrent increase in chloride concentration. Nevertheless, in the deeper parts of the vadose zone (< 17 m), perchlorate concentration increased, suggesting its mobilization down through the cross section. Breakthrough of DOC and bromide at different depths across the unsaturated zone showed limited migration capacity of biologically consumable carbon and energy sources due to their enhanced biodegradation in the upper soil layers. Nevertheless, the increased DOC concentration with concurrent reduction in perchlorate and increase in the chloride-to-perchlorate ratio in the top 13 m indicate partial degradation of perchlorate in this zone. There was no evidence of improved degradation conditions in the deeper parts where the initial concentrations of perchlorate were significantly higher.

Large Root Cortical Cell Size Improves Drought Tolerance in Maize1[C][W][OPEN

PubMed Central

Chimungu, Joseph G.; Brown, Kathleen M.

2014-01-01

The objective of this study was to test the hypothesis that large cortical cell size (CCS) would improve drought tolerance by reducing root metabolic costs. Maize (Zea mays) lines contrasting in root CCS measured as cross-sectional area were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the United States and Malawi. CCS varied among genotypes, ranging from 101 to 533 µm2. In mesocosms, large CCS reduced respiration per unit of root length by 59%. Under water stress in mesocosms, lines with large CCS had between 21% and 27% deeper rooting (depth above which 95% of total root length is located in the soil profile), 50% greater stomatal conductance, 59% greater leaf CO2 assimilation, and between 34% and 44% greater shoot biomass than lines with small CCS. Under water stress in the field, lines with large CCS had between 32% and 41% deeper rooting (depth above which 95% of total root length is located in the soil profile), 32% lighter stem water isotopic ratio of 18O to 16O signature, signifying deeper water capture, between 22% and 30% greater leaf relative water content, between 51% and 100% greater shoot biomass at flowering, and between 99% and 145% greater yield than lines with small cells. Our results are consistent with the hypothesis that large CCS improves drought tolerance by reducing the metabolic cost of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. These results, coupled with the substantial genetic variation for CCS in diverse maize germplasm, suggest that CCS merits attention as a potential breeding target to improve the drought tolerance of maize and possibly other cereal crops. PMID:25293960

Subsurface soil carbon losses offset surface carbon accumulation in abandoned agricultural fields

NASA Astrophysics Data System (ADS)

Yang, Y.; Knops, J. M. H.

2017-12-01

Soil carbon is widely understood to accumulate after agricultural abandonment. However, most of the studies have been focused on shallow depths (10 to 30 cm), and there is a lack of deeper soil carbon data. It was reported that in temperate grasslands, 58% of the soil organic carbon in the first meter was stored between 20 and 100 cm, and organic matter in deeper soil might also be susceptible to agricultural disturbance. We used repeated sampling in 2001 and 2014 to directly measure rates of soil carbon change in both surface and subsurface soil in 21 abandoned agricultural fields at Cedar Creek Ecosystem Science Reserve, MN. Congruent with many other studies, we found carbon accumulated 384.2 C g/m2 in surface soil (0 - 20 cm) over the 13 years. However, we also found carbon pool declined 688.1 C g/m2 in the subsurface soil (40-100 cm), which resulted in a net total loss of soil carbon. We investigated the ecosystem carbon pools and fluxes to explore the mechanisms of the observed soil carbon changes. We found root carbon was not significantly correlated with soil carbon in any of the depth. In situ soil incubation showed nitrogen mineralization rates in subsurface soil are lower than that of surface soil. However, the estimated nitrogen and carbon output through decomposition is higher than inputs from roots, therefore leading to carbon loss in subsurface soil. These results suggest that the decomposition of soil organic matter by microorganisms in subsurface soil is significant, and should be incorporated in ecosystem carbon budget models.

Deep soil layer is fundamental for evaluating carbon accumulation in agroecosystems

NASA Astrophysics Data System (ADS)

Dal Ferro, Nicola; Morari, Francesco; Simonetti, Gianluca; Polese, Riccardo; Berti, Antonio

2015-04-01

Soil organic carbon (SOC) is essential to secure key ecosystem services such as the provision of food and other biomass production, the filtering, buffering and transformation capacity and the climate regulation. It has been estimated that approximately 57% of the globally emitted C (8.7 Gt y-1) to the atmosphere is adsorbed by biospheric C pools, ascertaining the potential soil C sink capacity of managed ecosystems at 55 to 78 Gt, of which only 50 to 66% attainable. Therefore it is essential the full knowledge of soil management practices that can affect SOC dynamics and, in turn, climate change. Several studies focussed on the evaluation of the best cropping management practices to accumulate C in the soil profile. Nevertheless, in most cases soil analyses were made in the topsoil (generally in the 0-30 cm layer), ignoring the effect of C translocation in the deeper soil profile as a result of tillage practices, crop root deepening etc. In this context, in a long-term experiment established in the early 1960s, we quantified the SOC accumulation within the soil profile (0-90 cm) and evaluate the effects of different cropping system on SOC dynamics. The experiment is located at the experimental farm of the University of Padova, in northeastern Italy. The trial compares four rotations with three levels of mineral fertilisation and with or without organic fertilisation. The rotations considered are: continuous crops (grain maize, forage maize, winter wheat and permanent meadow); two-year (maize-wheat); four-year (sugarbeet, soybean, wheat, maize) and six-year (maize, sugarbeet, maize, wheat, alfalfa, alfalfa) with different levels of mineral, organic and mixed fertilisations. Crops with superficially developed rooting systems (e.g. permanent meadow) highly increased SOC only in the topsoil. This effect was enhanced by the contribution of organic amendment-C. Root-derived carbon played a pivotal role also in the deepest soil profile (60-90 cm) by increasing the SOC translocation. Considering the whole profile, the highest C accumulation was observed in cropping systems with high biomass production and deep rooting systems. Results indicated that for estimating the effects of cropping systems and agricultural practices on C accumulation, analyses in the topsoil can be misleading and it is necessary to consider the whole profile.

Quantification of dynamic soil-vegetation feedbacks following an isotopically labelled precipitation pulse

NASA Astrophysics Data System (ADS)

Piayda, Arndt; Dubbert, Maren; Siegwolf, Rolf; Cuntz, Matthias; Werner, Christiane

2017-05-01

The presence of vegetation alters hydrological cycles of ecosystems. Complex plant-soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soil-vegetation-atmosphere interfaces. The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water use in a Mediterranean cork oak woodland during dry conditions. An irrigation experiment using δ18O labelled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on the infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water use, water uptake depth plasticity, and contribution to ecosystem soil evaporation and transpiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive evaporation for transpiration, but infiltration rates decreased. No adjustments of main root water uptake depth to changes in water availability could be observed during the experiment. This forces understorey plants to compete with adjacent trees for water in deeper soil layers at the onset of summer. Thus, understorey plants are subjected to chronic water deficits faster, leading to premature senescence at the onset of drought. Despite this water competition, the presence of cork oak trees fosters infiltration and reduces evapotranspirative water losses from the understorey and the soil, both due to altered microclimatic conditions under crown shading. This study highlights complex soil-plant-atmosphere and inter-species interactions controlling rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

The significance of visitors' pressure for soil status in an urban park in Tel-Aviv

NASA Astrophysics Data System (ADS)

Zhevelev, Helena; Sarah, Pariente; Oz, Atar

2010-05-01

A park is one of the most important elements of sustainable development and optimization of the urban environment. The equilibrium within the complex of natural and anthropogenic factors defines the status of a park's ecosystem. The seasonal dynamics and spatial variations of soil properties in areas under differing levels of visitors' pressure were studied in a park in Tel-Aviv. Soil was sampled twice a year, in wet (March) and dry (July) seasons, from three types of areas, subjected to differing levels of visitors' pressure: high, low and none (control). In each type of area samples were taken from two depths (0-2 cm and 5-10 cm), at 14-39 points. In total, 268 soil samples were taken. Before the soil sampling, penetration depth was determined at each point. In addition, the numbers of barbecue fires in each of the three areas were counted. Gravimetric soil moisture, organic matter, pH, electrical conductivity, and soluble ions were measured in 1:1 water extraction. Penetration depth and electrical conductivity, and organic matter, sodium, potassium and chlorite contents differed under differing levels of visitors' pressure, whereas soil moisture, pH and calcium content exhibited only minor differences. Soil moisture, electrical conductivity, and magnesium and chlorite contents exhibited strong seasonal changes, whereas the organic matter, potassium and pH levels were unaffected by seasonal dynamics. Calcium, organic matter, magnesium and chlorite contents, and electrical conductivity were significantly affected by the depth of soil sampling, whereas pH was not so affected. The seasonal changes in soil properties in the area subjected to high visitors' pressure were higher than in the one under low visitors' pressure. In most cases, visitors' pressure led to increases in variance and coefficient of variation. Different soil properties were differently affected by visitors' pressure, seasonal dynamics and soil depth. The surface of the soil was more sensitive to both seasonal dynamics and visitors' pressure, than the deeper layer. Visitors' pressure increased seasonal changes in the studied soil properties, and also increased the spatial heterogeneity of the soil. The differences in organic matter, electrical conductivity and soluble ions among the areas under differing visitors' pressure are attributed to anthropogenic additions, which accompanied the recreational activities in the urban parks: remnants of barbecue fires and meals, and excreta of urban animals. Addition of urban dust, enriched in CaCO3, minimized the effect of visitors' pressure on soil calcium content. All the above anthropogenic additions enhance the differentiation in soil layers. The notable effect of visitors' pressure on variations in soil properties highlighted its high significance for urban parks.

Multiscale Geophysical Characterization of Weathering Fronts Along a Climate and Vegetation Gradient in Chile

NASA Astrophysics Data System (ADS)

Dal Bo, I.; Klotzsche, A.; Schaller, M.; Ehlers, T. A.; Vereecken, H.; Van Der Kruk, J.

2017-12-01

Understanding how weathering processes act is non-trivial. Direct methods are spatially restricted, time consuming, and expensive. Here, we show how to upscale and extend the point-scale layering information from dug pits deploying a multi-scale geophysical approach. Many studies have recently shown the potential of geophysics in bridging the gap between scales, although limited to specific environments. We applied Electromagnetic Induction (EMI), Ground Penetrating Radar (GPR), and Electrical Resistivity Tomography (ERT) in four study areas separated by 1600 km in the Chilean Coastal Cordillera, and ranging from the arid Atacama Desert in the north and temperate forests in the south. The main goals were to understand how the soil profile and the weathering front vary: 1) from north to south along these gradients, 2) in north- and south-facing hillslopes, and 3) within a single hillslope. We measured at the large-scale (EMI), at the profile scale (EMI, ERT, and GPR), and at the point-scale (GPR). The total length of the EMI, GPR and ERT measurements was 28.95 km, 3.67 km, and 0.27 km. GPR wide angle reflection and refraction measurements were the link between ground-truth data and geophysics. The low electrical conductivity (EC) regime limited the applicability of the EMI and ERT. However, still relative patterns of apparent electrical conductivity (ECa) from EMI could be used. Generally, ECa increased moving uphill and from north to south. Due to the low EC values in the study areas, GPR could image several reflections up to 8 m depth partially confirmed by the pit layering. Thicker layers on GPR profiles were present going from north to south and in the bottom-mid part of the hillslopes, as confirmed by ground-truth data. The main recognizable feature in the GPR profiles was the transition between B and C horizon. Here, hyperbolic-shape signatures were observed that probably were related to the presence of heterogeneities. The soil pits showed deeper layers in more vegetated south-facing hillslopes, which could be correlated with increased signal penetration and reflection depths in the GPR profiles. Soil depths and their interaction with biota in soil-mantled landscapes will be better characterized by combining geophysics with more environmental parameters within the interdisciplinary EarthShape project.

Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

USDA-ARS?s Scientific Manuscript database

No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but the effects deeper in the soil profile are uncertain. Subsequent tillage could counter SOC stabilized through NT practices by disrupting soil aggregation and promoting decomposition. We followed a long-term ti...

[Soil organic carbon mineralization of Black Locust forest in the deep soil layer of the hilly region of the Loess Plateau, China].

PubMed

Ma, Xin-Xin; Xu, Ming-Xiang; Yang, Kai

2012-11-01

The deep soil layer (below 100 cm) stores considerable soil organic carbon (SOC). We can reveal its stability and provide the basis for certification of the deep soil carbon sinks by studying the SOC mineralization in the deep soil layer. With the shallow soil layer (0-100 cm) as control, the SOC mineralization under the condition (temperature 15 degrees C, the soil water content 8%) of Black Locust forest in the deep soil layer (100-400 cm) of the hilly region of the Loess Plateau was studied. The results showed that: (1) There was a downward trend in the total SOC mineralization with the increase of soil depth. The total SOC mineralization in the sub-deep soil (100-200 cm) and deep soil (200-400 cm) were equivalent to approximately 88.1% and 67.8% of that in the shallow layer (0-100 cm). (2) Throughout the carbon mineralization process, the same as the shallow soil, the sub-deep and deep soil can be divided into 3 stages. In the rapid decomposition phase, the ratio of the mineralization or organic carbon to the total mineralization in the sub-deep and deep layer (0-10 d) was approximately 50% of that in the shallow layer (0-17 d). In the slow decomposition phase, the ratio of organic carbon mineralization to total mineralization in the sub-deep, deep layer (11-45 d) was 150% of that in the shallow layer (18-45 d). There was no significant difference in this ratio among these three layers (46-62 d) in the relatively stable stage. (3) There was no significant difference (P > 0.05) in the mineralization rate of SOC among the shallow, sub-deep, deep layers. The stability of SOC in the deep soil layer (100-400 cm) was similar to that in the shallow soil layer and the SOC in the deep soil layer was also involved in the global carbon cycle. The change of SOC in the deep soil layer should be taken into account when estimating the effects of soil carbon sequestration in the Hilly Region of the Loess Plateau, China.

Study on hydraulic property models for water retention and unsaturated hydraulic conductivity in MATSIRO with representation of water table dynamics

NASA Astrophysics Data System (ADS)

Yoshida, N.; Oki, T.

2016-12-01

Appropriate initial condition of soil moisture and water table depth are important factors to reduce uncertainty in hydrological simulations. Approaches to determine the initial water table depth have been developed because of difficulty to get information on global water table depth and soil moisture distributions. However, how is equilibrium soil moisture determined by climate conditions? We try to discuss this issue by using land surface model with representation of water table dynamics (MAT-GW). First, the global pattern of water table depth at equilibrium soil moisture in MAT-GW was verified. The water table depth in MAT-GW was deeper than the previous one at fundamentally arid region because the negative recharge and continuous baseflow made water table depth deeper. It indicated that the hydraulic conductivity used for estimating recharge and baseflow need to be reassessed in MAT-GW. In soil physics field, it is revealed that proper hydraulic property models for water retention and unsaturated hydraulic conductivity should be selected for each soil type. So, the effect of selecting hydraulic property models on terrestrial soil moisture and water table depth were examined.Clapp and Hornburger equation(CH eq.) and Van Genuchten equation(VG eq.) were used as representative hydraulic property models. Those models were integrated on MAT-GW and equilibrium soil moisture and water table depth with using each model were compared. The water table depth and soil moisture at grids which reached equilibrium in both simulations were analyzed. The equilibrium water table depth were deeper in VG eq. than CH eq. in most grids due to shape of hydraulic property models. Then, total soil moisture were smaller in VG eq. than CH eq. at almost all grids which water table depth reached equilibrium. It is interesting that spatial patterns which water table depth reached equilibrium or not were basically similar in both simulations but reverse patterns were shown in east and west part of America. Selection of each hydraulic property model based on soil types may compensate characteristic of models in initialization.

Gouty pitch midge damage to ponderosa pines planted on fertile and infertile soils in the western Sierra Nevada

Treesearch

George T. Ferrell; William D. Bedard; James L. Jenkinson

1987-01-01

Crown damage caused by gouty pitch midge (GPM) and its effects on tree growth were assessed in two 14-year-old ponderosa pine plantations, one on a shallow, infertile soil derived from serpentine and the other on a deeper, more fertile nonserpentine soil of marine parent material. Seed sources for each plantation were nearby indigenous stands on the same soils. Trees...

Permafrost carbon—climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koven, Charles D.; Lawrence, David M.; Riley, William J.

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon–nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost regionmore » is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. The future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.« less

Permafrost carbon—climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

DOE PAGES

Koven, Charles D.; Lawrence, David M.; Riley, William J.

2015-03-09

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon–nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost regionmore » is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. The future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.« less

Permafrost carbon−climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

PubMed Central

Koven, Charles D.; Lawrence, David M.; Riley, William J.

2015-01-01

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon−nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw. PMID:25775603

30. DETAILED FRONTAL VIEW WEST OF EXCAVATION AT SUSPECTED MICA ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

30. DETAILED FRONTAL VIEW WEST OF EXCAVATION AT SUSPECTED MICA PIT, SHOWING SOIL MIXED WITH MICA FLAKES AT REAR, AND DEEPER HOLE OF VIRGIN SOIL AT FRONT. - Vulcan Crucible Steel Company, Building No. 3, 100 First Street, Aliquippa, Beaver County, PA

Response of Surface Soil Hydrology to the Micro-Pattern of Bio-Crust in a Dry-Land Loess Environment, China

PubMed Central

Wei, Wei; Yu, Yun; Chen, Liding

2015-01-01

The specific bio-species and their spatial patterns play crucial roles in regulating eco-hydrologic process, which is significant for large-scale habitat promotion and vegetation restoration in many dry-land ecosystems. Such effects, however, are not yet fully studied. In this study, 12 micro-plots, each with size of 0.5 m in depth and 1 m in length, were constructed on a gentle grassy hill-slope with a mean gradient of 8° in a semiarid loess hilly area of China. Two major bio-crusts, including mosses and lichens, had been cultivated for two years prior to the field simulation experiments, while physical crusts and non-crusted bare soils were used for comparison. By using rainfall simulation method, four designed micro-patterns (i.e., upper bio-crust and lower bare soil, scattered bio-crust, upper bare soil and lower bio-crust, fully-covered bio-crust) to the soil hydrological response were analyzed. We found that soil surface bio-crusts were more efficient in improving soil structure, water holding capacity and runoff retention particularly at surface 10 cm layers, compared with physical soil crusts and non-crusted bare soils. We re-confirmed that mosses functioned better than lichens, partly due to their higher successional stage and deeper biomass accumulation. Physical crusts were least efficient in water conservation and erosion control, followed by non-crusted bare soils. More importantly, there were marked differences in the efficiency of the different spatial arrangements of bio-crusts in controlling runoff and sediment generation. Fully-covered bio-crust pattern provides the best option for soil loss reduction and runoff retention, while a combination of upper bio-crust and lower bare soil pattern is the least one. These findings are suggested to be significant for surface-cover protection, rainwater infiltration, runoff retention, and erosion control in water-restricted and degraded natural slopes. PMID:26207757

Freeze-Thaw Cycles and Soil Biogeochemistry: Implications for Greenhouse Gas emission

NASA Astrophysics Data System (ADS)

Rezanezhad, F.; Milojevic, T.; Oh, D. H.; Parsons, C. T.; Smeaton, C. M.; Van Cappellen, P.

2016-12-01

Freeze-thaw cycles represent a major natural climate forcing acting on soils at middle and high latitudes. Repeated freezing and thawing of soils changes their physical properties, geochemistry, and microbial community structure, which together govern the biogeochemical cycling of carbon and nutrients. In this presentation, we focus on how freeze-thaw cycles regulate carbon and nitrogen cycling and how these transformations influence greenhouse gas (GHG) fluxes. We present a novel approach, which combines the acquisition of physical and chemical data in a newly developed experimental soil column system. This system simulates realistic soil temperature profiles during freeze-thaw cycles. A high-resolution, Multi-Fiber Optode (MuFO) microsensor technique was used to detect oxygen (O2) continuously in the column at multiple depths. Surface and subsurface changes to gas and aqueous phase chemistry were measured to delineate the pathways and quantify soil respiration rates during freeze-thaw cycles. The results indicate that the time-dependent release of GHG from the soil surface is influenced by a combination of two key factors. Firstly, fluctuations in temperature and O2 availability affect soil biogeochemical activity and GHG production. Secondly, the recurrent development of a physical ice barrier prevents exchange of gaseous compounds between the soil and atmosphere during freezing conditions; removal of this barrier during thaw conditions increases GHG fluxes. During freezing, O2 levels in the unsaturated zone decreased due to restricted gas exchange with the atmosphere. As the soil thawed, O2 penetrated deeper into the soil enhancing the aerobic mineralization of organic carbon and nitrogen. Additionally, with the onset of thawing a pulse of gas flux occurred, which is attributed to the build-up of respiratory gases in the pore space during freezing. The latter implies enhanced anaerobic respiration as O2 supply ceases when the upper soil layer freezes.

Response of Surface Soil Hydrology to the Micro-Pattern of Bio-Crust in a Dry-Land Loess Environment, China.

PubMed

Wei, Wei; Yu, Yun; Chen, Liding

2015-01-01

The specific bio-species and their spatial patterns play crucial roles in regulating eco-hydrologic process, which is significant for large-scale habitat promotion and vegetation restoration in many dry-land ecosystems. Such effects, however, are not yet fully studied. In this study, 12 micro-plots, each with size of 0.5 m in depth and 1 m in length, were constructed on a gentle grassy hill-slope with a mean gradient of 8° in a semiarid loess hilly area of China. Two major bio-crusts, including mosses and lichens, had been cultivated for two years prior to the field simulation experiments, while physical crusts and non-crusted bare soils were used for comparison. By using rainfall simulation method, four designed micro-patterns (i.e., upper bio-crust and lower bare soil, scattered bio-crust, upper bare soil and lower bio-crust, fully-covered bio-crust) to the soil hydrological response were analyzed. We found that soil surface bio-crusts were more efficient in improving soil structure, water holding capacity and runoff retention particularly at surface 10 cm layers, compared with physical soil crusts and non-crusted bare soils. We re-confirmed that mosses functioned better than lichens, partly due to their higher successional stage and deeper biomass accumulation. Physical crusts were least efficient in water conservation and erosion control, followed by non-crusted bare soils. More importantly, there were marked differences in the efficiency of the different spatial arrangements of bio-crusts in controlling runoff and sediment generation. Fully-covered bio-crust pattern provides the best option for soil loss reduction and runoff retention, while a combination of upper bio-crust and lower bare soil pattern is the least one. These findings are suggested to be significant for surface-cover protection, rainwater infiltration, runoff retention, and erosion control in water-restricted and degraded natural slopes.

Quantification of dynamic soil - vegetation feedbacks following an isotopically labelled precipitation pulse

NASA Astrophysics Data System (ADS)

Piayda, Arndt; Dubbert, Maren; Siegwolf, Rolf; Cuntz, Matthias; Werner, Christiane

2017-04-01

The presence of vegetation alters hydrological cycles of ecosystems. Complex plant-soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and pivotal foundation for understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soil-vegetation-atmosphere interfaces. The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water-use in a Mediterranean cork-oak woodland during dry conditions. An irrigation experiment using δ18O-labeled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water-use, water uptake depth plasticity and contribution to ecosystem evapotranspiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive water loss for biomass production, carbon sequestration and nitrogen fixation. During the experiment no adjustments of main root water uptake depth to changes of water availability could be observed, rendering light to medium precipitation events under dry conditions useless. This forces understory plants to compete with adjacent trees for soil water in deeper soil layers. Thus understory plants are faster subject to chronic drought, leading to premature senescence at the onset of drought. Despite this water competition, the presence of Cork oak trees fosters infiltration to large degrees. That reduces drought stress, caused by evapotranspiration, due to favourable micro climatic conditions under tree crown shading. This study highlights complex soil-plant-atmosphere and inter-species interactions in both space and time controlling the fate of rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

Stratification and Storage of Soil Organic Carbon and Nitrogen as Affected by Tillage Practices in the North China Plain

PubMed Central

Zhang, Xiang-Qian; Kong, Fan-Lei; Chen, Fu; Lal, Rattan; Zhang, Hai-Lin

2015-01-01

Tillage practices can redistribute the soil profiles, and thus affects soil organic carbon (SOC), and its storage. The stratification ratio (SR) can be an indicator of soil quality. This study was conducted to determine tillage effects on the profile distribution of certain soil properties in winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) systems in the North China Plain (NCP). Three tillage treatments, including no till (NT), rotary tillage (RT), and plow tillage (PT), were established in 2001 in Luancheng County, Hebei Province. The concentration, storage, and SR of SOC and soil total nitrogen (TN) were assessed in both the wheat and maize seasons. Compared with RT and PT, the mean SRs for all depth ratios of SOC under NT increased by 7.85% and 30.61% during the maize season, and by 14.67% and 30.91% during the wheat season, respectively. The SR of TN for 0–5:30–50 cm increased by 140%, 161%, and 161% in the maize season, and 266%, 154%, and 122% in the wheat season compared to the SR for 0–5:5–10 cm under NT, RT and PT, respectively. The data indicated that SOC and TN were both concentrated in the surface-soil layers (0–10 cm) under NT but were distributed relatively evenly through the soil profile under PT. Meanwhile, the storage of SOC and TN was higher under NT for the surface soil (0–10 cm) but was higher under PT for the deeper soil (30–50 cm). Furthermore, the storage of SOC and TN was significantly related to SR of SOC and TN along the whole soil profile (P<0.0001). Therefore, SR could be used to explain and indicate the changes in the storage of SOC and TN. Further, NT stratifies SOC and TN, enhances the topsoil SOC storage, and helps to improve SOC sequestration and soil quality. PMID:26075391

Exploring rock fissures: does a specialized root morphology explain endemism on granite outcrops?

PubMed Central

Poot, Pieter; Hopper, Stephen D.; van Diggelen, Josepha M.H.

2012-01-01

Background and Aims Worldwide, many plant species are confined to open, shallow-soil, rocky habitats. Although several hypotheses have been proposed to explain this habitat specificity, none has been convincing. We suggest that the high level of endemism on shallow soils is related to the edaphic specialization needed to survive in these often extremely drought-prone habitats. Previous research has shown that species endemic to ironstone communities in SW Australia have a specialized root morphology that enhances their chance to access fissures in the underlying rock. Here we test the generality of these findings for species that are confined to a shallow-soil habitat that is of much greater global significance: granite outcrops. Methods We compared temporal and spatial root growth and allocation of three endemic woody perennials of SW Australian granite outcrop communities with those of congeners occurring on nearby deeper soils. Seedlings of all species were grown in 1·2 m long custom-made containers with a transparent bottom that allowed monitoring of root growth over time. Key Results The granite outcrop endemics mostly differed in a predictable way from their congeners from deeper soils. They generally invested a larger portion of their biomass in roots, distributed their roots faster and more evenly over the container and had a lower specific root length. In different species pairs the outcrop endemics achieved their apparent advantage by a different combination of the aforementioned traits. Conclusions Our results are consistent with earlier work, indicating that species restricted to different types of drought-prone shallow-soil communities have undergone similar selection pressures. Although adaptive in their own habitat in terms of obtaining access to fissures in the underlying rock, these root system traits are likely to be maladaptive in deeper soil habitats. Therefore, our results may provide an explanation for the narrow endemism of many shallow-soil endemics. PMID:22238122

Exploring rock fissures: does a specialized root morphology explain endemism on granite outcrops?

PubMed

Poot, Pieter; Hopper, Stephen D; van Diggelen, Josepha M H

2012-07-01

Worldwide, many plant species are confined to open, shallow-soil, rocky habitats. Although several hypotheses have been proposed to explain this habitat specificity, none has been convincing. We suggest that the high level of endemism on shallow soils is related to the edaphic specialization needed to survive in these often extremely drought-prone habitats. Previous research has shown that species endemic to ironstone communities in SW Australia have a specialized root morphology that enhances their chance to access fissures in the underlying rock. Here we test the generality of these findings for species that are confined to a shallow-soil habitat that is of much greater global significance: granite outcrops. We compared temporal and spatial root growth and allocation of three endemic woody perennials of SW Australian granite outcrop communities with those of congeners occurring on nearby deeper soils. Seedlings of all species were grown in 1·2 m long custom-made containers with a transparent bottom that allowed monitoring of root growth over time. The granite outcrop endemics mostly differed in a predictable way from their congeners from deeper soils. They generally invested a larger portion of their biomass in roots, distributed their roots faster and more evenly over the container and had a lower specific root length. In different species pairs the outcrop endemics achieved their apparent advantage by a different combination of the aforementioned traits. Our results are consistent with earlier work, indicating that species restricted to different types of drought-prone shallow-soil communities have undergone similar selection pressures. Although adaptive in their own habitat in terms of obtaining access to fissures in the underlying rock, these root system traits are likely to be maladaptive in deeper soil habitats. Therefore, our results may provide an explanation for the narrow endemism of many shallow-soil endemics.

Reduced Lateral Root Branching Density Improves Drought Tolerance in Maize1[OPEN

PubMed Central

Zhan, Ai; Schneider, Hannah

2015-01-01

An emerging paradigm is that root traits that reduce the metabolic costs of soil exploration improve the acquisition of limiting soil resources. Here, we test the hypothesis that reduced lateral root branching density will improve drought tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length (few but long [FL] and many but short [MS]) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit of axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water isotopic signature, signifying deeper water capture, 51% to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves drought tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the drought tolerance of maize and possibly other cereal crops. PMID:26077764

Phosphorus budgets in Everglades wetland ecosystems: The effects of hydrology and nutrient enrichment

USGS Publications Warehouse

Noe, G.B.; Childers, D.L.

2007-01-01

The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough ('Slough'), shallower water oligotrophic Cladium jamaicense ('Cladium'), partially enriched C. jamaicense/Typha spp. mixture ('Cladium/Typha'), and enriched Typha spp. ('Typha') marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m-2 yr-1 in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m-2 yr -1 in partially enriched Cladium/Typha, and 1.6 g P m-2 yr-1 in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface waters in P-enriched areas of the Everglades. ?? 2007 Springer Science+Business Media, Inc.

Big maggots dig deeper: size-dependent larval dispersal in flies.

PubMed

Davis, Jeremy M; Coogan, Laura E; Papaj, Daniel R

2015-09-01

The ability of individual animals to select habitats optimal for development and survival can be constrained by the costs of moving through the environment. Animals that seek overwintering sites underground, for example, may be constrained by the energy required to burrow into the soil. We conducted field and laboratory studies to determine the relationship between individual size and overwintering site selection in the tephritid flies, Rhagoletis juglandis and Rhagoletis suavis. We also explored the effect of site selection on pupal mortality, parasitism, and the ability to emerge from overwintering sites after eclosion. In both species, and in both lab and field tests, larger pupae were found at deeper soil depths. In addition, marginally non-significant trends indicated pupae in deeper sites were 48% more likely to survive the overwintering period. Finally, larger individuals were more likely to eclose and emerge from the soil at a given depth, but flies in deep overwintering sites were less likely to emerge from those sites than flies in shallow sites. Our data indicate that overwintering site selection represents a trade-off between avoiding predators and parasites that occur at shallow sites, and the energetic and mortality costs of burrowing to, overwintering in, and emerging from, deeper sites. The size-dependent overwintering site selection demonstrated here has implications for population dynamics and pest control strategies. Some fly control measures, such as the introduction of parasites or predators, will be mitigated when the deepest and least accessible overwintering pupae represent a disproportionately large amount of the population's reproductive capacity.

Vadose zone controls on damping of climate-induced transient recharge fluxes in U.S. agroecosystems

NASA Astrophysics Data System (ADS)

Gurdak, Jason

2017-04-01

Understanding the physical processes in the vadose zone that link climate variability with transient recharge fluxes has particular relevance for the sustainability of groundwater-supported irrigated agriculture and other groundwater-dependent ecosystems. Natural climate variability on interannual to multidecadal timescales has well-documented influence on precipitation, evapotranspiration, soil moisture, infiltration flux, and can augment or diminish human stresses on water resources. Here the behavior and damping depth of climate-induced transient water flux in the vadose zone is explored. The damping depth is the depth in the vadose zone that the flux variation damps to 5% of the land surface variation. Steady-state recharge occurs when the damping depth is above the water table, and transient recharge occurs when the damping depth is below the water table. Findings are presented from major agroecosystems of the United States (U.S.), including the High Plains, Central Valley, California Coastal Basin, and Mississippi Embayment aquifer systems. Singular spectrum analysis (SSA) is used to identify quasi-periodic signals in precipitation and groundwater time series that are coincident with the Arctic Oscillation (AO) (6-12 mo cycle), Pacific/North American oscillation (PNA) (<1-4 yr cycle), El Niño/Southern Oscillation (ENSO) (2-7 yr cycle), North Atlantic Oscillation (NAO) (3-6 yr cycle), Pacific Decadal Oscillation (PDO) (15-30 yr cycle), and Atlantic Multidecadal Oscillation (AMO) (50-70 yr cycle). SSA results indicate that nearly all of the quasi-periodic signals in the precipitation and groundwater levels have a statistically significant lag correlation (95% confidence interval) with the AO, PNA, ENSO, NAO, PDO, and AMO indices. Results from HYDRUS-1D simulations indicate that transient water flux through the vadose zone are controlled by highly nonlinear interactions between mean infiltration flux and infiltration period related to the modes of climate variability and the local soil textures, layering, and depth to the water table. Simulation results for homogeneous profiles generally show that shorter-period climate oscillations, smaller mean fluxes, and finer-grained soil textures generally produce damping depths closer to land surface. Simulation results for layered soil textures indicate more complex responses in the damping depth, including the finding that finer-textured layers in a coarser soil profile generally result in damping depths closer to land surface, while coarser-textured layers in coarser soil profile result in damping depths deeper in the vadose zone. Findings from this study improve understanding of how vadose zone properties influences transient recharge flux and damp climate variability signals in groundwater systems, and have important implications for sustainable management of groundwater resources and coupled agroecosystems under future climate variability and change.

[Changes of soil physical properties during the conversion of cropland to agroforestry system].

PubMed

Wang, Lai; Gao, Peng Xiang; Liu, Bin; Zhong, Chong Gao; Hou, Lin; Zhang, Shuo Xin

2017-01-01

To provide theoretical basis for modeling and managing agroforestry systems, the influence of conversion of cropland to agroforestry system on soil physical properties was investigated via a walnut (Juglans regia)-wheat (Triticum aestivum) intercropping system, a wide spreading local agroforestry model in northern Weihe River of loess area, with the walnut and wheat monoculture systems as the control. The results showed that the improvement of the intercropping system on soil physical properties mainly appeared in the 0-40 cm soil layer. The intercropping system could prevent soil bulk density rising in the surface soil (0-20 cm), and the plow pan in the 20-40 cm soil layer could be significantly alleviated. The intercropping system had conti-nuous improvement on soil field capacity in each soil layer with the planting age increase, and the soil field capacity was higher than that of each monoculture system in each soil layer (except 20-40 cm soil layer) since the 5th year after planting. The intercropping system had continuous improvement on soil porosity in each soil layer, but mainly in the 0-20 and 20-40 cm soil layer, and the ratio of capillary porosity was also improved. The soil bulk density, field capacity and soil porosity obtained continuous improvement during the conversion of cropland to agroforestry system, and the improvement on soil physical properties was stronger in shallow soil layer than in deep soil.

Flux canceling in three-dimensional radiative magnetohydrodynamic simulations

NASA Astrophysics Data System (ADS)

Thaler, Irina; Spruit, H. C.

2017-05-01

We aim to study the processes involved in the disappearance of magnetic flux between regions of opposite polarity on the solar surface using realistic three-dimensional (3D) magnetohydrodynamic (MHD) simulations. "Retraction" below the surface driven by magnetic forces is found to be a very effective mechanism of flux canceling of opposite polarities. The speed at which flux disappears increases strongly with initial mean flux density. In agreement with existing inferences from observations we suggest that this is a key process of flux disappearance within active complexes. Intrinsic kG strength concentrations connect the surface to deeper layers by magnetic forces, and therefore the influence of deeper layers on the flux canceling process is studied. We do this by comparing simulations extending to different depths. For average flux densities of 50 G, and on length scales on the order of 3 Mm in the horizontal and 10 Mm in depth, deeper layers appear to have only a mild influence on the effective rate of diffusion.

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.

Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO 2 and CH 4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ 2H and δ 18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface activemore » layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ 2H vs δ 18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.« less

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

DOE PAGES

Throckmorton, Heather M.; Newman, Brent D.; Heikoop, Jeffrey M.; ...

2016-04-16

Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO 2 and CH 4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ 2H and δ 18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface activemore » layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ 2H vs δ 18O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.« less

The effect of Bahiagrass roots on soil erosion resistance of Aquults in subtropical China

NASA Astrophysics Data System (ADS)

Ye, Chao; Guo, Zhonglu; Li, Zhaoxia; Cai, Chongfa

2017-05-01

Herbaceous species, especially their roots, are believed to have an important role in enhancing soil strength and protecting soil against erosion. This study evaluated the effects of root distribution characteristics on soil shear resistance and soil detachment rates, correlations among root mechanical properties, root chemical composition and root parameters, and whether the Wu-Waldron model can accurately estimate soil reinforcement by roots. Bahiagrass (Paspalum notatum) was planted in planter boxes by overlapping four rectangle frames (0.4 × 0.1 × 0.1 m). A series of laboratory tests of direct shear strength and soil detachment were conducted on two soils that were derived from granite and shale with different soil depths and sowing densities. The results indicated that soil aggregate stability was positively correlated with root characteristics. Over 70% of the total measured root parameters were distributed in the upper 20 cm of the soil, and they decreased with increasing soil depth and decreasing sowing density. The tensile properties (root tensile strength and root tensile force) were significantly correlated with root diameter. The contents of root main chemical compositions were significantly correlated with root diameter while hemicellulose showed no obvious trend with root diameter (P = 0.12). Root tensile strength and root tensile force were also significantly correlated with the contents of these four compositions, except hemicellulose. The relative soil detachment demonstrated a significant negative correlation with root parameters with sowing densities from 5 to 30 g m- 2, and it remained at a relatively low value when the sowing density was > 20 g m- 2. The soil detachment rate, erodibility factor and critical flow shear stress were well correlated with the root area ratio, sowing density, and soil depth. The Wu-Waldron model was found to be inappropriate for these soils, as it overestimated additional soil shear strength due to roots by 152-366% in the upper 20 cm, and 11-48% in deeper soil layers. This study demonstrated that the root area ratio was a more suitable root characteristic parameter that contributes to soil reinforcement.

Vertical stratification of microbial communities in the Red Sea revealed by 16S rDNA pyrosequencing.

PubMed

Qian, Pei-Yuan; Wang, Yong; Lee, On On; Lau, Stanley C K; Yang, Jiangke; Lafi, Feras F; Al-Suwailem, Abdulaziz; Wong, Tim Y H

2011-03-01

The ecosystems of the Red Sea are among the least-explored microbial habitats in the marine environment. In this study, we investigated the microbial communities in the water column overlying the Atlantis II Deep and Discovery Deep in the Red Sea. Taxonomic classification of pyrosequencing reads of the 16S rRNA gene amplicons showed vertical stratification of microbial diversity from the surface water to 1500 m below the surface. Significant differences in both bacterial and archaeal diversity were observed in the upper (20 [corrected] and 50 m) and deeper layers (200 and 1500 m). There were no obvious differences in community structure at the same depth for the two sampling stations. The bacterial community in the upper layer was dominated by Cyanobacteria whereas the deeper layer harbored a large proportion of Proteobacteria. Among Archaea, Euryarchaeota, especially Halobacteriales, were dominant in the upper layer but diminished drastically in the deeper layer where Desulfurococcales belonging to Crenarchaeota became the dominant group. The results of our study indicate that the microbial communities sampled in this study are different from those identified in water column in other parts of the world. The depth-wise compositional variation in the microbial communities is attributable to their adaptations to the various environments in the Red Sea.

Methane efflux measured by eddy covariance in Alaskan upland tundra undergoing permafrost degradation

NASA Astrophysics Data System (ADS)

Taylor, M.; Celis, G.; Ledman, J.; Bracho, R. G.; Schuur, E.

