Effect of soil type and moisture availability on the foraging behavior of the Formosan subterranean termite (Isoptera: Rhinotermitidae).

PubMed

Cornelius, Mary L; Osbrink, Weste L A

2010-06-01

This study examined the influence of soil type and moisture availability on termite foraging behavior. Physical properties of the soil affected both tunneling behavior and shelter tube construction. Termites tunneled through sand faster than top soil and clay. In containers with top soil and clay, termites built shelter tubes on the sides of the containers. In containers with sand, termites built shelter tubes directly into the air and covered the sides of the container with a layer of sand. The interaction of soil type and moisture availability affected termite movement, feeding, and survival. In assays with moist soils, termites were more likely to aggregate in top soil over potting soil and peat moss. However, termites were more likely to move into containers with dry peat moss and potting soil than containers with dry sand and clay. Termites were also significantly more likely to move into containers with dry potting soil than dry top soil. In the assay with dry soils, termite mortality was high even though termites were able to travel freely between moist sand and dry soil, possibly due to desiccation caused by contact with dry soil. Evaporation from potting soil and peat moss resulted in significant mortality, whereas termites were able to retain enough moisture in top soil, sand, and clay to survive for 25 d. The interaction of soil type and moisture availability influences the distribution of foraging termites in microhabitats.

Hydraulic redistribution in a Mediterranean wild olive-pasture ecosystem: A key to tree survival and a limit to tree-patch size.

NASA Astrophysics Data System (ADS)

Curreli, Matteo; Montaldo, Nicola; Oren, Ram

2017-04-01

In water-limited environments, such as certain Mediterranean ecosystems, trees may survive prolonged droughts by uptake of water by dimorphic root system: deep roots, growing vertically, and shallower lateral roots, extending beyond the crown projection of tree clumps into zones of seasonal vegetative cover. In such ecosystems, therefore, the balance between soil water under tree canopy versus that in treeless patches plays a crucial role on sustaining tree physiological performance and surface water fluxes during drought periods. The study has been performed at the Orroli site, Sardinia (Italy). The landscape is covered by patchy vegetation: wild olives trees in clumps, herbaceous species, drying to bare soil in late spring. The climate is Mediterranean maritime with long droughts from May to October, and an historical mean yearly rain of about 670 mm concentrated in the autumn and winter months. Soil depth varies from 10 to 50 cm, with underlying fractured rocky layer of basalt. From 2003, a 10 meters micrometeorological tower equipped with eddy-covariance system has been used for measuring water and energy surface fluxes, as well as key state variables (e.g. leaf and soil skin temperature, radiations, air humidity and wind velocity). Soil moisture was measured with five soil water reflectometers (two below the olive canopy and three in patches with pasture vegetation alternating with bare soil in the dry season). Early analyses show that wild olive continue to transpire even as the soil dries and the pasture desiccates. In 2015, to estimate plant water use and in the context of soil water dynamic, 33 Granier-type thermal dissipation probes were installed for estimating sap flow in stems of wild olives trees, 40 cm aboveground, in representative trees over the eddy-covariance foot-print. The combined data of sap flow, soil water content, and eddy covariance, revealed hydraulic redistribution system through the plant and the soil at different layers, allowing to quantify the reliance of the system on different horizontally and vertically differentiated soil compartments. Results shows that during light hours, until transpiration decreases in midday, shallow roots uptake deplete the water content in the upper layer. As transpiration decreases, hydraulically redistributed water provides for both transpiration of wild olives and recharge of shallow soil layers. This buffering, attained by long recharge time of shallow soil, allow woody vegetation to remain physiologically active during very dry conditions. The hydraulically redistributed water is the main source of water for evapotranspiration in the dry summer, and its relevance increases with decreasing water availability. Thus, the spatial coverage and distribution of tree clumps is regulated by the soil water available in the inter-tree clump areas, suggesting that, if Mediterranean areas dry as predicted by IPCC, the proportion of an area occupied by tree clumps will shrink in the future, with predictable consequences to ecosystem services.

Ecohydrology of the wetland-forestland interface: hydrophobicity in leaf litter and its potential effect on surface evaporation

NASA Astrophysics Data System (ADS)

Probert, Samantha; Kettridge, Nicholas; Devito, Kevin; Hurley, Alexander

2017-04-01

Riparian wetlands represent an important ecotone at the interface of peatlands and forests within the Western Boreal Plain of Canada. Water storage and negative feedbacks to evaporation in these systems is crucial for the conservation and redistribution of water during dry periods and providing ecosystem resilience to disturbance. Litter cover can alter the relative importance of the physical processes that drive soil evaporation. Negative feedbacks to drying are created as the hydrophysical properties of the litter and soil override atmospheric controls on evaporation in dry conditions, subsequently dampening the effects of external forcings on the wetland moisture balance. In this study, water repellency in leaf litter has been shown to significantly correlate with surface-atmosphere interactions, whereby severely hydrophobic leaf litter is linked to the highest surface resistances to evaporation, and therefore lowest instantaneous evaporation. Decreasing moisture is associated with increasing hydrophobicity, which may reduce the evaporative flux further as the dry hydrophobic litter creates a hydrological disconnect between soil moisture and the atmosphere. In contrast, hydrophilic litter layers exhibited higher litter moistures, which is associated with reduced resistances to evaporation and enhanced evaporative fluxes. Water repellency of the litter layer has a greater control on evaporation than the presence or absence of litter itself. Litter removal had no significant effect on instantaneous evaporation or surface resistance to evaporation except under the highest evaporation conditions, where litter layers produced higher resistance values than bare peat soils. However, litter removal modified the dominant physical controls on evaporation: moisture loss in plots with leaf litter was driven by leaf and soil hydrophysical properties. Contrastingly, bare peat soils following litter removal exhibited cooler, wetter surfaces and were more strongly correlated to atmospheric controls. The interaction between evaporation, hydrophobicity and moisture of the soil surface, or litter, presents a potentially significant negative feedback to drying across wetland-forestland interfaces.

7 CFR 457.135 - Onion crop insurance provisions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... avoirdupois. Lifting or digging. A pre-harvest process in which the onion roots are severed from the soil and the onion bulbs laid on the surface of the soil for drying in the field. Non-storage onions. Onions of... dried to a lower moisture content, are firmer, have more outer layers of paper-like skin, and are darker...

7 CFR 457.135 - Onion crop insurance provisions.

Code of Federal Regulations, 2014 CFR

2014-01-01

... avoirdupois. Lifting or digging. A pre-harvest process in which the onion roots are severed from the soil and the onion bulbs laid on the surface of the soil for drying in the field. Non-storage onions. Onions of... dried to a lower moisture content, are firmer, have more outer layers of paper-like skin, and are darker...

7 CFR 457.135 - Onion crop insurance provisions.

Code of Federal Regulations, 2011 CFR

2011-01-01

... digging. A pre-harvest process in which the onion roots are severed from the soil and the onion bulbs laid on the surface of the soil for drying in the field. Non-storage onions. Generally of a Bermuda... that are harvested as a bulb and dried to a lower moisture content, are firmer, have more outer layers...

7 CFR 457.135 - Onion crop insurance provisions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... digging. A pre-harvest process in which the onion roots are severed from the soil and the onion bulbs laid on the surface of the soil for drying in the field. Non-storage onions. Generally of a Bermuda... that are harvested as a bulb and dried to a lower moisture content, are firmer, have more outer layers...

Nitrate retention capacity of milldam-impacted legacy sediments and relict A horizon soils

NASA Astrophysics Data System (ADS)

Weitzman, Julie N.; Kaye, Jason P.

2017-05-01

While eutrophication is often attributed to contemporary nutrient pollution, there is growing evidence that past practices, like the accumulation of legacy sediment behind historic milldams, are also important. Given their prevalence, there is a critical need to understand how N flows through, and is retained in, legacy sediments to improve predictions and management of N transport from uplands to streams in the context of climatic variability and land-use change. Our goal was to determine how nitrate (NO3-) is cycled through the soil of a legacy-sediment-strewn stream before and after soil drying. We extracted 10.16 cm radius intact soil columns that extended 30 cm into each of the three significant soil horizons at Big Spring Run (BSR) in Lancaster, Pennsylvania: surface legacy sediment characterized by a newly developing mineral A horizon soil, mid-layer legacy sediment consisting of mineral B horizon soil and a dark, organic-rich, buried relict A horizon soil. Columns were first preincubated at field capacity and then isotopically labeled nitrate (15NO3-) was added and allowed to drain to estimate retention. The columns were then air-dried and subsequently rewet with N-free water and allowed to drain to quantify the drought-induced loss of 15NO3- from the different horizons. We found the highest initial 15N retention in the mid-layer legacy sediment (17 ± 4 %) and buried relict A soil (14 ± 3 %) horizons, with significantly lower retention in the surface legacy sediment (6 ± 1 %) horizon. As expected, rewetting dry soil resulted in 15N losses in all horizons, with the greatest losses in the buried relict A horizon soil, followed by the mid-layer legacy sediment and surface legacy sediment horizons. The 15N remaining in the soil following the post-drought leaching was highest in the mid-layer legacy sediment, intermediate in the surface legacy sediment, and lowest in the buried relict A horizon soil. Fluctuations in the water table at BSR which affect saturation of the buried relict A horizon soil could lead to great loses of NO3- from the soil, while vertical flow through the legacy-sediment-rich soil profile that originates in the surface has the potential to retain more NO3-. Restoration that seeks to reconnect the groundwater and surface water, which will decrease the number of drying-rewetting events imposed on the relict A horizon soils, could initially lead to increased losses of NO3- to nearby stream waters.

The Ups and Downs of Rhizosphere Resource Exchange

NASA Astrophysics Data System (ADS)

Cardon, Z. G.; Fu, C.; Wang, G.; Stark, J.

2014-12-01

Hydraulic redistribution (HR) of soil water by plants occurs in seasonally dry ecosystems worldwide. During HR, soil water flows from wet soil into roots, through the root system, and out of roots into dry rhizosphere soil. Hydraulic redistribution affects plant physiology and landscape hydrology, and it has long been hypothesized that upward HR of deep water to dry, nutrient-rich surface soil may also stimulate soil nutrient cycling and thus enhance nutrient availability to plants in the field. We report results from a sagebrush-steppe field experiment in northern Utah, USA, showing that stimulation of sagebrush-mediated HL increased rates of nitrogen cycling in the surface soil layer around shrubs at summer's end, and more than quadrupled uptake of nitrogen into developing sagebrush inflorescences. We have built on these empirical data by folding Ryel et al.'s (2002) HR formulation into CLM4.5 and examining how well the combined model can simultaneously simulate measured evapotranspiration, the vertical profile of soil moisture, and the amplitude of HR-associated diel changes in water content, at multiple seasonally-dry Ameriflux sites: Wind River Crane (US-Wrc), Southern California Climate Gradient (US-SCs,g,f,w,d,&c), and Santa Rita Mesquite Savanna (US-SRM). The simulated hydraulic lift during the dry periods has an average value in the range from 0.09 (at US-SCc) to 0.64 (at US-SCf) mm H2O d-1. In many cases, the combined model reproduced seasonal and daily (diel) observations with reasonable accuracy. Among the many model parameters tested, the Clapp and Hornberger parameter "B" in CLM4.5 was critical for a realistic simulation of soil moisture. Modeled HR was also sensitive to the maximum radial soil-root conductance and the soil water potential where that conductance is reduced by 50%. Our next step is to explore how modeled carbon and nutrient cycling in soil layers are affected by redistributed water in the soil column caused by inclusion of HR in CLM4.5.

[Effects of nitrogen application rate on light interception and dry matter distribution at diffe-rent layers in wheat canopy under supplemental irrigation based on measuring soil moisture.

PubMed

Zheng, Xue Jiao; Yu, Zhen Wen; Zhang, Yong Li; Shi, Yu

2018-02-01

With the large-spike wheat cultivar Shannong 23 as test material,a field experiment was conducted by increasing the relative soil moisture content to 70% and 65% at jointing and anthesis stages. Four nitrogen levels,0 (N 0 ), 180 (N 1 ), 240 (N 2 ) and 300 kg·hm -2 (N 3 ), were designed to examine the effects of nitrogen application rates on the interception of photosynthetic active radiation (PAR) and dry matter distribution of wheat at different canopy layers. The results showed that the total stem number of wheat population at anthesis stage, the leaf area index at 10, 20 and 30 days after anthesis, PAR capture ratio at upper and middle layers and total PAR capture ratio in wheat canopy on day 20 after anthesis of treatment N 2 were significantly higher than those in the treatments of both N 0 and N 1 . Those indexes showed no significant increase when the application rate increased to 300 kg·hm -2 (N 3 ). The vegetative organ dry matter accumulation of all layers at maturity stage of treatment N 2 were significantly higher than N 0 and N 1 . Compared with treatment N 0 and N 1 , N 2 increased the grain and total dry matter accumulation by 36.7% and 35.4%, 9.5% and 10.2%, respectively, but had no significant difference with treatment N 3 . The vegetative organ dry matter accumulation at all layers, grain and total dry matter accumulation were significantly and positively correlated with PAR capture ratio at upper and middle layers, and had no significant correlation with that at lower layer. The vegetative organ dry matter accumulation at all layers was significantly and positively correlated with grain dry matter accumulation. The application rate at 240 kg·hm -2 (N 2 ) would be the optimum treatment under the present experimental condition.

[Characteristics of floor litter and soil arthropod community in different types ot subtropical forest in Ailao Mountain of Yunnan, Southwest China].

PubMed

Yang, Zhao; Yang, Xiao-Dong

2011-11-01

By using line transect method, an investigation was conducted on the floor litter and soil arthropod community in a mid mountain wet evergreen broad-leaved forest, a mossy dwarf forest, and a Populus bonatii forest in Ailao Mountain of Yunnan in April (dry and hot season), June (rainy season), and December (dry and cold season), 2005. In both dry and rainy seasons, the existing floor litter mass, C storage, and C/N ratio in the three forests all increased in the order of mossy dwarf forest > P. bonatii forest > evergreen broad-leaved forest, but the N storage had less difference. In the floor litter layer of the forests, Acari and Collembola were the dominant groups of soil arthropod community, while Diptera larvae, Coleoptera, ants, and Homoptera were the common groups. The Sorenson coefficients of soil arthropod community in the three forests were extremely great. No significant differences were observed in the soil arthropod density (ind x m(-2)) in the floor litter layer among the three forests, but the relative density (ind x g(-1)) of soil arthropods was higher in the evergreen broad-leaved forest and P. bonatii forest than in the mossy dwarf forest. In the three forests, the density of soil arthropods was significantly higher in dry season than in rainy season, but the Shannon diversity index had less difference. There were significant positive correlations between the existing floor litter mass and the individual density (ind x m(-2)) and dominant groups of soil arthropod communities in dry and hot season (April), but negative correlations between the existing floor litter mass and the relative density (ind x g(-1)) of soil arthropod communities and Acari in dry and cold season (December). The individual densities of Collembola and Coleoptera also had positive correlations with the N storage of the existing floor litter mass in the three forests. It was considered that the floor litter and the development of soil arthropod community in the litter layer of the subtropical forests in Ailao Mountain had a close relation with the vegetation structure of the forests, and the individual density and the diversity of the soil arthropod community were controlled by the floor litter, whereas the environmental factors such as temperature and moisture in the forests also had obvious effects on the seasonal dynamics of the individual density of the soil arthropods.

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.

Rational Water and Nitrogen Management Improves Root Growth, Increases Yield and Maintains Water Use Efficiency of Cotton under Mulch Drip Irrigation

PubMed Central

Zhang, Hongzhi; Khan, Aziz; Tan, Daniel K. Y.; Luo, Honghai

2017-01-01

There is a need to optimize water-nitrogen (N) applications to increase seed cotton yield and water use efficiency (WUE) under a mulch drip irrigation system. This study evaluated the effects of four water regimes [moderate drip irrigation from the third-leaf to the boll-opening stage (W1), deficit drip irrigation from the third-leaf to the flowering stage and sufficient drip irrigation thereafter (W2), pre-sowing and moderate drip irrigation from the third-leaf to the boll-opening stage (W3), pre-sowing and deficit drip irrigation from the third-leaf to the flowering stage and sufficient drip irrigation thereafter (W4)] and N fertilizer at a rate of 520 kg ha-1 in two dressing ratios [7:3 (N1), 2:8 (N2)] on cotton root morpho-physiological attributes, yield, WUE and the relationship between root distribution and dry matter production. Previous investigations have shown a strong correlation between root activity and water consumption in the 40–120 cm soil layer. The W3 and especially W4 treatments significantly increased root length density (RLD), root volume density (RVD), root mass density (RMD), and root activity in the 40–120 cm soil layer. Cotton RLD, RVD, RMD was decreased by 13.1, 13.3, and 20.8%, respectively, in N2 compared with N1 at 70 days after planting (DAP) in the 0–40 cm soil layer. However, root activity in the 40–120 cm soil layer at 140 DAP was 31.6% higher in N2 than that in N1. Total RMD, RLD and root activity in the 40–120 cm soil were significantly and positively correlated with shoot dry weight. RLD and root activity in the 40–120 cm soil layer was highest in the W4N2 treatments. Therefore increased water consumption in the deep soil layers resulted in increased shoot dry weight, seed cotton yield and WUE. Our data can be used to develop a water-N management strategy for optimal cotton yield and high WUE. PMID:28611817

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.

Bryoid layer response to soil disturbance by fuel reduction treatments in a dry conifer forest

Treesearch

Amanda Hardman; Bruce McCune

2010-01-01

We investigated the response of the bryoid layer, bryophyte and lichen communities on the soil surface three years after fuel reduction treatment (logging and burning) in the central Blue Mountains of eastern Oregon. Both treatment and control areas had been decimated by spruce budworm and drought before the fuel reduction treatments. Treatments reduced overstory and...

Modeling soil moisture memory in savanna ecosystems

NASA Astrophysics Data System (ADS)

Gou, S.; Miller, G. R.

2011-12-01

Antecedent soil conditions create an ecosystem's "memory" of past rainfall events. Such soil moisture memory effects may be observed over a range of timescales, from daily to yearly, and lead to feedbacks between hydrological and ecosystem processes. In this study, we modeled the soil moisture memory effect on savanna ecosystems in California, Arizona, and Africa, using a system dynamics model created to simulate the ecohydrological processes at the plot-scale. The model was carefully calibrated using soil moisture and evapotranspiration data collected at three study sites. The model was then used to simulate scenarios with various initial soil moisture conditions and antecedent precipitation regimes, in order to study the soil moisture memory effects on the evapotranspiration of understory and overstory species. Based on the model results, soil texture and antecedent precipitation regime impact the redistribution of water within soil layers, potentially causing deeper soil layers to influence the ecosystem for a longer time. Of all the study areas modeled, soil moisture memory of California savanna ecosystem site is replenished and dries out most rapidly. Thus soil moisture memory could not maintain the high rate evapotranspiration for more than a few days without incoming rainfall event. On the contrary, soil moisture memory of Arizona savanna ecosystem site lasts the longest time. The plants with different root depths respond to different memory effects; shallow-rooted species mainly respond to the soil moisture memory in the shallow soil. The growing season of grass is largely depended on the soil moisture memory of the top 25cm soil layer. Grass transpiration is sensitive to the antecedent precipitation events within daily to weekly timescale. Deep-rooted plants have different responses since these species can access to the deeper soil moisture memory with longer time duration Soil moisture memory does not have obvious impacts on the phenology of woody plants, as these can maintain transpiration for a longer time even through the top soil layer dries out.

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.

Analysis of radiocaesium in the Lebanese soil one decade after the Chernobyl accident.

PubMed

El Samad, O; Zahraman, K; Baydoun, R; Nasreddine, M

2007-01-01

Fallout from the Chernobyl reactor accident due to the transport of a radioactive cloud over Lebanon in the beginning of May 1986 was studied 12 years after the accident for determining the level of (137)Cs concentration in soil. Gamma spectroscopy measurements were performed by using coaxial high sensitivity HPGe detectors. More than 90 soil samples were collected from points uniformly distributed throughout the land of Lebanon in order to evaluate their radioactivity. The data obtained showed a relatively high (137)Cs activity per surface area contamination, up to 6545Bqm(-2) in the top soil layer 0-3cm. The average activity of (137)Cs in the top soil layer 0-3cm in depth was 59.7Bqkg(-1) dry soil ranging from 15 to 119Bqkg(-1) dry soil. The horizontal variability was found to be about 45% between the sampling sites. The depth distribution of total (137)Cs activity in soil showed an exponential decrease. Estimation of the annual effective dose due to external radiation from (137)Cs contaminated soil for selected sites gave values ranging from 19.3 to 91.6 micro Svy(-1).

Antisoiling Coatings for Solar-Energy Devices

NASA Technical Reports Server (NTRS)

Cuddihy, E. F.; Willis, P.

1986-01-01

Fluorocarbons resist formation of adherent deposits. Promising coating materials reduce soiling of solar photovoltaic modules and possibly solar thermal collectors. Contaminating layers of various degrees of adherence form on surfaces of devices, partially blocking incident solar energy, reducing output power. Loose soil deposits during dry periods but washed off by rain. New coatings help prevent formation of more-adherent, chemically and physically bonded layers rain alone cannot wash away.

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.

Differences on nitrogen availability in a soil amended with fresh, composted and thermally-dried sewage sludge.

PubMed

Tarrasón, D; Ojeda, G; Ortiz, O; Alcañiz, J M

2008-01-01

Anaerobically-digested sludge called fresh sludge (F), composted sludge (C) and thermally-drying sludge (T), all from the same batch, were applied to the surface of a calcareous Udic Calciustept with loamy texture. Dosage equivalent was 10 t ha(-1) of dry matter. The concentration of mineral nitrogen (ammonium and nitrate) in the soil was measured in order to estimate the effects of the post-treatments to which the different kinds of sewage sludge are subjected in relation to the availability of N in the surface layer of the soil. The most significant differences in NH(4)-N and NO(3)-N concentrations due to the transformation of the organic matter were observed during the first three weeks following soil amendment. Thermally-dried and composted sludge initially displayed higher concentrations of ammonium and nitrate in soil. Five months after the amendment, soil applied with fresh sludge showed the highest concentrations of NH(4)-N and NO(3)-N (6.1 and 36.6 mg kg(-1), respectively). It is clear that the processes of composting and thermal-drying influence the bioavailability of nitrogen from the different types of sewage sludge.

[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.

Linking hydraulic properties of fire-affected soils to infiltration and water repellency

USGS Publications Warehouse

Moody, John A.; David Kinner,; Xavier Úbeda,

2009-01-01

Heat from wildfires can produce a two-layer system composed of extremely dry soil covered by a layer of ash, which when subjected to rainfall, may produce extreme floods. To understand the soil physics controlling runoff for these initial conditions, we used a small, portable disk infiltrometer to measure two hydraulic properties: (1) near-saturated hydraulic conductivity, Kf and (2) sorptivity, S(θi), as a function of initial soil moisture content, θi, ranging from extremely dry conditions (θi < 0.02 cm3 cm−3) to near saturation. In the field and in the laboratory replicate measurements were made of ash, reference soils, soils unaffected by fire, and fire-affected soils. Each has a different degrees of water repellency that influences Kf and S(θi).Values of Kf ranged from 4.5 × 10−3 to 53 × 10−3 cm s−1 for ash; from 0.93 × 10−3 to 130 × 10−3 cm s−1 for reference soils; and from 0.86 × 10−3 to 3.0 × 10−3 cm s−1, for soil unaffected by fire, which had the lowest values of Kf. Measurements indicated that S(θi) could be represented by an empirical non-linear function of θi with a sorptivity maximum of 0.18–0.20 cm s−0.5, between 0.03 and 0.08 cm3 cm−3. This functional form differs from the monotonically decreasing non-linear functions often used to represent S(θi) for rainfall–runoff modeling. The sorptivity maximum may represent the combined effects of gravity, capillarity, and adsorption in a transitional domain corresponding to extremely dry soil, and moreover, it may explain the observed non-linear behavior, and the critical soil-moisture threshold of water repellent soils. Laboratory measurements of Kf and S(θi) are the first for ash and fire-affected soil, but additional measurements are needed of these hydraulic properties for in situ fire-affected soils. They provide insight into water repellency behavior and infiltration under extremely dry conditions. Most importantly, they indicate how existing rainfall–runoff models can be modified to accommodate a possible two-layer system in extremely dry conditions. These modified models can be used to predict floods from burned watersheds under these initial conditions.

The influence of pore-fluid in the soil on ground vibrations from a tunnel embedded in a layered half-space

NASA Astrophysics Data System (ADS)

Yuan, Zonghao; Cao, Zhigang; Boström, Anders; Cai, Yuanqiang

2018-04-01

A computationally efficient semi-analytical solution for ground-borne vibrations from underground railways is proposed and used to investigate the influence of hydraulic boundary conditions at the scattering surfaces and the moving ground water table on ground vibrations. The arrangement of a dry soil layer with varying thickness resting on a saturated poroelastic half-space, which includes a circular tunnel subject to a harmonic load at the tunnel invert, creates the scenario of a moving water table for research purposes in this paper. The tunnel is modelled as a hollow cylinder, which is made of viscoelastic material and buried in the half-space below the ground water table. The wave field in the dry soil layer consists of up-going and down-going waves while the wave field in the tunnel wall consists of outgoing and regular cylindrical waves. The complete solution for the saturated half-space with a cylindrical hole is composed of down-going plane waves and outgoing cylindrical waves. By adopting traction-free boundary conditions on the ground surface and continuity conditions at the interfaces of the two soil layers and of the tunnel and the surrounding soil, a set of algebraic equations can be obtained and solved in the transformed domain. Numerical results show that the moving ground water table can cause an uncertainty of up to 20 dB for surface vibrations.

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.

Effects of Gravel Mulch Properties and Thickness on Evaporation from Underlying Soil

NASA Astrophysics Data System (ADS)

Li, Z.; Smits, K. M.

2017-12-01

Evaporation is the process of mass and heat transfer between the atmosphere and the shallow subsurface, and it is critical to many natural and industrial applications. In arid areas with very little rainfall, gravel has been widely used as a mulch layer to suppress evaporation from the underlying soil. The properties of mulch layers have a significant effect on the evaporation process, and the effect of grain size and mulch thickness has been previously studied experimentally. However, there is debate on the effect of the gravel mulch hydraulic properties on the evaporation suppression and role of the gravel mulch layer just after precipitation has not been discussed. The goal of this work is to investigate in more depth the impact of the gravel mulch hydraulic properties and the thickness of the mulch layer on evaporation from underlying soil with the combination of experiments and theoretical models. For this work, we developed a fully coupled numerical model of layered porous media that solves for heat, liquid water and water vapor flux under both wet and dry soil conditions. Various mulch layers with different texture and thickness were employed in the numerical simulation to study the effect of the hydraulic properties and thickness on the underlying soil evaporation. The water and heat transport in the soil and across the soil-atmosphere interface were presented and analyzed. In addition, results from numerical simulations were also compared with a series of mulch layer experiments performed using bench-scale porous media tanks interfaced with an open-return wind tunnel. Results demonstrated that gravel mulch is effective in significantly delaying and suppressing evaporation from underlying soil, and the evaporation behavior varies from different mulch types and thicknesses. The reason for evaporation suppression is that the gravel mulch retards the evaporation from the underlying soil first, and then cuts the hydraulic connection between the drying front and the atmosphere. The delaying time and evaporation reduction increases with the decrease of the grain size and increase of the air entry value of the gravel mulch, in which the air entry value is the primary factor. Thicker mulch layers have a better performance in both retarding and preventing evaporation from the underlying soil.

Eucalyptus obliqua seedling growth in organic vs. mineral soil horizons

PubMed Central

Barry, Karen M.; Janos, David P.; Nichols, Scott; Bowman, David M. J. S.

2015-01-01

Eucalyptus obliqua, the most widespread timber tree in Tasmania, is a pioneer after fire which can eliminate the organic layer of forest soil, exposing the underlying mineral soil. We compared seedling growth, mycorrhiza formation, and mineral nutrient limitation in organic layer vs. mineral soil. We grew E. obliqua seedlings separately in pots of organic layer and mineral soil in a glasshouse. Additional treatments of organic soil only, involved fully crossed methyl-bromide fumigation and fertilization. Fertilization comprised chelated iron for 121 days after transplant (DAT) followed by soluble phosphorus. At 357 DAT, whole plant dry weight was three times greater in ambient organic than in mineral soil. In organic soil, fumigation halved ectomycorrhiza abundance and reduced seedling growth at 149 DAT, but by 357 DAT when negative effects of fumigation on seedling growth had disappeared, neither fumigation nor fertilization affected mycorrhiza abundance. Iron fertilization diminished seedling growth, but subsequent phosphorus fertilization improved it. E. obliqua seedlings grow much better in organic layer soil than in mineral soil, although phosphorus remains limiting. The prevalent forestry practice of burning to mineral soil after timber harvest exposes a poor growth medium likely only partially compensated by fire-induced mineral soil alterations. PMID:25750650

Impact of hydraulic redistribution on multispecies vegetation water use in a semi-arid ecosystem: An experimental and modeling synthesis

NASA Astrophysics Data System (ADS)

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

2017-12-01

A key challenge in critical zone science is to understand and predict the interaction between aboveground and belowground ecohydrologic processes. One of the links that facilitates the interaction is hydraulic redistribution (HR), a phenomenon by which roots serve as preferential pathways for water movement from wet to dry soil layers. We use a multi-layer canopy model in conjunction with experimental data to examine the influence of HR on eco-hydrologic processes, such as transpiration, soil evaporation, and soil moisture, which characterize the competitive and facilitative dynamics between velvet mesquite and understory bunchgrass. Both measured and simulated results show that hydraulic descent (HD) dominates sap flux during the wet monsoon season, whereas hydraulic lift (HL) occurs between precipitation events. About 17% of precipitation is absorbed as soil-moisture, with the rest of the precipitation returning to the atmosphere as evapotranspiration. In the wet season, 13% of precipitation is transferred to deep soil (>2m) through mesquite roots, and in the dry season, 9% of this redistributed water is transported back to shallow soil depth (<0.5m). Assuming water supplied through HR is well-mixed with moisture transported directly through the soil matrix and supports vegetation evapotranspiration, HR supports about 47% of mesquite transpiration and 9% of understory transpiration. Through modeling and experimental synthesis, this study demonstrates that in the dry land ecosystem of southwestern U.S., Mesquite exhibits competitive advantage over understory bunchgrass through HR.

Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelianagro-ecosystems

EPA Science Inventory

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 reticulat...

[Characteristics of soil moisture variation in different land use types in the hilly region of the Loess Plateau, China].

PubMed

Tang, Min; Zhao, Xi Ning; Gao, Xiao Dong; Zhang, Chao; Wu, Pu Te

2018-03-01

Soil water availability is a key factor restricting the ecological construction and sustainable land use in the loess hilly region. It is of great theoretical and practical significance to understand the soil moisture status of different land use types for the vegetation restoration and the effective utilization of land resources in this area. In this study, EC-5 soil moisture sensors were used to continuously monitor the soil moisture content in the 0-160 cm soil profile in the slope cropland, terraced fields, jujube orchard, and grassland during the growing season (from May to October) in the Yuanzegou catchment on the Loess Plateau, to investigate soil moisture dynamics in these four typical land use types. The results showed that there were differences in seasonal variation, water storage characteristics, and vertical distribution of soil moisture under different land use types in both the normal precipitation (2014) and dry (2015) years. The terraced fields showed good water retention capacity in the dry year, with the average soil moisture content of 0-60 cm soil layer in the growing season being 2.6%, 4.2%, and 1.8% higher than that of the slope cropland, jujube orchard, and grassland (all P<0.05). The water storage of 0-160 cm soil profile was 43.90, 32.08, and 18.69 mm higher than that of slope cropland, jujube orchard, and grassland, respectively. In the normal precipitation year, the average soil moisture content of 0-60 cm soil layer in jujube orchard in the growing season was 2.9%, 3.8%, and 4.5% lower than that of slope cropland, terraced fields, and grassland, respectively (all P<0.05). In the dry year, the effective soil water storage of 0-160 cm soil profile in the jujube orchard accounted for 35.0% of the total soil water storage. The grey relational grade between the soil moisture in the surface layer (0-20 cm) and soil moisture in the middle layer (20-100 cm) under different land use types was large, and the trend for the similarity degree of soil moisture variation followed terraced fields > grassland > slope cropland > jujube orchard. The slope cropland in this area could be transformed into terraced fields to improve the utilization of precipitation and promote the construction of ecological agriculture. Aiming at resolving the severe water shortage in the rain-fed jujube orchard for the sustainable development of jujube orchard in the loess hilly region, appropriate water management measures should be taken to reduce the water consumption of jujube trees and other inefficient water consumption.

[Review on water eco-environment in vegetation restoration in Loess Plateau].

PubMed

Hu, Liangjun; Shao, Mingan

2002-08-01

Water is the crucial factor influencing vegetation restoration and eco-environmental reconstruction in Loess Plateau region. In this paper, the previous studies on water eco-environment under vegetation construction were summarized from seven aspects, i.e., soil water resource, background of soil water, dynamics of soil water, dry soil layer, relationship between soil water and vegetarian productivity, classification of soil water position, and strategy for vegetation construction. Meanwhile, some problems in the relevant researches were pointed out and discussed.

40 CFR 63.461 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... the layer of air inside the solvent cleaning machine freeboard located above the solvent/air interface... speed from the initial loading of soiled or wet parts through the removal of the cleaned or dried parts... fresh unused solvent, recycled solvent, or used solvent that has been cleaned of soils (e.g., skimmed of...

40 CFR 63.461 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... the layer of air inside the solvent cleaning machine freeboard located above the solvent/air interface... speed from the initial loading of soiled or wet parts through the removal of the cleaned or dried parts... fresh unused solvent, recycled solvent, or used solvent that has been cleaned of soils (e.g., skimmed of...

40 CFR 63.461 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-07-01

... the layer of air inside the solvent cleaning machine freeboard located above the solvent/air interface... speed from the initial loading of soiled or wet parts through the removal of the cleaned or dried parts... fresh unused solvent, recycled solvent, or used solvent that has been cleaned of soils (e.g., skimmed of...

40 CFR 146.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... point before the waste fluids drain into the underlying soils. For a dry well, it is likely to be the.... Stratum (plural strata) means a single sedimentary bed or layer, regardless of thickness, that consists of... (Hydrocompaction); oxidation of organic matter in soils; or added load on the land surface. Subsurface fluid...

40 CFR 63.461 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... the layer of air inside the solvent cleaning machine freeboard located above the solvent/air interface... speed from the initial loading of soiled or wet parts through the removal of the cleaned or dried parts... fresh unused solvent, recycled solvent, or used solvent that has been cleaned of soils (e.g., skimmed of...

40 CFR 146.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... point before the waste fluids drain into the underlying soils. For a dry well, it is likely to be the.... Stratum (plural strata) means a single sedimentary bed or layer, regardless of thickness, that consists of... (Hydrocompaction); oxidation of organic matter in soils; or added load on the land surface. Subsurface fluid...

DRY–WET CYCLES INCREASE PESTICIDE RESIDUE RELEASE FROM SOIL

PubMed Central

Jablonowski, Nicolai David; Linden, Andreas; Köppchen, Stephan; Thiele, Björn; Hofmann, Diana; Burauel, Peter

2012-01-01

Soil drying and rewetting may alter the release and availability of aged pesticide residues in soils. A laboratory experiment was conducted to evaluate the influence of soil drying and wetting on the release of pesticide residues. Soil containing environmentally long-term aged (9–17 years) 14C-labeled residues of the herbicides ethidimuron (ETD) and methabenzthiazuron (MBT) and the fungicide anilazine (ANI) showed a significantly higher release of 14C activity in water extracts of previously dried soil compared to constantly moistened soil throughout all samples (ETD: p < 0.1, MBT and ANI: p < 0.01). The extracted 14C activity accounted for 44% (ETD), 15% (MBT), and 20% (ANI) of total residual 14C activity in the samples after 20 successive dry–wet cycles, in contrast to 15% (ETD), 5% (MBT), and 6% (ANI) in extracts of constantly moistened soils. In the dry–wet soils, the dissolved organic carbon (DOC) content correlated with the measured 14C activity in the aqueous liquids and indicated a potential association of DOC with the pesticide molecules. Liquid chromatography MS/MS analyses of the water extracts of dry–wet soils revealed ETD and MBT in detectable amounts, accounting for 1.83 and 0.01%, respectively, of total applied water-extractable parent compound per soil layer. These findings demonstrate a potential remobilization of environmentally aged pesticide residue fractions from soils due to abiotic stresses such as wet–dry cycles. Environ. Toxicol. Chem. 2012; 31: 1941–1947. © 2012 SETAC PMID:22782855

7 CFR 305.25 - Dry heat treatment schedules.

Code of Federal Regulations, 2010 CFR

2010-01-01

... minutes. Spread soil in layers 0.5 inches in depth to ensure uniform heat penetration. T412-a 248 15... Spread the ears of corn in single layers on slats or wire shelves. T303-c-1 212 1 hour. T303-d-1 180-200...

Aggregate Stability and Erodibility of Purple Soil on Sloping Farmland as affected by different Soil Thickness

NASA Astrophysics Data System (ADS)

Huang, Xinjun; Zhang, Qingwen; Chen, Shanghong; Dong, Yuequn; Xiao, Meijia; Hamed, Lamy Mamdoh Mohamed

2017-04-01

Soil thickness is basic limiting condition for purple soil, not only due to its effect on crop production, but also its effect on soil structure. Steady-state of soil thickness will be achieved over time, as result the soil aggregate which the key factor of soil erodibility can be enhanced as well. However, the effect of soil thickness on aggregates stability and the characteristics of soil erodibility in sloping land have not yet fully understood.A field survey was conducted in hilly area of Sichuan region located in southeast China to study the relationship between soil aggregate stability and soil erodibility on sloping farmland under different four thickness (100cm, 80cm, 60cm, 30cm) of purple soil. Based on two different sieving methods (Dry and Wet sieving), we analyzed soil aggregate stability and its effect on soil erodibility within depth of 0-30cm soil layers. The results indicated that: Water stable aggregate on sloping farmland was ranged between 37.9% to 58.6%, where it increased with increasing the soil thickness. Moreover, fractal dimension calculated from dry-sieving and wet-sieving was 2.06-2.49 and 2.70-2.85 respectively, where it decreased with decreasing the soil thickness. The overall soil erodibility was 0.05-1.00 and a negative significant correlation was found between soil aggregate stability and erodibility(P<0.01). Moreover, farmland with thick soil profile tended to be high in soil erodibility within the top soil layer (0-30cm). The results reveal that soil thickness can affect soil aggregate stability as well as erodibility. As soil thickness increased, the top soil became more stable and less erodible. Keywords：purple soil; soil thickness; soil aggregate；soil erodibility

Coordinating Chemical and Mineralogical Analyses of Antarctic Dry Valley Sediments as Potential Analogs for Mars

NASA Technical Reports Server (NTRS)

Patel, S. N.; Bishop, J. L.; Englert, P.; Gibson, E. K.

2015-01-01

The Antarctic Dry Valleys (ADV) provide a unique terrestrial analog for Martian surface processes as they are extremely cold and dry sedimentary environments. The surface geology and the chemical composition of the Dry Valleys that are similar to Mars suggest the possible presence of these soil-formation processes on Mars. The soils and sediments from Wright Valley, Antarctica were investigated in this study to examine mineralogical and chemical changes along the surface layer in this region and as a function of depth. Surface samples collected near Prospect Mesa and Don Juan Pond of the ADV were analyzed using visible/near-infrared (VNIR) and mid-IR reflectance spectroscopy and major and trace element abundances.

Wet-dry cycles impact DOM retention in subsurface soils

NASA Astrophysics Data System (ADS)

Olshansky, Yaniv; Root, Robert A.; Chorover, Jon

2018-02-01

Transport and reactivity of carbon in the critical zone are highly controlled by reactions of dissolved organic matter (DOM) with subsurface soils, including adsorption, transformation and exchange. These reactions are dependent on frequent wet-dry cycles common to the unsaturated zone, particularly in semi-arid regions. To test for an effect of wet-dry cycles on DOM interaction and stabilization in subsoils, samples were collected from subsurface (Bw) horizons of an Entisol and an Alfisol from the Catalina-Jemez Critical Zone Observatory and sequentially reacted (four batch steps) with DOM extracted from the corresponding soil litter layers. Between each reaction step, soils either were allowed to air dry (wet-dry treatment) before introduction of the following DOM solution or were maintained under constant wetness (continually wet treatment). Microbial degradation was the dominant mechanism of DOM loss from solution for the Entisol subsoil, which had higher initial organic C content, whereas sorptive retention predominated in the lower C Alfisol subsoil. For a given soil, bulk dissolved organic C losses from solution were similar across treatments. However, a combination of Fourier transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic analyses revealed that wet-dry treatments enhanced the interactions between carboxyl functional groups and soil particle surfaces. Scanning transmission X-ray microscopy (STXM) data suggested that cation bridging by Ca2+ was the primary mechanism for carboxyl association with soil surfaces. STXM data also showed that spatial fractionation of adsorbed OM on soil organo-mineral surfaces was diminished relative to what might be inferred from previously published observations pertaining to DOM fractionation on reaction with specimen mineral phases. This study provides direct evidence of the role of wet-dry cycles in affecting sorption reactions of DOM to a complex soil matrix. In the soil environment, where wet-dry cycles occur at different frequencies from site to site and along the soil profile, different interactions between DOM and soil surfaces are expected and need to be considered for the overall assessment of carbon dynamics.

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.

Observed Local Soil Moisture-Atmosphere Feedbacks within the Context of Remote SST Anomalies: Lessons From Recent Droughts

NASA Astrophysics Data System (ADS)

Tawfik, A. B.; Dirmeyer, P.; Lawrence, D. M.

2015-12-01

The existence and possible transition from positive to negative soil moisture-atmosphere feedbacks is explored in this presentation using collocated flux tower measurements (Ameriflux) and atmospheric profiles from reanalysis. The focus is on the series of physical processes that lead to these local feedbacks connecting remote sea surface temperature changes (SST anomalies) to local soil moisture and boundary layer responses. Seasonal and Agricultural droughts are particularly useful test beds for examining these feedback processes because they are typically characterized by prolonged stretches of rain-free days followed by some termination condition. To quantify the full process-chain across these distinct spatial scales, complimentary information from several well-established land-atmosphere coupling metrics are used including, but not limited to, Mixing Diagram approaches, Soil Moisture Memory, and the Heated Condensation Framework. Preliminary analysis shows that there may be transitions from negative and positive soil moisture-atmosphere feedbacks as droughts develop. This is largely instigated by persistent atmospheric forcing that initially promotes increased surface latent heat flux, which limits boundary layer depth and dry air entrainment. However, if stagnant synoptic conditions continue eventually soil moisture is depleted to the point of shutting off surface latent heat flux producing deep boundary layers and increased dry air entrainment thus deepening drought stress. A package of standardized Fortran 90 modules called the Coupling Metrics Toolkit (CoMeT; https://github.com/abtawfik/coupling-metrics) used to calculate these land-atmosphere coupling metrics is also briefly presented.

Stable annual pattern of water use by Acacia tortilis in Sahelian Africa.

PubMed

Do, Frederic C; Rocheteau, Alain; Diagne, Amadou L; Goudiaby, Venceslas; Granier, André; Lhomme, Jean-Paul

2008-01-01

Water use by mature trees of Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan var. raddiana growing in the northern Sahel was continuously recorded over 4 years. Water use was estimated from xylem sap flow measured by transient heat dissipation. Concurrently, cambial growth, canopy phenology, leaf water potential, climatic conditions and soil water availability (SWA) were monitored. In addition to the variation attributable to interannual variation in rainfall, SWA was increased by irrigation during one wet season. The wet season lasted from July to September, and annual rainfall ranged between 146 and 367 mm. The annual amount and pattern of tree water use were stable from year-to-year despite interannual and seasonal variations in SWA in the upper soil layers. Acacia tortilis transpired readily throughout the year, except for one month during the dry season when defoliation was at a maximum. Maximum water use of about 23 l (dm sapwood area)(-2) day(-1) was recorded at the end of the wet season. While trees retained foliage in the dry season, the decline in water use was modest at around 30%. Variation in predawn leaf water potential indicated that the trees were subject to soil water constraint. The rapid depletion of water in the uppermost soil layers after the wet season implies that there was extensive use of water from deep soil layers. The deep soil profile revealed (1) the existence of living roots at 25 m and (2) that the availability of soil water was low (-1.6 MPa) down to the water table at a depth of 31 m. However, transpiration was recorded at a predawn leaf water potential of -2.0 MPa, indicating that the trees used water from both intermediary soil layers and the water table. During the full canopy stage, mean values of whole-tree hydraulic conductance were similar in the wet and dry seasons. We propose that the stability of water use at the seasonal and annual scales resulted from a combination of features, including an extensive rooting habit related to deep water availability and an effective regulation of canopy conductance. Despite a limited effect on tree water use, irrigation during the wet season sharply increased predawn leaf water potential and cambial growth of trunks and branches.

Influence of smectite hydration and swelling on atrazine sorption behavior.

PubMed

Chappell, Mark A; Laird, David A; Thompson, Michael L; Li, Hui; Teppen, Brian J; Aggarwal, Vaneet; Johnston, Cliff T; Boyd, Stephen A

2005-05-01

Smectites, clay minerals commonly found in soils and sediments, vary widely in their ability to adsorb organic chemicals. Recent research has demonstrated the importance of surface charge density and properties of exchangeable cations in controlling the affinity of smectites for organic molecules. In this study, we induced hysteresis in the crystalline swelling of smectites to test the hypothesis that the extent of crystalline swelling (or interlayer hydration status) has a large influence on the ability of smectites to adsorb atrazine from aqueous systems. Air-dried K-saturated Panther Creek (PC) smectite swelled less (d(001) = 1.38 nm) than never-dried K-PC (d(001) = 1.7 nm) when rehydrated in 20 mM KCl. Correspondingly, the air-dried-rehydrated K-PC had an order of magnitude greater affinity for atrazine relative to the never-dried K-PC. Both air-dried-rehydrated and never-dried Ca-PC expanded to approximately 2.0 nm in 10 mM CaCl2 and both samples had similar affinities for atrazine that were slightly lower than that of never-dried K-PC. The importance of interlayer hydration status in controlling sorption affinity was confirmed by molecular modeling, which revealed much greater interaction between interlayer water molecules and atrazine in a three-layer hydrate relative to a one-layer hydrate. The entropy change on moving atrazine from a fully hydrated state in the bulk solution to a partially hydrated state in the smectite interlayers is believed to be a major factor influencing sorption affinity. In an application test, choice of background solution (20 mM KCl versus 10 mM CaCl2) and air-drying treatments significantly affected atrazine sorption affinities for three-smectitic soils; however, the trends were not consistent with those observed for the reference smectite. Further, extending the initial rehydration time from 24 to 240 h (prior to adding atrazine) significantly decreased the soil's sorption affinity for atrazine. We conclude that interlayer hydration status has a large influence on the affinity of smectites for atrazine and that air-drying treatments have the potential to modify the sorption affinity of smectitic soils for organic molecules such as atrazine.

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...

Hydraulic lift through transpiration suppression in shrubs from two arid ecosystems: patterns and control mechanisms.

PubMed

Prieto, Iván; Martínez-Tillería, Karina; Martínez-Manchego, Luis; Montecinos, Sonia; Pugnaire, Francisco I; Squeo, Francisco A

2010-08-01

Hydraulic lift (HL) is the passive movement of water through the roots from deep wet to dry shallow soil layers when stomata are closed. HL has been shown in different ecosystems and species, and it depends on plant physiology and soil properties. In this study we explored HL patterns in several arid land shrubs, and developed a simple model to simulate the temporal evolution and magnitude of HL during a soil drying cycle under relatively stable climatic conditions. This model was then used to evaluate the influence of soil texture on the quantity of water lifted by shrubs in different soil types. We conducted transpiration suppression experiments during spring 2005 in Chile and spring 2008 in Spain on five shrub species that performed HL, Flourensia thurifera, Senna cumingii and Pleocarphus revolutus (Chile), Retama sphaerocarpa and Artemisia barrelieri (Spain). Shrubs were covered with a black, opaque plastic fabric for a period of 48-72 h, and soil water potential was recorded at different depths under the shrubs. While the shrubs remained covered, water potential continuously increased in shallow soil layers until the cover was removed. The model output indicated that the amount of water lifted by shrubs is heavily dependent on soil texture, as shrubs growing in loamy soils redistributed up to 3.6 times more water than shrubs growing on sandy soils. This could be an important consideration for species growing in soils with different textures, as their ability to perform HL would be context dependent.