2017-12-01

Permafrost thaw can increase landscape heterogeneity, leading to wetter and drier soil conditions that affect the magnitude and form (carbon dioxide - CO2 and methane - CH4) of carbon produced via microbial decomposition. Environmental controls on CH4 emissions, especially in drier upland tundra systems, are not well understood. In degrading upland tundra permafrost, cold season CH4 fluxes may contribute significantly to annual emissions from CH4 production within unfrozen layers deep in the soil profile. Eight Mile Lake (EML), located in Interior Alaska near Denali National Park, is a moist acidic tussock tundra ecosystem undergoing permafrost degradation. Perennially frozen soils have warmed between 1985 and 2016 from -1.2 to -0.75˚C resulting in a deeper active layer depth from 61 to 70 cm between 2004-2016. Depth from the soil/moss surface to the water table perched on the permafrost surface has decreased from 30 to 20 cm over the same interval. Here we present the first year of continuous CH4 flux measurements made at EML (May 2016 - May 2017). The site was a net source of low-level CH4 emissions throughout the year. Annual CH4 emissions (1.3 g C yr-1) made up 8.8% of total annual C emissions (14.7 g m-2yr-1). Methane flux is related with soil temperatures during both summer and non-summer seasons. Emissions increased throughout the summer season as thaw depth and soil temperatures increased. In contrast with wetland sites where water table is at or above the soil surface for much of the growing season, EML is relatively dry and there was no relationship between soil moisture and emissions. Non-summer season CH4 emissions are related to increases in atmospheric and shallow soil temperatures. Winter season emissions account for 37% of the annual CH4 budget, the bulk of which occurred between October and January when deep soils remained thawed. Non-summer season CH4 and CO2 pulses appear to be coupled, suggesting a similar mechanism for release. We hypothesize that this relationship is the result of surface soils warming and cracking, allowing for the escape of microbially produced gases at depth. While annual CH4 emissions made up 8.8% of total annual C emissions at this site, taking into account the greenhouse warming potential of CH4 relative to CO2, the climate impact of CH4 is 15.6 g m-2yr-1, or 69% of the C budget.

Savanna Vegetation Dynamics and their Influence on Landscape-Scale C, N, and P Biogeochemistry

NASA Astrophysics Data System (ADS)

Boutton, T. W.; Zhou, Y.; Wu, X. B.; Hyodo, A.

2017-12-01

Soil carbon (C), nitrogen (N) and phosphorus (P) cycles are strongly interlinked and controlled through biological processes, and the P cycle is further controlled through geochemical processes. In grasslands, savannas, and other dryland ecosystems throughout the world, woody plant encroachment often modifies soil C, N, and P stores, although it remains unknown if these three elements change proportionally in response to this vegetation change. We evaluated proportional changes and spatial patterns of soil organic C (SOC), total N (TN), and total P (TP) following woody encroachment by taking spatially-explicit soil cores to a depth of 1.2 m across a subtropical savanna landscape which has undergone encroachment by trees and shrubs during the past century in the Rio Grande Plains, USA. SOC and TN were coupled with respect to increasing magnitudes and spatial patterns along the soil profile following woody encroachment. In contrast, TP increased slower than SOC and TN in surface soils, but faster in subsurface soils. Spatial patterns of TP strongly resembled those of vegetation cover throughout the soil profile, but differed from those of SOC and TN, especially in deeper portions of the profile. The encroachment of woody plants into this P-limited ecosystem resulted in the accumulation of proportionally less soil P compared to C and N in surface soils; however, proportionally more P accrued in deeper portions of the profile beneath woody patches where alkaline soil pH and high carbonate concentrations would favor precipitation of P as relatively insoluble calcium phosphates. Structural equation models (SEM) showed that fine root density explained the greatest proportion of variation in SOC, TN, and TP in the surface soil. In deeper portions of the profile, SEM showed that silt and clay explained much of the variation in SOC and TN, while soil pH strongly controlled TP. This imbalanced relationship highlights that the relative importance of biotic vs. abiotic mechanisms controlling C and N vs. P accumulation following vegetation change may vary with depth in the profile. Our findings suggest that efforts to incorporate the effects of land cover changes into coupled climate-biogeochemical models should attempt to represent C-N-P imbalances that may arise following vegetation change.

Desert grassland responses to climate and soil moisture suggest divergent vulnerabilities across the southwestern US

USGS Publications Warehouse

Gremer, Jennifer; Bradford, John B.; Munson, Seth M.; Duniway, Michael C.

2015-01-01

Climate change predictions include warming and drying trends, which are expected to be particularly pronounced in the southwestern United States. In this region, grassland dynamics are tightly linked to available moisture, yet it has proven difficult to resolve what aspects of climate drive vegetation change. In part, this is because it is unclear how heterogeneity in soils affects plant responses to climate. Here, we combine climate and soil properties with a mechanistic soil water model to explain temporal fluctuations in perennial grass cover, quantify where and the degree to which incorporating soil water dynamics enhances our ability to understand temporal patterns, and explore the potential consequences of climate change by assessing future trajectories of important climate and soil water variables. Our analyses focused on long-term (20 to 56 years) perennial grass dynamics across the Colorado Plateau, Sonoran, and Chihuahuan Desert regions. Our results suggest that climate variability has negative effects on grass cover, and that precipitation subsidies that extend growing seasons are beneficial. Soil water metrics, including the number of dry days and availability of water from deeper (>30 cm) soil layers, explained additional grass cover variability. While individual climate variables were ranked as more important in explaining grass cover, collectively soil water accounted for 40 to 60% of the total explained variance. Soil water conditions were more useful for understanding the responses of C3 than C4 grass species. Projections of water balance variables under climate change indicate that conditions that currently support perennial grasses will be less common in the future, and these altered conditions will be more pronounced in the Chihuahuan Desert and Colorado Plateau. We conclude that incorporating multiple aspects of climate and accounting for soil variability can improve our ability to understand patterns, identify areas of vulnerability, and predict the future of desert grasslands.

Desert grassland responses to climate and soil moisture suggest divergent vulnerabilities across the southwestern United States.

PubMed

Gremer, Jennifer R; Bradford, John B; Munson, Seth M; Duniway, Michael C

2015-11-01

Climate change predictions include warming and drying trends, which are expected to be particularly pronounced in the southwestern United States. In this region, grassland dynamics are tightly linked to available moisture, yet it has proven difficult to resolve what aspects of climate drive vegetation change. In part, this is because it is unclear how heterogeneity in soils affects plant responses to climate. Here, we combine climate and soil properties with a mechanistic soil water model to explain temporal fluctuations in perennial grass cover, quantify where and the degree to which incorporating soil water dynamics enhances our ability to understand temporal patterns, and explore the potential consequences of climate change by assessing future trajectories of important climate and soil water variables. Our analyses focused on long-term (20-56 years) perennial grass dynamics across the Colorado Plateau, Sonoran, and Chihuahuan Desert regions. Our results suggest that climate variability has negative effects on grass cover, and that precipitation subsidies that extend growing seasons are beneficial. Soil water metrics, including the number of dry days and availability of water from deeper (>30 cm) soil layers, explained additional grass cover variability. While individual climate variables were ranked as more important in explaining grass cover, collectively soil water accounted for 40-60% of the total explained variance. Soil water conditions were more useful for understanding the responses of C3 than C4 grass species. Projections of water balance variables under climate change indicate that conditions that currently support perennial grasses will be less common in the future, and these altered conditions will be more pronounced in the Chihuahuan Desert and Colorado Plateau. We conclude that incorporating multiple aspects of climate and accounting for soil variability can improve our ability to understand patterns, identify areas of vulnerability, and predict the future of desert grasslands. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Assimilating soil moisture into an Earth System Model

NASA Astrophysics Data System (ADS)

Stacke, Tobias; Hagemann, Stefan

2017-04-01

Several modelling studies reported potential impacts of soil moisture anomalies on regional climate. In particular for short prediction periods, perturbations of the soil moisture state may result in significant alteration of surface temperature in the following season. However, it is not clear yet whether or not soil moisture anomalies affect climate also on larger temporal and spatial scales. In an earlier study, we showed that soil moisture anomalies can persist for several seasons in the deeper soil layers of a land surface model. Additionally, those anomalies can influence root zone moisture, in particular during explicitly dry or wet periods. Thus, one prerequisite for predictability, namely the existence of long term memory, is evident for simulated soil moisture and might be exploited to improve climate predictions. The second prerequisite is the sensitivity of the climate system to soil moisture. In order to investigate this sensitivity for decadal simulations, we implemented a soil moisture assimilation scheme into the Max-Planck Institute for Meteorology's Earth System Model (MPI-ESM). The assimilation scheme is based on a simple nudging algorithm and updates the surface soil moisture state once per day. In our experiments, the MPI-ESM is used which includes model components for the interactive simulation of atmosphere, land and ocean. Artificial assimilation data is created from a control simulation to nudge the MPI-ESM towards predominantly dry and wet states. First analyses are focused on the impact of the assimilation on land surface variables and reveal distinct differences in the long-term mean values between wet and dry state simulations. Precipitation, evapotranspiration and runoff are larger in the wet state compared to the dry state, resulting in an increased moisture transport from the land to atmosphere and ocean. Consequently, surface temperatures are lower in the wet state simulations by more than one Kelvin. In terms of spatial pattern, the largest differences between both simulations are seen for continental areas, while regions with a maritime climate are least sensitive to soil moisture assimilation.

Does plant diversity affect the water balance of established grassland systems?

NASA Astrophysics Data System (ADS)

Leimer, Sophia; Bischoff, Sebastian; Blaser, Stefan; Boch, Steffen; Busch, Verena; Escher, Peter; Fischer, Markus; Kaupenjohann, Martin; Kerber, Katja; Klaus, Valentin; Michalzik, Beate; Prati, Daniel; Schäfer, Deborah; Schmitt, Barbara; Schöning, Ingo; Schwarz, Martin T.; Siemens, Jan; Thieme, Lisa; Wilcke, Wolfgang

2017-04-01

The water cycle drives nutrient cycles and plant productivity. The impact of land use on the water cycle has been extensively studied and there is experimental evidence that biodiversity modifies the water cycle in grasslands. However, the combined influences of land-use and associated biodiversity on the water cycle in established land-use systems are unclear. Therefore, we investigated how evapotranspiration (ETa), downward water flux (DF), and capillary rise (CR) in topsoil and subsoil are related to land-use and plant diversity in established, commercially managed grassland and compared these results to findings from experiments where plant diversity was manipulated. In three Central European regions ("Biodiversity Exploratories"), we studied 29 grassland plots (50 m x 50 m; 9-11 plots per region) from 2010 to 2015. The land-use types cover pasture, mown pasture, and meadow in at least triplicate per region. On each plot, we measured soil water contents, meteorological data (hourly resolution), cumulative precipitation (biweekly), plant species richness, the number of plants in the functional groups of grasses, herbs, and legumes (annually), and root biomass (once). Potential evapotranspiration (ETp) was calculated from meteorological data per plot. Missing data points of ETp and soil water contents were estimated with Bayesian hierarchical models. ETa, DF, and CR were calculated for two soil layers with a soil water balance model. The model is based on changes in soil water storage between subsequent observation dates and ETp, which was partitioned between soil layers according to root distribution. Water fluxes in annual resolution were statistically analyzed for land-use and biodiversity effects using repeated-measures analysis of variance (ANOVA). Land-use type did not affect water fluxes. Species richness did not influence DF and CR. DF from topsoil was higher on plots with more grass species, which is opposite to the results from a manipulative biodiversity experiment. The number of grasses and herbs influenced CR into topsoil. ETa from topsoil decreased with increasing species richness while ETa from subsoil increased. Opposing effects on ETa in the two soil layers were also observed for the numbers of herb and legume species. In manipulative biodiversity experiments, opposing effects on ETa from different soil layers are explained by higher plant cover and biomass in species-rich mixtures, reducing evaporation by shading of the topsoil, and deeper roots in species-rich mixtures, facilitating water use and increasing transpiration from subsoil. In our study, biomass decreased with increasing species richness because fertilizer application increased biomass production and decreased species richness. Plots with more grasses showed lower ETa from topsoil than plots with less grasses. However, the within-subject effects indicated higher ETa from topsoil in years with more grasses on individual plots than in years with less grasses. The latter finding complies with the results from a manipulative biodiversity experiment, which has homogeneous soil properties and management. The opposite between-subject effect is probably caused by variations in environmental conditions between plots. This indicates that processes controlling the biodiversity-water cycle relationship vary in real-world systems with environmental conditions, which are largely controlled for in manipulative biodiversity experiments.

Water-retaining barrier and method of construction

DOEpatents

Adams, Melvin R.; Field, Jim G.

1996-01-01

An agricultural barrier providing a medium for supporting plant life in an arid or semi-arid land region having a ground surface, the barrier being disposed on native soil of the region, the barrier including: a first layer composed of pieces of basalt, the first layer being porous and being in contact with the native soil; a porous second layer of at least one material selected from at least one of sand and gravel, the second layer being less porous than, and overlying, the first layer; and a porous third layer containing soil which favors plant growth, the third layer being less porous than, and overlying, the second layer and having an exposed upper surface, wherein the porosities of the second and third layers differ from one another by an amount which impedes transport of soil from the first layer into the second layer. Soil for the third layer may be provided by washing salinated or contaminated soil with water and using the washed soil for the third layer.

Water-retaining barrier and method of construction

DOEpatents

Adams, M.R.; Field, J.G.

1996-02-20

An agricultural barrier is disclosed which provides a medium for supporting plant life in an arid or semi-arid land region having a ground surface. The barrier is disposed on native soil of the region. The barrier includes a first porous layer composed of pieces of basalt, and is in contact with the native soil. There is a less porous second layer of at least one material selected from at least one of sand and gravel. The second layer overlies the first layer. A third layer, less porous than the second layer, contains soil which favors plant growth. The third layer overlies the second layer and has an exposed upper surface. The porosities of the second and third layers differ from one another by an amount which impedes transport of soil from the first layer into the second layer. Soil for the third layer may be provided by washing salinated or contaminated soil with water and using the washed soil for the third layer. 2 figs.

Arsenic-containing soil from geogenic source in Hong Kong: Leaching characteristics and stabilization/solidification.

PubMed

Li, Jiang-Shan; Beiyuan, Jingzi; Tsang, Daniel C W; Wang, Lei; Poon, Chi Sun; Li, Xiang-Dong; Fendorf, Scott

2017-09-01

Geogenic sources of arsenic (As) have aroused extensive environmental concerns in many countries. This study evaluated the vertical profiles, leaching characteristics, and surface characteristics of As-containing soils in Hong Kong. The results indicated that elevated levels of As (486-1985 mg kg -1 ) were mostly encountered in deeper layer (15-20 m below ground). Despite high concentrations, geogenic As displayed a high degree of chemical stability in the natural geochemical conditions, and there was minimal leaching of As in various leaching tests representing leachability, mobility, phytoavailability, and bioaccessibility. Microscopic/spectroscopic investigations suggested that As in the soils was predominantly present as As(V) in a coordination environment with Fe oxides. Sequential extraction indicated that the majority of As were strongly bound with crystalline Fe/Al oxides and residual phase. Yet, uncertainties may remain with potential As exposure through accidental ingestion and abiotic/biotic transformation due to changes in geochemical conditions. Hence, the effectiveness of stabilization/solidification (S/S) treatment was evaluated. Although the leached concentrations of As from the S/S treated soils increased to varying extent in different batch leaching tests due to the increase in alkalinity, the mobility of As was considered very low based on semi-dynamic leaching test. This suggested that As immobilization in the S/S treated soils was predominantly dependent on physical encapsulation by interlocking framework of hydration products, which could also prevent potential exposure and allow controlled utilization of S/S treated soils as monolithic materials. These results illustrate the importance of holistic assessment and treatment/management of As-containing soils for enabling flexible future land use. Copyright © 2017 Elsevier Ltd. All rights reserved.

A model for phosphorus transformation and runoff loss for surface-applied manures.

PubMed

Vadas, P A; Gburek, W J; Sharpley, A N; Kleinman, P J A; Moore, P A; Cabrera, M L; Harmel, R D

2007-01-01

Agricultural P transport in runoff is an environmental concern. An important source of P runoff is surface-applied, unincorporated manures, but computer models used to assess P transport do not adequately simulate P release and transport from surface manures. We developed a model to address this limitation. The model operates on a daily basis and simulates manure application to the soil surface, letting 60% of manure P infiltrate into soil if manure slurry with less than 15% solids is applied. The model divides manure P into four pools, water-extractable inorganic and organic P, and stable inorganic and organic P. The model simulates manure dry matter decomposition, and manure stable P transformation to water-extractable P. Manure dry matter and P are assimilated into soil to simulate bioturbation. Water-extractable P is leached from manure when it rains, and a portion of leached P can be transferred to surface runoff. Eighty percent of manure P leached into soil by rain remains in the top 2 cm, while 20% leaches deeper. This 2-cm soil layer contributes P to runoff via desorption. We used data from field studies in Texas, Pennsylvania, Georgia, and Arkansas to build and validate the model. Validation results show the model accurately predicted cumulative P loads in runoff, reflecting successful simulation of the dynamics of manure dry matter, manure and soil P pools, and storm-event runoff P concentrations. Predicted runoff P concentrations were significantly related to (r2=0.57) but slightly less than measured concentrations. Our model thus represents an important modification for field or watershed scale models that assess P loss from manured soils.

Is there a climatological signature to deep root functioning?

NASA Astrophysics Data System (ADS)

Bamzai, A.; de Beurs, K.

2014-12-01

Vegetation has the ability to influence local water, carbon and energy fluxes in complex ways. In many climate models, dynamic vegetation is closely linked to soil moisture since 95% of all roots are located in the upper 2m of soil. However, in some ecosystems this bottom 5% of roots contributes an important percentage of net transpiration through the processes of hydraulic lift and redistribution. Hydraulic lift and redistribution is the movement of water by vegetation through the use of a passive water potential gradient. During periods where water is readily available, vegetation is able to store excess water in deeper soils. When conditions become more arid, the vegetation is able to bring this water back up to the near surface in order to re-hydrate the soil. This water is then used in transpiration and also aids in soil decomposition and nutrient breakdown in the upper soil layers. While hydraulic lift and redistribution has been identified in individual plant species, there has been limited work to understand the contribution of deep root functioning on broader spatial scales. Here we propose to use satellite data products in conjunction with ground-based observations in order to better determine the atmospheric link to deep moisture across land cover types within the state of Oklahoma. For this preliminary assessment, we will utilize the 8-day MOD 16 evapotranspiration product along with soil moisture observations from the Oklahoma Mesonet to compare and contrast a paired dry and wet case study period. We hypothesize that the presence of deep root functioning in certain land cover types increases resiliency to drought and will be observable between the case studies as reduced suppression of evapotranspiration and enhanced latent cooling of the surface.

The lead (Pb) isotope signature, behaviour and fate of traffic-related lead pollution in roadside soils in The Netherlands.

PubMed

Walraven, N; van Os, B J H; Klaver, G Th; Middelburg, J J; Davies, G R

2014-02-15

In this study the origin, behaviour and fate of anthropogenic Pb in sandy roadside soils were assessed by measuring soil characteristics, Pb isotope composition and content. In 1991 and 2003 samples were taken at different depth intervals at approximately 8 and 75 m from two highways in The Netherlands. The Pb isotope composition of the litter layer ((206)Pb/(207)Pb=1.12-1.14) differs from the deeper soil samples ((206)Pb/(207)Pb=1.20-1.21). Based on a mixing model it is concluded that the samples contain two Pb sources: natural Pb and anthropogenic Pb, the latter mainly derived from gasoline. (206)Pb/(207)Pb ratios demonstrate that the roadside soils were polluted to a depth of ~15 cm. Within this depth interval, anthropogenic Pb content is associated with organic matter. Although Pb pollution only reached a depth of ~15 cm, this does not mean that the topsoils retain all anthropogenic Pb. Due to the low pH and negligible binding capacity of soils at depths >15 cm, anthropogenic Pb migrated towards groundwater after reaching depths of >15 cm. The Pb isotope composition of the groundwater ((206)Pb/(207)Pb=1.135-1.185) establishes that groundwater is polluted with anthropogenic Pb. The contribution of anthropogenic Pb to the groundwater varies between ~30 and 100%. Based on the difference in soil Pb content and Pb isotope compositions over a period of 12 years, downward Pb migration is calculated to vary from 72 ± 95 to 324 ± 279 mg m(-2)y(-1). Assuming that the downward Pb flux is constant over time, it is calculated that 35-90% of the atmospherically delivered Pb has migrated to the groundwater. Copyright © 2013 Elsevier B.V. All rights reserved.

Effects of zinc complexes on the distribution of zinc in calcareous soil and zinc uptake by maize.

PubMed

Alvarez, José M; Rico, María I

2003-09-10

The movement and availability of Zn from six organic Zn sources in a Typic Xerorthent (calcareous) soil were compared by incubation, column assay, and in a greenhouse study with maize (Zea mays L.). Zinc soil behavior was studied by sequential, diethylenetriaminepentaacetate, and Mehlich-3 extractions. In the incubation experiment, the differences in Zn concentration observed in the water soluble plus exchangeable fraction strongly correlated with Zn uptake by plants in the greenhouse experiment. Zinc applied to the surface of soil columns scarcely moved into deeper layers except for Zn-ethylenediaminetetraacetate (EDTA) that showed the greatest distribution of labile Zn throughout the soil and the highest proportion of leaching of the applied Zn. In the upper part of the column, changes in the chemical forms of all treatments occurred and an increase in organically complexed and amorphous Fe oxide-bound fractions was detected. However, the water soluble plus exchangeable fraction was not detected. The same results were obtained at the end of the greenhouse experiment. Significant increases were found in plant dry matter yield and Zn concentration as compared with the control treatment without Zn addition. Increasing Zn rate in the soil increased dry matter yield in all cases but Zn concentration in the plant increased only with Zn-EDTA and Zn-ethylenediaminedi-o-hydroxyphenyl-acetate (EDDHA) fertilizers. Higher Zn concentration in plants (50.9 mg kg(-)(1)) occurred when 20 mg Zn kg(-)(1) was added to the soil as Zn-EDTA. The relative effectiveness of the different Zn carriers in increasing Zn uptake was in the order: Zn-EDTA > Zn-EDDHA > Zn-heptagluconate >/= Zn-phenolate approximately Zn-polyflavonoid approximately Zn-lignosulfonate.

Digging a Little Deeper: Microbial Communities, Molecular Composition and Soil Organic Matter Turnover along Tropical Forest Soil Depth Profiles

NASA Astrophysics Data System (ADS)

Pett-Ridge, J.; McFarlane, K. J.; Heckman, K. A.; Reed, S.; Green, E. A.; Nico, P. S.; Tfaily, M. M.; Wood, T. E.; Plante, A. F.

2016-12-01

Tropical forest soils store more carbon (C) than any other terrestrial ecosystem and exchange vast amounts of CO2, water, and energy with the atmosphere. Much of this C is leached and stored in deep soil layers where we know little about its fate or the microbial communities that drive deep soil biogeochemistry. Organic matter (OM) in tropical soils appears to be associated with mineral particles, suggesting deep soils may provide greater C stabilization. However, few studies have evaluated sub-surface soils in tropical ecosystems, including estimates of the turnover times of deep soil C, the sensitivity of this C to global environmental change, and the microorganisms involved. We quantified bulk C pools, microbial communities, molecular composition of soil organic matter, and soil radiocarbon turnover times from surface soils to 1.5m depths in multiple soil pits across the Luquillo Experimental Forest, Puerto Rico. Soil C, nitrogen, and root and microbial biomass all declined exponentially with depth; total C concentrations dropped from 5.5% at the surface to <0.5% at 140cm depth. High-throughput sequencing highlighted distinct microbial communities in surface soils (Acidobacteria and Proteobacteria) versus those below the active rooting zone (Verrucomicrobia and Thaumarchaea). High resolution mass spectrometry (FTICR-MS) analyses suggest a shift in the composition of OM with depth (especially in the water soluble fraction), an increase in oxidation, and decreasing H/C with depth (indicating higher aromaticity). Additionally, surface samples were rich in lignin-like compounds of plant origin that were absent with depth. Soil OM 14C and mean turnover times were variable across replicate horizons, ranging from 3-1500 years at the surface, to 5000-40,000 years at depth. In comparison to temperate deciduous forests, these 14C values reflect far older soil C. Particulate organic matter (free light fraction), with a relatively modern 14C was found in low but measureable concentration in even the deepest soil horizons. Our results indicate these tropical subsoils contain small but metabolically active microbial communities that are highly OM limited and may persist via degradation of recent inputs.

Models for root water uptake under deficit irrigation

NASA Astrophysics Data System (ADS)

Lazarovitch, Naftali; Krounbi, Leilah; Simunek, Jirka

2010-05-01

Modern agriculture, with its dependence on irrigation, fertilizers, and pesticide application, contributes significantly to the water and solute influx through the soil into the groundwater, specifically in arid areas. The quality and quantity of this water as it passes through the vadose zone is influenced primarily by plant roots. Root water uptake is a function of both a physical root parameter, commonly referred to as the root length density, and the soil water status. The location of maximum water uptake in a homogenous soil profile of uniform water content and hydraulic conductivity occurs in the soil layer containing the largest root length density. Under field conditions, in a drying soil, plants are both subject to, and the source of, great spatial variability in the soil water content. The upper soil layers containing the bulk of the root zone are usually the most water depleted, while the deeper regions of the soil profile containing fewer roots are wetter. Changes in the physiological functioning of plants have been shown to result from extended periods of water stress, but the short term effects of water stress on root water uptake are less well understood. While plants can minimize transpiration and the resulting growth rates under limiting conditions to conserve water, many plants maintain a constant potential transpiration rate long after the commencement of the drying process. Compensatory uptake, whereby plants respond to non-uniform, limiting conditions by increasing water uptake from areas in the root zone characterized by more favorable conditions, is one such mechanism by which plants sustain potential transpiration rates in drying soils. The development of models which accurately characterize temporal and spatial root water uptake patterns is important for agricultural resource optimization, upon which subsequent management decisions affecting resource conservation and environmental pollution are based. Numerical simulations of root water uptake in various irrigation and fertilization regimes provide a much-needed alternative to tiring and expensive field work. These simulations can aid in raising agricultural water use efficiency while preserving soil and water resources. In this research, controlled lab experiments were carried out in soil-packed lysimeters designed for plant cultivation. Both the water balance of the growing plants as well as the temporary matric head distribution in the soil profile were calculated and measured. The experiment was conducted with sweet sorghum grown in two different soil profiles with different hydraulic properties. The experiment provided the data necessary to calculate the parameters of various models used to simulate root water uptake, by using an inverse solution method imbedded in the HYDRUS-1D code. The observed increase in uptake from the wetter soil regions under drying conditions, as measured and calculated, sheds light on the dominant role of soil hydraulic properties over the root distribution, and consequently root water uptake.

Vadose zone microbiology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kieft, Thomas L.; Brockman, Fred J.

2001-01-17

The vadose zone is defined as the portion of the terrestrial subsurface that extends from the land surface downward to the water table. As such, it comprises the surface soil (the rooting zone), the underlying subsoil, and the capillary fringe that directly overlies the water table. The unsaturated zone between the rooting zone and the capillary fringe is termed the "intermediate zone" (Chapelle, 1993). The vadose zone has also been defined as the unsaturated zone, since the sediment pores and/or rock fractures are generally not completely water filled, but instead contain both water and air. The latter characteristic results inmore » the term "zone of aeration" to describe the vadose zone. The terms "vadose zone," "unsaturated zone", and "zone of aeration" are nearly synonymous, except that the vadose zone may contain regions of perched water that are actually saturated. The term "subsoil" has also been used for studies of shallow areas of the subsurface immediately below the rooting zone. This review focuses almost exclusively on the unsaturated region beneath the soil layer since there is already an extensive body of literature on surface soil microbial communities and process, e.g., Paul and Clark (1989), Metting (1993), Richter and Markowitz, (1995), and Sylvia et al. (1998); whereas the deeper strata of the unsaturated zone have only recently come under scrutiny for their microbiological properties.« less

Umbrisols at Lower Altitudes, Case Study from Borská lowland (Slovakia)

NASA Astrophysics Data System (ADS)

Jenčo, Marián; Matečný, Igor; Putiška, René; Burian, Libor; Tančárová, Kristína; Kušnirák, Dávid

2018-05-01

Umbrisols generally develop in a cool and humid climate. Therefore, occurrence of these soils in the Borská lowland of southwestern Slovakia is very uncommon, and this inspired the aim of this paper: Analysis of the natural conditions suitable for Umbrisol development. Umbrisols in the Borská lowland developed from aeolian quartz sands accumulated on Neogenne marine clay sediments. Their occurrence is connected with the groundwater table relatively close to the ground surface and this particularly determines Umbrisol genesis in this area. Sufficient input via organic matter is an important factor for formation of the umbric horizon, and only the rich herbaceous undergrowth of the prevailing planted pine and mixed pine-oak forests is capable of providing it. A growth of diep-rooted grass is closely connected with higher soil moisture content, and quite moist areas occur in the deeper inter-dunes depressions. Constant soil moisture in these sites is facilitated by water capillary elevation. While Umbrisols are transformed to Arenosols at increased altitude, they can be transformed to Gleysols in deep depressions. Herein, induced polarization provided suitable geophysical method for detection of arenic Umbrisol inclusions. Sharp transformation of the humus layer to dry non-polarized aeolian quartz sands enabled the surface horizon to be distinguished by induced polarization

Rare earth elements profile in a cultivated and non-cultivated soil determined by laser ablation-inductively coupled plasma mass spectrometry.

PubMed

Neves, Vinicius M; Heidrich, Graciela M; Hanzel, Flavia B; Muller, Edson I; Dressler, Valderi L

2018-05-01

Rare earth elements (REEs) have several applications but the effects on environment are not well known. Therefore, the aim of this work is to establish a method for direct solid sample analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the concentration and distribution of REEs in cultivated and non-cultivated soil. Samples were collected in two areas to 40 cm of depth. The LA-ICP-MS method is easy to be implemented and the sample treatment is very fast comprising only its drying, grounding and pressing as a pellet. The accuracy of the method was evaluated by using a certified reference material (BCR 667 - Estuarine Sediment, Institute for Reference Materials and Measurements (IRMM)) where good agreement with the certified values was obtained. Analyte recovery at two levels of concentration (2.5 and 15.0 μg g -1 ) was also performed and recoveries in the range of 85%-120% were achieved, values that are acceptable for LA-ICP-MS analysis. In general, the concentration of the REEs is higher in the cultivated soil and increased from the surface to deeper layers, which can be a consequence of fertilizer application. Copyright © 2018 Elsevier Ltd. All rights reserved.

Characterization of the prokaryotic diversity through a stratigraphic permafrost core profile from the Qinghai-Tibet Plateau.

PubMed

Hu, Weigang; Zhang, Qi; Tian, Tian; Li, Dingyao; Cheng, Gang; Mu, Jing; Wu, Qingbai; Niu, Fujun; An, Lizhe; Feng, Huyuan

2016-05-01

Permafrost on the Qinghai-Tibet Plateau is one of the most sensitive regions to climate warming, thus characterizing its microbial diversity and community composition may be important for understanding their potential responses to climate changes. Here, we investigated the prokaryotic diversity in a 10-m-long permafrost core from the Qinghai-Tibet Plateau by restriction fragment length polymorphism analysis targeting the 16S rRNA gene. We detected 191 and 17 bacterial and archaeal phylotypes representing 14 and 2 distinct phyla, respectively. Proteobacteria was the dominant bacterial phylum, while archaeal communities were characterized by a preponderance of Thaumarchaeota. Some of prokaryotic phylotypes were closely related to characterized species involved in carbon and nitrogen cycles, including nitrogen fixation, methane oxidation and nitrification. However, the majority of the phylotypes were only distantly related to known taxa at order or species level, suggesting the potential of novel diversity. Additionally, both bacterial α diversity and community composition changed significantly with sampling depth, where these communities mainly distributed according to core horizons. Arthrobacter-related phylotypes presented at high relative abundance in two active layer soils, while the deeper permafrost soils were dominated by Psychrobacter-related clones. Changes in bacterial community composition were correlated with most measured soil variables, such as carbon and nitrogen contents, pH, and conductivity.

Determination of absorption changes from moments of distributions of times of flight of photons: optimization of measurement conditions for a two-layered tissue model.

PubMed

Liebert, Adam; Wabnitz, Heidrun; Elster, Clemens

2012-05-01

Time-resolved near-infrared spectroscopy allows for depth-selective determination of absorption changes in the adult human head that facilitates separation between cerebral and extra-cerebral responses to brain activation. The aim of the present work is to analyze which combinations of moments of measured distributions of times of flight (DTOF) of photons and source-detector separations are optimal for the reconstruction of absorption changes in a two-layered tissue model corresponding to extra- and intra-cerebral compartments. To this end we calculated the standard deviations of the derived absorption changes in both layers by considering photon noise and a linear relation between the absorption changes and the DTOF moments. The results show that the standard deviation of the absorption change in the deeper (superficial) layer increases (decreases) with the thickness of the superficial layer. It is confirmed that for the deeper layer the use of higher moments, in particular the variance of the DTOF, leads to an improvement. For example, when measurements at four different source-detector separations between 8 and 35 mm are available and a realistic thickness of the upper layer of 12 mm is assumed, the inclusion of the change in mean time of flight, in addition to the change in attenuation, leads to a reduction of the standard deviation of the absorption change in the deeper tissue layer by a factor of 2.5. A reduction by another 4% can be achieved by additionally including the change in variance.

Modelling of the long-term fate of pesticide residues in agricultural soils and their surface exchange with the atmosphere: Part II. Projected long-term fate of pesticide residues.

PubMed

Scholtz, M T; Bidleman, T F

2007-05-01

In the first part of this paper, a simple coupled dynamic soil-atmosphere model for studying the gaseous exchange of pesticide soil residues with the atmosphere is described and evaluated by comparing model results with published measurements of pesticide concentrations in air and soil. In Part II, the model is used to study the concentration profiles of pesticide residues in both undisturbed and annually tilled agricultural soils. Future trends are estimated for the measured air and soil concentrations of lindane and six highly persistent pesticides (toxaphene, p,p'-DDE, dieldrin, cis- and trans-chlordane and trans-nonachlor) over a twenty-year period due to volatilization and leaching into the deeper soil. Wet deposition and particle associated pesticide deposition (that increase soil residue concentrations) and soil erosion, degradation in the soil (other than for lindane) and run-off in precipitation are not considered in this study. Estimates of the rain deposition fluxes are reported that show that, other than for lindane, net volatilization fluxes greatly exceed rain deposition fluxes. The model shows that the persistent pesticides studied are highly immobile in soil and that loss of these highly persistent residues from the soil is by volatilization rather than leaching into the deeper soil. The soil residue levels of these six pesticides are currently sources of net volatilization to the atmosphere and will remain so for many years. The maximum rate of volatilization from the soil was simulated by setting the atmospheric background concentration to zero; these simulations show that the rates of volatilization will not be significantly increased since soil resistance rather than the atmospheric concentration controls the volatilization rates. Annual tilling of the soils increases the volatilization loss to the atmosphere. Nonetheless, the model predicts that, if only air-soil exchange is considered, more than 76% of current persistent pesticide residues will remain after 20 years in the top 7 cm of annually tilled soils. In contrast, lindane is relatively mobile in soil due to weaker binding to soil carbon and leaching of lindane into soil is the main removal route for current lindane residues near the soil surface. The model predicts that the soil is a sink for lindane in the atmosphere and that soil residue levels of lindane in the surface soil are determined by a balance between dry gaseous deposition to the soil from the atmosphere and leaching from the surface soil into the deeper soil where degradation is the dominant loss route. The model suggests that deposition of lindane from the atmosphere will sustain residues in the soil and, in the absence of fresh applications of lindane to the soil, eliminating lindane from the atmosphere would lead to a rapid decline of lindane residues in agricultural soils of the southern U.S.

[Contents of different soil fluorine forms in North Anhui and their affecting factors].

PubMed

Yu, Qun-ying; Ci, En; Yang, Lin-zhang

2007-06-01

By the method of consecutive extraction, this paper studied the contents and vertical distribution of soil fluorine (F) forms in North Anhui, with their relations to the soil physical and chemical properties analyzed. The results showed that the soil total F (T-F) content in North Anhui was ranged from 265.8 mg . kg(-1) to 612.8 mg . kg(-1), with an average of 423.7 mg . kg(-1), and decreased in the sequence of vegetable soil > fluvo-aquic soil > paddy soil > shajiang black soil > yellow brown soil. Among the T-F, residual F (Res-F) was the main form, occupying > 95% of total F, followed by water soluble F (Ws-F), being about 1.5% of the total, and organic-F (Or-F), Fe and Mn oxide-F (Fe/Mn-F) and exchangeable-F (Ex-F) only had very small amount. The Ws-F content in test soils ranged from 1.35 mg . kg(-1) to 17.98 mg . kg(-1), with a mean value of 6.62 mg . kg(-1). Vegetable soil, fluvo-aquic soil and shajiang black soil had a relatively higher content of Ws-F, while yellow brown soil was in adverse. Soil pH and the contents of soil organic matter, total and available phosphorus, and physical clay were the main factors affecting the contents of various F forms. Soil Ws-F was significantly positively correlated with soil pH and soil total and available phosphorus, soil Ex-F was significantly positively correlated with soil clay ( < 0.01 mm and <0.001 mm), soil Fe/Mn-F was significantly positively correlated with soil total phosphorus, and soil Or-F had a significant positive correlation with soil organic matter. Soil Ws-F content also had a close connection to the parent material. The soil developed from shallow lacustrine and marsh sediments usually had the highest Ws-F content, followed by those developed from Huang River alluvial deposit, Q3 loess, Huaihe River alluvial deposit, and light-texture yellow brown soil, with the mean Ws-F content being 9.05, 8.12, 2.97, 2.05 and 1.91 mg . kg(-1), respectively. The contents of soil Or-F and Fe/Mn-F decreased with increasing soil depth, and those of T-F and Ws-F in vegetable soil were higher in upper than in deeper soil layers.

Hydrogeologic and hydraulic characterization of aquifer and nonaquifer layers in a lateritic terrain (West Bengal, India)

NASA Astrophysics Data System (ADS)

Biswal, Sabinaya; Jha, Madan K.; Sharma, Shashi P.

2018-02-01

The hydrogeologic and hydraulic characteristics of a lateritic terrain in West Bengal, India, were investigated. Test drilling was conducted at ten sites and grain-size distribution curves (GSDCs) were prepared for 275 geologic samples. Performance evaluation of eight grain-size-analysis (GSA) methods was carried out to estimate the hydraulic conductivity (K) of subsurface formations. Finally, the GSA results were validated against pumping-test data. The GSDCs indicated that shallow aquifer layers are coarser than the deeper aquifer layers (uniformity coefficient 0.19-11.4). Stratigraphy analysis revealed that both shallow and deep aquifers of varying thickness exist at depths 9-40 and 40-79 m, respectively. The mean K estimates by the GSA methods are 3.62-292.86 m/day for shallow aquifer layers and 0.97-209.93 m/day for the deeper aquifer layers, suggesting significant aquifer heterogeneity. Pumping-test data indicated that the deeper aquifers are leaky confined with transmissivity 122.69-693.79 m2/day, storage coefficient 1.01 × 10-7-2.13 × 10-4 and leakance 2.01 × 10-7-34.56 × 10-2 day-1. Although the K values yielded by the GSA methods are generally larger than those obtained from the pumping tests, the Slichter, Harleman and US Bureau Reclamation (USBR) GSA methods yielded reasonable values at most of the sites (1-3 times higher than K estimates by the pumping-test method). In conclusion, more reliable aquifers exist at deeper depths that can be tapped for dependable water supply. GSA methods such as Slichter, Harleman and USBR can be used for the preliminary assessment of K in lateritic terrains in the absence of reliable field methods.