The Soil-Plant-Atmosphere System - Past and Present.

NASA Astrophysics Data System (ADS)

Berry, J. A.; Baker, I. T.; Randall, D. A.; Sellers, P. J.

2012-12-01

Plants with stomata, roots and a vascular system first appeared on earth about 415 million years ago. This evolutionary innovation helped to set in motion non-linear feedback mechanisms that led to an acceleration of the hydrologic cycle over the continents and an expansion of the climate zones favorable for plant (and animal) life. Skeletal soils that developed long before plants came onto the land would have held water and nutrients in their pore space, yet these resources would have been largely unavailable to primitive, surface-dwelling non-vascular plants due to physical limitations on water transport once the surface layer of soil dries. Plants with roots and a vascular system that could span this dry surface layer could gain increased and prolonged access to the water and nutrients stored in the soil for photosynthesis. Maintenance of the hydraulic connections permitting water to be drawn through the vascular system from deep in the soil to the sites of evaporation in the leaves required a cuticle and physiological regulation of stomata. These anatomical and physiological innovations changed properties of the terrestrial surface (albedo, roughness, a vascular system and control of surface conductance) and set in motion complex interactions of the soil - plant - atmosphere system. We will use coupled physiological and meteorological models to examine some of these interactions.

Patterns of nocturnal rehydration in root tissues of Vaccinium corymbosum L. under severe drought conditions

PubMed Central

Valenzuela-Estrada, Luis R.; Richards, James H.; Diaz, Andres; Eissensat, David M.

2009-01-01

Although roots in dry soil layers are commonly rehydrated by internal hydraulic redistribution during the nocturnal period, patterns of tissue rehydration are poorly understood. Rates of nocturnal rehydration were examined in roots of different orders in Vaccinium corymbosum L. ‘Bluecrop’ (Northern highbush blueberry) grown in a split-pot system with one set of roots in relatively moist soil and the other set of roots in dry soil. Vaccinium is noted for a highly branched and extremely fine root system. It is hypothesized that nocturnal root tissue rehydration would be slow, especially in the distal root orders because of their greater hydraulic constraints (smaller vessel diameters and fewer number of vessels). Vaccinium root hydraulic properties delayed internal water movement. Even when water was readily available to roots in the wet soil and transpiration was minimal, it took a whole night-time period of 12 h for the distal finest roots (1st to 4th order) under dry soil conditions to reach the same water potentials as fine roots in moist soil (1st to 4th order). Even though roots under dry soil equilibrated with roots in moist soil, the equilibrium point reached before sunrise was about –1.2 MPa, indicating that tissues were not fully rehydrated. Using a single-branch root model, it was estimated that individual roots exhibiting the lowest water potentials in dry soil were 1st order roots (distal finest roots of the root system). However, considered at the branch level, root orders with the highest hydraulic resistances corresponded to the lowest orders of the permanent root system (3rd-, 4th-, and 5th-order roots), thus indicating possible locations of hydraulic safety control in the root system of this species. PMID:19188275

Patterns of nocturnal rehydration in root tissues of Vaccinium corymbosum L. under severe drought conditions.

PubMed

Valenzuela-Estrada, Luis R; Richards, James H; Diaz, Andres; Eissensat, David M

2009-01-01

Although roots in dry soil layers are commonly rehydrated by internal hydraulic redistribution during the nocturnal period, patterns of tissue rehydration are poorly understood. Rates of nocturnal rehydration were examined in roots of different orders in Vaccinium corymbosum L. 'Bluecrop' (Northern highbush blueberry) grown in a split-pot system with one set of roots in relatively moist soil and the other set of roots in dry soil. Vaccinium is noted for a highly branched and extremely fine root system. It is hypothesized that nocturnal root tissue rehydration would be slow, especially in the distal root orders because of their greater hydraulic constraints (smaller vessel diameters and fewer number of vessels). Vaccinium root hydraulic properties delayed internal water movement. Even when water was readily available to roots in the wet soil and transpiration was minimal, it took a whole night-time period of 12 h for the distal finest roots (1st to 4th order) under dry soil conditions to reach the same water potentials as fine roots in moist soil (1st to 4th order). Even though roots under dry soil equilibrated with roots in moist soil, the equilibrium point reached before sunrise was about -1.2 MPa, indicating that tissues were not fully rehydrated. Using a single-branch root model, it was estimated that individual roots exhibiting the lowest water potentials in dry soil were 1st order roots (distal finest roots of the root system). However, considered at the branch level, root orders with the highest hydraulic resistances corresponded to the lowest orders of the permanent root system (3rd-, 4th-, and 5th-order roots), thus indicating possible locations of hydraulic safety control in the root system of this species.

Anisotropic capillary barrier for waste site surface covers

DOEpatents

Stormont, J.C.

1996-08-27

Waste sites are capped or covered upon closure. The cover structure incorporates a number of different layers each having a contributory function. One such layer is the barrier layer. Traditionally the barriers have been compacted soil and geosynthetics. These types of barriers have not been successfully implemented in unsaturated ground conditions like those found in dry climates. Capillary barriers have been proposed as barrier layers in dry environments, but the divergence length of these barriers has been found to be inadequate. An alternative to the capillary barrier is a anisotropic capillary barrier. An anisotropic capillary barrier has an increased divergence length which results in more water being diverted laterally preventing the majority of water from percolating in a downward direction through the barrier. 10 figs.

Anisotropic capillary barrier for waste site surface covers

DOEpatents

Stormont, John C.

1996-01-01

Waste sites are capped or covered upon closure. The cover structure incorporates a number of different layers each having a contributory function. One such layer is the barrier layer. Traditionally the barriers have been compacted soil and geosynthetics. These types of barriers have not been successfully implemented in unsaturated ground conditions like those found in dry climates. Capillary barriers have been proposed as barrier layers in dry environments, but the divergence length of these barriers has been found to be inadequate. An alternative to the capillary barrier is a anisotropic capillary barrier. An anisotropic capillary barrier has an increased divergence length which results in more water being diverted laterally preventing the majority of water from percolating in a downward direction through the barrier.

Divergent surface and total soil moisture projections under global warming

USGS Publications Warehouse

Berg, Alexis; Sheffield, Justin; Milly, Paul C.D.

2017-01-01

Land aridity has been projected to increase with global warming. Such projections are mostly based on off-line aridity and drought metrics applied to climate model outputs but also are supported by climate-model projections of decreased surface soil moisture. Here we comprehensively analyze soil moisture projections from the Coupled Model Intercomparison Project phase 5, including surface, total, and layer-by-layer soil moisture. We identify a robust vertical gradient of projected mean soil moisture changes, with more negative changes near the surface. Some regions of the northern middle to high latitudes exhibit negative annual surface changes but positive total changes. We interpret this behavior in the context of seasonal changes in the surface water budget. This vertical pattern implies that the extensive drying predicted by off-line drought metrics, while consistent with the projected decline in surface soil moisture, will tend to overestimate (negatively) changes in total soil water availability.

Registration of a small-red dry bean germplasm, TARS-LFR1, with multiple disease resistance and superior performance in low nitrogen soils

USDA-ARS?s Scientific Manuscript database

Root rots, caused primarily by soil-borne fungi and Oomycetes, are important constraints to common bean production. These diseases are becoming a more serious problem under low-input and low fertility production zones with changing climatic conditions adding another layer of constraints. The objecti...

The distribution of organic carbon fractions in a typical loess-paleosol profile and its paleoenvironmental significance

PubMed Central

Hu, Feinan; Huo, Na; Shang, Yingni; Chang, Wenqian

2018-01-01

Background The loess-paleosol sequence on the Loess Plateau has been considered an important paleoclimatic archive to study global climatic and environmental changes in the Quaternary. So far, little attention has been paid to the characteristics of soil organic carbon fractions in loess-paleosol sequences, which may provide valuable information for exploring the evolution of climate and environment in the Quaternary on the Loess Plateau. Methods In order to explore the significance of mineral-associated organic carbon to total organic carbon (MOC/TOC) ratios in the loess-paleosol sequence for reconstructing paleoenvironmental and paleoclimatic evolution in the Quaternary on the Loess Plateau, we selected a typical loess-paleosol profile in Chunhua county, Xianyang city, Shaanxi province, as the research object. The content of total organic carbon (TOC) and MOC/TOC ratio in each loess and paleosol layers of the Chunhua loess-paleosol profile were analyzed, together with the paleoclimatic proxies, such as soil grain size, CaCO3 content and their correlations with organic carbon parameters. Results The main results were as follows: (1) the total content of soil organic carbon and MOC/TOC ratios were generally higher in paleosol layers than in the underlying loess layers of the Chunhua loess-paleosol profile. Compared to total organic carbon content, MOC/TOC ratios changed more obviously in soil layers below a paleosol layer S8; (2) soil clay content and median grain size (Md (ϕ)) were higher in paleosol than in the underlying loess, while CaCO3 content showed an opposite tendency. In the Chunhua profile, the distribution characteristics of the three paleoclimatic proxies showed good indications of paleoclimate changes in the Quaternary; (3) in the Chunhua loess-paleosol profile, MOC/TOC ratios were positively correlated with clay content and median grain size (ϕ), while negatively correlated with CaCO3 content, and the correlations were more significant in soil layers below S8. Discussion Our results indicated that MOC/TOC ratios in the Chunhua loess-paleosol profile correlated with the cold dry-warm wet paleoclimatic cycle in the Quaternary. The high MOC/TOC ratios in the loess-paleosol profile might reflect warm and humid climate, while lower ratios indicated relatively cold and dry climate. That is because when the climate changed from warm-humid to cold-dry, the vegetation coverage and pedogenesis intensity decreased, which increased soil CaCO3 content and decreased soil clay content and Md (ϕ), leading to decreased MOC/TOC ratios. Compared to TOC, MOC/TOC ratios had greater significance in indicating paleoenvironmental evolution in the Quaternary on the Loess Plateau. Therefore, investigating MOC/TOC ratios in loess-paleosol profile can offer new evidence to reconstructing paleoenvironmental changes, and also provide a basis for predicting responses of soil organic carbon pools to vegetation and climate changes in the future. PMID:29666763

Seasonal variations in soil water in two woodland savannas of central Brazil with different fire history.

PubMed

Quesada, Carlos Alberto; Hodnett, Martin G; Breyer, Lacê M; Santos, Alexandre J B; Andrade, Sérgio; Miranda, Heloisa S; Miranda, Antonio Carlos; Lloyd, Jon

2008-03-01

Changes in soil water content were determined in two cerrado (sensu stricto) areas with contrasting fire history and woody vegetation density. The study was undertaken near Brasília, Brazil, from 1999 to 2001. Soil water content was measured with a neutron probe in three access tubes per site to a depth of 4.7 m. One site has been protected from fire for more than 30 years and, as a consequence, has a high density of woody plants. The other site had been frequently burned, and has a high herbaceous vegetation density and less woody vegetation. Soil water uptake patterns were strongly seasonal, and despite similarities in hydrological processes, the protected area systematically used more water than the burned area. Three temporarily contiguous patterns of water absorption were differentiated, characterized by variation in the soil depth from which water was extracted. In the early dry season, vegetation used water from throughout the soil profile but with a slight preference for water in the upper soil layers. Toward the peak of the dry season, vegetation had used most or all available water from the surface to a depth of 1.7 m, but continued to extract water from greater depths. Following the first rains, all water used was from the recently wetted upper soil layers only. Evaporation rates were a linear function of soil water availability, indicating a strong coupling of atmospheric water demand and the physiological response of the vegetation.

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.

The effects of antecedent dry days on the nitrogen removal in layered soil infiltration systems for storm run-off control.

PubMed

Cho, Kang-Woo; Yoon, Min-Hyuk; Song, Kyung-Guen; Ahn, Kyu-Hong

2011-01-01

The effects of antecedent dry days (ADD) on nitrogen removal efficiency were investigated in soil infiltration systems, with three distinguishable layers: mulch layer (ML), coarse soil layer (CSL) and fine soil layer (FSL). Two sets of lab-scale columns with loamy CSL (C1) and sandy CSL (C2) were dosed with synthetic run-off, carrying chemical oxygen demand of 100 mg L(-1) and total nitrogen of 13 mg L(-1). The intermittent dosing cycle was stepwise adjusted for 5, 10 and 20 days. The influent ammonium and organic nitrogen were adsorbed to the entire depth in C1, while dominantly to the FSL in C2. In both columns, the effluent ammonium concentration increased while the organic nitrogen concentration decreased, as ADD increased from 5 to 20 days. The effluent of C1 always showed nitrate concentration exceeding influent, caused by nitrification, by increasing amounts as ADD increased. However, the wash-out of nitrate in C1 was not distinct in terms of mass since the effluent flow rate was only 25% of the influent. In contrast, efficient reduction (>95%) of nitrate loading was observed in C2 under ADD of 5 and 10 days, because of insignificant nitrification in the CSL and denitrification in the FSL. However, for the ADD of 20 days, a significant nitrate wash-out appeared in C2 as well, possibly because of the re-aeration by the decreasing water content in the FSL. Consequently, the total nitrogen load escaping with the effluent was always smaller in C2, supporting the effectiveness of sandy CSL over loamy FSL for nitrogen removal under various ADDs.

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.

Dynamics of Soil Water Evaporation during Soil Drying: Laboratory Experiment and Numerical Analysis

PubMed Central

Han, Jiangbo; Zhou, Zhifang

2013-01-01

Laboratory and numerical experiments were conducted to investigate the evolution of soil water evaporation during a continuous drying event. Simulated soil water contents and temperatures by the calibrated model well reproduced measured values at different depths. Results show that the evaporative drying process could be divided into three stages, beginning with a relatively high evaporation rate during stage 1, followed by a lower rate during transient stage and stage 2, and finally maintaining a very low and constant rate during stage 3. The condensation zone was located immediately below the evaporation zone in the profile. Both peaks of evaporation and condensation rate increased rapidly during stage 1 and transition stage, decreased during stage 2, and maintained constant during stage 3. The width of evaporation zone kept a continuous increase during stages 1 and 2 and maintained a nearly constant value of 0.68 cm during stage 3. When the evaporation zone totally moved into the subsurface, a dry surface layer (DSL) formed above the evaporation zone at the end of stage 2. The width of DSL also presented a continuous increase during stage 2 and kept a constant value of 0.71 cm during stage 3. PMID:24489492

Dynamics of soil water evaporation during soil drying: laboratory experiment and numerical analysis.

PubMed

Han, Jiangbo; Zhou, Zhifang

2013-01-01

Laboratory and numerical experiments were conducted to investigate the evolution of soil water evaporation during a continuous drying event. Simulated soil water contents and temperatures by the calibrated model well reproduced measured values at different depths. Results show that the evaporative drying process could be divided into three stages, beginning with a relatively high evaporation rate during stage 1, followed by a lower rate during transient stage and stage 2, and finally maintaining a very low and constant rate during stage 3. The condensation zone was located immediately below the evaporation zone in the profile. Both peaks of evaporation and condensation rate increased rapidly during stage 1 and transition stage, decreased during stage 2, and maintained constant during stage 3. The width of evaporation zone kept a continuous increase during stages 1 and 2 and maintained a nearly constant value of 0.68 cm during stage 3. When the evaporation zone totally moved into the subsurface, a dry surface layer (DSL) formed above the evaporation zone at the end of stage 2. The width of DSL also presented a continuous increase during stage 2 and kept a constant value of 0.71 cm during stage 3.

Estimation of bare soil evaporation using multifrequency airborne SAR

NASA Technical Reports Server (NTRS)

Soares, Joao V.; Shi, Jiancheng; Van Zyl, Jakob; Engman, E. T.

1992-01-01

It is shown that for homogeneous areas soil moisture can be derived from synthetic aperture radar (SAR) measurements, so that the use of microwave remote sensing can given realistic estimates of energy fluxes if coupled to a simple two-layer model repesenting the soil. The model simulates volumetric water content (Wg) using classical meterological data, provided that some of the soil thermal and hydraulic properties are known. Only four parameters are necessary: mean water content, thermal conductivity and diffusitivity, and soil resistance to evaporation. They may be derived if a minimal number of measured values of Wg and surface layer temperature (Tg) are available together with independent measurements of energy flux to compare with the estimated values. The estimated evaporation is shown to be realistic and in good agreement with drying stage theory in which the transfer of water in the soil is in vapor form.

An estimation of the main wetting branch of the soil water retention curve based on its main drying branch using the machine learning method

NASA Astrophysics Data System (ADS)

Lamorski, Krzysztof; Šimūnek, Jiří; Sławiński, Cezary; Lamorska, Joanna

2017-02-01

In this paper, we estimated using the machine learning methodology the main wetting branch of the soil water retention curve based on the knowledge of the main drying branch and other, optional, basic soil characteristics (particle size distribution, bulk density, organic matter content, or soil specific surface). The support vector machine algorithm was used for the models' development. The data needed by this algorithm for model training and validation consisted of 104 different undisturbed soil core samples collected from the topsoil layer (A horizon) of different soil profiles in Poland. The main wetting and drying branches of SWRC, as well as other basic soil physical characteristics, were determined for all soil samples. Models relying on different sets of input parameters were developed and validated. The analysis showed that taking into account other input parameters (i.e., particle size distribution, bulk density, organic matter content, or soil specific surface) than information about the drying branch of the SWRC has essentially no impact on the models' estimations. Developed models are validated and compared with well-known models that can be used for the same purpose, such as the Mualem (1977) (M77) and Kool and Parker (1987) (KP87) models. The developed models estimate the main wetting SWRC branch with estimation errors (RMSE = 0.018 m3/m3) that are significantly lower than those for the M77 (RMSE = 0.025 m3/m3) or KP87 (RMSE = 0. 047 m3/m3) models.

Hydraulic lift in a neotropical savanna: experimental manipulation and model simulations

Treesearch

Fabian G. Scholz; Sandra J. Bucci; William A. Hoffmann; Frederick C. Meinzer; Guillermo Goldstein

2010-01-01

The objective of this study was to assess the magnitude of hydraulic lift in Brazilian savannas (Cerrado) and to test the hypothesis that hydraulic lift by herbaceous plants contributes substantially to slowing the decline of water potential and water storage in the upper soil layers during the dry season. To this effect, field observations of soil water content and...

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.

Shallow groundwater systems in a polar desert, McMurdo Dry Valleys, Antarctica

NASA Astrophysics Data System (ADS)

Gooseff, Michael N.; Barrett, John E.; Levy, Joseph S.

2013-02-01

The McMurdo Dry Valleys (MDVs), Antarctica, exist in a hyperarid polar desert, underlain by deep permafrost. With an annual mean air temperature of -18 °C, the MDVs receive <10 cm snow-water equivalent each year, collecting in leeward patches across the landscape. The landscape is dominated by expansive ice-free areas of exposed soils, mountain glaciers, permanently ice-covered lakes, and stream channels. An active layer of seasonally thawed soil and sediment extends to less than 1 m from the surface. Despite the cold and low precipitation, liquid water is generated on glaciers and in snow patches during the austral summer, infiltrating the active layer. Across the MDVs, groundwater is generally confined to shallow depths and often in unsaturated conditions. The current understanding and the biogeochemical/ecological significance of four types of shallow groundwater features in the MDVs are reviewed: local soil-moisture patches that result from snow-patch melt, water tracks, wetted margins of streams and lakes, and hyporheic zones of streams. In general, each of these features enhances the movement of solutes across the landscape and generates soil conditions suitable for microbial and invertebrate communities.

Compost quality and its function as a soil conditioner of recultivation layers - a critical review

NASA Astrophysics Data System (ADS)

Beck-Broichsitter, Steffen; Fleige, Heiner; Horn, Rainer

2018-01-01

During a period of 4 years, soil chemical and physical properties of the temporary capping system in Rastorf (Northern Germany) were estimated, whereby compost was partly used as soil improver in the upper recultivation layer. The air capacity and the available water capacity of soil samples were first determined in 2013 (without compost), and then in 2015 (with compost) under laboratory conditions. Herein, the addition of compost had a positive effect on: the air capacity up to 13.4 cm3 cm-3; and the available water capacity up to 20.1 cm3 cm-3 in 2015, in the recultivation layer (0-20 cm). However, taking into account the in situ results of the tensiometer and frequency domain reflectometry measurements, the addition of compost had a negative effect. The soil-compost mixture led to restricted remoistening even after a normal summer drying period in autumn and induced more negative matric potentials in the recultivation layer. In summary, the soil-improving effect of the compost addition, in conjunction with an increased water storage capacity, is undeniable and was demonstrated in a combined field and laboratory study. Therefore, intensive hydrophobicity can inhibit the homogeneous remoistening of the soil, resulting in a decreased hydraulic effectiveness of the sealing system.

The mobility of thiobencarb and fipronil in two flooded rice-growing soils.

PubMed

Doran, Gregory; Eberbach, Philip; Helliwell, Stuart

2008-08-01

The mobility of the rice pesticides thiobencarb (S-[(4-chlorophenyl) methyl] diethylcarbamothioate) and fipronil ([5-amino-3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]pyrazole) were investigated in the glasshouse under flooded conditions using two Australian rice-growing soils. When using leakage rates of 10 mm day(-1), less than 20% of applied thiobencarb and fipronil remained in the water column after 10 days due to rapid transfer to the soil phase. Up to 70% and 65% of the applied thiobencarb and fipronil, respectively, were recovered from the 0-1 cm layer of soils. Only 5-7% of each pesticide was recovered from the 1-2 cm layer, and less than 2% was recovered from each 1 cm layer in the 2-10 cm region of the soils. Analysis of the water leaking from the base of the soil cores showed between 5-10% of the applied thiobencarb and between 10-20% of the applied fipronil leaching from the soil cores. The high levels of pesticide in the effluent was attributed to preferential flow of pesticide-laden water via soil macropores resulting from the wetting and drying process, worm holes and root channels.

Sensitivity of soil moisture initialization for decadal predictions under different regional climatic conditions in Europe

NASA Astrophysics Data System (ADS)

Khodayar, S.; Sehlinger, A.; Feldmann, H.; Kottmeier, C.

2015-12-01

The impact of soil initialization is investigated through perturbation simulations with the regional climate model COSMO-CLM. The focus of the investigation is to assess the sensitivity of simulated extreme periods, dry and wet, to soil moisture initialization in different climatic regions over Europe and to establish the necessary spin up time within the framework of decadal predictions for these regions. Sensitivity experiments consisted of a reference simulation from 1968 to 1999 and 5 simulations from 1972 to 1983. The Effective Drought Index (EDI) is used to select and quantify drought status in the reference run to establish the simulation time period for the sensitivity experiments. Different soil initialization procedures are investigated. The sensitivity of the decadal predictions to soil moisture initial conditions is investigated through the analysis of water cycle components' (WCC) variability. In an episodic time scale the local effects of soil moisture on the boundary-layer and the propagated effects on the large-scale dynamics are analysed. The results show: (a) COSMO-CLM reproduces the observed features of the drought index. (b) Soil moisture initialization exerts a relevant impact on WCC, e.g., precipitation distribution and intensity. (c) Regional characteristics strongly impact the response of the WCC. Precipitation and evapotranspiration deviations are larger for humid regions. (d) The initial soil conditions (wet/dry), the regional characteristics (humid/dry) and the annual period (wet/dry) play a key role in the time that soil needs to restore quasi-equilibrium and the impact on the atmospheric conditions. Humid areas, and for all regions, a humid initialization, exhibit shorter spin up times, also soil reacts more sensitive when initialised during dry periods. (e) The initial soil perturbation may markedly modify atmospheric pressure field, wind circulation systems and atmospheric water vapour distribution affecting atmospheric stability conditions, thus modifying precipitation intensity and distribution even several years after the initialization.

Evaluation of Mercury Contamination in Fungi Boletus Species from Latosols, Lateritic Red Earths, and Red and Yellow Earths in the Circum-Pacific Mercuriferous Belt of Southwestern China.

PubMed

Falandysz, Jerzy; Zhang, Ji; Wang, Yuan-Zhong; Saba, Martyna; Krasińska, Grażyna; Wiejak, Anna; Li, Tao

2015-01-01

For the first time, highly elevated levels of mercury (Hg) have been documented for several species of the edible Fungi genus Boletus growing in latosols, lateritic red earths, and red and yellow earths from the Yunnan province of China. Analysis of Hg concentrations in the genus suggests that geogenic Hg is the dominant source of Hg in the fungi, whereas anthropogenic sources accumulate largely in the organic layer of the forest soil horizon. Among the 21 species studied from 32 locations across Yunnan and 2 places in Sichuan Province, the Hg was found at elevated level in all samples from Yunnan but not in the samples from Sichuan, which is located outside the mercuriferous belt. Particularly abundant in Hg were the caps of fruiting bodies of Boletus aereus (up to 13 mg kg-1 dry matter), Boletus bicolor (up to 5.5 mg kg-1 dry matter), Boletus edulis (up to 22 mg kg-1 dry matter), Boletus luridus (up to 11 mg kg-1 dry matter), Boletus magnificus (up to 13 mg kg-1 dry matter), Boletus obscureumbrinus (up to 9.4 mg kg-1 dry matter), Boletus purpureus (up to 16 mg kg-1 dry matter), Boletus sinicus (up to 6.8 mg kg-1 dry matter), Boletus speciosus (up to 4.9mg kg-1 dry matter), Boletus tomentipes (up to 13 mg kg-1 dry matter), and Boletus umbriniporus (up to 4.9 mg kg-1 dry matter). Soil samples of the 0-10 cm topsoil layer from the widely distributed locations had mercury levels ranging between 0.034 to 3.4 mg kg-1 dry matter. In Yunnan, both the soil parent rock and fruiting bodies of Boletus spp. were enriched in Hg, whereas the same species from Sichuan, located outside the mercuriferous belt, had low Hg concentrations, suggesting that the Hg in the Yunnan samples is mainly from geogenic sources rather than anthropogenic sources. However, the contribution of anthropogenically-derived Hg sequestered within soils of Yunnan has not been quantified, so more future research is required. Our results suggest that high rates of consumption of Boletus spp. from Yunnan can deliver relatively high doses of Hg to consumers, but that rates can differ widely because of large variability in mercury concentrations between species and locations.

Evaluation of Mercury Contamination in Fungi Boletus Species from Latosols, Lateritic Red Earths, and Red and Yellow Earths in the Circum-Pacific Mercuriferous Belt of Southwestern China

PubMed Central

Falandysz, Jerzy; Zhang, Ji; Wang, Yuan-Zhong; Saba, Martyna; Krasińska, Grażyna; Wiejak, Anna; Li, Tao

2015-01-01

For the first time, highly elevated levels of mercury (Hg) have been documented for several species of the edible Fungi genus Boletus growing in latosols, lateritic red earths, and red and yellow earths from the Yunnan province of China. Analysis of Hg concentrations in the genus suggests that geogenic Hg is the dominant source of Hg in the fungi, whereas anthropogenic sources accumulate largely in the organic layer of the forest soil horizon. Among the 21 species studied from 32 locations across Yunnan and 2 places in Sichuan Province, the Hg was found at elevated level in all samples from Yunnan but not in the samples from Sichuan, which is located outside the mercuriferous belt. Particularly abundant in Hg were the caps of fruiting bodies of Boletus aereus (up to 13 mg kg-1 dry matter), Boletus bicolor (up to 5.5 mg kg-1 dry matter), Boletus edulis (up to 22 mg kg-1 dry matter), Boletus luridus (up to 11 mg kg-1 dry matter), Boletus magnificus (up to 13 mg kg-1 dry matter), Boletus obscureumbrinus (up to 9.4 mg kg-1 dry matter), Boletus purpureus (up to 16 mg kg-1 dry matter), Boletus sinicus (up to 6.8 mg kg-1 dry matter), Boletus speciosus (up to 4.9mg kg-1 dry matter), Boletus tomentipes (up to 13 mg kg-1 dry matter), and Boletus umbriniporus (up to 4.9 mg kg-1 dry matter). Soil samples of the 0–10 cm topsoil layer from the widely distributed locations had mercury levels ranging between 0.034 to 3.4 mg kg-1 dry matter. In Yunnan, both the soil parent rock and fruiting bodies of Boletus spp. were enriched in Hg, whereas the same species from Sichuan, located outside the mercuriferous belt, had low Hg concentrations, suggesting that the Hg in the Yunnan samples is mainly from geogenic sources rather than anthropogenic sources. However, the contribution of anthropogenically-derived Hg sequestered within soils of Yunnan has not been quantified, so more future research is required. Our results suggest that high rates of consumption of Boletus spp. from Yunnan can deliver relatively high doses of Hg to consumers, but that rates can differ widely because of large variability in mercury concentrations between species and locations. PMID:26606425

In-situ evaluation of internal drainage in layered soils (Tukulu, Sepane and Swartland)

NASA Astrophysics Data System (ADS)

Mavimbela, S. S. W.; van Rensburg, L. D.

2011-11-01

The soil water release (SWC) and permeability properties of layered soils following deep infiltration depends on the structural and layering composition of the profiles diagnostic horizons. Three layered soils, the Tukulu, Sepane and Swartland soil forms, from the Free State province of South Africa, were selected for internal drainage evaluation. The soil water release curves as a function of suction (h) and unsaturated hydraulic conductivity (K-coefficient) as a function of soil water content, SWC (θ), were characterised alongside the pedological properties of the profiles. The water hanging column in collaboration with the in-situ instantaneous profile method (IPM) was appropriate for this work. Independently, the saturated hydraulic conductivity (Ks) was measured using double ring infiltrometers. The three soils had a generic orthic A horizon but differed remarkable with depth. A clay rich layer was found in the Tukulu and Sepane at depths of 600 to 850 mm and 300 to 900 mm, respectively. The Swartland was weakly developed with a saprolite rock found at depth of 400-700 mm. During the 1200 h drainage period, soil water loss amounted to 21, 20 and 51 mm from the respective Tukulu, Sepane and Swartland profiles. An abrupt drop in Ks in conjunction with a steep K-coefficient gradient with depth was observed from the Tukulu and Sepane. Hydromorphic colours found on the clay-rich horizons suggested a wet soil water regime that implied restriction of internal drainage. It was therefore concluded that the clay rich horizons gave the Tukulu and Sepane soil types restricted internal drainage properties required for soil water storage under infield rainwater harvesting production technique. The coarseness of the Swartland promoted high drainage losses that proliferated a dry soil water regime.

Microwave Remote Sensing of Soil Moisture

NASA Technical Reports Server (NTRS)

Schmugge, T. J.

1985-01-01

Because of the large contrast between the dielectric constant of liquid water and that of dry soil at microwave wavelength, there is a strong dependence of the thermal emission and radar backscatter from the soil on its moisture content. This dependence provides a means for the remote sensing of the moisture content in a surface layer approximately 5 cm thick. The feasibility of these techniques is demonstrated from field, aircraft and spacecraft platforms. The soil texture, surface roughness, and vegetative cover affect the sensitivity of the microwave response to moisture variations with vegetation being the most important. It serves as an attenuating layer which can totally obscure the surface. Research indicates that it is possible to obtain five or more levels of moisture discrimination and that a mature corn crop is the limiting vegetation situation.

The Amazon Boundary Layer Experiment (ABLE 2A) - Dry season 1985

NASA Technical Reports Server (NTRS)

Harriss, R. C.; Browell, E. V.; Hoell, J. M., Jr.; Bendura, R. J.; Beck, S. M.; Wofsy, S. C.; Mcneal, R. J.; Navarro, R. L.; Riley, J. T.; Snell, R. L.

1988-01-01

The Amazon Boundary Layer Experiment (ABLE 2A) used data from aircraft, ground-based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during the early-to-middle dry season, July and August 1985. This paper reports the conceptual framework and experimental approach used in ABLE 2A and serves as an introduction to the detailed papers which follow in this issue. The results of ABLE 2A demonstrate that isoprene, methane, carbon dioxide, nitric oxide, dimethylsulfide, and organic aerosol emissions from soils and vegetation play a major role in determining the chemical composition of the atmospheric mixed layer over undisturbed forest and wetland environments. As the dry season progresses, emissions from both local and distant biomass burning become an important source of carbon monoxide, nitric oxide and ozone in the atmosphere over the central Amazon Basin.

Is soil moisture initialization important for seasonal to decadal predictions?

NASA Astrophysics Data System (ADS)

Stacke, Tobias; Hagemann, Stefan

2014-05-01

The state of soil moisture can can have a significant impact on regional climate conditions for short time scales up to several months. However, focusing on seasonal to decadal time scales, it is not clear whether the predictive skill of global a Earth System Model might be enhanced by assimilating soil moisture data or improving the initial soil moisture conditions with respect to observations. As a first attempt to provide answers to this question, we set up an experiment to investigate the life time (memory) of extreme soil moisture states in the coupled land-atmosphere model ECHAM6-JSBACH, which is part of the Max Planck Institute for Meteorology's Earth System Model (MPI-ESM). This experiment consists of an ensemble of 3 years simulations which are initialized with extreme wet and dry soil moisture states for different seasons and years. Instead of using common thresholds like wilting point or critical soil moisture, the extreme states were extracted from a reference simulation to ensure that they are within the range of simulated climate variability. As a prerequisite for this experiment, the soil hydrology in JSBACH was improved by replacing the bucket-type soil hydrology scheme with a multi-layer scheme. This new scheme is a more realistic representation of the soil, including percolation and diffusion fluxes between up to five separate layers, the limitation of bare soil evaporation to the uppermost soil layer and the addition of a long term water storage below the root zone in regions with deep soil. While the hydrological cycle is not strongly affected by this new scheme, it has some impact on the simulated soil moisture memory which is mostly strengthened due to the additional deep layer water storage. Ensemble statistics of the initialization experiment indicate perturbation lengths between just a few days up to several seasons for some regions. In general, the strongest effects are seen for wet initialization during northern winter over cold and humid regions, while the shortest memory is found during northern spring. For most regions, the soil moisture memory is either sensitive to wet or to dry perturbations, indicating that soil moisture anomalies interact with the respective weather pattern for a given year and might be able to enhance or dampen extreme conditions. To further investigate this effect, the simulations will be repeated using JSBACH with prescribed meteorological forcing to better disentangle the direct effects of soil moisture initialization and the atmospheric response.

Radar reflectivity of bare and vegetation-covered soil

NASA Technical Reports Server (NTRS)

Ulaby, F. T.; Dobson, M. C.; Bradley, G. A.

1981-01-01

Radar sensitivity to soil moisture content has been investigated experimentally for bare and vegetation-covered soil using detailed spectral measurements obtained by a truck-mounted radar spectrometer in the 1-8 GHz band and by airborne scatterometer observations at 1.6, 4.75, and 13.3 GHz. It is shown that radar can provide quantitative information on the soil moisture content of both bare and vegetation-covered soil. The observed soil moisture is in the form of the soil matric potential or a related quantity such as the percent of field capacity. The depth of the monitored layer varies from 1 cm for very wet soil to about 15 cm for very dry soil.

Effect of in-situ disturbance within the soil mass on the stress-strain behaviour of silty soil

NASA Astrophysics Data System (ADS)

Noor, Sarah T.; Rabika Rahman, SS; Nahar, Sabiqun

2018-04-01

To date, different techniques have been evolved to collect soil in undisturbed condition so that the in-situ soil behaviour can be determined by carrying out laboratory tests. For the same reason, the execution of undisturbed soil sampling in practice is given a lot of efforts. However, this study brings the fact into consideration that the in-situ soil condition may not remain constant, rather it might vary time to time, because of different internal or external reasons. For example, the internal stress state of soil layers, existing below or above the swelling soil layer, become modified during shrinking and swelling resulting from drying and wetting of swelling clay, respectively. Further, foundations of building may transfer cyclic loads (generated by vibration installed in the building) to the soil below the foundation. Therefore, this study investigates the effects of stress-strain behaviour due to the disturbances on the shear strength of the soil with respect to that of undisturbed specimens. The shear strength of disturbed soil shows deviation from that of undisturbed specimen depending on the different parameters defining the severity of disturbance.

State-dependent anisotrophy: Comparison of quasi-analytical solutions with stochastic results for steady gravity drainage

USGS Publications Warehouse

Green, Timothy R.; Freyberg, David L.

1995-01-01

Anisotropy in large-scale unsaturated hydraulic conductivity of layered soils changes with the moisture state. Here, state-dependent anisotropy is computed under conditions of large-scale gravity drainage. Soils represented by Gardner's exponential function are perfectly stratified, periodic, and inclined. Analytical integration of Darcy’s law across each layer results in a system of nonlinear equations that is solved iteratively for capillary suction at layer interfaces and for the Darcy flux normal to layering. Computed fluxes and suction profiles are used to determine both upscaled hydraulic conductivity in the principal directions and the corresponding “state-dependent” anisotropy ratio as functions of the mean suction. Three groups of layered soils are analyzed and compared with independent predictions from the stochastic results of Yeh et al. (1985b). The small-perturbation approach predicts appropriate behaviors for anisotropy under nonarid conditions. However, the stochastic results are limited to moderate values of mean suction; this limitation is linked to a Taylor series approximation in terms of a group of statistical and geometric parameters. Two alternative forms of the Taylor series provide upper and lower bounds for the state-dependent anisotropy of relatively dry soils.

Evaluating uncertainties in multi-layer soil moisture estimation with support vector machines and ensemble Kalman filtering

NASA Astrophysics Data System (ADS)

Liu, Di; Mishra, Ashok K.; Yu, Zhongbo

2016-07-01

This paper examines the combination of support vector machines (SVM) and the dual ensemble Kalman filter (EnKF) technique to estimate root zone soil moisture at different soil layers up to 100 cm depth. Multiple experiments are conducted in a data rich environment to construct and validate the SVM model and to explore the effectiveness and robustness of the EnKF technique. It was observed that the performance of SVM relies more on the initial length of training set than other factors (e.g., cost function, regularization parameter, and kernel parameters). The dual EnKF technique proved to be efficient to improve SVM with observed data either at each time step or at a flexible time steps. The EnKF technique can reach its maximum efficiency when the updating ensemble size approaches a certain threshold. It was observed that the SVM model performance for the multi-layer soil moisture estimation can be influenced by the rainfall magnitude (e.g., dry and wet spells).

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.

Survival of Escherichia coli in common garden mulches spiked with synthetic greywater.

PubMed

Boyte, S; Quaife, S; Horswell, J; Siggins, A

2017-05-01

Reuse of domestic wastewater is increasingly practiced as a means to address global demands on fresh water. Greywater is primarily reused via subsurface irrigation of gardens, where the soil environment is seen to be an integral part of the treatment process. The fate of biological contaminants (i.e. pathogens) in the soil is reasonably well understood, but their persistence and survival in soil cover layers is largely unexplored. This study investigated the ability of Escherichia coli to survive in common soil cover layers. Three garden mulches were investigated: pea straw mulch, a bark-based mulch and a coconut husk mulch. Each mulch was treated with an E. coli solution, a synthetic greywater with E. coli, or a freshwater control. Escherichia coli was applied at 1 × 10 4  most probable number (MPN) per g dry weight mulch. Subsamples were temporally analysed for E. coli. The bark and coconut husk mulches showed a steady decline in E. coli numbers, while E. coli increased in the pea straw mulch for the duration of the 50 days experiment, peaking at 1·8 × 10 8  MPN per g dry weight mulch. This study highlighted the importance of selection of a suitable material for covering areas that are subsurface irrigated with greywater. Potential for microbial contamination is one of the limiting factors for domestic greywater reuse. Although subsurface irrigation is considered to be one of the lowest risk applications, there is still a possibility of microbes reaching the soil surface if the environmental conditions are not favourable or if soil movement inadvertently exposes the irrigation line. In these circumstances, the soil cover layer may be contaminated by greywater microbes. This study assesses the survival rates of the pathogen indicator organism Escherichia coli in three soil cover materials commonly used worldwide and makes clear recommendations to facilitate the safe reuse of domestic greywater. © 2017 The Society for Applied Microbiology.

Biogenic NO emission from a spruce forest soil in the Fichtelgebirge (Germany) under the influence of different understorey vegetation cover

NASA Astrophysics Data System (ADS)

Bargsten, A.; Andreae, M. O.; Meixner, F. X.

2009-04-01

Within the framework of the EGER project (ExchanGE processes in mountainous Regions) soil samples have been taken from the spruce forest site "Weidenbrunnen" (Fichtelgebirge, Germany) in September 2008 to determine the NO exchange in the laboratory and for a series of soil analyses. The soil was sampled below different understorey vegetation covers: young Norway spruce, moss/litter, blueberries and grass. We investigated the net NO release rate from corresponding organic layers as well as from the A horizon of respective soils. Additionally we measured pH, C/N ratio, contents of ammonium, nitrate, and organic C, bulk density, the thickness of the organic layer and the quality of the organic matter. Net NO release rates (as well as the NO production and NO consumption rates) from the soil samples were determined by a fully automated laboratory incubation & fumigation system. Purified dry air passed five dynamic incubation chambers, four containing water saturated soil samples and one reference chamber. By this procedure, the soil samples dried out slowly (within 2-6 days), covering the full range of soil moisture (0-300% gravimetric soil moisture). To quantify NO production and NO consumption rates separately, soil samples were fumigated with zero-air (approx. 0 ppb NO) and air of 133 ppb NO. The chambers were placed in a thermostatted cabinet for incubation at 10 an 20˚ C. NO and H2O concentrations at the outlet of the five dynamic chambers were measured sequentially by chemiluminescence and IR-absorption based analyzers, switching corresponding valves every two minutes. Net NO release rates were determined from the NO concentration difference between soil containing and reference chambers. Corresponding measurements of H2O mixing ratio yielded the evaporation loss of the soil samples, which (referenced to the gravimetric soil water content before and after the incubation experiment) provided the individual soil moisture contents of each soil samples during the incubation experiment. Our contribution focus net NO release rates, NO production and NO consumption rates of spruce forest soils sampled under different understorey vegetation covers. Generally, organic layers show significant higher NO production and NO consumption rates than the soils from the corresponding A horizons. Soils under the understorey vegetation cover "moos/litter" revealed the lowest NO production and NO consumption rates. Net NO release rates, NO production and NO consumption rates of soil samples obtained below the four different under- storey vegetation covers will be discussed in terms of pH, C/N ratio, contents of ammonium, nitrate, and organic C, bulk density, thickness of organic layer, as well as quality of the organic matter.

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.

A source of methane from upland forests in the Brazilian Amazon.

Treesearch

Janaina Braga do Carmo; Michael Keller; Jadson Dezincourt Dias; Plinio Barbosa de Camargo; Patrick Crill

2006-01-01

We sampled air in the canopy layer of undisturbed upland forests during wet and dry seasons at three sites in the Brazilian Amazon region and found that both methane(CH4) and carbon dioxide (CO2) mixing ratios increased at night. Such increases were consistent across sites and seasons. A canopy layer budget model based on measured soil-atmosphere fluxes of CO2 was...

[Effects of short-term deep vertically rotary tillage on topsoil structure of lime concretion black soil and wheat growth in Huang-Huai-Hai Plain, China].

PubMed

Zhai, Zhen; Li, Yu Yi; Zhang, Li; Pang, Bo; Pang, Huan Cheng; Wei, Ben Hui; Wang, Qing Wei; Qi, Shao Wei

2017-04-18

Annual rotary tillage can often create a compacted plough pan and shallow arable layer which hampers the high crop yield in Huang-Huai-Hai region. A brand new farming method named Vertically Rotary Tillage was introduced to solve this problem. One short-term field experiment was conducted to explore the effect of deep vertically rotary tillage on soil physical properties and photosynthetic characteristics at flowering stage of winter wheat. Two tillage treatments were designed including subsoiling tillage with 20 cm depth (SS 20 , CK) and deep vertically rotary tillage with 30 cm depth (DVR 30 ). The result showed that compared with SS 20 treatment, DVR 30 treatment could thoroughly break the plow pan and loose the arable layer. The soil bulk density at 10-20 cm and 20-30 cm layers under DVR 30 treatment was decreased by 9.5% and 11.2% respectively than that under SS 20 treatment. Meanwhile, the penetration resistance at 20-30 cm layer under DVR 30 treatment was also decreased by 42.3% than that under SS 20 treatment. Moreover, water infiltration under DVR 30 treatment and the soil water storage in the deep soil layers was then increased. The mass water content of soil increased significantly with the increase of soil depth. There was significant difference of mass water content of 30-40 cm 40-50 cm between SS 20 and DVR 30 . The mass water content 30-40 cm and 40-50 cm layers under DVR 30 treatment was increased by 16.9% and 10.6% compared with SS 20 treatment, respectively. Furthermore, DVR 30 treatment promoted the improvement of the photosynthetic capacity of wheat which could contribute to the dry matter accumulation of winter wheat. The net photosynthesis rate and SPAD at flowering stage of winter wheat leaves under DVR 30 treatment were increased by 1.3% and 15.5% respectively than that under SS 20 treatment, thereby the above and underground dry matter accumulation of winter wheat under DVR 30 was increased significantly. Due to all the superiority of DVR 30 treatment over SS 20 treatment showed above, the winter wheat yield under DVR 30 treatment was increased by 12.4% than that under SS 20 . It was concluded that deep vertically rotary tillage could provide a new and effective way to break up the compacted plough pan, build a reasonable soil structure and increase crop yield.

Fractal behavior of soil water storage at multiple depths

NASA Astrophysics Data System (ADS)

Ji, Wenjun; Lin, Mi; Biswas, Asim; Si, Bing C.; Chau, Henry W.; Cresswell, Hamish P.

2016-08-01

Spatiotemporal behavior of soil water is essential to understand the science of hydrodynamics. Data intensive measurement of surface soil water using remote sensing has established that the spatial variability of soil water can be described using the principle of self-similarity (scaling properties) or fractal theory. This information can be used in determining land management practices provided the surface scaling properties are kept at deep layers. The current study examined the scaling properties of sub-surface soil water and their relationship to surface soil water, thereby serving as supporting information for plant root and vadose zone models. Soil water storage (SWS) down to 1.4 m depth at seven equal intervals was measured along a transect of 576 m for 5 years in Saskatchewan. The surface SWS showed multifractal nature only during the wet period (from snowmelt until mid- to late June) indicating the need for multiple scaling indices in transferring soil water variability information over multiple scales. However, with increasing depth, the SWS became monofractal in nature indicating the need for a single scaling index to upscale/downscale soil water variability information. In contrast, all soil layers during the dry period (from late June to the end of the growing season in early November) were monofractal in nature, probably resulting from the high evapotranspirative demand of the growing vegetation that surpassed other effects. This strong similarity between the scaling properties at the surface layer and deep layers provides the possibility of inferring about the whole profile soil water dynamics using the scaling properties of the easy-to-measure surface SWS data.

Wildfires caused by self-heating ignition of carbon-rich soil

NASA Astrophysics Data System (ADS)

Restuccia, Francesco; Huang, Xinyan; Rein, Guillermo

2017-04-01

Carbon-rich soils, like peat, cover more than 3% of the earth's land surface, and store roughly three times more carbon than the earth's plants. Carbon-rich soils are reactive porous materials, prone to smouldering combustion if the inert and moisture content are low enough. An example of carbon-rich soil combustion happens in peatlands, which are prone to wildfires both in boreal and tropical regions and where combustion is a commonly seen phenomena. The experimental work presented here focuses on understanding one of the ways carbon-rich soil can ignite. The ignition phenomenon is known as self-heating, which is due to soil undergoing spontaneous exothermic reactions in the presence of oxygen. In this work we investigate the effect of soil inorganic content by creating under controlled conditions soil samples with inorganic contents ranging from 3% to 86% of dry weight. Combining oven experiments with the Frank-Kamenetskii theory of ignition, the lumped kinetic and thermal parameters are determined. We then use these parameters to upscale the laboratory experiments to soil layers of different depths for a range of ambient temperatures ranging from 0 °C to 40 °C. Experimental results show that self-heating ignition in the different soil layers is possible. The kinetic analysis predicts the critical soil layer thicknesses required for self-ignition. For example, at 40 °C a soil layer of 3% inorganic content can be ignited through self-heating if it is thicker than 8.8 m. This is also the first experimental quantification of soil self-heating showing that indeed it is possible that wildfires are initiated by self-heating of the soil.

Reducing Methyl Halide Emissions from Soils

NASA Astrophysics Data System (ADS)

Yates, S. R.; Xuan, R.; Ashworth, D.; Luo, L.

2011-12-01

Volatilization and soil transformation are major pathways by which pesticides dissipate from treated agricultural soil. Methyl bromide (MeBr) emissions from agricultural fumigation can lead to depletion of the stratospheric ozone layer. This has led to a gradual phase-out of MeBr and replacement by other halogenated chemicals. However, MeBr continues to be widely used under Critical Use Exemptions and development of emission-reduction strategies remains important. Several methods to reduce emissions of MeBr, and other halogenated soil fumigants, have been developed and are currently being tested under field conditions. In this paper, several approaches for reducing fumigant emissions to the atmosphere are described and include the use of virtually impermeable films, the creation of reactive soil barriers and a recently developed reactive film which was designed to limit loss of MeBr from soil without adding any material to the soil surface. Ammonium thiosulfate (ATS) was used to create a reactive layer. For a reactive soil layer, ATS was sprayed on the soil surface or incorporated to a depth of 1-2 cm. For the reactive film, ATS was placed between two layers of plastic film. The lower plastic layer was a high-density polyethylene film (HDPE), which is readily permeable to MeBr. The upper layer was a virtually impermeable film (VIF) and limits MeBr diffusion. MeBr diffusion and transformation through VIFs and reactive layers were tested in laboratory and field experiments. Although ineffective when dry, when sufficient water was present, reactive barriers substantially depleted halogenated fumigants, including MeBr. When ATS was activated in laboratory experiments, MeBr half-life was about 9.0 h (20C) in a reactive film barrier, and half life decreased with increasing temperature. When the soil was covered with VIF, less than 10% of the added MeBr diffused through the film and the remainder was transformed within the soil. This compares with 60 to 90% emission losses, respectively, for a soil covered with HDPE or for a bare soil surface. These findings demonstrate that several methods are available to reduce atmospheric emissions of MeBr and other halogenated fumigants.

Depth of soil water uptake by tropical rainforest trees during dry periods: does tree dimension matter?

PubMed

Stahl, Clément; Hérault, Bruno; Rossi, Vivien; Burban, Benoit; Bréchet, Claude; Bonal, Damien

2013-12-01

Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (Ψpd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. Ψpd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models.

Soil moisture controls on phenology and productivity in a semi-arid critical zone.

PubMed

Cleverly, James; Eamus, Derek; Restrepo Coupe, Natalia; Chen, Chao; Maes, Wouter; Li, Longhui; Faux, Ralph; Santini, Nadia S; Rumman, Rizwana; Yu, Qiang; Huete, Alfredo

2016-10-15

The Earth's Critical Zone, where physical, chemical and biological systems interact, extends from the top of the canopy to the underlying bedrock. In this study, we investigated soil moisture controls on phenology and productivity of an Acacia woodland in semi-arid central Australia. Situated on an extensive sand plain with negligible runoff and drainage, the carry-over of soil moisture content (θ) in the rhizosphere enabled the delay of phenology and productivity across seasons, until conditions were favourable for transpiration of that water to prevent overheating in the canopy. Storage of soil moisture near the surface (in the top few metres) was promoted by a siliceous hardpan. Pulsed recharge of θ above the hardpan was rapid and depended upon precipitation amount: 150mm storm(-1) resulted in saturation of θ above the hardpan (i.e., formation of a temporary, discontinuous perched aquifer above the hardpan in unconsolidated soil) and immediate carbon uptake by the vegetation. During dry and inter-storm periods, we inferred the presence of hydraulic lift from soil storage above the hardpan to the surface due to (i) regular daily drawdown of θ in the reservoir that accumulates above the hardpan in the absence of drainage and evapotranspiration; (ii) the dimorphic root distribution wherein most roots were found in dry soil near the surface, but with significant root just above the hardpan; and (iii) synchronisation of phenology amongst trees and grasses in the dry season. We propose that hydraulic redistribution provides a small amount of moisture that maintains functioning of the shallow roots during long periods when the surface soil layer was dry, thereby enabling Mulga to maintain physiological activity without diminishing phenological and physiological responses to precipitation when conditions were favourable to promote canopy cooling. Copyright © 2016 Elsevier B.V. All rights reserved.

Quantifying the influence of deep soil moisture on ecosystem albedo: The role of vegetation

NASA Astrophysics Data System (ADS)

Sanchez-Mejia, Zulia Mayari; Papuga, Shirley Anne; Swetish, Jessica Blaine; van Leeuwen, Willem Jan Dirk; Szutu, Daphne; Hartfield, Kyle

2014-05-01

As changes in precipitation dynamics continue to alter the water availability in dryland ecosystems, understanding the feedbacks between the vegetation and the hydrologic cycle and their influence on the climate system is critically important. We designed a field campaign to examine the influence of two-layer soil moisture control on bare and canopy albedo dynamics in a semiarid shrubland ecosystem. We conducted this campaign during 2011 and 2012 within the tower footprint of the Santa Rita Creosote Ameriflux site. Albedo field measurements fell into one of four Cases within a two-layer soil moisture framework based on permutations of whether the shallow and deep soil layers were wet or dry. Using these Cases, we identified differences in how shallow and deep soil moisture influence canopy and bare albedo. Then, by varying the number of canopy and bare patches within a gridded framework, we explore the influence of vegetation and soil moisture on ecosystem albedo. Our results highlight the importance of deep soil moisture in land surface-atmosphere interactions through its influence on aboveground vegetation characteristics. For instance, we show how green-up of the vegetation is triggered by deep soil moisture, and link deep soil moisture to a decrease in canopy albedo. Understanding relationships between vegetation and deep soil moisture will provide important insights into feedbacks between the hydrologic cycle and the climate system.

[Effects of elevated atmospheric CO2 and nitrogen application on cotton biomass, nitrogen utilization and soil urease activity].

PubMed

Lyu, Ning; Yin, Fei-hu; Chen, Yun; Gao, Zhi-jian; Liu, Yu; Shi, Lei

2015-11-01

In this study, a semi-open-top artificial climate chamber was used to study the effect of CO2 enrichment (360 and 540 µmol · mol(-1)) and nitrogen addition (0, 150, 300 and 450 kg · hm(-2)) on cotton dry matter accumulation and distribution, nitrogen absorption and soil urease activity. The results showed that the dry matter accumulation of bud, stem, leaf and the whole plant increased significantly in the higher CO2 concentration treatment irrespective of nitrogen level. The dry matter of all the detected parts of plant with 300 kg · hm(-2) nitrogen addition was significantly higher than those with the other nitrogen levels irrespective of CO2 concentration, indicating reasonable nitrogen fertilization could significantly improve cotton dry matter accumulation. Elevated CO2 concentration had significant impact on the nitrogen absorption contents of cotton bud and stem. Compared to those under CO2 concentration of 360 µmol · mol(-1), the nitrogen contents of bud and stem both increased significantly under CO2 concentration of 540 µmol · mol(-1). The nitrogen content of cotton bud in the treatment of 300 kg · hm(-2) nitrogen was the highest among the four nitrogen fertilizer treatments. While the nitrogen contents of cotton stem in the treatments of 150 kg · hm(-2) and 300 kg · hm(-2) nitrogen levels were higher than those in the treatment of 0 kg · hm(-2) and 450 kg · hm(-2) nitrogen levels. The nitrogen content of cotton leaf was significantly influenced by the in- teraction of CO2 elevation and N addition as the nitrogen content of leaf increased in the treatments of 0, 150 and 300 kg · hm(-2) nitrogen levels under the CO2 concentration of 540 µmol · mol(-1). The nitrogen content in cotton root was significantly increased with the increase of nitrogen fertilizer level under elevated CO2 (540 µmol · mol(-1)) treatment. Overall, the cotton nitrogen absorption content under the elevated CO2 (540 µmol · mol(-1)) treatment was higher than that under the ambient CO2- (360 µmol · mol(-1)) treatment. The order of nitrogen accumulation content in organs was bud > leaf > stem > root. Soil urease activity of both layers increased significantly with the elevation of CO2 concentration in all the nitrogen treatments. Under each CO2 concentration treatment, the soil urease activity in the upper layer (0-20 cm) increased significantly with nitrogen application, while the urease activity under the application of 300 kg · hm(-2) nitrogen was highest in the lower layer (20- 40 cm). The average soil urease activity in the upper layer (0-20 cm) was significantly higher than that in the lower layer (20-40 cm). This study suggested that the cotton dry matter accumulation and nitrogen absorption content were significantly increased in response to the elevated CO2 concentration (540 µmol · mol(-1)) and higher nitrogen addition (300 kg · hm(-2)).

Wet-dry cycles effect on ash water repellency. A laboratory experiment.

NASA Astrophysics Data System (ADS)

Pereira, Paulo; Cerdà, Artemi; Oliva, Marc; Mataix, Jorge; Jordán, Antonio

2014-05-01

In the immediate period after the fire, the ash layer has a strong influence on soil hydrological processes, as runoff, infiltration and erosion. Ash is very dynamic in the space and time. Until the first rainfall periods, ash is (re)distributed by the wind. After it can cover the soil surface, infiltrate or transported to other areas by water transport (Pereira et al., 2013a, b). This will have strong implications on nutrient redistribution and vegetation recovery. Ash layer may affect soil water repellency in different ways, depending on fire severity, soil properties and vegetation. Ash produced at low temperatures after low-severity burning is usually hydrophobic (Bodi et al., 2011, 2012). Wet-dry cycles have implications on ash physical and chemical properties, changing their effects in space and time. The aim of this study is to analyse the effects of fire temperature and severity on ash water repellency. Pinus sylvestris needles were collected in a Lithuania forest in Dzukija National Park (53º 54' N and 24º 22' E), transported to laboratory and washed with deionized water to remove soil particles and other residues. Needle samples were dried during 24 hours and exposed to different temperatures: 200, 300, 400 and 500 ºC, during 2 hours. Ash colour was analysed according to the Munsell Soil Color charts. Ash was black (10 YR 2/1) at 200 ºC, very dark grey (10YR 3/1) at 300 ºC, gray (10YR 5/1) at 400 ºC and light gray (10YR 7/1) at 500 ºC. Ten samples of ash released after each treatment were placed in plastic dishes (50 mm in diameter) in an amount enough to form a 5 mm thick layer, and ash water repellency was measured according to the Water Drop Penetration Test. Later, ash was carefully wetted with 15 ml of deionized water and placed in an oven during 4 days (96 hours), as in Bodí et al. (2012). This procedure was repeated 5 times in order to observe the effects of wet-dry cycles in ash water repellency. The results showed significant differences among wet-dry cycles (Chi Sqr = 184.13 p <0.001) and among temperatures, immediately after treatments (Kruskal-Wallis test: H = 13.64, p<0.01) and after first wet-dry cycle (Kruskal-Wallis test: H =13.85 p<0.01). In the second (Kruskal-Wallis test: =5.80, p >0.05), third (Kruskal-Wallis test: H =3.07, p>0.05), fourth (Kruskal-Wallis test: H=0.75, p>0.05) and fifth (Kruskal-Wallis test: H =0.199, p<0.05) wet-dry cycles, ash water repellency did not show significant differences. After wetting, ash water repellency decreased substantially in the first cycle. These results suggest that wet-dry cycles have important impacts in the reduction of ash water repellency. Nevertheless, this reduction at least in the first cycle is different according to the temperature/severity. Black ash (200 ºC) water repellency was significantly higher than the other temperatures/severities. Further research will be carried out using burned soils and different species. References Bodi, M.B., Doerr, S., Cerda, A., Mataix-Solera, J. (2012) Hydrological effects of a layer of vegetation ash on underlying wettable and water repellent soil. Geoderma, 161, 14-23, 2011. DOI: 10.1016/j.geoderma.2012.01.006. Bodí, M.B., Mataix-Solera, J., Doerr, S.H., Cerdà, A. (2011). The wettability of ash from burned vegetation and its relationship to Mediterranean plant species type, burn severity and total organic carbon content. Geoderma 160, 599-607. DOI:10.1016/j.geoderma.2010.11.009. Pereira, P., Cerdà, A., Úbeda, X., Mataix-Solera, J. Arcenegui, V., Zavala, L. (2013a) Modelling the impacts of wildfire on ash thickness in a short-term period, Land Degradation and Development. DOI: 10.1002/ldr.2195. Pereira, P., Cerdà, A., Úbeda, X., Mataix-Solera, J., Jordan, A. Burguet, M. (2013b) Spatial models for monitoring the spatio-temporal evolution of ashes after fire - a case study of a burnt grassland in Lithuania, Solid Earth, 4, 153-165. DOI: 10.5194/se-4-153-2013.

Interrelationships between soil biota and soil physical properties in forest areas of the Pieniny National Park (Poland)

NASA Astrophysics Data System (ADS)

Józefowska, Agnieszka; Zaleski, Tomasz; Sokołowska, Justyna; Dzierwa, Agata

2017-04-01

The study area was located in the Pieniny National Park (PNP) in the Carpathian Mountain (Southern Poland). Investigated soil belonged to Eutric Cambisols and had silt or silt loam texture. The purpose of this research was to investigated relationship between soil biota, such as microbial activity, soil Oligochaeta (Lumbricidae and Enchytraeidae) and soil physical properties, such as water retention or aggregates stability. This research was conducted at six forest monitoring areas of the PNP. Sampling was collected in the September 2016. For each of the 6 places, undisturbed and disturbed soil samples were taken from the 0-15-cm and 15-30-cm layer in 3 to 5 replicates. Undisturbed soil was taken: i) into Kopecky cylinders to determined soil physical properties; ii) a soil cores to determined enchytraeids and fine roots biomass (RB). Disturbed soil was collected in 3 reps and homogenized. Next such soil samples were divided into three parts: i) fresh one to determined dehydrogenase activity (ADh), microbial carbon biomass (MC) and labile carbon (LC); ii) air-dried, passed through a sieve (2-mm mesh size) and used for analysis: pH, organic carbon and bulk density; iii) last part air dried was used to determined stability of different size aggregates. In field, earthworms were collected in 3 reps using hand sorting method. Investigated soils were strongly acidic to neutral (pH 4.8-6.8). Organic carbon (Corg) content was varied from 0.8% to 4.5% and was higher in 0-15-cm layers than in 15-30-cm layers. Higher Corgcontent was connected with lower bulk density. Enchytraeids density was ranged from 1807 ind. m-2 to 88855 ind. m-2 and was correlated with microbial activity (ADh and MB) and RB. Earthworms density (ED) was ranged from 7 ind. m-2to 507 ind. m-2. In investigated soil was 6 genus and 7 species (Octolasion lacteum, Aporrectodea caliginosa, Aporrectodea rosea, Aporrectodea jassyensis, Lumbricus rubellus, Eisenia lucens, and Fitzingeria platyura depressa). ED was closely related with soil moisture and water field capacity. This Research was financed by the Ministry of Science and Higher Education of the Republic of Poland, No. BM - 4175/16

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.

[Relationships between soil moisture and needle-fall in Masson pine forests in acid rain region of Chongqing, Southwest China].

PubMed

Wang, Yi-Hao; Wang, Yan-Hui; Li, Zhen-Hua; Yu, Peng-Tao; Xiong, Wei; Hao, Jia; Duan, Jian

2012-10-01

From March 2009 to November 2011, an investigation was conducted on the spatiotemporal variation of soil moisture and its effects on the needle-fall in Masson pine (Pinus massoniana) forests in acid rain region of Chongqing, Southeast China, with the corresponding soil moisture thresholds determined. No matter the annual precipitation was abundant, normal or less than average, the seasonal variation of soil moisture in the forests could be obviously divided into four periods, i.e., sufficient (before May), descending (from June to July), drought (from August to September), and recovering (from October to November). With increasing soil depth, the soil moisture content increased after an initial decrease, but the difference of the soil moisture content among different soil layers decreased with decreasing annual precipitation. The amount of monthly needle-fall in the forests in growth season was significantly correlated with the water storage in root zone (0-60 cm soil layer), especially in the main root zone (20-50 cm soil layer). Soil field capacity (or capillary porosity) and 82% of field capacity (or 80% of capillary porosity) were the main soil moisture thresholds affecting the litter-fall. It was suggested that in acid rain region, Masson pine forest was easily to suffer from water deficit stress, especially in dry-summer period. The water deficit stress, together with already existed acid rain stress, would further threaten the health of the Masson forest.

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.

Estimating temporal changes in soil carbon stocks at ecoregional scale in Madagascar using remote-sensing

NASA Astrophysics Data System (ADS)

Grinand, C.; Maire, G. Le; Vieilledent, G.; Razakamanarivo, H.; Razafimbelo, T.; Bernoux, M.

2017-02-01

Soil organic carbon (SOC) plays an important role in climate change regulation notably through release of CO2 following land use change such a deforestation, but data on stock change levels are lacking. This study aims to empirically assess SOC stocks change between 1991 and 2011 at the landscape scale using easy-to-access spatially-explicit environmental factors. The study area was located in southeast Madagascar, in a region that exhibits very high rate of deforestation and which is characterized by both humid and dry climates. We estimated SOC stock on 0.1 ha plots for 95 different locations in a 43,000 ha reference area covering both dry and humid conditions and representing different land cover including natural forest, cropland, pasture and fallows. We used the Random Forest algorithm to find out the environmental factors explaining the spatial distribution of SOC. We then predicted SOC stocks for two soil layers at 30 cm and 100 cm over a wider area of 395,000 ha. By changing the soil and vegetation indices derived from remote sensing images we were able to produce SOC maps for 1991 and 2011. Those estimates and their related uncertainties where combined in a post-processing step to map estimates of significant SOC variations and we finally compared the SOC change map with published deforestation maps. Results show that the geologic variables, precipitation, temperature, and soil-vegetation status were strong predictors of SOC distribution at regional scale. We estimated an average net loss of 10.7% and 5.2% for the 30 cm and the 100 cm layers respectively for deforested areas in the humid area. Our results also suggest that these losses occur within the first five years following deforestation. No significant variations were observed for the dry region. This study provides new solutions and knowledge for a better integration of soil threats and opportunities in land management policies.

The impact of non-isothermal soil moisture transport on evaporation fluxes in a maize cropland

NASA Astrophysics Data System (ADS)

Shao, Wei; Coenders-Gerrits, Miriam; Judge, Jasmeet; Zeng, Yijian; Su, Ye

2018-06-01

The process of evaporation interacts with the soil, which has various comprehensive mechanisms. Multiphase flow models solve air, vapour, water, and heat transport equations to simulate non-isothermal soil moisture transport of both liquid water and vapor flow, but are only applied in non-vegetated soils. For (sparsely) vegetated soils often energy balance models are used, however these lack the detailed information on non-isothermal soil moisture transport. In this study we coupled a multiphase flow model with a two-layer energy balance model to study the impact of non-isothermal soil moisture transport on evaporation fluxes (i.e., interception, transpiration, and soil evaporation) for vegetated soils. The proposed model was implemented at an experimental agricultural site in Florida, US, covering an entire maize-growing season (67 days). As the crops grew, transpiration and interception became gradually dominated, while the fraction of soil evaporation dropped from 100% to less than 20%. The mechanisms of soil evaporation vary depending on the soil moisture content. After precipitation the soil moisture content increased, exfiltration of the liquid water flow could transport sufficient water to sustain evaporation from soil, and the soil vapor transport was not significant. However, after a sufficient dry-down period, the soil moisture content significantly reduced, and the soil vapour flow significantly contributed to the upward moisture transport in topmost soil. A sensitivity analysis found that the simulations of moisture content and temperature at the soil surface varied substantially when including the advective (i.e., advection and mechanical dispersion) vapour transport in simulation, including the mechanism of advective vapour transport decreased soil evaporation rate under wet condition, while vice versa under dry condition. The results showed that the formulation of advective soil vapor transport in a soil-vegetation-atmosphere transfer continuum can affect the simulated evaporation fluxes, especially under dry condition.

Sensitivity of stomatal conductance to soil moisture: implications for tropospheric ozone

NASA Astrophysics Data System (ADS)

Anav, Alessandro; Proietti, Chiara; Menut, Laurent; Carnicelli, Stefano; De Marco, Alessandra; Paoletti, Elena

2018-04-01

Soil moisture and water stress play a pivotal role in regulating stomatal behaviour of plants; however, in the last decade, the role of water availability has often been neglected in atmospheric chemistry modelling studies as well as in integrated risk assessments, despite the fact that plants remove a large amount of atmospheric compounds from the lower troposphere through stomata. The main aim of this study is to evaluate, within the chemistry transport model CHIMERE, the effect of soil water limitation on stomatal conductance and assess the resulting changes in atmospheric chemistry testing various hypotheses of water uptake by plants in the rooting zone. Results highlight how dry deposition significantly declines when soil moisture is used to regulate the stomatal opening, mainly in the semi-arid environments: in particular, over Europe the amount of ozone removed by dry deposition in one year without considering any soil water limitation to stomatal conductance is about 8.5 TgO3, while using a dynamic layer that ensures that plants maximize the water uptake from soil, we found a reduction of about 10 % in the amount of ozone removed by dry deposition ( ˜ 7.7 TgO3). Although dry deposition occurs from the top of canopy to ground level, it affects the concentration of gases remaining in the lower atmosphere, with a significant impact on ozone concentration (up to 4 ppb) extending from the surface to the upper troposphere (up to 650 hPa). Our results shed light on the importance of improving the parameterizations of processes occurring at plant level (i.e. from the soil to the canopy) as they have significant implications for concentration of gases in the lower troposphere and resulting risk assessments for vegetation or human health.

The impact of extreme environmental factors on the mineralization potential of the soil

NASA Astrophysics Data System (ADS)

Zinyakova, Natalia; Semenov, Vyacheslav

2016-04-01

Warming, drying, wetting are the prevalent disturbing natural impacts that affect the upper layers of uncultivated and arable soils. The effect of drying-wetting cycles act as a physiological stress for the soil microbial community and cause changes in its structure, the partial death or lysis of the microbial biomass. The mobilization of the SOM and the stabilization of the potentially mineralizable components lead to change of mineralization potential in the soil. To test the effects of different moisture regime on plant growth and soil biological properties, plot experiment with the gray forest soil including trials with plants (corn) and bare fallow was performed. Different regimes of soil moisture (conditionally optimal, relatively deficient soil moisture and repeated cycles of drying-wetting) were created. Control of soil moisture was taken every two or three days. Gas sampling was carried out using closed chambers. Soil samples were collected at the end of the pot experiment. The potentially mineralizable content of soil organic carbon (SOC) was measured by biokinetic method based on (1) aerobic incubation of soil samples under constant temperature and moisture conditions during 158 days, (2) quantitation of C-CO2, and (3) fitting of C-CO2 cumulative curve by a model of first-order kinetic. Total soil organic carbon was measured by Tyrin's wet chemical oxidation method. Permanent deficient moisture in the soil favored the preservation of potentially mineralizable SOC. Two repeated cycles of drying-wetting did not reduce the potentially mineralizable carbon content in comparison with control under optimal soil moisture during 90 days of experiment. The emission loss of C-CO2 from the soil with plants was 1.4-1.7 times higher than the decrease of potentially mineralizable SOC due to the contribution of root respiration. On the contrary, the decrease of potentially mineralized SOC in the soil without plants was 1.1-1.2 times larger than C-CO2 emissions from the soil as a result of stabilization processes. Thus, the alternation of drying-wetting cycles results in 1) the death of microbial biomass and recolonization of the soil microorganisms; 2) favors the splitting and degradation of soil aggregates, as well as the reaggregation and stabilization of aggregates; 3) contributes to the mobilization of the SOM and also 4) initiates the stabilization of the potentially mineralizable components. The effect of drying-wetting cycles is expressed not so much in the loss of the total soil organic carbon as in the degradation of the SOM quality with decreasing its mineralization potential. We can conclude that different soil moisture regimes lead to essential changes of mineralization potential in the gray forest soil. The amount of mineralization loss soil carbon via C-CO2 emission is directly associated with the decrease of potentially mineralizable carbon. Deficient moisture is a reason for temporarily sequestration of SOC potentially mineralizable under optimal moisture. This work was supported by RSF. Project number 14-14-00625

ESTIMATING GASEOUS EXCHANGES BETWEEN THE ATMOSPHERE AND PLANTS USING A COUPLED BIOCHEMICAL DRY DEPOSITION MODEL

EPA Science Inventory

To study gaseous exchanges between the soil, biosphere and atmosphere, a biochemical model was coupled with the latest version of Meyers Multi-Layer Deposition Model. The biochemical model describes photosynthesis and respiration and their coupling with stomatal resistance for...

Enhanced Cover Assessment Project:Soil Manipulation and Revegetation Tests

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

Waugh, W. Joseph; Albright, Dr. Bill; Benson, Dr. Craig

2014-02-01

The U.S. Department of Energy Office of Legacy Management is evaluating methods to enhance natural changes that are essentially converting conventional disposal cell covers for uranium mill tailings into water balance covers. Conventional covers rely on a layer of compacted clayey soil to limit exhalation of radon gas and percolation of rainwater. Water balance covers rely on a less compacted soil “sponge” to store rainwater, and on soil evaporation and plant transpiration (evapotranspiration) to remove stored water and thereby limit percolation. Over time, natural soil-forming and ecological processes are changing conventional covers by increasing hydraulic conductivity, loosening compaction, and increasingmore » evapotranspiration. The rock armor on conventional covers creates a favorable habitat for vegetation by slowing soil evaporation, increasing soil water storage, and trapping dust and organic matter, thereby providing the water and nutrients needed for plant germination, survival, and sustainable transpiration. Goals and Objectives Our overall goal is to determine if allowing or enhancing these natural changes could improve cover performance and reduce maintenance costs over the long term. This test pad study focuses on cover soil hydrology and ecology. Companion studies are evaluating effects of natural and enhanced changes in covers on radon attenuation, erosion, and biointrusion. We constructed a test cover at the Grand Junction disposal site to evaluate soil manipulation and revegetation methods. The engineering design, construction, and properties of the test cover match the upper three layers of the nearby disposal cell cover: a 1-foot armoring of rock riprap, a 6-inch bedding layer of coarse sand and gravel, and a 2-foot protection layer of compacted fine soil. The test cover does not have a radon barrier—cover enhancement tests leave the radon barrier intact. We tested furrowing and ripping as means for creating depressions parallel to the slope contour, bringing soil up into the rock riprap layer, and loosening and blending compacted fine soil with coarse sand and gravel layers. Objectives of these manipulations include (1) enhancing root growth, (2) increasing seed-soil contact, (3) catching runoff water for plant germination and growth, (4) increasing soil water storage capacity, and (5) enhancing deep drying by disrupting the capillary barrier at the interface of the bedding and protection layers.« less

Soils characterisation along ecological forest zones in the Eastern Himalayas

NASA Astrophysics Data System (ADS)

Simon, Alois; Dhendup, Kuenzang; Bahadur Rai, Prem; Gratzer, Georg

2017-04-01

Elevational gradients are commonly used to characterise vegetation patterns and, to a lesser extent, also to describe soil development. Furthermore, interactions between vegetation cover and soil characteristics are repeatedly observed. Combining information on soil development and easily to distinguish forest zones along elevational gradients, creates an added value for forest management decisions especially in less studied mountain regions. For this purpose, soil profiles along elevational gradients in the temperate conifer forests of Western and Central Bhutan, ranging from 2600-4000m asl were investigated. Thereby, 82 soil profiles were recorded and classified according to the World Reference Base for Soil Resources. Based on 19 representative profiles, genetic horizons were sampled and analysed. We aim to provide fundamental information on forest soil characteristics along these elevational transects. The results are presented with regard to ecological forest zones. The elevational distribution of the reference soil groups showed distinct distribution ranges for most of the soils. Cambisols were the most frequently recorded reference soil group with 58% of the sampled profiles, followed by Podzols in higher elevations, and Stagnosols, at intermediate elevations. Fluvisols occurred only at the lower end of the elevational transects and Phaeozems only at drier site conditions in the cool conifer dry forest zone. The humus layer thickness differs between forest zones and show a shift towards increased organic layer (O-layer) with increasing elevation. The reduced biomass productivity with increasing elevation and subsequently lower litter input compensates for the slow decomposition rates. The increasing O-layer thickness is an indicator of restrained intermixing of organic and mineral components by soil organisms at higher elevation. Overall, the soil types and soil characteristics along the elevational gradient showed a continuous and consistent change, instead of abrupt changes. We interpret these as manifestations of changes of temperature and precipitation with elevation which also drives forest zonation in these least anthropogenically influenced forest ecosystems. The elevational distribution of forest zones is correlated with the distribution of soil types and thus also reflects soil characteristics.

Pathways of soil moisture controls on boundary layer dynamics

NASA Astrophysics Data System (ADS)

Siqueira, M.; Katul, G.; Porporato, A.

2007-12-01

Soil moisture controls on precipitation are now receiving significant attention in climate systems because the memory of their variability is much slower than the memory of the fast atmospheric processes. We propose a new model that integrates soil water dynamics, plant hydraulics and stomatal responses to water availability to estimate root water uptake and available energy partitioning, as well as feedbacks to boundary layer dynamics (in terms of water vapor and heat input to the atmospheric system). Using a simplified homogenization technique, the model solves the intrinsically 3-D soil water movement equations by two 1-D coupled Richards' equations. The first resolves the radial water flow from bulk soil to soil-root interface to estimate root uptake (assuming the vertical gradients in moisture persist during the rapid lateral flow), and then it solves vertical water movement through the soil following the radial moisture adjustments. The coupling between these two equations is obtained by area averaging the soil moisture in the radial domain (i.e. homogenization) to calculate the vertical fluxes. For each vertical layer, the domain is discretized in axi-symmetrical grid with constant soil properties. This is deemed to be appropriate given the fact that the root uptake occurs on much shorter time scales closely following diurnal cycles, while the vertical water movement is more relevant to the inter-storm time scale. We show that this approach was able to explicitly simulate known features of root uptake such as diurnal hysteresis of canopy conductance, water redistribution by roots (hydraulic lift) and downward shift of root uptake during drying cycles. The model is then coupled with an atmospheric boundary layer (ABL) growth model thereby permitting us to explore low-dimensional elements of the interaction between soil moisture and ABL states commensurate with the lifting condensation level.

Soil moisture and the persistence of North American drought

NASA Technical Reports Server (NTRS)

Oglesby, Robert J.; Erickson, David J., III

1989-01-01

Numerical sensitivity experiments on the effects of soil moisture on North American summertime climate are performed using a 12-layer global atmospheric general circulation model. Consideration is given to the hypothesis that reduced soil moisture may induce and amplify warm, dry summers of midlatitude continental interiors. The simulations resemble the conditions of the summer of 1988, including an extensive drought over much of North America. It is found that a reduction in soil moisture leads to an increase in surface temperature, lower surface pressure, increased ridging aloft, and a northward shift of the jet stream. It is shown that low-level moisture advection from the Gulf of Mexico is important in the maintenance of persistent soil moisture deficits.

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.

[Effects of cotton straw returning on soil organic carbon, nitrogen, phosphorus and potas-sium contents in soil aggregates].

PubMed

Wang, Shuang Lei; Liu, Yan Hui; Song, Xian Liang; Wei, Shao Bin; Li, Jin Pu; Nie, Jun Jun; Qin, Du Lin; Sun, Xue Zhen

2016-12-01

To clarify the effects of cotton straw returning on the composition and contents of nu-trients in different particle sizes of aggregates, two treatments with or without cotton straw returning were tested in continuous three years. After three years straw treatments, we collected undisturbed soil within 0-5, 5-10, 10-20 and 20-30 cm soil layers, and to measure the composition, soil organic carbon, nitrogen, phosphorus and potassium contents in different particle sizes of aggregates classified using dry sieving. Returning cotton straw into the field significantly increased particle contents of 2-5 mm and >5 mm aggregates in 0-5 cm soil layer, while the content of <0.25 mm micro-aggregates was decreased. Cotton straw returning significantly improved soil organic carbon, nitrogen, and potassium contents by 19.2%, 14.2% and 17.3%, respectively, compared to no returning control. In 5-10 cm soil layer, cotton straw returning increased the contents of 2-5 mm and >5 mm aggregates, reduced the content of <0.25 mm micro-aggregate, but significantly increased contents of soil organic carbon, available nitrogen and potassium by 19.6%, 12.6% and 23.4%, compared to no straw returning control. In 10-20 cm soil layer, cotton straw returning significantly reduced the content of <0.25 mm micro-aggregates, and significantly enhanced soil organic carbon, nitrogen, and potassium contents by 8.4%, 10.9% and 11.5%, compared to the control. However, in 20-30 cm soil layer, cotton straw returning only increased soil available potassium content by 12.0%, while there were no significant changes in particle size, organic carbon, nitrogen and phosphorus contents. We concluded that cotton straw returning could significantly improve the structure of surface soil by increasing the number of macro-aggregates, contents of organic carbon, available nitrogen and potassium in aggregates, while decreasing micro-aggregate content. The enhancement of the contribution of macro-aggregates to soil fertility by returning cotton straw could improve soil physical structure, fertility and then increase cotton yield.

Intraspecific variation in the use of water sources by the circum-Mediterranean conifer Pinus halepensis.

PubMed

Voltas, Jordi; Lucabaugh, Devon; Chambel, Maria Regina; Ferrio, Juan Pedro

2015-12-01

The relevance of interspecific variation in the use of plant water sources has been recognized in drought-prone environments. By contrast, the characterization of intraspecific differences in water uptake patterns remains elusive, although preferential access to particular soil layers may be an important adaptive response for species along aridity gradients. Stable water isotopes were analysed in soil and xylem samples of 56 populations of the drought-avoidant conifer Pinus halepensis grown in a common garden test. We found that most populations reverted to deep soil layers as the main plant water source during seasonal summer droughts. More specifically, we detected a clear geographical differentiation among populations in water uptake patterns even under relatively mild drought conditions (early autumn), with populations originating from more arid regions taking up more water from deep soil layers. However, the preferential access to deep soil water was largely independent of aboveground growth. Our findings highlight the high plasticity and adaptive relevance of the differential access to soil water pools among Aleppo pine populations. The observed ecotypic patterns point to the adaptive relevance of resource investment in deep roots as a strategy towards securing a source of water in dry environments for P. halepensis. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Visualizing Rhizosphere Soil Structure Around Living Roots

NASA Astrophysics Data System (ADS)

Menon, M.; Berli, M.; Ghezzehei, T. A.; Nico, P.; Young, M. H.; Tyler, S. W.

2008-12-01

The rhizosphere, a thin layer of soil (0 to 2 mm) surrounding a living root, is an important interface between bulk soil and plant root and plays a critical role in root water and nutrient uptake. In this study, we used X-ray Computerized Microtomography (microCT) to visualize soil structure around living roots non-destructively and with high spatial resolution. Four different plant species (Helianthus annuus, Lupinus hartwegii, Vigna radiata and Phaseolus lunatus), grown in four different porous materials (glass beads, medium and coarse sand, loam aggregates), were scanned with 10 ìm spatial resolution, using the microtomography beamline 8.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA. Sample cross section images clearly show contacts between roots and soil particles, connecting water films, air-water interfaces as well as some cellular features of the plants taproots. We found with a simulation experiment, inflating a cylindrical micro-balloon in a pack of air-dry loam aggregates, that soil fracturing rather than compaction might occur around a taproot growing in dry soil. Form these preliminary experiments, we concluded that microCT has potential as a tool for a more process-based understanding of the role of rhizosphere soil structure on soil fertility, plant growth and the water balance at the earth-atmosphere interface.

On the performance of capillary barriers as landfill cover

NASA Astrophysics Data System (ADS)

Kämpf, M.; Montenegro, H.

Landfills and waste heaps require an engineered surface cover upon closure. The capping system can vary from a simple soil cover to multiple layers of earth and geosynthetic materials. Conventional design features a compacted soil layer, which suffers from drying out and cracking, as well as root and animal intrusion. Capillary barriers consisting of inclined fine-over-coarse soil layers are investigated as an alternative cover system. Under unsaturated conditions, the textural contrast delays vertical drainage by capillary forces. The moisture that builds up above the contact will flow downdip along the interface of the layers. Theoretical studies of capillary barriers have identified the hydraulic properties of the layers, the inclination angle, the length of the field and the infiltration rate as the fundamental characteristics of the system. However, it is unclear how these findings can lead to design criteria for capillary barriers. To assess the uncertainty involved in such approaches, experiments have been carried out in a 8 m long flume and on large scale test sites (40 m x 15 m). In addition, the ability of a numerical model to represent the relevant flow processes in capillary barriers has been examined.

Directional optical transmission through a sand layer: a preliminary laboratory experiment

NASA Astrophysics Data System (ADS)

Tian, Jia; Philpot, William D.

2017-10-01

Given the importance of penetration of light in the soil for seed germination, soil warming, and the photolytic degradation of pesticides, directional transmission of thin sand samples are studied in this paper under both dry and saturated conditions. The detector views upward through a glass-bottom sample holder, filled to 3 or 4 mm with a coarse, translucent, quartz sand sample. Transmission through the samples was measured as the illumination zenith angle moved from 0 to 70° in 5° intervals. In the most cases, transmission decreased monotonically, but slowly with increasing illumination angle at all wavelengths. A peak in transmission only appeared at 0° illumination for the low bulk density, dry sample at 3 mm depth. The 0° peak disappeared when the sample was wetted, when the bulk density increased, or when the depth of the sample increased, which indicates that the radiation transmitting through a sand layer can be diffused thoroughly with a millimeters-thin sand layer. For the saturated samples, water influences light transmission in contrasting ways in shorter and longer wavelength. Transmission increased in the VNIR when saturated relative to dry, while transmission decreased sharply after 1300 nm, with spectral absorption features characteristic of water absorption. In VNIR region, water absorption is low and the low relative index of refraction enhanced transmission through sand sample. In contrast, water absorption became dominant at longer wavelengths region leading to the strongly reduced transmission.

Lime utilization in the laboratory, field, and design of pavement layers : final report.

DOT National Transportation Integrated Search

2017-01-01

The objective of this study was to review and report the best practices of using lime (i.e., granulated lime, hydrated lime, and slurry lime) to dry soil, in working tables, and in pavement applications. The project also reviewed and documented the i...

Changes in soil thermal regime lead to substantial shifts in carbon and energy fluxes in drained Arctic tundra

NASA Astrophysics Data System (ADS)

Goeckede, M.; Kwon, M. J.; Kittler, F.; Heimann, M.; Zimov, N.; Zimov, S. A.

2016-12-01

Climate change impacts in the Arctic will not only depend on future temperature trajectories in this region. In particular, potential shifts in hydrologic regimes, e.g. linked to altered precipitation patterns or changes in topography following permafrost degradation, can dramatically modify ecosystem feedbacks to warming. Here, we analyze how severe drainage affects both biogeochemical and biogeophysical processes within a formerly wet Arctic tundra, with a special focus on the interactions between hydrology and soil temperatures, and related effects on the fluxes of carbon and energy. Our findings are based on year-round observations from a decade-long drainage experiment conducted near Chersky, Northeast Siberia. Through our multi-disciplinary observations we can document that the drainage triggered a suite of secondary changes in ecosystem properties, including e.g. adaptation processes in the vegetation community structure, or shifts in snow cover regime. Most profoundly, a combination of low heat capacity and reduced heat conductivity in dry organic soils lead to warmer soil temperatures near the surface, while deeper soil layers remained colder. These changes in soil thermal regime reduced the contribution of deeper soil layers with older carbon pools to overall ecosystem respiration, as documented through radiocarbon signals. Regarding methane, the observed steeper temperature gradient along the vertical soil profile slowed down methane production in deep layers, while promoting CH4 oxidation near the surface. Taken together, both processes contributed to a reduction in CH4 emissions up to a factor of 20 following drainage. Concerning the energy budget, we observed an intensification of energy transfer to the lower atmosphere, particularly in form of sensible heat, but the reduced energy transfer into deeper soil layers also led to systematically shallower thaw depths. Summarizing, drainage may contribute to slow down decomposition of old carbon from deep soil layers, counterbalancing direct warming effects on permafrost carbon pools.

SMOS brightness temperature assimilation into the Community Land Model

NASA Astrophysics Data System (ADS)

Rains, Dominik; Han, Xujun; Lievens, Hans; Montzka, Carsten; Verhoest, Niko E. C.

2017-11-01

SMOS (Soil Moisture and Ocean Salinity mission) brightness temperatures at a single incident angle are assimilated into the Community Land Model (CLM) across Australia to improve soil moisture simulations. Therefore, the data assimilation system DasPy is coupled to the local ensemble transform Kalman filter (LETKF) as well as to the Community Microwave Emission Model (CMEM). Brightness temperature climatologies are precomputed to enable the assimilation of brightness temperature anomalies, making use of 6 years of SMOS data (2010-2015). Mean correlation R with in situ measurements increases moderately from 0.61 to 0.68 (11 %) for upper soil layers if the root zone is included in the updates. A reduced improvement of 5 % is achieved if the assimilation is restricted to the upper soil layers. Root-zone simulations improve by 7 % when updating both the top layers and root zone, and by 4 % when only updating the top layers. Mean increments and increment standard deviations are compared for the experiments. The long-term assimilation impact is analysed by looking at a set of quantiles computed for soil moisture at each grid cell. Within hydrological monitoring systems, extreme dry or wet conditions are often defined via their relative occurrence, adding great importance to assimilation-induced quantile changes. Although still being limited now, longer L-band radiometer time series will become available and make model output improved by assimilating such data that are more usable for extreme event statistics.

Biologically Active Organic Matter in Soils of European Russia

NASA Astrophysics Data System (ADS)

Semenov, V. M.; Kogut, B. M.; Zinyakova, N. B.; Masyutenko, N. P.; Malyukova, L. S.; Lebedeva, T. N.; Tulina, A. S.

2018-04-01

Experimental and literature data on the contents and stocks of active organic matter in 200 soil samples from the forest-tundra, southern-taiga, deciduous-forest, forest-steppe, dry-steppe, semidesert, and subtropical zones have been generalized. Natural lands, agrocenoses, treatments of long-term field experiments (bare fallow, unfertilized and fertilized crop rotations, perennial plantations), and different layers of soil profile are presented. Sphagnum peat and humus-peat soil in the tundra and forest-tundra zones are characterized by a very high content of active organic matter (300-600 mg C/100 g). Among the zonal soils, the content of active organic matter increases from the medium (75-150 mg C/100 g) to the high (150-300 mg C/100 g) level when going from soddy-podzolic soil to gray forest and dark-gray forest soils and then to leached chernozem. In the series from typical chernozem to ordinary and southern chernozem and chestnut and brown semidesert soils, a decrease in the content of active organic matter to the low (35-75 mg C/100 g) and very low (<35 mg C/100 g) levels is observed. Acid brown forest soil in the subtropical zone is characterized by a medium supply with active organic matter. Most arable soils are mainly characterized by low or very low contents of active organic matter. In the upper layers of soils, active organic matter makes up 1.2-11.1% of total Corg. The profile distribution of active organic matter in the studied soils coincides with that of Corg: their contents appreciably decrease with depth, except for brown semidesert soil. The stocks of active organic matter vary from 0.4 to 5.4 t/ha in the layer of 0-20 cm and from 1.0 to 12.4/ha in the layer of 0-50 cm of different soil types.

Wet and dry atmospheric depositions of inorganic nitrogen during plant growing season in the coastal zone of Yellow River Delta.

PubMed

Yu, Junbao; Ning, Kai; Li, Yunzhao; Du, Siyao; Han, Guangxuan; Xing, Qinghui; Wu, Huifeng; Wang, Guangmei; Gao, Yongjun

2014-01-01

The ecological problems caused by dry and wet deposition of atmospheric nitrogen have been widespread concern in the world. In this study, wet and dry atmospheric depositions were monitored in plant growing season in the coastal zone of the Yellow River Delta (YRD) using automatic sampling equipment. The results showed that SO4 (2-) and Na(+) were the predominant anion and cation, respectively, in both wet and dry atmospheric depositions. The total atmospheric nitrogen deposition was ~2264.24 mg m(-2), in which dry atmospheric nitrogen deposition was about 32.02%. The highest values of dry and wet atmospheric nitrogen deposition appeared in May and August, respectively. In the studied area, NO3 (-)-N was the main nitrogen form in dry deposition, while the predominant nitrogen in wet atmospheric deposition was NH4 (+)-N with ~56.51% of total wet atmospheric nitrogen deposition. The average monthly attribution rate of atmospheric deposition of NO3 (-)-N and NH4 (+)-N was ~31.38% and ~20.50% for the contents of NO3 (-)-N and NH4 (+)-N in 0-10 cm soil layer, respectively, suggested that the atmospheric nitrogen was one of main sources for soil nitrogen in coastal zone of the YRD.

Rooting depth explains [CO2] x drought interaction in Eucalyptus saligna.

PubMed

Duursma, Remko A; Barton, Craig V M; Eamus, Derek; Medlyn, Belinda E; Ellsworth, David S; Forster, Michael A; Tissue, David T; Linder, Sune; McMurtrie, Ross E

2011-09-01

Elevated atmospheric [CO(2)] (eC(a)) often decreases stomatal conductance, which may delay the start of drought, as well as alleviate the effect of dry soil on plant water use and carbon uptake. We studied the interaction between drought and eC(a) in a whole-tree chamber experiment with Eucalyptus saligna. Trees were grown for 18 months in their C(a) treatments before a 4-month dry-down. Trees grown in eC(a) were smaller than those grown in ambient C(a) (aC(a)) due to an early growth setback that was maintained throughout the duration of the experiment. Pre-dawn leaf water potentials were not different between C(a) treatments, but were lower in the drought treatment than the irrigated control. Counter to expectations, the drought treatment caused a larger reduction in canopy-average transpiration rates for trees in the eC(a) treatment compared with aC(a). Total tree transpiration over the dry-down was positively correlated with the decrease in soil water storage, measured in the top 1.5 m, over the drying cycle; however, we could not close the water budget especially for the larger trees, suggesting soil water uptake below 1.5 m depth. Using neutron probe soil water measurements, we estimated fractional water uptake to a depth of 4.5 m and found that larger trees were able to extract more water from deep soil layers. These results highlight the interaction between rooting depth and response of tree water use to drought. The responses of tree water use to eC(a) involve interactions between tree size, root distribution and soil moisture availability that may override the expected direct effects of eC(a). It is essential that these interactions be considered when interpreting experimental results.

Phytotoxicity of water-soluble substances from alfalfa and barley soil extracts on four crop species.

PubMed

Read, J J; Jensen, E H

1989-02-01

Problems associated with continuously planting alfalfa (Medicago saliva L.) or seeding to thicken depleted alfalfa stands may be due to autotoxicity, an intraspecific form of allelopathy. A bioassay approach was utilized to characterize the specificity and chemical nature of phytotoxins in extracts of alfalfa soils as compared to fallow soil or soil where a cereal was the previous crop. In germination chamber experiments, water-soluble substances present in methanol extracts of soil cropped to alfalfa or barley (Hordeum vulgare L.) decreased seedling root length of alfalfa L-720, winter wheat (Triticum aestivum L. Nugaines) and radish (Raphanus sativa L. Crimson Giant). Five days after germination, seedling dry weights of alfalfa and radish in alfalfa soil extracts were lower compared to wheat or red clover (Trifolium pralense L. Kenland). Growth of red clover was not significantly reduced by soil extracts from cropped soil. Extracts of crop residue screened from soil cropped to alfalfa or barley significantly reduced seedling root length; extracts of alfalfa residue caused a greater inhibition of seedling dry weight than extracts of barely residue. A phytotoxic, unidentified substance present in extracts of crop residue screened from alfalfa soil, which inhibited seedling root length of alfalfa, was isolated by thin-layer chromatography (TLC). Residues from a soil cropped continuously to alfalfa for 10 years had the greatest phytotoxic activity.