The role of wildfires and forest succession in stream biogeochemistry within the continuous permafrost zone of Central Siberia

NASA Astrophysics Data System (ADS)

Prokushkin, Anatoly

2016-04-01

Wildfires transform boreal and subarctic forested landscapes leading to the changes in organic matter and inorganic nutrient turnover in terrestrial ecosystems. To get an insight to the fire effect on C fluxes and general hydrochemical characteristics of streams draining continuous permafrost terrains of Central Siberian Plateau (64o N 100o E), we have selected the chronosequence of basins (n = 17) which were severely affected by fires (>80% of basin area) in the time range from 1 to 116 years ago. Stream waters were sampled continuously during frost free seasons (May-September) of 2006-2015. Four streams have been equipped with water level, temperature and conductivity probes for continuous monitoring. The strongest negative effect of wildfires on dissolved organic carbon (DOC) concentrations in streams has occurred right after a fire event, and minimum mean annual concentrations of DOC appeared between 15 and 20 years elapsed after a fire. The most pronounced decrease in DOC concentrations during an annual cycle found in freshet period (May-June) and summer-fall storm events: differences of DOC concentrations among "intact" (>100 years after fire) and recent fire basins (<6 years) reached as much as 2-fold. Less differentiation among basins appears under lowflow conditions, as DOC-depleted solutes from deeper soil layers become dominating in stream flow. Following the post-fire forest recovery, the seasonal mean DOC concentrations in streams demonstrated linear growth at the rate of ca. 0.11 mgC/l/a and approached the initial values already after ca. 60 years after fire disturbance. An opposite trend (i.e. increasing load to streams after fire impact) was observed for dissolved inorganic carbon, major anions and cations. Sulfate was found to be a good tracer of fire affect as increased 200-fold in stream waters right after a fire and steady decreased at the rate [SO42-] = 3.65 x (year after fire)^-0.75 as terrestrial ecosystems were recovering after a fire. For study area, Na+ and Cl- in streams appear to be good indicators of permafrost degradation as they reflect talik formation and connection of a stream to underlying evaporitic deposits. While evidence of permafrost degradation is currently not apparent in the region, we expect increasing concentrations of Na+ and Cl- in streams of Central Siberian Plateau as permafrost degrades due to decreased fire return interval and warming temperatures. The generalized data of active layer thickness (ALT) within analyzed watersheds have demonstrated that fire-driven deepening of ALT results in increasing stream inorganic compounds concentrations. The inverse relationship found between DOC and ALT might be attributed to deeper infiltration of solutions, sorption of DOC on clay minerals, and an increasing rate of DOC microbiological mineralization to CO2 due to increased soil temperatures. Post-fire forest recovery and, particularly, the accumulation of organic mater in the moss-lichen layer and soil organic horizon on watersheds accounted for increasing mean DOC concentrations in the streams. In opposite, increased insulation of soils by organic matter accumulating on the soil surface leads to steadily decreasing ALT and constrains an infiltration of solutes to subsoil. As a result, inorganic solute loading to stream channels is tended to decrease during post-fire forest succession in permafrost affected terrains.

Surficial geology of the Cane Creek basin, Lauderdale County, Tennessee

USGS Publications Warehouse

Miller, J.H.

1991-01-01

The surficial geology of the Cane Creek basin, in Lauderdale County, West Tennessee, was studied from 1985-88. Peoria Loess is the parent material from which soils in the Cane Creek drainage basin were derived. In general, a brown silt grades into a gray silt from 5 to I7 feet below ground surface. This color change probably represents depth to water table prior to the channelization of Cane Creek. Only at river mile 11.9 does rock outcrop near the main channel. Lower reaches of major tributaries have surficial geology similar to the main channel. In upper reaches of Hyde Creek and Fain Spring Creek, the sequence from the St&ace is sand and gravels, red-brown sandstone, sand and clay layers, and then, an orange sand layer. Coarse-grained deposits are found most often along the northern boundary of the basin and only occasionally in areas to the west and south of the main channel. Depth to sand or gravel ranges from about 0 to 158 feet in the uplands, and generally deeper than 40 feet near the main channel.

Using machine learning to produce near surface soil moisture estimates from deeper in situ records at U.S. Climate Reference Network (USCRN) locations: Analysis and applications to AMSR-E satellite validation

USDA-ARS?s Scientific Manuscript database

Surface soil moisture is critical parameter for understanding the energy flux at the land atmosphere boundary. Weather modeling, climate prediction, and remote sensing validation are some of the applications for surface soil moisture information. The most common in situ measurement for these purpo...

Examining the Suitability of a Sparse In Situ Soil Moisture Monitoring Network for Assimilation into a Spatially Distributed Hydrologic Model

NASA Astrophysics Data System (ADS)

De Vleeschouwer, N.; Verhoest, N.; Pauwels, V. R. N.

2015-12-01

The continuous monitoring of soil moisture in a permanent network can yield an interesting data product for use in hydrological data assimilation. Major advantages of in situ observations compared to remote sensing products are the potential vertical extent of the measurements, the finer temporal resolution of the observation time series, the smaller impact of land cover variability on the observation bias, etc. However, two major disadvantages are the typical small integration volume of in situ measurements and the often large spacing between monitoring locations. This causes only a small part of the modelling domain to be directly observed. Furthermore, the spatial configuration of the monitoring network is typically temporally non-dynamic. Therefore two questions can be raised. Do spatially sparse in situ soil moisture observations contain a sufficient data representativeness to successfully assimilate them into the largely unobserved spatial extent of a distributed hydrological model? And if so, how is this assimilation best performed? Consequently two important factors that can influence the success of assimilating in situ monitored soil moisture are the spatial configuration of the monitoring network and the applied assimilation algorithm. In this research the influence of those factors is examined by means of synthetic data-assimilation experiments. The study area is the ± 100 km² catchment of the Bellebeek in Flanders, Belgium. The influence of the spatial configuration is examined by varying the amount of locations and their position in the landscape. The latter is performed using several techniques including temporal stability analysis and clustering. Furthermore the observation depth is considered by comparing assimilation of surface layer (5 cm) and deeper layer (50 cm) observations. The impact of the assimilation algorithm is assessed by comparing the performance obtained with two well-known algorithms: Newtonian nudging and the Ensemble Kalman Filter.

Wildfire, legacy carbon combustion, and the centennial carbon balance of permafrost ecosystems

NASA Astrophysics Data System (ADS)

Mack, M. C.; Walker, X. J.; Melvin, A. M.; Schuur, E.

2017-12-01

One of the most rapid pathways through which climate warming could alter the carbon (C) balance of high northern latitude permafrost ecosystems is through intensification of wildfire disturbance. The majority of organic C sequestered in arctic tundra and boreal coniferous forest and peatlands resides in thick soil organic layers (SOL) that can be hundreds to thousands of years old, a C legacy of past ecosystems. Combustion of the SOL dominates C emissions during fire, and more intense fires result in deeper burning. Because rates of soil C accumulation vary across the landscape, deeper burning may not always combust legacy C. But deeper burning that does combust legacy C could rapidly shift ecosystems across a centennial-scale C cycling threshold: from net accumulation of C from the atmosphere over multiple fire cycles, to net loss. Thus, the vulnerability of this C pool—the material legacy of past disturbance events—to more intense wildfires could ultimately determine the C balance of these ecosystems and their net feedback to climate warming. In addition to determining net C balance over the disturbance cycle, combustion of legacy C provides historic context for the current fire's severity. Fires that are greater in severity than past fires are expected to be most likely to push ecosystems across thresholds in permafrost and plant composition, rendering ecosystem C cycling vulnerable to additional state change after fire. Although substantial progress has been made in understanding patterns of deep burning across boreal landscapes, much less is known about the vulnerability of legacy C to combustion and the ecosystem consequences of its loss. In this talk, we will present the concept of legacy C and discuss mass balance and radiocarbon-based methods for estimating its combustion. We will present a synthesis of data from burned Alaskan arctic tundra ecosystems, and Alaskan and Canadian boreal forests and peatlands and discuss the implications for the C balance of permafrost ecosystems. While most ecosystems in wet to moderately-drained landscape positions harbored SOL C that was hundreds to thousands of years old, loss of C that was older than the last disturbance event was limited to moderately-drained sites.

30 CFR 715.16 - Topsoil handling.

Code of Federal Regulations, 2010 CFR

2010-07-01

... as the surface soil layers. Where the A horizon is less than 6 inches, a 6-inch layer that includes... replaced as the surface soil layer. (3) Where necessary to obtain soil productivity consistent with... amounts and analyses as determined by soil tests shall be applied to the surface soil layer so that it...

30 CFR 715.16 - Topsoil handling.

Code of Federal Regulations, 2011 CFR

2011-07-01

... as the surface soil layers. Where the A horizon is less than 6 inches, a 6-inch layer that includes... replaced as the surface soil layer. (3) Where necessary to obtain soil productivity consistent with... amounts and analyses as determined by soil tests shall be applied to the surface soil layer so that it...

30 CFR 715.16 - Topsoil handling.

Code of Federal Regulations, 2014 CFR

2014-07-01

... as the surface soil layers. Where the A horizon is less than 6 inches, a 6-inch layer that includes... replaced as the surface soil layer. (3) Where necessary to obtain soil productivity consistent with... amounts and analyses as determined by soil tests shall be applied to the surface soil layer so that it...

30 CFR 715.16 - Topsoil handling.

Code of Federal Regulations, 2012 CFR

2012-07-01

... as the surface soil layers. Where the A horizon is less than 6 inches, a 6-inch layer that includes... replaced as the surface soil layer. (3) Where necessary to obtain soil productivity consistent with... amounts and analyses as determined by soil tests shall be applied to the surface soil layer so that it...

30 CFR 715.16 - Topsoil handling.

Code of Federal Regulations, 2013 CFR

2013-07-01

... as the surface soil layers. Where the A horizon is less than 6 inches, a 6-inch layer that includes... replaced as the surface soil layer. (3) Where necessary to obtain soil productivity consistent with... amounts and analyses as determined by soil tests shall be applied to the surface soil layer so that it...

Reduced Root Cortical Cell File Number Improves Drought Tolerance in Maize1[C][W][OPEN

PubMed Central

Chimungu, Joseph G.; Brown, Kathleen M.

2014-01-01

We tested the hypothesis that reduced root cortical cell file number (CCFN) would improve drought tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration. Maize genotypes with contrasting CCFN were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the United States and Malawi. CCFN ranged from six to 19 among maize genotypes. In mesocosms, reduced CCFN was correlated with 57% reduction of root respiration per unit of root length. Under water stress in the mesocosms, genotypes with reduced CCFN had between 15% and 60% deeper rooting, 78% greater stomatal conductance, 36% greater leaf CO2 assimilation, and between 52% to 139% greater shoot biomass than genotypes with many cell files. Under water stress in the field, genotypes with reduced CCFN had between 33% and 40% deeper rooting, 28% lighter stem water oxygen isotope enrichment (δ18O) signature signifying deeper water capture, between 10% and 35% greater leaf relative water content, between 35% and 70% greater shoot biomass at flowering, and between 33% and 114% greater yield than genotypes with many cell files. These results support the hypothesis that reduced CCFN improves drought tolerance by reducing the metabolic costs of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. The large genetic variation for CCFN in maize germplasm suggests that CCFN merits attention as a breeding target to improve the drought tolerance of maize and possibly other cereal crops. PMID:25355868

Soil Compaction Assessment Using Spectral Analysis of Surface Waves (SASW)

NASA Astrophysics Data System (ADS)

Afiq Roslan, Muhammad; Madun, Aziman; Hazreek Zainalabidin, Mohd; Dan@Azlan, Mohd Firdaus Md; Khaidir Abu Talib, Mohd; Nur Hidayat Zahari, Muhammad; Ambak, Kamaruddin; Ashraf Mohamad Ismail, Mohd

2018-04-01

Compaction is a process of soil densification in earthworks via by pressing the soil particles with air being expelled from the soil mass, thereby increasing its unit weight. Thus, it is important to evaluate the quality of soil compaction as prescribed in the technical requirement. SASW method is widely used for estimating material properties in layered structures based on the dispersion characteristics of Rayleigh Waves. The small scale at dimension area of 1.0 m width x 1.0 m length x 0.9 m depth was excavated and back filled with laterite soil. The soil was compacted for every layer at 0.3 m thickness. Each layer of soil compaction was conducted compaction test using core cutter methods and SASW test to determine the density and shear wave velocity. The phase velocity for layer 1 was between 112 m/s and 114 m/s, layer 2 was between 67 m/s and 74 m/s and layer 3 was between 74 m/s and 97 m/s. The result shows that the compacted soil layers are not fulfilled the quality of compacted soil layers where supposedly the expected shear wave velocity for the compacted layers should be higher than 180 m/s which is classified as stiff soil.

[Spatial variation of soil phosphorus in flooded area of the Yellow River based on GIS and geo-statistical methods: A case study in Zhoukou City, Henan, China.

PubMed

Jia, Zhen Yu; Zhang, Jun Hua; Ding, Sheng Yan; Feng, Shu; Xiong, Xiao Bo; Liang, Guo Fu

2016-04-22

Soil phosphorus is an important indicator to measure the soil fertility, because the content of soil phosphorus has an important effect on physical and chemical properties of soil, plant growth, and microbial activity in soil. In this study, the soil samples collecting and indoor analysis were conducted in Zhoukou City located in the flooded area of the Yellow River. By using GIS combined with geo-statistics, we tried to analyze the spatial variability and content distribution of soil total phosphorus (TP) and soil available phosphorus (AP) in the study area. Results showed that TP and AP of both soil layers (0-20 cm and 20-40 cm) were rich, and the contents of TP and AP in surface layer (0-20 cm) were higher than in the second layer (20-40 cm). TP and AP of both soil layers exhibited variation at medium level, and AP had varied much higher than TP. TP of both layers showed medium degree of anisotropy which could be well modeled by the Gaussian model. TP in the surface layer showed strong spatial correlation, but that of the second layer had medium spatial correlation. AP of both layers had a weaker scope in anisotropy which could be simulated by linear model, and both soil layers showed weaker spatial correlations. TP of both soil layers showed a slowly rising change from southwest to northeast of the study area, while it gradually declined from northwest to southeast. AP in soil surface layer exhibited an increase tendency firstly and then decrease from southwest to the northeast, while it decreased firstly and then increased from southeast to the northwest. AP in the second soil layer had an opposite change in the southwest to the northeast, while it showed continuously increasing tendency from northwest to the southeast. The contents of TP and AP in the surface layer presented high grades and the second layer of TP belonged to medium grade, but the second layer of AP was in a lower grade. The artificial factors such as land use type, cropping system, irrigation and fertilization were the main factors influencing the distribution and spatial variation of soil phosphorus in this area.

Assessing Impacts of 20 yr Old Miscanthus on Soil Organic Carbon Quality

NASA Astrophysics Data System (ADS)

Hu, Yaxian; Schäfer, Gerhard; Kuhn, Nikolaus

2015-04-01

The use of biomass as a renewable energy source has become increasingly popular in Upper Rhine Region to meet the demand for renewable energy. Miscanthus is one of the most favorite biofuel crops, due to its long life and large yields, as well as low energy and fertilizer inputs. However, current research on Miscanthus is mostly focused on the techniques and economics to produce biofuel or the impacts of side products such as ash and sulfur emissions to human health. Research on the potential impacts of Miscanthus onto soil quality, especially carbon quality after long-term adoption, is very limited. Some positive benefits, such as sequestrating organic carbon, have been repeatedly reported in previous research. Yet the quality of newly sequestrated organic carbon and its potential impacts onto global carbon cycling remain unclear. To fully account for the risks and benefits of Miscanthus, it is required to investigate the quality as well as the potential CO2 emissions of soil organic carbon on Miscanthus fields. As a part of the Interreg Project to assess the environmental impacts of biomass production in the Upper Rhine Region, this study aims to evaluate the carbon quality and the potential CO2 emissions after long-term Miscanthus adoption. Soils were sampled at 0-10, 10-40, 40-70, and 70-100 cm depths on three Miscanthus fields with up to 20 years of cultivation in Ammerzwiller France, Münchenstein Switzerland, and Farnsburg Switzerland. Soil texture, pH, organic carbon and nitrogen content were measured for each sampled layer. Topsoils of 0-10 cm and subsoils of 10-40 cm were also incubated for 40 days to determine the mineralization potential of the soil organic matter. Our results show that: 1) only in top soils of 0-10 cm, the 20 year old Miscanthus field has significantly higher soil organic carbon concentrations, than the control site. No significant differences were observed in deeper soil layers. Similar tendencies were also observed for organic nitrogen content as well C/N ratios. This indicates that the positive benefits of Miscanthus in sequestrating organic carbon and improving soil quality are probably only effective in top soils. 2) Soils from the 20 years old Miscanthus fields produced significantly more CO2 than the control site, suggesting the great susceptibility of organic carbon on Miscanthus fields to mineralization. Overall, our results indicate a potentially additional contribution of Miscanthus fields to atmospheric CO2 compared to reference soils, cautioning the widespread adoption of Miscanthus. Consequently, further studies aiming at a full emission balance are required to assess the overall environmental impacts of biomass production in the Upper Rhine Region.

Controls on methane released through ebullition in peatlands affected by permafrost degradation

USGS Publications Warehouse

Klapstein, Sara J.; Turetsky, Merritt R.; McGuire, A. David; Harden, Jennifer W.; Czimczik, C.I.; Xu, Xiaomei; Chanton, J.P.; Waddington, James Michael

2014-01-01

Permafrost thaw in peat plateaus leads to the flooding of surface soils and the formation of collapse scar bogs, which have the potential to be large emitters of methane (CH4) from surface peat as well as deeper, previously frozen, permafrost carbon (C). We used a network of bubble traps, permanently installed 20 cm and 60 cm beneath the moss surface, to examine controls on ebullition from three collapse bogs in interior Alaska. Overall, ebullition was dominated by episodic events that were associated with changes in atmospheric pressure, and ebullition was mainly a surface process regulated by both seasonal ice dynamics and plant phenology. The majority (>90%) of ebullition occurred in surface peat layers, with little bubble production in deeper peat. During periods of peak plant biomass, bubbles contained acetate-derived CH4 dominated (>90%) by modern C fixed from the atmosphere following permafrost thaw. Post-senescence, the contribution of CH4 derived from thawing permafrost C was more variable and accounted for up to 22% (on average 7%), in the most recently thawed site. Thus, the formation of thermokarst features resulting from permafrost thaw in peatlands stimulates ebullition and CH4 release both by creating flooded surface conditions conducive to CH4 production and bubbling as well as by exposing thawing permafrost C to mineralization.

Time series models for prediction the total and dissolved heavy metals concentration in road runoff and soil solution of roadside embankments

NASA Astrophysics Data System (ADS)

Aljoumani, Basem; Kluge, Björn; sanchez, Josep; Wessolek, Gerd

2017-04-01

Highways and main roads are potential sources of contamination for the surrounding environment. High traffic rates result in elevated heavy metal concentrations in road runoff, soil and water seepage, which has attracted much attention in the recent past. Prediction of heavy metals transfer near the roadside into deeper soil layers are very important to prevent the groundwater pollution. This study was carried out on data of a number of lysimeters which were installed along the A115 highway (Germany) with a mean daily traffic of 90.000 vehicles per day. Three polyethylene (PE) lysimeters were installed at the A115 highway. They have the following dimensions: length 150 cm, width 100 cm, height 60 cm. The lysimeters were filled with different soil materials, which were recently used for embankment construction in Germany. With the obtained data, we will develop a time series analysis model to predict total and dissolved metal concentration in road runoff and in soil solution of the roadside embankments. The time series consisted of monthly measurements of heavy metals and was transformed to a stationary situation. Subsequently, the transformed data will be used to conduct analyses in the time domain in order to obtain the parameters of a seasonal autoregressive integrated moving average (ARIMA) model. Four phase approaches for identifying and fitting ARIMA models will be used: identification, parameter estimation, diagnostic checking, and forecasting. An automatic selection criterion, such as the Akaike information criterion, will use to enhance this flexible approach to model building

Role of Micro-Topographic Variability on the Distribution of Inorganic Soil-Nitrogen Age in Intensively Managed Landscape

NASA Astrophysics Data System (ADS)

Woo, Dong K.; Kumar, Praveen

2017-10-01

How does the variability of topography structure the spatial heterogeneity of nutrient dynamics? In particular, what role does micro-topographic depression play in the spatial and temporal dynamics of nitrate, ammonia, and ammonium? We explore these questions using the 3-D simulation of their joint dynamics of concentration and age. To explicitly resolve micro-topographic variability and its control on moisture, vegetation, and carbon-nitrogen dynamics, we use a high-resolution LiDAR data over an agricultural site under a corn-soybean rotation in the Intensively Managed landscapes Critical Zone Observatory in the U.S. Midwest. We utilize a hybrid CPU-GPU parallel computing architecture to reduce the computational cost associated with such high-resolution simulations. Our results show that in areas that present closed topographic depressions, relatively lower nitrate concentration and age are observed compared to elsewhere. The periodic ponding in depressions increases the downward flux of water that carries more dissolved nitrate to the deeper soil layer. However, the variability in the depressions is relatively higher as a result of the episodic ponding pattern. When aggregate efflux from the soil domain at the bottom of the soil is considered, we find a gradual decrease in the age on the rising limb of nitrate efflux and a gradual increase on the falling limb. In addition, the age of the nitrate efflux ranges from 4 to 7 years. These are significantly higher as compared to the ages associated with a nonreactive tracer indicating that they provide an inaccurate estimate of residence time of a reactive constituent through the soil column.

Depth-Related Changes in Community Structure of Culturable Mineral Weathering Bacteria and in Weathering Patterns Caused by Them along Two Contrasting Soil Profiles

PubMed Central

Huang, Jing; Xi, Jun; Huang, Zhi; Wang, Qi; Zhang, Zhen-Dong

2014-01-01

Bacteria play important roles in mineral weathering and soil formation. However, few reports of mineral weathering bacteria inhabiting subsurfaces of soil profiles have been published, raising the question of whether the subsurface weathering bacteria are fundamentally distinct from those in surface communities. To address this question, we isolated and characterized mineral weathering bacteria from two contrasting soil profiles with respect to their role in the weathering pattern evolution, their place in the community structure, and their depth-related changes in these two soil profiles. The effectiveness and pattern of bacterial mineral weathering were different in the two profiles and among the horizons within the respective profiles. The abundance of highly effective mineral weathering bacteria in the Changshu profile was significantly greater in the deepest horizon than in the upper horizons, whereas in the Yanting profile it was significantly greater in the upper horizons than in the deeper horizons. Most of the mineral weathering bacteria from the upper horizons of the Changshu profile and from the deeper horizons of the Yanting profile significantly acidified the culture media in the mineral weathering process. The proportion of siderophore-producing bacteria in the Changshu profile was similar in all horizons except in the Bg2 horizon, whereas the proportion of siderophore-producing bacteria in the Yanting profile was higher in the upper horizons than in the deeper horizons. Both profiles existed in different highly depth-specific culturable mineral weathering community structures. The depth-related changes in culturable weathering communities were primarily attributable to minor bacterial groups rather than to a change in the major population structure. PMID:24077700

VHF SoOp (Signal of Opportunity) Technology Demonstration for Soil Moisture Measurement Using Microwave Hydraulic Boom Truck Platform

NASA Technical Reports Server (NTRS)

Joseph, A. T.; Deshpande, M.; O'Neill, P. E.; Miles, L.

2017-01-01

A goal of this research is to test deployable VHF antennas for 6U Cubesat platforms to enable validation of root zone soil moisture (RZSM) estimation algorithms for signal of opportunity (SoOp) remote sensing over the 240-270 MHz frequency band. The proposed work provides a strong foundation for establishing a technology development path for maturing a global direct surface soil moisture (SM) and RZSM measurement system over a variety of land covers. Knowledge of RZSM up to a depth of 1 meter and surface SM up to a depth of 0.05 meter on a global scale, at a spatial resolution of 1-10 km through moderate-to-heavy vegetation, is critical to understanding global water resources and the vertical moisture gradient in the Earths surface layer which controls moisture interactions between the soil, vegetation, and atmosphere. Current observations of surface SM from space by L-band radiometers (1.4 GHz) and radars (1.26 GHz) are limited to measurements of surface SM up to a depth of 0.05 meter through moderate amounts of vegetation. This limitation is mainly due to the inability of L-band signals to penetrate through dense vegetation and deep into the soil column. Satellite observations of the surface moisture conditions are coupled to sophisticated models which extrapolate the surface SM into the root zone, thus providing an indirect estimate rather than a direct measurement of RZSM. To overcome this limitation, low-frequency airborne radars operating at 435 MHz and 118 MHz have been investigated, since these lower frequencies should penetrate denser vegetation and respond to conditions deeper in the soil.

Analyzing the impacts of off-road vehicle (ORV) trails on watershed processes in Wrangell-St. Elias National Park and Preserve, Alaska.

PubMed

Arp, Christopher D; Simmons, Trey

2012-03-01

Trails created by off-road vehicles (ORV) in boreal lowlands are known to cause local impacts, such as denuded vegetation, soil erosion, and permafrost thaw, but impacts on stream and watershed processes are less certain. In Wrangell-St. Elias National Park and Preserve (WRST), Alaska, ORV trails have caused local resource damage in intermountain lowlands with permafrost soils and abundant wetlands and there is a need to know whether these impacts are more extensive. Comparison of aerial photography from 1957, 1981, and 2004 coupled with ground surveys in 2009 reveal an increase in trail length and number and show an upslope expansion of a trail system around points of stream channel initiation. We hypothesized that these impacts could also cause premature initiation and headward expansion of channels because of lowered soil resistance and greater runoff accumulation as trails migrate upslope. Soil monitoring showed earlier and deeper thaw of the active layer in and adjacent to trails compared to reference sites. Several rainfall-runoff events during the summer of 2009 showed increased and sustained flow accumulation below trail crossings and channel shear forces sufficient to cause headward erosion of silt and peat soils. These observations of trail evolution relative to stream and wetland crossings together with process studies suggest that ORV trails are altering watershed processes. These changes in watershed processes appear to result in increasing drainage density and may also alter downstream flow regimes, water quality, and aquatic habitat. Addressing local land-use disturbances in boreal and arctic parklands with permafrost soils, such as WRST, where responses to climate change may be causing concurrent shifts in watershed processes, represents an important challenge facing resource managers.

Isolation of a novel mutant gene for soil-surface rooting in rice (Oryza sativa L.)

PubMed Central

2013-01-01

Background Root system architecture is an important trait affecting the uptake of nutrients and water by crops. Shallower root systems preferentially take up nutrients from the topsoil and help avoid unfavorable environments in deeper soil layers. We have found a soil-surface rooting mutant from an M2 population that was regenerated from seed calli of a japonica rice cultivar, Nipponbare. In this study, we examined the genetic and physiological characteristics of this mutant. Results The primary roots of the mutant showed no gravitropic response from the seedling stage on, whereas the gravitropic response of the shoots was normal. Segregation analyses by using an F2 population derived from a cross between the soil-surface rooting mutant and wild-type Nipponbare indicated that the trait was controlled by a single recessive gene, designated as sor1. Fine mapping by using an F2 population derived from a cross between the mutant and an indica rice cultivar, Kasalath, revealed that sor1 was located within a 136-kb region between the simple sequence repeat markers RM16254 and 2935-6 on the terminal region of the short arm of chromosome 4, where 13 putative open reading frames (ORFs) were found. We sequenced these ORFs and detected a 33-bp deletion in one of them, Os04g0101800. Transgenic plants of the mutant transformed with the genomic fragment carrying the Os04g0101800 sequence from Nipponbare showed normal gravitropic responses and no soil-surface rooting. Conclusion These results suggest that sor1, a rice mutant causing soil-surface rooting and altered root gravitropic response, is allelic to Os04g0101800, and that a 33-bp deletion in the coding region of this gene causes the mutant phenotypes. PMID:24280269

Isolation of a novel mutant gene for soil-surface rooting in rice (Oryza sativa L.).

PubMed

Hanzawa, Eiko; Sasaki, Kazuhiro; Nagai, Shinsei; Obara, Mitsuhiro; Fukuta, Yoshimichi; Uga, Yusaku; Miyao, Akio; Hirochika, Hirohiko; Higashitani, Atsushi; Maekawa, Masahiko; Sato, Tadashi

2013-11-20

Root system architecture is an important trait affecting the uptake of nutrients and water by crops. Shallower root systems preferentially take up nutrients from the topsoil and help avoid unfavorable environments in deeper soil layers. We have found a soil-surface rooting mutant from an M2 population that was regenerated from seed calli of a japonica rice cultivar, Nipponbare. In this study, we examined the genetic and physiological characteristics of this mutant. The primary roots of the mutant showed no gravitropic response from the seedling stage on, whereas the gravitropic response of the shoots was normal. Segregation analyses by using an F2 population derived from a cross between the soil-surface rooting mutant and wild-type Nipponbare indicated that the trait was controlled by a single recessive gene, designated as sor1. Fine mapping by using an F2 population derived from a cross between the mutant and an indica rice cultivar, Kasalath, revealed that sor1 was located within a 136-kb region between the simple sequence repeat markers RM16254 and 2935-6 on the terminal region of the short arm of chromosome 4, where 13 putative open reading frames (ORFs) were found. We sequenced these ORFs and detected a 33-bp deletion in one of them, Os04g0101800. Transgenic plants of the mutant transformed with the genomic fragment carrying the Os04g0101800 sequence from Nipponbare showed normal gravitropic responses and no soil-surface rooting. These results suggest that sor1, a rice mutant causing soil-surface rooting and altered root gravitropic response, is allelic to Os04g0101800, and that a 33-bp deletion in the coding region of this gene causes the mutant phenotypes.

Effects of plant size and water relations on gas exchange and growth of the desert shrub Larrea tridentata.

PubMed

Franco, A C; de Soyza, A G; Virginia, R A; Reynolds, J F; Whitford, W G

1994-03-01

Larrea tridentata is a xerophytic evergreen shrub, dominant in the arid regions of the southwestern United States. We examined relationships between gasexchange characteristics, plant and soil water relations, and growth responses of large versus small shrubs of L. tridentata over the course of a summer growing season in the Chihuahuan Desert of southern New Mexico, USA. The soil wetting front did not reach 0.6 m, and soils at depths of 0.6 and 0.9 m remained dry throughout the summer, suggesting that L. tridentata extracts water largely from soil near the surface. Surface soil layers (<0.3 m) were drier under large plants, but predawn xylem water potentials were similar for both plant sizes suggesting some access to deeper soil moisture reserves by large plants. Stem elongation rates were about 40% less in large, reproductively active shrubs than in small, reproductively inactive shrubs. Maximal net photosynthetic rates (P max ) occurred in early summer (21.3 μ mol m -2 s -1 ), when pre-dawn xylem water potential (XWP) reached ca. -1 MPa. Although both shrub sizes exhibited similar responses to environmental factors, small shrubs recovered faster from short-term drought, when pre-dawn XWP reached about -4.5 MPa and P max decreased to only ca. 20% of unstressed levels. Gas exchange measurements yielded a strong relationship between stomatal conductance and photosynthesis, and the relationship between leaf-to-air vapor pressure deficit and stomatal conductance was found to be influenced by pre-dawn XWP. Our results indicate that stomatal responses to water stress and vapor pressure deficit are important in determining rates of carbon gain and water loss in L. tridentata.

Amazon soil charcoal: Pyrogenic carbon stock depends of ignition source distance and forest type in Roraima, Brazil.

PubMed

da Silva Carvalho, Lidiany C; Fearnside, Philip M; Nascimento, Marcelo T; Barbosa, Reinaldo I

2018-04-18

Pyrogenic carbon (PyC) derived from charcoal particles (paleo + modern) deposited in the soil column has been little studied in the Amazon, and our understanding of the factors that control the spatial and vertical distribution of these materials in the region's forest soils is still unclear. The objective of this study was to test the effect of forest type and distance from the ignition source on the PyC stocks contained in macroscopic particles of soil charcoal (≥2 mm; 1 m depth) dispersed in ecotone forests of the northern Brazilian Amazon. Thirty permanent plots were set up near a site that had been occupied by pre-Columbian and by modern populations until the late 1970s. The sampled plots represent seasonal and ombrophilous forests that occur under different hydro-edaphic restrictions. Our results indicate that the largest PyC stock was spatially dependent on distance to the ignition source (<3 km), occurring mainly in flood-free ombrophilous forests (3.46 ± 5.22 Mg PyC/ha). The vertical distribution of PyC in the deeper layers of the soil (> 50 cm) in seasonal forests was limited by hydro-edaphic impediments that restricted the occurrence of charcoal. These results suggest that PyC stocks derived from macroscopic charcoal particles in the soil of this Brazilian Amazon ecotone region are controlled by the distance from the ignition source of the fire, and that forest types with higher hydro-edaphic restrictions can inhibit formation and accumulation of charcoal. Making use of these distinctions reduces uncertainty and improves our ability to understand the variability of PyC stocks in forests with a history of fire in the Amazon. © 2018 John Wiley & Sons Ltd.

Soil carbon stocks and carbon sequestration rates in seminatural grassland in Aso region, Kumamoto, Southern Japan.

PubMed

Toma, Yo; Clifton-Brown, John; Sugiyama, Shinji; Nakaboh, Makoto; Hatano, Ryusuke; Fernández, Fabián G; Ryan Stewart, J; Nishiwaki, Aya; Yamada, Toshihiko

2013-06-01

Global soil carbon (C) stocks account for approximately three times that found in the atmosphere. In the Aso mountain region of Southern Japan, seminatural grasslands have been maintained by annual harvests and/or burning for more than 1000 years. Quantification of soil C stocks and C sequestration rates in Aso mountain ecosystem is needed to make well-informed, land-use decisions to maximize C sinks while minimizing C emissions. Soil cores were collected from six sites within 200 km(2) (767-937 m asl.) from the surface down to the k-Ah layer established 7300 years ago by a volcanic eruption. The biological sources of the C stored in the Aso mountain ecosystem were investigated by combining C content at a number of sampling depths with age (using (14) C dating) and δ(13) C isotopic fractionation. Quantification of plant phytoliths at several depths was used to make basic reconstructions of past vegetation and was linked with C-sequestration rates. The mean total C stock of all six sites was 232 Mg C ha(-1) (28-417 Mg C ha(-1) ), which equates to a soil C sequestration rate of 32 kg C ha(-1)  yr(-1) over 7300 years. Mean soil C sequestration rates over 34, 50 and 100 years were estimated by an equation regressing soil C sequestration rate against soil C accumulation interval, which was modeled to be 618, 483 and 332 kg C ha(-1)  yr(-1) , respectively. Such data allows for a deeper understanding in how much C could be sequestered in Miscanthus grasslands at different time scales. In Aso, tribe Andropogoneae (especially Miscanthus and Schizoachyrium genera) and tribe Paniceae contributed between 64% and 100% of soil C based on δ(13) C abundance. We conclude that the seminatural, C4 -dominated grassland system serves as an important C sink, and worthy of future conservation. © 2013 Blackwell Publishing Ltd.

Distribution and speciation of mercury in the peat bog of Xiaoxing'an Mountain, northeastern China.

PubMed

Liu, Ruhai; Wang, Qichao; Lu, Xianguo; Fang, Fengman; Wang, Yan

2003-01-01

Most reports on mercury (Hg) in boreal ecosystems are from the Nordic countries and North America. Comparatively little information is available on Hg in wetlands in China. We present here a study on Hg in the Tangwang River forested catchment of the Xiaoxing'an Mountain in the northeast of China. The average total Hg (THg) in peat profile ranged from 65.8 to 186.6 ng g(-1) dry wt with the highest at the depth of 5-10 cm. THg in the peat surface was higher than the background in Heilongjiang province, the Florida Everglades, and Birkeness in Sweden. MethylHg (MeHg) concentration ranged from 0.16 to 1.86 ng g(-1) dry wt, with the highest amount at 10-15 cm depth. MeHg content was 0.2-1.2% of THg. THg and MeHg all decreased with the depth. THg in upland layer of soil (0-20 cm) was comparable to the peat surface, but in deeper layers THg concentration in peat was much higher than that in the forested mineral soil. THg in the peat bog increased, but MeHg decreased after it was drained. THg content in plant was different; THg contents in moss (119 ng g(-1) dry wt, n=12) were much higher than in the herbage, the arbor, and the shrubs. The peat bog has mainly been contaminated by Hg deposition from the atmosphere.

A commentary on 'mineral soil carbon fluxes in forests and implications for carbon balance assessments': a deeper look at the data

Treesearch

Coeli M. Hoover; Linda S. Heath

2014-01-01

Forestry practitioners contacted us with their concerns about a recent review article by Buchholz T, Friedland AJ, Hornig CE, Keeton WS, Zanchi G, Nunery J (2013) GCB Bioenergy who questioned the way soil carbon is treated in many models and protocols, and indicated that an increasing number of research studies showed meaningful soil organic carbon (...

[Dynamics of soil physical properties and biological soil crust during the vegetation restoration process of abandoned croplands in the Ordos Plateau, China].

PubMed

Cai, Wen Tao; Li, He Yi; Lai, Li Ming; Zhang, Xiao Long; Guan, Tian Yu; Zhou, Ji Hua; Jiang, Lian He; Zheng, Yuan Run

2017-03-18

A series of typical abandoned croplands in the regions of Ruanliang and Yingliang in the Ordos Plateau, China, were selected, and dynamics of the surface litter, biological soil crust and soil bulk density, soil texture, and soil moisture in different soil layers were investigated. The results showed that in the abandoned cropland in Ruanliang, the clay particle content and surface litter of the surface soil layer (0-10 cm) increased during the restoration process, while that of soil bulk density substantially decreased and soil water content slightly increased in the surface soil. In the medium soil layer (10-30 cm), the clay particle content increased and the soil water content slightly decreased. In the deep soil layer (30-50 cm), there was a relatively large variation in the physical properties. In the abandoned cropland in Yingliang, the coverage of litter and the coverage and thickness of the biological soil crust increased during the abandonment process. The surface soil bulk density, soil clay particle content and soil water content remained constant in 0-10 cm soil layer, while the physical properties varied substantially in 10-40 cm soil layer. The shallow distribution of the soil water content caused by the accumulation of the litter and clay particles on the soil surface might be the key reason of the replacement of the semi-shrub Artemisia ordosica community with a perennial grass community over the last 20 years of the abandoned cropland in Ruanliang. The relatively high soil water content in the shallow layer and the development of the biological soil crust might explain why the abandoned cropland in Yingliang was not invaded by the semi-shrub A. ordosica during the restoration process.

Comparison of remote sensing and in-situ soil moisture measurements: 6 years survey of SMOS data and agrometeorological stations in Eastern Poland

NASA Astrophysics Data System (ADS)

Szlazak, Radoslaw; Rojek, Edyta; Lukowski, Mateusz; Marczewski, Wojciech; Slominski, Jan; Sagan, Joanna; Gluba, Lukasz; Usowicz, Jerzy; Usowicz, Boguslaw

2017-04-01

Long term measurements of soil moisture on a large scale provide important information about not only periodical changes in water content, but also its contribute to better understanding of water cycle in environment. In addition, if in the studied area occurred extreme weather conditions or even anomalies, it is scientifically challenging to compare and validate data from two such different techniques like remote sensing and in-situ measurements. The aim of our research was to compare data of independent soil moisture measurements from SMOS (Soil Moisture and Ocean Salinity) satellite and 9 agrometeorological stations installed on Eastern Poland (Polesie and Podlasie regions). Those regions have similar climatic and topographic conditions, however, different vegetation covers and soil properties. Radiometric SMOS data contain surface water content values (approx. 45 km) for the area corresponding to the positions of chosen agrometeorological stations. For the purpose of those studies only morning satellite overpasses (ascending) were used. In-situ sensors in stations measure precisely soil moisture at 5-10 cm depth, but each only in one point. Both datasets were 7-days averaged in order to standardize. Analysis of a long term data is very interesting, especially because of occurrence of flood and drought events during the analyzed period of time. For example, the analyses revealed clear rainfall trend between ground and satellite data. Some shifts between SMOS and ground measurements were also observed, what may be explained by impact of different depths of SMOS measurements (<5 cm) and layer measured by sensors in the stations (0-10 cm). The influence of different sensing depths for both techniques is also reflected in bigger variability of SMOS data as they came from shallower layer of soil that have smaller "inertia" (in terms of soil moisture variability) than deeper in situ measurements. The results from SMOS and those obtained with the soil moisture sensor for Eastern Poland in 2010-2016 including rainfall and air temperature data will be presented and compared for compliance using classical statistics methods and Bland-Altman test. The work was partially funded under two ESA projects: 1) "ELBARA_PD (Penetration Depth)" No. 4000107897/13/NL/KML, funded by the Government of Poland through an ESA-PECS contract (Plan for European Cooperating States). 2) "Technical Support for the fabrication and deployment of the radiometer ELBARA-III in Bubnow, Poland" No. 4000113360/15/NL/FF/gp

Mass loading of typical artificial sweeteners in a pig farm and their dissipation and uptake by plants in neighboring farmland.