Polymer tensiometers in a saline environment.

NASA Astrophysics Data System (ADS)

van der Ploeg, Martine; Gooren, H. P. A.; Bakker, G.; Russell, W.; Hoogendam, C. W.; Huiskes, C.; Shouse, P.; de Rooij, G. H.

2010-05-01

It is estimated that 20% of all cultivated land and nearly half of the irrigated land is salt-affected, which pose major economic and environmental problems. Salinity may be the result of two processes; dryland and irrigation salinity. Dryland salinity is caused by a rise in the groundwater table, which occurs as a result of the replacement of deep-rooted, perennial native vegetation by shallow-rooted annual species meant for production. Irrigation salinity may occur as a result of poor water quality, poor drainage, or inefficient use of water. Consequently, new strategies to enhance crop yield stability on saline soils represent a major research priority (Botella et al. 2005). At the same time, native vegetation is capable of thriving under saline and/or dry conditions. The plant physiology of such vegetation has been investigated thoroughly, but the relation with in situ soil properties (soil moisture and salinity) may be more difficult to unravel as soil moisture sensors are less sensitive in dry soil, and the signal of most soil moisture content sensors is strongly attenuated by soil salinity. Recently, polymer tensiometer were developed that are able to measure matric potentials (closely related to a soil's moisture status) in dry soils. Polymer tensiometers consist of a solid ceramic, a stainless steel cup and a pressure transducer. The ceramic consist of a support layer and a membrane with 2 nm pore-size to prevent polymer leakage. Between the ceramic membrane and the pressure transducer a tiny chamber is located, which contains the polymer solution. The polymer's osmotic potential strongly reduces the total water potential inside the polymer tensiometer, which causes build-up of osmotic pressure. Polymer tensiometers would thus be an ideal instrument to measure in dry soil, if the polymer inside the tensiometer is not affected by the salts in the soil solution. We will address some key issues regarding the use of POTs in saline environments by showing results from a field experiment conducted in a very saline soil. This research was funded by the Dutch Technology Foundation (STW).

Faunal Drivers of Soil Flux Dynamics via Alterations in Crack Structure

NASA Astrophysics Data System (ADS)

DeCarlo, Keita; Caylor, Kelly

2016-04-01

Organismal activity, in addition to its role in ecological feedbacks, has the potential to serve as instigators or enhancers of atmospheric and hydrologic processes via alterations in soil structural regimes. We investigated the biomechanical effect of faunal activity on soil carbon dynamics via changes in soil crack structure, focusing on three dryland soil systems: bioturbated, biocompacted and undisturbed soils. Carbon fluxes were characterized using a closed-system respiration chamber, with CO2 concentration differences measured using an infrared gas analyzer (IRGA). Results show that faunal influences play a divergent biomechanics role in bulk soil cracking: bioturbation induced by belowground fauna creates "surficial" (shallow, large, well-connected) networks relative to the "systematic" (deep, moderate, poorly connected) networks created by aboveground fauna. The latter also shows a "memory" of past wetting/drying events in the consolidated soil through a crack layering effect. These morphologies further drive differences in soil carbon flux: under dry conditions, bioturbated and control soils show a persistently high and low mean carbon flux, respectively, while biocompacted soils show a large diurnal trend, with daytime lows and nighttime highs comparable to the control and bioturbated soils, respectively. Overall fluxes under wet conditions are considerably higher, but also more variable, though higher mean fluxes are observed in the biocompacted and bioturbated soils. Our results suggest that the increased surface area in the bioturbated soils create enhanced but constant diffusive processes, whereas the increased thermal gradient in the biocompacted soils create novel convective processes that create high fluxes that are diurnal in nature.

Reduction of bacteria and somatic coliphages in constructed wetlands for the treatment of combined sewer overflow (retention soil filters).

PubMed

Ruppelt, Jan P; Tondera, Katharina; Schreiber, Christiane; Kistemann, Thomas; Pinnekamp, Johannes

2018-05-01

Combined sewer overflows (CSOs) introduce numerous pathogens from fecal contamination, such as bacteria and viruses, into surface waters, thus endangering human health. In Germany, retention soil filters (RSFs) treat CSOs at sensitive discharge points and can contribute to reducing these hygienically relevant microorganisms. In this study, we evaluated the extent of how dry period, series connection and filter layer thickness influence the reduction efficiency of RSFs for Escherichia coli (E. coli), intestinal enterococci (I. E.) and somatic coliphages. To accomplish this, we had four pilot scale RSFs built on a test field at the wastewater treatment plant Aachen-Soers. While two filters were replicates, the other two filters were installed in a series connection. Moreover, one filter had a thinner filtration layer than the other three. Between April 2015 and December 2016, the RSFs were loaded in 37 trials with pre-conditioned CSO after dry periods ranging from 4 to 40 days. During 17 trials, samples for microbial analysis were taken and analyzed. The series connection of two filters showed that the removal increases when two systems with a filter layer of the same height are operated in series. Since the microorganisms are exposed twice to the environmental conditions on the filter surface and in the upper filter layers, there is a greater chance for abiotic adsorption increase. The same effect could be shown when filters with different depths were compared: the removal efficiency increases as filter thickness increases. This study provides new evidence that regardless of seasonal effects and dry period, RSFs can improve hygienic situation significantly. Copyright © 2018 Elsevier GmbH. All rights reserved.

Accuracy of the cosmic-ray soil water content probe in humid forest ecosystems: The worst case scenario

NASA Astrophysics Data System (ADS)

Bogena, H. R.; Huisman, J. A.; Baatz, R.; Hendricks Franssen, H.-J.; Vereecken, H.

2013-09-01

Soil water content is one of the key state variables in the soil-vegetation-atmosphere continuum due to its important role in the exchange of water and energy at the soil surface. A new promising method to measure integral soil water content at the field or small catchment scale is the cosmic-ray probe (CRP). Recent studies of CRP measurements have mainly presented results from test sites located in very dry areas and from agricultural fields with sandy soils. In this study, distributed continuous soil water content measurements from a wireless sensor network (SoilNet) were used to investigate the accuracy of CRP measurements for soil water content determination in a humid forest ecosystem. Such ecosystems are less favorable for CRP applications due to the presence of a litter layer. In addition, lattice water and carbohydrates of soil organic matter and belowground biomass reduce the effective sensor depth and thus were accounted for in the calibration of the CRP. The hydrogen located in the biomass decreased the level of neutron count rates and thus also decreased the sensitivity of the cosmic-ray probe, which in turn resulted in an increase of the measurement uncertainty. This uncertainty was compensated by using longer integration times (e.g., 24 h). For the Wüstebach forest site, the cosmic-ray probe enabled the assessment of integral daily soil water content dynamics with a RMSE of about 0.03 cm3/cm3 without explicitly considering the litter layer. By including simulated water contents of the litter layer in the calibration, a better accuracy could be achieved.

Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

NASA Astrophysics Data System (ADS)

Sawicki, Andrzej; Kulczykowski, Marek; Jankowski, Robert

2012-12-01

Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

[Dynamics of soil water reservoir of wheat field in rain-fed area of the Loess Tableland, China].

PubMed

Li, Peng Zhan; Wang, Li; Wang, Di

2017-11-01

Soil reservoir is the basis of stable grain production and sustainable development in dry farming area. Based on the long-term field experiment, this paper investigated the changes of soil moisture in wheat field located in the rain-fed Changwu Tableland, and analyzed the interannual and annual variation characteristics and dynamics trends of soil reservoir from 2012 to 2015. The results showed that the vertical distribution curves of average soil water content were double peaks and double valleys: first peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, while for the second peak and valley, the corresponding soil layer was the 100 and 280 cm soil layer. Soil reservoir did not coincide with precipitation for all yearly precipitation patterns but lagged behind. Yearly precipitation patterns had a great influence on the interannual and annual dynamic changes of soil reservoir. Compared with rainy year, the depth of soil moisture consumption decreased and supplementary effect of precipitation on soil moisture became obvious under effects of drought year and normal year. In rainy year, soil reservoir had a large surplus (84.2 mm), water balance was compensated; in normal year, it had a slight surplus (9.5 mm), water balance was compensated; while in drought year, it was slightly deficient (1.5 mm), water balance was negatively compensated. The dynamics of soil water in winter wheat field in the rain-fed Changwu Tableland could be divided into four periods: seedling period, slow consumption period, large consumption period, and harvest period, the order of evapotranspiration was large consumption period> seedling period> harvest period> slow consumption period.

Effects of Carbon and Cover Crop Residues on N2O and N2 Emissions

NASA Astrophysics Data System (ADS)

Burger, M.; Cooperman, Y.; Horwath, W. R.

2016-12-01

In Mediterranean climate, nitrous oxide emissions occurring with the first rainfall after the dry summer season can contribute up to 50% of agricultural systems' total annual emissions, but the drivers of these emissions have not been clearly identified, and there are only few measurements of atmospheric nitrogen (N2) production (denitrification) during these events. In lab incubations, we investigated N2O and N2 production, gross ammonification and nitrification, and microbial N immobilization with wet-up in soil from a vineyard that was previously fallow or where cover crop residue had been incorporated the previous spring. Before the first rainfall, we measured 120 mg dissolved organic carbon (DOC-C) kg-1 soil in the 0-5 cm layer of this vineyard, and after the rain 10 mg DOC-C kg-1, while nitrate levels before the rain were <5 mg N kg-1 in fallow and <10 mg N kg-1 in previously cover cropped soil. The N2O/N2 production was 2, 7, 9, and 86% in fallow, legume-grass mixture, rye, and legume cover cropped soil. The N2O/N2 ratio tended to increase with lower DOC (post-rain) levels in the soil. The results suggest that accumulated carbon in dry surface soil is the main driving factor of N2O and N2 emissions through denitrification with the first rainfall after prolonged dry periods.

Seasonal and diurnal patterns of soil water potential in the rhizosphere of blue oaks: evidence for hydraulic lift.

PubMed

Ishikawa, C Millikin; Bledsoe, C S

2000-12-01

In a 3-year study, seasonal and daily soil water fluctuations in a California blue oak woodland were investigated by measuring soil water potential (Ψ s ) at hourly intervals. Soil water potential remained relatively high well into the annual summer drought, with values above -0.5 MPa until June even in a dry year. As drought progressed, Ψ s (at 25, 50, 75, and 100 cm depth) decreased to less than -3 MPa, providing evidence for continued blue oak root activity throughout the summer. We observed diurnal Ψ s fluctuations (gradual increase at night and rapid decrease during daytime) characteristic of hydraulic lift, a process by which plant roots redistribute water from wet to dry soil layers. These diurnal fluctuations were observed at all four soil depths and began to appear when Ψ s reached approximately -0.3 MPa. When Ψ s reached approximately -3 MPa, fluctuations became "offset" from those typical of hydraulic lift. These offset fluctuations (apparent at low water potentials when temperature fluctuations were large) closely followed diurnal fluctuations in soil temperature. We propose that these offset patterns resulted from a combination of hydraulic lift cessation and an over-correction for temperature in the model used to calculate Ψ s from raw sensor data. The appearance and disappearance of hydraulic lift fluctuations seemed to depend on Ψ s . While soil temperatures and dates at which hydraulic lift appeared (and disappeared) were significantly different between wet and dry years, Ψ s values associated with hydraulic lift appearance were not significantly different. Hydraulic lift occurred too late in summer to benefit annual forage grasses. However, water released by blue oak trees at night could slow the rate of soil water depletion and extend blue oaks' growing season.

Biochar increased water holding capacity but accelerated organic carbon leaching from a sloping farmland soil in China.

PubMed

Liu, Chen; Wang, Honglan; Tang, Xiangyu; Guan, Zhuo; Reid, Brian J; Rajapaksha, Anushka Upamali; Ok, Yong Sik; Sun, Hui

2016-01-01

A hydrologically contained field study, to assess biochar (produced from mixed crop straws) influence upon soil hydraulic properties and dissolved organic carbon (DOC) leaching, was conducted on a loamy soil (entisol). The soil, noted for its low plant-available water and low soil organic matter, is the most important arable soil type in the upper reaches of the Yangtze River catchment, China. Pore size distribution characterization (by N2 adsorption, mercury intrusion, and water retention) showed that the biochar had a tri-modal pore size distribution. This included pores with diameters in the range of 0.1-10 μm that can retain plant-available water. Comparison of soil water retention curves between the control (0) and the biochar plots (16 t ha(-1) on dry weight basis) demonstrated biochar amendment to increase soil water holding capacity. However, significant increases in DOC concentration of soil pore water in both the plough layer and the undisturbed subsoil layer were observed in the biochar-amended plots. An increased loss of DOC relative to the control was observed upon rainfall events. Measurements of excitation-emission matrix (EEM) fluorescence indicated the DOC increment originated primarily from the organic carbon pool in the soil that became more soluble following biochar incorporation.

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.

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.

Estimation of available water capacity components of two-layered soils using crop model inversion: Effect of crop type and water regime

NASA Astrophysics Data System (ADS)

Sreelash, K.; Buis, Samuel; Sekhar, M.; Ruiz, Laurent; Kumar Tomer, Sat; Guérif, Martine

2017-03-01

Characterization of the soil water reservoir is critical for understanding the interactions between crops and their environment and the impacts of land use and environmental changes on the hydrology of agricultural catchments especially in tropical context. Recent studies have shown that inversion of crop models is a powerful tool for retrieving information on root zone properties. Increasing availability of remotely sensed soil and vegetation observations makes it well suited for large scale applications. The potential of this methodology has however never been properly evaluated on extensive experimental datasets and previous studies suggested that the quality of estimation of soil hydraulic properties may vary depending on agro-environmental situations. The objective of this study was to evaluate this approach on an extensive field experiment. The dataset covered four crops (sunflower, sorghum, turmeric, maize) grown on different soils and several years in South India. The components of AWC (available water capacity) namely soil water content at field capacity and wilting point, and soil depth of two-layered soils were estimated by inversion of the crop model STICS with the GLUE (generalized likelihood uncertainty estimation) approach using observations of surface soil moisture (SSM; typically from 0 to 10 cm deep) and leaf area index (LAI), which are attainable from radar remote sensing in tropical regions with frequent cloudy conditions. The results showed that the quality of parameter estimation largely depends on the hydric regime and its interaction with crop type. A mean relative absolute error of 5% for field capacity of surface layer, 10% for field capacity of root zone, 15% for wilting point of surface layer and root zone, and 20% for soil depth can be obtained in favorable conditions. A few observations of SSM (during wet and dry soil moisture periods) and LAI (within water stress periods) were sufficient to significantly improve the estimation of AWC components. These results show the potential of crop model inversion for estimating the AWC components of two-layered soils and may guide the sampling of representative years and fields to use this technique for mapping soil properties that are relevant for distributed hydrological modelling.

The role of water tracks in altering biotic and abiotic soil properties and processes in a polar desert in Antarctica

NASA Astrophysics Data System (ADS)

Ball, Becky A.; Levy, Joseph

2015-02-01

Groundwater discharge via water tracks is a largely unexplored passageway routing salts and moisture from high elevations to valley floors in the McMurdo Dry Valleys (MDV) of Antarctica. Given the influence that water tracks have on the distribution of liquid water in seasonally thawed Antarctic soils, it is surprising how little is known about their role in structuring biotic and abiotic processes this cold desert ecosystem. Particularly, it is unclear how soil biota will respond to the activation of new water tracks resulting from enhanced active layer thickening or enhanced regional snowmelt. In the MDV, water tracks are both wetter and more saline than the surrounding soils, constituting a change in soil habitat suitability for soil biology and therefore the ecological processes they carry out. To investigate the net impact that water tracks have on Dry Valley soil biology, and therefore the ecosystem processes for which they are responsible, we analyzed microbial biomass and activity in soils inside and outside of three water tracks and relate this to the physical soil characteristics. Overall, our results suggest that water tracks can significantly influence soil properties, which can further impact biological biovolume and both biotic and abiotic fluxes of CO2. However, the nature of its impact differs with water track, further suggesting that not all water tracks can be regarded the same.

An environmental cost-benefit analysis of alternative green roofing strategies

NASA Astrophysics Data System (ADS)

Richardson, M.; William, R. K.; Goodwell, A. E.; Le, P. V.; Kumar, P.; Stillwell, A. S.

2016-12-01

Green roofs and cool roofs are alternative roofing strategies that mitigate urban heat island effects and improve building energy performance. Green roofs consist of soil and vegetation layers that provide runoff reduction, thermal insulation, and potential natural habitat, but can require regular maintenance. Cool roofs involve a reflective layer that reflects more sunlight than traditional roofing materials, but require additional insulation during winter months. This study evaluates several roofing strategies in terms of energy performance, urban heat island mitigation, water consumption, and economic cost. We use MLCan, a multi-layer canopy model, to simulate irrigated and non-irrigated green roof cases with shallow and deep soil depths during the spring and early summer of 2012, a drought period in central Illinois. Due to the dry conditions studied, periodic irrigation is implemented in the model to evaluate its effect on evapotranspiration. We simulate traditional and cool roof scenarios by altering surface albedo and omitting vegetation and soil layers. We find that both green roofs and cool roofs significantly reduce surface temperature compared to the traditional roof simulation. Cool roof temperatures always remain below air temperature and, similar to traditional roofs, require low maintenance. Green roofs remain close to air temperature and also provide thermal insulation, runoff reduction, and carbon uptake, but might require irrigation during dry periods. Due to the longer lifetime of a green roof compared to cool and traditional roofs, we find that green roofs realize the highest long term cost savings under simulated conditions. However, using longer-life traditional roof materials (which have a higher upfront cost) can help decrease this price differential, making cool roofs the most affordable option due to the higher maintenance costs associated with green roofs

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.

Localized application of soil organic matter shifts distribution of cluster roots of white lupin in the soil profile due to localized release of phosphorus

PubMed Central

Li, Hai-Gang; Shen, Jian-Bo; Zhang, Fu-Suo; Lambers, Hans

2010-01-01

Background and Aims Phosphorus (P) is a major factor controlling cluster-root formation. Cluster-root proliferation tends to concentrate in organic matter (OM)-rich surface-soil layers, but the nature of this response of cluster-root formation to OM is not clear. Cluster-root proliferation in response to localized application of OM was characterized in Lupinus albus (white lupin) grown in stratified soil columns to test if the stimulating effect of OM on cluster-root formation was due to (a) P release from breakdown of OM; (b) a decrease in soil density; or (c) effects of micro-organisms other than releasing P from OM. Methods Lupin plants were grown in three-layer stratified soil columns where P was applied at 0 or 330 mg P kg−1 to create a P-deficient or P-sufficient background, and OM, phytate mixed with OM, or perlite was applied to the top or middle layers with or without sterilization. Key Results Non-sterile OM stimulated cluster-root proliferation and root length, and this effect became greater when phytate was supplied in the presence of OM. Both sterile OM and perlite significantly decreased cluster-root formation in the localized layers. The OM position did not change the proportion of total cluster roots to total roots in dry biomass among no-P treatments, but more cluster roots were concentrated in the OM layers with a decreased proportion in other places. Conclusions Localized application of non-sterile OM or phytate plus OM stimulated cluster-root proliferation of L. albus in the localized layers. This effect is predominantly accounted for by P release from breakdown of OM or phytate, but not due to a change in soil density associated with OM. No evidence was found for effects of micro-organisms in OM other than those responsible for P release. PMID:20150198

Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface.

PubMed

Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

2014-01-01

In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account.

Study of the effect of wind speed on evaporation from soil through integrated modeling of the atmospheric boundary layer and shallow subsurface

PubMed Central

Davarzani, Hossein; Smits, Kathleen; Tolene, Ryan M; Illangasekare, Tissa

2014-01-01

In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account. PMID:25309005

Elevated [CO2] mitigates the effect of surface drought by stimulating root growth to access sub-soil water.

PubMed

Uddin, Shihab; Löw, Markus; Parvin, Shahnaj; Fitzgerald, Glenn J; Tausz-Posch, Sabine; Armstrong, Roger; O'Leary, Garry; Tausz, Michael

2018-01-01

Through stimulation of root growth, increasing atmospheric CO2 concentration ([CO2]) may facilitate access of crops to sub-soil water, which could potentially prolong physiological activity in dryland environments, particularly because crops are more water use efficient under elevated [CO2] (e[CO2]). This study investigated the effect of drought in shallow soil versus sub-soil on agronomic and physiological responses of wheat to e[CO2] in a glasshouse experiment. Wheat (Triticum aestivum L. cv. Yitpi) was grown in split-columns with the top (0-30 cm) and bottom (31-60 cm; 'sub-soil') soil layer hydraulically separated by a wax-coated, root-penetrable layer under ambient [CO2] (a[CO2], ∼400 μmol mol-1) or e[CO2] (∼700 μmol mol-1) [CO2]. Drought was imposed from stem-elongation in either the top or bottom soil layer or both by withholding 33% of the irrigation, resulting in four water treatments (WW, WD, DW, DD; D = drought, W = well-watered, letters denote water treatment in top and bottom soil layer, respectively). Leaf gas exchange was measured weekly from stem-elongation until anthesis. Above-and belowground biomass, grain yield and yield components were evaluated at three developmental stages (stem-elongation, anthesis and maturity). Compared with a[CO2], net assimilation rate was higher and stomatal conductance was lower under e[CO2], resulting in greater intrinsic water use efficiency. Elevated [CO2] stimulated both above- and belowground biomass as well as grain yield, however, this stimulation was greater under well-watered (WW) than drought (DD) throughout the whole soil profile. Imposition of drought in either or both soil layers decreased aboveground biomass and grain yield under both [CO2] compared to the well-watered treatment. However, the greatest 'CO2 fertilisation effect' was observed when drought was imposed in the top soil layer only (DW), and this was associated with e[CO2]-stimulation of root growth especially in the well-watered bottom layer. We suggest that stimulation of belowground biomass under e[CO2] will allow better access to sub-soil water during grain filling period, when additional water is converted into additional yield with high efficiency in Mediterranean-type dryland agro-ecosystems. If sufficient water is available in the sub-soil, e[CO2] may help mitigating the effect of drying surface soil.

35 GHz Measurements of CO2 Crystals for Simulating Observations of the Martian Polar Caps

NASA Technical Reports Server (NTRS)

Foster, J. L.; Chang, A. T. C.; Hall, D. K.; Tait, A. B.; Barton, J. S.

1998-01-01

In order to learn more about the Martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Relatively little attention has been given, thus far, to observing the thermal microwave part of the spectrum. In this experiment, passive microwave radiation emanating from within a 33 cm snowpack was measured with a 35 GHz hand-held radiometer, and in addition to the natural snow measurements, the radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice). A 1 m x 2 m plate of aluminum sheet metal was positioned beneath the natural snow so that microwave emissions from the underlying soil layers would be minimized. Compared to the natural snow crystals, results for the dry ice layers exhibit lower' microwave brightness temperatures for similar thicknesses, regardless of the incidence angle of the radiometer. For example, at 50 degree H (horizontal polarization) and with a covering of 21 cm of snow and 18 cm of dry ice, the brightness temperatures were 150 K and 76 K, respectively. When the snow depth was 33 cm, the brightness temperature was 144 K, and when the total thickness of the dry ice was 27 cm, the brightness temperature was 86 K. The lower brightness temperatures are due to a combination of the lower physical temperature and the larger crystal sizes of the commercial CO2 Crystals compared to the snow crystals. As the crystal size approaches the size of the microwave wavelength, it scatters microwave radiation more effectively, thus lowering the brightness temperature. The dry ice crystals in this experiment were about an order of magnitude larger than the snow crystals and three orders of magnitude larger than the CO2 Crystals produced in the cold stage of a scanning electron microscope. Spreading soil, approximately 2 mm in thickness, on the dry ice appeared to have no effect on the brightness temperatures.

Erodibility of waste (Loess) soils from construction sites under water and wind erosional forces.

PubMed

Tanner, Smadar; Katra, Itzhak; Argaman, Eli; Ben-Hur, Meni

2018-03-01

Excess soils from construction sites (waste soils) become a problem when exposed to soil erosion by water or wind. Understanding waste soil erodibility can contribute to its proper reuse for various surface applications. The general objective of the study was to provide a better understanding of the effects of soil properties on erodibility of waste soils excavated from various depths in a semiarid region under rainfall and wind erosive forces. Soil samples excavated from the topsoil (0-0.3m) and subsoil layers (0.3-0.9 and >1m depths) were subjected to simulated rainfall and wind. Under rainfall erosive forces, the subsoils were more erodible than the topsoil, in contrast to the results obtained under wind erosive forces. Exchangeable sodium percentage was the main factor controlling soil erodibility (K i ) under rainfall, and a significant logarithmic regression line was found between these two parameters. In addition, a significant, linear regression was found between K i and slaking values for the studied soil samples, suggesting that the former can be predicted from the latter. Soil erodibility under wind erosion force was controlled mainly by the dry aggregate characteristics (mean weight diameter and aggregate density): their higher values in the subsoil layers resulted in lower soil erodibility compared to the topsoil. Copyright © 2017 Elsevier B.V. All rights reserved.

Variations in soil carbon sequestration and their determinants along a precipitation gradient in seasonally dry tropical forest ecosystems.

PubMed

Campo, Julio; Merino, Agustín

2016-05-01

The effect of precipitation regime on the C cycle of tropical forests is poorly understood, despite the existence of models that suggest a drier climate may substantially alter the source-sink function of these ecosystems. Along a precipitation regime gradient containing 12 mature seasonally dry tropical forests growing under otherwise similar conditions (similar annual temperature, rainfall seasonality, and geological substrate), we analyzed the influence of variation in annual precipitation (1240 to 642 mm) and duration of seasonal drought on soil C. We investigated litterfall, decomposition in the forest floor, and C storage in the mineral soil, and analyzed the dependence of these processes and pools on precipitation. Litterfall decreased slightly - about 10% - from stands with 1240 mm yr(-1) to those with 642 mm yr(-1), while the decomposition decreased by 56%. Reduced precipitation strongly affected C storage and basal respiration in the mineral soil. Higher soil C storage at the drier sites was also related to the higher chemical recalcitrance of litter (fine roots and forest floor) and the presence of charcoal across sites, suggesting an important indirect influence of climate on C sequestration. Basal respiration was controlled by the amount of recalcitrant organic matter in the mineral soil. We conclude that in these forest ecosystems, the long-term consequences of decreased precipitation would be an increase in organic layer and mineral soil C storage, mainly due to lower decomposition and higher chemical recalcitrance of organic matter, resulting from changes in litter composition and, likely also, wildfire patterns. This could turn these seasonally dry tropical forests into significant soil C sinks under the predicted longer drought periods if primary productivity is maintained. © 2016 John Wiley & Sons Ltd.

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 a layer of vegetative ash layer on wettable and water repellent soil hydrology

NASA Astrophysics Data System (ADS)

Bodí, Merche B.; Doerr, Stefan H.; Cerdà, Artemi; Mataix-Solera, Jorge

2010-05-01

Following a wildfire, a layer of vegetative ash often covers the ground until it is dissolved or redistributed by wind and water erosion. Much of the existing literature suggests that the ash layer temporally reduces infiltration by clogging soil pores or by forming a surface crust (Mallik et al., 1984; Onda et al., 2008). However, an increasing number of field-based studies have found that, at least in the short term, ash increases infiltration by storing rainfall and protecting the underlying soil from sealing (Cerdà and Doerr, 2008; Woods and Balfour, 2008). On the other hand, after a fire the soil may have produced, enhanced or reduced its water repellency (Doerr et al., 2000). Very few studies have been taken into account the interaction of the ash and the repellent soil. The layer of ash may have similar role as a litter layer in delaying runoff and reducing erosion by storing water. In order to examine this interaction, it was been made a series of experiments using a laboratory rainfall simulation. It has been assessed the effects of an ash layer i) on a wettable and water repellent soil (WDPT > 7200s), ii) with different ash thicknesses (bare soil and 5 mm, 15 mm and 30 mm of ash), iii) preceding and following the first rain after a fire when the ground is still wetted and after being partially dried. Three replicates were done, being a total of 40 simulations. The ash used was collected from a Wildfire in Teruel (Spain) during summer of 2009. The simulations were conducted in metal boxes of 30x30 cm and filled with 3 cm of soil. The slope of the box was set at 10° (17%) and the intensity applied was 78-84 mm h-1during 40 minutes. The splash detachment was determined also using four splash cups. Overland flow and subsurface drainage was collected at 1-minute intervals and the former stored every 5 min to allow determination of sediment concentrations, yield and erosion rates. Each sample was examined at the end in terms of water repellency, infiltration pattern and ash incorporation into the soil. The results show that when ash covers the wettable soil, runoff occur for a short period of time in the middle of the event. It occurred latter on time but larger in quantity as the ash thickness increases (from 0% to 2% of runoff coefficient) and at the same time drainage is reduced (from 57 to 24%). This suggests that the ash layer became saturated and produce runoff until the water is able to drain into the soil. Oppositely, in water repellent soil as ash thickness increases both runoff is reduced (from 78% to 26%) and drainage is increased (from 0 to 16%). That fact indicates a modification in the hydraulic conductivity of the repellent soil due to the pressure of the ash layer. Splash and erosion rates are bigger in water repellent soils yet erosion rates never exceed 2.5 g m-2 h-1. The fact of wetting increases the runoff and drainage rates in wettable but reduce them in the water repellent soil. An irregular infiltration pattern is observed afterwards. After drying the soil, the increase in runoff indicates a crust formation. Moreover, in water repellent soils part of the repellency is reestablished. These findings demonstrate that the interaction of the soil-ash layer should be considered and better studied in the immediate hydrological response after wildfire due to its particular behavior. References Cerdà, A. and Doerr, S.H., 2008. The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period. Catena, 74: 256-263. Doerr, S.H., Shakesby, R.A. and Walsh, R.P.D., 2000. Soil Water repellency: Its causes, characteristics and hydro-geomorphological significance. Earth Science Reviews, 51: 33-65. Mallik, A.U., Gimingham, C.H. and Rahman, A.A., 1984. Ecological effects of heater burning. I. Water infiltration, moisture retention and porosity of surface soil. Journal of Ecology, 72: 767-776. Onda, Y., Dietrich, W.E. and Booker, F., 2008. Evolution of overland flow after a severe forest fire, Point Reyes, California. Catena, 72: 13-20. Woods, S.W. and Balfour, V., 2008. The effect of ash on runoff and erosion after a forest wildfire, Montana, U.S.A. International Journal of Wildland Fire, 17(5): 535-548.

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.

Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas.

PubMed

Mousseau, Timothy A; Milinevsky, Gennadi; Kenney-Hunt, Jane; Møller, Anders Pape

2014-05-01

The effects of radioactive contamination from Chernobyl on decomposition of plant material still remain unknown. We predicted that decomposition rate would be reduced in the most contaminated sites due to an absence or reduced densities of soil invertebrates. If microorganisms were the main agents responsible for decomposition, exclusion of large soil invertebrates should not affect decomposition. In September 2007 we deposited 572 bags with uncontaminated dry leaf litter from four species of trees in the leaf litter layer at 20 forest sites around Chernobyl that varied in background radiation by more than a factor 2,600. Approximately one quarter of these bags were made of a fine mesh that prevented access to litter by soil invertebrates. These bags were retrieved in June 2008, dried and weighed to estimate litter mass loss. Litter mass loss was 40% lower in the most contaminated sites relative to sites with a normal background radiation level for Ukraine. Similar reductions in litter mass loss were estimated for individual litter bags, litter bags at different sites, and differences between litter bags at pairs of neighboring sites differing in level of radioactive contamination. Litter mass loss was slightly greater in the presence of large soil invertebrates than in their absence. The thickness of the forest floor increased with the level of radiation and decreased with proportional loss of mass from all litter bags. These findings suggest that radioactive contamination has reduced the rate of litter mass loss, increased accumulation of litter, and affected growth conditions for plants.

The Characters of Dry Soil Layer on the Loess Plateau in China and Their Influencing Factors

PubMed Central

Yan, Weiming; Deng, Lei; Zhong, Yangquanwei; Shangguan, Zhouping

2015-01-01

A dry soil layer (DSL) is a common soil desiccation phenomenon that generally forms at a particular depth in the soil profile because of climatic factors and poor land management, and this phenomenon can influence the water cycle and has been observed on the Loess Plateau of China and other similar regions around the world. Therefore, an investigation of the DSL formation depth (DSLFD), thickness (DSLT) and mean water content (MWDSL) on the Loess Plateau can provide valuable information. This paper synthesized 69 recent publications (1,149 observations of DSLs from 73 sites) that focused on DSLs in this region, and the results indicated that DSLs are significantly affected by climatic and vegetation factors. The mean annual precipitation had a significant positive relationship with DSLFD (p = 0.0003) and MWDSL (p<0.0001) and a negative relationship with DSLT (p = 0.0071). Crops had the lowest DSLT and highest MWDSL values compared with other vegetation types. A significant correlation was observed between the occurrence of DSLs and the years since planting for grasses, shrubs, trees and orchards, and the severity of DSLs increased with increasing planting years and wheat yield. Our results suggest that optimizing land-use management can mitigate DSL formation and development on the Loess Plateau. Understanding the dominant factors affecting DSLs will provide information for use in guidelines for the sustainable development of economies and restoration of natural environments experiencing water deficiencies. PMID:26241046

The Characters of Dry Soil Layer on the Loess Plateau in China and Their Influencing Factors.

PubMed

Yan, Weiming; Deng, Lei; Zhong, Yangquanwei; Shangguan, Zhouping

2015-01-01

A dry soil layer (DSL) is a common soil desiccation phenomenon that generally forms at a particular depth in the soil profile because of climatic factors and poor land management, and this phenomenon can influence the water cycle and has been observed on the Loess Plateau of China and other similar regions around the world. Therefore, an investigation of the DSL formation depth (DSLFD), thickness (DSLT) and mean water content (MWDSL) on the Loess Plateau can provide valuable information. This paper synthesized 69 recent publications (1,149 observations of DSLs from 73 sites) that focused on DSLs in this region, and the results indicated that DSLs are significantly affected by climatic and vegetation factors. The mean annual precipitation had a significant positive relationship with DSLFD (p = 0.0003) and MWDSL (p<0.0001) and a negative relationship with DSLT (p = 0.0071). Crops had the lowest DSLT and highest MWDSL values compared with other vegetation types. A significant correlation was observed between the occurrence of DSLs and the years since planting for grasses, shrubs, trees and orchards, and the severity of DSLs increased with increasing planting years and wheat yield. Our results suggest that optimizing land-use management can mitigate DSL formation and development on the Loess Plateau. Understanding the dominant factors affecting DSLs will provide information for use in guidelines for the sustainable development of economies and restoration of natural environments experiencing water deficiencies.

Dynamics of Soil Water Evaporation during Soil Drying in the Presence of a Shallow Water Table: Laboratory Experiment and Numerical Analysis

NASA Astrophysics Data System (ADS)

Han, J.; Lin, J.; Liu, P.; Li, W.

2017-12-01

Evaporation from a porous medium plays a key role in hydrological, agricultural, environmental, and engineering applications. Laboratory and numerical experiments were conducted to investigate the evolution of soil water evaporation during a continuous drying event. Simulated soil water contents and temperatures by the calibrated model well reproduced measured values at different depths. Results show that the evaporative drying process could be divided into three stages, beginning with a relatively high evaporation rate during stage 1, followed by a lower rate during transient stage and stage 2, and finally maintaining a very low and constant rate during stage 3. The condensation zone was located immediately below the evaporation zone in the profile. Both peaks of evaporation and condensation rate increased rapidly during stage 1 and transition stage, decreased during stage 2, and maintained constant during stage 3. The width of evaporation zone kept a continuous increase during stages 1 and 2 and maintained a nearly constant value of 0.68 cm during stage 3. When the evaporation zone totally moved into the subsurface, a dry surface layer (DSL) formed above the evaporation zone at the end of stage 2. The width of DSL also presented a continuous increase during stage 2 and kept a constant value of 0.71 cm during stage 3. Although the magnitude of condensation zone was much smaller than that for the evaporation zone, the importance of the contribution of condensation zone to soil water dynamics should not be underestimated. Results from our experiment and numerical simulation show that this condensation process resulted in an unexpected and apparent water content increase in the middle of vadose zone profile.

Wet and Dry Atmospheric Depositions of Inorganic Nitrogen during Plant Growing Season in the Coastal Zone of Yellow River Delta

PubMed Central

Li, Yunzhao; Du, Siyao; Han, Guangxuan; Xing, Qinghui; Wu, Huifeng; Wang, Guangmei

2014-01-01

The ecological problems caused by dry and wet deposition of atmospheric nitrogen have been widespread concern in the world. In this study, wet and dry atmospheric depositions were monitored in plant growing season in the coastal zone of the Yellow River Delta (YRD) using automatic sampling equipment. The results showed that SO4 2− and Na+ were the predominant anion and cation, respectively, in both wet and dry atmospheric depositions. The total atmospheric nitrogen deposition was ~2264.24 mg m−2, in which dry atmospheric nitrogen deposition was about 32.02%. The highest values of dry and wet atmospheric nitrogen deposition appeared in May and August, respectively. In the studied area, NO3 −–N was the main nitrogen form in dry deposition, while the predominant nitrogen in wet atmospheric deposition was NH4 +–N with ~56.51% of total wet atmospheric nitrogen deposition. The average monthly attribution rate of atmospheric deposition of NO3 −–N and NH4 +–N was ~31.38% and ~20.50% for the contents of NO3 −–N and NH4 +–N in 0–10 cm soil layer, respectively, suggested that the atmospheric nitrogen was one of main sources for soil nitrogen in coastal zone of the YRD. PMID:24977238

Spatial and temporal effects of drought on soil CO2 efflux in a cacao agroforestry system in Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

van Straaten, O.; Veldkamp, E.; Köhler, M.; Anas, I.

2010-04-01

Climate change induced droughts pose a serious threat to ecosystems across the tropics and sub-tropics, particularly to those areas not adapted to natural dry periods. In order to study the vulnerability of cacao (Theobroma cacao) - Gliricidia sepium agroforestry plantations to droughts a large scale throughfall displacement roof was built in Central Sulawesi, Indonesia. In this 19-month experiment, we compared soil surface CO2 efflux (soil respiration) from three roof plots with three adjacent control plots. Soil respiration rates peaked at intermediate soil moisture conditions and decreased under increasingly dry conditions (drought induced), or increasingly wet conditions (as evidenced in control plots). The roof plots exhibited a slight decrease in soil respiration compared to the control plots (average 13% decrease). The strength of the drought effect was spatially variable - while some measurement chamber sites reacted strongly (responsive) to the decrease in soil water content (up to R2=0.70) (n=11), others did not react at all (non-responsive) (n=7). A significant correlation was measured between responsive soil respiration chamber sites and sap flux density ratios of cacao (R=0.61) and Gliricidia (R=0.65). Leaf litter CO2 respiration decreased as conditions became drier. The litter layer contributed approximately 3-4% of the total CO2 efflux during dry periods and up to 40% during wet periods. Within days of roof opening soil CO2 efflux rose to control plot levels. Thereafter, CO2 efflux remained comparable between roof and control plots. The cumulative effect on soil CO2 emissions over the duration of the experiment was not significantly different: the control plots respired 11.1±0.5 Mg C ha-1 yr-1, while roof plots respired 10.5±0.5 Mg C ha-1 yr-1. The relatively mild decrease measured in soil CO2 efflux indicates that this agroforestry ecosystem is capable of mitigating droughts with only minor stress symptoms.

Drought effects on soil CO

NASA Astrophysics Data System (ADS)

van Straaten, O.; Veldkamp, E.; Köhler, M.; Anas, I.

2009-12-01

Climate change induced droughts pose a serious threat to ecosystems across the tropics and sub-tropics, particularly to those areas not adapted to natural dry periods. In order to study the vulnerability of cacao (Theobroma cacao) - Gliricidia sepium agroforestry plantations to droughts a large scale throughfall displacement roof was built in Central Sulawesi, Indonesia. In this 19-month replicated experiment, we measured soil surface CO2 efflux (soil respiration) in three simulated drought plots compared with three adjacent control plots. Soil respiration rates peaked at intermediate soil moisture and decreased under increasingly dry conditions (drought induced), but also decreased when soils became water saturated, as evidenced in control plots. The simulated drought plots exhibited a slight decrease in soil respiration compared to the control plots (average 13% decrease). The strength of the drought effect was spatially variable - while some measurement chamber sites reacted strongly ("responsive") to the decrease in soil water content (up to R2=0.70) (n=11), others did not react at all ("non-responsive") (n=7). The degree of soil CO2 respiration drought response was highest around cacao tree stems and decreased with distance from the stem (R2=0.22). A significant correlation was measured between "responsive" soil respiration chamber sites and sap flux density ratios of cacao (R=0.61) and Gliricidia (R=0.65). Leaf litter CO2 respiration decreased as conditions became drier. During dry periods the litter layer contributed approximately 3-4% of the total CO2 efflux and up to 40% during wet periods. A CO2 flush was recorded during the rewetting phase that lasted for approximately two weeks, during which time accumulated labile carbon stocks mineralized. The net effect on soil CO2 emissions over the duration of the experiment was neutral, control plots respired 11.1±0.5 Mg C ha-1 yr-1, while roof plots respired 10.5±0.5 Mg C ha-1 yr-1.

Organic carbon, water repellency and soil stability to slaking at aggregate and intra-aggregate scales

NASA Astrophysics Data System (ADS)

Jordán López, Antonio; García-Moreno, Jorge; Gordillo-Rivero, Ángel J.; Zavala, Lorena M.; Cerdà, Artemi; Alanís, Nancy; Jiménez-Compán, Elizabeth

2015-04-01

Water repellency (WR) is a property of some soils that inhibits or delays water infiltration between a few seconds and days or weeks. Inhibited or delayed infiltration contributes to ponding and increases runoff flow generation, often increasing soil erosion risk. In water-repellent soils, water infiltrates preferentially through cracks or macropores, causing irregular soil wetting patterns, the development of preferential flow paths and accelerated leaching of nutrients. Although low inputs of hydrophobic organic substances and high mineralization rates lead to low degrees of WR in cropped soils, it has been reported that conservative agricultural practices may induce soil WR. Although there are many studies at catchment, slope or plot scales very few studies have been carried out at particle or aggregate scale. Intra-aggregate heterogeneity of physical, biological and chemical properties conditions the transport of substances, microbial activity and biochemical processes, including changes in the amount, distribution and chemical properties of organic matter. Some authors have reported positive relationships between soil WR and aggregate stability, since it may delay the entry of water into aggregates, increase structural stability and contribute to reduce soil erosion risk. Organic C (OC) content, aggregate stability and WR are therefore strongly related parameters. In the case of agricultural soils, where both the type of management as crops can influence all these parameters, it is important to evaluate the interactions among them and their consequences. Studies focused on the intra-aggregate distribution of OC and WR are necessary to shed light on the soil processes at a detailed scale. It is extremely important to understand how the spatial distribution of OC in soil aggregates can protect against rapid water entry and help stabilize larger structural units or lead to preferential flow. The objectives of this research are to study [i] the OC content and the intensity of WR in aggregates of different sizes. [ii] the intra-aggregate distribution of OC and the intensity of WR and [iii] the structural stability of soil aggregates relative to the OC content and the intensity of WR in soils under different crops (apricot, citrus and wheat) and different treatments (conventional tilling and mulching). Soil samples were collected from an experimental area (Luvic Calcisols and Calcic Luvisols) in the province of Sevilla (Southern Spain) under different crops (apricot, citrus and wheat) and different management types (conventional tillage with moldboard plow) and mulching (no-tilling and addition of wheat residues at rates varying between 5 and 8 Mg/ha/year). At each sampling site, soil blocks (50 cm long × 50 cm wide × 10 cm deep) were carefully collected to avoid disturbance of aggregates as much as possible and transported to the laboratory. At field moist condition, undisturbed soil aggregates were separated by hand. In order to avoid possible interferences due to disturbance by handling, aggregates broken during this process were discarded. Individual aggregates were arranged in paper trays and air-dried during 7 days under laboratory standard conditions. After air-drying, part of each sample was carefully divided for different analyses: [i] part of the original samples was sieved (2 mm) to eliminate coarse soil particles and homogenized for characterization of OC and N contents, C/N ratio and texture; [ii] part of the aggregates were dry-sieved (0.25-0.5, 0.5-1 and 1-2 mm) or measured with a caliper (2-5, 5-10 and 10-15 mm) and separated in different sieve-size classes for determination of WR and OC content; [iii] aggregates 10-15 mm in size were selected for obtaining aggregate layers using a soil aggregate erosion (SAE) apparatus and WR and OC content were determined at each layer; finally, [iv] in order to study the relation between stability to slaking, WR and OC, these properties were determined in 90 air-dried aggregates (about 10 mm in size) selected per treatment (mulched or conventional tillage) and crop (apricot, citrus and wheat). In this case, every set of aggregates was randomly divided in three groups (n = 30) for assessing stability to slaking, WR and OC, respectively. OC content in the fine earth fraction of soils under different crops did not show important variations, although it increased significantly from conventionally tilled to mulched soils. The distribution of OC content in aggregates with different size varied among soils under different crops, generally increasing with decreasing size. At the intra-aggregate level, OC concentrated preferably in the exterior layer of differently sized aggregates and of aggregate coatings and interior from conventionally tilled soils, probably because of recent organic inputs or leachates. In the case of mulched soils, higher concentrations were observed, but no significant differences among aggregate regions were found. The intensity of water repellency, determined by the ethanol method, did not show great variations among differently sized aggregates under different crops in the 0-10 cm layer, but increased significantly from conventionally tilled to mulched soils. Coarser aggregates were generally wettable, while finer aggregates showed slight water repellency. Regardless of variations in the distribution of OC in different layers of aggregate from conventionally tilled soils, great or significant differences in the distribution of water repellency at the intra-aggregate level were not found. In case of mulched soils such differences were not significant. Finally, the intensity of water repellency was much more important than the concentration of OC in the stability to slaking of aggregates.

Exchange of soil moisture between patches of wild-olive and pasture sustains evapotranspiration of a Mediterranean ecosystem in both wet and dry seasons

NASA Astrophysics Data System (ADS)

Curreli, M.; Montaldo, N.; Oren, R.

2017-12-01

Partitioning evapotranspiration in water-limited environments, such as Mediterranean ecosystems, could give information on vegetation and hydraulic dynamics. Indeed, in such ecosystems, trees may survive prolonged droughts by uptake of water by dimorphic root system: deep roots and shallower lateral roots, extending beyond the crown into inter-trees grassy areas. The water exchange between under canopy areas and treeless patches plays a crucial role on sustaining tree and grass physiological performance during droughts. The study has been performed at the Orroli site, Sardinia (Italy). The landscape is covered by patchy vegetation: wild olives trees in clumps and herbaceous species, drying to bare soil in summer. The climate is characterized by long droughts from May to October and rain events concentrated in the autumn and winter, whit a mean yearly rain of about 700 mm. A 10 m micrometeorological tower equipped with eddy-covariance system has been used for measuring water and energy surface fluxes, as well as key state variables (e.g. temperature, radiations, humidity and wind velocity). Soil moisture was measured with five soil water reflectometers (two below the olive canopy and three in the pasture). To estimate plant water use in the context of soil water dynamic, 33 Granier-type thermal dissipation probes were installed 40 cm aboveground, in representative trees over the eddy covariance footprint. Early analyses show that wild olive continue to transpire even as the soil dries and the pasture desiccates. This reveled hydraulic redistribution system through the plant and the soil, and allows to quantify the reliance of the system on horizontally and vertically differentiated soil compartments. Results shows that during light hours, until transpiration decreases in midday, shallow roots uptake deplete the shallow water content. As transpiration decreases, hydraulically redistributed water provides for both transpiration of wild olives and recharge of shallow soil layers in the inter-tree areas. This consents trees to remain physiologically active during very dry conditions and represent a mechanism of facilitation of the coexistence of tree-grass system.

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).

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.