PubMed

Ma, Ling; Liu, Yarui; Xu, Jiayao; Sun, Hongwen; Chen, Hao; Yao, Yiming; Zhang, Peng; Shen, Fengju; Alder, Aldredo C

2017-12-15

Pig farm is an important potential source for artificial sweeteners (ASs) in the environment due to their wide use as additives in pig feed. The objective of this study was to evaluate the fate of typical ASs in pig farm and neighboring farmland. For this purpose, the levels of four typical artificial ASs, i.e. saccharin (SAC), cyclamate (CYC), acesulfame (ACE) and sucralose (SUC), in pig feed and manure from a pig farm and water samples from an on-farm wastewater treatment plant (WWTP) in Tianjin, China were measured and the mass loadings and removal efficiencies were assessed. Moreover, the levels of ASs in different layers of soil and vegetables in neighboring farmland that received manure fertilizers and wastewater from the farm were consecutively monitored for 60-80days. The SAC, CYC and ACE were widely determined in all kinds of the samples, while SUC was only found in few soil samples. The mass loadings of the ASs in pig feed were estimated up to 311kg/year for SAC, 59.1kg/year for CYC, and 17.1kg/year for ACE, respectively. The fractions of the total mass of ASs excreted via manure were estimated to be 36.0% for SAC, 59.4% for CYC, and 36.7% for ACE as compared to those in pig feed. High removal efficiencies (>90%) of ASs in the on-farm WWTP was achieved. In greenhouse soils, CYC, SAC, ACE, and SUC were degraded quickly, with half-lives of 4.3-5.9 d, 2.7-4.2 d, 8.4-12.3 d, and 7.3-10.8 d, respectively. Lower levels of ASs were found in deeper soil layer (20-30cm). The ASs were considerably absorbed by plants when the ASs' concentrations were high in soil. This study presents the first comprehensive overview of ASs fate from a pig farm to the neighboring agricultural ecosystem. Copyright © 2017. Published by Elsevier B.V.

Root system-based limits to agricultural productivity and efficiency: the farming systems context

PubMed Central

Thorup-Kristensen, Kristian; Kirkegaard, John

2016-01-01

Background There has been renewed global interest in both genetic and management strategies to improve root system function in order to improve agricultural productivity and minimize environmental damage. Improving root system capture of water and nutrients is an obvious strategy, yet few studies consider the important interactions between the genetic improvements proposed, and crop management at a system scale that will influence likely success. Scope To exemplify these interactions, the contrasting cereal-based farming systems of Denmark and Australia were used, where the improved uptake of water and nitrogen from deeper soil layers has been proposed to improve productivity and environmental outcomes in both systems. The analysis showed that water and nitrogen availability, especially in deeper layers (>1 m), was significantly affected by the preceding crops and management, and likely to interact strongly with deeper rooting as a specific trait of interest. Conclusions In the semi-arid Australian environment, grain yield impacts from storage and uptake of water from depth (>1 m) could be influenced to a stronger degree by preceding crop choice (0·42 t ha–1), pre-crop fallow management (0·65 t ha–1) and sowing date (0·63 t ha–1) than by current genetic differences in rooting depth (0·36 t ha–1). Matching of deep-rooted genotypes to management provided the greatest improvements related to deep water capture. In the wetter environment of Denmark, reduced leaching of N was the focus. Here the amount of N moving below the root zone was also influenced by previous crop choice or cover crop management (effects up to 85 kg N ha–1) and wheat crop sowing date (up to 45 kg ha–1), effects which over-ride the effects of differences in rooting depth among genotypes. These examples highlight the need to understand the farming system context and important G × E × M interactions in studies on proposed genetic improvements to root systems for improved productivity or environmental outcomes. PMID:27411680

Time domain reflectometry measurements of solute transport across a soil layer boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nissen, H.H.; Moldrup, P.; Kachanoski, R.G.

2000-02-01

The mechanisms governing solute transport through layered soil are not fully understood. Solute transport at, above, and beyond the interface between two soil layers during quasi-steady-state soil water movement was investigated using time domain reflectometry (TDR). A 0.26-m sandy loam layer was packed on top of a 1.35-m fine sand layer in a soil column. Soil water content ({theta}) and bulk soil electrical conductivity (EC{sub b}) were measured by 50 horizontal and 2 vertical TDR probes. A new TDR calibration method that gives a detailed relationship between apparent relative dielectric permittivity (K{sub s}) and {theta} was applied. Two replicate solutemore » transport experiments were conducted adding a conservative tracer (CCl) to the surface as a short pulse. The convective lognormal transfer function model (CLT) was fitted to the TDR-measured time integral-normalized resident concentration breakthrough curves (BTCs). The BTCs and the average solute-transport velocities showed preferential flow occurred across the layer boundary. A nonlinear decrease in TDR-measured {theta} in the upper soil toward the soil layer boundary suggests the existence of a 0.10-m zone where water is confined towards fingered flow, creating lateral variations in the area-averaged water flux above the layer boundary. A comparison of the time integral-normalized flux concentration measured by vertical and horizontal TDR probes at the layer boundary also indicates a nonuniform solute transport. The solute dispersivity remained constant in the upper soil layer, but increased nonlinearly (and further down, linearly) with depth in the lower layer, implying convective-dispersive solute transport in the upper soil, a transition zone just below the boundary, and stochastic-convective solute transport in the remaining part of the lower soil.« less

Effects of forest conversion on soil microbial communities depend on soil layer on the eastern Tibetan Plateau of China.

PubMed

He, Ruoyang; Yang, Kaijun; Li, Zhijie; Schädler, Martin; Yang, Wanqin; Wu, Fuzhong; Tan, Bo; Zhang, Li; Xu, Zhenfeng

2017-01-01

Forest land-use changes have long been suggested to profoundly affect soil microbial communities. However, how forest type conversion influences soil microbial properties remains unclear in Tibetan boreal forests. The aim of this study was to explore variations of soil microbial profiles in the surface organic layer and subsurface mineral soil among three contrasting forests (natural coniferous forest, NF; secondary birch forest, SF and spruce plantation, PT). Soil microbial biomass, activity and community structure of the two layers were investigated by chloroform fumigation, substrate respiration and phospholipid fatty acid analysis (PLFA), respectively. In the organic layer, both NF and SF exhibited higher soil nutrient levels (carbon, nitrogen and phosphorus), microbial biomass carbon and nitrogen, microbial respiration, PLFA contents as compared to PT. However, the measured parameters in the mineral soils often did not differ following forest type conversion. Irrespective of forest types, the microbial indexes generally were greater in the organic layer than in the mineral soil. PLFAs biomarkers were significantly correlated with soil substrate pools. Taken together, forest land-use change remarkably altered microbial community in the organic layer but often did not affect them in the mineral soil. The microbial responses to forest land-use change depend on soil layer, with organic horizons being more sensitive to forest conversion.

Fumigation efficacy and emission reduction using low-permeability film in orchard soil fumigation.

PubMed

Gao, Suduan; Sosnoskie, Lynn M; Cabrera, Jose Alfonso; Qin, Ruijun; Hanson, Bradley D; Gerik, James S; Wang, Dong; Browne, Greg T; Thomas, John E

2016-02-01

Many orchards use fumigation to control soilborne pests prior to replanting. Controlling emissions is mandatory to reduce air pollution in California. This research evaluated the effects of plastic film type [polyethylene (PE) or totally impermeable film (TIF)], application rate of Telone C35 [full (610 kg ha(-1) ), 2/3 or 1/3 rates] and carbonation at 207 kPa on fumigant transport (emission and in soil) and efficacy. While increasing fumigant concentrations under the tarp, TIF reduced emissions >95% (∼2% and <1% of total applied 1,3-dichloropropene and chloropicrin respectively) relative to bare soil, compared with ∼30% reduction by PE. All fumigation treatments, regardless of film type, provided good nematode control above 100 cm soil depth; however, nematode survival was high at deeper depths. Weed emergence was mostly affected by tarping and fumigant rate, with no effects from the carbonation. TIF can effectively reduce fumigant emissions. Carbonation under the studied conditions did not improve fumigant dispersion and pest control. The 2/3 rate with TIF controlled nematodes as effectively as the full rate in bare soil or under the PE film to 100 cm soil depth. However, control of nematodes in deeper soil remains a challenge for perennial crops. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Modelling Soil Heat and Water Flow as a Coupled Process in Land Surface Models

NASA Astrophysics Data System (ADS)

García González, Raquel; Verhoef, Anne; Vidale, Pier Luigi; Braud, Isabelle

2010-05-01

To improve model estimates of soil water and heat flow by land surface models (LSMs), in particular in the first few centimetres of the near-surface soil profile, we have to consider in detail all the relevant physical processes involved (see e.g. Milly, 1982). Often, thermal and iso-thermal vapour fluxes in LSMs are neglected and the simplified Richard's equation is used as a result. Vapour transfer may affect the water fluxes and heat transfer in LSMs used for hydrometeorological and climate simulations. Processes occurring in the top 50 cm soil may be relevant for water and heat flux dynamics in the deeper layers, as well as for estimates of evapotranspiration and heterotrophic respiration, or even for climate and weather predictions. Water vapour transfer, which was not incorporated in previous versions of the MOSES/JULES model (Joint UK Land Environment Simulator; Cox et al., 1999), has now been implemented. Furthermore, we also assessed the effect of the soil vertical resolution on the simulated soil moisture and temperature profiles and the effect of the processes occurring at the upper boundary, mainly in terms of infiltration rates and evapotranspiration. SiSPAT (Simple Soil Plant Atmosphere Transfer Model; Braud et al., 1995) was initially used to quantify the changes that we expect to find when we introduce vapour transfer in JULES, involving parameters such as thermal vapour conductivity and diffusivity. Also, this approach allows us to compare JULES to a more complete and complex numerical model. Water vapour flux varied with soil texture, depth and soil moisture content, but overall our results suggested that water vapour fluxes change temperature gradients in the entire soil profile and introduce an overall surface cooling effect. Increasing the resolution smoothed and reduced temperature differences between liquid (L) and liquid/vapour (LV) simulations at all depths, and introduced a temperature increase over the entire soil profile. Thermal gradients rather than soil water potential gradients seem to cause temporal and spatial (vertical) soil temperature variability. We conclude that a multi-soil layer configuration may improve soil water dynamics, heat transfer and coupling of these processes, as well as evapotranspiration estimates and land surface-atmosphere coupling. However, a compromise should be reached between numerical and process-simulation aspects. References: Braud I., A.C. Dantas-Antonino, M. Vauclin, J.L. Thony and P. Ruelle, 1995b: A Simple Soil Plant Atmo- sphere Transfer model (SiSPAT), Development and field verification, J. Hydrol, 166: 213-250 Cox, P.M., R.A. Betts, C.B. Bunton, R.L.H. Essery, P.R. Rowntree, and J. Smith (1999), The impact of new land surface physics on the GCM simulation of climate and climate sensitivity. Clim. Dyn., 15, 183-203. Milly, P.C.D., 1982. Moisture and heat transport in hysteric inhomogeneous porous media: a matric head- based formulation and a numerical model, Water Resour. Res., 18:489-498

Soil gas radon concentrations measurements in terms of great soil groups.

PubMed

Içhedef, Mutlu; Saç, Müslim Murat; Camgöz, Berkay; Bolca, Mustafa; Harmanşah, Çoşkun

2013-12-01

In this study, soil gas radon concentrations were investigated according to locations, horizontal soil layers and great soil groups around Tuzla Fault, Seferihisar-İzmir. Great soil groups are a category that described the horizontal soil layers under soil classification system and distributions of radon concentration in the great soil groups are firstly determined by the present study. According to the obtained results, it has been showed that the radon concentrations in the Koluvial soil group are higher than the other soil groups in the region. Also significant differences on location in same great soil group were determined. The radon concentrations in the Koluvial soil groups were measured with respect to soil layers structures (A, B, C1, and C2). It has been observed that the values increase with depth of soil (C2>C1>B>A). The main reason may be due to the meteorological factors that have limited effect on radon escape from deep layers. Although fault lines pass thought the study area radon concentrations were varied location to location, layer to layer and great group to great group. The study shows that a detailed location description should be performed before soil radon measurements for earthquake predictions. Copyright © 2013 Elsevier Ltd. All rights reserved.

Shifts of tundra bacterial and archaeal communities along a permafrost thaw gradient in Alaska.

PubMed

Deng, Jie; Gu, Yunfu; Zhang, Jin; Xue, Kai; Qin, Yujia; Yuan, Mengting; Yin, Huaqun; He, Zhili; Wu, Liyou; Schuur, Edward A G; Tiedje, James M; Zhou, Jizhong

2015-01-01

Understanding the response of permafrost microbial communities to climate warming is crucial for evaluating ecosystem feedbacks to global change. This study investigated soil bacterial and archaeal communities by Illumina MiSeq sequencing of 16S rRNA gene amplicons across a permafrost thaw gradient at different depths in Alaska with thaw progression for over three decades. Over 4.6 million passing 16S rRNA gene sequences were obtained from a total of 97 samples, corresponding to 61 known classes and 470 genera. Soil depth and the associated soil physical-chemical properties had predominant impacts on the diversity and composition of the microbial communities. Both richness and evenness of the microbial communities decreased with soil depth. Acidobacteria, Verrucomicrobia, Alpha- and Gamma-Proteobacteria dominated the microbial communities in the upper horizon, whereas abundances of Bacteroidetes, Delta-Proteobacteria and Firmicutes increased towards deeper soils. Effects of thaw progression were absent in microbial communities in the near-surface organic soil, probably due to greater temperature variation. Thaw progression decreased the abundances of the majority of the associated taxa in the lower organic soil, but increased the abundances of those in the mineral soil, including groups potentially involved in recalcitrant C degradation (Actinomycetales, Chitinophaga, etc.). The changes in microbial communities may be related to altered soil C sources by thaw progression. Collectively, this study revealed different impacts of thaw in the organic and mineral horizons and suggests the importance of studying both the upper and deeper soils while evaluating microbial responses to permafrost thaw. © 2014 John Wiley & Sons Ltd.

Effect on a long-term afforestation of pine in a beech domain in NE-Spain as reflected in soil C and N isotopic signature

NASA Astrophysics Data System (ADS)

Girona García, Antonio; Badía-Villas, David; González-Pérez, José Antonio; Tomás Jiménez-Morillo, Nicasio; Martí-Dalmau, Clara

2015-04-01

The replacement of native beech forests (Fagus sylvatica) by Scots pine (Pinus sylvestris) afforestation may exert changes in soil properties, particularly in soil organic matter (SOM) (Carceller and Vallejo, 1996). Stable isotopic signatures of light elements (d13C, d15N) in soils and plants are valuable proxies for the identification of biogeochemical processes and their rates in the pedosphere (Andreeva et al., 2013 and refs therein). In this work the C and N stable isotopic analysis is used as a proxy to detect changes in SOM surrogated to the effect of centennial replacement of beech by the Scots pinewood. Two acid soil profiles, developed on quartzites under a humid climate at an altitude of 1400-1500 masl, have been sampled in Moncayo (Iberian range, NE-Spain). For each soil profile three O-layers (litter: OL, fragmented litter OF and humified litter OH) and mineral soil horizons (Ah, E, Bhs and C) were sampled. Content and bulk isotopic signature of light elements (C and N) were analysed in a Flash 2000 elemental micro-analyser coupled via a ConFlo IV interface to a Delta V Advantage isotope ratio mass spectrometer (IRMS) (Thermo Scientific, Bremen, Germany). Isotopic ratios are reported as parts per thousand deviations from appropriate standards. The standard deviations of d13C and d15N were typically less than ± 0.05 per thousand, ± 0.2 per thousand, respectively. After 100 years since the pine afforestation, no differences on C content were observed in the O-layers, ranging from 30-47% in pine soils and 37-47 % in beech soils. Similarly, no differences on N content were observed in the O-layers, ranging from 1.24-1.86 % in pine soils and 1.70-1.71 % in beech soils. C and N contents decrease progressively in depth with the exception of E-horizons where the lowest C and N content values were found. C/N ratio is higher in pine soil (20.7-38.1) than in beech O soil horizons (21.8-27.5), showing similar behavior with soil depth. Pine biomass was slightly enriched in 13C as compared to that from beech (OL enrichment factor= 1.24 ± 0.13 per thousand). Along the soil profile the C isotopic signature (d13C) reflects the main vegetation signature being higher in pine than beech in the organic soil horizons (OL, OF and OH) down to the first mineral Ah horizon. At deeper horizons d13C value tends to equal that of the original beech soil indicating a limited influence of the afforested specie with depth even 100 years after afforestation. A consistent enrichment in d15N with depth was observed in the two profiles. This N enrichments have been related with progressive N losses being particularly pronounced in forest soils (Szpak, 2014 and refs therein). This phenomenon can be also related to migrations of N forms in a more evolved organic matter. In this view N losses in organic layers under beech seem to be less pronounced that under the alien pine. REFERENCES: Andreeva BD, Zech M, Glaser B, Erbajeva MA, Chimitdorgieva, Ermakova OD, Zech, W. (2013). Stable isotope (δ13C, δ15N, δ18O) record of soils in Buryatia, southern Siberia: Implications for biogeochemical and paleoclimatic interpretations. Quaternary International 290-291 (2013) 82-94 pp. Carceller F, Vallejo VR (1996). Influencia de la vegetación en los procesos de podsolización en los suelos de la Sierra del Moncayo (Zaragoza). Geogaceta 1127-1130. Szpak P (2014). Complexities of nitrogen isotope biogeochemistry in plant-soil systems: implications for the study of ancient agricultural and animal management practices. Front. Plant Sci. 5: 288 1-19 pp. Acknowledgements: This study is part of the results of the FUEGOSOL (CGL2013-43440-R) and GEOFIRE Projects (CGL2012-38655-C04-01) funded by the Spanish Ministry for Economy and Competitiveness. N.T Jiménez-Morillo is funded by a FPI research grant (BES-2013-062573).

Radioisotope tracer approach for understanding the impacts of global change-induced pedoturbation on soil C dynamics

NASA Astrophysics Data System (ADS)

Gonzalez-Meler, M. A.; Sturchio, N. C.; Sanchez-de Leon, Y.; Blanc-Betes, E.; Taneva, L.; Poghosyan, A.; Norby, R. J.; Filley, T. R.; Guilderson, T. P.; Welker, J. M.

2010-12-01

Biogeochemical carbon-cycle feedbacks to climate are apparent but uncertain, primarily because of gaps in mechanistic understanding on the ecosystem processes that drive carbon cycling and storage in terrestrial ecosystems, particularly in soils. Recent findings are increasingly recognizing the interaction between soil biota and the soil physical environment. Soil carbon turnover is partly determined by burial of organic matter and its physical and chemical protection. These factors are potentially affected by changes in climate (freezing-thawing or wet-drying cycles) or ecosystem structure including biological invasions. A major impediment to understanding dynamics of soil C in terrestrial systems is our inability to measure soil physical processes such as soil mixing rates or turnover of soil structures, including aggregates. Here we present a multiple radioisotope tracer approach (naturally occurring and man-made) to measure soil mixing rates in response to global change. We will present evidence of soil mixing rate changes in a temperate forest exposed to increased levels of atmospheric CO2 and in a tundra ecosystem exposed to increased thermal insulation. In both cases, radioisotope tracers proved to be an effective way to measure effects of global change on pedoturbation. Results also provided insights into the specific mechanisms involved in the responses. Elevated CO2 resulted in deeper soil mixing cells (increased by about 5cm on average) when compared to control soils as a consequence of changes in biota (increased root growth, higher earthworm density). In the tundra, soil warming induced higher rates of cryoturbation, resulting in what appears to be a net uplift of organic matter to the surface thereby exposing deeper C to decomposers. In both cases, global change factors affected the vertical distribution of C and changed the amount of bulk soil actively involved in soil processes. As a consequence, comparisons of C budgets to a given soil depth in response to global change factors may be misleading if they do not account for the depth change in the soil mixing cells.

Antisoiling technology: Theories of surface soiling and performance of antisoiling surface coatings

NASA Technical Reports Server (NTRS)

Cuddihy, E. F.; Willis, P. B.

1984-01-01

Physical examination of surfaces undergoing natural outdoor soiling suggests that soil matter accumulates in up to three distinct layers. The first layer involves strong chemical attachment or strong chemisorption of soil matter on the primary surface. The second layer is physical, consisting of a highly organized arrangement of soil creating a gradation in surface energy from a high associated with the energetic first layer to the lowest possible state on the outer surfce of the second layer. The lowest possible energy state is dictated by the physical nature of the regional atmospheric soiling materials. These first two layers are resistant to removal by rain. The third layer constitutes a settling of loose soil matter, accumulating in dry periods and being removed during rainy periods. Theories and evidence suggest that surfaces that should be naturally resistant to the formation of the first two-resistant layers should be hard, smooth, hydrophobic, free of first-period elements, and have the lowest possible surface energy. These characteristics, evolving as requirements for low-soiling surfaces, suggest that surfaces or surface coatings should be of fluorocarbon chemistry. Evidence for the three-soil-layer concept, and data on the positive performance of candidate fluorocarbon coatings on glass and transparent plastic films after 28 months of outdoor exposure, are presented.

BOREAS Soils Data over the SSA in Raster Format and AEAC Projection

NASA Technical Reports Server (NTRS)

Knapp, David; Rostad, Harold; Hall, Forrest G. (Editor)

2000-01-01

This data set consists of GIS layers that describe the soils of the BOREAS SSA. The original data were submitted as vector layers that were gridded by BOREAS staff to a 30-meter pixel size in the AEAC projection. These data layers include the soil code (which relates to the soil name), modifier (which also relates to the soil name), and extent (indicating the extent that this soil exists within the polygon). There are three sets of these layers representing the primary, secondary, and tertiary soil characteristics. Thus, there is a total of nine layers in this data set along with supporting files. The data are stored in binary, image format files.

[Characteristics of soil moisture in artificial impermeable layers].

PubMed

Suo, Gai-Di; Xie, Yong-Sheng; Tian, Fei; Chuai, Jun-Feng; Jing, Min-Xiao

2014-09-01

For the problem of low water and fertilizer use efficiency caused by nitrate nitrogen lea- ching into deep soil layer and soil desiccation in dryland apple orchard, characteristics of soil moisture were investigated by means of hand tamping in order to find a new approach in improving the water and fertilizer use efficiency in the apple orchard. Two artificial impermeable layers of red clay and dark loessial soil were built in soil, with a thickness of 3 or 5 cm. Results showed that artificial impermeable layers with the two different thicknesses were effective in reducing or blocking water infiltration into soil and had higher seepage controlling efficiency. Seepage controlling efficiency for the red clay impermeable layer was better than that for the dark loessial soil impermeable layer. Among all the treatments, the red clay impermeable layer of 5 cm thickness had the highest bulk density, the lowest initial infiltration rate (0.033 mm · min(-1)) and stable infiltration rate (0.018 mm · min(-1)) among all treatments. After dry-wet alternation in summer and freezing-thawing cycle in winter, its physiochemical properties changed little. Increase in years did not affect stable infiltration rate of soil water. The red clay impermeable layer of 5 cm thickness could effectively increase soil moisture content in upper soil layer which was conducive to raise the water and nutrient use efficiency. The approach could be applied to the apple production of dryland orchard.

Soil Respiration Controls Ionic Nutrient Concentration In Percolating Water In Rice Fields

NASA Astrophysics Data System (ADS)

Kimura, M.

2004-12-01

Soil water in the plow layer in rice fields contains various kinds of cations and anions, and they are lost from the plow layer by water percolation. Some portions of CO2 produced by respirations of rice roots and soil microorganisms are also leached by water percolation to the subsoil layer as HCO3-. As the electrical neutrality of inorganic substances in percolating water is maintained when they are assumed to be in the form of simple cations and anions, soil respiration accelerates the leaching of ionic nutrients from the plow layer by water percolation. The proportion of inorganic carbon (Σ CO2) originated from photosynthates in the total Σ CO2 in soil solution in the plow layer was from 28 to 36 % in the rice straw amended soil and from 16 to 31 % in the soil without rice straw amendment in a soil pot experiment with rice plant after the maximum tillering stage. Most of Σ CO2 in percolating water from the plow layer accumulates in the subsoil layer. Periodical measurement of Σ CO2 in percolating water at 13 and 40 cm soil depths indicated that 10 % of total soil organic C in the plow layer was leached down from the plow layer (13 cm), and that about 90 % of it was retained in the subsoil layer to the depth of 40 cm. Water soluble organic materials are also leached from the plow layer by water percolation, and the leaching is accelerated by soil reduction. Soil reduction decreased the content of organic materials that were bound with ferric iron in soil (extractable by 0.1M Na4P2O7 + NaBH4) and increased the content of organic materials that were extractable by the neutral chelating solution (0.1M Na4P2O7). In addition, water percolation transformed the latter organic materials to those that were extractable by water and a neutral salt. Considerable portions of organic materials in percolating water are adsorbed in the subsoil layer, and then partially decomposed and polymerized to specific soil organic materials in the subsoil. Organic materials that were leached from the plow layer by percolating water amounted to 170 kgC ha-1 in a Japanese rice field, among which 120 kgC of organic materials were adsorbed in the subsoil layer between 13 and 40 cm depth.

Effects of forest conversion on soil microbial communities depend on soil layer on the eastern Tibetan Plateau of China

PubMed Central

He, Ruoyang; Yang, Kaijun; Li, Zhijie; Schädler, Martin; Yang, Wanqin; Wu, Fuzhong; Tan, Bo; Zhang, Li

2017-01-01

Forest land-use changes have long been suggested to profoundly affect soil microbial communities. However, how forest type conversion influences soil microbial properties remains unclear in Tibetan boreal forests. The aim of this study was to explore variations of soil microbial profiles in the surface organic layer and subsurface mineral soil among three contrasting forests (natural coniferous forest, NF; secondary birch forest, SF and spruce plantation, PT). Soil microbial biomass, activity and community structure of the two layers were investigated by chloroform fumigation, substrate respiration and phospholipid fatty acid analysis (PLFA), respectively. In the organic layer, both NF and SF exhibited higher soil nutrient levels (carbon, nitrogen and phosphorus), microbial biomass carbon and nitrogen, microbial respiration, PLFA contents as compared to PT. However, the measured parameters in the mineral soils often did not differ following forest type conversion. Irrespective of forest types, the microbial indexes generally were greater in the organic layer than in the mineral soil. PLFAs biomarkers were significantly correlated with soil substrate pools. Taken together, forest land-use change remarkably altered microbial community in the organic layer but often did not affect them in the mineral soil. The microbial responses to forest land-use change depend on soil layer, with organic horizons being more sensitive to forest conversion. PMID:28982191

Modelling spatiotemporal distribution patterns of earthworms in order to indicate hydrological soil processes

NASA Astrophysics Data System (ADS)

Palm, Juliane; Klaus, Julian; van Schaik, Loes; Zehe, Erwin; Schröder, Boris

2010-05-01

Soils provide central ecosystem functions in recycling nutrients, detoxifying harmful chemicals as well as regulating microclimate and local hydrological processes. The internal regulation of these functions and therefore the development of healthy and fertile soils mainly depend on the functional diversity of plants and animals. Soil organisms drive essential processes such as litter decomposition, nutrient cycling, water dynamics, and soil structure formation. Disturbances by different soil management practices (e.g., soil tillage, fertilization, pesticide application) affect the distribution and abundance of soil organisms and hence influence regulating processes. The strong relationship between environmental conditions and soil organisms gives us the opportunity to link spatiotemporal distribution patterns of indicator species with the potential provision of essential soil processes on different scales. Earthworms are key organisms for soil function and affect, among other things, water dynamics and solute transport in soils. Through their burrowing activity, earthworms increase the number of macropores by building semi-permanent burrow systems. In the unsaturated zone, earthworm burrows act as preferential flow pathways and affect water infiltration, surface-, subsurface- and matrix flow as well as the transport of water and solutes into deeper soil layers. Thereby different ecological earthworm types have different importance. Deep burrowing anecic earthworm species (e.g., Lumbricus terrestris) affect the vertical flow and thus increase the risk of potential contamination of ground water with agrochemicals. In contrast, horizontal burrowing endogeic (e.g., Aporrectodea caliginosa) and epigeic species (e.g., Lumbricus rubellus) increase water conductivity and the diffuse distribution of water and solutes in the upper soil layers. The question which processes are more relevant is pivotal for soil management and risk assessment. Thus, finding relevant environmental predictors which explain the distribution and dynamics of different ecological earthworm types can help us to understand where or when these processes are relevant in the landscape. Therefore, we develop species distribution models which are a useful tool to predict spatiotemporal distributions of earthworm occurrence and abundance under changing environmental conditions. On field scale, geostatistical distribution maps have shown that the spatial distribution of earthworms depends on soil parameters such as food supply, soil moisture, bulk density but with different patterns for earthworm stages (adult, juvenile) and ecological types (anecic, endogeic, epigeic). On landscape scales, earthworm distribution seems to be strongly controlled by management/disturbance-related factors. Our study shows different modelling approaches for predicting distribution patterns of earthworms in the Weiherbach area, an agricultural site in Kraichtal (Baden-Württemberg, Germany). We carried out field studies on arable fields differing in soil management practices (conventional, conservational), soil properties (organic matter content, texture, soil moisture), and topography (slope, elevation) in order to identify predictors for earthworm occurrence, abundance and biomass. Our earthworm distribution models consider all ecological groups as well as different life stages, accounting for the fact that the activity of juveniles is sometimes different from those of adults. Within our BIOPORE-project it is our final goal to couple our distribution models with population dynamic models and a preferential flow model to an integrated ecohydrological model to analyse feedbacks between earthworm engineering and transport characteristics affecting the functioning of (agro-) ecosystems.

The soil hydrologic response to forest regrowth: a case study from southwestern Amazonia

NASA Astrophysics Data System (ADS)

Godsey, Sarah; Elsenbeer, Helmut

2002-05-01

As a large and dynamic land-use category, tropical secondary forests may affect climate, soils, and hydrology in a manner different from primary forests or agricultural areas. We investigated the saturated hydraulic conductivity Ksat of a Kandiudult under different land uses in Rondonia, Brazil. We measured Ksat at four depths (12·5, 20, 30 and 50 cm) under (a) primary forest, (b) a former banana-cacao plantation (SF1), and (c) an abandoned pasture (SF2). At 12·5 cm, all three land uses differ significantly ( = 0·1), but not at the 20 and 30 cm depths. At 50 cm, Ksat was significantly greater in the former pasture than in other land uses. Lateral subsurface flow is expected during intense rainfall (about 30 times per year) at 30 cm depth in SF1 and at 50 cm depth in the forest, whereas the relatively low permeability at shallow 12·5 cm in the SF2 may result not only in lateral subsurface flow, but also saturation overland flow. For modelling purposes, recovering systems seem to have Ksat values distinct from primary forest at shallow depths, whereas at deeper layers (>20 cm) they may be considered similar to forests.

[Effects of altitudes on soil microbial biomass and enzyme activity in alpine-gorge regions.

PubMed

Cao, Rui; Wu, Fu Zhong; Yang, Wan Qin; Xu, Zhen Feng; Tani, Bo; Wang, Bin; Li, Jun; Chang, Chen Hui

2016-04-22

In order to understand the variations of soil microbial biomass and soil enzyme activities with the change of altitude, a field incubation was conducted in dry valley, ecotone between dry valley and mountain forest, subalpine coniferous forest, alpine forest and alpine meadow from 1563 m to 3994 m of altitude in the alpine-gorge region of western Sichuan. The microbial biomass carbon and nitrogen, and the activities of invertase, urease and acid phosphorus were measured in both soil organic layer and mineral soil layer. Both the soil microbial biomass and soil enzyme activities showed the similar tendency in soil organic layer. They increased from 2158 m to 3028 m, then decreased to the lowest value at 3593 m, and thereafter increased until 3994 m in the alpine-gorge region. In contrast, the soil microbial biomass and soil enzyme activities in mineral soil layer showed the trends as, the subalpine forest at 3028 m > alpine meadow at 3994 m > montane forest ecotone at 2158 m > alpine forest at 3593 m > dry valley at 1563 m. Regardless of altitudes, soil microbial biomass and soil enzyme activities were significantly higher in soil organic layer than in mineral soil layer. The soil microbial biomass was significantly positively correlated with the activities of the measured soil enzymes. Moreover, both the soil microbial biomass and soil enzyme activities were significantly positively correlated with soil water content, organic carbon, and total nitrogen. The activity of soil invertase was significantly positively correlated with soil phosphorus content, and the soil acid phosphatase was so with soil phosphorus content and soil temperature. In brief, changes in vegetation and other environmental factors resulting from altitude change might have strong effects on soil biochemical properties in the alpine-gorge region.

Microbiome dynamics of human epidermis following skin barrier disruption

PubMed Central

2012-01-01

Background Recent advances in sequencing technologies have enabled metagenomic analyses of many human body sites. Several studies have catalogued the composition of bacterial communities of the surface of human skin, mostly under static conditions in healthy volunteers. Skin injury will disturb the cutaneous homeostasis of the host tissue and its commensal microbiota, but the dynamics of this process have not been studied before. Here we analyzed the microbiota of the surface layer and the deeper layers of the stratum corneum of normal skin, and we investigated the dynamics of recolonization of skin microbiota following skin barrier disruption by tape stripping as a model of superficial injury. Results We observed gender differences in microbiota composition and showed that bacteria are not uniformly distributed in the stratum corneum. Phylogenetic distance analysis was employed to follow microbiota development during recolonization of injured skin. Surprisingly, the developing neo-microbiome at day 14 was more similar to that of the deeper stratum corneum layers than to the initial surface microbiome. In addition, we also observed variation in the host response towards superficial injury as assessed by the induction of antimicrobial protein expression in epidermal keratinocytes. Conclusions We suggest that the microbiome of the deeper layers, rather than that of the superficial skin layer, may be regarded as the host indigenous microbiome. Characterization of the skin microbiome under dynamic conditions, and the ensuing response of the microbial community and host tissue, will shed further light on the complex interaction between resident bacteria and epidermis. PMID:23153041

Depth matters: Soil pH and dilution effects in the northern Great Plains

USDA-ARS?s Scientific Manuscript database

In the northern Great Plans (NGP), surface sampling depths of 0-15.2 cm or 0-20.3 cm are suggested for testing soil characteristics such as pH. However, acidification is often most pronounced near-surface (e.g., <10 cm). Thus, sampling deeper can potentially dilute (increase) pH measurements and the...

Linking water and carbon fluxes in a Mediterranean oak woodland using a combined flux and ?18O partitioning approach

NASA Astrophysics Data System (ADS)

Dubbert, M.; Piayda, A.; Costa e Silva, F.; Correia, A.; Pereira, J. S.; Cuntz, M.; Werner, C.

2013-12-01

Water is one of the key factors driving ecosystem productivity, especially in water-limited ecosystems, where global climate change is expected to intensify drought and alter precipitation patterns. One such ecosystem is the ';Montado', where two vegetation layers respond differently to drought: oak trees avoid drought due to their access to deeper soil layers and ground water while herbaceous plants, surviving the summer in the form of seeds. We aimed at 1) quantifying the impact of the understory herbaceous vegetation on ecosystem carbon and water fluxes throughout the year, 2) determining the driving environmental factors for evapotranspiration (ET) and net ecosystem exchange (NEE) and 3) disentangling how ET components of the ecosystem relate to carbon dioxide exchange. We present one year data set comparing modeled and measured stable oxygen isotope signatures (δ18O) of soil evaporation, confirming that the Craig and Gordon equation leads to good agreement with measured δ18O of evaporation (Dubbert et al. 2013). Partitioning ecosystem ET and NEE into its three sources revealed a strong contribution of soil evaporation (E) and herbaceous transpiration (T) to ecosystem ET during spring and fall. In contrast, soil respiration (R) and herbaceous net carbon gain contributed to a lesser amount to ecosystem NEE during spring and fall, leading to consistently smaller water use efficiencies (WUE) of the herbaceous understory compared to the cork-oaks. Here, we demonstrate that the ability to assess ET, NEE and WUE independent of soil evaporation dynamics enables the understanding of the mechanisms of the coupling between water and carbon fluxes and their responses to drought. Dubbert, M., Cuntz, M., Piayda, A., Maguas, C., Werner, C., 2013: Partitioning evapotranspiration - Testing the Craig and Gordon model with field measurements of oxygen isotope ratios of evaporative fluxes. J Hydrol. a) Oxygen isotope signatures of soil evaporation on bare soil plots calculated with the Craig and Gordon equation versus measured values for the open (white circles) and tree site (black circles) of every measurement point (mean values × SD; n=3; R2=0.8; p<0.001). b) Modeled δ18O of leaf water at the evaporating sites in the non steady state versus measured leaf water δ18Ofor the open and tree site (R2=0.9,p<0.001). Relative contribution (%) of soil, herbaceous vegetation and cork-oaks to ecosystem evapotranspiration and net ecosystem CO2 exchange

Can shallow-layer measurements at a single location be used to predict deep soil water storage at the slope scale?

NASA Astrophysics Data System (ADS)

Gao, Lei; Lv, Yujuan; Wang, Dongdong; Tahir, Muhammad; Peng, Xinhua

2015-12-01

Knowing the amount of soil water storage (SWS) in agricultural soil profiles is important for understanding physical, chemical, and biological soil processes. However, measuring the SWS in deep soil layers is more expensive and time consuming than in shallower layers. Whether deep SWS can be predicted from shallow-layer measurements through temporal stability analysis (TSA) remains unclear. To address this issue, the soil water content was measured at depths of 0-1.6 m (0.2-m depth intervals) at 79 locations along an agricultural slope on 28 occasions between July 2013 and October 2014. SWSs values were then calculated for the 0-0.4, 0.4-0.8, 0.8-1.2, 1.2-1.6, and 0-1.6 m soil layers. The SWS exhibited strong temporal stability, with mean Spearman's ranking coefficients (rs) of 0.83, 0.92, 0.83, and 0.79 in the 0-0.4, 0.4-0.8, 0.8-1.2, and 1.2-1.6 m soil layers, respectively. As expected, the most temporally stable location (MTSL1) accurately predicted the average SWS of the corresponding soil layer, and the values of absolute bias relative to mean (ARB) were lower than 3% for all of the investigated soil layers. Using TSA, deep-layer SWS information could be predicted using a single-location measurement in the 0-0.4 m soil layer. The mean ARB values between the observed and predicted mean SWS values were 2.9%, 4.3%, 3.9%, and 2.7% in the 0.4-0.8, 0.8-1.2, 1.2-1.6, and 0-1.6 m soil layers, respectively. The prediction accuracy of the spatial distribution generally decreased with increasing depth, with linear determination coefficients (R2) of 0.93, 0.79, 0.72, and 0.84 for the four soil layers, respectively. The proposed method could further expand the application of the temporal stability technique in the estimation of SWS.

[Effects of snow pack on soil nitrogen transformation enzyme activities in a subalpine Abies faxioniana forest of western Sichuan, China].

PubMed

Xiong, Li; Xu, Zhen-Feng; Wu, Fu-Zhong; Yang, Wan-Qin; Yin, Rui; Li, Zhi-Ping; Gou, Xiao-Lin; Tang, Shi-Shan

2014-05-01

This study characterized the dynamics of the activities of urease, nitrate reductase and nitrite reductase in both soil organic layer and mineral soil layer under three depths of snow pack (deep snowpack, moderate snowpack and shallow snowpack) over the three critical periods (snow formed period, snow stable period, and snow melt period) in the subalpine Abies faxoniana forest of western Sichuan in the winter of 2012 and 2013. Throughout the winter, soil temperature under deep snowpack increased by 46.2% and 26.2%, respectively in comparison with moderate snowpack and shallow snowpack. In general, the three nitrogen-related soil enzyme activities under shallow snowpack were 0.8 to 3.9 times of those under deep snowpack during the winter. In the beginning and thawing periods of seasonal snow pack, shallow snowpack significantly increased the activities of urease, nitrate and nitrite reductase enzyme in both soil organic layer and mineral soil layer. Although the activities of the studied enzymes in soil organic layer and mineral soil layer were observed to be higher than those under deep- and moderate snowpacks in deep winter, no significant difference was found under the three snow packs. Meanwhile, the effects of snowpack on the activities of the measured enzymes were related with season, soil layer and enzyme type. Significant variations of the activities of nitrogen-related enzymes were found in three critical periods over the winter, and the three measured soil enzymes were significantly higher in organic layer than in mineral layer. In addition, the activities of the three measured soil enzymes were closely related with temperature and moisture in soils. In conclusion, the decrease of snow pack induced by winter warming might increase the activities of soil enzymes related with nitrogen transformation and further stimulate the process of wintertime nitrogen transformation in soils of the subalpine forest.

Asporin stably expressed in the surface layer of mandibular condylar cartilage and augmented in the deeper layer with age.