Physicochemical properties and carbon density of alpine sod layer with their variation across habitat gradients in the Zoige Plateau

NASA Astrophysics Data System (ADS)

Peixi, Su; Zijuan, Zhou; Rui, Shi; tingting, Xie

2017-04-01

The alpine sod layer is a soft, tough and resistant to shifting surface soil layer under the formation of the natural vegetation in the plateau cold region, understanding its ecological function is a prerequisite to promote grass and animal husbandry production for recuperation and protection, and the active use of project construction. Based on the extensive investigation on the alpine vegetation of the Zoige Plateau in the Eastern Qinghai-Tibetan Plateau of China, set up moisture gradient community sample plots: swamp, degraded swamp, swampy meadow, wet meadow, dry meadow and degraded meadow, and the elevation gradient community sample plots: subalpine meadow, subalpine shrub meadow, alpine shrub meadow and alpine meadow were set up. The sod layer bulk density, soil particle composition and soil organic carbon (SOC) content of different types of community plots were analyzed and to compare its carbon sequestration capacity on the moisture and elevation gradients. The results showed that the average thickness of the sod layer was 30 cm, the bulk density of the swamp was the smallest, and the SOC content was above 300 g/kg. The bulk density of degraded meadow was the highest while its SOC content was decreased significantly. The SOC density of sod layer in different communities was between 10 and 24 kg C/m2, and decreased with the decreasing of soil water availability, and meadow degradation significantly decreased the soil organic carbon storage in sod layer. The sod layer SOC density of alpine shrub meadow was 15% higher than that of meadow on the altitudinal gradient. It was concluded that the mass water content threshold value for maintaining the sod layer stable is 30%. In the degraded succession of alpine vegetation from swamp to meadow, the bulk density and compactness of sod layer became larger, while the organic carbon content, carbon density and carbon storage decreased. The higher the gravel content of swamp, the more easily degraded, and the higher the sand content of the meadow, the more easily degraded. Shrub meadow had higher carbon sequestration capacity than that of meadow, but the productive function of shrub meadow was lower. Keeping the sustainable development of grassland productivity and maintaining the carbon sequestration ecological function, it is necessary to prevent the degradation of the sod layer, and restrain the succession from meadow to scrub meadow. Key Words: surface soil layer, soil organic carbon, carbon density, alpine vegetation, Zoige Plateau

Observed response of vulnerable forest ecosystems to ongoing site condition changes

NASA Astrophysics Data System (ADS)

Bidló, András; Gulyás, Krisztina; Gálos, Borbála; Horváth, Adrienn

2017-04-01

In the last decades, several symptoms of drought damages have been observed in the Hungarian forests (e.g. sparse canopy, leaf drop, top drying, fungal diseases). Forest responses are also influenced by other factors beyond climate (e.g. available water content, soil conditions, biotic damages, adaptive capacity, etc.). Our aim was to prepare a complex analysis of the change of all site conditions, that could lead to the observed health status decline of the forest tree species. For a case study region in Hungary (Keszthely Mountains, near to Lake Balaton) precipitation and temperature tendencies as well as the frequency of extreme dry summers have been determined for the period 1961-2100. Soil conditions have been investigated in 9 profiles and soil mapping analysis has been carried out including 100 sites with hand soil auger. For the investigation of the water-balance we used the modified Thornthwaite-type monthly model and determined water stress when the relative extractable water (REW) decreased below 40% (Granier et al., 1999). In the last 30 years three severe droughts have been detected when duration of extremely dry and hot periods exceeded 3-4 years. Not only orographic and microclimate conditions but also soil types show a large diversity within a relatively small distance in the case study area. On rendzina with shallow topsoil layer thickness, low water holding capacity, black pine was planted. Brown earth with medium and brown forest soils with deep topsoil layer thickness is favourable for oak (sessile or Turkey) and beech. These microscale differences between the three site condition types resulted different available water contents quantified by the modified Thornthwaite-type monthly water-balance model. Our results show the different sensitivity of the studied sites to water stress. It means that the local scale orographic and soil conditions can enhance the projected drought risk of the region. However, the favourable microclimatic effects of the existing forest stands are still a knowledge gap and the topic of the ongoing research. The research is supported by the "Agroclimate-2" (VKSZ_12-1-2013-0034) joint EU-national research project and by the ÚNKP-16-4-3 New National Excellence Program of the Ministry of Human Capacities. Keywords: climate extremes, changing site conditions, water stress

Soil methane and CO2 fluxes in rainforest and rubber plantations

NASA Astrophysics Data System (ADS)

Lang, Rong; Blagodatsky, Sergey; Goldberg, Stefanie; Xu, Jianchu

2017-04-01

Expansion of rubber plantations in South-East Asia has been a land use transformation trend leading to losses of natural forest cover in the region. Besides impact on ecosystem carbon stocks, this conversion influences the dynamics of greenhouse gas fluxes from soil driven by microbial activity, which has been insufficiently studied. Aimed to understand how land use change affects the soil CO2 and CH4 fluxes, we measured surface gas fluxes, gas concentration gradient, and 13C signature in CH4 and soil organic matter in profiles in a transect in Xishuangbanna, including a rainforest site and three rubber plantation sites with age gradient. Gas fluxes were measured by static chamber method and open chamber respiration system. Soil gases were sampled from installed gas samplers at 5, 10, 30, and 75cm depth at representative time in dry and rainy season. The soil CO2 flux was comparable in rainforest and old rubber plantations, while young rubber plantation had the lowest rate. Total carbon content in the surface soil well explained the difference of soil CO2 flux between sites. All sites were CH4 sinks in dry season and uptake decreased in the order of rainforest, old rubber plantations and young rubber plantation. From dry season to rainy season, CH4 consumption decreased with increasing CH4 concentration in the soil profile at all depths. The enrichment of methane by 13CH4 shifted towards to lowerδ13C, being the evidence of enhanced CH4 production process while net surface methane flux reflected the consumption in wet condition. Increment of CH4 concentration in the profile from dry to rainy season was higher in old rubber plantation compared to rainforest, while the shifting of δ13CH4 was larger in rainforest than rubber sites. Turnover rates of soil CO2 and CH4 suggested that the 0-5 cm surface soil was the most active layer for gaseous carbon exchange. δ13C in soil organic matter and soil moisture increased from rainforest, young rubber plantation to old rubber plantations. Conversion the forest into rubber plantation decreased soil respiration in young plantation and it recovered during rubber development. However, the CH4consumption by tropical upland forest soil decreased in converted rubber plantations of all ages, with more decrement in old plantation. Change forest into rubber plantations weakened the soil function as CH4 sink.

Effect of Lime Stabilization on Vertical Deformation of Laterite Halmahera Soil

NASA Astrophysics Data System (ADS)

Saing, Zubair; Djainal, Herry

2018-04-01

In this paper, the study was conducted to determine the lime effect on vertical deformation of road base physical model of laterite Halmahera soil. The samples of laterite soil were obtained from Halmahera Island, North Maluku Province, Indonesia. Soil characteristics were obtained from laboratory testing, according to American Standard for Testing and Materials (ASTM), consists of physical, mechanical, minerals, and chemical. The base layer of physical model testing with the dimension; 2m of length, 2m of width, and 1.5m of height. The addition of lime with variations of 3, 5, 7, an 10%, based on maximum dry density of standard Proctor test results and cured for 28 days. The model of lime treated laterite Halmahera soil with 0,1m thickness placed on subgrade layer with 1,5m thickness. Furthermore, the physical model was given static vertical loading. Some dial gauge is placed on the lime treated soil surface with distance interval 20cm, to read the vertical deformation that occurs during loading. The experimentals data was analyzed and validated with numerical analysis using finite element method. The results showed that the vertical deformation reduced significantly on 10% lime content (three times less than untreated soil), and qualify for maximum deflection (standard requirement L/240) on 7-10% lime content.

Characteristics of pristine volcanic materials: Beneficial and harmful effects and their management for restoration of agroecosystem.

PubMed

Anda, Markus; Suparto; Sukarman

2016-02-01

Eruption of Sinabung volcano in Indonesia began again in 2010 after resting for 1200 years. The volcano is daily emitting ash and pyroclastic materials since September 2013 to the present, damaging agroecosystems and costing for management restoration. The objective of the study was to assess properties and impacts of pristine volcanic material depositions on soil properties and to provide management options for restoring the affected agroecosytem. Land satellite imagery was used for field studies to observe the distribution, thickness and properties of ashfall deposition. The pristine ashfall deposits and the underlying soils were sampled for mineralogical, soluble salt, chemical, physical and toxic compound analyses. Results showed that uneven distribution of rainfall at the time of violent eruption caused the areas receiving mud ashfall developed surface encrustation, which was not occur in areas receiving dry ashfall. Ashfall damaged the agroecosytem by burning vegetation, forming surface crusts, and creating soil acidity and toxicity. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses of encrustated layer indicated the presence of gypsum and jarosite minerals. Gypsum likely acted as a cementing agent in the formation of the encrustation layer with extremely low pH (2.9) and extremely high concentrations of Al, Ca and S. Encrustation is responsible for limited water infiltration and root penetration, while the extremely high concentration of Al is responsible for crop toxicity. Mud ashfall and dry ashfall deposits also greatly changed the underlying soil properties by decreasing soil pH and cation exchange capacity and by increasing exchangeable Ca, Al, and S availability. Despite damaging vegetation in the short-term, the volcanic ashfall enriched the soil in the longer term by adding nutrients like Ca, Mg, K, Na, P, Si and S. Suggested management practices to help restore the agroecosystem after volcanic eruptions include: (i) the application of lime to increase soil pH, increase cation exchange capacity and decrease Al and S toxicities, (ii) the selection of crops which are tolerant to low pH and high concentrations of soluble Al and S, (iii) physically disrupting the hard surface crusts that form on some soils (if <2 cm thick) to allow water infiltration and root penetration, (iv) application of N and K fertilizers, and (v) incorporation of dry ashfall into the soil (if <5 cm thick) to exploit the newly deposited nutrients. Copyright © 2015 Elsevier B.V. All rights reserved.

Impact of charcoal waste application on the soil organic matter content and composition of an Haplic Cambisol from South Brazil

NASA Astrophysics Data System (ADS)

dos Anjos Leal, Otávio; Pinheiro Dick, Deborah; Cylene Lombardi, Kátia; Gonçalves Maciel, Vanessa

2014-05-01

In some regions in Brazil, charcoal is usually applied to the soil with the purpose to improve its fertility and its organic carbon (SOC) content. In Brazil, the use of charcoal waste from steel industry with agronomic purposes represents also an alternative and sustainable fate for this material. In this context, the objective of this work was to evaluate the impact of Eucalyptus charcoal waste application on the SOC content and on the soil organic matter (SOM) composition. Increasing doses of charcoal (0, 10, 20 and 40 Mg ha-1) were applied to an Haplic Cambisol, in Irati, South-Brazil. Charcoal was initially applied on the soil surface, and then it was incorporated at 10 cm with a harrow. Soil undisturbed and disturbed samples (four replicates) were collected in September 2011 (1 y and 9 months) after charcoal incorporation. Four soil depths were evaluated (0-5, 5-10, 10-20 and 20-30 cm) and each replicate was composed by three subsamples collected within each plot. The soil samples were air dried, passed through a 9.51 mm sieve and thereafter through a 2.00 mm sieve. The SOC content and total N were quantified by dry combustion. The SOM was concentrated with fluoridric acid 10% and then the SOM composition was evaluated by thermogravimetric analysis along the soil profile. The main impact of charcoal application occurred at the 0-5 cm layer of the area treated with the highest dose: SOC content increased in 15.5 g kg-1 in comparison to the soil without charcoal application. The intermediary doses also increased the SOC content, but the differences were not significant. No differences for N content were found in this soil depth. Further results were observed in the 10-20 cm soil depth, where the highest dose increased the SOC content and N content. Furthermore, this treatment increased the recalcitrance of the SOM, mainly at the 0-5 cm and 10-20 cm soil layers. No differences between doses of charcoal application were found in the 20-30 cm soil depth, suggesting that the charcoal has not migrated so deep in soil even after almost two years of its incorporation.

Travel of pollution, and purification en route, in sandy soils

PubMed Central

Baars, J. K.

1957-01-01

The travel of pollution in sandy soils, and the extent to which purification takes place en route, are discussed, with special reference to the possible contamination of ground water—a problem which is of particular importance in the Netherlands, where the water-supply for many of the large towns is drawn from the water underneath the dunes. Specifically, two types of soil pollution are considered: (a) severe pollution of the surface layers with matter concentrated in a small volume of water (e.g., faecal matter from pit privies at camping-sites); and (b) moderate pollution of the surface layers with matter contained in large quantities of water (e.g., organic matter and bacteria in river water used for the artificial recharge of ground water). It is shown that in both these types of pollution the self-purification is sufficient to prevent contamination of the ground water, provided that the soil is very fine and—in the case of the first type—dry and well aerated, and provided that the ground-water level is not too high or the rate of infiltration too great. PMID:13472428

Dissolved organic carbon (DOC) in soil extracts investigated by FT-ICR-MS

NASA Astrophysics Data System (ADS)

Hofmann, D.; Steffen, D.; Jablonowski, N. D.; Burauel, P.

2012-04-01

Soil drying and rewetting usually increases the release of xenobiotics like pesticides present in agricultural soils. Besides the effect on the release of two aged 14C-labeled pesticide residues we focus on the characterisation of simultaneously remobilized dissolved organic carbon (DOC) to gain new insights into structure and stability aspects of soil organic carbon fractions. The test soil (gleyic cambisol; Corg 1.2%, pH 7.2) was obtained from the upper soil layer of two individual outdoor lysimeter studies containing either environmentally long-term aged 14C residues of the herbicide ethidimuron (0-10 cm depth; time of aging: 9 years) or methabenzthiazuron (0-30 cm depth; time of aging: 17 years). Soil samples (10 g dry soil equivalents) were (A=dry/wet) previously dried (45°C) or (B=wet/wet) directly mixed with pure water (1+2, w:w), shaken (150 rpm, 1 h), and centrifuged (2000 g). This extraction procedure was repeated several individual times, for both setups. The first three individual extractions, respectively were used for further investigations. Salt was removed from samples prior analysis because of a possible quench effect in the electrospray (ESI) source by solid phase extraction (SPE) with Chromabond C18 Hydra-cartridges (Macherey-Nagel) and methanol as backextraction solvent. The so preconcentrated and desalted samples were introduced by flow injection analysis (FIA) in a fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS), equipped with an ESI source and a 7 T supra-conducting magnet (LTQ-FT Ultra, ThermoFisher Scientific). This technique is the key technique for complex natural systems attributed by their outstanding mass resolution (used 400.000 at m/z 400 Da) and mass accuracy (≤ 1ppm) by simultaneously providing molecular level details of thousands of compounds and was successful applied for the investigations of natural organic matter (NOM) different sources like marine and surface water, soil, sediment, bog and crude oil. The characteristics of measured DOM mass spectra were demonstrated. Furthermore, an algorithm to compute all chemically relevant C,H,O-, C,H,(O,S),N- as well as C,H,(O),S molecular compositions, designed and exercised by ourself using Scilab routines, was used for entire structure elucidation. Various methods for data evaluation of such an amount of peaks are applied to describe the characteristics of DOC. The van Krevelen diagram is widely used to classify the DOC compounds regarding polarity and aromaticity, whereas the Kendrick diagram allow to identify ions with elemental formulas that differ only in CH2, and molecular formulas with similar Kendrick Mass Defect (KMD) can be sorted by nominal mass series. Both kind of diagrams were developed and results are discussed together with the findings of ETD, MBT, and metabolites after soil drying and rewetting. Overall, the results suggest that intermittent soil drying and rewetting alters the disaggregation of soil aggregates, resulting in a release of entrapped organic carbon as well as pesticide molecules.

Post-fire geomorphic response in steep, forested landscapes: Oregon Coast Range, USA

NASA Astrophysics Data System (ADS)

Jackson, Molly; Roering, Joshua J.

2009-06-01

The role of fire in shaping steep, forested landscapes depends on a suite of hydrologic, biologic, and geological characteristics, including the propensity for hydrophobic soil layers to promote runoff erosion during subsequent rainfall events. In the Oregon Coast Range, several studies postulate that fire primarily modulates sediment production via root reinforcement and shallow landslide susceptibility, although few studies have documented post-fire geomorphic response. Here, we describe field observations and topographic analyses for three sites in the central Oregon Coast Range that burned in 1999, 2002, and 2003. The fires generated strongly hydrophobic soil layers that did not promote runoff erosion because the continuity of the layers was interrupted by pervasive discontinuities that facilitated rapid infiltration. At each of our sites, fire generated significant colluvial transport via dry ravel, consistent with other field-based studies in the western United States. Fire-driven dry ravel accumulation in low-order valleys of our Sulphur Creek site equated to a slope-averaged landscape lowering of 2.5 mm. Given Holocene estimates of fire frequency, these results suggest that fire may contribute 10-20% of total denudation across steep, dissected portions of the Oregon Coast Range. In addition, we documented more rapid decline of root strength at our sites than has been observed after timber harvest, suggesting that root strength was compromised prior to fire or that intense heat damaged roots in the shallow subsurface. Given that fire frequencies in the Pacific Northwest are predicted to increase with continued climate change, our findings highlight the importance of fire-induced dry ravel and post-fire debris flow activity in controlling sediment delivery to channels.

Mulching as a means of exploiting dew for arid agriculture?

NASA Astrophysics Data System (ADS)

Graf, Alexander; Kuttler, Wilhelm; Werner, Julius

2008-03-01

A traditional mulching technique used in Lanzarote, Canary Islands, allows dry farming as well as pronounced water savings in irrigation. It is known to reduce evaporational losses, but is also supposed to enhance the nocturnal condensation of water vapour from the atmosphere. The mulch layer consists of porous volcanic rock fragments abundantly available on the island. The mulched surface is believed to cool rapidly and to be more hygroscopic than a bare soil surface. This was investigated during a field experiment conducted over 68 nights during different seasons in 2001 and 2002, as well as some simple laboratory measurements. It was found that nocturnal condensation on the mulch surface (max 0.33 mm) was lower than on the bare soil surface (max 0.57 mm) or any one of three alternative mulch substrates. However, a slightly stronger nocturnal cooling of the mulched as compared to the bare surface was present. It is shown that these contrary findings can be explained by the higher hygroscopicity of the dry loam soil, resulting in condensation gains beyond the strict definition of dew. Differences in plant-availability of non-hygroscopic dew water and hygroscopic water uptakes are discussed, and conditions under which mulching would show positive condensation effects are defined. This includes a theoretical section demonstrating that non-hygroscopic mulch layers of a proper thickness can provide small amounts of dew to plant roots at the mulch-soil interface. This condensation could also happen during the day and would be favoured by a high amplitude of the diurnal atmospheric moisture cycle.

Spatial Variability of Soil-Water Storage in the Southern Sierra Critical Zone Observatory: Measurement and Prediction

NASA Astrophysics Data System (ADS)

Oroza, C.; Bales, R. C.; Zheng, Z.; Glaser, S. D.

2017-12-01

Predicting the spatial distribution of soil moisture in mountain environments is confounded by multiple factors, including complex topography, spatial variably of soil texture, sub-surface flow paths, and snow-soil interactions. While remote-sensing tools such as passive-microwave monitoring can measure spatial variability of soil moisture, they only capture near-surface soil layers. Large-scale sensor networks are increasingly providing soil-moisture measurements at high temporal resolution across a broader range of depths than are accessible from remote sensing. It may be possible to combine these in-situ measurements with high-resolution LIDAR topography and canopy cover to estimate the spatial distribution of soil moisture at high spatial resolution at multiple depths. We study the feasibility of this approach using six years (2009-2014) of daily volumetric water content measurements at 10-, 30-, and 60-cm depths from the Southern Sierra Critical Zone Observatory. A non-parametric, multivariate regression algorithm, Random Forest, was used to predict the spatial distribution of depth-integrated soil-water storage, based on the in-situ measurements and a combination of node attributes (topographic wetness, northness, elevation, soil texture, and location with respect to canopy cover). We observe predictable patterns of predictor accuracy and independent variable ranking during the six-year study period. Predictor accuracy is highest during the snow-cover and early recession periods but declines during the dry period. Soil texture has consistently high feature importance. Other landscape attributes exhibit seasonal trends: northness peaks during the wet-up period, and elevation and topographic-wetness index peak during the recession and dry period, respectively.

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.

Thermal properties of degraded lowland peat-moorsh soils

NASA Astrophysics Data System (ADS)

Gnatowski, Tomasz

2016-04-01

Soil thermal properties, i.e.: specific heat capacity (c), thermal conductivity (K), volumetric heat capacity (C) govern the thermal environment and heat transport through the soil. Hence the precise knowledge and accurate predictions of these properties for peaty soils with high amount of organic matter are especially important for the proper forecasting of soil temperature and thus it may lead to a better assessment of the greenhouse gas emissions created by microbiological activity of the peatlands. The objective of the study was to develop the predictive models of the selected thermal parameters of peat-moorsh soils in terms of their potential applicability for forecasting changes of soil temperature in degraded ecosystems of the Middle Biebrza River Valley area. Evaluation of the soil thermal properties was conducted for the parameters: specific heat capacity (c), volumetric heat capacities of the dry and saturated soil (Cdry, Csat) and thermal conductivities of the dry and saturated soil (Kdry, Ksat). The thermal parameters were measured using the dual-needle probe (KD2-Pro) on soil samples collected from seven peaty soils, representing total 24 horizons. The surface layers were characterized by different degrees of advancement of soil degradation dependent on intensiveness of the cultivation practises (peaty and humic moorsh). The underlying soil layers contain peat deposits of different botanical composition (peat-moss, sedge-reed, reed and alder) and varying degrees of decomposition of the organic matter, from H1 to H7 (von Post scale). Based on the research results it has been shown that the specific heat capacity of the soils differs depending on the type of soil (type of moorsh and type of peat). The range of changes varied from 1276 J.kg-1.K-1 in the humic moorsh soil to 1944 J.kg-1.K-1 in the low decomposed sedge-moss peat. It has also been stated that in degraded peat soils with the increasing of the ash content in the soil the value of specific heat has decreased in a non-linear manner. Thermal parameters of the dry mass of the studied soils (Kdry, Cdry) were characterised by the mean value of approximately 0.11±0.028 W.m-1.K-1 and 0.781±0.220 MJ.m-3.K-1. The application of the correlation analysis showed that the most significant predictor of these properties of soils is the soil bulk density which, respectively explains: 54.6% and 67.1% of their variation. The increase of the accuracy in determining Kdry and Cdry was obtained by developing regression models, which apart from the bulk density also include the chemical properties of the peat soils. In the fully saturated soil the Ksat value ranged from 0.47 to 0.63 W.m-1.K-1, and the Csat varied from 3.200 to 3.995 MJ.m-3.K-1. The variation coefficients of these soil thermal features are at the level of approx. 5%. The obtained results allowed to conclude that the significant diversity of studied soils doesn't cause the significant differences in thermal soil parameters in fully saturated soils. The developed statistical relationships indicate that parameters Ksat and Csat were poorly correlated with saturated moisture content.

Plants, microorganisms, and soil temperatures contribute to a decrease in methane fluxes on a drained Arctic floodplain.

PubMed

Kwon, Min Jung; Beulig, Felix; Ilie, Iulia; Wildner, Marcus; Küsel, Kirsten; Merbold, Lutz; Mahecha, Miguel D; Zimov, Nikita; Zimov, Sergey A; Heimann, Martin; Schuur, Edward A G; Kostka, Joel E; Kolle, Olaf; Hilke, Ines; Göckede, Mathias

2017-06-01

As surface temperatures are expected to rise in the future, ice-rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH 4 , and investigating effects of soil hydrology on CH 4 fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade-long drying manipulation on an Arctic floodplain influences CH 4 -associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage-induced changes may then modify CH 4 fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH 4 cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0-15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH 4 oxidation, thereby decreasing net CH 4 fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH 4 was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH 4 oxidation and leading to a decrease in net CH 4 fluxes compared to a control site. Drainage lowered CH 4 fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH 4 emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long-term drainage considerably reduced CH 4 fluxes through modified ecosystem properties. © 2016 John Wiley & Sons Ltd.

Geology of the dry creek site; a stratified early man site in Interior Alaska

USGS Publications Warehouse

Thorson, R.M.; Hamilton, T.D.

1977-01-01

The Dry Creek archeologic site contains a stratified record of late Pleistocene human occupation in central Alaska. Four archeologic components occur within a sequence of multiple loess and sand layers which together form a 2-m cap above weathered glacial outwash. The two oldest components appear to be of late Pleistocene age and occur with the bones of extinct game animals. Geologic mapping, stratigraphic correlations, radiocarbon dating, and sediment analyses indicate that the basal loess units formed part of a widespread blanket that was associated with an arctic steppe environment and with stream aggradation during waning phases of the last major glaciation of the Alaska Range. These basal loess beds contain artifacts for which radiocarbon dates and typologic correlations suggest a time range of perhaps 12,000-9000 yr ago. A long subsequent episode of cultural sterility was associated with waning loess deposition and development of a cryoturbated tundra soil above shallow permafrost. Sand deposition from local source areas predominated during the middle and late Holocene, and buried Subarctic Brown Soils indicate that a forest fringe developed on bluff-edge sand sheets along Dry Creek. The youngest archeologic component, which is associated with the deepest forest soil, indicates intermittent human occupation of the site between about 4700 and 3400 14C yr BP. ?? 1977.

Arbuscular mycorrhizal fungi in saline soils: Vertical distribution at different soil depth

PubMed Central

Becerra, Alejandra; Bartoloni, Norberto; Cofré, Noelia; Soteras, Florencia; Cabello, Marta

2014-01-01

Arbuscular mycorrhizal fungi (AMF) colonize land plants in every ecosystem, even extreme conditions such as saline soils. In the present work we report for the first time the mycorrhizal status and the vertical fungal distribution of AMF spores present in the rhizospheric soil samples of four species of Chenopodiaceae (Allenrolfea patagonica, Atriplex argentina, Heterostachys ritteriana and Suaeda divaricata) at five different depths in two saline of central Argentina. Roots showed medium, low or no colonization (0–50%). Nineteen morphologically distinctive AMF species were recovered. The number of AMF spores ranged between 3 and 1162 per 100 g dry soil, and AMF spore number decreased as depth increased at both sites. The highest spore number was recorded in the upper soil depth (0–10 cm) and in S. divaricata. Depending of the host plant, some AMF species sporulated mainly in the deep soil layers (Glomus magnicaule in Allenrolfea patagonica, Septoglomus aff. constrictum in Atriplex argentina), others mainly in the top layers (G. brohultti in Atriplex argentina and Septoglomus aff. constrictum in Allenrolfea patagonica). Although the low percentages of colonization or lack of it, our results show a moderate diversity of AMF associated to the species of Chenopodiaceae investigated in this study. The taxonomical diversity reveals that AMF are adapted to extreme environmental conditions from saline soils of central Argentina. PMID:25242945

Microbial responses and nitrous oxide emissions during wetting and drying of organically and conventionally managed soil under tomatoes

USGS Publications Warehouse

Burger, M.; Jackson, L.E.; Lundquist, E.J.; Louie, D.T.; Miller, R.L.; Rolston, D.E.; Scow, K.M.

2005-01-01

The types and amounts of carbon (C) and nitrogen (N) inputs, as well as irrigation management are likely to influence gaseous emissions and microbial ecology of agricultural soil. Carbon dioxide (CO2) and nitrous oxide (N2O) efflux, with and without acetylene inhibition, inorganic N, and microbial biomass C were measured after irrigation or simulated rainfall in two agricultural fields under tomatoes (Lycopersicon esculentum). The two fields, located in the California Central Valley, had either a history of high organic matter (OM) inputs ("organic" management) or one of low OM and inorganic fertilizer inputs ("conventional" management). In microcosms, where short-term microbial responses to wetting and drying were studied, the highest CO2 efflux took place at about 60% water-filled pore space (WFPS). At this moisture level, phospholipid fatty acids (PLFA) indicative of microbial nutrient availability were elevated and a PLFA stress indicator was depressed, suggesting peak microbial activity. The highest N 2O efflux in the organically managed soil (0.94 mg N2O-N m-2 h-1) occurred after manure and legume cover crop incorporation, and in the conventionally managed soil (2.12 mg N2O-N m-2 h-1) after inorganic N fertilizer inputs. Elevated N2O emissions occurred at a WFPS >60% and lasted <2 days after wetting, probably because the top layer (0-150 mm) of this silt loam soil dried quickly. Therefore, in these cropping systems, irrigation management might control the duration of elevated N2O efflux, even when C and inorganic N availability are high, whereas inorganic N concentrations should be kept low during times when soil moisture cannot be controlled.

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.

Influence of soil moisture on sunflower oil extraction of polycyclic aromatic hydrocarbons from a manufactured gas plant soil.

PubMed

Gong, Zongqiang; Wilke, B-M; Alef, Kassem; Li, Peijun

2005-05-01

The influence of soil moisture on efficiency of sunflower oil extraction of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil was investigated. The PAH-contaminated soil was collected from a manufactured gas plant (MGP) site in Berlin, Germany. Half of the soil was air-dried, and the other half was kept as field-moist soil. Batch experiments were performed using air-dried and field-moist soils, and sunflower oil was used as extractant at oil/soil ratios of 2:1 and 1:1 (v/m). The experimental data were fitted to a first-order empirical model to describe mass-transfer profiles of the PAHs. Column extraction experiments were also conducted. Field-moist and air-dried soils in the column were extracted using sunflower oil at an oil/soil ratio of 2:1. In the batch experiments, PAHs were more rapidly extracted from air-dried soil than from field-moist soil. Removal rate of total PAH increased 23% at oil/soil ratio of 1:1 and 15.5% at oil/soil ratio of 2:1 after the soil was air dried. The most favorable conditions for batch extraction were air-dried soil, with an oil/soil ratio of 2:1. In the column experiments, the removal rate of total PAH from air-dried soil was 30.7% higher than that from field-moist soil. For field-moist soil, extraction efficiencies of the batch extraction (67.2% and 81.5%) were better than that for column extraction (65.6%). However, this difference between the two methods became less significant for the air-dried soil, with a total removal rate of 96.3% for column extraction and 90.2% and 97% for batch extractions. A mass-balance test was carried out for analytical quality assurance. The results of both batch and column experiments indicated that drying the soil increased efficiency of extraction of PAHs from the MGP soil.

Deccesion of peat-moorsh soils under different land use

NASA Astrophysics Data System (ADS)

Lipka, K.; Zając, E.

2009-04-01

Use of peatlands has a serious impact on soil properties as well as on loss of organic matter. On the basis of survey carried out in 1976, 1993 and 2001 in the Mrowla river valley near Rzeszow, authors analysed changes of the peat-moorsh soils under different land use. The 25- year period was analysed. Survey results comprised: loss of organic matter, advance of moorsh forming process and change of prognostic soil-moisture complexes (after Okruszko). Stratigraphic profiles made in the years1996-2001 were compared and rate of organic mass loss was calculated. The highest values were stated for ploughfields with crop rotation (root plants, industrial plants and cereals). Intensified soil aeration and moorsh forming process as well as wind erosion caused gradual lowering of ground level. Depth of degraded peat layer in roof of surveyed peat deposits was between 0,2 and 0,8 m. Ground surface was lowering of 1,68 cm per year. It was found that, for ploughfields especially, peat-moorhs soil showing medium degree of moorsh forming process (MtII) and prognostic soil-moisture complex BC (periodically drying), after 17 years already, had changed into a soil with high degree of moorsh forming process (MtIII) and prognostic soil-moisture complex C (drying). For meadows and pastures land used such evident change wasn't noticed. During the whole investigation period (25 years) mean lowering of the peat-moorsh soils level along transects lines for different land use was: 1,15 cm per year for meadows and pastures, 1,58 cm pea year for plougfields and 1,38 cm per year for alder wood.

Burkholderia terrae BS001 migrates proficiently with diverse fungal hosts through soil and provides protection from antifungal agents

PubMed Central

Nazir, Rashid; Tazetdinova, Diana I.; van Elsas, Jan Dirk

2014-01-01

Soil bacteria can benefit from co-occurring soil fungi in respect of the acquisition of carbonaceous nutrients released by fungal hyphae and the access to novel territories in soil. Here, we investigated the capacity of the mycosphere-isolated bacterium Burkholderia terrae BS001 to comigrate through soil along with hyphae of the soil fungi Trichoderma asperellum, Rhizoctonia solani, Fusarium oxysporum, F. oxysporum pv lini, Coniochaeta ligniaria, Phanerochaete velutina, and Phallus impudicus. We used Lyophyllum sp. strain Karsten as the reference migration-inciting fungus. Bacterial migration through presterilized soil on the extending fungal hyphae was detected with six of the seven test fungi, with only Phallus impudicus not showing any bacterial transport. Much like with Lyophyllum sp. strain Karsten, intermediate (106–108 CFU g-1 dry soil) to high (>108 CFU g-1 dry soil) strain BS001 cell population sizes were found at the hyphal migration fronts of four fungi, i.e., T. asperellum, Rhizoctonia solani, F. oxysporum and F. oxysporum pv lini, whereas for two fungi, Coniochaeta ligniaria and Phanerochaete velutina, the migration responses were retarded and population sizes were lower (103–106 CFU g-1 dry soil). Consistent with previous data obtained with the reference fungus, migration with the migration-inciting fungi occurred only in the direction of the hyphal growth front. Remarkably, Burkholderia terrae BS001 provided protection from several antifungal agents to the canonical host Lyophyllum sp. strain Karsten. Specifically, this host was protected from Pseudomonas fluorescens strain CHA0 metabolites, as well as from the anti-fungal agent cycloheximide. Similar protection by strain BS001was observed for T. asperellum, and, to a lower extent, F. oxysporum and Rhizoctonia solani. The protective effect may be related to the consistent occurrence of biofilm-like cell layers or agglomerates at the surfaces of the protected fungi. The current study represents the first report of protection of soil fungi against antagonistic agents present in the soil provided by fungal-associated Burkholderia terrae cells. PMID:25426111

Studying of Forests Potentials for Introducing of Mediterranean Industrial Woody Species to Desertification Combating

NASA Astrophysics Data System (ADS)

Mahdavi Najafabadi, R.; Khajeddin, S. J.; Sofyanian, A. R.; Karimzadeh, H. R.; Rezaei, M.

2009-04-01

Most of arid and semiarid parts of the world suffer from great lack of forest land. Therefore taking a good care of these forest lands quantity and quality and control of renewable natural resources is very important. Zagroass forests are located in semiarid parts of Iran. The main purpose of this research is to determine the potential habitat of forest olive for Chaharmahal va Bakhtiary using GIS. This province has a total area of 1653300 hectars. The main steps of this project are as follows: collecting data and maps, digitizing topographic maps with scale of 1:25000, and developing maps of slope, elevation levels, aspect, climatic classification. Regretion analysis was performed on the climatic data and the gradian equations were developed with a high R2 value. Using these equations the following maps were developed. For the whole province: isothermal, isoheytal, abs. max isothermal, relative humidity relative humidity of dry months. Soil maps were also digitized and the information system suitable for this study was developed. Using this bank the following layers were made: land units, soil depth, two soil textures, EC, pH, CaCo3. The following layers were made using digitized data, land use hydraulic network, lake and marsh land. Considering ecological needs of olive and extracting them from all diferent layers using boolean method. The layers showing suitable locations for planting olive(olea europea) was made. One of these maps includes all types of soils suitable for planting olive and the other excludes silty clay loam soils which are not so suitable. The total area achived was 9500 hectars in the whole province and the area excluding silty clay loam soils was determined to be 900 hectars. Using RS information and GIS technology in these types of projects can increase accuracy specialy including some more layers is recommended.

Turbulent transports over tundra

NASA Technical Reports Server (NTRS)

Fitzjarrald, David R.; Moore, Kathleen E.

1992-01-01

An extensive period of eddy correlation surface flux measurements was conducted at a site distant from the coast on the western Alaskan tundra. The surface exchange of heat and moisture over tundra during the summer was limited by a strong resistance to transfer from the upper soil layer through the ground cover, with canopy resistances to evaporation observed to be approximately 200 s/m. Though July 1988 was anomalously warm and dry in the region and August was close to normal temperature and rainfall, there was no appreciable difference in the canopy resistance between the periods. During the dry sunny period at the end of July, the observed evaporation rate was 2 mm/d. High canopy resistance led to an approximate equipartition of net radiation between latent and sensible heat, each accounting for 40 percent of the available energy, with heat balance apparently going into soil heat flux.

Root systems of chaparral shrubs.

PubMed

Kummerow, Jochen; Krause, David; Jow, William

1977-06-01

Root systems of chaparral shrubs were excavated from a 70 m 2 plot of a mixed chaparral stand located on a north-facing slope in San Diego County (32°54' N; 900 m above sea level). The main shrub species present were Adenostoma fasciculatum, Arctostaphylos pungens, Ceanothus greggii, Erigonum fasciculatum, and Haplopappus pinifolius. Shrubs were wired into their positions, and the soil was washed out beneath them down to a depth of approximately 60 cm, where impenetrable granite impeded further washing and root growth was severely restricted. Spacing and interweaving of root systems were recorded by an in-scale drawing. The roots were harvested in accordance to their depths, separated into diameter size classes for each species, and their dry weights measured. Roots of shrubs were largely confined to the upper soil levels. The roots of Eriogonum fasciculatum were concentrated in the upper soil layer. Roots of Adenostoma fasciculatum tended to be more superficial than those from Ceanothus greggii. It is hypothesized that the shallow soil at the excavation site impeded a clear depth zonation of the different root systems. The average dry weight root:shoot ratio was 0.6, ranging for the individual shrubs from 0.8 to 0.4. The root area always exceeded the shoot area, with the corresponding ratios ranging from 6 for Arctostaphylos pungens to 40 for Haplopappus pinifolius. The fine root density of 64 g dry weight per m 2 under the canopy was significantly higher than in the unshaded area. However, the corresponding value of 45 g dry weight per m 2 for the open ground is still high enough to make the establishment of other shrubs difficult.

Content and bioconcentration of mercury in mushrooms from northern Poland.

PubMed

Falandysz, J; Gucia, M; Brzostowski, A; Kawano, M; Bielawski, L; Frankowska, A; Wyrzykowska, B

2003-03-01

Mercury (Hg) was quantified using cold vapour-atomic absorption spectrometry (CV-AAS) in the fruiting bodies of nine edible and five inedible mushrooms and in underlying soil substrate samples. In total, 404 samples comprising caps and stalks and 202 samples of soil substrate (0-10 cm layer) were collected in 1996 from Trójmiejski Landscape Park, northern Poland. Mean Hg concentrations in the soil substrate for different species varied between 10 +/- 3 and 780 +/- 500 ng x g(-1) dry wt (range 2.3-1700). Among edible mushroom species, Horse Mushroom (Agaricus arvensis), Brown Birch Scaber Stalk (Leccinum scabrum), Parasol Mushroom (Macrolepiota procera), King Bolete (Boletus edulis) and Yellow-cracking Bolete (Xerocomus subtomentosus) contained elevated concentrations of Hg ranging from 1600 +/- 930 to 6800 +/- 4000 ng x g(-1) dry wt in the caps. Concentrations of Hg in the stalks were 2.6 +/- 1.1 to 1.7 +/- 1.0 times lower than those in the caps. Some mushroom species investigated had high Hg levels when compared with specimens collected from the background reference sites elsewhere (located far away from the big cities) in northern Poland. Bioconcentration factors of Hg in the caps of Horse Mushroom, Parasol Mushroom and Brown Birch Scaber Stalk were between 150 +/- 58 and 230 +/- 150 ng x g(-1) dry wt, respectively, and for inedible Pestle-shaged Puffball (Claviata excipulformis) was 960 +/- 300 ng x g(-1) dry wt. Linear regression coefficients between Hg in caps and in stalks and Hg soil concentrations showed a positive relationship for A. arvensis and Horse mushroom (p < 0.05) and a negative correlation for the caps of Death Caps (Amanita phalloides) and Woolly Milk Cap (Lactarius torminosus) (p < 0.05), while for other species no clear trend was found.

High copper content in vineyard soils promotes modifications in photosynthetic parameters and morphological changes in the root system of 'Red Niagara' plantlets.

PubMed

Ambrosini, Vítor Gabriel; Rosa, Daniel José; Bastos de Melo, George Wellington; Zalamena, Jovani; Cella, Cesar; Simão, Daniela Guimarães; Souza da Silva, Leandro; Pessoa Dos Santos, Henrique; Toselli, Moreno; Tiecher, Tadeu Luis; Brunetto, Gustavo

2018-05-08

High copper (Cu) soil contents, due to the continuous vineyard application of Cu fungicides throughout the years, may impair the growth of the shoot and modify the structure of the root system. The current study aimed to investigate the threshold levels of available Cu in the soil causing toxicity effects in young grapevine plants of 'Red Niagara' cultivated in clay soils. Grapevine plantlets were cultivated in pots containing vineyard devoted soils with increasing contents of available Cu (25, 80, 100 and 165 mg kg -1 ), for 53 days. Photosynthesis and transpiration rates, and the quantum yield of photosystem II (Fv/Fm) were evaluated during the cultivation period. At the end of the experiment, the plant nutrient and leaf chlorophyll were determined, along with the anatomical analysis of the root system structure and plant dry matter determination. Higher levels of available Cu in the soil increased the apoplastic, symplastic and total fraction of the metal in the roots, reducing the other nutrients, especially in the shoots. Photosynthesis, transpiration rates and Fv/Fm were also reduced. Higher levels of Cu led to anatomical changes in the roots, that increased diameter, number of layers in the cortex, vascular cylinder and total root areas. It also resulted in reduced dry matter production by grapevines. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

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.

Soil-atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

USGS Publications Warehouse

Tang, X.; Liu, S.; Zhou, G.; Zhang, Dongxiao; Zhou, C.

2006-01-01

The magnitude, temporal, and spatial patterns of soil-atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil-atmospheric CO2, CH4, and N2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean ?? SD) were 7.7 ?? 4.6MgCO2-Cha-1 yr-1, 3.2 ?? 1.2 kg N2ONha-1 yr-1, and 3.4 ?? 0.9 kgCH4-Cha-1 yr-1, respectively. The climate was warm and wet from April through September 2003 (the hot-humid season) and became cool and dry from October 2003 through March 2004 (the cool-dry season). The seasonality of soil CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O emission rates were often observed in the hot-humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO2 and N2O emissions and CH4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO2 effluxes by 17-44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer. ?? 2006 Blackwell Publishing Ltd.

Fire Ecology of Seeds from Rubus Spp.: A Competitor During Natural Pine Regeneration

Treesearch

Michael D. Cain; Michael G. Shelton

1999-01-01

Air-dried blackbeny (Rubus spp.) fruits were placed at three depths in a reconstructed forest floor and subjected to a simulated prescribed summer bum. Within the forest floor, fruits were placed on the L layer, at the upper-F/lower-F interface, and at the lower-F/mineral-soil interface. Wind for a headfire was generated by electric boxfans....

Superabsorbent Multilayer Fabric

NASA Technical Reports Server (NTRS)

Coreale, J. V.; Dawn, F. S.

1982-01-01

Material contains gel-forming polymer and copolymer that absorb from 70 to 200 times their weight of liquid. Superabsorbent Polymer and Copolymer form gels to bind and retain liquid in multiply fabric. Until reaction between liquid and absorbent masses forms gel, backing layer retains liquids within fabric; also allows material to "breathe." Possible applications include baby diapers, female hygiene napkins, and hospital bedpads. Might also have uses in improvement of dry soil.

A Drought Index for Forest Fire Control

Treesearch

John J. Keetch; George M. Byram

1968-01-01

The moisture content of the upper soil, as well as that of the covering layer of duff, has an important effect on the fire suppression effort in forest and wildland areas. In certain forested areas of the United States, fires in deep duff fuels are of particular concern to the fire control manager. When these fuels are dry, fires burn deeply, dam-age is excessive, and...

Effect of soil moisture on diurnal convection and precipitation in Large-Eddy Simulations

NASA Astrophysics Data System (ADS)

Cioni, Guido; Hohenegger, Cathy

2017-04-01

Soil moisture and convective precipitation are generally thought to be strongly coupled, although limitations in the modeling set-up of past studies due to coarse resolutions, and thus poorly resolved convective processes, have prevented a trustful determination of the strength and sign of this coupling. In this work the soil moisture-precipitation feedback is investigated by means of high-resolution simulations where convection is explicitly resolved. To that aim we use the LES (Large Eddy Simulation) version of the ICON model with a grid spacing of 250 m, coupled to the TERRA-ML soil model. We use homogeneous initial soil moisture conditions and focus on the precipitation response to increase/decrease of the initial soil moisture for various atmospheric profiles. The experimental framework proposed by Findell and Eltahir (2003) is revisited by using the same atmospheric soundings as initial condition but allowing a full interaction of the atmosphere with the land-surface over a complete diurnal cycle. In agreement with Findell and Eltahir (2003) the triggering of convection can be favoured over dry soils or over wet soils depending on the initial atmospheric sounding. However, total accumulated precipitation is found to always decrease over dry soils regardless of the employed sounding, thus highlighting a positive soil moisture-precipitation feedback (more rain over wetter soils) for the considered cases. To understand these differences and to infer under which conditions a negative feedback may occur, the total accumulated precipitation is split into its magnitude and duration component. While the latter can exhibit a dry soil advantage, the precipitation magnitude strongly correlates with the surface latent heat flux and thus always exhibits a wet soil advantage. The dependency is so strong that changes in duration cannot offset it. This simple argument shows that, in our idealised setup, a negative feedback is unlikely to be observed. The effects of other factors on the soil moisture-precipitation coupling, namely cloud radiative effects, large-scale forcing, winds, and plants are investigated by conducting further sensitivity experiments. All the experiments support a positive soil moisture-precipitation feedback. References: -Findell, K. L., and E. A. Eltahir, 2003: Atmospheric controls on soil moisture-boundary layer interactions. part I: Framework development. Journal of Hydrometeorology, 4 (3), 552-569.

A new tool for laboratory studies on volatilization: extension of applicability of the photovolatility chamber.

PubMed

Wolters, André; Kromer, Thomas; Linnemann, Volker; Schäffer, Andreas; Vereecken, Harry

2003-04-01

Volatilization from soil and plant surfaces after application is an important source of pesticide residues to the atmosphere. The laboratory photovolatility chamber allows the simultaneous measurement of volatilization and photodegradation of 14C-labeled pesticides under controlled climatic conditions. Both continuous air sampling, which quantifies volatile organic compounds and 14CO2 separately, and the detection of surface-located residues allow for a mass balance of radioactivity. The setup of the photovolatility chamber was optimized, and additional sensors were installed to characterize the influence of soil moisture, soil temperature, and evaporation on volatilization. The modified flow profile in the glass dome of the chamber arising from the use of a high-performance metal bellows pump was measured. Diminished air velocity near the soil surface and a wind velocity of 0.2 m/s in 3 cm height allowed the requirements of the German guideline on assessing pesticide volatilization for registration purposes to be fulfilled. Determination of soil moisture profiles of the upper soil layer illustrated that defined water content in the soil up to a depth of 4 cm could be achieved by water saturation of air. Cumulative volatilization of [phenyl-UL-14C]parathion-methyl ranged from 2.4% under dry conditions to 32.9% under moist conditions and revealed the clear dependence of volatilization on the water content in the top layer.

Controls on surface soil drying rates observed by SMAP and simulated by the Noah land surface model

NASA Astrophysics Data System (ADS)

Shellito, Peter J.; Small, Eric E.; Livneh, Ben

2018-03-01

Drydown periods that follow precipitation events provide an opportunity to assess controls on soil evaporation on a continental scale. We use SMAP (Soil Moisture Active Passive) observations and Noah simulations from drydown periods to quantify the role of soil moisture, potential evaporation, vegetation cover, and soil texture on soil drying rates. Rates are determined using finite differences over intervals of 1 to 3 days. In the Noah model, the drying rates are a good approximation of direct soil evaporation rates, and our work suggests that SMAP-observed drying is also predominantly affected by direct soil evaporation. Data cover the domain of the North American Land Data Assimilation System Phase 2 and span the first 1.8 years of SMAP's operation. Drying of surface soil moisture observed by SMAP is faster than that simulated by Noah. SMAP drying is fastest when surface soil moisture levels are high, potential evaporation is high, and when vegetation cover is low. Soil texture plays a minor role in SMAP drying rates. Noah simulations show similar responses to soil moisture and potential evaporation, but vegetation has a minimal effect and soil texture has a much larger effect compared to SMAP. When drying rates are normalized by potential evaporation, SMAP observations and Noah simulations both show that increases in vegetation cover lead to decreases in evaporative efficiency from the surface soil. However, the magnitude of this effect simulated by Noah is much weaker than that determined from SMAP observations.

[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.

DREB1A promotes root development in deep soil layers and increases water extraction under water stress in groundnut.

PubMed

Vadez, V; Rao, J S; Bhatnagar-Mathur, P; Sharma, K K

2013-01-01

Water deficit is a major yield-limiting factor for many crops, and improving the root system has been proposed as a promising breeding strategy, although not in groundnut (Arachis hypogaea L.). The present work was carried out mainly to assess how root traits are influenced under water stress in groundnut, whether transgenics can alter root traits, and whether putative changes lead to water extraction differences. Several transgenic events, transformed with DREB1A driven by the rd29 promoter, along with wild-type JL24, were tested in a lysimeter system that mimics field conditions under both water stress (WS) and well-watered (WW) conditions. The WS treatment increased the maximum rooting depth, although the increase was limited to about 20% in JL24, compared to 50% in RD11. The root dry weight followed a similar trend. Consequently, the root dry weight and length density of transgenics was higher in layers below 100-cm depth (Exp. 1) and below 30 cm (Exp. 2). The root diameter was unchanged under WS treatment, except a slight increase in the 60-90-cm layer. The root diameter increased below 60 cm in both treatments. In the WW treatment, total water extraction of RD33 was higher than in JL24 and other transgenic events, and somewhat lower in RD11 than in JL24. In the WS treatment, water extraction of RD2, RD11 and RD33 was higher than in JL24. These water extraction differences were mostly apparent in the initial 21 days after treatment imposition and were well related to root length density in the 30-60-cm layer (R(2) = 0.68), but not to average root length density. In conclusion, water stress promotes rooting growth more strongly in transgenic events than in the wild type, especially in deep soil layers, and this leads to increased water extraction. This opens an avenue for tapping these characteristics toward the improvement of drought adaptation in deep soil conditions, and toward a better understanding of genes involved in rooting in groundnut. © 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.

Soil moisture and soil temperature variability among three plant communities in a High Arctic Lake Basin

NASA Astrophysics Data System (ADS)

Davis, M. L.; Konkel, J.; Welker, J. M.; Schaeffer, S. M.

2017-12-01

Soil moisture and soil temperature are critical to plant community distribution and soil carbon cycle processes in High Arctic tundra. As environmental drivers of soil biochemical processes, the predictability of soil moisture and soil temperature by vegetation zone in High Arctic landscapes has significant implications for the use of satellite imagery and vegetation distribution maps to estimate of soil gas flux rates. During the 2017 growing season, we monitored soil moisture and soil temperature weekly at 48 sites in dry tundra, moist tundra, and wet grassland vegetation zones in a High Arctic lake basin. Soil temperature in all three communities reflected fluctuations in air temperature throughout the season. Mean soil temperature was highest in the dry tundra community at 10.5±0.6ºC, however, did not differ between moist tundra and wet grassland communities (2.7±0.6 and 3.1±0.5ºC, respectively). Mean volumetric soil moisture differed significantly among all three plant communities with the lowest and highest soil moisture measured in the dry tundra and wet grassland (30±1.2 and 65±2.7%), respectively. For all three communities, soil moisture was highest during the early season snow melt. Soil moisture in wet grassland remained high with no significant change throughout the season, while significant drying occurred in dry tundra. The most significant change in soil moisture was measured in moist tundra, ranging from 61 to 35%. Our results show different gradients in soil moisture variability within each plant community where: 1) soil moisture was lowest in dry tundra with little change, 2) highest in wet grassland with negligible change, and 3) variable in moist tundra which slowly dried but remained moist. Consistently high soil moisture in wet grassland restricts this plant community to areas with no significant drying during summer. The moist tundra occupies the intermediary areas between wet grassland and dry tundra and experiences the widest range of soil moisture variability. As climate projections predict wetter summers in the High Arctic, expansion of areas with seasonally inundated soils and increased soil moisture variability could result in an expansion of wet grassland and moist tundra communities with a commensurate decrease in dry tundra area.

Research on the Effects of Drying Temperature on Nitrogen Detection of Different Soil Types by Near Infrared Sensors.

PubMed

Nie, Pengcheng; Dong, Tao; He, Yong; Xiao, Shupei

2018-01-29

Soil is a complicated system whose components and mechanisms are complex and difficult to be fully excavated and comprehended. Nitrogen is the key parameter supporting plant growth and development, and is the material basis of plant growth as well. An accurate grasp of soil nitrogen information is the premise of scientific fertilization in precision agriculture, where near infrared sensors are widely used for rapid detection of nutrients in soil. However, soil texture, soil moisture content and drying temperature all affect soil nitrogen detection using near infrared sensors. In order to investigate the effects of drying temperature on the nitrogen detection in black soil, loess and calcium soil, three kinds of soils were detected by near infrared sensors after 25 °C placement (ambient temperature), 50 °C drying (medium temperature), 80 °C drying (medium-high temperature) and 95 °C drying (high temperature). The successive projections algorithm based on multiple linear regression (SPA-MLR), partial least squares (PLS) and competitive adaptive reweighted squares (CARS) were used to model and analyze the spectral information of different soil types. The predictive abilities were assessed using the prediction correlation coefficients (R P ), the root mean squared error of prediction (RMSEP), and the residual predictive deviation (RPD). The results showed that the loess (R P = 0.9721, RMSEP = 0.067 g/kg, RPD = 4.34) and calcium soil (R P = 0.9588, RMSEP = 0.094 g/kg, RPD = 3.89) obtained the best prediction accuracy after 95 °C drying. The detection results of black soil (R P = 0.9486, RMSEP = 0.22 g/kg, RPD = 2.82) after 80 °C drying were the optimum. In conclusion, drying temperature does have an obvious influence on the detection of soil nitrogen by near infrared sensors, and the suitable drying temperature for different soil types was of great significance in enhancing the detection accuracy.

‘Natural background’ soil water repellency in conifer forests of the north-western USA: Its prediction and relationship to wildfire occurrence

NASA Astrophysics Data System (ADS)

Doerr, S. H.; Woods, S. W.; Martin, D. A.; Casimiro, M.

2009-06-01

SummarySoils under a wide range of vegetation types exhibit water repellency following the passage of a fire. This is viewed by many as one of the main causes for accelerated post-fire runoff and soil erosion and it has often been assumed that strong soil water repellency present after wildfire is fire-induced. However, high levels of repellency have also been reported under vegetation types not affected by fire, and the question arises to what degree the water repellency observed at burnt sites actually results from fire. This study aimed at determining 'natural background' water repellency in common coniferous forest types in the north-western USA. Mature or semi-mature coniferous forest sites ( n = 81), which showed no evidence of recent fires and had at least some needle cast cover, were sampled across six states. After careful removal of litter and duff at each site, soil water repellency was examined in situ at the mineral soil surface using the Water Drop Penetration Time (WDPT) method for three sub-sites, followed by collecting near-surface mineral soil layer samples (0-3 cm depth). Following air-drying, samples were further analyzed for repellency using WDPT and contact angle ( θsl) measurements. Amongst other variables examined were dominant tree type, ground vegetation, litter and duff layer depth, slope angle and aspect, elevation, geology, and soil texture, organic carbon content and pH. 'Natural background' water repellency (WDPT > 5 s) was detected in situ and on air-dry samples at 75% of all sites examined irrespective of dominant tree species ( Pinus ponderosa, Pinus contorta, Picea engelmanii and Pseudotsuga menziesii). These findings demonstrate that the soil water repellency commonly observed in these forest types following burning is not necessarily the result of recent fire but can instead be a natural characteristic. The notion of a low background water repellency being typical for long-unburnt conifer forest soils of the north-western USA is therefore incorrect. It follows that, where pre-fire water repellency levels are not known or highly variable, post-fire soil water repellency conditions are an unreliable indicator in classifying soil burn severity. The terrain and soil variables examined showed, overall, no convincing relationship with the repellency levels observed ( R2 < 0.15) except that repellency was limited in soils (i) developed over meta-sedimentary lithology and (ii) with clay contents >4%. This suggests that water repellency levels cannot be predicted with confidence from common terrain or soil variables.

'Natural background' soil water repellency in conifer forests of the north-western USA: Its prediction and relationship to wildfire occurrence

USGS Publications Warehouse

Doerr, S.H.; Woods, S.W.; Martin, D.A.; Casimiro, M.

2009-01-01

Soils under a wide range of vegetation types exhibit water repellency following the passage of a fire. This is viewed by many as one of the main causes for accelerated post-fire runoff and soil erosion and it has often been assumed that strong soil water repellency present after wildfire is fire-induced. However, high levels of repellency have also been reported under vegetation types not affected by fire, and the question arises to what degree the water repellency observed at burnt sites actually results from fire. This study aimed at determining 'natural background' water repellency in common coniferous forest types in the north-western USA. Mature or semi-mature coniferous forest sites (n = 81), which showed no evidence of recent fires and had at least some needle cast cover, were sampled across six states. After careful removal of litter and duff at each site, soil water repellency was examined in situ at the mineral soil surface using the Water Drop Penetration Time (WDPT) method for three sub-sites, followed by collecting near-surface mineral soil layer samples (0-3 cm depth). Following air-drying, samples were further analyzed for repellency using WDPT and contact angle (??sl) measurements. Amongst other variables examined were dominant tree type, ground vegetation, litter and duff layer depth, slope angle and aspect, elevation, geology, and soil texture, organic carbon content and pH. 'Natural background' water repellency (WDPT > 5 s) was detected in situ and on air-dry samples at 75% of all sites examined irrespective of dominant tree species (Pinus ponderosa, Pinus contorta, Picea engelmanii and Pseudotsuga menziesii). These findings demonstrate that the soil water repellency commonly observed in these forest types following burning is not necessarily the result of recent fire but can instead be a natural characteristic. The notion of a low background water repellency being typical for long-unburnt conifer forest soils of the north-western USA is therefore incorrect. It follows that, where pre-fire water repellency levels are not known or highly variable, post-fire soil water repellency conditions are an unreliable indicator in classifying soil burn severity. The terrain and soil variables examined showed, overall, no convincing relationship with the repellency levels observed (R2 < 0.15) except that repellency was limited in soils (i) developed over meta-sedimentary lithology and (ii) with clay contents >4%. This suggests that water repellency levels cannot be predicted with confidence from common terrain or soil variables. ?? 2009 Elsevier B.V.

Glyphosate and aminomethylphosphonic acid chronic risk assessment for soil biota.

PubMed

von Mérey, Georg; Manson, Philip S; Mehrsheikh, Akbar; Sutton, Peter; Levine, Steven L

2016-11-01

Glyphosate is a broad-spectrum herbicide used widely in agriculture, horticulture, private gardens, and public infrastructure, where it is applied to areas such as roadsides, railway tracks, and parks to control the growth of weeds. The exposure risk from glyphosate and the primary soil metabolite aminomethylphosphonic acid (AMPA) on representative species of earthworms, springtails, and predatory soil mites and the effects on nitrogen-transformation processes by soil microorganisms were assessed under laboratory conditions based on internationally recognized guidelines. For earthworms, the reproductive no-observed-effect concentration (NOEC) was 472.8 mg glyphosate acid equivalent (a.e.)/kg dry soil, which was the highest concentration tested, and 198.1 mg/kg dry soil for AMPA. For predatory mites, the reproductive NOEC was 472.8 mg a.e./kg dry soil for glyphosate and 320 mg/kg dry soil for AMPA, the highest concentrations tested. For springtails, the reproductive NOEC was 472.8 mg a.e./kg dry soil for glyphosate and 315 mg/kg dry soil for AMPA, the highest concentrations tested. Soil nitrogen-transformation processes were unaffected by glyphosate and AMPA at 33.1 mg a.e./kg soil and 160 mg/kg soil, respectively. Comparison of these endpoints with worst-case soil concentrations expected for glyphosate (6.62 mg a.e./kg dry soil) and AMPA (6.18 mg/kg dry soil) for annual applications at the highest annual rate of 4.32 kg a.e./ha indicate very low likelihood of adverse effects on soil biota. Environ Toxicol Chem 2016;35:2742-2752. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Effect of channelling on water balance, oxygen diffusion and oxidation rate in mine waste rock with an inclined multilayer soil cover

NASA Astrophysics Data System (ADS)

Song, Qing; Yanful, Ernest K.

2010-05-01

Engineered soil covers provide an option to mitigate acid rock drainage through reduced water flow and gaseous oxygen influx to underlying mine waste. Channels such as fissures, cracks or fractures developed in the barrier may influence the long-term performance of the soil cover. However, limited published information is available on the extent to which soil cover performance is impacted by these fissures and cracks. This study was conducted to investigate the effect of channelling in a barrier layer on water flow and oxygen transport in a soil cover. Two inclined (a slope of 20%) multilayer soil covers were examined under laboratory conditions. One cover had a 10-cm wide sand-filled channel in a compacted barrier layer (silty clay) at the upslope section, while the other cover was a normal one without the channel pathway. The soil covers were installed in plastic boxes measuring 120 cm × 120 cm × 25 cm (width × height × thickness). The sand-filled channel was designed to represent the aggregate of fissures and cracks that may be present in the compacted barrier. The soil covers were subjected to controlled drying and wetting periods selected to simulate field situation at the Whistle mine site near Capreol, Ontario, Canada. The measured results indicated that interflow decreased from 72.8% of the total precipitation in the soil cover without channel flow to 35.3% in the cover with channel flow, and percolation increased from zero in the normal soil cover to 43.0% of the total precipitation in the cover with channel flow. Gaseous oxygen transfer into the waste rock below the cover soils was 1091 times greater in the cover with channel than in the soil cover without channel. The channel pathway present in the barrier layer acted as a major passage for water movement and gaseous oxygen diffusion into the waste rock layer, thus decreasing the performance of the soil cover. The spacing of the channel with respect to the length of the test box is similar to those found in other published fracture networks. The distribution and partitioning of the water balance components would be expected to be similar to other situations with the same cover slope. This, of course, would depend on rainfall intensity.

Comparison between the land surface response of the ECMWF model and the FIFE-1987 data

NASA Technical Reports Server (NTRS)

Betts, Alan K.; Ball, John H.; Beljaars, Anton C. M.

1993-01-01

An averaged time series for the surface data for the 15 x 15 km FIFE site was prepared for the summer of 1987. Comparisons with 48-hr forecasts from the ECMWF model for extended periods in July, August, and October 1987 identified model errors in the incoming SW radiation in clear skies, the ground heat flux, the formulation of surface evaporation, the soil-moisture model, and the entrainment at boundary-layer top. The model clear-sky SW flux is too high at the surface by 5-10 percent. The ground heat flux is too large by a factor of 2 to 3 because of the large thermal capacity of the first soil layer (which is 7 cm thick), and a time truncation error. The surface evaporation was near zero in October 1987, rather than of order 70 W/sq m at noon. The surface evaporation falls too rapidly after rainfall, with a time-scale of a few days rather than the 7-10 d (or more) of the observations. On time-scales of more than a few days the specified 'climate layer' soil moisture, rather than the storage of precipitation, has a large control on the evapotranspiration. The boundary-layer-top entrainment is too low. This results in a moist bias in the boundary-layer mixing ratio of order 2 g/Kg in forecasts from an experimental analysis with nearly realistic surface fluxes; this because there is insufficient downward mixing of dry air.

The role of organic soil layer on the fate of Siberian larch forest and near-surface permafrost under changing climate: A simulation study

NASA Astrophysics Data System (ADS)

SATO, H.; Iwahana, G.; Ohta, T.

2013-12-01

Siberian larch forest is the largest coniferous forest region in the world. In this vast region, larch often forms nearly pure stands, regenerated by recurrent fire. This region is characterized by a short and dry growing season; the annual mean precipitation for Yakutsk was only about 240 mm. To maintain forest ecosystem under such small precipitation, underlying permafrost and seasonal soil freezing-thawing-cycle have been supposed to play important roles; (1) frozen ground inhibits percolation of soil water into deep soil layers, and (2) excess soil water at the end of growing season can be carried over until the next growing season as ice, and larch trees can use the melt water. As a proof for this explanation, geographical distribution of Siberian larch region highly coincides with continuous and discontinuous permafrost zone. Recent observations and simulation studies suggests that existences of larch forest and permafrost in subsurface layer are co-dependent; permafrost maintains the larch forest by enhancing water use efficiency of trees, while larch forest maintains permafrost by inhibiting solar radiation and preventing heat exchanges between soil and atmosphere. Owing to such complexity and absence of enough ecosystem data available, current-generation Earth System Models significantly diverse in their prediction of structure and key ecosystem functions in Siberian larch forest under changing climate. Such uncertainty should in turn expand uncertainty over predictions of climate, because Siberian larch forest should have major role in the global carbon balance with its huge area and vast potential carbon pool within the biomass and soil, and changes in boreal forest albedo can have a considerable effect on Northern Hemisphere climate. In this study, we developed an integrated ecosystem model, which treats interactions between plant-dynamics and freeze-thaw cycles. This integrated model contains a dynamic global vegetation model SEIB-DGVM, which simulates plant and carbon dynamics. It also contains a one-dimensional land surface model NOAH 2.7.1, which simulates soil moisture (both liquid and frozen), soil temperature, snowpack depth and density, canopy water content, and the energy and water fluxes. This integrated model quantitatively reconstructs post-fire development of forest structure (i.e. LAI and biomass) and organic soil layer, which dampens heat exchanges between soil and atmosphere. With the post-fire development of LAI and the soil organic layer, the integrated model also quantitatively reconstructs changes in seasonal maximum of active layer depth. The integrated model is then driven by the IPCC A1B scenario of rising atmospheric CO2, and by climate changes during the twenty-first century resulting from the change in CO2. This simulation suggests that forecasted global warming would causes decay of Siberian larch ecosystem, but such responses could be delayed by "memory effect" of the soil organic layer for hundreds of years.

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.

[Difference of water relationships of poplar trees in Zhangbei County, Hebei, China based on stable isotope and thermal dissipation method].

PubMed

Miao, Bo; Meng, Ping; Zhang, Jin Song; He, Fang Jie; Sun, Shou Jia

2017-07-18

The water sources and transpiration of poplar trees in Zhangbei County were measured using stable hydrogen isotope and thermal dissipation method. The differences in water relationships between dieback and non-dieback poplar trees were analyzed. The results showed that the dieback trees mainly used shallow water from 0-30 cm soil layer during growing season while the non-dieback trees mainly used water from 30-80 cm soil layer. There was a significant difference in water source between them. The non-dieback trees used more water from middle and deep soil layers than that of the dieback trees during the dry season. The percentage of poplar trees using water from 0-30 cm soil layer increased in wet season, and the increase of dieback trees was higher than that of non-dieback trees. The contributions of water from 30-180 cm soil layer of dieback and non-dieback trees both decreased in wet season. The sap flow rate of non-dieback trees was higher than that of dieback trees. There was a similar variation tend of sap flow rate between dieback and non-dieback trees in different weather conditions, but the start time of sap flow of non-dieback trees was earlier than that of dieback trees. Correlation analysis showed that the sap flow rate of either dieback or non-dieback poplar trees strongly related to soil temperature, wind speed, photosynthetically active radiation, relative humidity and air temperature. The sap flow rate of die-back poplar trees strongly negatively related to soil temperature and relative humidity, and strongly positively related to the other factors. The sap flow rate of non-dieback poplar trees only strongly negatively related to relative humidity but positively related to the other factors. The results revealed transpiration of both poplar trees was easily affected by environmental factors. The water consumption of dieback trees was less than non-dieback trees because the cumulative sap flow amount of dieback trees was lower. Reduced transpiration of dieback trees couldn't help to prevent poplar forest declining due to shallow water source.

Surface atmosphere exchange in dry and a wet regime over the Ganges valley: a comprehensive investigation with direct observations and numerical simulations

NASA Astrophysics Data System (ADS)

Sathyanadh, Anusha; Prabhakaran, Thara; Karipot, Anandakumar

2017-04-01

Land atmosphere interactions in the Ganges Valley basin is a topic of significant importance as it is most vulnerable region due to extreme weather, air pollution, etc. The complete energy balance observations over this region was conducted as part of the CAIPEEX-IGOC (Cloud Aerosol Interaction and Precipitation Enhancement Experiment - Integrated Ground based Observational Campaign) experiment for an entire year. These observations give first insight into the partitioning of energy in this vulnerable environment during the dry and wet regimes, which are typically part of the intraseasonal oscillations during the Indian monsoon season. These transitions wet-dry and dry-wet are poorly represented in GCMs and is the motivation for the detailed investigation here. Observations conducted with micrometeorological tower instrumented with eddy covariance sensors, radiation balance, soil heat flux measurements, microwave radiometer, sodar, radiosonde data are used in the present study. A set of numerical investigations of different Planetary Boundary Layer (PBL) schemes is also carried out to investigate features of the diurnal cycle during the wet and dry regimes. General behaviour of both local and nonlocal PBL schemes found from the investigation is to accomplish enhanced mixing, leading to a deeper PBL in the valley. However, observations give clear evidence of residual boundary layer characterised by a weak stratification, playing a key role in the exchange of PBL air mass with that of free atmosphere. Impact of changes in parameterization and controlling factors on the PBL height are investigated. Case studies for a dry phase during the incidence of a heat wave and a wet phase during a land depression are presented. Observed diurnal features of the surface meteorological parameters including the surface energy budget components were well captured by local and nonlocal PBL schemes during both the cases. Vertical profiles of temperature, mixing ratio and winds from microwave radiometer, radiosonde sounding and SODAR measurements compared well with the model vertical profiles. All the schemes are able to capture the development of a drying phase, its persistence and revival after the drying, similar to observation. The characteristic features of the drying such as decrease in mixing ratio, PBL warming, enhanced PBL growth, variations in wind speed, etc were reproduced by the model simulations. Results indicate that model is simulating a drier and deeper surface and mixed layer, compared to the observations, which is assisted by enhanced mixing through deep updrafts rooted from the surface layer and downdrafts associated with the subsiding air reaching down to the surface. Two issues are identified with model as a) relating to enhanced mixing also assisted by the subsiding air at top of the boundary layer and b) the energy partitioning at the surface with significantly excess energy partitioned in to sensible heat flux, thus warming the model surface layer. A few aircraft observations are used to investigate entrainment issue and results from these analysis and inferences will be presented. The surface layer eddy covariance measurements of sensible and latent heat fluxes and surface layer relationships are used to tune the surface layer exchanges.

Influence of root-water-uptake parameterization on simulated heat transport in a structured forest soil

NASA Astrophysics Data System (ADS)

Votrubova, Jana; Vogel, Tomas; Dohnal, Michal; Dusek, Jaromir

2015-04-01

Coupled simulations of soil water flow and associated transport of substances have become a useful and increasingly popular tool of subsurface hydrology. Quality of such simulations is directly affected by correctness of its hydraulic part. When near-surface processes under vegetation cover are of interest, appropriate representation of the root water uptake becomes essential. Simulation study of coupled water and heat transport in soil profile under natural conditions was conducted. One-dimensional dual-continuum model (S1D code) with semi-separate flow domains representing the soil matrix and the network of preferential pathways was used. A simple root water uptake model based on water-potential-gradient (WPG) formulation was applied. As demonstrated before [1], the WPG formulation - capable of simulating both the compensatory root water uptake (in situations when reduced uptake from dry layers is compensated by increased uptake from wetter layers), and the root-mediated hydraulic redistribution of soil water - enables simulation of more natural soil moisture distribution throughout the root zone. The potential effect on heat transport in a soil profile is the subject of the present study. [1] Vogel T., M. Dohnal, J. Dusek, J. Votrubova, and M. Tesar. 2013. Macroscopic modeling of plant water uptake in a forest stand involving root-mediated soil-water redistribution. Vadose Zone Journal, 12, 10.2136/vzj2012.0154. The research was supported by the Czech Science Foundation Project No. 14-15201J.

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.

Influence of Disturbance on Soil Respiration in Biologically Crusted Soil during the Dry Season

PubMed Central

Feng, Wei; Zhang, Yu-qing; Wu, Bin; Zha, Tian-shan; Jia, Xin; Qin, Shu-gao; Shao, Chen-xi; Liu, Jia-bin; Lai, Zong-rui; Fa, Ke-yu

2013-01-01

Soil respiration (Rs) is a major pathway for carbon cycling and is a complex process involving abiotic and biotic factors. Biological soil crusts (BSCs) are a key biotic component of desert ecosystems worldwide. In desert ecosystems, soils are protected from surface disturbance by BSCs, but it is unknown whether Rs is affected by disturbance of this crust layer. We measured Rs in three types of disturbed and undisturbed crusted soils (algae, lichen, and moss), as well as bare land from April to August, 2010, in Mu Us desert, northwest China. Rs was similar among undisturbed soils but increased significantly in disturbed moss and algae crusted soils. The variation of Rs in undisturbed and disturbed soil was related to soil bulk density. Disturbance also led to changes in soil organic carbon and fine particles contents, including declines of 60–70% in surface soil C and N, relative to predisturbance values. Once BSCs were disturbed, Q 10 increased. Our findings indicate that a loss of BSCs cover will lead to greater soil C loss through respiration. Given these results, understanding the disturbance sensitivity impact on Rs could be helpful to modify soil management practices which promote carbon sequestration. PMID:24453845

Contrasting response of coexisting plant's water-use patterns to experimental precipitation manipulation in an alpine grassland community of Qinghai Lake watershed, China.

PubMed

Wu, Huawu; Li, Jing; Li, Xiao-Yan; He, Bin; Liu, Jinzhao; Jiang, Zhiyun; Zhang, Cicheng

2018-01-01

Understanding species-specific changes in water-use patterns under recent climate scenarios is necessary to predict accurately the responses of seasonally dry ecosystems to future climate. In this study, we conducted a precipitation manipulation experiment to investigate the changes in water-use patterns of two coexisting species (Achnatherum splendens and Allium tanguticum) to alterations in soil water content (SWC) resulting from increased and decreased rainfall treatments. The results showed that the leaf water potential (Ψ) of A. splendens and A. tanguticum responded to changes in shallow and middle SWC at both the control and treatment plots. However, A. splendens proportionally extracted water from the shallow soil layer (0-10cm) when it was available but shifted to absorbing deep soil water (30-60 cm) during drought. By contrast, the A. tanguticum did not differ significantly in uptake depth between treatment and control plots but entirely depended on water from shallow soil layers. The flexible water-use patterns of A.splendens may be a key factor facilitating its dominance and it better acclimates the recent climate change in the alpine grassland community around Qinghai Lake.

Contrasting response of coexisting plant’s water-use patterns to experimental precipitation manipulation in an alpine grassland community of Qinghai Lake watershed, China

PubMed Central

Li, Xiao-Yan; He, Bin; Liu, Jinzhao; Jiang, Zhiyun; Zhang, Cicheng

2018-01-01

Understanding species-specific changes in water-use patterns under recent climate scenarios is necessary to predict accurately the responses of seasonally dry ecosystems to future climate. In this study, we conducted a precipitation manipulation experiment to investigate the changes in water-use patterns of two coexisting species (Achnatherum splendens and Allium tanguticum) to alterations in soil water content (SWC) resulting from increased and decreased rainfall treatments. The results showed that the leaf water potential (Ψ) of A. splendens and A. tanguticum responded to changes in shallow and middle SWC at both the control and treatment plots. However, A. splendens proportionally extracted water from the shallow soil layer (0–10cm) when it was available but shifted to absorbing deep soil water (30–60 cm) during drought. By contrast, the A. tanguticum did not differ significantly in uptake depth between treatment and control plots but entirely depended on water from shallow soil layers. The flexible water-use patterns of A.splendens may be a key factor facilitating its dominance and it better acclimates the recent climate change in the alpine grassland community around Qinghai Lake. PMID:29677195

Identification and paleoclimatic significance of magnetite nanoparticles in soils

NASA Astrophysics Data System (ADS)

Ahmed, Imad A. M.; Maher, Barbara A.

2018-02-01

In the world-famous sediments of the Chinese Loess Plateau, fossil soils alternate with windblown dust layers to record monsoonal variations over the last ˜3 My. The less-weathered, weakly magnetic dust layers reflect drier, colder glaciations. The fossil soils (paleosols) contain variable concentrations of nanoscale, strongly magnetic iron oxides, formed in situ during the wetter, warmer interglaciations. Mineralogical identification of the magnetic soil oxides is essential for deciphering these key paleoclimatic records. Formation of magnetite, a mixed Fe2+/Fe3+ ferrimagnet, has been linked to soil redox oscillations, and thence to paleorainfall. An opposite hypothesis states that magnetite can only form if the soil is water saturated for significant periods in order for Fe3+ to be reduced to Fe2+, and suggests instead the temperature-dependent formation of maghemite, an Fe3+-oxide, much of which ages subsequently into hematite, typically aluminum substituted. This latter, oxidizing pathway would have been temperature, but not rainfall dependent. Here, through structural fingerprinting and scanning transmission electron microscopy and electron energy loss spectroscopy analysis, we prove that magnetite is the dominant soil-formed ferrite. Maghemite is present in lower concentrations, and shows no evidence of aluminum substitution, negating its proposed precursor role for the aluminum-substituted hematite prevalent in the paleosols. Magnetite dominance demonstrates that magnetite formation occurs in well-drained, generally oxidizing soils, and that soil wetting/drying oscillations drive the degree of soil magnetic enhancement. The magnetic variations of the Chinese Loess Plateau paleosols thus record changes in monsoonal rainfall, over timescales of millions of years.

Rain water transport and storage in a model sandy soil with hydrogel particle additives.

PubMed

Wei, Y; Durian, D J

2014-10-01

We study rain water infiltration and drainage in a dry model sandy soil with superabsorbent hydrogel particle additives by measuring the mass of retained water for non-ponding rainfall using a self-built 3D laboratory set-up. In the pure model sandy soil, the retained water curve measurements indicate that instead of a stable horizontal wetting front that grows downward uniformly, a narrow fingered flow forms under the top layer of water-saturated soil. This rain water channelization phenomenon not only further reduces the available rain water in the plant root zone, but also affects the efficiency of soil additives, such as superabsorbent hydrogel particles. Our studies show that the shape of the retained water curve for a soil packing with hydrogel particle additives strongly depends on the location and the concentration of the hydrogel particles in the model sandy soil. By carefully choosing the particle size and distribution methods, we may use the swollen hydrogel particles to modify the soil pore structure, to clog or extend the water channels in sandy soils, or to build water reservoirs in the plant root zone.

Development and survival of Anopheles gambiae eggs in drying soil: influence of the rate of drying, egg age, and soil type.

PubMed

Shililu, J I; Grueber, W B; Mbogo, C M; Githure, J I; Riddiford, L M; Beier, J C

2004-09-01

Little is known about the contribution made by the egg stage of African malaria vectors to the rapid rise in adult populations following the onset of seasonal rains. To examine this issue, we evaluated the viability of Anopheles gambiae eggs in drying soil in the laboratory. Survival data were collected from field-caught mosquitoes kept in sandy loam soil and laboratory-reared colonies kept in sandy loam soil and black cotton soil. Under high, medium, and low soil-moisture regimes, egg viability declined sharply with increased duration of drying. Eggs remained viable in drying sandy loam soil for 1, 5, and 10 days, but not after 15 or 20 days. The most dramatic decline in hatching success occurred between drying days 1 (78-83% hatch) and 5 (20-23% hatch). In contrast, eggs reared in high-moisture black cotton soil remained viable for up to 15 days. Furthermore, after 5 drying days, high-, medium-, and low-moisture soils averaged 59, 47, and 31% hatching success, respectively. We recovered unhatched eggs from sandy loam soils to examine the developmental status of the embryos. A majority of the unhatched eggs that were recovered from days 15 and 20 in sandy loam soils contained fully developed late-stage embryos. Thus, unhatched eggs completed embryonic development but probably died before receiving an appropriate hatching stimulus. Our results suggest that the absolute moisture content of the soil does not alone determine hatching success of anopheline eggs. Rather, soil moisture, together with the rate of drying, physiological factors associated with the age of the egg, and the type of soil in which the egg rests likely influence survival.

Soil and surface layer type affect non-rainfall water inputs

NASA Astrophysics Data System (ADS)

Agam, Nurit; Berliner, Pedro; Jiang, Anxia

2017-04-01

Non-rainfall water inputs (NRWIs), which include fog deposition, dew formation, and direct water vapor adsorption by the soil, play a vital role in arid and semiarid regions. Environmental conditions, namely radiation, air temperature, air humidity, and wind speed, largely affect the water cycle driven by NRWIs. The substrate type (soil type and the existence/absence of a crust layer) may as well play a major role. Our objective was to quantify the effects of soil type (loess vs. sand) and surface layer (bare vs. crusted) on the gain and posterior evaporation of NRWIs in the Negev Highlands throughout the dry summer season. Four undisturbed soil samples (20 cm diameter and 50 cm depth) were excavated and simultaneously introduced into a PVC tube. Two samples were obtained in the Negev's Boker plain (loess soil) and two in the Nizzana sand dunes in the Western Negev. On one sample from each site the crust was removed while on the remaining one the natural crust was left in place. The samples were brought to the research site at the Jacob Bluestein Institutes for Desert Research, Ben-Gurion University of the Negev, Israel (31˚08' N, 34˚53' E, 400 meter above the sea level) where they were exposed to the same environmental conditions. The four samples in their PVC tubes were placed on top of scales and the samples mass was continuously monitored. Soil temperatures were monitored at depths of 1, 2, 3, 5 and10 cm in each microlysimeter (ML) using Copper-Constantan thermocouples. The results of particle size distribution indicated that the crust of the loess soil is probably a physical crust, i.e., a crust that forms due to raindroplets impact; while the crust on the sand soil is biological. On most days, the loess soils adsorbed more water than their corresponding sand soil samples. For both soils, the samples for which the crust was removed adsorbed more water than the samples for which it was intact. The difference in daily water adsorption amount between crusted and non-crusted sandy soils often exceeded that between crusted and non-crusted loess soils.

Humus in some soils from Western Antarctica

NASA Astrophysics Data System (ADS)

Abakumov, E.

2009-04-01

Soils of Antarctica are well known as a thick profile soils with low amounts of humus concentrated in the upper layers - O or A horizons. Also there are specific soils of seashore landscapes which affected by penguins guano accumulation and, therefore characterized by high stocks of organic matter in solum. These two types of soils were studied during the Western Antarctica part of 53th Russian Antarctic Expedition in 2008 International Polar Year. These rote of expedition was on Polar stations "Russkaya", "Leningradskaya" and "Bellinsgausen" and also two places, not affected by polar men's - Lindsey Island and Hudson mountains (Ross Sea). Typical soils of "Russkaya" and "Leningradskaya" stations was a Cryosoils with low humus content (0,02 - 0,20 %) which was a product of lichens decaying and further humification. The humus profile was not deep and humic substances migration stopped on the 30 cm deeps maximally. Soils of Sub-Antarctica (Bellinsgausen station, King-George Island) show higher portions of humus which maximum was 3,00 % under the mosses. Humus distribution was more gradual through profile due to the higher thickness of active layer and longer period of biological activity. Soils under the penguin's beaches shows big portions of organic matter, in some cases more than 50 % to total soil mass. Humification starts in first years in cases of Sub-Antarctic guano soils and only after 3-7 years of leaching in seashore Antarctic guano-soils. Soils under the guano layers were extremely reached by nitrogen, and in some cases there were not any plants there due to toxicity of guano. This event was more typical for cold seashore soils of Antarctica. In all cases humus consists mostly of fulvic acids and low molecular non-specific organic acids. The CHA/CFA ratio in all cases were lesser than 1,0 and in more that 50 % of cases it was lesser than 0,5. The investigations conducted shows that the stocks of humus in soil of Antarctica are not estimated and till now we didn't know the total stocks of organic matter in automorphous dry plains and valleys and seashore landscapes of this continent.

Soil moisture decline due to afforestation across the Loess Plateau, China

NASA Astrophysics Data System (ADS)

Jia, Xiaoxu; Shao, Ming'an; Zhu, Yuanjun; Luo, Yi

2017-03-01

The Loess Plateau of China is a region with one of the most severe cases of soil erosion in the world. Since the 1950s, there has been afforestation measure to control soil erosion and improve ecosystem services on the plateau. However, the introduction of exotic tree species (e.g., R. pseudoacacia, P. tabulaeformis and C. korshinskii) and high-density planting has had a negative effect on soil moisture content (SMC) in the region. Any decrease in SMC could worsen soil water shortage in both the top and deep soil layers, further endangering the sustainability of the fragile ecosystem. This study analyzed the variations in SMC following the conversion of croplands into forests in the Loess Plateau. SMC data within the 5-m soil profile were collected at 50 sites in the plateau region via field survey, long-term in-situ observations and documented literature. The study showed that for the 50 sites, the depth-averaged SMC was much lower under forest than under cropland. Based on in-situ measurements of SMC in agricultural plots and C. korshinskii plots in 2004-2014, SMC in the 0-4 m soil profile in both plots declined significantly (p < 0.01) during the growing season. The rate of decline in SMC in various soil layers under C. korshinskii plots (-0.008 to -0.016 cm3 cm-3 yr-1) was much higher than those under agricultural plots (-0.004 to -0.005 cm3 cm-3 yr-1). This suggested that planting C. korshinskii intensified soil moisture decline in China's Loess Plateau. In the first 20-25 yr of growth, the depth-averaged SMC gradually decreased with stand age in R. pseudoacacia plantation, but SMC somehow recovered with increasing tree age over the 25-year period. Irrespectively, artificial forests consumed more deep soil moisture than cultivated crops in the study area, inducing soil desiccation and dry soil layer formation. Thus future afforestation should consider those species that use less water and require less thinning for sustainable soil conservation without compromising future water resources demands in the Loess Plateau.

Response of millet and sorghum to a varying water supply around the primary and nodal roots

PubMed Central

Rostamza, M.; Richards, R. A.; Watt, M.

2013-01-01

Background and Aims Cereals have two root systems. The primary system originates from the embryo when the seed germinates and can support the plant until it produces grain. The nodal system can emerge from stem nodes throughout the plant's life; its value for yield is unclear and depends on the environment. The aim of this study was to test the role of nodal roots of sorghum and millet in plant growth in response to variation in soil moisture. Sorghum and millet were chosen as both are adapted to dry conditions. Methods Sorghum and millet were grown in a split-pot system that allowed the primary and nodal roots to be watered separately. Key Results When primary and nodal roots were watered (12 % soil water content; SWC), millet nodal roots were seven times longer than those of sorghum and six times longer than millet plants in dry treatments, mainly from an 8-fold increase in branch root length. When soil was allowed to dry in both compartments, millet nodal roots responded and grew 20 % longer branch roots than in the well-watered control. Sorghum nodal roots were unchanged. When only primary roots received water, nodal roots of both species emerged and elongated into extremely dry soil (0·6–1·5 % SWC), possibly with phloem-delivered water from the primary roots in the moist inner pot. Nodal roots were thick, short, branchless and vertical, indicating a tropism that was more pronounced in millet. Total nodal root length increased in both species when the dry soil was covered with plastic, suggesting that stubble retention or leaf mulching could facilitate nodal roots reaching deeper moist layers in dry climates. Greater nodal root length in millet than in sorghum was associated with increased shoot biomass, water uptake and water use efficiency (shoot mass per water). Millet had a more plastic response than sorghum to moisture around the nodal roots due to (1) faster growth and progression through ontogeny for earlier nodal root branch length and (2) partitioning to nodal root length from primary roots, independent of shoot size. Conclusions Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth. PMID:23749473

Response of millet and sorghum to a varying water supply around the primary and nodal roots.

PubMed

Rostamza, M; Richards, R A; Watt, M

2013-07-01

Cereals have two root systems. The primary system originates from the embryo when the seed germinates and can support the plant until it produces grain. The nodal system can emerge from stem nodes throughout the plant's life; its value for yield is unclear and depends on the environment. The aim of this study was to test the role of nodal roots of sorghum and millet in plant growth in response to variation in soil moisture. Sorghum and millet were chosen as both are adapted to dry conditions. Sorghum and millet were grown in a split-pot system that allowed the primary and nodal roots to be watered separately. When primary and nodal roots were watered (12 % soil water content; SWC), millet nodal roots were seven times longer than those of sorghum and six times longer than millet plants in dry treatments, mainly from an 8-fold increase in branch root length. When soil was allowed to dry in both compartments, millet nodal roots responded and grew 20 % longer branch roots than in the well-watered control. Sorghum nodal roots were unchanged. When only primary roots received water, nodal roots of both species emerged and elongated into extremely dry soil (0.6-1.5 % SWC), possibly with phloem-delivered water from the primary roots in the moist inner pot. Nodal roots were thick, short, branchless and vertical, indicating a tropism that was more pronounced in millet. Total nodal root length increased in both species when the dry soil was covered with plastic, suggesting that stubble retention or leaf mulching could facilitate nodal roots reaching deeper moist layers in dry climates. Greater nodal root length in millet than in sorghum was associated with increased shoot biomass, water uptake and water use efficiency (shoot mass per water). Millet had a more plastic response than sorghum to moisture around the nodal roots due to (1) faster growth and progression through ontogeny for earlier nodal root branch length and (2) partitioning to nodal root length from primary roots, independent of shoot size. Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth.

More than carbon sequestration: Biophysical climate benefits of restored savanna woodlands.

PubMed

Syktus, Jozef I; McAlpine, Clive A

2016-07-04

Deforestation and climate change are interconnected and represent major environmental challenges. Here, we explore the capacity of regional-scale restoration of marginal agricultural lands to savanna woodlands in Australia to reduce warming and drying resulting from increased concentration of greenhouse gases. We show that restoration triggers a positive feedback loop between the land surface and the atmosphere, characterised by increased evaporative fraction, eddy dissipation and turbulent mixing in the boundary-layer resulting in enhanced cloud formation and precipitation over the restored regions. The increased evapotranspiration results from the capacity deep-rooted woody vegetation to access soil moisture. As a consequence, the increase in precipitation provides additional moisture to soil and trees, thus reinforcing the positive feedback loop. Restoration reduced the rate of warming and drying under the transient increase in the radiative forcing of greenhouse gas emissions (RCP8.5). At the continental scale, average summer warming for all land areas was reduced by 0.18 (o)C from 4.1 (o)C for the period 2056-2075 compared to 1986-2005. For the restored regions (representing 20% of Australia), the averaged surface temperature increase was 3.2 °C which is 0.82 °C cooler compared to agricultural landscapes. Further, there was reduction of 12% in the summer drying of the near-surface soil for the restored regions.

SMAP soil moisture drying more rapid than observed in situ following rainfall events

USDA-ARS?s Scientific Manuscript database

We examine soil drying rates by comparing observations from the NASA Soil Moisture Active Passive (SMAP) mission to surface soil moisture from in situ probes during drydown periods at SMAP validation sites. SMAP and in situ probes record different soil drying dynamics after rainfall. We modeled this...

Nitrogen supply modulates the effect of changes in drying-rewetting frequency on soil C and N cycling and greenhouse gas exchange.

PubMed

Morillas, Lourdes; Durán, Jorge; Rodríguez, Alexandra; Roales, Javier; Gallardo, Antonio; Lovett, Gary M; Groffman, Peter M

2015-10-01

Climate change and atmospheric nitrogen (N) deposition are two of the most important global change drivers. However, the interactions of these drivers have not been well studied. We aimed to assess how the combined effect of soil N additions and more frequent soil drying-rewetting events affects carbon (C) and N cycling, soil:atmosphere greenhouse gas (GHG) exchange, and functional microbial diversity. We manipulated the frequency of soil drying-rewetting events in soils from ambient and N-treated plots in a temperate forest and calculated the Orwin & Wardle Resistance index to compare the response of the different treatments. Increases in drying-rewetting cycles led to reductions in soil NO3- levels, potential net nitrification rate, and soil : atmosphere GHG exchange, and increases in NH4+ and total soil inorganic N levels. N-treated soils were more resistant to changes in the frequency of drying-rewetting cycles, and this resistance was stronger for C- than for N-related variables. Both the long-term N addition and the drying-rewetting treatment altered the functionality of the soil microbial population and its functional diversity. Our results suggest that increasing the frequency of drying-rewetting cycles can affect the ability of soil to cycle C and N and soil : atmosphere GHG exchange and that the response to this increase is modulated by soil N enrichment. © 2015 John Wiley & Sons Ltd.

Assay of the Martian Regolith with Neutrons

NASA Technical Reports Server (NTRS)

Drake, Darrell M.

1997-01-01

The purpose of the research is to combine experiments and Monte Carlo transport of neutrons through volume of soil in an attempt to model neutron leakage from planetary surfaces. Emphasis is given to the change of neutron spectra as a function of water content and location. During the first stage of effort, two experiments were conducted in which leakage of neutrons from a Pu-Be source through about 30 g/cm(exp 2) of soil were measured with several counters. A Monte Carlo code, MCNP, has been used to model many of the 100 individual runs of the experiment. Hydrogen is the element that has the most dramatic effect on the neutron spectrum and its effect on the neutron spectrum is almost the same whether it is in the form of water or polyethylene. In order to simulate various water configurations, sheets of polyethylene have been used between layers of soil as well as water in several concentrations up to 18%. Comparison of experimental results to theoretical predictions made with the MCNP code were disappointing for low concentrations of water. We have made extensive calculations to see if room return could be the cause of the discrepancies. Water concentrations of the 'dry' soil were measured by two different laboratories and differed only by 0.5%. We have made calculations to optimize the next experiment and are investigating other methods of determining the water content of 'dry' soil.