PubMed

Miyamoto, Yutaka; Kanzaki, Hiroyuki; Wada, Satoshi; Tsuruoka, Sari; Itohiya, Kanako; Kumagai, Kenichi; Hamada, Yoshiki; Nakamura, Yoshiki

2017-12-01

Mandibular condylar cartilage (MCC) exhibits dual roles both articular cartilage and growth center. Of many growth factors, TGF-β has been implicated in the growth of articular cartilage including MCC. Recently, Asporin, decoy to TGF-β, was discovered and it blocks TGF-β signaling. Asporin is expressed in a variety of tissues including osteoarthritic articular cartilage, though there was no report of Asporin expression in MCC. In the present study, we investigated the temporal and spatial expression of Asporin in MCC. Gene expression profile of MCC and epiphyseal cartilage in tibia of 5 weeks old ICR mice were firstly compared with microarray analysis using the laser capture microdissected samples. Variance of gene expression was further confirmed by real-time RT-PCR and immunohistochemical staining at 1,3,10, and 20 weeks old. TGF-β and its signaling molecule, phosphorylated Smad-2/3 (p-Smad2/3), were also examined by immunohistochemical staining. Microarray analysis revealed that Asporin was highly expressed in MCC. Real-time RT-PCR analysis confirmed that the fibrous layer of MCC exhibited stable higher Asporin expression at any time points as compared to epiphyseal cartilage. This was also observed in immunohistochemical staining. Deeper layer in MCC augmented Asporin expression with age. Whereas, TGF-β was stably highly observed in the layer. The fibrous layer of MCC exhibited weak staining of p-Smad2/3, though the proliferating layer of MCC was strongly stained as compared to epiphyseal cartilage of tibia at early time point. Consistent with the increase of Asporin expression in the deeper layer of MCC, the intensity of p-Smad-2/3 staining was decreased with age. In conclusion, we discovered that Asporin was stably expressed at the fibrous layer of MCC, which makes it possible to manage both articular cartilage and growth center at the same time.

Monsoon dependent ecosystems: Implications of the vertical distribution of soil moisture on land surface-atmosphere interactions

NASA Astrophysics Data System (ADS)

Sanchez-Mejia, Zulia M.

Uncertainty of predicted change in precipitation frequency and intensity motivates the scientific community to better understand, quantify, and model the possible outcome of dryland ecosystems. In pulse dependent ecosystems (i.e. monsoon driven) soil moisture is tightly linked to atmospheric processes. Here, I analyze three overarching questions; Q1) How does soil moisture presence or absence in a shallow or deep layer influence the surface energy budget and planetary boundary layer characteristics?, Q2) What is the role of vegetation on ecosystem albedo in the presence or absence of deep soil moisture?, Q3) Can we develop empirical relationships between soil moisture and the planetary boundary layer height to help evaluate the role of future precipitation changes in land surface atmosphere interactions? . To address these questions I use a conceptual framework based on the presence or absence of soil moisture in a shallow or deep layer. I define these layers by using root profiles and establish soil moisture thresholds for each layer using four years of observations from the Santa Rita Creosote Ameriflux site. Soil moisture drydown curves were used to establish the shallow layer threshold in the shallow layer, while NEE (Net Ecosystem Exchange of carbon dioxide) was used to define the deep soil moisture threshold. Four cases were generated using these thresholds: Case 1, dry shallow layer and dry deep layer; Case 2, wet shallow layer and dry deep layer; Case 3, wet shallow layer and wet deep layer, and Case 4 dry shallow and wet deep layer. Using this framework, I related data from the Ameriflux site SRC (Santa Rita Creosote) from 2008 to 2012 and from atmospheric soundings from the nearby Tucson Airport; conducted field campaigns during 2011 and 2012 to measure albedo from individual bare and canopy patches that were then evaluated in a grid to estimate the influence of deep moisture on albedo via vegetation cover change; and evaluated the potential of using a two-layer bucket model and empirical relationships to evaluate the link between deep soil moisture and the planetary boundary layer height under changing precipitation regime. My results indicate that (1) the presence or absence of water in two layers plays a role in surface energy dynamics, (2) soil moisture presence in the deep layer is linked with decreased ecosystem albedo and planetary boundary layer height, (3) deep moisture sustains vegetation greenness and decreases albedo, and (4) empirical relationships are useful in modeling planetary boundary layer height from dryland ecosystems. Based on these results we argue that deep soil moisture plays an important role in land surface-atmosphere interactions.

Vertical distribution of bacterial community is associated with the degree of soil organic matter decomposition in the active layer of moist acidic tundra.

PubMed

Kim, Hye Min; Lee, Min Jin; Jung, Ji Young; Hwang, Chung Yeon; Kim, Mincheol; Ro, Hee-Myong; Chun, Jongsik; Lee, Yoo Kyung

2016-11-01

The increasing temperature in Arctic tundra deepens the active layer, which is the upper layer of permafrost soil that experiences repeated thawing and freezing. The increasing of soil temperature and the deepening of active layer seem to affect soil microbial communities. Therefore, information on soil microbial communities at various soil depths is essential to understand their potential responses to climate change in the active layer soil. We investigated the community structure of soil bacteria in the active layer from moist acidic tundra in Council, Alaska. We also interpreted their relationship with some relevant soil physicochemical characteristics along soil depth with a fine scale (5 cm depth interval). The bacterial community structure was found to change along soil depth. The relative abundances of Acidobacteria, Gammaproteobacteria, Planctomycetes, and candidate phylum WPS-2 rapidly decreased with soil depth, while those of Bacteroidetes, Chloroflexi, Gemmatimonadetes, and candidate AD3 rapidly increased. A structural shift was also found in the soil bacterial communities around 20 cm depth, where two organic (upper Oi and lower Oa) horizons are subdivided. The quality and the decomposition degree of organic matter might have influenced the bacterial community structure. Besides the organic matter quality, the vertical distribution of bacterial communities was also found to be related to soil pH and total phosphorus content. This study showed the vertical change of bacterial community in the active layer with a fine scale resolution and the possible influence of the quality of soil organic matter on shaping bacterial community structure.

Tundra fire disturbance homogonizes belowground food web structure, function and dynamics

NASA Astrophysics Data System (ADS)

Moore, J. C.; Pressler, Y.; Koltz, A.; Asmus, A.; Simpson, R.

2016-12-01

Tundra fires on Alaska's North Slope are on the rise due to increased lightning strikes since 2000. On July 16, 2007 lightning ignited the Anaktuvuk River fire, burning a 40-by-10 mile swath of tundra about 24 miles north of Toolik Field Station. The fire burned 401 square miles, was visible from space, and released more than 2.3 million tons of carbon into the atmosphere. A large amount of the organic layer of the soil was burned, changing the over all composition of the site and exposing deeper soil horizons. Due to fundamental transitions in soil characteristics and vegetation we hypothesized that the belowground food web community would be affected both in terms of biomass and location within the soil profile. Microbial biomass was reduced with burn severity. In the lower organic horizon there was a significant reduction in fungal biomass but we did not observe this effect in the upper organic soil. We did not observe a significant effect of burn severity on individual group biomass within higher trophic levels. Canonical Discriminant Analysis using the biomass estimates of the functional groups in the food webs found that the webs are becoming increasingly homogenized in the severely burned site compared to the moderately burned and unburned sites. The unburned soils differed significantly from soil at both burn sites; the greatest effects on food web structure were at the lower organic depth, whereas. We modeled the effects of the fire on soil organic matter processing rates and energy flow through the three food webs. The model estimated a decrease in C and N mineralization with fire severity, due in large part to the loss of organic material. While the organic horizon at the unburned site had 12 times greater C and N mineralization than the mineral soils, we observed little to no difference in C and N mineralization between the organic and mineral soil horizons in the moderately and severely burned sites. Our results show that the fire significantly altered the trophic structure of the soil food web, with loss of trophic complexity with increasing fire severity, which correlated strongly with C and N processing and food web stability.

Day-to-day variations in the amplitude of the soil temperature cycle and impact on adult eclosion timing of the onion fly.

PubMed

Tanaka, Kazuhiro; Watari, Yasuhiko

2017-06-01

The onion fly Delia antiqua advances its eclosion timing with decreasing temperature amplitude to compensate for a depth-dependent phase delay of the zeitgeber. To elucidate whether or not naturally occurring day-to-day variations in the amplitude of soil temperature cycle disturb this compensatory response, we monitored daily variations in the temperature amplitude in natural soils and evaluated the impact on adult eclosion timing. Our results indicated that both median and variance of the soil temperature amplitude become smaller as depth increases. Insertion of a larger temperature fluctuation into the thermoperiod with smaller temperature amplitude induced a stronger phase delay, while insertion of a smaller temperature fluctuation into the thermoperiod with larger temperature amplitude had a weaker phase-advancing effect. It is therefore expected that larger diurnal temperature fluctuations disturb the compensatory response, particularly if they occur at deeper locations, while smaller temperature fluctuations do so only at shallower locations. Under natural conditions, however, the probability of occurrence of smaller or larger temperature fluctuations in shallower or deeper soils, respectively, is relatively small. Thus, naturally occurring day-to-day variations in the temperature amplitude rarely disturb the compensatory response, thereby having a subtle or negligible impact on adult eclosion timing.

N cycle and retention of croplands in complex terrain, South Korea

NASA Astrophysics Data System (ADS)

Kettering, J.; Arnhold, S.; Kuzyakov, Y.; Lee, B.; Lindner, S.; Ok, Y.; Ruidisch, M.; Tenhunen, J. D.

2009-12-01

The aims of our research are to gain a deeper understanding of processes and interactions in agricultural ecosystems as well as to make a contribution to sustainable agricultural production in changing environments. While crop production is highly desirable, negative effects include high input of nutrients, greater erosion rates, removal of nutrients and carbon in harvests, and decreases in the quality of soil organic matter. The field sites of this project are located in Haean basin in the central part of Korea, just south of the demilitarized zone. Intensive land use with high levels of fertilization together with distinctive erosion during the summer monsoon can be found on site. One part of this study focuses on general fertilizer budgets at catchment scale as well as on detailed information about the dynamics and pathways of nitrogen in soil-plant systems on upland slopes. These balances of elements and their fluxes are the main background information in soil-plant studies. The integrative approach of a general budget is based on a large spatial allocation of the field sites, different management types (conventional, organic), and on several typical crops of the Haean basin. In this project, various perspectives are combined (i.e. insects, weed, crops, nutrients). This allows representative conclusions for the entire catchment as well as for the modeling. The approach of a detailed N cycle uses an integrated experimental strategy within run-off plots. Charred biomass and synthetic polymers were additionally applied in these run-off plots to determine whether these additives can contribute significantly to sustainable farming methods in such complex terrain. Within this integrative approach, each treatment was tested for erosion prevention, soil hydrological parameters and flow systems, nutrient balances, as well as plant growth and yields. Finally, best agricultural management practices for sustainable land use of sloping uplands will be suggested. The methods of this research are primarily based on application of isotopes (13C, 14C, 15N). The approaches aim both on monitoring (natural abundance) as well as on experiments (tracer application). Isotope studies with 15N in the field sites allow examination of N uptake by aboveground plants, movement by percolation to deeper soil layers, surface run-off and overall retention within the farmland ecosystem. Isotope studies using 14C will be conducted under stable conditions in the laboratories of the University of Bayreuth this winter. 14C as a tracer provides insights about carbon fluxes in soil plant systems, such as total CO2 efflux dynamics of soils as well as C sequestration. 14C labeled maize and rice residues will be used for differentiating and quantifying the contribution of plant residues-derived C and native soil organic C. Fieldwork in South Korea started in summer 2009. Therefore, at the most partial results can be presented at the AGU Fall Meeting.

Review of crop growth and soil moisture monitoring from a ground-based instrument implementing the Interference Pattern GNSS-R Technique

NASA Astrophysics Data System (ADS)

Rodriguez-Alvarez, N.; Bosch-Lluis, X.; Camps, A.; Aguasca, A.; Vall-Llossera, M.; Valencia, E.; Ramos-Perez, I.; Park, H.

2011-12-01

Reflectometry using Global Navigation Satellite Systems signals (GNSSR) has been the focus of many studies during the past few years for a number of applications over different scenarios as land, ocean or snow and ice surfaces. In the past decade, its potential has increased yearly, with improved receivers and signal processors, from generic GNSS receivers whose signals were recorded in magnetic tapes to instruments that measure full Delay Doppler Maps (the power distribution of the reflected GNSS signal over the 2-D space of delay offsets and Doppler shifts) in real time. At present, these techniques are considered to be promising tools to retrieve geophysical parameters such as soil moisture, vegetation height, topography, altimetry, sea state and ice and snow thickness, among others. This paper focuses on the land geophysical retrievals (topography, vegetation height and soil moisture) performed from a ground-based instrument using the Interference Pattern Technique (IPT). This technique consists of the measurement of the power fluctuations of the interference signal resulting from the simultaneous reception of the direct and the reflected GNSS signals. The latest experiment performed using this technique over a maize field is shown in this paper. After a review of the previous results, this paper presents the latest experiment performed using this technique over a maize field. This new study provides a deeper analysis on the soil moisture retrieval by observing three irrigation-drying cycles and comparing them to different depths soil moisture probes. Furthermore, the height of the maize, almost 300 cm, has allowed testing the capabilities of the technique over dense and packed vegetation layers, with high vegetation water content.

A field experimental study on non-methane hydrocarbon (NMHC) emissions from a straw-returned maize cropping system.

PubMed

Zhang, Shuangqi; Deng, Mengsi; Shan, Ming; Zhou, Chuang; Liu, Wei; Xu, Xiaoqiu; Yang, Xudong

2018-04-28

Non-methane hydrocarbons (NMHCs) play an important role in the atmospheric environment. However, NMHC emissions from agricultural fields, especially their variations with straw return, are poorly understood. Therefore, a field study comprising two treatments, i.e., (1) S0 (straw removal) and (2) S1 (incorporation of maize straw at a rate of 9000 kg ha -1 ), was conducted in a straw-returned maize cropping system to characterize NMHC emissions as well as to estimate the effect of straw return on those emissions. Using a Gas Chromatography-Mass Spectrometer (GC-MS) method, 28 types of NMHCs were identified. The total NMHC emission from S0 was 2018 g ha -1 , where 1-methyl-3-propyl-benzene, (1-methylethyl)-benzene, and toluene were obviously predominant, whereas the total NMHC emission from S1 was 1903 g ha -1 , where 1-methyl-3-propyl-benzene, 2-methyl-pentane, and (1-methylethyl)-benzene were the main species. The results showed that straw return had opposing effects on NMHC emissions, ranging from -55.4% to 478.6%. Overall, the total NMHC emission with returned straw alone decreased by 2963 ng kg straw -1  h -1 . Furthermore, NMHC fluxes had higher correlations with soil temperature than with soil moisture or pH. Notably, the higher correlations of NMHC fluxes with 10 cm soil temperature than with 5 cm soil temperature indicate that soil in the deeper layer might play a more important role in NMHC fluxes. The results also suggest that more field study is needed to accurately estimate the effect of straw return on NMHC emissions from agroecosystems and fully understand its underlying mechanism. Copyright © 2018 Elsevier B.V. All rights reserved.

Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status.

PubMed

Domec, J C; Scholz, F G; Bucci, S J; Meinzer, F C; Goldstein, G; Villalobos-Vega, R

2006-01-01

Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occurring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential (psi root) was about -2.6 MPa, and recovered to 25-40% loss of conductivity in the morning when psi root was about -1.0 MPa. Daily variation in psi root decreased, and root xylem vulnerability and capacitance increased with rooting depth. However, all species experienced seasonal minimum psi root close to complete hydraulic failure independent of their rooting depth or resistance to embolism. Predawn psi root was lower than psi soil when psi soil was relatively high (> -0.7 MPa) but became less negative than psi soil, later in the dry season, consistent with a transition from a disequilibrium between plant and soil psi induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers. Shallow longitudinal root incisions external to the xylem prevented reversal of embolism overnight, suggesting that root mechanical integrity was necessary for recovery, consistent with the hypothesis that if embolism is a function of tension, refilling may be a function of internal pressure imbalances. All species shared a common relationship in which maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season. Daily embolism and refilling in roots is a common occurrence and thus may be an inherent component of a hydraulic signaling mechanism enabling stomata to maintain the integrity of the hydraulic pipeline in long-lived structures such as stems.

Reliance on deep soil water in the tree species Argania spinosa.

PubMed

Zunzunegui, M; Boutaleb, S; Díaz Barradas, M C; Esquivias, M P; Valera, J; Jáuregui, J; Tagma, T; Ain-Lhout, F

2017-12-07

In South-western Morocco, water scarcity and high temperature are the main factors determining species survival. Argania spinosa (L.) Skeels is a tree species, endemic to Morocco, which is suffering from ongoing habitat shrinkage. Argan trees play essential local ecological and economic roles: protecting soils from erosion, shading different types of crops, helping maintain soil fertility and, even more importantly, its seeds are used by the local population for oil production, with valuable nutritional, medicinal and cosmetic purposes. The main objective of this study was to identify the sources of water used by this species and to assess the effect of water availability on the photosynthetic rate and stem water potential in two populations: one growing on the coast and a second one 10 km inland. Stem water potential, photosynthetic rate and xylem water isotopic composition (δ18O) were seasonally monitored during 2 years. Trees from both populations showed a similar strategy in the use of the available water sources, which was strongly dependent on deep soil water throughout the year. Nevertheless, during the wet season or under low precipitation a more complex water uptake pattern was found with a mixture of water sources, including precipitation and soil at different depths. No evidence was found of the use of either groundwater or atmospheric water in this species. Despite the similar water-use strategy, the results indicate that Argania trees from the inland population explored deeper layers than coastal ones as suggested by more depleted δ18O values recorded in the inland trees and better photosynthetic performance, hence suggesting that the coastal population of A. spinosa could be subjected to higher stress. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Predicting Soil Strength in Terms of Cone Index and California Bearing Ratio for Trafficability

DTIC Science & Technology

2016-03-01

conditions, however, soil strength will be a key factor. The Wet- Slippery conditions are considered when the top layer has reached a point of...the soil . Modeling moisture content of a soil in a layered system can be conducted using a finite difference water budget model illustrated in...Figure 2 (Sellers et al. 1986). Figure 2 shows how flow Q through the soil layer ij is modeled. In general, saturation of layer Qi due to rainfall is

A Tower-based Prototype VHF/UHF Radar for Subsurface Sensing: System Description and Data Inversion Results

NASA Technical Reports Server (NTRS)

Moghaddam, Mahta; Pierce, Leland; Tabatabaeenejad, Alireza; Rodriguez, Ernesto

2005-01-01

Knowledge of subsurface characteristics such as permittivity variations and layering structure could provide a breakthrough in many terrestrial and planetary science disciplines. For Earth science, knowledge of subsurface and subcanopy soil moisture layers can enable the estimation of vertical flow in the soil column linking surface hydrologic processes with that in the subsurface. For planetary science, determining the existence of subsurface water and ice is regarded as one of the most critical information needs for the study of the origins of the solar system. The subsurface in general can be described as several near-parallel layers with rough interfaces. Each homogenous rough layer can be defined by its average thickness, permittivity, and rms interface roughness assuming a known surface spectral distribution. As the number and depth of layers increase, the number of measurements needed to invert for the layer unknowns also increases, and deeper penetration capability would be required. To nondestructively calculate the characteristics of the rough layers, a multifrequency polarimetric radar backscattering approach can be used. One such system is that we have developed for data prototyping of the Microwave Observatory of Subcanopy and Subsurface (MOSS) mission concept. A tower-mounted radar makes backscattering measurements at VHF, UHF, and L-band frequencies. The radar is a pulsed CW system, which uses the same wideband antenna to transmit and receive the signals at all three frequencies. To focus the beam at various incidence angles within the beamwidth of the antenna, the tower is moved vertically and measurements made at each position. The signals are coherently summed to achieve focusing and image formation in the subsurface. This requires an estimate of wave velocity profiles. To solve the inverse scattering problem for subsurface velocity profile simultaneously with radar focusing, we use an iterative technique based on a forward numerical solution of the layered rough surface problem. The layers are each defined in terms of a small number of unknown distributions as given above. An a priori estimate of the solution is first assumed, based on which the forward problem is solved for the backscattered measurements. This is compared with the measured data and using iterative techniques an update to the solution for the unknowns is calculated. The process continues until convergence is achieved. Numerical results will be shown using actual radar data acquired with the MOSS tower radar system in Arizona in Fall 2003, and compared with in-situ measurements.

How far can we prevent further physical soil degradation in the future?

NASA Astrophysics Data System (ADS)

Horn, Rainer

2017-04-01

Arable as well as forest soils are exposed to increasing external stresses, which coincide with a further and deeper reaching soil degradation, which may result in an aggravation of hydraulic, gaseous, thermal but also physicochemical and chemical soil functions. The decline coincides with a simultaneous reduction in useable land areas and worsens food production amongst others. Therefore, it is mandatory, that stable soil structure from the surface down to depth prevents soil compaction, sustains water infiltration, reduces rates of soil erosion by water and wind in each case to the minimum possible under the soil, terrain, land use, and climatic conditions in which the soils occur. It improves organic carbon storage in soils and optimizes microbial activity and functions. These benefits coincide with sustainable soil properties and soil management systems, which prevent - deep mechanical stress propagation which can cause irreversible soil deformation, - loss of surface soil layers with coinciding organic and mineral nutrient pool available for microbial processing and plant uptake, - Truncation of soil horizons, or damage on private and public infrastructures (roads, houses) and downstream fields. In order to prevent negative impacts on soils, it is recommended, that A) concerning prevention of soil compaction - stresses applied to soils shall not exceed the mechanical soil stability to maintain the actual functioning of chemical, physical and biological processes and to utilize their resilience (i.e. the elasticity), - land use management strategies have to be related to the actual soil properties in order to optimize plant growth, yield, filtering and buffering of infiltrating water, and carbon sequestration. B) soil erosion by - water, wind, and tillage is counteracted by an adequate surface soil stability including a site specific residue management (e.g. conservation tillage), controlled traffic and harvesting, ecological grassland use strategies (e.g. fodder production and harvesting, adequate animal grazing), - wind is furthermore minimized by adequate hedgerow plantations, continuous cover crop growth, optimized particle bindings by water, infiltrating organic acids, appropriate grazing intensity. Agroforestry can be considered as an additional positive measure to reduce soil erosion risks generally and to ameliorate degraded sites. C) -plant cover on slopes remains untouched, overgrazing and consecutive soil homogenization especially under moist climatic conditions must be prevented but adjusted to the actual structure stability of the hillsides. The communication of these findings followed by application of such measures can help farmers and foresters as well as landowners to prevent (further) physical soil degradation in the future.

Water Redistribution, Temperature Change and CO2 Diffusion of Reconstruction Soil Profiles Filled with Gangue in Coal Mining Areas

NASA Astrophysics Data System (ADS)

Wang, S.; Zhan, H.; Chen, X.; Hu, Y.

2017-12-01

There were a great many projects of reconstruction soil profile filled with gangue to restore ecological environment and land resources in coal mining areas. A simulation experimental system in laboratory was designed for studying water transport and gas-heat diffusion of the reconstruction soil as to help the process of engineering and soil-ripening technology application. The system could be used for constantly measuring soil content, temperature and soil CO2 concentration by laid sensors and detectors in different depth of soil column. The results showed that soil water infiltration process was slowed down and the water-holding capacity of the upper soil was increased because of good water resistance from coal gangue layer. However, the water content of coal gangue layer, 10% approximately, was significantly lower than that of topsoil for the poor water-holding capacity of gangue. The temperature of coal gangue layer was also greater than that of soil layer and became easily sustainable temperature gradient under the condition with heating in reconstruction soil due to the higher thermal diffusivity from gangue, especially being plenty of temperature difference between gangue and soil layers. The effects of heated from below on topsoil was small, which it was mainly influenced from indoor temperature in the short run. In addition, the temperature changing curve of topsoil is similar with the temperature of laboratory and its biggest fluctuation range was for 2.89°. The effects of aerating CO2 from column bottom on CO2 concentration of topsoil soil was also very small, because gas transport from coal gangue layers to soil ones would easily be cut off as so to gas accumulated below the soil layer. The coal gangue could have a negative impact on microbial living environment to adjacent topsoil layers and declined microorganism activities. The effects of coal gangue on topsoil layer were brought down when the cove soil thickness was at 60 cm. And the influences gradually would be weakened with the thickness increasing.

Soil moisture dynamics and dominant controls at different spatial scales over semiarid and semi-humid areas

NASA Astrophysics Data System (ADS)

Suo, Lizhu; Huang, Mingbin; Zhang, Yongkun; Duan, Liangxia; Shan, Yan

2018-07-01

Soil moisture dynamics plays an active role in ecological and hydrological processes, and it depends on a large number of environmental factors, such as topographic attributes, soil properties, land use types, and precipitation. However, studies must still clarify the relative significance of these environmental factors at different soil depths and at different spatial scales. This study aimed: (1) to characterize temporal and spatial variations in soil moisture content (SMC) at four soil layers (0-40, 40-100, 100-200, and 200-500 cm) and three spatial scales (plot, hillslope, and region); and (2) to determine their dominant controls in diverse soil layers at different spatial scales over semiarid and semi-humid areas of the Loess Plateau, China. Given the high co-dependence of environmental factors, partial least squares regression (PLSR) was used to detect relative significance among 15 selected environmental factors that affect SMC. Temporal variation in SMC decreased with increasing soil depth, and vertical changes in the 0-500 cm soil profile were divided into a fast-changing layer (0-40 cm), an active layer (40-100 cm), a sub-active layer (100-200 cm), and a relatively stable layer (200-500 cm). PLSR models simulated SMC accurately in diverse soil layers at different scales; almost all values for variation in response (R2) and goodness of prediction (Q2) were >0.5 and >0.0975, respectively. Upper and lower layer SMCs were the two most important factors that influenced diverse soil layers at three scales, and these SMC variables exhibited the highest importance in projection (VIP) values. The 7-day antecedent precipitation and 7-day antecedent potential evapotranspiration contributed significantly to SMC only at the 0-40 cm soil layer. VIP of soil properties, especially sand and silt content, which influenced SMC strongly, increased significantly after increasing the measured scale. Mean annual precipitation and potential evapotranspiration also influenced SMC at the regional scale significantly. Overall, this study indicated that dominant controls of SMC varied among three spatial scales on the Loess Plateau, and VIP was a function of spatial scale and soil depth.

3D Bedrock Structure of Bornova Plain and Its surroundings (İzmir/Western Turkey)

NASA Astrophysics Data System (ADS)

Pamuk, Eren; Gönenç, Tolga; Özdağ, Özkan Cevdet; Akgün, Mustafa

2018-01-01

An earthquake record is needed on engineering bedrock to perform soil deformation analysis. This record could be obtained in different ways (seismographs on engineering bedrock; by the help of the soil transfer function; scenario earthquakes). S-wave velocity ( V s) profile must be known at least till engineering bedrock for calculating soil transfer functions true and completely. In addition, 2D or 3D soil, engineering-seismic bedrock models are needed for soil response analyses to be carried out. These models are used to determine changes in the amplitude and frequency content of earthquake waves depending on the seismic impedance from seismic bedrock to the ground surface and the basin effects. In this context, it is important to use multiple in situ geophysical techniques to create the soil-bedrock models. In this study, 2D and 3D soil-bedrock models of Bornova plain and its surroundings (Western Turkey), which are very risky in terms of seismicity, were obtained by combined survey of surface wave and microgravity methods. Results of the study show that the engineering bedrock depths in the middle part of Bornova plain range from 200 to 400 m and the southern and northern parts which are covered limestone and andesite show the engineering bedrock ( V s > 760 m/s) feature. In addition, seismic bedrock ( V s < 3000 m/s) depth changes from 550 to 1350 m. The predominant period values obtained from single station microtremor method change from 0.45 to 1.6 s while they are higher than 1 s in the middle part of Bornova plain where the basin is deeper. Bornova Plain has a very thick sediment units which have very low V s values above engineering bedrock. In addition, it is observed sudden changes at the interfaces of the layer in horizontal and vertical directions.

Water sources and controls on water-loss rates of epigeous ectomycorrhizal fungal sporocarps during summer drought

Treesearch

Erik A. Lilleskov; Thomas D. Bruns; Todd E. Dawson; Francisco J. Camacho

2009-01-01

Access to deeper soil water and water-conserving traits should reduce water stress for ectomycorrhizal fungi, permitting function during drought. Here, we explored whether epigeous fruiting of ectomycorrhizal fungi during drought was facilitated by access to deep soil water, how much water was lost from sporocarps, and how sporocarp surface to volume ratios affected...

[Effects of intensive management on soil C and N pools and soil enzyme activities in Moso bamboo plantations.

PubMed

Yang, Meng; Li, Yong Fu; Li, Yong Chun; Xiao, Yong Heng; Yue, Tian; Jiang, Pei Kun; Zhou, Guo Mo; Liu, Juan

2016-11-18

In order to elucidate the effects of intensive management on soil carbon pool, nitrogen pool, enzyme activities in Moso bamboo (Phyllostachys pubescens) plantations, we collected soil samples from the soil surface (0-20 cm) and subsurface (20-40 cm) layers in the adjacent Moso bamboo plantations with extensive and intensive managements in Sankou Township, Lin'an City, Zhejiang Province. We determined different forms of C, N and soil invertase, urease, catalase and acid phosphatase activities. The results showed that long-term intensive management of Moso bamboo plantations significantly decreased the content and storage of soil organic carbon (SOC), with the SOC storage in the soil surface and subsurface layers decreased by 13.2% and 18.0%, respectively. After 15 years' intensive management of Masoo bamboo plantations, the contents of soil water soluble carbon (WSOC), hot water soluble carbon (HWSOC), microbial carbon (MBC) and readily oxidizable carbon (ROC) were significantly decreased in the soil surface and subsurface layers. The soil N storage in the soil surface and subsurface layers in intensively managed Moso bamboo plantations increased by 50.8% and 36.6%, respectively. Intensive management significantly increased the contents of nitrate-N (NO 3 - -N) and ammonium-N (NH 4 + -N), but decreased the contents of water-soluble nitrogen (WSON) and microbial biomass nitrogen (MBN). After 15 years' intensive management of Masoo bamboo plantations, the soil invertase, urease, catalase and acid phosphatase activities in the soil surface layer were significantly decreased, the soil acid phosphatase activity in the soil subsurface layer were significantly decreased, and other enzyme activities in the soil subsurface layer did not change. In conclusion, long-term intensive management led to a significant decline of soil organic carbon storage, soil labile carbon and microbial activity in Moso bamboo plantations. Therefore, we should consider the use of organic fertilizer in the intensive mana-gement process for the sustainable management of Moso bamboo plantations in the future.

Observing the seasonal cycle of the upper ocean in the Ross Sea, Antarctica, with autonomous profiling floats

NASA Astrophysics Data System (ADS)

Porter, D. F.; Springer, S. R.; Padman, L.; Fricker, H. A.; Bell, R. E.

2017-12-01

The upper layers of the Southern Ocean where it meets the Antarctic ice sheet undergoes a large seasonal cycle controlled by surface radiation and by freshwater fluxes, both of which are strongly influenced by sea ice. In regions where seasonal sea ice and icebergs limit use of ice-tethered profilers and conventional moorings, autonomous profiling floats can sample the upper ocean. The deployment of seven Apex floats (by sea) and six ALAMO floats (by air) provides unique upper ocean hydrographic data in the Ross Sea close to the Ross Ice Shelf front. A novel choice of mission parameters - setting parking depth deeper than the seabed - limits their drift, allowing us to deploy the floats close to the ice shelf front, while sea ice avoidance algorithms allow the floats to to sample through winter under sea ice. Hydrographic profiles show the detailed development of the seasonal mixed layer close to the Ross front, and interannual variability of the seasonal mixed layer and deeper water masses on the central Ross Sea continental shelf. After the sea ice breakup in spring, a warm and fresh surface mixed layer develops, further warming and deepening throughout the summer. The mixed layer deepens, with maximum temperatures exceeding 0ºC in mid-February. By March, the surface energy budget becomes negative and sea ice begins to form, creating a cold, saline and dense surface layer. Once these processes overcome the stable summer stratification, convection erodes the surface mixed layer, mixing some heat downwards to deeper layers. There is considerable interannual variability in the evolution and strength of the surface mixed layer: summers with shorter ice-free periods result in a cooler and shallower surface mixed layer, which accumulates less heat than the summers with longer ice-free periods. Early ice breakup occurred in all floats in 2016/17 summer, enhancing the absorbed solar flux leading to a warmer surface mixed layer. Together, these unique measurements from autonomous profilers provide insight into the hydrographic state of the Ross Sea at the start of the spring period of sea-ice breakup, and how ocean mixing and sea ice interact to initiate the summer open-water season.

Leaving moss and litter layers undisturbed reduces the short-term environmental consequences of heathland managed burns.

PubMed

Grau-Andrés, Roger; Davies, G Matt; Waldron, Susan; Scott, E Marian; Gray, Alan

2017-12-15

Variation in the structure of ground fuels, i.e. the moss and litter (M/L) layer, may be an important control on fire severity in heather moorlands and thus influence vegetation regeneration and soil carbon dynamics. We completed experimental fires in a Calluna vulgaris-dominated heathland to study the role of the M/L layer in determining (i) fire-induced temperature pulses into the soil and (ii) post-fire soil thermal dynamics. Manually removing the M/L layer before burning increased fire-induced soil heating, both at the soil surface and 2 cm below. Burnt plots where the M/L layer was removed simulated the fuel structure after high severity fires where ground fuels are consumed but the soil does not ignite. Where the M/L layer was manually removed, either before or after the fire, post-fire soil thermal dynamics showed larger diurnal and seasonal variation, as well as similar patterns to those observed after wildfires, compared to burnt plots where the M/L layer was not manipulated. We used soil temperatures to explore potential changes in post-fire soil respiration. Simulated high fire severity (where the M/L layer was manually removed) increased estimates of soil respiration in warm months. With projected fire regimes shifting towards higher severity fires, our results can help land managers develop strategies to balance ecosystem services in Calluna-dominated habitats. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

High severity experimental burns in Siberian larch forests increase permafrost thaw and larch tree regeneration

NASA Astrophysics Data System (ADS)

Alexander, H. D.; Davydov, S.; Zimov, N.; Mack, M. C.

2013-12-01

Global change models predict increased fire activity in boreal forests as climate warms and dries. We hypothesized that fire-driven decreases in soil organic layer (SOL) depth will (1) increase permafrost thaw by reducing the insulating capacity of the SOL and (2) improve seedbed conditions for tree regeneration. Over time, these changes will lead to altered patterns of above- and belowground carbon (C) accumulation. To test these hypotheses, we conducted plot-level experimental burns in July 2012 in a low-density, mature larch stand near the Northeast Science Station in Cherskii, Siberia. Dried fuels of naturally occurring vegetation were added to plots to achieve four burn severity treatments based on residual SOL depths: control, low (> 8 cm), moderate (5-8 cm), and high severity (2-5 cm). Pre-fire and during two growing seasons post-fire, we measured thaw depth, soil moisture, and soil temperature to determine severity effects on permafrost thaw. We also sowed larch seeds in fall 2012 and quantified germination rates the following growing season. By 1 wk post-fire, thaw depth was 15-25 cm deeper in plots burned at high severity (55 cm) compared to other treatments (30-40 cm). These differences in thaw depth with burn severity were maintained during the subsequent growing season and were associated with increased soil temperature and moisture. Larch regeneration was 10x higher on severely burned plots than those unburned. Our findings highlight the potential for increased fire severity to degrade permafrost and alter successional dynamics and patterns of C accumulation.

Woody debris along an upland chronosequence in boreal Manitoba and its impact on long-term carbon storage

USGS Publications Warehouse

Manies, K.L.; Harden, J.W.; Bond-Lamberty, B. P.; O'Neill, K. P.

2005-01-01

This study investigated the role of fire-killed woody debris as a source of soil carbon in black spruce (Picea mariana (Mill.) BSP) stands in Manitoba, Canada. We measured the amount of standing dead and downed woody debris along an upland chronosequence, including wood partially and completely covered by moss growth. Such woody debris is rarely included in measurement protocols and composed up to 26% of the total amount of woody debris in older stands, suggesting that it is important to measure all types of woody debris in ecosystems where burial by organic matter is possible. Based on these data and existing net primary production (NPP) values, we used a mass-balance model to assess the potential impact of fire-killed wood on long-term carbon storage at this site. The amount of carbon stored in deeper soil organic layers, which persists over millennia, was used to represent this long-term carbon. We estimate that between 10% and 60% of the deep-soil carbon is derived from wood biomass. Sensitivity analyses suggest that this estimate is most affected by the fire return interval, decay rate of wood, amount of NPP, and decay rate of the char (postfire) carbon pool. Landscape variations in these terms could account for large differences in deep-soil carbon. The model was less sensitive to fire consumption rates and to rates at which standing dead becomes woody debris. All model runs, however, suggest that woody debris plays an important role in long-term carbon storage for this area. ?? 2005 NRC Canada.

Slab detachment under the Eastern Alps seen by seismic anisotropy

PubMed Central

Qorbani, Ehsan; Bianchi, Irene; Bokelmann, Götz

2015-01-01

We analyze seismic anisotropy for the Eastern Alpine region by inspecting shear-wave splitting from SKS and SKKS phases. The Eastern Alpine region is characterized by a breakdown of the clear mountain-chain-parallel fast orientation pattern that has been previously documented for the Western Alps and for the western part of the Eastern Alps. The main interest of this paper is a more detailed analysis of the anisotropic character of the Eastern Alps, and the transition to the Carpathian–Pannonian region. SK(K)S splitting measurements reveal a rather remarkable lateral change in the anisotropy pattern from the west to the east of the Eastern Alps with a transition area at about 12°E. We also model the backazimuthal variation of the measurements by a vertical change of anisotropy. We find that the eastern part of the study area is characterized by the presence of two layers of anisotropy, where the deeper layer has characteristics similar to those of the Central Alps, in particular SW–NE fast orientations of anisotropic axes. We attribute the deeper layer to a detached slab from the European plate. Comparison with tomographic studies of the area indicates that the detached slab might possibly connect with the lithosphere that is still in place to the west of our study area, and may also connect with the slab graveyard to the East, at the depth of the upper mantle transition zone. On the other hand, the upper layer has NW–SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body. The anisotropy of the upper layer shows large-scale NW–SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle. PMID:25843968

Slab detachment under the Eastern Alps seen by seismic anisotropy

NASA Astrophysics Data System (ADS)

Qorbani, Ehsan; Bianchi, Irene; Bokelmann, Götz

2015-01-01

We analyze seismic anisotropy for the Eastern Alpine region by inspecting shear-wave splitting from SKS and SKKS phases. The Eastern Alpine region is characterized by a breakdown of the clear mountain-chain-parallel fast orientation pattern that has been previously documented for the Western Alps and for the western part of the Eastern Alps. The main interest of this paper is a more detailed analysis of the anisotropic character of the Eastern Alps, and the transition to the Carpathian-Pannonian region. SK(K)S splitting measurements reveal a rather remarkable lateral change in the anisotropy pattern from the west to the east of the Eastern Alps with a transition area at about 12°E. We also model the backazimuthal variation of the measurements by a vertical change of anisotropy. We find that the eastern part of the study area is characterized by the presence of two layers of anisotropy, where the deeper layer has characteristics similar to those of the Central Alps, in particular SW-NE fast orientations of anisotropic axes. We attribute the deeper layer to a detached slab from the European plate. Comparison with tomographic studies of the area indicates that the detached slab might possibly connect with the lithosphere that is still in place to the west of our study area, and may also connect with the slab graveyard to the East, at the depth of the upper mantle transition zone. On the other hand, the upper layer has NW-SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body. The anisotropy of the upper layer shows large-scale NW-SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle.

Soil organic carbon response to shrub encroachment regulated by soil aggregates

NASA Astrophysics Data System (ADS)

Zhu, Y.; Li, H.; Shen, H.; Feng, Y.; Fang, J.

2017-12-01

Shrub encroachment leads to change in soil organic carbon content, but there still exists a lot of uncertainty in its mechanism as it relates to deep soil research. Soil organic carbon is usually associated with stable aggregate quantity. In this study, we conducted a field investigation for typical steppe and desert steppe in Inner Mongolia with the view to examining the impact of shrub encroachment on soil organic carbon with soil aggregate at a depth of 0-500 cm. The results show that in the desert steppe, the particle size of soil aggregate content level in different depth are presented the trend of shrub patches is lower than the herb matrix, organic carbon content of soil aggregate under 50 cm deeper presents the trend of shrub patches is higher than herb matrix, eventually leading to shrub patches whole soil organic carbon in the 0 to 50 cm depth lower than the herb matrix, and in deeper soil below 50 cm higher than the herb matrix. In the typical steppe, there is no significant difference between soil aggregate structure of shrub patches and herb matrix, but organic carbon content of soil aggregate, especially large aggregate organic carbon content in the shrub patches is significantly higher than the herb matrix, so that the whole soil organic carbon content in the shrub patches is significantly higher than herb matrix. The rate of soil organic carbon content change (0-100 cm) by shrub encroachment showed significant negative correlation with the mean weight diameter of soil aggregate of herb matrix. We also found that the variations of soil organic carbon in desert steppe is not dominant by aggregates of some size, but the change of the typical steppe soil organic carbon mainly contributed by > 0.25 mm and 0.053-0.25 mm aggregates. The results suggested that the effects of shrub encroachment on soil organic carbon is regulated by soil aggregate, but it is varied for different type of grassland, which should provide some insights into our understanding on regional carbon budget under global environment change.

Increased soil organic carbon stocks under agroforestry: A survey of six different sites in France

NASA Astrophysics Data System (ADS)

Cardinael, Rémi; Chevallier, Tiphaine; Cambou, Aurélie; Beral, Camille; Barthes, Bernard; Dupraz, Christian; Kouakoua, Ernest; Chenu, Claire

2017-04-01

Introduction: Agroforestry systems are land use management systems in which trees are grown in combination with crops or pasture in the same field. In silvoarable systems, trees are intercropped with arable crops, and in silvopastoral systems trees are combined with pasture for livestock. These systems may produce forage and timber as well as providing ecosystem services such as climate change mitigation. Carbon (C) is stored in the aboveground and belowground biomass of the trees, and the transfer of organic matter from the trees to the soil can increase soil organic carbon (SOC) stocks. Few studies have assessed the impact of agroforestry systems on carbon storage in soils in temperate climates, as most have been undertaken in tropical regions. Methods: This study assessed five silvoarable systems and one silvopastoral system in France. All sites had an agroforestry system with an adjacent, purely agricultural control plot. The land use management in the inter-rows in the agroforestry systems and in the control plots were identical. The age of the study sites ranged from 6 to 41 years after tree planting. Depending on the type of soil, the sampling depth ranged from 20 to 100 cm and SOC stocks were assessed using equivalent soil masses. The aboveground biomass of the trees was also measured at all sites. Results: In the silvoarable systems, the mean organic carbon stock accumulation rate in the soil was 0.24 (0.09-0.46) Mg C ha-1 yr-1 at a depth of 30 cm and 0.65 (0.004-1.85) Mg C ha-1 yr-1 in the tree biomass. Increased SOC stocks were also found in deeper soil layers at two silvoarable sites. Young plantations stored additional SOC but mainly in the soil under the rows of trees, possibly as a result of the herbaceous vegetation growing in the rows. At the silvopastoral site, the SOC stock was significantly greater at a depth of 30-50 cm than in the control. Overall, this study showed the potential of agroforestry systems to store C in both soil and biomass in temperate regions.

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

NASA Astrophysics Data System (ADS)

Weber, Tobias Karl David; Iden, Sascha Christian; Durner, Wolfgang

2017-12-01

In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these processes is crucial to assess effects of changed environmental conditions on the future development of these ecosystems. We show that the Richards equation can be used to accurately describe the moisture dynamics under evaporative conditions in variably saturated peat soil, encompassing the transition from the topmost living moss layer to the decomposed peat as part of the vadose zone. Soil hydraulic properties (SHP) were identified by inverse simulation of evaporation experiments on samples from the entire acrotelm. To obtain consistent descriptions of the observations, the traditional van Genuchten-Mualem model was extended to account for non-capillary water storage and flow. We found that the SHP of the uppermost moss layer reflect a pore-size distribution (PSD) that combines three distinct pore systems of the Sphagnum moss. For deeper samples, acrotelm pedogenesis changes the shape of the SHP due to the collapse of inter-plant pores and an infill with smaller particles. This leads to gradually more homogeneous and bi-modal PSDs with increasing depth, which in turn can serve as a proxy for increasing state of pedogenesis in peatlands. From this, we derive a nomenclature and size classification for the pore spaces of Sphagnum mosses and define inter-, intra-, and inner-plant pore spaces, with effective pore diameters of > 300, 300-30, and 30-10 µm, respectively.

The use of positrons to survey alteration layers on synthetic nuclear waste glasses

NASA Astrophysics Data System (ADS)

Reiser, Joelle T.; Parruzot, Benjamin; Weber, Marc H.; Ryan, Joseph V.; McCloy, John S.; Wall, Nathalie A.

2017-07-01

In order to safeguard society and the environment, understanding radioactive waste glass alteration mechanisms in interactions with solutions and near-field materials, such as Fe, is essential to nuclear waste repository performance assessments. Alteration products are formed at the surface of glasses after reaction with solution. In this study, glass altered in the presence of Fe0 in aqueous solution formed two alteration layers: one embedded with Fe closer to the surface and one without Fe found deeper in the sample. Both layers were found to be thinner than the alteration layer found in glass altered in aqueous solution only. For the first time, Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) is used to non-destructively characterize the pore structures of glass altered in the presence of Fe0. Advantages and disadvantages of DB-PAS compared to other techniques used to analyze pore structures for altered glass samples are discussed. Ultimately, DB-PAS has shown to be an excellent choice for pore structure characterization for glasses with multiple alteration layers. Monte Carlo modeling predicted positron trajectories through the layers, and helped explain DB-PAS data, which showed that the deeper alteration layer without Fe had a similar composition and pore structure to layers on glass altered in water only.

The use of positrons to survey alteration layers on synthetic nuclear waste glasses

DOE PAGES

Reiser, Joelle T.; Parruzot, Benjamin; Weber, Marc H.; ...

2017-07-01

Here, in order to safeguard society and the environment, understanding radioactive waste glass alteration mechanisms in interactions with solutions and near-field materials, such as Fe, is essential to nuclear waste repository performance assessments. Alteration products are formed at the surface of glasses after reaction with solution. In this study, glass altered in the presence of Fe 0 in aqueous solution formed two alteration layers: one embedded with Fe closer to the surface and one without Fe found deeper in the sample. Both layers were found to be thinner than the alteration layer found in glass altered in aqueous solution only.more » For the first time, Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) is used to non-destructively characterize the pore structures of glass altered in the presence of Fe 0. Advantages and disadvantages of DB-PAS compared to other techniques used to analyze pore structures for altered glass samples are discussed. Ultimately, DB-PAS has shown to be an excellent choice for pore structure characterization for glasses with multiple alteration layers. Monte Carlo modeling predicted positron trajectories through the layers, and helped explain DB-PAS data, which showed that the deeper alteration layer without Fe had a similar composition and pore structure to layers on glass altered in water only.« less

The use of positrons to survey alteration layers on synthetic nuclear waste glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reiser, Joelle T.; Parruzot, Benjamin; Weber, Marc H.

Here, in order to safeguard society and the environment, understanding radioactive waste glass alteration mechanisms in interactions with solutions and near-field materials, such as Fe, is essential to nuclear waste repository performance assessments. Alteration products are formed at the surface of glasses after reaction with solution. In this study, glass altered in the presence of Fe 0 in aqueous solution formed two alteration layers: one embedded with Fe closer to the surface and one without Fe found deeper in the sample. Both layers were found to be thinner than the alteration layer found in glass altered in aqueous solution only.more » For the first time, Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) is used to non-destructively characterize the pore structures of glass altered in the presence of Fe 0. Advantages and disadvantages of DB-PAS compared to other techniques used to analyze pore structures for altered glass samples are discussed. Ultimately, DB-PAS has shown to be an excellent choice for pore structure characterization for glasses with multiple alteration layers. Monte Carlo modeling predicted positron trajectories through the layers, and helped explain DB-PAS data, which showed that the deeper alteration layer without Fe had a similar composition and pore structure to layers on glass altered in water only.« less

Plant Water Uptake in Drying Soils1

PubMed Central

Lobet, Guillaume; Couvreur, Valentin; Meunier, Félicien; Javaux, Mathieu; Draye, Xavier

2014-01-01

Over the last decade, investigations on root water uptake have evolved toward a deeper integration of the soil and roots compartment properties, with the goal of improving our understanding of water acquisition from drying soils. This evolution parallels the increasing attention of agronomists to suboptimal crop production environments. Recent results have led to the description of root system architectures that might contribute to deep-water extraction or to water-saving strategies. In addition, the manipulation of root hydraulic properties would provide further opportunities to improve water uptake. However, modeling studies highlight the role of soil hydraulics in the control of water uptake in drying soil and call for integrative soil-plant system approaches. PMID:24515834

Root depth and morphology in response to soil drought: comparing ecological groups along the secondary succession in a tropical dry forest.

PubMed

Paz, Horacio; Pineda-García, Fernando; Pinzón-Pérez, Luisa F

2015-10-01

Root growth and morphology may play a core role in species-niche partitioning in highly diverse communities, especially along gradients of drought risk, such as that created along the secondary succession of tropical dry forests. We experimentally tested whether root foraging capacity, especially at depth, decreases from early successional species to old-growth forest species. We also tested for a trade-off between two mechanisms for delaying desiccation, the capacity to forage deeper in the soil and the capacity to store water in tissues, and explored whether successional groups separate along such a trade-off. We examined the growth and morphology of roots in response to a controlled-vertical gradient of soil water, among seedlings of 23 woody species dominant along the secondary succession in a tropical dry forest of Mexico. As predicted, successional species developed deeper and longer root systems than old-growth forest species in response to soil drought. In addition, shallow root systems were associated with high plant water storage and high water content per unit of tissue in stems and roots, while deep roots exhibited the opposite traits, suggesting a trade-off between the capacities for vertical foraging and water storage. Our results suggest that an increased capacity of roots to forage deeper for water is a trait that enables successional species to establish under the warm-dry conditions of the secondary succession, while shallow roots, associated with a higher water storage capacity, are restricted to the old-growth forest. Overall, we found evidence that the root depth-water storage trade-off may constrain tree species distribution along secondary succession.

Spatial extent and dissipation of the deep chlorophyll layer in Lake Ontario during the Lake Ontario lower foodweb assessment, 2003 and 2008

USGS Publications Warehouse

Watkins, J. M.; Weidel, Brian M.; Rudstam, L. G.; Holek, K. T.

2014-01-01

Increasing water clarity in Lake Ontario has led to a vertical redistribution of phytoplankton and an increased importance of the deep chlorophyll layer in overall primary productivity. We used in situ fluorometer profiles collected in lakewide surveys of Lake Ontario in 2008 to assess the spatial extent and intensity of the deep chlorophyll layer. In situ fluorometer data were corrected with extracted chlorophyll data using paired samples from Lake Ontario collected in August 2008. The deep chlorophyll layer was present offshore during the stratified conditions of late July 2008 with maximum values from 4-13 μg l-1 corrected chlorophyll a at 10 to 17 m depth within the metalimnion. Deep chlorophyll layer was closely associated with the base of the thermocline and a subsurface maximum of dissolved oxygen, indicating the feature's importance as a growth and productivity maximum. Crucial to the deep chlorophyll layer formation, the photic zone extended deeper than the surface mixed layer in mid-summer. The layer extended through most of the offshore in July 2008, but was not present in the easternmost transect that had a deeper surface mixed layer. By early September 2008, the lakewide deep chlorophyll layer had dissipated. A similar formation and dissipation was observed in the lakewide survey of Lake Ontario in 2003.

The Redox Dynamics of Iron in a Seasonally Waterlogged Forest Soil (Chaux Forest, Eastern France) Traced with Rare Earth Element Distribution Patterns

NASA Astrophysics Data System (ADS)

Steinmann, M.; Floch, A. L.; Lucot, E.; Badot, P. M.

2014-12-01

The oxyhydroxides of iron are common soil minerals and known to control the availability of various major and trace elements essential for biogeochemical processes. We present a study from acidic natural forest soils, where reducing redox conditions due to seasonal waterlogging lead to the dissolution of Fe-oxyhydroxides, and to the release of Fe to soil water. In order to study in detail the mechanism of redox cycling of Fe, we used Rare Earth Element (REE) distribution patterns, because an earlier study has shown that they are a suitable tool to identify trace metal sources during soil reduction in wetland soils (Davranche et al., 2011). The REE patterns of soil leachates obtained with the modified 3-step BCR extraction scheme of Rauret et al., (1999) were compared with those of natural soil water. The adsorbed fractions (F1 leach), the reducible fraction of the deepest soil horizon H4 (F2 leach, 50-120 cm), and the oxidizable fractions of horizons H2 to H4 (F3 leachs, 24-120 cm) yielded REE patterns almost identical to soil water (see figure), showing that the REE and trace metal content of soil water was mainly derived from the F1 pool, and from the F2 and F3 pools of the clay mineral-rich deep soil horizons. In contrast, the F2 leach mobilized mainly Fe-oxyhydroxides associated with organic matter of the surface soil and yielded REE patterns significantly different from those of soil water. These results suggest that the trace metal content of soil water in hydromorphic soils is primarily controlled by the clay fraction of the deeper soil horizons and not by organic matter and related Fe-oxyhydroxides of the surface soil. Additional analyses are in progress in order to verify whether the REE and trace metals of the deeper soil horizons were directly derived from clay minerals or from associated Fe-oxyhydroxide coatings. Refs cited: Davranche et al. (2011), Chem. Geol. 284; Rauret et al. (1999), J. Environ. Monit. 1.

Agriculture Canada Central Saskatchewan Vector Soils Data

NASA Technical Reports Server (NTRS)

Knapp, David; Hall, Forrest G. (Editor); Rostad, Harold

2000-01-01

This data set consists of GIS layers that describe the soils of the BOREAS SSA. These original data layers were submitted as vector data in ARC/INFO EXPORT format. These data also include the soil name and soil layer files, which provide additional information about the soils. There are three sets of attributes that include information on the primary, secondary, and tertiary soil type within each polygon. Thus, there is a total of nine main attributes in this data set.

The effects of ultraviolet light on the degradation of organic compounds: a possible explanation for the absence of organic matter on Mars.

PubMed

Oro, J; Holzer, G

1979-01-01

The analysis of the top layer of the Martian regolith at the two Viking landing sites did not reveal any indigenous organic compounds. However the existence of such compounds at deeper layers cannot be ruled out. Cosmochemical considerations indicate various potential sources for organic matter on Mars, such as comets and meteorites. Its disappearance from the top layer could be caused by degradation processes on the surface of the planet. Possible destructive agents include ultraviolet light, oxygen and metal oxides. In this study we tested the stability of a sample of the Murchison meteorite and various organic substances which have been detected in carbonaceous chondrites, such as glycine, adenine and naphthalene, to the action of ultraviolet light. The compounds were adsorbed on powdered quartz and on California desert soil and were irradiated in the presence or absence of oxygen. The organic content, before and after irradiation, was measured by carbon elementary analysis, UV-absorption, amino acid analysis or pyrolysis-gas chromatography-mass spectrometry. In the absence of oxygen, adenine and glycine appear to be stable over the given period of irradiation. A definite degradation was noticed in the case of naphthalene and the Murchison meteorite. In the presence of oxygen in amounts comparable to those on Mars all compounds were degraded. The degree of degradation was influenced by the irradiation time, temperature and oxygen content.

Effect of integrating straw into agricultural soils on soil infiltration and evaporation.

PubMed

Cao, Jiansheng; Liu, Changming; Zhang, Wanjun; Guo, Yunlong

2012-01-01

Soil water movement is a critical consideration for crop yield in straw-integrated fields. This study used an indoor soil column experiment to determine soil infiltration and evaporation characteristics in three forms of direct straw-integrated soils (straw mulching, straw mixing and straw inter-layering). Straw mulching is covering the land surface with straw. Straw mixing is mixing straw with the top 10 cm surface soil. Then straw inter-layering is placing straw at the 20 cm soil depth. There are generally good correlations among the mulch integration methods at p < 0.05, and with average errors/biases <10%. Straw mixing exhibited the best effect in terms of soil infiltration, followed by straw mulching. Due to over-burden weight-compaction effect, straw inter-layering somehow retarded soil infiltration. In terms of soil water evaporation, straw mulching exhibited the best effect. This was followed by straw mixing and then straw inter-layering. Straw inter-layering could have a long-lasting positive effect on soil evaporation as it limited the evaporative consumption of deep soil water. The responses of the direct straw integration modes to soil infiltration and evaporation could lay the basis for developing efficient water-conservation strategies. This is especially useful for water-scarce agricultural regions such as the arid/semi-arid regions of China.

Mapping SOC content and bulk density of a disturbed peatland relict with electromagnetic induction and DEM data

NASA Astrophysics Data System (ADS)

Altdorff, Daniel; Bechtold, Michel; van der Kruk, Jan; Tiemeyer, Bärbel; von Hebel, Christian; Huisman, Johan Alexander

2014-05-01

Peatlands represent a huge storage of soil organic carbon (SOC), and there is considerable interest to assess the total amount of carbon stored in these ecosystems. However, reliable field-scale information about peat properties, particularly SOC content and bulk density (BD) necessary to estimate C stocks, remains difficult to obtain. A potential way to acquire information on these properties and its spatial variation is the non-invasive mapping of easily recordable physical variables that correlate with peat properties, such as bulk electrical conductivity (ECa) measured with electromagnetic induction (EMI). However, ECa depends on a range of soil properties, including BD, soil and water chemistry, and water content, and thus results often show complex and site-specific relationships. Therefore, a reliable prediction of SOC and BD from ECa data is not necessarily given. In this study, we aim to explore the usefulness of Multiple Linear Regression (MLR) models to predict the peat soil properties SOC and BD from multi-offset EMI and high-resolution DEM data. The quality of the MLR models is assessed by cross-validation. We use data from a medium-scale disturbed peat relict (approximately 35ha) in Northern Germany. The potential explanatory variables considered in MLR were: EMI data of six different integral depths (approximately 0.25, 0.5, 0.6, 0.9, 1, and 1.80 m), their vertical heterogeneity, as well as several topographical variables extracted from the DEM. Ground truth information for SOC, BD content and peat layer thickness was obtained from 34 soil cores of 1 m depth. Each core was divided into several 5 to 20 cm thick layers so that integral information of the upper 0.25, 0.5, and 1 m as well as from the total peat layer was obtained. For cross-validation of results, we clustered the 34 soil cores into 4 classes using K-means clustering and selected 8 cores for validation from the clusters with a probability that depended on the size of the cluster. With the remaining 26 samples, we performed a stepwise MLR and generated separate models for each depth and soil property. Preliminary results indicate reliable model predictions for SOC and BD (R² = 0.83- 0.95). The RMSE values of the validation ranged between 3.5 and 7.2 vol. % for SOC and 0.13 and 0.37 g/cm³ for BD for the independent samples. This equates roughly the quality of SOC predictions obtained by field application of vis-NIR (visible-near infrared) presented in literature for a similar peatland setting. However, the EMI approach offers the potential to derive information from deeper depths and allows non-invasive mapping of BD variability, which is not possible with vis-NIR. Therefore, this new approach potentially provides a more useful tool for total carbon stock assessment in peatlands.

Dynamics of Gross Methane Production and Oxidation in a Peatland Soil

NASA Astrophysics Data System (ADS)

McNicol, G.; Yang, W. H.; Teh, Y.; Silver, W. L.

2012-12-01

Globally, peatlands are major sources of the potent greenhouse gas methane (CH4) that is implicated in 20% of the post-industrial increase in radiative forcing. Many temperate peatlands have been drained for alternative land-use and are characterized by a layer of unsaturated soil overlying the remnant organic histosol. Drained soil layers may attenuate surface CH4 emissions from deeper, flooded peat layers via microbial CH4 consumption. We measured gross rates of CH4 production and oxidation seasonally across a range of topographic landforms in a partially drained peatland on Sherman Island, California. Net CH4 fluxes across the soil-atmosphere interface ranged from -7.4 to 1096 mg-C m-2 d-1 across all landforms. Fluxes were highest in May and in irrigation ditches (date, p < 0.001; landform, p < 0.001; n = 55). Gross CH4 production rates ranged from 0-1461 mg-C m-2 d-1 and oxidation rates ranged from 0-40 mg-C m-2 d-1. Excluding the irrigation ditches, gross fluxes did not vary seasonally. Gross CH4 fluxes were significantly higher in the hollow/hummock than in the slope. We subsequently selected the hollow/hummock based upon the observation of a strong redox gradient with depth and characterized gross fluxes of CH4 both in the field and in laboratory incubations of four soil depth increments (0-10 cm, 10-30 cm, 30-60 cm, 60-80 cm). The laboratory incubation consisted of 3 separate gross flux experiments: the first using fresh soil under ambient headspace, the second after incubation in an N2 headspace, and the third after incubation in an ambient headspace. Gross CH4 fluxes in the field varied from a slight sink (-0.11 mg-C m-2 d-1) to a large source (23.9 mg-C m-2 d-1). In 3 plots net fluxes were reduced by competing CH4 oxidation. In the depth profile experiment, production and consumption were observed in the fresh soil, but without a clear depth trend. In contrast, we found that consumption rates increased with depth following the aerobic incubation and production showed the same trend with depth under N2. Our field results demonstrate that flooded drainage ditches can act as CH4 emission hotspots in drained peatlands due to high production rates and low oxidation rates, disproportionately impacting ecosystem CH4 emissions. In contrast CH4 oxidation rates in the drained landforms even led to negative fluxes at times. The depth profile experiment showed that the strongest potential for both production and consumption of CH4 was at depths close to, or below, the water table. Thus despite significant CH4 production potential at depth, drained peatlands may be only minor sources, or even slight sinks, of CH4 if the extent and persistence of flooded landforms is minimal.

Radioecology of Vertebrate Animals in the Area Adjacent to the Chernobyl Nuclear Power Plant Site in 1986-2008

NASA Astrophysics Data System (ADS)

Farfan, E. B.; Gashchak, S. P.; Makliuk, Y. A.; Maksymenko, A. M.; Bondarkov, M. D.; Jannik, G. T.; Marra, J. C.

2009-12-01

A widespread environmental contamination of the areas adjacent to the Chernobyl Nuclear Power Plant (ChNPP) site attracted a great deal of publicity to the biological consequences of the ChNPP catastrophe. However, only a few studies focused on a detailed analysis of radioactive contamination of the local wild fauna and most of them were published in Eastern European languages, making them poorly accessible for Western scientists. In addition, evaluation of this information appears difficult due to significant differences in raw data acquisition and analysis methodologies and final data presentation formats. Using an integrated approach to assessment of all available information, the International Radioecology Laboratory scientists showed that the ChNPP accident had increased the average values of the animals 137Cs and 90Sr contamination by a factor of thousands, followed by its decrease by a factor of tens, primarily resulting from a decrease in the biological accessibility of the radionuclides. However, this trend depended on many factors. Plant and bottom feeding fish species were the first to reach the maximum contamination levels. No data are available on other vertebrates, but it can be assumed that the same trend was true for all plant feeding animals and animals searching for food on the soil surface. The most significant decrease of the average values occurred during the first 3-5 years after the accident and it was the most pronounced for elks and plant and plankton feeding fish. Their diet included elements “alienated” from the major radionuclide inventory; for example, upper soil layers and bottom deposits where the fallout that had originally precipitated on plants, water and soils gradually migrated. Further radionuclide penetration into deeper layers of soils and its bonding with their mineral components intensified decontamination of the fauna. It took a while for the contamination of predatory fish and mammals (wolves) to reach the maximum followed by its similar slow decrease. Currently, these species are found to be the most contaminated. Species that are environmentally connected with soils or bottom deposits (terrestrial amphibians, rodents, burrowing animals, birds searching for food in soils and underlying layers and wild hogs) also show relatively high contamination levels. In general, by the mid 1990’s, fluctuations in 137Cs contamination primarily depended on seasonal changes in food patterns, physiology and migration for animal species and on all these factors plus seasonal changes of water temperature and flood patterns for fish species. An increase of 90Sr biological accessibility in soils affected its average accumulation. Currently, due to stabilization of environmental complexes and processes in the region, long-term profiles of radioactive contamination of vertebrate animals mostly indicate a gradual decay of radionuclides, with further changes in biological accessibility of radionuclides being practically unnoticeable due to significant seasonal and geographical fluctuations of the contamination.

Can next-generation soil data products improve soil moisture modelling at the continental scale? An assessment using a new microclimate package for the R programming environment

NASA Astrophysics Data System (ADS)

Kearney, Michael R.; Maino, James L.

2018-06-01

Accurate models of soil moisture are vital for solving core problems in meteorology, hydrology, agriculture and ecology. The capacity for soil moisture modelling is growing rapidly with the development of high-resolution, continent-scale gridded weather and soil data together with advances in modelling methods. In particular, the GlobalSoilMap.net initiative represents next-generation, depth-specific gridded soil products that may substantially increase soil moisture modelling capacity. Here we present an implementation of Campbell's infiltration and redistribution model within the NicheMapR microclimate modelling package for the R environment, and use it to assess the predictive power provided by the GlobalSoilMap.net product Soil and Landscape Grid of Australia (SLGA, ∼100 m) as well as the coarser resolution global product SoilGrids (SG, ∼250 m). Predictions were tested in detail against 3 years of root-zone (3-75 cm) soil moisture observation data from 35 monitoring sites within the OzNet project in Australia, with additional tests of the finalised modelling approach against cosmic-ray neutron (CosmOz, 0-50 cm, 9 sites from 2011 to 2017) and satellite (ASCAT, 0-2 cm, continent-wide from 2007 to 2009) observations. The model was forced by daily 0.05° (∼5 km) gridded meteorological data. The NicheMapR system predicted soil moisture to within experimental error for all data sets. Using the SLGA or the SG soil database, the OzNet soil moisture could be predicted with a root mean square error (rmse) of ∼0.075 m3 m-3 and a correlation coefficient (r) of 0.65 consistently through the soil profile without any parameter tuning. Soil moisture predictions based on the SLGA and SG datasets were ≈ 17% closer to the observations than when using a chloropleth-derived soil data set (Digital Atlas of Australian Soils), with the greatest improvements occurring for deeper layers. The CosmOz observations were predicted with similar accuracy (r = 0.76 and rmse of ∼0.085 m3 m-3). Comparisons at the continental scale to 0-2 cm satellite data (ASCAT) showed that the SLGA/SG datasets increased model fit over simulations using the DAAS soil properties (r ∼ 0.63 &rmse 15% vs. r 0.48 &rmse 18%, respectively). Overall, our results demonstrate the advantages of using GlobalSoilMap.net products in combination with gridded weather data for modelling soil moisture at fine spatial and temporal resolution at the continental scale.

Vertical electric sounding of selected Arctic and Antarctic soils: advances in express field investigation of the Cryosols

NASA Astrophysics Data System (ADS)

Abakumov, Evgeny

2016-04-01

Physical properties of the soils of the cold environments are underestimated. Soil and permafrost border and active layer thickness are the key classification indicators for the polar soils. That is why electrophysical research has been conducted with aim to determine the soil-permafrost layer heterogeneity and the depth of the uppermost permafrost layer on examples of selected plots in Antarctic region and Russian Arctic. The electric resistivity (ER) was measured directly in the soil profiles using the vertical electrical sounding (VERS) method, which provides data on the changes in the electrical resistivity throughout the profile from the soil surface without digging pits or drilling. This method allows dividing the soil layer vertically into genetic layers, which are different on main key properties and characteristics Different soil layers have different ER values, that is why the sharp changes in ER values in soil profile can be interpreted as results of transition of one horizon to another. In our study, the resistivity measurements were performed using four-electrode (AB + MN) arrays of the AMNB configuration with use of the Schlumberger geometry. A Landmapper ERM-03 instrument (Landviser, USA) was used for the VES measurements in this study. Electrodes were situated on the soil surface, distance between M and N was fixes, while distance from A to B were changed during the sounding. Vertical Electrical Resistivity Soundings (VERS) using Schlumberger array were carried out at stations, situated on the different plots of terrestrial ecosystems of Arctic and Antarctic. The resistance readings at every VERS point were automatically displayed on the digital readout screen and then written down on the field note book. The soils had been 'sounded' thoroughly and found to vary between 5 cm and 3-5 m in A-B distances. It was shown that use of VES methodology in soil survey is quite useful for identification of the permafrost depth without digging of soil pit. This method allow identify soil heterogeneity, because the ER values are strongly affected by soil properties and intensively changes on the border of different geochemical regimes, i.e. on the border of active layer and permafrost. VES data obtained show that the upper border of the permafrost layer coincides with that border, which were identified in field on the base of soil profile morphology. The VERS method also can used for identification of Gleyic, Histic and Podzolic layers. It has been also shown that permafrost layer is less homogenous in upper part of permafrost, than in lower one. It is caused by number of cracks, channels and other paths of dissolved organic matter and iron containing compounds migration. VES methodology is useful for preliminary soil survey in the regions with permafrost affected soil cover. It is also can be applied for detalization of soil-permafrost layer stratification in field soil pits.

Selective Sorption of Dissolved Organic Carbon Compounds by Temperate Soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jagadamma, Sindhu; Mayes, Melanie; Phillips, Jana Randolph

Physico-chemical sorption of dissolved organic carbon (DOC) on soil minerals is one of the major processes of organic carbon (OC) stabilization in soils, especially in deeper layers. The attachment of C on soil solids is related to the reactivity of the soil minerals and the chemistry of the sorbate functional groups, but the sorption studies conducted without controlling microbial activity may overestimate the sorption potential of soil. This study was conducted to examine the sorptive characteristics of a diverse functional groups of simple OC compounds (D-glucose, L-alanine, oxalic acid, salicylic acid, and sinapyl alcohol) on temperate climate soil orders (Mollisols,more » Ultisols and Alfisols) with and without biological degradative processes. Equilibrium batch experiments were conducted using 0-100 mg C L-1 at a solid-solution ratio of 1:60 for 48 hrs and the sorption parameters were calculated by Langmuir model fitting. The amount of added compounds that remained in the solution phase was detected by high performance liquid chromatography (HPLC) and total organic C (TOC) analysis. Soil sterilization was performed by -irradiation technique and experiments were repeated to determine the contribution of microbial degradation to apparent sorption. Overall, Ultisols did not show a marked preference for apparent sorption of any of the model compounds, as indicated by a narrower range of maximum sorption capacity (Smax) of 173-527 mg kg soil-1 across compounds. Mollisols exhibited a strong preference for apparent sorption of oxalic acid (Smax of 5290 mg kg soil-1) and sinapyl alcohol (Smax of 2031 mg kg soil-1) over the other compounds. The propensity for sorption of oxalic acid is mainly attributed to the precipitation of insoluble Ca-oxalate due to the calcareous nature of most Mollisol subsoils and its preference for sinapyl alcohol could be linked to the polymerization of this lignin monomer on 2:2 mineral dominated soils. The reactivity of Alfisols to DOC was in between that of Ultisols and Mollisols. HPLC results revealed significantly higher sorption of D-glucose and L-alanine than did TOC results, and duplicate experiments with sterilized soils confirmed that glucose and alanine were mineralized leading to higher apparent sorption values via HPLC. This study demonstrated that three common temperate soil orders experienced differential sorption of simple OC compounds, indicating that sorbate chemistry plays a significant role in the sorptive stabilization of DOC.« less

The influence of wildfire severity on soil char composition and nitrogen dynamics

NASA Astrophysics Data System (ADS)

Rhoades, Charles; Fegel, Timothy; Chow, Alex; Tsai, Kuo-Pei; Norman, John, III; Kelly, Eugene

2017-04-01

Forest fires cause lasting ecological changes and alter the biogeochemical processes that control stream water quality. Decreased plant nutrient uptake is the mechanism often held responsible for lasting post-fire shifts in nutrient supply and demand, though other upland and in-stream factors also likely contribute to elevated stream nutrient losses. Soil heating, for example, creates pyrogenic carbon (C) and char layers that influence C and nitrogen (N) cycling. Char layer composition and persistence vary across burned landscapes and are influenced first by fire behavior through the temperature and duration of combustion and then by post-fire erosion. To evaluate the link between soil char and stream C and N export we studied areas burned by the 2002 Hayman Fire, the largest wildfire in Colorado, USA history. We compared soil C and N pools and processes across ecotones that included 1) unburned forests, 2) areas with moderate and 3) high wildfire severity. We analyzed 1-2 cm thick charred organic layers that remain visible 15 years after the fire, underlying mineral soils, and soluble leachate from both layers. Unburned soils released more dissolved organic C and N (DOC and DON) from organic and mineral soil layers than burned soils. The composition of DOC leachate characterized by UV-fluorescence, emission-excitation matrices (EEMs) and Fluorescence Regional Integration (FRI) found similarity between burned and unburned soils, underscoring a common organic matter source. Humic and fulvic acid-like fractions, contained in regions V and III of the FRI model, comprised the majority of the fluorescing DOM in both unburned and char layers. Similarity between two EEMs indices (Fluorescence and Freshness), further denote that unburned soils and char layers originate from the same source and are consistent with visual evidence char layers contain significant amounts of unaltered OM. However, the EEMs humification index (HIX) and compositional analysis with pyrolysis GCMS both indicate that C contained or leached from severely-burned char layers has higher aromaticity and thus chemical stability compared to C in unburned soils. Mineral soil (0-5 cm depth) beneath char layers in high severity portions of the Hayman Fire had significantly more soil N and C and lower pH. Potential net mineralization - an index of the supply of plant-available nitrogen - differed between the severely-burned areas and both unburned and moderately-burn areas. Negative net mineralization in unburned and moderately burned soils indicates immobilization or retention of inorganic N by soil microbes. In contrast, soils burned at high severity produced inorganic N sources available to plants, leaching and gas losses. Water soluble nitrate comprised a larger proportion of inorganic N leached from the char layer of high severity burns. Mineral soil in those areas had both higher water soluble nitrate and total inorganic N in leachate. Char layers that have persisted for fifteen years influence soil N turnover within the Hayman Fire affected area and may contribute to elevated N losses in streams burned at high severity. The chemical stability of soil char layers perpetuates their importance for C sequestration and N dynamics in burned landscapes.

Spectral Signatures of Feedforward and Recurrent Circuitry in Monkey Area MT.

PubMed

Solomon, Selina S; Morley, John W; Solomon, Samuel G

2017-05-01

Recordings of local field potential (LFP) in the visual cortex can show rhythmic activity at gamma frequencies (30-100 Hz). While the gamma rhythms in the primary visual cortex have been well studied, the structural and functional characteristics of gamma rhythms in extrastriate visual cortex are less clear. Here, we studied the spatial distribution and functional specificity of gamma rhythms in extrastriate middle temporal (MT) area of visual cortex in marmoset monkeys. We found that moving gratings induced narrowband gamma rhythms across cortical layers that were coherent across much of area MT. Moving dot fields instead induced a broadband increase in LFP in middle and upper layers, with weaker narrowband gamma rhythms in deeper layers. The stimulus dependence of LFP response in middle and upper layers of area MT appears to reflect the presence (gratings) or absence (dot fields and other textures) of strongly oriented contours. Our results suggest that gamma rhythms in these layers are propagated from earlier visual cortex, while those in the deeper layers may emerge in area MT. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

[Effects of ex situ rice straw incorporation on organic matter content and main physical properties of hilly red soil].

PubMed

Zhu, Han-hua; Huang, Dao-you; Liu, Shou-long; Zhu, Qi-hong

2007-11-01

Two typical land-use types, i.e., newly cultivated slope land and mellow upland, were selected to investigate the effects of ex situ rice straw incorporation on the organic matter content, field water-holding capacity, bulk density, and porosity of hilly red soil, and to approach the correlations between these parameters. The results showed that ex situ incorporation of rice straw increased soil organic matter content, ameliorated soil physical properties, and improved soil water storage. Comparing with non-fertilization and applying chemical fertilizers, ex situ incorporation of rice straw increased the contents of organic matter (5.8%-28.9%) and > 0.25 mm water-stable aggregates in 0-20 cm soil layer, and increased the field water-holding capacity (6.8%-16.2%) and porosity (4.8%-7.7%) significantly (P < 0.05) while decreased the bulk density (4.5%-7.5%) in 10-15 cm soil layer. The organic matter content in 0-20 cm soil layer was significantly correlated to the bulk density, porosity, and field water-holding capacity in 10-15 cm soil layer (P < 0.01), and the field water-holding capacity in 0-20 cm and 10-15 cm soil layers was significantly correlated to the bulk density and porosity in these two layers (P < 0.05).

Soil organic carbon and nitrogen accumulation on coal mine spoils reclaimed with maritime pine (Pinus pinaster Aiton) in Agacli-Istanbul.

PubMed

Sever, Hakan; Makineci, Ender

2009-08-01

Mining operations on open coal mines in Agacli-Istanbul have resulted in the destruction of vast amounts of land. To rehabilitate these degraded lands, plantations on this area began in 1988. Twelve tree species were planted, however, the most planted tree species was maritime pine (Pinus pinaster Aiton). This study performed on 14 sample plots randomly selected in maritime pine plantations on coal mine soil/spoils in 2005. Soil samples were taken from eight different soil layers (0-1, 1-3, 3-5, 5-10, 10-20, 20-30, 30-40 and 40-50 cm) into the soil profile. On soil samples; fine soil fraction (<2 mm), soil acidity (pH), organic carbon (C(org)) and total nitrogen (N(t)) contents were investigated, and results were compared statistically among soil layers. As a result, 17 years after plantations, total forest floor accumulation determined as 17,973.20 kg ha(-1). Total nitrogen and organic matter amounts of forest floor were 113.90 and 14,640.92 kg ha(-1) respectively. Among soil layers, the highest levels of organic carbon (1.77%) and total nitrogen (0.096%) and the lowest pH value (pH 5.38) were found in 0-1 cm soil layer, and the variation differs significantly among soil layers. Both organic carbon and total nitrogen content decreased, pH values increased from 0-1 to 5-10 cm layer. In conclusion, according to results obtained maritime pine plantations on coal mine spoils; slow accumulation and decomposition of forest floor undergo simultaneously. Depending on these changes organic carbon and total nitrogen contents increased in upper layer of soil/spoil.

The variation of methane flux rates from boreal tree species at the beginning of the growing season

NASA Astrophysics Data System (ADS)

Haikarainen, Iikka; Halmeenmäki, Elisa; Machacova, Katerina; Pihlatie, Mari

2016-04-01

Boreal forests are considered as net sink for atmospheric methane (CH4) because of the CH4 oxidizing bacteria in the aerobic soil layer. However, within the last decades it has become more evident that trees play an important role in the global CH4 budget by offering pathways for anaerobically produced CH4 from deeper soil layers to the atmosphere. Furthermore, trees may also act as independent sources of CH4. To confirm magnitude, variability and the origin of the tree mediated CH4 emissions more research is needed, especially in boreal forests which have been in a minority in such investigation. We measured tree stem and shoot CH4 exchange of three boreal tree species at the beginning of the growing season (13.4.-13.6.2015) at SMEAR II station in Hyytiälä, located in southern Finland (61° 51'N, 24° 17'E, 181 asl). The fluxes were measured from silver birch (Betula pendula), downy birch (B. pubescens) and Norway spruce (Picea abies) on two sites with differing soil type and characteristics (paludified and mineral soil), vegetation and forest structure by using the static chamber technique. Scaffold towers were used for measurements at multiple stem heights and shoots. The aim was to study the vertical profile of CH4 fluxes at stem and shoot level and compare these fluxes among the studied species, and to observe temporal changes in CH4 flux over the beginning of the growing season. We found that all the trees emitted CH4 from their stems and shoots. Overall, the birches showed higher emissions compared to the spruces. The emission rates were considerably larger in the lower parts of the birch stems than upper parts, and these emissions increased during the growing season. The spruces had more variation in the stem CH4 flux, but the emission rates of the upper parts of the stem exceeded the birch emissions at the same height. The shoot fluxes of all the studied trees indicated variable CH4 emissions without a clear pattern regarding the vertical profile and progress of the growing season.