Rainfall and wet and dry cycle's impact on ash thickness. A laboratory experiment

NASA Astrophysics Data System (ADS)

Pereira, Paulo; Keestra, Saskia; Peters, Piet; Cerdà, Artemi

2016-04-01

Ash is the most important and effective soil protection in the immediate period after the fire (Cerda and Doerr, 2008; Pereira et al., 2015a). This protection can last for days or weeks depending on the fire severity, topography of the burned area and post-fire meteorological conditions. In the initial period after the fire, ash is easily transported by wind. However after the first rainfalls, ash is eroded, or bind in soil surface (Pereira et al., 2013, 2015a). Ash thickness has implications on soil protection. The soil protection against the erosion and the ash capacity to retain water increases with the ash thickness (Bodi et al., 2014). Ash cover is very important after fire because store water and releases into soil a large amount of nutrients, fundamental to vegetation recuperation (Pereira et al., 2014). Despite the importance of ash thickness in post fire environments, little information is available about the effects of rainfall and wet and dry cycle's effects on ash thickness. This work aims to fill this gap. The objective of this study is to investigate the impacts of rainfall and wet and dry cycles in the ash thickness of two different under laboratory conditions. Litter from Oak (Quercus robur) and Spruce (Picea abis) were collected to and exposed during 2 hours to produce ash at 200 and 400 C. Subsequently a layer of 15 mm ash was spread on soil surface in small boxes (24x32 cm) and then subjected to rainfall simulation. Boxes were placed at a 17% of inclination and a rainfall intensity of 55 mm/h during 40 minutes was applied. After the rainfall simulation the plots were stored in an Oven at the temperature of 25 C during four days, in order to identify the effects of wet and dry cycles (Bodi et al., 2013). Ash thickness was measured after the first rainfall (AFR), before the second rainfall (BSR) - after the dry period of 4 days - and after the second rainfall (ASR). In each box a grid with 57 points was designed in order to analyse ash thickness AFR, BSR and ASR. The results showed that AFR, ash thickness was reduced by 7.97% (±18.13) and 32.02 % (±37.44) in the Oak ash produced at 200 C (Oak 200) and 400 C (Oak 400), respectively. The spruce ash layer produced at 200 (Spruce 200) decreased 7.26% (±15.11) and 13.11 % (±18.40) in the ash produced at 400 C (Spruce 400). Before the second rainfall we identified that Oak 200 ash layer reduced approximately 15.95 (±15.81) while Oak 400 decreased 47.98% (±28.97). Spruce 200 ash layer was reduced by 14.52 (±14.57) and Spruce 400 by 18.68 (±17.54). In the last rainfall experiment, it was observed that Oak 200 ash layer decreased 14.88 (±14.09) and Oak 400 ash layer 44.52 (±28.85). Spruce 200 ash layer reduced 13.10 (±14.76) and spruce 400 18.33 (±21.69). The spatial pattern (assessed with Moran's I index) of the ash later of Oak 200 and Oak 400 AFR was significantly clustered (p<0.001). The spatial pattern of Spruce 200 was random (p>0.05) and Spruce 400 significantly clustered (p<0.001). Before the second rainfall, the spatial pattern of Oak 200 and Oak 400 was significantly clustered at a p<0.05 and p<0.001. The same situation was identified in Spruce 200 and Spruce 400 (p<0.001). Finally, ASR, the spatial pattern observed in Oak 200 and Oak 400 was significantly clustered at a p<0.05 and p<0.001. This was also identified in Spruce 200 and Spruce 400. Overall, the thickness decrease was higher in the ash layers produced at high temperature. The differences were mainly observed in oak ash. The dry cycle did not have an important impact on ash thickness in both species as the second rainfall cycle. The results from the Moran's I analysis showed that after the rainfall experiment the ash was mainly concentrated in a specific part of the plot. In this case it was located in the bottom of the experimental plot. Acknowledgments The authors are thankful to the Soil Physics and Land Management Group from Wageningen University, The Netherlands for provide the infrastructure to develop this work, to the RECARE project (grant agreement n° 603498), and to the COST action ES1306: Connecting European Connectivity Research for funding a STSM at the Wageningen University. References Bodi, M., Martin, D.A., Santin, C., Balfour, V., Doerr, S.H., Pereira, P., Cerda, A., Mataix-Solera, J. (2014) Wildland fire ash: production, composition and eco-hydro-geomorphic effects. Earth-Science Reviews, 130, 103-127. Bodi, M.B., Doerr, S.H., Cerda, A., Mataix-Solera, J. (2013) Hydrological effects of a layer of vegetation ash on underlying wettable and water repellent soil. Geoderma, 191, 14-23. Cerdà, A., Doerr, S.H., 2008. The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period. Catena 74, 256-263. Pereira, P., Cerdà, A., Úbeda, X., Mataix-Solera, J., Jordan, A. Burguet, M. (2013) Spatial models for monitoring the spatio-temporal evolution of ashes after fire - a case study of a burnt grassland in Lithuania, Solid Earth, 4, 153-165. Pereira, P., Cerdà, A., Úbeda, X., Mataix-Solera, J. Arcenegui, V., Zavala, L. (2015) Modelling the impacts of wildfire on ash thickness in a short-term period, Land Degradation and Development, 26, 180-192. Pereira, P., Jordan, A., Cerda, A., Martin, D. 2015a. Editorial: The role of ash in fire-affected ecosystems, Catena, 135, 337 - 379. Pereira, P., Úbeda, X., Martin, D., Mataix-Solera, J., Cerdà, A., Burguet, M. (2014)Wildfire effects on extractable elements in ash from a Pinus pinaster forest in Portugal, Hydrological Processes, 28, 3681-3690

The effect of plant water storage on water fluxes within the coupled soil-plant system.

PubMed

Huang, Cheng-Wei; Domec, Jean-Christophe; Ward, Eric J; Duman, Tomer; Manoli, Gabriele; Parolari, Anthony J; Katul, Gabriel G

2017-02-01

In addition to buffering plants from water stress during severe droughts, plant water storage (PWS) alters many features of the spatio-temporal dynamics of water movement in the soil-plant system. How PWS impacts water dynamics and drought resilience is explored using a multi-layer porous media model. The model numerically resolves soil-plant hydrodynamics by coupling them to leaf-level gas exchange and soil-root interfacial layers. Novel features of the model are the considerations of a coordinated relationship between stomatal aperture variation and whole-system hydraulics and of the effects of PWS and nocturnal transpiration (Fe,night) on hydraulic redistribution (HR) in the soil. The model results suggest that daytime PWS usage and Fe,night generate a residual water potential gradient (Δψp,night) along the plant vascular system overnight. This Δψp,night represents a non-negligible competing sink strength that diminishes the significance of HR. Considering the co-occurrence of PWS usage and HR during a single extended dry-down, a wide range of plant attributes and environmental/soil conditions selected to enhance or suppress plant drought resilience is discussed. When compared with HR, model calculations suggest that increased root water influx into plant conducting-tissues overnight maintains a more favorable water status at the leaf, thereby delaying the onset of drought stress. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Effects of Air Drying on Soil Available Phosphorus in Two Grassland Soils

NASA Astrophysics Data System (ADS)

Schaerer, M.; Frossard, E.; Sinaj, S.

2003-04-01

Mobilization of P from the soil to ground and surface water is principally determined by the amount of P in the soil and physico-chemical as well as biological processes determining the available P-pool that is in equilibrium with soil solution. Soil available P is commonly estimated on air dry soil using a variety of methods (extraction with water, dilute acids and bases, anion exchange resin, isotopic exchange or infinite sinks). Recently, attempts have been made to use these measurements to define the potential for transport of P from soil to water by overland flow or subsurface flow. The effect of air drying on soil properties in general, and plant nutrient status in particular, have been subject of a number of studies. The main objective of this paper was to evaluate the effect of air-drying on soil properties and available P. For this experiment, grassland soils were sampled on two study sites located on slopes in the watershed of Lake Greifensee, 25 km south-east of Zurich. Both soils (0-4 cm depth) are rich in P with 1.7 and 1.3 g kg-1 total P at site I and site II, respectively. The concentrations on isotopically exchangeable P within 1 minute (E1min, readily available P) for the same depth were also very high, 58 and 27 mg P kg soil-1 for the site I and II, respectively. In the present study both field moist and air dried soil samples were analyzed for microbial P (Pmic), resin extractable P (P_r), isotopically exchangeable P (E1min) and amorphous Al and Fe (Alox, Feox). Generally, the microbial P in field moist soils reached values up to 120 mg P/kg soil, whereas after drying they decreased by 73% in average for both soils. On the contrary to Pmic, available P estimated by different methods strongly increased after drying of the soil samples. The concentration of phosphate ions in the soil solution c_p, E1min and P_r were 4.2, 2.2 and 2 times higher in dry soils than in field moist soils. The increase in available P shows significant semilogarithmic correlations with the decrease in microbial P (r^2 = 0.66, r^2 = 0.53 and r^2 = 0.75 respectively for c_p, E(1 min) and resin P). The parameter R_0/r1min from the isotopic exchange approach, which is well correlated with the soil P fixing capacity, generally decreased after drying. Drying of the soil significantly modifies soil properties that control P availability, such as amorphous Fe- and Al-oxides. The amount of Feox and Alox was decreased by 3 and 6% respectively. It can be concluded that drying of the soils leads a strong increase in available P as estimated by different methods. The observed available P increase is mainly related to a modification of both soil chemistry and biology. Especially for grassland soils with a high organic matter content and microbial biomass, available P measurements on dry soil seem to overestimate the available P mainly due to a release of microbial P.

Responses of seminal wheat seedling roots to soil water deficits.

PubMed

Trejo, Carlos; Else, Mark A; Atkinson, Christopher J

2018-04-01

The aims of this paper are to develop our understanding of the ways by which soil water deficits influence early wheat root growth responses, particularly how seminal roots respond to soil drying and the extent to which information on differences in soil water content are conveyed to the shoot and their impact on shoot behaviour. To achieve this, wheat seedlings have been grown, individually for around 25 days after germination in segmented soil columns within vertical plastic compartments. Roots were exposed to different soil volumetric moisture contents (SVMC) within the two compartments. Experiments where the soil in the lower compartment was allowed to dry to different extents, while the upper was maintained close to field capacity, showed that wheat seedlings allocated proportionally more root dry matter to the lower drier soil compartment. The total production of root, irrespective of the upper or lower SVMC, was similar and there were no detected effects on leaf growth rate or gas exchange. The response of seminal roots to proportionally increase their allocation of dry matter, to the drier soil was unexpected with such plasticity of roots system development traditionally linked to heterogeneous nutrient distribution than accessing soil water. In experiments where the upper soil compartment was allowed to dry, root growth slowed and leaf growth and gas exchange declined. Subsequent experiments used root growth rates to determine when seminal root tips first came into contact with drying soil, with the intentions of determining how the observed root growth rates were maintained as an explanation for the observed changes in root allocation. Measurements of seminal root ABA and ethylene from roots within the drying soil are interpreted with respect to what is known about the physiological control of root growth in drying soil. Copyright © 2018 Elsevier GmbH. All rights reserved.

Study on rhizobium interaction with osmoprotectant rhizobacteria for improving mung bean yield

NASA Astrophysics Data System (ADS)

Maryani, Y.; Sudadi; Dewi, W. S.; Yunus, A.

2018-03-01

Gunungkidul has calcareous soil with limitations including calcareous stone, mostly hilly terrain, and shallow cultivated layer. Furthermore, nowadays we face the disadvantages climates such as long dry seasons, a short rainy season and high temperatures caused by climate change. Climate change leads to irregular rainwater availability for microbes and crops. Research in this field is currently needed as climate change affected directly on crop production, while we need to find the strategy to keep high productivity of the plant. This research aimed to determine the ability of osmoprotectant rhizobacteria and rhizobium to support mung bean yield. Osmoprotectant rhizobacteria were isolated and screened from the calcareous soil in Gunungkidul with disadvantageous climates such as a long dry season, a short rainy season and high temperature. This research was arranged in Completely Randomized Design. The result showed that osmoprotectant rhizobacteria isolate of strain Al24-k and Ver5-k can produce 9.6306 mg g‑1 cell of glycine betaine in a soil density 1.7667 x 107 CFU g‑1 and 11.4870 mg g‑1 cell of glycine betaine in a soil density 1.9667 x 107 CFU g‑1. Inoculation of isolates osmoprotectant rhizobacteria can support mung bean yield. Osmoprotectant rhizobacteria isolate did not effect rhizobium in mung bean rhizosphere.

Monitoring Soil Infiltration In Semi-Arid Regions With Meteosat And A Coupled Model Approach Using PROMET And SLC

NASA Astrophysics Data System (ADS)

Klug, P.; Bach, H.; Migdall, S.

2013-12-01

In arid regions the infiltration of sparse rainfalls and resulting ground water recharge is a critical quantity for the water cycle. With the PROMET model the infiltration process can be simulated in detail, since 4 soil layers together with the hourly calculation time step allow simulating the vertical water transport. Wet soils are darker than dry soils. Using the SLC reflectance model this effect can be simulated and compared to temporal high resolution time series of measured reflectances from Meteosat in order to monitor the drying process. This study demonstrates how MSG can be used to better parameterize the simulation of the infiltration process and reduce uncertainties in ground water recharge estimation. The study is carried out in the frame of the EU FP7 project CLIMB (Climate Induced Changes on the Hydrology of Mediterranean Basins). According to climate projections, Mediterranean countries are at risk of changes in the hydrological budget, the agricultural productivity and drinking water supply in the future. The CLIMB FP-7 project coordinated by the University of Munich (LMU) aims at employing integrated hydrological modelling in a new framework to reduce existing uncertainties in climate change impact analysis of the Mediterranean region [1, 2].

Compost and sulfur affect the mobilization and phyto-availability of Cd and Ni to sorghum and barnyard grass in a spiked fluvial soil.

PubMed

Shaheen, Sabry M; Balbaa, Ali A; Khatab, Alaa M; Rinklebe, Jörg

2017-12-01

Soil reclamation via additives can cause contradictory effects on the mobilization of toxic elements in soils under dry and wet conditions. Therefore, our aim was to investigate the impact of compost and sulfur in two rates (1.25 and 2.5%) on fractionation, mobilization, and phyto-availability of cadmium (Cd) and nickel (Ni) to sorghum (dry soil) and barnyard grass (wet soil) in a fluvial soil spiked with 25 mg Cd or 200 mg Ni/kg soil. Compost decreased the solubility and mobilization of Cd (especially in dry soil) and Ni (in both soils). Sulfur increased the solubility of Cd (31% in dry soil-49% in wet soil) and Ni (4.6% in wet soil-8.7% in dry soil). Sulfur altered the carbonate fraction of Cd to the soluble fraction and the residual fraction of Cd and Ni to the non-residual fraction. Compost decreased Cd and increased Ni in sorghum, but enhanced Cd and degraded Ni in grass. Sulfur increased Cd and Ni in both plants, and the increasing rate of Cd was higher in grass than in sorghum, while Ni was higher in sorghum than in grass. These results suggest that compost can be used as an immobilizing agent for Cd in the dry soil and Ni in the wet soil; however, it might be used as mobilizing agent for Cd in the wet soil and Ni in the dry soil. Sulfur (with rate 2.5%) can be used for enhancing the phyto-extraction of Cd and Ni (especially Cd) from contaminated alkaline soils.

Dry deposition profile of small particles within a model spruce canopy.

PubMed

Ould-Dada, Zitouni

2002-03-08

Data on dry deposition of 0.82 microm MMAD uranium particles to a small scale, 'model' Norway spruce (Picea abies) canopy have been determined by means of wind tunnel experiments. These are presented for both the total canopy and for five horizontal layers within the canopy. The results show a complex pattern of deposition within the canopy. The highest deposition velocity Vg (0.19 cm s(-1)) was recorded for the topmost layer within the canopy (i.e. the layer in direct contact with the boundary layer) whereas the lowest Vg (0.02 cm s(-1)) occurred at the soil surface. Vertical penetration of depositing aerosol through the canopy was influenced by variations in biomass, wind velocity and turbulence within the canopy. A total canopy Vg of 0.5 cm s(-1) was obtained and this is in line with field measurements of Vg reported in literature for both anthropogenic and radionuclide aerosols of similar size ranges. Extrapolation of wind tunnel data to 'real' forest canopies is discussed. The information presented here is of importance in predicting the likely contribution of dry deposition of aerosols to pollutant inputs to forest ecosystems, particularly in the context of radioactive aerosol releases from nuclear installations. The application of the present data may also be appropriate for other pollutant aerosols such as SO4, NO3 and NH4, which are characterised by particle sizes in the range used in this study.

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.

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.

Subsurface Hydrologic Processes Revealed by Time-lapse GPR in Two Contrasting Soils in the Shale Hills CZO

NASA Astrophysics Data System (ADS)

Guo, L.; Lin, H.; Nyquist, J.; Toran, L.; Mount, G.

2017-12-01

Linking subsurface structures to their functions in determining hydrologic processes, such as soil moisture dynamics, subsurface flow patterns, and discharge behaviours, is a key to understanding and modelling hydrological systems. Geophysical techniques provide a non-invasive approach to investigate this form-function dualism of subsurface hydrology at the field scale, because they are effective in visualizing subsurface structure and monitoring the distribution of water. In this study, we used time-lapse ground-penetrating radar (GPR) to compare the hydrologic responses of two contrasting soils in the Shale Hills Critical Zone Observatory. By integrating time-lapse GPR with artificial water injection, we observed distinct flow patterns in the two soils: 1) in the deep Rushtown soil (over 1.5 m depth to bedrock) located in a concave hillslope, a lateral preferential flow network extending as far as 2 m downslope was identified above a less permeable layer and via a series of connected macropores; whereas 2) in the shallow Weikert soil ( 0.3 m depth to saprock) located in a planar hillslope, vertical infiltration into the permeable fractured shale dominated the flow field, while the development of lateral preferential flow along the hillslope was restrained. At the Weikert soil site, the addition of brilliant blue dye to the water injection followed by in situ excavation supported GPR interpretation that only limited lateral preferential flow formed along the soil-saprock interface. Moreover, seasonally repeated GPR surveys indicated different patterns of profile moisture distribution in the two soils that in comparison with the dry season, a dense layer within the BC horizon in the deep Rushtown soil prevented vertical infiltration in the wet season, leading to the accumulation of soil moisture above this layer; whereas, in the shallow Weikert soil, water infiltrated into saprock in wet seasons, building up water storage within the fractured bedrock (i.e., the rock moisture). Results of this study demonstrated the strong interplay between soil structures and subsurface hydrologic behaviors, and time-lapse GPR is an effective method to establish such a relationship under the field conditions.

Polyphenols as enzyme inhibitors in different degraded peat soils: Implication for microbial metabolism in rewetted peatlands

NASA Astrophysics Data System (ADS)

Zak, Dominik; Roth, Cyril; Gelbrecht, Jörg; Fenner, Nathalie; Reuter, Hendrik

2015-04-01

Recently, more than 30,000 ha of drained minerotrophic peatlands (= fens) in NE Germany were rewetted to restore their ecological functions. Due to an extended drainage history, a re-establishment of their original state is not expected in the short-term. Elevated concentrations of dissolved organic carbon, ammonium and phosphate have been measured in the soil porewater of the upper degraded peat layers of rewetted fens at levels of one to three orders higher than the values in pristine systems; an indicator of increased microbial activity in the upper degraded soil layers. On the other hand there is evidence that the substrate availability within the degraded peat layer is lowered since the organic matter has formerly been subject to intense decomposition over the decades of drainage and intense agricultural use of the areas. Previously however, it was suggested that inhibition of hydrolytic enzymes by polyphenolic substances is suspended during aeration of peat soils mainly due to the decomposition of the inhibiting polyphenols by oxidising enzymes such as phenol oxidase. Accordingly we hypothesised a lack of enzyme inhibiting polyphenols in degraded peat soils of rewetted fens compared to less decomposed peat of more natural fens. We collected both peat samples at the soil surface (0-20 cm) and fresh roots of dominating vascular plants and mosses (as peat parent material) from five formerly drained rewetted sites and five more natural sites of NE Germany and NW Poland. Less decomposed peat and living roots were used to obtain an internal standard for polyphenol analysis and to run enzyme inhibition tests. For all samples we determined the total phenolic contents and in addition we distinguished between the contents of hydrolysable and condensed tannic substances. From a methodical perspective the advantage of internal standards compared to the commercially available standards cyanidin chloride and tannic acid became apparent. Quantification with cyanidin or tannic acid led to a considerable underestimation (up to 90%) of polyphenolic concentrations in peat soils. As hypothesised we found that highly degraded peat contains far lower levels of total polyphenolics (factor 8) and condensed tannins (factor 50) than less decomposed peat. In addition we detected large differences between different plant species with highest polyphenolic contents for the roots of Carex appropinquata that were more than 10-fold higher than Sphagnum spp. (450 mg/g dry mass vs. 39 mg/g dry mass). Despite these differences, we did not find a significant correlation between enzyme activities and peat degradation state, indicating that there is no simple linear relationship between polyphenolic contents and microbial activity.

Dry heat effects on survival of indigenous soil particle microflora and particle viability studies of Kennedy Space Center soil

NASA Technical Reports Server (NTRS)

Ruschmeyer, O. R.; Pflug, I. J.; Gove, R.; Heisserer, Y.

1975-01-01

Research efforts were concentrated on attempts to obtain data concerning the dry heat resistance of particle microflora in Kennedy Space Center soil samples. The in situ dry heat resistance profiles at selected temperatures for the aggregate microflora on soil particles of certain size ranges were determined. Viability profiles of older soil samples were compared with more recently stored soil samples. The effect of increased particle numbers on viability profiles after dry heat treatment was investigated. These soil particle viability data for various temperatures and times provide information on the soil microflora response to heat treatment and are useful in making selections for spacecraft sterilization cycles.

Meteorological and Land Surface Properties Impacting Sea Breeze Extent and Aerosol Distribution in a Dry Environment

NASA Astrophysics Data System (ADS)

Igel, Adele L.; van den Heever, Susan C.; Johnson, Jill S.

2018-01-01

The properties of sea breeze circulations are influenced by a variety of meteorological and geophysical factors that interact with one another. These circulations can redistribute aerosol particles and pollution and therefore can play an important role in local air quality, as well as impact remote sensing. In this study, we select 11 factors that have the potential to impact either the sea breeze circulation properties and/or the spatial distribution of aerosols. Simulations are run to identify which of the 11 factors have the largest influence on the sea breeze properties and aerosol concentrations and to subsequently understand the mean response of these variables to the selected factors. All simulations are designed to be representative of conditions in coastal sub tropical environments and are thus relatively dry, as such they do not support deep convection associated with the sea breeze front. For this dry sea breeze regime, we find that the background wind speed was the most influential factor for the sea breeze propagation, with the soil saturation fraction also being important. For the spatial aerosol distribution, the most important factors were the soil moisture, sea-air temperature difference, and the initial boundary layer height. The importance of these factors seems to be strongly tied to the development of the surface-based mixed layer both ahead of and behind the sea breeze front. This study highlights potential avenues for further research regarding sea breeze dynamics and the impact of sea breeze circulations on pollution dispersion and remote sensing algorithms.

Spatial variability of hillslope water balance, wolf creek basin, subarctic yukon

NASA Astrophysics Data System (ADS)

Carey, Sean K.; Woo, Ming-Ko

2001-11-01

A hydrological study was conducted between 1997 and 1999 in the subalpine open woodland of the Wolf Creek Basin, Yukon, to assess the interslope water balance variability. The water balance during the snowmelt and summer periods on four hillslopes revealed strong contrasts in process magnitudes and highlighted important factors including frost, vegetation, soils and microclimate that controlled vertical and lateral fluxes of water. Snow accounted for approximately half the annual water input, while differences in accumulation among hillslopes were related to interception properties of vegetation. Available energy at the snow surface controlled the melt sequence and the snow on some slopes disappeared up to two months earlier than others. Snowmelt runoff was confined to slopes with ice-rich substrates that inhibited deep percolation, with the runoff magnitude governed by the snow storage and the antecedent moisture of the desiccated organic soils prior to melt. During summer, evapotranspiration exceeded rainfall, largely sustained by water from the soil moisture reservoir recharged during the melt period. Differences in net radiation on slopes controlled the potential evapotranspiration, with the actual rates limited by the phenology of the deciduous forests and shrubs. Evapotranspiration was further suppressed on slopes where the organic soils became dry in late summer. Summer runoff was confined to slopes with porous organic layers overlying mineral soils to form a two-layer flow system: (1) quickflow in the surface organic layer and (2) slowflow in the mineral soil. Differences in the rates of flow were related to the position of the water table which may rise into the organic layer to activate quickflow. The presence of ice-rich frost and permafrost impeded vertical drainage and indirectly regulated the position of the water table. The location of the hillslope within a basin influenced recharge and discharge dynamics. Slope segments with large inflows sustained discharge throughout the summer to enhance basin runoff. In this way, the present study provides insight into basin hydrology.

Effects of drying-wetting and freezing-thawing cycle on leachability of metallic elements in mine soils

NASA Astrophysics Data System (ADS)

Bang, H.; Kim, J.; Hyun, S.

2016-12-01

Mine leachate derived from contaminated mine sites with metallic elements can pose serious risks on human society and environment. Only labile fraction of metallic elements in mine soils is subject to leaching and movement by rainfall. Lability of metallic element in soil is a function of bond strengths between metal and soil surfaces, which is influenced by environmental condition (e.g., rainfall intensity, duration, temperature, etc.) The purpose of this study was to elucidate the effects of various climate conditions on the leaching patterns and lability of metallic elements in mine soils. To do this, two mine soils were sampled from two abandoned mine sites located in Korea. Leaching test were conducted using batch decant-refill method. Various climatic conditions were employed in leaching test such as (1) oven drying (40oC) - wetting cycles, (2) air drying (20oC) - wetting cycle, and (3) freezing (-40oC) - thawing cycles. Duration of drying and freezing were varied from 4 days to 2 weeks. Concentration of metallic elements, pH, Eh and concentration of dissolved iron and sulfate in leachate from each leaching process was measured. To identify the changes of labile fraction in mine soils after each of drying or freezing period, sequential extraction procedure (five fraction) was used to compare labile fraction (i.e., F1 + F2) of metallic elements. The concentration of metallic elements in mine leachate was increased after drying and freezing procedure. The amounts of released metallic element from mine soils was changed depending on their drying or freezing period. In addition, labile fraction of metallic elements in soil was also changed after drying and freezing. The changes in labile fraction after drying and freezing might be due to the increased soil surface area by pore water volume expansion. Further study is therefore needed to evaluate the impact of altered physical properties of soils such as hydration of soil surface area and shrinking by drying and freezing cycles.

The effects of climate changes on soil methane oxidation in a dry Arctic tundra

NASA Astrophysics Data System (ADS)

D'Imperio, Ludovica

2014-05-01

The effects of climate changes on soil methane oxidation in a dry Arctic tundra. Ludovica D'Imperio1, Anders Michelsen1, Christian J. Jørgensen1, Bo Elberling1 1Center for Permafrost (CENPERM), Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark At Northern latitudes climatic changes are predicted to be most pronounced resulting in increasing active layer depth and changes in growing season length, vegetation cover and nutrient cycling. As a consequence of increased temperature, large stocks of carbon stored in the permafrost-affected soils could become available for microbial transformations and under anoxic conditions result in increasing methane production affecting net methane (CH4) budget. Arctic tundra soils also serves as an important sink of atmospheric CH4 by microbial oxidation under aerobic conditions. While several process studies have documented the mechanisms behind both production and emissions of CH4 in arctic ecosystems, an important knowledge gap exists with respect to the in situ dynamics of microbial-driven uptake of CH4 in arctic dry lands which may be enhanced as a consequence of global warming and thereby counterbalancing CH4 emissions from Arctic wetlands. In-situ methane measurements were made in a dry Arctic tundra in Disko Island, Western Greenland, during the summer 2013 to assess the role of seasonal and inter-annual variations in temperatures and snow cover. The experimental set-up included snow fences installed in 2012, allowed investigations of the emissions of GHGs from soil under increased winter snow deposition and ambient field conditions. The soil fluxes of CH4 and CO2 were measured using closed chambers in manipulated plots with increased summer temperatures and shrub removal with or without increased winter precipitation. At the control plots, the averaged seasonal CH4 oxidation rates ranged between -0.05 mg CH4 m-2 hr-1 (end of August) and -0.32 mg CH4 m-2 hr-1 (end of June). In the plots with increased summer temperatures the rates ranged between -0.08 mg CH4 m-2 hr-1 (end of August) and -0.40 mg CH4 m-2 hr-1 (beginning of July). Preliminary results show a significant effect of increased winter precipitation (p<0.01) over the season as well as a significant warming effect (p<0.05) during July and August. These results suggest that in a warmer climate increasing CH4 uptake rates in dry Arctic soils could become an important factor for net CH4 budget.

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

PubMed Central

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

2015-01-01

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. PMID:26089535

Can differences in root responses to soil drying and compaction explain differences in performance of trees growing on landfill sites?

PubMed

Liang, Jiansheng; Zhang, Jianhua; Chan, Gilbert Y. S.; Wong, M. H.

1999-07-01

Two tropical woody species, Acacia confusa Merrill and Litsea glutinosa (Lour.) C.B. Robinson, were grown under controlled conditions in PVC pipes filled with John Innes No. 2 soil. To investigate root distribution, physiological characteristics and hydraulic conductivity, four soil treatments were imposed-well-watered and noncompacted (control), well-watered and compacted; unwatered and noncompacted, and unwatered and compacted. In L. glutinosa, rooting depth and root elongation were severely restricted when soil bulk density increased from around 1.12 to 1.62 g cm(-3), whereas soil compaction had little effect on these parameters in A. confusa. As soil drying progressed, root water potential and osmotic potential declined more slowly in L. glutinosa than in A. confusa. Both the soil drying and compaction treatments significantly stimulated the accumulation of root abscisic acid (ABA) in both species. Soil drying damaged the root cell membrane of A. confusa, but had little influence on the root cell membrane of L. glutinosa. Soil drying had a greater effect on root hydraulic conductivity (L(p)) in L. glutinosa than in A. confusa, whereas the effect of soil compaction on L(p) was less in L. glutinosa than in A. confusa. Soil drying enhanced the effects of soil compaction on root L(p). We conclude that soil drying and compaction have large species-specific effects on the distribution, growth and physiology of roots. The relationships of these root properties to the species' ability to tolerate unfavorable soil conditions were examined.

Tunneling behavior of the formosan subterranean termite (isoptera: rhinotermitadae) in dry soil

USDA-ARS?s Scientific Manuscript database

This study examines the effect of dry soil on tunnel construction by the Formosan subterranean termite, Cptotermes formosanus. Termites did not construct tunnels in dry soil in any of the treatments. Termites only constructed tunnels in moist areas in treatments where the soil was partially moistene...

EXTRACTION METHODS FOR RECOVERY OF VOLATILE ORGANIC COMPOUNDS FROM FORTIFIED DRY SOILS

EPA Science Inventory

Recovery of 8 volatile organic compounds (VOCs) from dry soils, each fortified at 800 ng/g soil, was studied in relation to the extraction method and time of extraction. Extraction procedures studied on desiccator-dried soils were modifications of EPA low-and high-level purge-and...

Centrifuge Modeling of the Thermo-Mechanical Response of Energy Foundations

NASA Astrophysics Data System (ADS)

Goode, Joseph Collin, III

This thesis presents the results from a series of centrifuge tests performed to understand the profiles of thermo-mechanical axial strain, axial displacement, and axial stress in semi-floating and end-bearing energy foundations installed in dry Nevada sand and Bonny silt layers during different combinations of mechanical loading and foundation heating. In addition to the construction details for the centrifuge scale-model reinforced concrete energy foundations, the results from 1 g thermo-mechanical characterization tests performed on the foundations to evaluate their mechanical and thermal material properties are presented in this thesis. In general, the centrifuge-scale tests involve application of an axial load to the head of the foundation followed by circulation of a heat exchange fluid through embedded tubing to bring the foundation to a constant temperature. After this point, mechanical loads were applied to the foundation to characterize their thermo-mechanical response. Specifically, loading tests to failure were performed on the semi-floating foundation installed in different soil layers to characterize the impact of temperature on the load-settlement curve, and elastic loading tests were performed on the end-bearing foundation to characterize the impact of temperature on the mobilized side shear distributions. During application of mechanical loads and changes in foundation temperature, the axial strains are measured using embedded strain gages. The soil and foundation temperatures, foundation head movement, and soil surface deformations are also monitored to characterize the thermo-mechanical response of the system. The tests performed in this study were used to investigate different phenomena relevant to the thermo-mechanical response of energy foundations. First, the role of end-restraint boundary conditions in both sand and silt were investigated by comparing the strain distributions for the end-bearing and semi-floating foundations in each soil type. The tests on sand and silt permit evaluation of the soil-structure interaction in dry and unsaturated soils with different mechanisms of side shear resistance (i.e., primarily frictional and primarily cohesive, respectively). End-bearing foundations were observed to have higher magnitudes of thermal axial stress than semi-floating foundations, with a more uniform distribution in thermal axial strain in the sand. A general conclusion from these tests is that the unsaturated silt led to a more pronounced soil structure interaction effect than the dry sand. For example, temperature did not affect the ultimate capacity of the semi-floating foundation in dry sand, while it had a pronounced effect in unsaturated silt. Two approaches for controlling the foundation head restraint boundary condition were investigated for the end-bearing foundation in sand: load control conditions (free expansion) as well as stiffness control conditions (restrained expansion). As expected, greater expansion was observed in the case of free expansion, and greater thermal axial stresses were observed in the case of restrained expansion. The effects of temperature cycles were also investigated for the semi-floating foundation in Bonny silt, and less upward movement was observed during each cycle of heating, with a slight softening in behavior on each cycle. Overall, the results provide a suite of information which is suitable to define soil-structure interaction parameters under realistic stress states for deep foundations.

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

Carbon Structural Investigations of Concentric Layers Within Macro-aggregates From Forest and Agricultural Soils

NASA Astrophysics Data System (ADS)

Dria, K. J.; Gamblin, D. E.; Smucker, A. J.; Park, E.; Filley, T. R.

2004-12-01

Much of the current research on the potential of agricultural and forest soils to act as sinks for greenhouse gases focuses on the capacity of the systems to form long-term stabilized fractions of soil organic matter (SOM). One proposed mechanism is that carbon is sequestered within soil aggregate interiors during the aggregation process. Repeated wetting-drying cycles change internal pore geometries and associated microhabitats and create more stable macro-aggregates. Research by Smucker and coworkers (EGU Abstracts, 2004) suggest that the exterior portions of aggregates contain greater concentrations of C and N than their interiors, establishing gradients of \\ä13C values across these aggregates. We present the results of a study to test if there exists molecular evidence of such gradients. Soil samples from forest, conventional tillage (CT) and no tillage (NT) agriculture ecosystems in Hoytville and Wooster LTER sites were gently sieved into various size fractions. Soil macro-aggregates (6.3-9.5mm) were peeled, by mechanical erosion chambers, into concentric layers and separated into exterior, transitional and interior regions. Alkaline CuO oxidation was used to determine the composition of lignin, suberin, and cutin biopolymers to determine changes in source and degradative states of SOM. Preliminary results indicate that both soils show similar relative yields of lignin and hydroxyl fatty acids with a greater abundance of lignin than cutin and suberin acids. Greater abundances (per 100mg organic carbon) of CuO products were observed in the native forest than in either agricultural system. The lignin in the NT agricultural soil was least oxidized, followed by the forest soils, then the CT agricultural soils. For both soils, slight trends in biopolymer concentrations were observed between the exterior, transitional and interior regions of the aggregates from the forest and CT or NT ecosystems.

Exploring the sensitivity of soil carbon dynamics to climate change, fire disturbance and permafrost thaw in a black spruce ecosystem

USGS Publications Warehouse

O'Donnell, J. A.; Harden, J.W.; McGuire, A.D.; Romanovsky, V.E.

2011-01-01

In the boreal region, soil organic carbon (OC) dynamics are strongly governed by the interaction between wildfire and permafrost. Using a combination of field measurements, numerical modeling of soil thermal dynamics, and mass-balance modeling of OC dynamics, we tested the sensitivity of soil OC storage to a suite of individual climate factors (air temperature, soil moisture, and snow depth) and fire severity. We also conducted sensitivity analyses to explore the combined effects of fire-soil moisture interactions and snow seasonality on OC storage. OC losses were calculated as the difference in OC stocks after three fire cycles (???500 yr) following a prescribed step-change in climate and/or fire. Across single-factor scenarios, our findings indicate that warmer air temperatures resulted in the largest relative soil OC losses (???5.3 kg C mg-2), whereas dry soil conditions alone (in the absence of wildfire) resulted in the smallest carbon losses (???0.1 kg C mg-2). Increased fire severity resulted in carbon loss of ???3.3 kg C mg-2, whereas changes in snow depth resulted in smaller OC losses (2.1-2.2 kg C mg-2). Across multiple climate factors, we observed larger OC losses than for single-factor scenarios. For instance, high fire severity regime associated with warmer and drier conditions resulted in OC losses of ???6.1 kg C mg-2, whereas a low fire severity regime associated with warmer and wetter conditions resulted in OC losses of ???5.6 kg C mg-2. A longer snow-free season associated with future warming resulted in OC losses of ???5.4 kg C mg-2. Soil climate was the dominant control on soil OC loss, governing the sensitivity of microbial decomposers to fluctuations in temperature and soil moisture; this control, in turn, is governed by interannual changes in active layer depth. Transitional responses of the active layer depth to fire regimes also contributed to OC losses, primarily by determining the proportion of OC into frozen and unfrozen soil layers. ?? 2011 Author(s).

Solubility of aluminum and silica in Spodic horizons as affected by drying and freezing

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

Simonsson, M.; Berggren, D.; Gustafsson, J.P.

The release of toxic Al{sup 3+} is one of the most serious consequences of anthropogenic soil acidification. Therefore, the mechanisms controlling Al solubility have been a topic of intense research for more than a decade. For convenience, soil samples are often dried before storage and experimental use. However, the literature offers examples of drying that results in changes in pH, solubility of organic matter, and dissolution rates of Al. In this study, the authors examined the solubility of Al and Si in fresh soil and in soil that had been dried or deep-frozen. Five Spodosol B horizon soils were subjectedmore » to batch titrations, where portions of each soil were equilibrated with solutions with varying concentrations of acid or base added. Extractions with acid oxalate and Na pyrophosphate indicated the presence of imogolite-type materials (ITM) in three of the soils. In the other two soils most secondary solid-phase Al was associated with humic substances. Deep-freezing did not significantly change pH nor the concentration of Al or Si as compared with fresh soil. Drying, on the other hand, yielded pH increases of up to 0.3 units at a given addition of acid or base, whereas Al{sup 3+} changed only slightly, implying a higher Al solubility in all of the soils. Furthermore, dissolved silica increased by up to 200% after drying, except in a soil that almost completely lacked oxalate-extractable Si. The authors suggest that drying enhanced the dissolution of ITM by disrupting soil organic matter, thus exposing formerly coated mineral surfaces. In the soil where dissolved Si did not change with drying, it has been demonstrated that Al-humus complexes controlled Al solubility. They suggest that fissures in the organic material caused by drying may have exposed formerly occluded binding sites that had a higher Al saturation than had sites at the surface of humus particles.« less

Evaluation of Populus and Salix continuously irrigated with landfill leachate II. soils and early tree development.

PubMed

Zalesny, Ronald S; Bauer, Edmund O

2007-01-01

Soil contaminant levels and early tree growth data are helpful for assessing phytoremediation systems. Populus (DN17, DN182, DN34, NM2, and NM6) and Salix (94003, 94012, S287, S566, and SX61) genotypes were irrigated with landfill leachate or municipal water and tested for differences in (1) element concentrations (P, K, Ca, Mg, S, Zn, B, Mn, Fe, Cu, Al, and Na) of a topsoil layer and a layer of sand in tanks with a cover crop of trees or no trees and (2) height, diameter, volume, and dry mass of leaves, stems, and roots. Trees were irrigated with leachate or water during the final 12 wk of the 18-wk study. Differences in most soil element concentrations were negligible (P > 0.05) for irrigation treatments and cover main effects. Phosphorous, K, Mg, S, Zn, Mn, Fe, and Al concentrations were greater in topsoil than sand (P = 0.0011 for Mg; P < 0.0001 for others). There was broad variation between genera and among clones for all growth traits. The treatment x clone interaction governed height, volume, and root dry mass, with (94012, SX61), (NM2, S566, SX61), and (S287, S566) exhibiting the greatest levels, respectively,following leachate application. Given the broad amount of variability among and within these genera, there is great potential for the identification and selection of specific genotypes with a combination of elevated phytoremediation capabilities and tree yield. From a practical standpoint, these results may be used as a baseline for the development of future remediation systems.

Soil drying procedure affects the DNA quantification of Lactarius vinosus but does not change the fungal community composition.

PubMed

Castaño, Carles; Parladé, Javier; Pera, Joan; Martínez de Aragón, Juan; Alday, Josu G; Bonet, José Antonio

2016-11-01

Drying soil samples before DNA extraction is commonly used for specific fungal DNA quantification and metabarcoding studies, but the impact of different drying procedures on both the specific fungal DNA quantity and the fungal community composition has not been analyzed. We tested three different drying procedures (freeze-drying, oven-drying, and room temperature) on 12 different soil samples to determine (a) the soil mycelium biomass of the ectomycorrhizal species Lactarius vinosus using qPCR with a specifically designed TaqMan® probe and (b) the fungal community composition and diversity using the PacBio® RS II sequencing platform. Mycelium biomass of L. vinosus was significantly greater in the freeze-dried soil samples than in samples dried at oven and room temperature. However, drying procedures had no effect on fungal community composition or on fungal diversity. In addition, there were no significant differences in the proportions of fungi according to their functional roles (moulds vs. mycorrhizal species) in response to drying procedures. Only six out of 1139 operational taxonomic units (OTUs) had increased their relative proportions after soil drying at room temperature, with five of these OTUs classified as mould or yeast species. However, the magnitude of these changes was small, with an overall increase in relative abundance of these OTUs of approximately 2 %. These results suggest that DNA degradation may occur especially after drying soil samples at room temperature, but affecting equally nearly all fungi and therefore causing no significant differences in diversity and community composition. Despite the minimal effects caused by the drying procedures at the fungal community composition, freeze-drying resulted in higher concentrations of L. vinosus DNA and prevented potential colonization from opportunistic species.

Colloid Mobilization in a Fractured Soil during Dry-Wet Cycles: Role of Drying Duration and Flow Path Permeability.

PubMed

Mohanty, Sanjay K; Saiers, James E; Ryan, Joseph N

2015-08-04

In subsurface soils, colloids are mobilized by infiltrating rainwater, but the source of colloids and the process by which colloids are generated between rainfalls are not clear. We examined the effect of drying duration and the spatial variation of soil permeability on the mobilization of in situ colloids in intact soil cores (fractured and heavily weathered saprolite) during dry-wet cycles. Measuring water flux at multiple sampling ports at the core base, we found that water drained through flow paths of different permeability. The duration of antecedent drying cycles affected the amount of mobilized colloids, particularly in high-flux ports that received water from soil regions with a large number of macro- and mesopores. In these ports, the amount of mobilized colloids increased with increased drying duration up to 2.5 days. For drying durations greater than 2.5 days, the amount of mobilized colloids decreased. In contrast, increasing drying duration had a limited effect on colloid mobilization in low-flux ports, which presumably received water from soil regions with fewer macro- and mesopores. On the basis of these results, we attribute this dependence of colloid mobilization upon drying duration to colloid generation from dry pore walls and distribution of colloids in flow paths, which appear to be sensitive to the moisture content of soil after drying and flow path permeability. The results are useful for improving the understanding of colloid mobilization during fluctuating weather conditions.

Short dry spells in the wet season increase mortality of tropical pioneer seedlings.

PubMed

Engelbrecht, Bettina M J; Dalling, James W; Pearson, Timothy R H; Wolf, Robert L; Gálvez, David A; Koehler, Tobias; Tyree, Melvin T; Kursar, Thomas A

2006-06-01

Variation in plant species performance in response to water availability offers a potential axis for temporal and spatial habitat partitioning and may therefore affect community composition in tropical forests. We hypothesized that short dry spells during the wet season are a significant source of mortality for the newly emerging seedlings of pioneer species that recruit in treefall gaps in tropical forests. An analysis of a 49-year rainfall record for three forests across a rainfall gradient in central Panama confirmed that dry spells of > or = 10 days during the wet season occur on average once a year in a deciduous forest, and once every other year in a semi-deciduous moist and an evergreen wet forest. The effect of wet season dry spells on the recruitment of pioneers was investigated by comparing seedling survival in rain-protected dry plots and irrigated control plots in four large artificially created treefall gaps in a semi-deciduous tropical forest. In rain-protected plots surface soil layers dried rapidly, leading to a strong gradient in water potential within the upper 10 cm of soil. Seedling survival for six pioneer species was significantly lower in rain-protected than in irrigated control plots after only 4 days. The strength of the irrigation effect differed among species, and first became apparent 3-10 days after treatments started. Root allocation patterns were significantly, or marginally significantly, different between species and between two groups of larger and smaller seeded species. However, they were not correlated with seedling drought sensitivity, suggesting allocation is not a key trait for drought sensitivity in pioneer seedlings. Our data provide strong evidence that short dry spells in the wet season differentially affect seedling survivorship of pioneer species, and may therefore have important implications to seedling demography and community dynamics.

Hydraulic performance of compacted clay liners under simulated daily thermal cycles.

PubMed

Aldaeef, A A; Rayhani, M T

2015-10-01

Compacted clay liners (CCLs) are commonly used as hydraulic barriers in several landfill applications to isolate contaminants from the surrounding environment and minimize the escape of leachate from the landfill. Prior to waste placement in landfills, CCLs are often exposed to temperature fluctuations which can affect the hydraulic performance of the liner. Experimental research was carried out to evaluate the effects of daily thermal cycles on the hydraulic performance of CCLs under simulated landfill conditions. Hydraulic conductivity tests were conducted on different soil specimens after being exposed to various thermal and dehydration cycles. An increase in the CCL hydraulic conductivity of up to one order of magnitude was recorded after 30 thermal cycles for soils with low plasticity index (PI = 9.5%). However, medium (PI = 25%) and high (PI = 37.2%) plasticity soils did not show significant hydraulic deviation due to their self-healing potential. Overlaying the CCL with a cover layer minimized the effects of daily thermal cycles, and maintained stable hydraulic performance in the CCLs even after exposure to 60 thermal cycles. Wet-dry cycles had a significant impact on the hydraulic aspect of low plasticity CCLs. However, medium and high plasticity CCLs maintained constant hydraulic performance throughout the test intervals. The study underscores the importance of protecting the CCL from exposure to atmosphere through covering it by a layer of geomembrane or an interim soil layer. Copyright © 2015 Elsevier Ltd. All rights reserved.

Pore-scale water dynamics during drying and the impacts of structure and surface wettability

NASA Astrophysics Data System (ADS)

Cruz, Brian C.; Furrer, Jessica M.; Guo, Yi-Syuan; Dougherty, Daniel; Hinestroza, Hector F.; Hernandez, Jhoan S.; Gage, Daniel J.; Cho, Yong Ku; Shor, Leslie M.

2017-07-01

Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loam soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. Lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.

Sphagnum-dwelling testate amoebae in subarctic bogs are more sensitive to soil warming in the growing season than in winter: the results of eight-year field climate manipulations.

PubMed

Tsyganov, Andrey N; Aerts, Rien; Nijs, Ivan; Cornelissen, Johannes H C; Beyens, Louis

2012-05-01

Sphagnum-dwelling testate amoebae are widely used in paleoclimate reconstructions as a proxy for climate-induced changes in bogs. However, the sensitivity of proxies to seasonal climate components is an important issue when interpreting proxy records. Here, we studied the effects of summer warming, winter snow addition solely and winter snow addition together with spring warming on testate amoeba assemblages after eight years of experimental field climate manipulations. All manipulations were accomplished using open top chambers in a dry blanket bog located in the sub-Arctic (Abisko, Sweden). We estimated sensitivity of abundance, diversity and assemblage structure of living and empty shell assemblages of testate amoebae in the living and decaying layers of Sphagnum. Our results show that, in a sub-arctic climate, testate amoebae are more sensitive to climate changes in the growing season than in winter. Summer warming reduced species richness and shifted assemblage composition towards predominance of xerophilous species for the living and empty shell assemblages in both layers. The higher soil temperatures during the growing season also decreased abundance of empty shells in both layers hinting at a possible increase in their decomposition rates. Thus, although possible effects of climate changes on preservation of empty shells should always be taken into account, species diversity and structure of testate amoeba assemblages in dry subarctic bogs are sensitive proxies for climatic changes during the growing season. Copyright © 2011 Elsevier GmbH. All rights reserved.

Canadian Field Soils IV: Modeling Thermal Conductivity at Dryness and Saturation

NASA Astrophysics Data System (ADS)

Tarnawski, V. R.; McCombie, M. L.; Leong, W. H.; Coppa, P.; Corasaniti, S.; Bovesecchi, G.

2018-03-01

The thermal conductivity data of 40 Canadian soils at dryness (λ _{dry}) and at full saturation (λ _{sat}) were used to verify 13 predictive models, i.e., four mechanistic, four semi-empirical and five empirical equations. The performance of each model, for λ _{dry} and λ _{sat}, was evaluated using a standard deviation ( SD) formula. Among the mechanistic models applied to dry soils, the closest λ _{dry} estimates were obtained by MaxRTCM (it{SD} = ± 0.018 Wm^{-1}\\cdot K^{-1}), followed by de Vries and a series-parallel model (S-{\\vert }{\\vert }). Among the semi-empirical equations (deVries-ave, Advanced Geometric Mean Model (A-GMM), Chaudhary and Bhandari (C-B) and Chen's equation), the closest λ _{dry} estimates were obtained by the C-B model (± 0.022 Wm^{-1}\\cdot K^{-1}). Among the empirical equations, the top λ _{dry} estimates were given by CDry-40 (± 0.021 Wm^{-1}\\cdot K^{-1} and ± 0.018 Wm^{-1}\\cdot K^{-1} for18-coarse and 22-fine soils, respectively). In addition, λ _{dry} and λ _{sat} models were applied to the λ _{sat} database of 21 other soils. From all the models tested, only the maxRTCM and the CDry-40 models provided the closest λ _{dry} estimates for the 40 Canadian soils as well as the 21 soils. The best λ _{sat} estimates for the 40-Canadian soils and the 21 soils were given by the A-GMM and the S-{\\vert }{\\vert } model.