Cadmium translocation by contractile roots differs from that in regular, non-contractile roots

PubMed Central

Lux, Alexander; Lackovič, Andrej; Van Staden, Johannes; Lišková, Desana; Kohanová, Jana; Martinka, Michal

2015-01-01

Background and Aims Contractile roots are known and studied mainly in connection with the process of shrinkage of their basal parts, which acts to pull the shoot of the plant deeper into the ground. Previous studies have shown that the specific structure of these roots results in more intensive water uptake at the base, which is in contrast to regular root types. The purpose of this study was to find out whether the basal parts of contractile roots are also more active in translocation of cadmium to the shoot. Methods Plants of the South African ornamental species Tritonia gladiolaris were cultivated in vitro for 2 months, at which point they possessed well-developed contractile roots. They were then transferred to Petri dishes with horizontally separated compartments of agar containing 50 µmol Cd(NO3)2 in the region of the root base or the root apex. Seedlings of 4-d-old maize (Zea mays) plants, which do not possess contractile roots, were also transferred to similar Petri dishes. The concentrations of Cd in the leaves of the plants were compared after 10 d of cultivation. Anatomical analyses of Tritonia roots were performed using appropriately stained freehand cross-sections. Key Results The process of contraction required specific anatomical adaptation of the root base in Tritonia, with less lignified and less suberized tissues in comparison with the subapical part of the root. These unusual developmental characteristics were accompanied by more intensive translocation of Cd ions from the basal part of contractile roots to the leaves than from the apical–subapical root parts. The opposite effects were seen in the non-contractile roots of maize, with higher uptake and transport by the apical parts of the root and lower uptake and transport by the basal part. Conclusions The specific characteristics of contractile roots may have a significant impact on the uptake of ions, including toxic metals from the soil surface layers. This may be important for plant nutrition, for example in the uptake of nutrients from upper soil layers, which are richer in humus in otherwise nutrient-poor soils, and also has implications for the uptake of surface-soil pollutants. PMID:25939652

New approach to analyzing soil-building systems

USGS Publications Warehouse

Safak, E.

1998-01-01

A new method of analyzing seismic response of soil-building systems is introduced. The method is based on the discrete-time formulation of wave propagation in layered media for vertically propagating plane shear waves. Buildings are modeled as an extension of the layered soil media by assuming that each story in the building is another layer. The seismic response is expressed in terms of wave travel times between the layers, and the wave reflection and transmission coefficients at layer interfaces. The calculation of the response is reduced to a pair of simple finite-difference equations for each layer, which are solved recursively starting from the bedrock. Compared with commonly used vibration formulation, the wave propagation formulation provides several advantages, including the ability to incorporate soil layers, simplicity of the calculations, improved accuracy in modeling the mass and damping, and better tools for system identification and damage detection.A new method of analyzing seismic response of soil-building systems is introduced. The method is based on the discrete-time formulation of wave propagation in layered media for vertically propagating plane shear waves. Buildings are modeled as an extension of the layered soil media by assuming that each story in the building is another layer. The seismic response is expressed in terms of wave travel times between the layers, and the wave reflection and transmission coefficients at layer interfaces. The calculation of the response is reduced to a pair of simple finite-difference equations for each layer, which are solved recursively starting from the bedrock. Compared with commonly used vibration formulation, the wave propagation formulation provides several advantages, including the ability to incorporate soil layers, simplicity of the calculations, improved accuracy in modeling the mass and damping, and better tools for system identification and damage detection.

The effect of harvest intensity on long-term calcium dynamics in soil and soil solution at three coniferous sites in Sweden

NASA Astrophysics Data System (ADS)

Zetterberg, Therese; Olsson, Bengt; Löfgren, Stefan; von Brömssen, Claudia; Brandtberg, Per-Olov

2013-04-01

Bioenergy from forests is a mean to reduce fossil fuel related carbon dioxide (CO2) emissions. The potential to replace fossil fuel with logging residues is large in countries with extensive forest resources such as Sweden where the supply of bioenergy to district heating plants has quintupled since the 1990's, now accounting for 46% of the total energy supply. However, the loss of nutrients and other elements in biomass is higher following harvest for bioenergy purposes (whole-tree harvest, WTH) compared with traditional clear-cutting (conventional harvest, CH). Calcium (Ca2+) is an important base cation, which buffer soils and surface water against acidification. The loss of Ca2+ and other base cations via harvest for bioenergy could therefore result in soil acidification and there is a growing concern in Sweden that the depletion in base cation pools would also lead to surface water acidification associated with lower base cation concentrations in runoff (Swedish Environmental Protection Agency, 2007). Furthermore, WTH may also prevent or delay a recovery from acidification in areas such as the southwestern parts of Sweden, where the pools of exchangeable cations have been substantially depleted as a result of historically high sulfate (SO42-) deposition. In this paper, long-term treatment differences in soil exchangeable Ca2+ pools (down to 20 cm) and soil solution Ca2+ concentrations at 50 cm soil depth were examined at three coniferous sites in Sweden following CH and WTH in 1974-76. The results showed that soil water concentrations of Ca2+were -17 μeq l-1 (or 40%) lower in WTH plots compared with CH plots, 27-30 years after harvest. The main treatment differences had largely disappeared 32 to 35 years after harvest although site specific treatment differences (ΔWTH-CH: -24 μeq l-1) were still measurable at the well-buffered site in northern Sweden. These results are in agreement with soil data showing that previously found treatment differences in Ca2+ pools had diminished in the forest floor but remained in deeper soil layers (-0.29, -0.37 and -0.24 kmolc ha-1 in the 5-10, 10-15 and 15-20 cm soil layer, respectively). The effects on soil Ca2+ pools appeared to be most pronounced at the well-buffered northern site. These results indicate that the effect of WTH on soil and soil solution concentrations is temporary but site specific. Contrary to common beliefs, the greatest effects were observed at the well-buffered site where the loss of Ca2+ during WTH is less likely to lead to acidification effects. The treatment effects on soil solution at the more acidic sites in southern Sweden were much smaller and probably not large enough to fully counterbalance the general recovery from acidification during the study period. References Swedish Environmental Protection Agency, 2007. Bara naturlig försurning. Bilagor till underlagsrapport till fördjupad utvärdering av miljömålen. Rapport 5780. 208 pp. In Swedish.

Transregional Collaborative Research Centre 32: Patterns in Soil-Vegetation-Atmosphere-Systems

NASA Astrophysics Data System (ADS)

Masbou, M.; Simmer, C.; Kollet, S.; Boessenkool, K.; Crewell, S.; Diekkrüger, B.; Huber, K.; Klitzsch, N.; Koyama, C.; Vereecken, H.

2012-04-01

The soil-vegetation-atmosphere system is characterized by non-linear exchanges of mass, momentum and energy with complex patterns, structures and processes that act at different temporal and spatial scales. Under the TR32 framework, the characterisation of these structures and patterns will lead to a deeper qualitative and quantitative understanding of the SVA system, and ultimately to better predictions of the SVA state. Research in TR32 is based on three methodological pillars: Monitoring, Modelling and Data Assimilation. Focusing our research on the Rur Catchment (Germany), patterns are monitored since 2006 continuously using existing and novel geophysical and remote sensing techniques from the local to the catchment scale based on ground penetrating radar methods, induced polarization, radiomagnetotellurics, electrical resistivity tomography, boundary layer scintillometry, lidar techniques, cosmic-ray, microwave radiometry, and precipitation radars with polarization diversity. Modelling approaches involve development of scaled consistent coupled model platform: high resolution numerical weather prediction (NWP; 400m) and hydrological models (few meters). In the second phase (2011-2014), the focus is on the integration of models from the groundwater to the atmosphere for both the m- and km-scale and the extension of the experimental monitoring in respect to vegetation. The coupled modelling platform is based on the atmospheric model COSMO, the land surface model CLM and the hydrological model ParFlow. A scale consistent two-way coupling is performed using the external OASIS coupler. Example work includes the transfer of laboratory methods to the field; the measurements of patterns of soil-carbon, evapotranspiration and respiration measured in the field; catchment-scale modeling of exchange processes and the setup of an atmospheric boundary layer monitoring network. These modern and predominantly non-invasive measurement techniques are exploited in combination with advanced modelling systems by data assimilation to yield improved numerical models for the prediction of water-, energy and CO2-transfer by accounting for the patterns occurring at various scales.

Thickness and Lower Limit Seismogenic Layer within the Crust beneath Japanese Islands on the Japan Sea Side

NASA Astrophysics Data System (ADS)

Matsubara, M.; Sato, H.

2015-12-01

1. Introduction I investigate the depth of the seismogenic layer in order to estimate the lower limit of the seismogenic fault plane since this depth is related to the size of the earthquake caused by the active fault. I have indexes D10 and D90 as the upper and lower limits of the seismogenic layer defined as the depth above which 10 % and 90 % of the whole crustal earthquakes occurred from the surface, respectively. The difference between the D10 and D90 is the thickness of the seismogenic layer. 2. Data and method The NIED Hi-net has a catalog of hypocenters determined with one-dimensional　velocity (1D) structure (Ukawa et al., 1984) and I estimated the D10 and D90 with this catalog at first. I construct the system to relocate the hypocenters from 2001 to 2013 with magnitude greater than 1.5 on the Japan Sea side shallower than 50 km depth with the three-dimensional velocity (3D) structure (Matsubara and Obara, 2011) obtained by seismic tomography. I estimate the D10 and D90 from the hypocenter catalog with 3D structure. 3. Result Many earthquakes shallower than 5 km with 1D structure are relocated to deeper with 3D structure and the earthquakes deeper than 15 km are relocated to about 5 km shallower. With 3D structure D10 deepens and D90 shallows from 1D structure. D90 beneath the northern Honshu is deeper than the other area and D90 beneath the Japan Sea is much deeper than the inland area. The thickness of the seismogenic layer beneath the Japan Sea is also thick from 8-16 km. D90 on the Japan Sea side of the southwestern Japan on the west side of the Itoigawa Shizuoka Tectonic Line is very shallow as 11-16 km and the thickness of the seismogenic layer is also thin as 2-7 km. 4. Discussion Omuralieva et al. (2012) relocated the JMA unified hypocenters with 3D structure and estimated shallower D90 than that from the JMA catalog. Very deep D90 beneath the northern Hokkaido and northern Honshu is consistent with our result. 5. Conclusion Using 3D velocity structure D10 deepens, D90 shallows, and the thickness of the seismogenic layer becomes thinner. The thickness of the seismogenic layer is thick beneath the northern Honshu, however, that is very thin beneath southwestern Japan on the Japan Sea side.

Molecular investigations into a globally important carbon pool: Permafrost-protected carbon in Alaskan soils

USGS Publications Warehouse

Waldrop, M.P.; Wickland, K.P.; White, Rickie; Berhe, A.A.; Harden, J.W.; Romanovsky, V.E.

2010-01-01

The fate of carbon (C) contained within permafrost in boreal forest environments is an important consideration for the current and future carbon cycle as soils warm in northern latitudes. Currently, little is known about the microbiology or chemistry of permafrost soils that may affect its decomposition once soils thaw. We tested the hypothesis that low microbial abundances and activities in permafrost soils limit decomposition rates compared with active layer soils. We examined active layer and permafrost soils near Fairbanks, AK, the Yukon River, and the Arctic Circle. Soils were incubated in the lab under aerobic and anaerobic conditions. Gas fluxes at -5 and 5 ??C were measured to calculate temperature response quotients (Q10). The Q10 was lower in permafrost soils (average 2.7) compared with active layer soils (average 7.5). Soil nutrients, leachable dissolved organic C (DOC) quality and quantity, and nuclear magnetic resonance spectroscopy of the soils revealed that the organic matter within permafrost soils is as labile, or even more so, than surface soils. Microbial abundances (fungi, bacteria, and subgroups: methanogens and Basidiomycetes) and exoenzyme activities involved in decomposition were lower in permafrost soils compared with active layer soils, which, together with the chemical data, supports the reduced Q10 values. CH4 fluxes were correlated with methanogen abundance and the highest CH4 production came from active layer soils. These results suggest that permafrost soils have high inherent decomposability, but low microbial abundances and activities reduce the temperature sensitivity of C fluxes. Despite these inherent limitations, however, respiration per unit soil C was higher in permafrost soils compared with active layer soils, suggesting that decomposition and heterotrophic respiration may contribute to a positive feedback to warming of this eco region. Published 2010. This article is a US Government work and is in the public domain in the USA.

Fate of the antibiotic sulfadiazine in natural soils: Experimental and numerical investigations.

PubMed

Engelhardt, Irina; Sittig, Stephan; Šimůnek, Jirka; Groeneweg, Joost; Pütz, Thomas; Vereecken, Harry

2015-01-01

Based on small-scale laboratory and field-scale lysimeter experiments, the sorption and biodegradation of sulfonamide sulfadiazine (SDZ) were investigated in unsaturated sandy and silty-clay soils. Sorption and biodegradation were low in the laboratory, while the highest leaching rates were observed when SDZ was mixed with manure. The leaching rate decreased when SDZ was mixed with pure water, and was smallest with the highest SDZ concentrations. In the laboratory, three transformation products (TPs) developed after an initial lag phase. However, the amount of TPs was different for different mixing-scenarios. The TP 2-aminopyrimidine was not observed in the laboratory, but was the most prevalent TP at the field scale. Sorption was within the same range at the laboratory and field scales. However, distinctive differences occurred with respect to biodegradation, which was higher in the field lysimeters than at the laboratory scale. While the silty-clay soil favored sorption of SDZ, the sandy, and thus highly permeable, soil was characterized by short half-lives and thus a quick biodegradation of SDZ. For 2-aminopyrimidine, half-lives of only a few days were observed. Increased field-scale biodegradation in the sandy soil resulted from a higher water and air permeability that enhanced oxygen transport and limited oxygen depletion. Furthermore, low pH was more important than the organic matter and clay content for increasing the biodegradation of SDZ. A numerical analysis of breakthrough curves of bromide, SDZ, and its TPs showed that preferential flow pathways strongly affected the solute transport within shallow parts of the soil profile at the field scale. However, this effect was reduced in deeper parts of the soil profile. Due to high field-scale biodegradation in several layers of both soils, neither SDZ nor 2-aminopyrimidine was detected in the discharge of the lysimeter at a depth of 1m. Synthetic 50 year long simulations, which considered the application of manure with SDZ for general agricultural practices in Germany and humid climate conditions, showed that the concentration of SDZ decreased below 0.1 μg/L in both soils below the depth of 50 cm. Copyright © 2015 Elsevier B.V. All rights reserved.

Fate of the antibiotic sulfadiazine in natural soils: Experimental and numerical investigations

NASA Astrophysics Data System (ADS)

Engelhardt, Irina; Sittig, Stephan; Šimůnek, Jirka; Groeneweg, Joost; Pütz, Thomas; Vereecken, Harry

2015-06-01

Based on small-scale laboratory and field-scale lysimeter experiments, the sorption and biodegradation of sulfonamide sulfadiazine (SDZ) were investigated in unsaturated sandy and silty-clay soils. Sorption and biodegradation were low in the laboratory, while the highest leaching rates were observed when SDZ was mixed with manure. The leaching rate decreased when SDZ was mixed with pure water, and was smallest with the highest SDZ concentrations. In the laboratory, three transformation products (TPs) developed after an initial lag phase. However, the amount of TPs was different for different mixing-scenarios. The TP 2-aminopyrimidine was not observed in the laboratory, but was the most prevalent TP at the field scale. Sorption was within the same range at the laboratory and field scales. However, distinctive differences occurred with respect to biodegradation, which was higher in the field lysimeters than at the laboratory scale. While the silty-clay soil favored sorption of SDZ, the sandy, and thus highly permeable, soil was characterized by short half-lives and thus a quick biodegradation of SDZ. For 2-aminopyrimidine, half-lives of only a few days were observed. Increased field-scale biodegradation in the sandy soil resulted from a higher water and air permeability that enhanced oxygen transport and limited oxygen depletion. Furthermore, low pH was more important than the organic matter and clay content for increasing the biodegradation of SDZ. A numerical analysis of breakthrough curves of bromide, SDZ, and its TPs showed that preferential flow pathways strongly affected the solute transport within shallow parts of the soil profile at the field scale. However, this effect was reduced in deeper parts of the soil profile. Due to high field-scale biodegradation in several layers of both soils, neither SDZ nor 2-aminopyrimidine was detected in the discharge of the lysimeter at a depth of 1 m. Synthetic 50 year long simulations, which considered the application of manure with SDZ for general agricultural practices in Germany and humid climate conditions, showed that the concentration of SDZ decreased below 0.1 μg/L in both soils below the depth of 50 cm.

Patterns of in-soil methane production and atmospheric emission among different land covers of a Lake Erie estuarine wetland

NASA Astrophysics Data System (ADS)

Rey Sanchez, C.; Morin, T. H.; Stefanik, K. C.; Angle, J.; Wrighton, K. C.; Bohrer, G.

2017-12-01

Wetland soils store a great amount of carbon, but also accumulate and emit methane (CH4), a powerful greenhouse gas. To better understand the vertical and horizontal spatial variability of CH4 emissions, we monitored production and fluxes of CH4 in Old Woman Creek, an estuarine wetland of Lake Erie, Ohio, during the growing seasons of 2015 and 2016. Our combined observation methods targeted three different scales: 1) the eddy covariance technique provided continuous high frequency observations integrated over a large spatial footprint; 2) monthly chamber measurements provided sparse point measurements of fluxes in four distinct land-cover types in the wetland: open water, emergent vegetation (Typha spp.), floating vegetation (Nelumbo spp.) and mud flats; and 3) in-situ porewater dialysis samplers, "peepers", provided vertical CH4 concentration data in the soil at the same locations and temporal time steps as the chambers. In addition, we studied gene transcripts to quantify methanogenesis activity along the vertical soil profile. Using integrated chamber and EC measurements, we found an average surface emission rate from Typha, the most abundant vegetated land cover, of 219.4 g CH4-C m-2 y-1, which was much higher than rates reported in similar emergent vegetation types in other wetlands. There was large spatial variation of flux rates, with mud flats having the highest rates of CH4 emission, followed by Nelumbo and Typha patches, and with open water having the lowest emissions. Within the soil column, we applied a numerical model to convert soil methane concentrations to emissions rates. We found that, contrary to current ideas of methane production, most methane was being produced in the well-oxygenated surface soils, probably in anoxic microsites within the oxic layer. Our metatranscriptomic data supported these findings, clearly showing nine times greater methanogenic activity in oxic surface soils relative to deeper anoxic soils. Combined, our results provide important insights for the representation of processes of methane production and consumption in models, which can largely affect the estimates of methane emission from wetlands.

Eucalyptus water use greater than rainfall input - possible explanation from southern India

NASA Astrophysics Data System (ADS)

Calder, I. R.; Rosier, P. T. W.; Prasanna, K. T.; Parameswarappa, S.

Hydrological and silvicultural studies carried out in southern India on the effects of plantations of Eucalyptus and other fast growing exotic tree species have determined the impacts of these plantations on water resources, erosion, soil nutrient status and growth rates at sites of differing rainfall and soil depth in Karnataka. Whilst providing new information on these issues, the studies also raised two important questions: what was the explanation for the anomalous result that the water use of 3400 mm from Eucalyptus plantations at Hosakote over a three year period exceeded the rainfall of 2100 mm over the same period and why were growth rates of woodlots on most farmer's fields higher than those of plantations on land owned by the Karnataka Forest Department? The records of the soil moisture depletion patterns under these plantations from the day of planting provide the basis for the answers to both questions: i) whilst roots are penetrating into deeper soil layers, they are able to extract from a reservoir of water additional to that available from the rainfall each year, ii) farmer's land on which short rooted agricultural crops have been grown previously is likely to have a much higher soil water status than land previously under forest or scrub vegetation. These new studies have also established that the development of the drying front under the Eucalyptus camaldulensis plantations is very rapid, indicating average root extension rates in excess of 2.5 m per year, whilst those under Tectona grandis and Artocarpus heterophyllus advanced at approximately half the rate. These results have obvious implications for the long term sustainability of growth rates from these plantations and the recharge of groundwater. The authors believe that this study may be the first to report neutron probe soil moisture depletion observations, from the date of planting, beneath tree plantations in a dry climate. The extent to which the roots were able to penetrate raises the question of whether other studies, which have estimated water use from soil moisture observations in dry climates, may have seriously underestimated both the actual soil moisture depletion and the water use through having soil moisture measurements located to insufficient depth.

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

NASA Astrophysics Data System (ADS)

Orlowski, Natalie; Kraft, Philipp; Pferdmenges, Jakob; Breuer, Lutz

2016-09-01

A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

Properties and variability of soil and trench fill at an arid waste-burial site

USGS Publications Warehouse

Andraski, Brian J.

1996-01-01

Arid sites commonly are assumed to be ideal for long-term isolation of wastes. Information on properties and variability of desert soils is limited, however, and little is known about how the natural site environment is altered by installation of a waste facility. During fall construction of two test trenches next to the waste facility on the Amargosa Desert near Beatty, NV, samples were collected to: (i) characterize physical and hydraulic properties of native soil (upper 5 m) and trench fill, (ii) determine effects of trench construction on selected properties and vertical variability of these properties, and (iii) develop conceptual models of vertical variation within the soil profile and trench fill. Water retention was measured to air dryness (ψ = 2 × 106 cm water suction). The 15 300-cm pressure-plate data were omitted from the analysis because water-activity measurements showed the actual suction values were significantly less than the expected 15 300-cm value (avg. difference = 8550 ± 2460 cm water). Trench construction significantly altered properties and variability of the natural site environment. For example, water content ranged from 0.029 to 0.041 m3 m-3 for fill vs. 0.030 to 0.095 m3 m-3 for soil; saturated hydraulic conductivity was ≈ 10-4 cm s-1 for fill vs. 10-2 to ≈ 10-4 cm s-1 for soil. Statistical analyses showed that the native soil may be represented by three major horizontal components and the fill by a single component. Under initial conditions, calculated liquid conductivity (Kl) plus isothermal vapor conductivity (Kv) for the upper two soil layers and the trench fill was ≈ 10-13 cm s-1, and Kl was ≤ Kv. For the deeper (2–5 m) soil, total conductivity was ≈ 10-10 cm s-1, and Kl was >Kv. This study quantitatively describes hydraulic characteristics of a site using data measured across a water-content range that is representative of arid conditions, but is seldom studied.

Seasonal and latitudinal variations of surface fluxes at two Arctic terrestrial sites

NASA Astrophysics Data System (ADS)

Grachev, Andrey A.; Persson, P. Ola G.; Uttal, Taneil; Akish, Elena A.; Cox, Christopher J.; Morris, Sara M.; Fairall, Christopher W.; Stone, Robert S.; Lesins, Glen; Makshtas, Alexander P.; Repina, Irina A.

2017-11-01

This observational study compares seasonal variations of surface fluxes (turbulent, radiative, and soil heat) and other ancillary atmospheric/surface/permafrost data based on in-situ measurements made at terrestrial research observatories located near the coast of the Arctic Ocean. Hourly-averaged multiyear data sets collected at Eureka (Nunavut, Canada) and Tiksi (East Siberia, Russia) are analyzed in more detail to elucidate similarities and differences in the seasonal cycles at these two Arctic stations, which are situated at significantly different latitudes (80.0°N and 71.6°N, respectively). While significant gross similarities exist in the annual cycles of various meteorological parameters and fluxes, the differences in latitude, local topography, cloud cover, snowfall, and soil characteristics produce noticeable differences in fluxes and in the structures of the atmospheric boundary layer and upper soil temperature profiles. An important factor is that even though higher latitude sites (in this case Eureka) generally receive less annual incoming solar radiation but more total daily incoming solar radiation throughout the summer months than lower latitude sites (in this case Tiksi). This leads to a counter-intuitive state where the average active layer (or thaw line) is deeper and the topsoil temperature in midsummer are higher in Eureka which is located almost 10° north of Tiksi. The study further highlights the differences in the seasonal and latitudinal variations of the incoming shortwave and net radiation as well as the moderating cloudiness effects that lead to temporal and spatial differences in the structure of the atmospheric boundary layer and the uppermost ground layer. Specifically the warm season (Arctic summer) is shorter and mid-summer amplitude of the surface fluxes near solar noon is generally less in Eureka than in Tiksi. During the dark Polar night and cold seasons (Arctic winter) when the ground is covered with snow and air temperatures are sufficiently below freezing, the near-surface environment is generally stably stratified and the hourly averaged turbulent fluxes are quite small and irregular with on average small downward sensible heat fluxes and upward latent heat and carbon dioxide fluxes. The magnitude of the turbulent fluxes increases rapidly when surface snow disappears and the air temperatures rise above freezing during spring melt and eventually reaches a summer maximum. Throughout the summer months strong upward sensible and latent heat fluxes and downward carbon dioxide (uptake by the surface) are typically observed indicating persistent unstable (convective) stratification. Due to the combined effects of day length and solar zenith angle, the convective boundary layer forms in the High Arctic (e.g., in Eureka) and can reach long-lived quasi-stationary states in summer. During late summer and early autumn all turbulent fluxes rapidly decrease in magnitude when the air temperature decreases and falls below freezing. Unlike Eureka, a pronounced zero-curtain effect consisting of a sustained surface temperature hiatus at the freezing point is observed in Tiksi during fall due to wetter and/or water saturated soils.

[Change characteristics of soil moisture and nutrients in rain-fed winter wheat field under different fertilization modes in Southern Shanxi of China during summer fallow period].

PubMed

Li, Ting-Liang; Xie, Ying-He; Hong, Jian-Ping; Feng, Qian; Sun, Cheng-Hong; Wang, Zhi-Wei

2013-06-01

In 2009-2011, a field experiment was conducted in a rain-fed winter wheat field in Southern Shanxi of China to study the effects of different fertilization modes on the change characteristics of soil moisture and nitrate-N contents in 0-200 cm layer and of soil available phosphorus (Oslen-P) and potassium contents in 0-40 cm layer during summer fallow period (from June to September). Three fertilization modes were installed, i. e., conventional fertilization (CF), recommended fertilization (RF), and ridge film furrow planting (RFFP) combined with straw mulch. The results showed that the rainfall in summer fallow period could complement the consumed water in 0-200 cm soil layer in dryland wheat field throughout the growth season, and more than 94% of the water storage was in 0-140 cm soil layer, with the fallow efficiency ranged from 6% to 27%. The rainfall in summer fallow period caused the soil nitrate-N moving downward. 357-400 mm rainfall could make the soil nitrate-N leaching down to 100 cm soil layer, with the peak in 20-40 cm soil layer. Straw mulching or plastic film with straw mulch in summer fallow period could effectively increase the Oslen-P and available K contents in 0-40 cm soil layer, and the accumulative increment in three summer fallow periods was 16-45% and 36-49%, respectively. Among the three modes, the binary coverage mode of RFFP plus furrow straw mulching had the best effect in maintaining soil water and fertility. The accumulative water storage and mineral N in 0-200 cm soil layer in three summer fallow periods were up to 215 mm and 90 kg x hm(-2), and the accumulative Oslen-P and available K contents in plough layer were increased by 2.7 mg x kg(-1) and 83 mg x kg(-1), respectively, being significantly higher than those in treatments CF and RF. There were no significant differences in the change characteristics in the soil moisture and nutrients between treatments CF and RF.

Stable oxygen isotope analysis reveal vegetation influence on soil water movement and ecosystem water fluxes in a semi-arid oak woodland

NASA Astrophysics Data System (ADS)

Piayda, Arndt; Dubbert, Maren; Werner, Christiane; Cuntz, Matthias

2015-04-01

Mechanistically disentangling the role and function of vegetation within the hydrological cycle is one of the key questions in the interdisciplinary field of ecohydrology. The presence of vegetation can have various impacts on soil water relations: transpiration of active vegetation causes great water losses, rainfall is intercepted, soil evaporation can be reduced and infiltration, hydraulic redistribution and translatory flow might be altered. In drylands, covering around 40% of the global land surface, the carbon cycle is closely coupled to water availability due to (seasonal) droughts. Specifically savannah type ecosystems, which cover large areas worldwide, are, due to their bi-layered structure, very suitable to study the effects of distinct vegetation types on the ecosystem water cycle. Oxygen isotope signatures (δ18O) have been used to partition ecosystem evapotranspiration (ET ) because of the distinct isotopic compositions of water transpired by leaves relative to soil evaporated vapor. Recent developments in laser spectroscopy enable measurements of δ18O in the vapor phase with high temporal resolution in the field and bear a novel opportunity to trace water movement within the ecosystem. In the present study, the effects of distinct vegetation layers (i.e. trees and herbaceous vegetation) on soil water infiltration and redistribution as well as ecosystem water fluxes in a Mediterranean cork-oak woodland are disentangled. An irrigation experiment was carried out using δ18O labeled water to quantify the distinct effects of trees and herbaceous vegetation on 1) infiltration and redistribution of water in the soil profile and 2) to disentangle the effects of tree cover on the contribution of unproductive soil evaporation and understory transpiration to total ET . First results proof that stable δ18O isotopes measured onsite with laser spectroscopy is a valuable tool to trace water movement in the soil showing a much higher sensitivity than common TDR-type probes. It was possible to track soil water redistribution even beyond zero net water flux measured with TDR probes. Under shaded conditions beneath tree crowns, infiltration of precipitation reaches much deeper depths due to the limited radiation energy input and thus, reduced evaporative losses, compared to open areas between crowns. As a consequence, the isotopic enrichment back to initial conditions (as observed before the artificial precipitation event) was strongly delayed. Despite the higher water availability beneath tree crowns, transpiration of understory plants and soil evaporation rates were reduced compared to the open area due to the lack of energy. However, transpiration could be maintained much longer and at higher rates after the precipitation event then soil evaporation. These first results support previous findings at this site where a clear difference in understory plant community structure was observed. Beneath tree crowns, favorable water conditions enables a higher occurrence of grasses and nitrogen fixing forbs, whereas in between tree crowns drought adapted native species became dominant.

Linking Dynamics of the Near-surface Flow to Deeper Boundary Layer Forcing in the Nocturnal Boundary Layer

DTIC Science & Technology

2012-06-01

Kaimal and Finnigan (1994), modified) Figure 2.2 illustrates the evolution from unstable CBL to a nocturnal Stable Bound- ary Layer ( SBL ) in the absence...mixed layer acts as a cap for the SBL . The SBL persists through the night until sunrise when surface heating resumes and a new unstable layer begins...to form at the surface, gradually returning to a CBL. 7 2.2.1 Dynamics of the stable boundary layer Because the SBL is stably stratified, buoyancy

Subsurface phosphorus transport through a no-till field in the semi arid Palouse region

NASA Astrophysics Data System (ADS)

Norby, J. C.; Brooks, E. S.; Strawn, D. G.

2017-12-01

Excess application of fertilizers containing nitrogen and phosphorus for farming use has led to ongoing water quality issues in the United States. When these nutrients leave agronomic systems, and enter water bodies in large quantities, algal bloom and eutrophication can occur. Extensive studies focusing on phosphorus as a pollutant from agronomic systems have been conducted in the many regions of the United States; however, there has been a lack of studies completed in the semiarid Palouse region of eastern Washington and western Idaho. The goal of this research study was to better understand how no-till farm management has altered soil P temporally and the current availability for off-site transport of P throughout an artificially drained catchment at the Cook Agronomy Farm in Pullman, WA. We also attempted to determine the processes responsible for subsurface flow of phosphorus, specifically through preferential flow pathways. Dissolved reactive P (DRP)concentrations of subsurface drainage from a artificial drain exceeded TMDL threshold concentrations during numerous seasonal high flow events over the two-year study time frame. Soil analyses show a highly variable distribution of water-extractable P across the sub-catchment area and initial results suggest a translocation of P species deeper into the soil profile after implementing no-till practices in 1998. We hypothesized that a greater network of macropores from lack of soil disturbance allow for preferential flow of nutrient-laden water deeper into the subsurface and to the artificial drain system. Simulated flow experiments on soil cores from the study site showed large-scale macropore development, extreme variability in soil conductivity, and high P adsorption potential for the soils, suggesting a disconnect between P movement through macropore soil and subsurface drainage water rich in DRP at the artificial drain line outlet.

Distinct temperature sensitivity of soil carbon decomposition in forest organic layer and mineral soil

PubMed Central

Xu, Wenhua; Li, Wei; Jiang, Ping; Wang, Hui; Bai, Edith

2014-01-01

The roles of substrate availability and quality in determining temperature sensitivity (Q10) of soil carbon (C) decomposition are still unclear, which limits our ability to predict how soil C storage and cycling would respond to climate change. Here we determined Q10 in surface organic layer and subsurface mineral soil along an elevation gradient in a temperate forest ecosystem. Q10 was calculated by comparing the times required to respire a given amount of soil C at 15 and 25°C in a 350-day incubation. Results indicated that Q10 of the organic layer was 0.22–0.71 (absolute difference) higher than Q10 of the mineral soil. Q10 in both the organic layer (2.5–3.4) and the mineral soil (2.1–2.8) increased with decreasing substrate quality during the incubation. This enhancement of Q10 over incubation time in both layers suggested that Q10 of more labile C was lower than that of more recalcitrant C, consistent with the Arrhenius kinetics. No clear trend of Q10 was found along the elevation gradient. Because the soil organic C pool of the organic layer in temperate forests is large, its higher temperature sensitivity highlights its importance in C cycling under global warming. PMID:25270905

Enhanced biogeochemical cycling and subsequent reduction of hydraulic conductivity associated with soil-layer interfaces in the vadose zone

PubMed Central

Hansen, David J.; McGuire, Jennifer T.; Mohanty, Binayak P.

2013-01-01

Biogeochemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions, but are nonetheless critical to understanding chemical fate and transport. This study explored the effects of a soil layer on linked geochemical, hydrological, and microbiological processes. Three laboratory soil columns were constructed: a homogenized medium-grained sand, a homogenized organic-rich loam, and a sand-over-loam layered column. Upward and downward infiltration of water was evaluated during experiments to simulate rising water table and rainfall events respectively. In-situ collocated probes measured soil water content, matric potential, and Eh while water samples collected from the same locations were analyzed for Br−, Cl−, NO3−, SO42−, NH4+, Fe2+, and total sulfide. Compared to homogenous columns, the presence of a soil layer altered the biogeochemistry and water flow of the system considerably. Enhanced biogeochemical cycling was observed in the layered column over the texturally homogeneous soil columns. Enumerations of iron and sulfate reducing bacteria showed 1-2 orders of magnitude greater community numbers in the layered column. Mineral and soil aggregate composites were most abundant near the soil-layer interface; the presence of which, likely contributed to an observed order-of-magnitude decrease in hydraulic conductivity. These findings show that quantifying coupled hydrologic-biogeochemical processes occurring at small-scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale. Findings also provide justification for considering soil layering in contaminant fate and transport models because of its potential to increase biodegradation and/or slow the rate of transport of contaminants. PMID:22031578

Reorganization of vegetation, hydrology and soil carbon after permafrost degradation across heterogeneous boreal landscapes

USGS Publications Warehouse

Jorgenson, M. Torre; Harden, Jennifer; Kanevskiy, Mikhail; O'Donnell, Jonathan; Wickland, Kim; Ewing, Stephanie; Manies, Kristen; Zhuang, Qianlai; Shur, Yuri; Striegl, Robert G.; Koch, Joshua C.

2013-01-01

The diversity of ecosystems across boreal landscapes, successional changes after disturbance and complicated permafrost histories, present enormous challenges for assessing how vegetation, water and soil carbon may respond to climate change in boreal regions. To address this complexity, we used a chronosequence approach to assess changes in vegetation composition, water storage and soil organic carbon (SOC) stocks along successional gradients within four landscapes: (1) rocky uplands on ice-poor hillside colluvium, (2) silty uplands on extremely ice-rich loess, (3) gravelly–sandy lowlands on ice-poor eolian sand and (4) peaty–silty lowlands on thick ice-rich peat deposits over reworked lowland loess. In rocky uplands, after fire permafrost thawed rapidly due to low ice contents, soils became well drained and SOC stocks decreased slightly. In silty uplands, after fire permafrost persisted, soils remained saturated and SOC decreased slightly. In gravelly–sandy lowlands where permafrost persisted in drier forest soils, loss of deeper permafrost around lakes has allowed recent widespread drainage of lakes that has exposed limnic material with high SOC to aerobic decomposition. In peaty–silty lowlands, 2–4 m of thaw settlement led to fragmented drainage patterns in isolated thermokarst bogs and flooding of soils, and surface soils accumulated new bog peat. We were not able to detect SOC changes in deeper soils, however, due to high variability. Complicated soil stratigraphy revealed that permafrost has repeatedly aggraded and degraded in all landscapes during the Holocene, although in silty uplands only the upper permafrost was affected. Overall, permafrost thaw has led to the reorganization of vegetation, water storage and flow paths, and patterns of SOC accumulation. However, changes have occurred over different timescales among landscapes: over decades in rocky uplands and gravelly–sandy lowlands in response to fire and lake drainage, over decades to centuries in peaty–silty lowlands with a legacy of complicated Holocene changes, and over centuries in silty uplands where ice-rich soil and ecological recovery protect permafrost.

Impact of Residential Prairie Gardens on the Physical Properties of Urban Soil in Madison, Wisconsin.

PubMed

Johnston, Marie R; Balster, Nick J; Zhu, Jun

2016-01-01

Prairie gardens have become a common addition to residential communities in the midwestern United States because prairie vegetation is native to the region, requires fewer resources to maintain than turfgrass, and has been promoted to help remediate urban soil. Although prairie systems typically have deeper and more diverse root systems than traditional turfgrass, no one has tested the effect of this vegetation type on the physical properties of urban soil. We hypothesized that residential prairie gardens would yield lower soil bulk density (BD), lower penetration resistance (PR), greater soil organic matter (SOM), and greater saturated hydraulic conductivity () compared with turfgrass lawns. To test this hypothesis, we examined 12 residential properties in Madison, WI, where homeowners had established a prairie garden within their turfgrass lawn. Despite a consistent trend in the difference between vegetation types, no significant main effects were found (i.e., a difference between vegetation types when averaged over depth) for any of the four soil properties measured in this study. Differences were found with depth and depended on a significant interaction with vegetation type. At the surface depth (0-0.15 m), soil beneath prairie gardens had 10% lower mean BD, 15% lower mean PR, 25% greater level of SOM, and 33% greater compared with soil beneath the adjacent lawns. These differences were not detected at deeper sampling intervals of 0.15 to 0.30 m and 0.30 to 0.45 m. Although not statistically significant, the consistent trend and direction among soil variables suggest that residential prairie gardens had changed the surface soil at a rate that marginally outpaced turfgrass and calls for controlled experiments to identify the mechanisms that might enhance these trends. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Influence of design variables on radiation hardness of silicon MINP solar cells

NASA Technical Reports Server (NTRS)

Anderson, W. A.; Solaun, S.; Rao, B. B.; Banerjee, S.

1985-01-01

Metal-insulator-N/P silicon (MINP) solar cells were fabricated using different substrate resistivity values, different N-layer designs, and different I-layer designs. A shallow junction into an 0.3 ohm-cm substrate gave best efficiency whereas a deeper junction into a 1 to 4 ohm-cm substrate gave improved radiation hardness. I-layer design variation did little to influence radiation hardness.

Controlled penetration of ceramides into and across the stratum corneum using various types of microemulsions and formulation associated toxicity studies.

PubMed

Sahle, Fitsum F; Wohlrab, Johannes; Neubert, Reinhard H H

2014-02-01

Several skin diseases such as psoriasis and atopic dermatitis are associated with the depletion or disturbance of stratum corneum (SC) lipids such as ceramides (CERs), free fatty acids and cholesterol. Studies suggested that replenishment of these lipids might help to treat diseased, affected or aged skin. With this premises in mind, there are some formulations in the market that contain SC lipids and currently, to facilitate permeation of the lipids deep into the SC, various CERs, and other SC lipid microemulsions (MEs) were developed and characterised using lecithin or TEGO® CARE PL 4 (TCPL4) as base surfactants. However, to date, there are no reports that involve the permeability of SC lipids into and across the SC, and therefore, the penetration of CER [NP] as a model ceramide from various formulations was investigated ex vivo using Franz diffusion cell. Besides, the toxicity of the MEs was assessed using hen's egg test chorioallantoic membrane (HET-CAM). The results of the study showed that CER [NP] could not permeate into deeper layers of the SC from a conventional hydrophilic cream. Unlike the cream, CER [NP] permeated into the deeper layers of the SC from both type of MEs, where permeation of the CER was more and into deeper layers from droplet type and lecithin-based MEs than bicontinuous (BC) type and TCPL4 based MEs, respectively. The CER also permeated into deeper layers from ME gels which was, however, shallow and to a lesser extent when compared with the MEs. The results of HET-CAM showed that both MEs are safe to be used topically, with lecithin-based MEs exhibiting better safety profiles than TCPL4 based MEs. Concluding, the study showed that the MEs are safe to be used on the skin for the controlled penetration of CER [NP] deep into the SC. Copyright © 2013 Elsevier B.V. All rights reserved.

Design and construction control guidance for chemically stabilized pavement base layers.

DOT National Transportation Integrated Search

2013-12-01

A laboratory and field study was conducted related to chemically stabilized pavement layers, which is also : referred to as soil-cement. Soil-cement practices within MDOT related to Class 9C soils used for base layers : were evaluated in this report....

Testing conceptual and physically based soil hydrology schemes against observations for the Amazon Basin

NASA Astrophysics Data System (ADS)

Guimberteau, M.; Ducharne, A.; Ciais, P.; Boisier, J. P.; Peng, S.; De Weirdt, M.; Verbeeck, H.

2014-06-01

This study analyzes the performance of the two soil hydrology schemes of the land surface model ORCHIDEE in estimating Amazonian hydrology and phenology for five major sub-basins (Xingu, Tapajós, Madeira, Solimões and Negro), during the 29-year period 1980-2008. A simple 2-layer scheme with a bucket topped by an evaporative layer is compared to an 11-layer diffusion scheme. The soil schemes are coupled with a river routing module and a process model of plant physiology, phenology and carbon dynamics. The simulated water budget and vegetation functioning components are compared with several data sets at sub-basin scale. The use of the 11-layer soil diffusion scheme does not significantly change the Amazonian water budget simulation when compared to the 2-layer soil scheme (+3.1 and -3.0% in evapotranspiration and river discharge, respectively). However, the higher water-holding capacity of the soil and the physically based representation of runoff and drainage in the 11-layer soil diffusion scheme result in more dynamic soil water storage variation and improved simulation of the total terrestrial water storage when compared to GRACE satellite estimates. The greater soil water storage within the 11-layer scheme also results in increased dry-season evapotranspiration (+0.5 mm d-1, +17%) and improves river discharge simulation in the southeastern sub-basins such as the Xingu. Evapotranspiration over this sub-basin is sustained during the whole dry season with the 11-layer soil diffusion scheme, whereas the 2-layer scheme limits it after only 2 dry months. Lower plant drought stress simulated by the 11-layer soil diffusion scheme leads to better simulation of the seasonal cycle of photosynthesis (GPP) when compared to a GPP data-driven model based on eddy covariance and satellite greenness measurements. A dry-season length between 4 and 7 months over the entire Amazon Basin is found to be critical in distinguishing differences in hydrological feedbacks between the soil and the vegetation cover simulated by the two soil schemes. On average, the multilayer soil diffusion scheme provides little improvement in simulated hydrology over the wet tropical Amazonian sub-basins, but a more significant improvement is found over the drier sub-basins. The use of a multilayer soil diffusion scheme might become critical for assessments of future hydrological changes, especially in southern regions of the Amazon Basin where longer dry seasons and more severe droughts are expected in the next century.

Multi-decadal time series of remotely sensed vegetation improves prediction of soil carbon in a subtropical grassland.

PubMed

Wilson, Chris H; Caughlin, T Trevor; Rifai, Sami W; Boughton, Elizabeth H; Mack, Michelle C; Flory, S Luke

2017-07-01

Soil carbon sequestration in agroecosystems could play a key role in climate change mitigation but will require accurate predictions of soil organic carbon (SOC) stocks over spatial scales relevant to land management. Spatial variation in underlying drivers of SOC, such as plant productivity and soil mineralogy, complicates these predictions. Recent advances in the availability of remotely sensed data make it practical to generate multidecadal time series of vegetation indices with high spatial resolution and coverage. However, the utility of such data largely is unknown, only having been tested with shorter (e.g., 1-2 yr) data summaries. Across a 2,000 ha subtropical grassland, we found that a long time series (28 yr) of a vegetation index (Enhanced Vegetation Index; EVI) derived from the Landsat 5 satellite significantly enhanced prediction of spatially varying SOC pools, while a short summary (2 yr) was an ineffective predictor. EVI was the best predictor for surface SOC (0-5 cm depth) and total measured SOC stocks (0-15 cm). The optimum models for SOC in the upper soil layer combined EVI records with elevation and calcium concentration, while deeper SOC was more strongly associated with calcium availability. We demonstrate how data from the open access Landsat archive can predict SOC stocks, a key ecosystem metric, and illustrate the rich variety of analytical approaches that can be applied to long time series of remotely sensed greenness. Overall, our results showed that SOC pools were closely coupled to EVI in this ecosystem, demonstrating that maintenance of higher average green leaf area is correlated with higher SOC. The strong associations of vegetation greenness and calcium concentration with SOC suggest that the ability to sequester additional SOC likely will rely on strategic management of pasture vegetation and soil fertility. © 2017 by the Ecological Society of America.

Short-chain chlorinated paraffins in the soils of two different Chinese cities: Occurrence, homologue patterns and vertical migration.

PubMed

Huang, Yumei; Chen, Laiguo; Feng, Yongbin; Ye, Zhixiang; He, Qiusheng; Feng, Qianhua; Qing, Xian; Liu, Ming; Gao, Bo

2016-07-01

Short-chain chlorinated paraffins (SCCPs) are candidate persistent organic pollutants (POPs) that are under review by the Stockholm Convention. China is currently the largest producer and consumer of chlorinated paraffins (CPs). To study the environmental behavior and fate of SCCPs in the soils of urban and suburban regions, the SCCP concentrations in 88 topsoils and 15 soil columns from land of different use types (e.g., woodland, vegetable field, paddy field and greenbelt) from Guangzhou and Chengdu have been determined. The SCCP concentrations in topsoils from Guangzhou (range: 1.45-25.5ngg(-1) dry weight (dw), average: 10.3ngg(-1) dw) were much higher than those from Chengdu (range: 0.218-3.26ngg(-1) dw, average: 1.43ngg(-1) dw). When compared to previously reported SCCP levels for topsoils from other areas, the SCCP concentrations measured in the present work were quite low. Much higher SCCP concentrations were observed in the greenbelt topsoils from Chengdu relative to the values measured from woodlands and vegetable and paddy fields. The composition profiles suggest that C10Cl6-10 and C11-13Cl6-8 were the major groups of SCCPs in topsoils from the woodlands and vegetable and paddy fields in Guangzhou and Chengdu. Vertical variations of the SCCP concentrations in the soil columns suggest that less chlorinated SCCPs (Cl5-6-SCCPs) are more capable of migrating to the deeper-layer soils than more chlorinated ones (Cl9-10-SCCPs). The SCCP concentrations displayed little dependence on organic matter (OM) for most topsoils (p>0.05), indicating that OM is not the controlling factor in the distribution of SCCPs in the soils. This study analyzed the occurrence, homologue patterns and vertical migration of SCCPs in the topsoils of two Chinese cities with different industrial structures and climate conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Carbon nitrogen ratio, δ13C, δ15N distribution in eroded and buried soil profiles along a small catena

NASA Astrophysics Data System (ADS)

Jakab, Gergely; Hegyi, István; Fullen, Michael; Szalai, Zoltán

2017-04-01

In addition to the serious environmental hazard soil erosion forms and reforms the soil surface. The intensity of these degrading and burial processes is highly variable, it fluctuates in time. One can only get a single view of the current status by the spatial analysis of soil depth and properties. Present study aims to estimate the dynamics of the former driving processes in detail those resulted the recent form of the landscape. Soil samples were taken along two intensively cultivated catenas from the surface to the parent material in vertical and from the ridge to the toe in horizontal direction. A non disturbed soil profile under continuous forest was also sampled as the initial, control status. Soil organic carbon (SOC), total nitrogen (TN), carbon nitrogen ratio (C/N), 13C and 15N stable isotope ratios were measured. Soil redistribution was supposed to be started right after the forest clearance 300 years before. Results indicated that the whole amount of solum (1 m) was taken by erosion in some local spots. Most of the soil loss was deposited at the toe, while vertical SOC and δ13C distributions (peaks) in the deposited profiles indicated the original soil surface at various depth. SOC peak in the profile indicated deeper in situ solum compared to the vertical peaks of the C/N and δ13C values. Presumably the layer of the highest SOC values in the sedimentation profiles is also formed by the deposition of initial soil loss from the upper parts of the catena. At this initial phase the selectivity of erosion was supposed to be quite effective for SOC that resulted the highest value. Therefore C/N and δ13C peaks fingerprint the original, in situ soil surface more adequately. The most effective erosion and deposition period was immediately after forest clearance. This emphasized that continuous tillage erosion had subordinate role compared to that of relief. Moreover, SOC erosion and burial in the present case was a sink in terms of mitigation of the atmospheric carbon content. G. Jakab was supported by the János Bolyai scholarship of the HAS, which is kindly acknowledged.

[Soil basal respiration and enzyme activities in the root-layer soil of tea bushes in a red soil].

PubMed

Yu, Shen; He, Zhenli; Zhang, Rongguang; Chen, Guochao; Huang, Changyong

2003-02-01

Soil basal respiration potential, metabolic quotient (qCO2), and activities of urease, invertase and acid phosphomonoesterase were investigated in the root-layer of 10-, 40-, and 90-yr-old tea bushes grown on the same type of red soil. The soil daily basal respiration potential ranged from 36.23 to 58.52 mg.kg-1.d-1, and the potentials in the root-layer of 40- or 90-yr-old were greater than that of 10-yr old tea bushes. The daily qCO2, ranging from 0.30 to 0.68, was in the reverse trend. The activities of test three enzymes changed differently with tea bushes' age. Urease activity in the root-layer of all age tea bushes ranged from 41.48 to 47.72 mg.kg-1.h-1 and slightly decreased with tea bushes' age. Invertase activity was 189.29-363.40 mg.kg-1.h-1 and decreased with tea bushes' age, but its activity in the root-layer of 10-year old tea bushes was significantly greater than that in the root-layer soil of 40- or 90-year old tea bushes. Acid phosphomonoesterase activity (444.22-828.32 mg.kg-1.h-1) increased significantly with tea bushes' age. Soil basal respiration potential, qCO2 and activities of 3 soil enzymes were closely related to soil pH, soil organic carbon, total nitrogen and C/N ratio, total soluble phenol, and microbial biomass carbon, respectively.

Spatial distribution of hydroxylamine and its role in aerobic N2O formation in a Norway spruce forest soil

NASA Astrophysics Data System (ADS)

Liu, S.; Weymann, D.; Gottselig, N.; Wiekenkamp, I.; Vereecken, H.; Brueggemann, N.

2014-12-01

Hydroxylamine (HA) as a crucial intermediate in the microbial oxidation of ammonium to nitrite (nitrification) is a potential precursor of abiotic N2O formation in the soil. However, the determination of HA concentration in natural soil samples has not been reported until now. Here, we determined the HA concentrations in organic (Oh) and mineral (Ah) layers of 135 soil samples collected from a spruce forest (Wüstebach, Eifel National Park, Germany) using a novel approach, based on the fast extraction of HA from the soil at a pH of 1.7, the oxidation of HA to N2O with Fe3+, and the analysis of produced N2O using gas chromatography (GC). Meanwhile, N2O emission rates were determined by means of aerobic laboratory incubations of 3-g soil in 22-mL vials. Subsequently, the spatial distribution of soil HA concentrations and N2O emission rates in the Oh and Ah layers of the whole sampling area were analyzed using a geostatistical approach. The correlations among soil HA, N2O emission rate, pH, soil C, N, Fe, Mn and soil water content (SWC) were further explored. The HA concentrations ranged from 0.3-44.6 μg N kg-1 dry soil and 0.02-16.2 μg N kg-1 dry soil in the Oh and the Ah layer, respectively. The spatial distribution of HA was similar in both layers, with substantial spatial variability dependent on soil type, tree density and distance to a stream. For example, HA concentration was greater at locations with a thick litter layer or at locations close to the stream. The average N2O emission rate in the Oh layer was 0.38 μg N kg-1 dry soil h-1, 10-fold larger than in the Ah layer. Interestingly, N2O emission rate exhibited high correlation with soil HA content in the Oh (R2 = 0.65, p < 0.01) and Ah (R2 = 0.45, p < 0.05) layer. The results demonstrated that HA is a crucial component for aerobic N2O formation and emission in spruce forest soils. Moreover, HA concentration was negatively correlated with pH and positively correlated with SWC in the Oh layer, while positively correlated with C and N as well as NO3- content in the Ah layer. Mn content was the most important factor for HA recovery at the specific extraction conditions. Further studies should focus on the effects of soil organic matter, Mn content, and pH on the production of N2O from HA under aerobic conditions.

[Nitrogen mineralization rate in different soil layers and its influence factors under plastic film mulched in Danjiangkou Reservoir area, China].

PubMed

Yu, Xing Xiu; Xui, Miao Miao; Zhao, Jin Hui; Zhang, Jia Peng; Wang, Wei; Guo, Ya Li; Xiao, Juan Hua

2018-04-01

The objective of this study was to investigate the rate of nitrogen mineralization in various soil layers (0-10, 10-20, and 20-30 cm) and its influencing factors under plastic film mulching ridge-furrow in a corn field of Wulongchi small watershed, Danjiangkou Reservoir Area. Results showed that the rate of soil ammonification decreased with soil depth during the entire maize growth period. The rate of nitrification in seedling, jointing, and heading stages decreased in the following order: 10-20 cm > 0-10 cm > 20-30 cm, while it increased with soil depth in maturation stage. The rate of soil nitrogen mineralization decreased with the increases in soil depth in the seedling, jointing and heading stages, whereas an opposite pattern was observed in maturation stage. Compared with non-filming, film mulching promoted the soil ammonification process in 0-10 cm and the soil nitrification and nitrogen mineralization processes in jointing, heading, and maturation stages in both 0-10 and 10-20 cm. However, the rates of soil nitrification and nitrogen mineralization under film mulching were much lower than those under non-filming in seedling stage. The stepwise regression analysis indicated that the main factors influencing soil nitrogen mineralization rate varied with soil depth. Soil moisture and total N content were the dominant controller for variation of soil nitrogen mineralization in 0-10 cm layer. Soil temperature, moisture, and total N content were dominant controller for that in 10-20 cm layer. Soil temperature drove the variation of soil nitrogen mineralization in 20-30 cm layer.

Should precipitation influence dust emission in global dust models?

NASA Astrophysics Data System (ADS)

Okin, Gregory

2016-04-01

Soil moisture modulates the threshold shear stress required to initiate aeolian transport and dust emission. Most of the theoretical and laboratory work that has confirmed the impact of soil moisture has appropriately acknowledged that it is the soil moisture of a surface layer a few grain diameters thick that truly controls threshold shear velocity. Global and regional models of dust emission include the effect of soil moisture on transport threshold, but most ignore the fact that only the moisture of the very topmost "active layer" matters. The soil moisture in the active layer can differ greatly from that integrated through the top 2, 5, 10, or 100 cm (surface layers used by various global models) because the top 2 mm of heavy texture soils dries within ~1/2 day while sandy soils dry within less than 2 hours. Thus, in drylands where dust emission occurs, it is likely that this top layer is drier than the underlying soil in the days and weeks after rain. This paper explores, globally, the time between rain events in relation to the time for the active layer to dry and the timing of high wind events. This analysis is carried out using the same coarse reanalyses used in global dust models and is intended to inform the soil moisture controls in these models. The results of this analysis indicate that the timing between events is, in almost all dust-producing areas, significantly longer than the drying time of the active layer, even when considering soil texture differences. Further, the analysis shows that the probability of a high wind event during the period after a rain where the surface is wet is small. Therefore, in coarse global models, there is little reason to include rain-derived soil moisture in the modeling scheme.

Neural responses of rat cortical layers due to infrared neural modulation and photoablation of thalamocortical brain slices

NASA Astrophysics Data System (ADS)

Jenkins, J. Logan; Kao, Chris C.; Cayce, Jonathan M.; Mahadevan-Jansen, Anita; Jansen, E. Duco

2017-02-01

Infrared neural modulation (INM) is a label-free method for eliciting neural activity with high spatial selectivity in mammalian models. While there has been an emphasis on INM research towards applications in the peripheral nervous system and the central nervous system (CNS), the biophysical mechanisms by which INM occurs remains largely unresolved. In the rat CNS, INM has been shown to elicit and inhibit neural activity, evoke calcium signals that are dependent on glutamate transients and astrocytes, and modulate inhibitory GABA currents. So far, in vivo experiments have been restricted to layers I and II of the rat cortex which consists mainly of astrocytes, inhibitory neurons, and dendrites from deeper excitatory neurons owing to strong absorption of light in these layers. Deeper cortical layers (III-VI) have vastly different cell type composition, consisting predominantly of excitatory neurons which can be targeted for therapies such as deep brain stimulation. The neural responses to infrared light of deeper cortical cells have not been well defined. Acute thalamocortical brain slices will allow us to analyze the effects of INS on various components of the cortex, including different cortical layers and cell populations. In this study, we present the use of photoablation with an erbium:YAG laser to reduce the thickness of the dead cell zone near the cutting surface of brain slices. This technique will allow for more optical energy to reach living cells, which should contribute the successful transduction of pulsed infrared light to neural activity. In the future, INM-induced neural responses will lead to a finer characterization of the parameter space for the neuromodulation of different cortical cell types and may contribute to understanding the cell populations that are important for allowing optical stimulation of neurons in the CNS.

[Soil moisture variation under different water and fertilization managements in apple orchard of Weibei dryland, China].

PubMed

Zhao, Zhi Yuan; Zheng, Wei; Liu, Jie; Ma, Peng Yi; Li, Zi Yan; Zhai, Bing Nian; Wang, Zhao Hui

2018-04-01

To evaluate the variations of soil moisture under different water and fertilizer treatments in apple orchard in the Weibei dryland, a field experiment was carried out in 2013-2016 at Tianjiawa Village, Baishui County, Shaanxi Province. There were three treatments, i.e., farmers traditional model (only addition of NPK chemical fertilizer, FM), extension model (swine manure and NPK chemical fertilizer combined with black plastic film in tree row space, EM), and optimized model (swine manure and NPK chemical fertilizer combined with black plastic film in tree row space and planting rape in the inter-row of apple trees, OM). The results showed that OM treatment significantly increased soil water storage capacity in 0-200 cm soil layer. Water content of 0-100 cm soil layer was increased by 5.6% and 15.3% in the dry season compared with FM and EM treatment, respectively. Moreover, the soil water relative deficit index of OM was lower than that of EM in 200-300 cm soil layer. The rainfall infiltration in the dry year could reach 300 cm depth under OM. Meanwhile, OM stabilized soil water content and efficiently alleviated the desiccation in deep soil layer. Compared with FM and EM, the 4-year average yield of OM was increased by 36.6% and 22.5%, respectively. In summary, OM could increase water use efficiency through increasing the contents of available soil water and improving the soil water condition in shallow and deep layers, which help alleviate the soil deficit in deep layer and increase yield.

Fine-scale Patterns in Thaw Depth, Micro-relief, and Ground Cover on Non-sorted Circles and Small Patterned Ground Features Along a Climatic Gradient From Low to High Arctic

NASA Astrophysics Data System (ADS)

Okie, J.; Gould, W. A.; González, G.

2006-12-01

Patterned ground is a ubiquitous feature in the Arctic and the related variation in microtopographic relief strongly affects biotic and abiotic patterns and processes. Patterned ground features are polygenic in origin and are often found superimposed in a complex pattern of multiple features. We investigated the relationship between thaw depth, micro-relief, the cover of vascular, bryophyte, cryptogamic crust and bare ground along transects traversing non-sorted circles and small non-sorted polygons at 8 research sites along a climatic gradient in bioclimatic subzones A-E in the North American Arctic. Non-sorted circles are the result of differential frost heave with circle centers typically showing greater heave during freezing than inter circle areas. Differential heave is a function of climate, soil texture, soil moisture, and vegetation cover. Differential heave and subsidence creates fine-scale gradients in microtopography that affect soil moisture, exposure to winds, and development of vegetation and soils. Non-sorted circles typically range from 20 to 200 cm in diameter and are most common in subzones C-E. Often superimposed on these features are the development of small non-sorted polygons 10-30 cm in diameter, and fine-scale desiccation cracking at a scale of less than 10 cm. These are most common in subzones A-C. We established three 20 m transects in zonal vegetation at each site. Thaw depth, micro-relief, and ground cover were measured at 10 cm intervals along each transect. Additionally, we measured vascular plant beta diversity in a set of 25 x 25 cm quadrates on 15 circles and 15 inter circles at each site. The resulting pattern of thaw depth and micro-relief is correlated with both summer temperatures and vegetation cover. The variability and degree of micro-relief decrease from the Low to the High Arctic. Non-sorted circle centers had deeper active layer than inter circle areas along the gradient. Thaw depths increase linearly with the degree of bare ground and nonlinearly with summer warmth. This unimodal pattern of shallower active layer at the warmest and coldest sites is due to the interaction of climate and the insulating vegetation layer. Greatest thaw depths are found on bare non-sorted circles in subzone C. Beta diversity is greatest in subzone D, where vegetated inter circle areas differ markedly from more barren non- sorted circles.

Vertical variation of a black soil's properties in response to freeze-thaw cycles and its links to shift of microbial community structure.

PubMed

Han, Ziming; Deng, Mingwen; Yuan, Anqi; Wang, Jiahui; Li, Hao; Ma, Jincai

2018-06-01

Soil freeze-thaw cycles (FTCs) change soil physical, chemical, and biological properties, however information regarding their vertical variations in response to FTCs is limited. In this work, black soil (silty loam) packed soil columns were exposed to 8 FTCs, and soil properties were determined for each of vertical layer of soil columns. The results revealed that after FTCs treatment, moisture and electrical conductivity (EC) salinity tended to increase in upper soil layers. Increments of ammonium nitrogen (NH 4 + -N) and nitrate nitrogen (NO 3 - -N) in top layers (0-10cm) were greater than those in other layers, and increments of water soluble organic carbon (WSOC) and decrease of microbial biomass carbon (MBC) in middle layers (10-20cm) were greater than those in both ends. Overall, microbial community structure was mainly influenced by soil physical properties (moisture and EC) and chemical properties (pH and WSOC). For bacterial (archaeal) and fungal communities, soil physical properties, chemical properties and their interaction explained 79.73% and 82.66% of total variation, respectively. Our results provided insights into the vertical variation of soil properties caused by FTCs, and such variation had a major impact on the change of structure and composition of soil bacterial and fungal communities. Copyright © 2017 Elsevier B.V. All rights reserved.

Experimental Investigation of Soil and Atmospheric Conditions on the Momentum, Mass, and Thermal Boundary Layers Above the Land Atmosphere Interface

NASA Astrophysics Data System (ADS)

Trautz, A.; Smits, K. M.; Illangasekare, T. H.; Schulte, P.

2014-12-01

The purpose of this study is to investigate the impacts of soil conditions (i.e. soil type, saturation) and atmospheric forcings (i.e. velocity, temperature, relative humidity) on the momentum, mass, and temperature boundary layers. The atmospheric conditions tested represent those typically found in semi-arid and arid climates and the soil conditions simulate the three stages of evaporation. The data generated will help identify the importance of different soil conditions and atmospheric forcings with respect to land-atmospheric interactions which will have direct implications on future numerical studies investigating the effects of turbulent air flow on evaporation. The experimental datasets generated for this study were performed using a unique climate controlled closed-circuit wind tunnel/porous media facility located at the Center for Experimental Study of Subsurface Environmental Processes (CESEP) at the Colorado School of Mines. The test apparatus consisting of a 7.3 m long porous media tank and wind tunnel, were outfitted with a sensor network to carefully measure wind velocity, air and soil temperature, relative humidity, soil moisture, and soil air pressure. Boundary layer measurements were made between the heights of 2 and 500 mm above the soil tank under constant conditions (i.e. wind velocity, temperature, relative humidity). The soil conditions (e.g. soil type, soil moisture) were varied between datasets to analyze their impact on the boundary layers. Experimental results show that the momentum boundary layer is very sensitive to the applied atmospheric conditions and soil conditions to a much less extent. Increases in velocity above porous media leads to momentum boundary layer thinning and closely reflect classical flat plate theory. The mass and thermal boundary layers are directly dependent on both atmospheric and soil conditions. Air pressure within the soil is independent of atmospheric temperature and relative humidity - wind velocity and soil moisture effects were observed. This data provides important insight into future work of accurately modeling the exchange processes associated with evaporation under various turbulent atmospheric conditions.

Relating results from earthworm toxicity tests to agricultural soil

USGS Publications Warehouse

Beyer, W.N.; Greig-Smith, P.W.

1992-01-01

The artificial soil tests of the European Economic Community and of the Organization for Economic Cooperation produce data relating earthworm mortality to pesticide concentrations in soil under laboratory conditions. To apply these results to agricultural soils it is necessary to relate these concentrations to amounts of pesticide applied per area. This paper reviews the relevant published literature and suggests a simple relation for regulatory use. Hazards to earthworms from pesticides are suggested to be greatest soon after application, when the pesticides may be concentrated in a soil layer a few millimeters thick. For estimating exposure of earthworms, however, a thicker soil layer should be considered, to account for their movement through soil. During favorable weather conditions, earthworms belonging to species appropriate to the artificial soil test have been reported to confine their activity to a layer about 5 cm. If a 5-cm layer is accepted as relevant for regulatory purposes, then an application of 1 kg/ha would be equivalent to 1-67 ppm (dry) in the artificial soil test.

Specific Features of Profile Distribution and Crystallochemistry of Phyllosilicates in Soils of the Cisbaikal Forest-Steppe

NASA Astrophysics Data System (ADS)

Chizhikova, N. P.; Gamzikov, G. P.; Chechetko, E. S.

2018-01-01

The mineralogical composition of agrogray, dark gray, and agro-dark gray soils (Luvic Greyzemic Retic Phaeozems); agro-dark gray residual-calcareous soils (Calcaric Cambic Phaeozems); clay-illuvial agrochernozems (Luvic Chernic Phaeozems); and agrochernozems with migrational-mycelial carbonates (Haplic Chernozems) developed in the forest-steppe of Central Siberia within the Irkutsk Depression has been studied. The clay (<1 μm) fraction separated from these soils consists of mixed-layer minerals with alternating layers of hydromica, smectite, vermiculite, and chlorite; the proportions between them change within the soil profiles. The clay fraction also contains hydromicas, kaolinite, chlorite, and some admixture of the fine-dispersed quartz. Each type of the soils is characterized by its own distribution pattern of clay material with specific alternation of layers in the mixed-layer formations. Mixed-layer minerals of the chlorite-vermiculite type predominate in the upper horizons of texture-differentiated soils. Down the soil profile, the content of mixed-layer mica-smectitic minerals increases. In the clay fraction of arable dark gray-humus soils with residual carbonates, the distribution of the clay fraction and major mineral phases in the soil profile is relatively even. An increased content of well-crystallized kaolinite is typical of these soils. The parent material of agrochernozems has a layered character: the upper horizons are generally depleted of clay, and the middle-profile and lower horizons are characterized by the considerable kaolinite content. In general, the clay material of soils of the Tulun-Irkutsk forest-steppe differs considerably from the clay material of foreststeppe soils developed from loesslike and mantle loams in the European part of Russia. In particular, this difference is seen in the proportions between major mineral phases and between biotitic and muscovitic components, as well as in the degree of crystallinity and behavior of kaolinite and chlorite.

Chemical characteristics of dissolved organic matter (DOM) in relation to heavy metal concentrations in soil water from boreal peatlands after clear-cut harvesting

NASA Astrophysics Data System (ADS)

Kiikkilä, O.; Nieminen, T.; Starr, M.; Ukonmaanaho, L.

2012-04-01

Boreal peatlands form an important terrestrial carbon reserve and are a major source of dissolved organic matter (DOM) to surface waters, particularly when disturbed through forestry practices such as draining or timber harvesting. Heavy metals show a strong affinity to organic matter and so, along with DOM, heavy metals can be mobilized and transported from the soil to surface waters and sediments where they may become toxic to aquatic organisms and pass up the food chain. The complexation of heavy metals with DOM can be expected to be related and determined by the chemical characteristics of DOM and oxidation/reducing conditions in the peat. We extracted interstitial water from peat samples and determined the concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and Al, Cu, Zn and Fe in various fractions of DOM isolated by adsorption properties (XAD-8 fractionation) and molecular-weight (ultrafiltration). The peat samples were taken from 0-30 and 30-50 cm depth in drained peatland catchments two years after whole-tree or stem-only clear-cut harvesting (Scots pine or Norway spruce) had been carried out. The samples from the upper layer had been subject to alternating saturation/aeration conditions while the deeper layer had been continuously under the water table. The fractionation of DOC and DON according to both adsorption properties and molecular-weight fractions clearly differed between the upper and lower peat layers. While the hydrophobic acid fraction contained proportionally more DOC and DON than the hydrophilic acid fraction in the upper peat layer the results were vice versa in the lower peat layer. High-molecular-weight compounds (> 100 kDa) were proportionally more abundant in the upper and low-molecular-weight compounds (< 1 kDa) in the lower peat layer. These differences are assumed to reflect differences in the aerobic/ anaerobic conditions and degree of decomposition between the two layers. The concentrations of Zn, Al, Fe and DON correlated positively with DOC concentrations whereas the concentration Cu did not correlate with DOC concentrations. Heavy metal concentrations in different molecular-weight fractions indicated that Al, Cu, Zn and Fe were mostly associated with high-molecular-weight compounds and only a small fraction existed as free metal ions in solution. There were no clear differences in the chemical characteristics of DOC or DON or heavy metal concentrations between the two harvesting treatments.

Occurrence of glyphosate and AMPA in an agricultural watershed from the southeastern region of Argentina.

PubMed

Lupi, Leonardo; Miglioranza, Karina S B; Aparicio, Virginia C; Marino, Damian; Bedmar, Francisco; Wunderlin, Daniel A

2015-12-01

Glyphosate (GLY) and AMPA concentrations were determined in sandy soil profiles, during pre- and post-application events in two agricultural soybean fields (S1 and S2). Streamwater and sediment samples were also analyzed. Post-application sampling was carried out one month later from the event. Concentrations of GLY+AMPA in surface soils (0-5 cm depth) during pre-application period showed values 20-fold higher (0.093-0.163 μg/g d.w.) than control area (0.005 μg/g d.w.). After application event soils showed markedly higher pesticide concentrations. A predominance of AMPA (80%) was observed in S1 (early application), while 34% in S2 for surface soils. GLY+AMPA concentrations decreased with depth and correlated strongly with organic carbon (r between 0.74 and 0.88, p<0.05) and pH (r between -0.81 and -0.76, p<0.001). The slight enrichment of pesticides observed from 25 cm depth to deeper layer, in addition to the alkaline pH along the profile, is of high concern about groundwater contamination. Sediments from pre-application period showed relatively lower pesticide levels (0.0053-0.0263 μg/g d.w.) than surface soil with a predominance of glyphosate, indicating a limited degradation. Levels of contaminants (mainly AMPA) in streamwater (ND-0.5 ng/mL) denote the low persistence of these compounds. However, a direct relationship in AMPA concentration was observed between sediment and streamwater. Despite the known relatively short half-life of glyphosate in soils, GLY+AMPA occurrence is registered in almost all matrices at different sampling times (pre- and post-application events). The physicochemical characteristics (organic carbon, texture, pH) and structure of soils and sediment in addition to the time elapsed from application determined the behavior of these contaminants in the environment. As a whole, the results warn us about vertical transport trough soil profile with the possibility of reaching groundwater. Copyright © 2015 Elsevier B.V. All rights reserved.

Seasonal variation in water uptake patterns of three plant species based on stable isotopes in the semi-arid Loess Plateau.

PubMed

Wang, Jian; Fu, Bojie; Lu, Nan; Zhang, Li

2017-12-31

Water is a limiting factor and significant driving force for ecosystem processes in arid and semi-arid areas. Knowledge of plant water uptake pattern is indispensable for understanding soil-plant interactions and species coexistence. The 'Grain for Green' project that started in 1999 in the Loess Plateau of China has led to large scale vegetation change. However, little is known about the water uptake patterns of the main plant species that inhabit in this region. In this study, the seasonal variations in water uptake patterns of three representative plant species, Stipa bungeana, Artemisia gmelinii and Vitex negundo, that are widely distributed in the semi-arid area of the Loess Plateau, were identified by using dual stable isotopes of δ 2 H and δ 18 O in plant and soil water coupled with a Bayesian mixing model MixSIAR. The soil water at the 0-120cm depth contributed 79.54±6.05% and 79.94±8.81% of the total water uptake of S. bungeana and A. gmelinii, respectively, in the growing season. The 0-40cm soil contributed the most water in July (74.20±15.20%), and the largest proportion of water (33.10±15.20%) was derived from 120-300cm soils in August for A. gmelinii. However, V. negundo obtained water predominantly from surface soil horizons (0-40cm) and then switched to deep soil layers (120-300cm) as the season progressed. This suggested that V. negundo has a greater degree of ecological plasticity as it could explore water sources from deeper soils as the water stress increased. This capacity can mainly be attributed to its functionally dimorphic root system. V. negundo may have a competitive advantage when encountering short-term drought. The ecological plasticity of plant water use needs to be considered in plant species selection and ecological management and restoration of the arid and semi-arid ecosystems in the Loess Plateau. Copyright © 2017 Elsevier B.V. All rights reserved.

Permafrost Thaw, Soil Moisture and Plant Community Change Alter Organic Matter Decomposition in Alaskan Tundra

NASA Astrophysics Data System (ADS)

Natali, S.; Mauritz, M.; Pegoraro, E.; Schuur, E.

2015-12-01

Climate warming in arctic tundra has been associated with increased plant productivity and a shift in plant community composition, specifically an increase in shrub cover, which can impact soil organic matter through changes in the size and composition of the leaf litter pool. Shifts in litter quantity and quality will in turn interact with changes in the soil environment as the climate continues to warm. We examined the effects of permafrost thaw, soil moisture changes, and plant community composition on leaf litter decomposition in an upland tundra ecosystem in Interior Alaska. We present warming and drying effects on decomposition rates of graminoid-dominated and shrub-dominated leaf litter mixtures over three years (2 cm depth), and annual decomposition of a common cellulose substrate (0-10 cm and 10-20 cm) over five years at a permafrost thaw and soil drying experiment. We expected that warming and drying would increase decomposition, and that decomposition would be greater in the shrub litter than in the graminoid litter mix. Decomposition of Betula nana, the dominant shrub, was 50% greater in the shrub-dominated litter mix compared to the graminoid-dominated litter. Surprisingly, there was no significant difference in total litter mass loss between graminoid and shrub litter mixtures, despite significant differences in decomposition rates of the dominant plant species when decomposed alone and in community mixtures. Drying decreased decomposition of B. nana and of the shrub community litter overall, but after two years there was no detected warming effect on shrub-community decomposition. In contrast to leaf litter decomposition, both warming and drying increased decomposition of the common substrate. Warming caused an almost twofold increase in cellulose decomposition in surface soil (0-10cm), and drying caused a twofold increase in cellulose decomposition from deeper organic layer soils (10-20cm). These results demonstrate the importance of interactions among temperature, moisture and vegetation changes on organic matter decomposition, and the potential for increased plant productivity and vegetation changes to alter the size and composition of the soil organic matter pool.

Organic layer serves as a hotspot of microbial activity and abundance in Arctic tundra soils.

PubMed

Lee, Seung-Hoon; Jang, Inyoung; Chae, Namyi; Choi, Taejin; Kang, Hojeong

2013-02-01

Tundra ecosystem is of importance for its high accumulation of organic carbon and vulnerability to future climate change. Microorganisms play a key role in carbon dynamics of the tundra ecosystem by mineralizing organic carbon. We assessed both ecosystem process rates and community structure of Bacteria, Archaea, and Fungi in different soil layers (surface organic layer and subsurface mineral soil) in an Arctic soil ecosystem located at Spitsbergen, Svalbard during the summer of 2008 by using biochemical and molecular analyses, such as enzymatic assay, terminal restriction fragment length polymorphism (T-RFLP), quantitative polymerase chain reaction (qPCR), and pyrosequencing. Activity of hydrolytic enzymes showed difference according to soil type. For all three microbial communities, the average gene copy number did not significantly differ between soil types. However, archaeal diversities appeared to differ according to soil type, whereas bacterial and fungal diversity indices did not show any variation. Correlation analysis between biogeochemical and microbial parameters exhibited a discriminating pattern according to microbial or soil types. Analysis of the microbial community structure showed that bacterial and archaeal communities have different profiles with unique phylotypes in terms of soil types. Water content and hydrolytic enzymes were found to be related with the structure of bacterial and archaeal communities, whereas soil organic matter (SOM) and total organic carbon (TOC) were related with bacterial communities. The overall results of this study indicate that microbial enzyme activity were generally higher in the organic layer than in mineral soils and that bacterial and archaeal communities differed between the organic layer and mineral soils in the Arctic region. Compared to mineral soil, peat-covered organic layer may represent a hotspot for secondary productivity and nutrient cycling in this ecosystem.

Influence of water table fluctuations on subsurface methane dynamics and surface fluxes in seasonally flooded subtropical pastures.

NASA Astrophysics Data System (ADS)

Chamberlain, S.; Gomez-Casanovas, N.; Boughton, E.; Keel, E.; Walter, M. T.; Groffman, P. M.; Sparks, J. P.

2015-12-01

Seasonally flooded subtropical pastures are major sources of methane (CH4), and periodic flooding drives complex emission dynamics from these ecosystems. Understanding the mechanisms of belowground CH4 dynamics driving soil surface fluxes is needed to better understand emissions from these systems and their response to environmental change. We investigated subsurface CH4 dynamics in relation to net surface fluxes using laboratory water table manipulations and compared these results to eddy covariance-measured fluxes to link within-soil CH4 dynamics to observed ecosystem fluxes. Pronounced hysteresis was observed in ecosystem CH4 fluxes during precipitation driven flooding events. This dynamic was replicated in mesocosm experiments, with maximum CH4 fluxes observed during periods of water table recession. Hysteresis dynamics were best explained by oxygen dynamics during precipitation recharge events and the oxidation of CH4 produced in organic soil horizons during water table recession. We observed distinct CH4 dynamics between surface organic and deeper mineral soil horizons. In surface organic soil horizons, high levels of CH4 production were temporally linked to observed surface emissions. In contrast, high concentrations of CH4 observed in deeper mineral soils did not contribute to surface fluxes. Methane production potentials in surface organic soils were orders of magnitude higher than in mineral soils, suggesting that over longer flooding regimes CH4 produced in mineral horizons is unlikely to be a significant component of net surface emissions. Our results demonstrate that distinct CH4 dynamics may be stratified by depth, and flooding of the near-surface organic soils drives the high magnitude CH4 fluxes observed from subtropical pastures. These results suggest that relatively small changes in pasture water table dynamics can drive large changes in net CH4 emissions if surface organic soils remain saturated over longer time scales.

Diversified cropping systems support greater microbial cycling and retention of carbon and nitrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, Alison E.; Hofmockel, Kirsten S.

2017-03-01

Diversifying biologically simple cropping systems often entails altering other management practices, such as tillage regime or nitrogen (N) source. We hypothesized that the interaction of crop rotation, N source, and tillage in diversified cropping systems would promote microbially-mediated soil C and N cycling while attenuating inorganic N pools. We studied a cropping systems trial in its 10th year in Iowa, USA, which tested a 2-yr cropping system of corn (Zea mays L.)/soybean [Glycine max (L.) Merr.] managed with conventional fertilizer N inputs and conservation tillage, a 3-yr cropping system of corn/soybean/small grain + red clover (Trifolium pratense L.), and amore » 4-yr cropping system of corn/soybean/small grain + alfalfa (Medicago sativa L.)/alfalfa. Three year and 4-yr cropping systems were managed with composted manure, reduced N fertilizer inputs, and periodic moldboard ploughing. We assayed soil microbial biomass carbon (MBC) and N (MBN), soil extractable NH4 and NO3, gross proteolytic activity of native soil, and potential activity of six hydrolytic enzymes eight times during the growing season. At the 0-20cm depth, native protease activity in the 4-yr cropping system was greater than in the 2-yr cropping system by a factor of 7.9, whereas dissolved inorganic N pools did not differ between cropping systems (P = 0.292). At the 0-20cm depth, MBC and MBN the 4-yr cropping system exceeded those in the 2-yr cropping system by factors of 1.51 and 1.57. Our findings suggest that diversified crop cropping systems, even when periodically moldboard ploughed, support higher levels of microbial biomass, greater production of bioavailable N from SOM, and a deeper microbially active layer than less diverse cropping systems.« less