Natural 'background' soil water repellency in conifer forests: its prediction and relationship to wildfire occurrence

NASA Astrophysics Data System (ADS)

Doerr, Stefan; Woods, Scott; Martin, Deborah; Casimiro, Marta

2013-04-01

Soils under a wide range of vegetation types exhibit water repellency following the passage of a fire. This is viewed by many as one of the main causes for accelerated post-fire runoff and soil erosion and it has often been assumed that strong soil water repellency present after wildfire is fire-induced. However, high levels of repellency have also been reported under vegetation types not affected by fire, and the question arises to what degree the water repellency observed at burnt sites actually results from fire. This study aimed at determining 'natural background' water repellency in common coniferous forest types in the north-western USA. Mature or semi-mature coniferous forest sites (n = 81), which showed no evidence of recent fires and had at least some needle cast cover, were sampled across six states. After careful removal of litter and duff at each site, soil water repellency was examined in situ at the mineral soil surface using the Water Drop Penetration Time (WDPT) method for three sub-sites, followed by col- lecting near-surface mineral soil layer samples (0-3 cm depth). Following air-drying, samples were fur- ther analyzed for repellency using WDPT and contact angle (hsl) measurements. Amongst other variables examined were dominant tree type, ground vegetation, litter and duff layer depth, slope angle and aspect, elevation, geology, and soil texture, organic carbon content and pH. 'Natural background' water repellency (WDPT > 5 s) was detected in situ and on air-dry samples at 75% of all sites examined irrespective of dominant tree species (Pinus ponderosa, Pinus contorta, Picea engelma- nii and Pseudotsuga menziesii). These findings demonstrate that the soil water repellency commonly observed in these forest types following burning is not necessarily the result of recent fire but can instead be a natural characteristic. The notion of a low background water repellency being typical for long- unburnt conifer forest soils of the north-western USA is therefore incorrect. It follows that, where pre-fire water repellency levels are not known or highly variable, post-fire soil water repellency conditions are an unreliable indicator in classifying soil burn severity. The terrain and soil variables examined showed, overall, no convincing relationship with the repellency levels observed (R2 < 0.15) except that repellency was limited in soils (i) developed over meta-sedimen- tary lithology and (ii) with clay contents >4%. This suggests that water repellency levels cannot be pre- dicted with confidence from common terrain or soil variables. This work is presented in the memory of the late Scott Woods, who was instrumental in the success of this study and an inspiration to us all.

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

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.

Experimental research on recolonisation with Anemone nemorosa of the beech forests of the Ruhr district (Germany) floristically impoverished by air pollution.

PubMed

Wittig, Rüdiger

2008-09-01

High SO(2) concentrations as have been observed over decades in the Ruhr district lead to a remarkable reduction of leaf area in the majority of the characteristic broad-leafed herbs of the Central European beech forests even after only a few months of experimental fumigation. Thus, it is no wonder in the time of high SO(2) pollution, e.g., in the town of Herne (centre of the Ruhr district), that there was not a single beech forest hosting, for instance, Viola reichenbachiana or Anemone nemorosa. As air quality has improved very much over some decades in the Ruhr district, one can expect a recolonisation of the beech forests by the species of former time characteristic for the herb layer. However, one has to consider that only the air pollution was reduced, while soil acidification and contamination with heavy metals and PAH are, on the short run, irreversible. That is why experiments were carried out, considering the question as to whether recolonisation of the forests of the Ruhr district by the aforementioned species is possible and why such a recolonisation up to now has not occurred. The experiments were carried out in a beech forest situated in the centre of the Ruhr district in the City of Herne. The wood anemone (A. nemorosa) was chosen as test plant because of its high frequency in beech forests on loess soils outside the Ruhr district, and its absence in beech forests in the Ruhr district. The experiments with A. nemorosa were carried out in three variants with different soils: (a): soil of the local forests (R); (b): soil of the local forests whose soot layer was removed (r); (c): imported soil from a clean air region far away from the Ruhr district (Odenwald). Survival of rhizomes of A. nemorosa is possible for some years in the soils of the Ruhr district; however, the establishment of a population could not be achieved. The results obtained by the imported soil show that it is no longer air pollution, but the soil which prevents the establishment of a population. Sexual reproduction is rather impossible because of the thick litter layer with which all of the Ruhr district's beech forests are covered. With respect to the unfavourable chemistry of the soil of the Ruhr district and in consideration of the unfavourable attributes of the soot layer, the author expected the following order of the development of shoot numbers: O > r > R. However, the result is: O > R > r. In contrast to the expected result, the soot layer has no negative but slightly positive effects on the implanted rhizomes. A possible explanation is that the soot layer, which is situated immediately below the top soil, prevents the top soil from drying up and thus even protects the rhizomes from desiccation. Also, the possibility has to be considered that the soot layer functions as a nutrient storage area. At present, a survival of the rhizomes of A. nemorosa in the soils of the Ruhr district is temporarily possible but does not lead to the establishment of a permanent population. This only can be achieved by additional sexual reproduction. However, the thick litter layer present in all beech forests of the Ruhr district prevents the establishment of seedlings, i.e., it does not allow sexual reproduction to contribute to the population. The soot layer situated below the litter layer represents a second hindrance for germination. Other than seedlings, rhizomes are not negatively affected by the soot layer but even a slight stabilisation has to be stated. As a reason for this slightly positive effect, a protection of the upper mineral soil from desiccation by the hydrophob soot layer has to be considered. Secondly, the soot layer may serve as a nutrient storage which is of particular importance in acid soils, because acidification generally leads to a leeching of nutrients. To answer these questions, detailed further research is necessary. In order to restore the formerly rich herbaceous layer of the forests of the Ruhr district, experiments (removal of the litter layer; liming; ploughing) should be carried out at broad-scale to solve the question of how the strong negative effects of the established thick raw humus layer can be reduced or even be avoided. When the problem of the humus layer is solved, the beech forests of the Ruhr district today highly impoverished in species will become a vivid ecosystem, rich in flowering herbaceous species and thus much more attractive for the people of the Ruhr district than at present.

The Effects of Light Intensity, Casing Layers, and Layering Styles on Royal Sun Medicinal Mushroom, Agaricus brasiliensis (Higher Basidiomycetes) Cultivation in Turkey.

PubMed

Adanacioglu, Neşe; Boztok, Kaya; Akdeniz, Ramazan Cengiz

2015-01-01

The aim of this research is to evaluate the effects of light intensity, casing layers, and layering styles on the production of the culinary-medicinal mushroom Agaricus brasiliensis in Turkey. The experiments were designed in split-split plots and replicated twice. Three different light intensities-I1, 350 lux; I2, 450 lux; and I3, 750 lux-were used in main plots as environmental factors. A mixture of 4 different casing layers- peat (100%), peat-perlite (75%:25%), peat-clinoptilolite (75%:25%), and peat-perlite-clinoptilolite (60%:20%:20%)-were used at split plots and at split plots. S1, a flat, 3-cm casing layer; S2, a flat, 5-cm casing layer; and S3, casing soil ridges 10 cm wide × 4 cm high, 10 cm apart, were deposited on top of 1-cm overall soil casing layers. At the end of the harvest phase, the total yield was estimated per 100 kg of substrate. Biological efficiency (percentage) was determined from the fresh weight of the mushrooms and the dry weight of the compost at the end of the harvesting period. The highest total yield (7.2 kg/100 kg compost) and biological efficiency (27.63%) were achieved from I2 × peat-perlite-clinoptilolite × S2 treatment. Influence of light intensity, casing layer, layering style, and their interaction in treatments with color values (L*, a*, b*, chroma*, and hue*) also were examined. It has been shown that within color values, chroma* (saturation) values of mushroom caps were affected by light intensity, casing layer, and layering style treatments and light intensity × casing layer treatments and the brightness of mushroom caps tended to increase as light intensity increased.

Americium-241 in surface soil associated with the Hanford site and vicinity

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

Price, K.R.; Gilbert, R.O.; Gano, K.A.

1981-05-01

Various kinds of surface soil samples were collected and analyzed for Americium-241 (/sup 241/Am) to examine the feasibility of improving soil sample data for the Hanford Surface Environmental Surveillance Program. Results do not indicate that a major improvement would occur if procedures were changed from the current practices. Conclusions from this study are somewhat tempered by the very low levels of /sup 241/Am (< 0.10 pCi/g dry weight) detected in surface soil samples and by the fact that statistical significance depended on the type of statistical tests used. In general, the average concentration of /sup 241/Am in soil crust (0more » to 1.0 cm deep) was greater than the corresponding subsurface layer (1.0 to 2.5 cm deep), and the average concentration of /sup 241/Am in some onsite samples collected near the PUREX facility was greater than comparable samples collected 60 km upwind at an offsite location.« less

Formation of Soil Water Repellency by Laboratory Burning and Its Effect on Soil Evaporation

NASA Astrophysics Data System (ADS)

Ahn, Sujung; Im, Sangjun

2010-05-01

Fire-induced soil water repellency can vary with burning conditions, and may lead to significant changes in soil hydraulic properties. However, isolation of the effects of soil water repellency from other factors is difficult, particularly under field conditions. This study was conducted to (i) investigate the effects of burning using different plant leaf materials and (ii) of different burning conditions on the formation of soil water repellency, and (iii) isolate the effects of the resulting soil water repellency on soil evaporation from other factors. Burning treatments were performed on the surface of homogeneous fully wettable sand soil contained in a steel frame (60 x 60 cm; 40 cm depth). As controls a sample without a heat treatment, and a heated sample without fuel, were also used. Ignition and heat treatments were carried out with a gas torch. For comparing the effects of different burning conditions, fuel types included oven-dried pine needles (fresh needles of Pinus densiflora), pine needle litter (litter on a coniferous forest floor, P. densiflora + P. rigida), and broad-leaf litter (Quercus mongolica + Q. aliena + Prunus serrulata var. spontanea + other species); fuel loads were 200 g, 300 g, and 500 g; and heating duration was 40 s, 90 s and 180 s. The heating duration was adjusted to control the temperature, based on previous experiments. The temperature was measured continuously at 3-second intervals and logged with two thermometers. After burning, undisturbed soil columns were sampled for subsequent experiments. Water Drop Penetration Time (WDPT) test was performed at every 1 mm depth of the soil columns to measure the severity of soil water repellency and its vertical extent. Soil water repellency was detected following all treatments. As the duration of heating increased, the thickness of the water repellent layer increased, whilst the severity of soil water repellency decreased. As regards fuel amount, the most severe soil water repellency was formed at a fuel load of 300 g. Pine needle litter formed the most severe soil water repellency and fresh pine needle formed the thickest water repellent layer, whilst broad-leaf litter did only cause water repellency on the surface of the sand. The soil evaporation rate was measured by a gravitational method at an isothermal condition. Undisturbed soil columns were sealed after adding 50 ml of tap water through the bottom. After twelve hours of stabilization, the columns were opened and covered with filter paper. The rate of soil evaporation through the soil surface was measured by the hourly weight change at 45° C. The initial 65 hours' evaporation rate was analyzed, while the slope of cumulative evaporation over time maintained its linearity. It was found that as the thickness of the water repellent layer increased, the evaporation rate tended to decrease. These two variables showed a good correlation (Pearson's correlation coefficient =-0.8916, p=0.0170) and a large coefficient of determination (R2=0.795) in the linear regression. This suggests that a layer of water repellent soil can affect water evaporation rate and that the rate is negatively correlated with the thickness of the repellent layer.

A comparison of bacterial and fungal biomass in several cultivated soils.

PubMed

Kaczmarek, W

1984-01-01

Bacterial and fungal biomass was estimated in incubated samples of three cultivated soils, the influence of glucose, ammonium nitrate and cattle slurry on its formation being studied. The microbial biomass was determined in stained microscopic preparations of soil suspension. Bacterial biomass in the control samples was from 0.17 to 0.66 mg dry wt per 1 g dry soil and independently of the applied supplements was on the average two times larger in muck soils than in sand. Fungal biomass in the control soils ranged from 0.013 to 0.161 mg dry wt per 1 g dry soil, no relationship being found between its size and the soil type. As a result, the ratio of the size of fungal to bacterial biomass was dependent on the soil type; in sand the fungal biomass corresponded to 1/3 of the bacterial biomass, and in muck soils--only to 1/7.

Dermally adhered soil: 2. Reconstruction of dry-sieve particle-size distributions from wet-sieve data.

PubMed

Choate, LaDonna M; Ranville, James F; Bunge, Annette L; Macalady, Donald L

2006-10-01

In the evaluation of soil particle-size effects on environmental processes, particle-size distributions are measured by either wet or dry sieving. Commonly, size distributions determined by wet and dry sieving differ because some particles disaggregate in water. Whereas the dry-sieve distributions are most relevant to the study of soil adherence to skin, soil can be recovered from skin only by washing with the potential for disaggregation whether or not it is subsequently wet or dry sieved. Thus, the possibility exists that wet-sieving measurements of the particle sizes that adhered to the skin could be skewed toward the smaller fractions. This paper provides a method by which dry-sieve particle-size distributions can be reconstructed from wet-sieve particle-size distributions for the same soil. The approach combines mass balances with a series of experiments in which wet sieving was applied to dry-sieve fractions from the original soil. Unless the soil moisture content is high (i.e., greater than or equal to the water content after equilibration with water-saturated air), only the soil particles of diameters less than about 63 microm adhere to the skin. Because of this, the adhering particle-size distribution calculated using the reconstruction method was not significantly different from the wet-sieving determinations.

Quantification of rock slope terrain properties

NASA Astrophysics Data System (ADS)

Volkwein, Axel; Gerber, Werner

2017-04-01

Rockfall trajectory simulation codes need information on the terrain properties to formulate appropriate rebound models. Usually, the manuals of rockfall simulation codes give sketches or photographs of terrain samples [1,2]. Based on these the user can select suitable terrains for the simulation area. We now would like to start a discussion whether it is possible to numerically quantify the terrain properties which would make the ground assignment more objective. Different ground properties play a role for the interaction between a falling rock and the ground: • Elastic deformation • plastic deformation • Energy absorption • friction • hardness • roughness • surface vs. underground • etc. The question is now whether it is possible to quantify above parameters and to finally provide tables that contain appropriate simulation parameters. In a first attempt we suggest different methods or parameters that might be evaluated in situ: • Small scale drop tests • Light weight deflectometer (LWD) • Particle sizes • Sliding angle • Particle distribution • Soil cover • Water content Of course, above measurements will never perfectly fit to different mountain slopes. However, if a number of measurements has been made their spreading will give an idea on the natural variability of the ground properties. As an example, the following table gives an idea on how the ME and Evd values vary for different soils. Table 1: LWD measurements on different soil types [3] Ground type Soil layer Soil humidityEvd (median)σ (median)Evd (average) Humus-carb. < 10cm dry 17.4 6.8 15.6 Regosol 10 - 30cm dry 8.6 3.9 9.4 Brownish 30 - 50cm dry 12.1 3.2 11.7 Calcaric 30 - 50cm dry 7.5 3.3 7.0 Acid brownish70 - 100cmdry 7.8 2.1 7.7 Fahlgley 10 - 30cm dry 9.2 4.0 7.7 References [1] Bartelt P et al (2016) RAMMS::rockfall user manual v1.6. SLF, Davos. [2] Dorren L.K.A., 2015. Rockyfor3D (v5.2) revealed - Transparent description of the complete 3D rockfall model. ecorisQ paper (www.ecorisq.org): 32 p. [3] Hoffmann P. (2015) Härte von Böden. Bsc thesis, ZHAW Waedenswil.

The Past as a Window to the Future - What Does Long Term Research in the McMurdo Dry Valleys, Antarctica Tell Us About the Trajectory of Polar Ecosystems?

NASA Astrophysics Data System (ADS)

Gooseff, M. N.; Adams, B.; Barrett, J. E.; Doran, P. T.; Fountain, A. G.; Lyons, W. B.; McKnight, D. M.; Takacs-Vesbach, C. D.; Priscu, J. C.; Sokol, E.; Virginia, R. A.; Wall, D. H.

2015-12-01

The McMurdo Dry Valleys of Antarctica represent the largest ice-free area of the continent. The landscape is dominated by glaciers, exposed soils, streams, and ice-covered lakes, and hosts an incredible ecosystem that is largely driven by microbes and some invertebrates. Given the low air temperatures (-18C annual mean), little precipitation (<10 cm water equivalent/yr), and lack of vegetation cover, the Dry Valleys ecosystem is strongly influenced by physical processes. In the past two decades, summer conditions have been observed to fluctuate significantly. From 1986-2001, the area experienced a cooling trend and the ecosystem responded with decreasing soil invertebrate populations, decreased streamflow, decreased primary productivity in lakes, and decreased algal biomass in streams. Since 2001, 3 very high glacial melt years have occurred producing record stream flows and extensive wetted soils. During this most recent decade, the levels of closed-basin lakes have risen substantially, with increasing heat contents, and we have observed increased permafrost degradation along streambanks. Here we assess the ecosystem responses of the cooling 'press' that occurred from 1986-2001 and the more most recent decade that has had several strong pulses of energy driving the system to develop expectations for the future state and function of this polar desert ecosystem. We propose that the future trajectory of climate and energy input to the region will likely be more inconsistent than the cooling period was. Hence, the ecosystem will be consistently responding to pulses of change over varying time periods. We also expect that recovery of the ozone layer over Antarctica may play an important role in modifying both regional climate and the Dry Valleys ecosystem.

Short-term soil loss by eolian erosion in response to different rain-fed agricultural practices

NASA Astrophysics Data System (ADS)

Tanner, Smadar; Katra, Itzhak; Zaady, Eli

2016-04-01

Eolian (wind) erosion is a widespread process and a major form of soil degradation in arid and semi-arid regions. The present study examined changes in soil properties and eolian soil loss at a field scale in response to different soil treatments in two rain-fed agricultural practices. Field experiments with a boundary-layer wind tunnel and soil analysis were used to obtain the data. Two practices with different soil treatments (after harvest), mechanical tillage and stubble grazing intensities, were applied in the fallow phase of the rotation (dry season). The mechanical tillage and the stubble grazing had an immediate and direct effects on soil aggregation but not on the soil texture, and the contents of soil water, organic matter, and CaCO3. Higher erosion rates, that was measured as fluxes of total eolian sediment and particulate matter <10 μm (PM10), were recorded under mechanical tillage and grazing intensities compared with the undisturbed topsoil of the control plots. The erosion rates were higher in grazing plots than in tillage plots. The calculated soil fluxes in this study indicate potentially rapid soil degradation due to loss of fine particles by wind. The finding may have implications for long-term management of agricultural soils in semi-arid areas.

Study of the effect of soil disturbance on vapor transport through integrated modeling of the atmospheric boundary layer and shallow subsurface

NASA Astrophysics Data System (ADS)

Trautz, A.; Smits, K. M.; Cihan, A.; Wallen, B.

2014-12-01

Soil-water evaporation is one of the governing processes responsible for controlling water and energy exchanges between the land and atmosphere. Despite its wide relevance and application in many natural and manmade environments (e.g. soil tillage practices, wheel-track compaction, fire burn environments, textural layering and buried ordinances), there are very few studies of evaporation from disturbed soil profiles. The purpose of this study was to explore the effect of soil disturbance and capillary coupling on water distribution and fluxes. We modified a theory previously developed by the authors that allows for coupling single-phase (gas), two-component (air and water vapor) transfer in the atmosphere and two-phase (gas, liquid), two-component (air and water vapor) flow in porous media at the REV scale under non-isothermal, non-equilibrium conditions to better account for the hydraulic and thermal interactions within the media. Modeling results were validated and compared using precision data generated in a two-dimensional soil tank consisting of a loosely packed soil surrounded by a tightly packed soil. The soil tank was outfitted with an array of sensors for the measurement of wind velocity, soil and air temperature, relative humidity, soil moisture, and weight. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process in heterogeneous soils with good accuracy. Evaporation from a heterogeneous soil consisting of a loose and tight packing condition is larger than the homogeneous equivalent systems. Liquid water is supplied from the loosely packed soil region to the tightly packed soil regions, sustaining a longer Stage I evaporation in the tightly packed regions with overall greater evaporation rate than uniform homogeneous packing. In contrast, lower evaporation rates from the loosely packed regions are observed due to a limited liquid water supply resulting from capillary flow to the tightly packed regions and a shorter stage 1 evaporation period.

A meteorologically-driven yield reduction model for spring and winter wheat

NASA Technical Reports Server (NTRS)

Ravet, F. W.; Cremins, W. J.; Taylor, T. W.; Ashburn, P.; Smika, D.; Aaronson, A. (Principal Investigator)

1983-01-01

A yield reduction model for spring and winter wheat was developed for large-area crop condition assessment. Reductions are expressed in percentage from a base yield and are calculated on a daily basis. The algorithm contains two integral components: a two-layer soil water budget model and a crop calendar routine. Yield reductions associated with hot, dry winds (Sukhovey) and soil moisture stress are determined. Input variables include evapotranspiration, maximum temperature and precipitation; subsequently crop-stage, available water holding percentage and stress duration are evaluated. No specific base yield is required and may be selected by the user; however, it may be generally characterized as the maximum likely to be produced commercially at a location.

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.

Atmospheric Boundary Layer of a pasture site in Amazônia

NASA Astrophysics Data System (ADS)

Trindade de Araújo Tiburtino Neves, Theomar; Fisch, Gilberto; Raasch, Siegfried

2013-04-01

A great effort has been made by the community of micrometeorology and planetary boundary layer for a better description of the properties of the Atmospheric Boundary Layer (ABL), such as its height, thermodynamics characteristics and its time evolution. This work aims to give a review of the main characteristics of Atmospheric Boundary Layer over a pasture site in Amazonia. The measurements dataset was carried out from 3 different LBA field campaigns: RBLE 3 (during the dry season from 1993), RaCCI (during the dry-to-wet transition season from 2002) and WetAMC (during the wet season from 1999), collected with tethered balloon, radiosondes and eddy correlation method in a pasture site in the southwestern Amazonia. Different techniques and instruments were used to estimate the ABĹs properties. During the daytime, it was possible to observe that there is an abrupt growth of the Convective Boundary Layer (CBL) between 08 and 11 LT, with a stationary pattern between 14 and 17 LT. The maximum heights at late afternoon were around 1600 m during the dry season, whilst the wet season it only reached 1000 m. This is due to the lower surface turbulent sensible heat flux as the soil is wetter and the partition of energy is completely different between wet to the dry season. For the transition period (RaCCI 2002), it was possible to analyze and compare several estimates from different instruments and methods. It showed that the parcel method overestimates the heights of all measurements (mainly at 14 LT) due to the high incidence of solar radiation and superadiabatic gradients. The profile and Richardson number methods gave results very similar to estimate the height of the CBL. The onset of the Nocturnal Boundary Layer (NBL) occurs before the sunset (18 LT) and its height is reasonable stable during the night (typical values around 180-250 m). An alternative method (Vmax) which used the height of the maximum windspeed derived from a SODAR instrument during RaCCI 2002 was proposed and it showed to be satisfactory comparing with the others methods. Besides that, it has the advantage to have measurements each 30 min.

The influence of vertical sorbed phase transport on the fate of organic chemicals in surface soils.

PubMed

McLachlan, Michael S; Czub, Gertje; Wania, Frank

2002-11-15

Gaseous exchange between surface soil and the atmosphere is an important process in the environmental fate of many chemicals. It was hypothesized that this process is influenced by vertical transport of chemicals sorbed to soil particles. Vertical sorbed phase transport in surface soils occurs by many processes such as bioturbation, cryoturbation, and erosion into cracks formed by soil drying. The solution of the advection/diffusion equation proposed by Jury et al. to describe organic chemical fate in a uniformly contaminated surface soil was modified to include vertical sorbed phase transport This process was modeled using a sorbed phase diffusion coefficient, the value of which was derived from soil carbon mass balances in the literature. The effective diffusivity of the chemical in a typical soil was greater in the modified model than in the model without sorbed phase transport for compounds with log K(OW) > 2 and log K(OA) > 6. Within this chemical partitioning space, the rate of volatilization from the surface soil was larger in the modified model than in the original model by up to a factor of 65. The volatilization rate was insensitive to the value of the sorbed phase diffusion coefficient throughout much of this chemical partitioning space, indicating that the surface soil layer was essentially well-mixed and that the mass transfer coefficient was determined by diffusion through the atmospheric boundary layer only. When this process was included in a non-steady-state regional multimedia chemical fate model running with a generic emissions scenario to air, the predicted soil concentrations increased by upto a factor of 25,whilethe air concentrations decreased by as much as a factor of approximately 3. Vertical sorbed phase transport in the soil thus has a major impact on predicted air and soil concentrations, the state of equilibrium, and the direction and magnitude of the chemical flux between air and soil. It is a key process influencing the environmental fate of persistent organic pollutants (POPs).

Evaporation from soils subjected to natural boundary conditions at the land-atmospheric interface

NASA Astrophysics Data System (ADS)

Smits, K.; Illngasekare, T.; Ngo, V.; Cihan, A.

2012-04-01

Bare soil evaporation is a key process for water exchange between the land and the atmosphere and an important component of the water balance in semiarid and arid regions. However, there is no agreement on the best methodology to determine evaporation under different boundary conditions at the land surface. This becomes critical in developing models that couples land to the atmosphere. Because it is difficult to measure evaporation from soil, with the exception of using lysimeters, numerous formulations have been proposed to establish a relationship between the rate of evaporation and soil moisture and/or soil temperature and thermal properties. Different formulations vary in how they partition available energy. A need exists to systematically compare existing methods to experimental data under highly controlled conditions not achievable in the field. The goal of this work is to perform controlled experiments under transient conditions of soil moisture, temperature and wind at the land/atmospheric interface to test different conceptual and mathematical formulations for the soil surface boundary conditions to develop appropriate numerical models to be used in simulations. In this study, to better understand the coupled water-vapor-heat flow processes in the shallow subsurface near the land surface, we modified a previously developed theory by Smits et al. [2011] that allows non-equilibrium liquid/gas phase change with gas phase vapor diffusion to better account for dry soil conditions. The model did not implement fitting parameters such as a vapor enhancement factor that is commonly introduced into the vapor diffusion coefficient as an arbitrary multiplication factor. In order to experimentally test the numerical formulations/code, we performed a two-dimensional physical model experiment under varying boundary conditions using test sand for which the hydraulic and thermal properties were well characterized. Precision data under well-controlled transient heat and wind boundary conditions was generated and results from numerical simulations were compared with experimental data. Results demonstrate that the boundary condition approaches varied in their ability to capture stage 1- and stage 2- evaporation. Results also demonstrated the importance of properly characterizing soil thermal properties and accounting for dry soil conditions. The contribution of film flow to hydraulic conductivity for the layer above the drying front is dominant compared to that of capillary flow, demonstrating the importance of including film flow in modeling efforts for dry soils, especially for fine grained soils. Comparisons of different formulations of the surface boundary condition validate the need for joint evaluation of heat and mass transfer for better modeling accuracy. This knowledge is applicable to many current hydrologic and environmental problems to include climate modeling and the simulation of contaminant transport and volatilization in the shallow subsurface. Smits, K. M., A. Cihan, T. Sakaki, and T. H. Illangasekare (2011). Evaporation from soils under thermal boundary conditions: Experimental and modeling investigation to compare equilibrium- and nonequilibrium-based approaches, Water Resour. Res., 47, W05540, doi:10.1029/2010WR009533.

The Nitrate Inventory of Unsaturated Soils at the Barrow Environmental Observatory: Current Conditions and Potential Future Trajectories

NASA Astrophysics Data System (ADS)

Heikoop, J. M.; Newman, B. D.; Arendt, C. A.; Andresen, C. G.; Lara, M. J.; Wainwright, H. M.; Throckmorton, H.; Graham, D. E.; Wilson, C. J.; Wullschleger, S. D.; Romanovsky, V. E.; Bolton, W. R.; Wales, N. A.; Rowland, J. C.

2016-12-01

Studies conducted in the Barrow Environmental Observatory under the auspices of the United States Department of Energy Next Generation Ecosystem Experiment (NGEE) - Arctic have demonstrated measurable nitrate concentrations ranging from <1 to 17 mg/L in the unsaturated centers of high-centered polygons. Conversely, nitrate concentrations in saturated areas of polygonal terrain were generally below the limit of detection. Isotopic analysis of this nitrate demonstrates that it results from microbial nitrification. The study site currently comprises mostly saturated soils. Several factors, however, could lead to drying of soils on different time scales. These include 1) topographic inversion of polygonal terrain associated with ice-wedge degradation, 2) increased connectivity and drainage of polygon troughs, similarly related to the thawing and subsidence of ice-wedges, and 3) near-surface soil drainage associated with wide-spread permafrost thaw and active layer deepening. Using a GIS approach we will estimate the current inventory of nitrate in the NGEE intensive study site using soil moisture data and existing unsaturated zone nitrate concentration data and new concentration data collected in the summer of 2016 from high- and flat-centered polygons and the elevated rims of low-centered polygons. Using this baseline, we will present potential future inventories based on various scenarios of active layer thickening and landscape geomorphic reorganization associated with permafrost thaw. Predicted inventories will be based solely on active layer moisture changes, ignoring for now potential changes associated with mineralization and nitrification of previously frozen old organic matter and changes in vegetation communities. We wish to demonstrate that physical landscape changes alone could have a profound effect on future nitrate availability. Nitrate data from recent NGEE campaigns in the Seward Peninsula of Alaska will also be presented.

Polycyclic aromatic hydrocarbons in mountain soils of the subtropical Atlantic.

PubMed

Ribes, A; Grimalt, J O; Torres García, C J; Cuevas, E

2003-01-01

Surface soil samples from various altitudes on Tenerife Island, ranging from sea level up to 3400 m above mean sea level, were analyzed to study the distribution of 26 polycyclic aromatic hydrocarbons (PAHs) in a remote subtropical area. The stable atmospheric conditions in this island define three vertically stratified layers: marine boundary, trade-wind inversion, and free troposphere. Total PAH concentrations, 1.9 to 6000 microg/kg dry wt., were high when compared with those in tropical areas and in a similar range to those in temperate areas. In the marine boundary layer, fluoranthene (Fla), pyrene (Pyr), benz [a]anthracene (BaA), and chrysene (C + T) were largely dominant. The predominance of Fla over Pyr may reflect photo-oxidative processes during atmospheric transport, although coal combustion inputs cannot be excluded. The PAHs found in higher concentration in the soils from the inversion layer were benzo[b + j]fluoranthene (BbjF) + benzo[k]fluoranthene (BkF) > benzo[e]pyrene (BeP) approximately indeno[1,2, 3-cd]pyrene (Ind) > benzo[a]pyrene (BaP) approximately benzo[ghi]perylene (Bghi) > coronene (Cor) approximately dibenz[a,h]anthracene (Dib), reflecting that high temperatures and insolation prevent the accumulation of PAHs more volatile than BbjF in significant amounts. These climatic conditions involve a process of standardization that prevents the identification of specific PAH sources such as traffic, forest fires, or industrial inputs. Only soils with high total organic carbon (TOC) (e.g., 10-30%) preserve the more volatile compounds such as phenanthrene (Phe), methylphenanthrenes (MPhe), dimethylphenanthrenes (DMPhe), and retene (Ret). However, no relation between PAHs and soil TOC and black carbon (BC) was found. The specific PAH distributions of the free tropospheric region suggest a direct input from pyrolytic processes related to the volcanic emission of gases in Teide.

Leaching of mercury from seal carcasses into Antarctic soils.

PubMed

Zvěřina, Ondřej; Coufalík, Pavel; Brat, Kristián; Červenka, Rostislav; Kuta, Jan; Mikeš, Ondřej; Komárek, Josef

2017-01-01

More than 400 seal mummies and skeletons are now mapped in the northern part of James Ross Island, Antarctica. Decomposing carcasses represent a rare source of both organic matter and associated elements for the soil. Owing to their high trophic position, seals are known to carry a significant mercury body burden. This work focuses on the extent of the mercury input from seal carcasses and shows that such carcasses represent locally significant sources of mercury and methylmercury for the environment. Mercury contents in soil samples from the surrounding areas were determined using a single-purpose AAS mercury analyzer. For the determination of methylmercury, an ultra-sensitive isotopic dilution HPLC-ICP-MS technique was used. In the soils lying directly under seal carcasses, mercury contents were higher, with levels reaching almost 40 μg/kg dry weight of which methylmercury formed up to 2.8 % of the total. The spatial distribution implies rather slow vertical transport to the lower soil layers instead of a horizontal spread. For comparison, the background level of mercury in soils of the investigated area was found to be 8 μg/kg dry weight, with methylmercury accounting for less than 0.1 %. Apart from the direct mercury input, an enhanced level of nutrients in the vicinity of carcasses enables the growth of lichens and mosses with accumulative ability with respect to metals. The enhanced capacity of soil to retain mercury is also anticipated due to the high content of total organic carbon (from 1.6 to 7.5 %). According to the results, seal remains represent a clear source of mercury in the observed area.

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.

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.

Growth and transpiration of Japanese cedar (Cryptomeria japonica) and Hinoki cypress (Chamaecyparis obtusa) seedlings in response to soil water content.

PubMed

Nagakura, Junko; Shigenaga, Hidetoshi; Akama, Akio; Takahashi, Masamichi

2004-11-01

To investigate the effects of soil water content on growth and transpiration of Japanese cedar (Cryptomeria japonica D. Don) and Hinoki cypress (Chamaecyparis obtusa (Siebold et Zucc.) Endl.), potted seedlings were grown in well-watered soil (wet treatment) or in drying soil (dry treatment) for 12 weeks. Seedlings in the wet treatment were watered once every 2 or 3 days, whereas seedlings in the dry treatment were watered when soil water content (Theta; m3 m(-3)) reached 0.30, equivalent to a soil matric potential of -0.06 MPa. From Weeks 7 to 12 after the onset of the treatments, seedling transpiration was measured by weighing the potted seedlings. After the last watering, changes in transpiration rate during soil drying were monitored intensely. The dry treatment restricted aboveground growth but increased biomass allocation to the roots in both species, resulting in no significant treatment difference in whole-plant biomass production. The species showed similar responses in relative growth rate (RGR), net assimilation rate (NAR) and shoot mass ratio (SMR) to the dry treatment. Although NAR did not change significantly in either C. japonica or C. obtusa as the soil dried, the two species responded differently to the dry treatment in terms of mean transpiration rate (E) and water-use efficiency (WUE), which are parameters that relate to NAR. In the dry treatment, both E and WUE of C. japonica were stable, whereas in C. obtusa, E decreased and WUE increased (E and WUE counterbalanced to maintain a constant NAR). Transpiration rates were lower in C. obtusa seedlings than in C. japonica seedlings, even in well-watered conditions. During soil drying, the transpiration rate decreased after Theta reached about 0.38 (-0.003 MPa) in C. obtusa and 0.32 (-0.028 MPa) in C. japonica. We conclude that C. obtusa has more water-saving characteristics than C. japonica, particularly when water supply is limited.

Advances in spectroscopic methods for quantifying soil carbon

USGS Publications Warehouse

Reeves, James B.; McCarty, Gregory W.; Calderon, Francisco; Hively, W. Dean

2012-01-01

The current gold standard for soil carbon (C) determination is elemental C analysis using dry combustion. However, this method requires expensive consumables, is limited by the number of samples that can be processed (~100/d), and is restricted to the determination of total carbon. With increased interest in soil C sequestration, faster methods of analysis are needed, and there is growing interest in methods based on diffuse reflectance spectroscopy in the visible, near-infrared or mid-infrared spectral ranges. These spectral methods can decrease analytical requirements and speed sample processing, be applied to large landscape areas using remote sensing imagery, and be used to predict multiple analytes simultaneously. However, the methods require localized calibrations to establish the relationship between spectral data and reference analytical data, and also have additional, specific problems. For example, remote sensing is capable of scanning entire watersheds for soil carbon content but is limited to the surface layer of tilled soils and may require difficult and extensive field sampling to obtain proper localized calibration reference values. The objective of this chapter is to discuss the present state of spectroscopic methods for determination of soil carbon.

Studies on mycorrhizal inoculation on dry matter yield and root colonization of some medicinal plants grown in stress and forest soils.

PubMed

Chandra, K K; Kumar, Neeraj; Chand, Gireesh

2010-11-01

Five medicinal plants viz. Abelmoschatus moschatus Linn., Clitoria tematea L., Plumbagozeylanica L., Psorolea corylifolia L. and Withania sominifera L. were grown in a polypot experiment in five soils representing coal mine soil, coppermine soil, fly ash, skeletal soil and forest soil with and without mycorrhizal inoculations in a completely randomized block design. Dry matter yield and mycorrhizal root colonization of plants varied both in uninoculated and inoculated conditions. The forest soil rendered highest dry matter due to higher yield of A. moschatus, P. zeylanica and P corylifolia while fly ash showed lowest dry matter without any inoculants. P. cematea were best in coalmine soil and W. sominifera in copper mine soil without mycorrhizal inoculation. The mycorrhiza was found to enhance the dry matter yield. This contributed minimum 0.19% to maximum up to 422.0% in different soils as compared to uninoculated plants. The mycorrhizal dependency was noticed maximum in plants grown in fly ash followed by coal mine soil, copper mine soil, skeletal soil and forest soil. The mycorrhizal response was increased maximum in W. sominifera due to survival in fly ash after inoculation followed by P corylifolia and P cematea. Percent root colonization in inoculated plant was increased minimum of 1.10 fold to maximum of 12.0 folds in comparison to un-inoculated plants . The native mycorrhiza fungi were also observed to colonize 4.0 to 32.0% roots in plants understudy. This study suggests that mycorrhizal inoculation increased the dry matter yield of medicinal plants in all soils under study. It also helps in survival of W. sominifera in fly ash.

Associations between soil variables and vegetation structure and composition of Caribbean dry forests

Treesearch

Elvia M. Melendez-Ackerman; Julissa Rojas-Sandoval; Danny S. Fernandez; Grizelle Gonzalez; Hana Lopez; Jose Sustache; Mariely Morales; Miguel Garcia-Bermudez; Susan Aragon

2016-01-01

Soil–vegetation associations have been understudied in tropical dry forests when compared to the amount of extant research on this issue in tropical wet forests. Recent studies assert that vegetation in tropical dry forests is highly heterogeneous and that soil variability may be a contributing factor. In this study, we evaluated the relationship between soil variables...

[Restoration of microbial ammonia oxidizers in air-dried forest soils upon wetting].

PubMed

Zhou, Xue; Huang, Rong; Song, Ge; Pan, Xianzhang; Jia, Zhongjun

2014-11-04

This study was aimed to investigate the abundance and community shift of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in air-dried forest soils in response to water addition, to explore the applicability of air-dried soil for microbial ecology study, and to elucidate whether AOA within the marine group 1. 1a dominate ammonia oxidizers communities in the acidic forest soils in China. Soil samples were collected from 10 forest sites of the China Ecosystem Research Network (CERN) and kept under air-drying conditions in 2010. In 2013 the air-dried soil samples were adjusted to 60% of soil maximum water holding capacity for a 28-day incubation at 28 degrees C in darkness. DGGE fingerprinting, clone library construction, pyrosequencing and quantitative PCR of amoA genes were performed to assess community change of ammonia oxidizers in air-dried and re-wetted soils. After incubation for 28 days, the abundance of bacteria and archaea increased significantly, up to 3,230 and 568 times, respectively. AOA increased significantly in 8 samples, and AOB increased significantly in 5 of 10 samples. However, pyrosequencing of amoA genes reveals insignificant changes in composition of AOA and AOB communities. Phylogenetic analysis of amoA genes indicates that archaeal ammonia oxidizers were predominated by AOA within the soil group 1. 1b lineage, while the Nitrosospira-like AOB dominate bacteria ammonia oxidizer communities. There was a significantly positive correlation between AOA/AOB ratio and total nitrogen (r2 = 0.54, P < 0.05), implying that soil ammonia oxidation might be dominated by AOA in association with ammonium released from soil mineralization. Phylogenetic analysis suggest that AOA members within the soil group 1. 1b lineage were not restricted to non-acidic soils as previously thought. The abundance rather than composition of AOA and AOB changed in response to water addition. This indicates that air-dried soil could be of help for microbial biogeography study.

Method for collecting spores from a mold

DOEpatents

Au, Frederick H. F.; Beckert, Werner F.

1977-01-01

A technique and apparatus used therewith for determining the uptake of plutonium and other contaminants by soil microorganisms which, in turn, gives a measure of the plutonium and/or other contaminants available to the biosphere at that particular time. A measured quantity of uncontaminated spores of a selected mold is added to a moistened sample of the soil to be tested. The mixture is allowed to sit a predetermined number of days under specified temperature conditions. An agar layer is then applied to the top of the sample. After three or more days, when spores of the mold growing in the sample have formed, the spores are collected by a miniature vacuum collection apparatus operated under preselected vacuum conditions, which collect only the spores with essentially no contamination by mycelial fragments or culture medium. After collection, the fungal spores are dried and analyzed for the plutonium and/or other contaminants. The apparatus is also suitable for collection of pollen, small insects, dust and other small particles, material from thin-layer chromatography plates, etc.

System for sampling and monitoring microscopic organisms and substances

DOEpatents

Au, Frederick H. F.; Beckert, Werner F.

1976-01-01

A technique and apparatus used therewith for determining the uptake of plutonium and other contaminants by soil microorganisms which, in turn, gives a measure of the plutonium and/or other contaminants available to the biosphere at that particular time. A measured quantity of uncontaminated spores of a selected mold is added to a moistened sample of the soil to be tested. The mixture is allowed to sit a predetermined number of days under specified temperature conditions. An agar layer is then applied to the top of the sample. After three or more days, when spores of the mold growing in the sample have formed, the spores are collected by a miniature vacuum collection apparatus operated under preselected vacuum conditions, which collect only the spores with essentially no contamination by mycelial fragments or culture medium. After collection, the fungal spores are dried and analyzed for the plutonium and/or other contaminants. The apparatus is also suitable for collection of pollen, small insects, dust and other small particles, material from thin-layer chromatography plates, etc.

Effects of soil moisture on dust emission from 2011 to 2015 observed over the Horqin Sandy Land area, China

NASA Astrophysics Data System (ADS)

Ju, Tingting; Li, Xiaolan; Zhang, Hongsheng; Cai, Xuhui; Song, Yu

2018-06-01

Using the observational data of dust concentrations and meteorological parameters from 2011 to 2015, the effects of soil moisture and air humidity on dust emission were studied at long (monthly) and short (several days or hours) time scales over the Horqin Sandy Land area, Inner Mongolia of China. The results show that the monthly mean dust concentrations and dust fluxes within the near-surface layer had no obvious relationship with the monthly mean soil moisture content but had a slightly negative correlation with monthly mean air relative humidity from 2011 to 2015. The daily mean soil moisture exhibited a significantly negative correlation with the daily mean dust concentrations and dust fluxes, as soil moisture changed obviously. However, such negative correlation between soil moisture and dust emission disappeared on dust blowing days. Additionally, the effect of soil moisture on an important parameter for dust emission, the threshold friction velocity (u∗t), was investigated during several saltation-bombardment and/or aggregation-disintegration dust emission (SADE) events. Under dry soil conditions, the values of u∗t were not influenced by soil moisture content; however, when the soil moisture content was high, the values of u∗t increased with increasing soil moisture content.

Infrared measurements of pristine and disturbed soils 1. Spectral contrast differences between field and laboratory data

USGS Publications Warehouse

Johnson, J. R.; Lucey, P.G.; Horton, K.A.; Winter, E.M.

1998-01-01

Comparison of emissivity spectra (8-13 ??m) of pristine soils in the field with laboratory reflectance spectra of the same soils showed that laboratory spectra tend to have less spectral contrast than field spectra (see following article). We investigated this the phenomenon by measuring emission spectra of both undisturbed (in situ) and disturbed soils (prepared as if for transport to the laboratory). The disturbed soils had much less spectral contrast than the undisturbed soils in the reststrahlen region near 9 ??m. While the increased porosity of a disturbed soil can decrease spectral contrast due to multiple scattering, we hypothesize that the effect is dominantly the result of a difference in grain-size distribution of the optically active layer (i.e., fine particle coatings). This concept was proposed by Salisbury et al. (1994) to explain their observations that soils washed free of small particles adhering the larger grains exhibited greater spectral contrast than unwashed soils. Our laboratory reflectance spectra of wet- and dry-sieved soils returned from field sites also show greater spectral contrast for wet-sieved (washed) soils. We therefore propose that undisturbed soils in the field can be characterized as 'clean' soils (washed free of fine particles at the surface due to rain and wind action) and that disturbed soils represent 'dirty' soils (contaminated with fine particle coatings). The effect of packing soils in the field and laboratory also increases spectral contrast but not to the magnitude of that observed for undisturbed and wet-sieved soils. Since it is a common practice to use laboratory spectra of field samples to interpret spectra obtained remotely, we suggest that the influence of fine particle coatings on disturbed soils, if unrecognized, could influence interpretations of remote sensing data.Comparison of emissivity spectra (8-13 ??m) of pristine soils in the field with laboratory reflectance spectra of the same soils showed that laboratory spectra tend to have less spectral contrast than field spectra (see following article). We investigated this phenomenon by measuring emission spectra of both undisturbed (in situ) and disturbed soils (prepared as if for transport to the laboratory). The disturbed soils had much less spectral contrast than the undisturbed soils in the reststrahlen region near 9 ??m. While the increased porosity of a disturbed soil can decrease spectral contrast due to multiple scattering, we hypothesize that the effect is dominantly the result of a difference in grain-size distribution of the optically active layer (i.e., fine particle coatings). This concept was proposed by Salisbury et al. (1994) to explain their observations that soils washed free of small particles adhering to larger grains exhibited greater spectral contrast than unwashed soils. Our laboratory reflectance spectra of wet- and dry-sieved soils returned from field sites also show greater spectral contrast for wet-sieved (washed) soils. We therefore propose that undisturbed soils in the field can be characterized as `clean' soils (washed free of fine particles at the surface due to rain and wind action) and that disturbed soils represent `dirty' soils (contaminated with fine particle coatings). The effect of packing soils in the field and laboratory also increases spectral contrast but not to the magnitude of that observed for undisturbed and wet-sieved soils. Since it is a common practice to use laboratory spectra of field samples to interpret spectra obtained remotely, we suggest that the influence of fine particle coatings on disturbed soils, if unrecognized, could influence interpretations of remote sensing data.

On the formation of glide-snow avalanches

NASA Astrophysics Data System (ADS)

Mitterer, C.; Schweizer, J.

2012-12-01

On steep slopes the full snowpack can glide on the ground; tension cracks may open and eventually the slope may fail as a glide-snow avalanche. Due to their large mass they have considerable destructive potential. Glide-snow avalanches typically occur when the snow-soil interface is moist or wet so that basal friction is reduced. The occurrence, however, of glide cracks and their evolution to glide avalanches are still poorly understood. Consequently, glides are difficult to predict as (i) not all cracks develop into an avalanche, and (ii) for those that do, the time between crack opening and avalanche event might vary from hours to weeks - or on the other hand be so short that there is no warning at all by crack opening. To improve our understanding we monitored several slopes and related glide snow activity to meteorological data. In addition, we explored conditions that favor the formation of a thin wet basal snowpack layer with a physical-based model representing water and heat flux at the snow-soil interface. The statistical analyses revealed that glide-snow avalanche activity might be associated to an early season and a spring condition. While early season conditions tend to have warm and dry autumns followed by heavy snowfalls, spring conditions showed good agreement with increasing air temperature. The model indicates that energy (summer heat) stored in the ground might be sufficient to melt snow at the bottom of the snowpack. Due to capillary forces, water will rise for a few centimeters into the snowpack and thereby reduce friction at the interface. Alternatively, we demonstrate that also in the absence of melt water production at the bottom of the snowpack water may accumulate in the bottom layer due to an upward flux into the snowpack if a dry snowpack overlies a wet soil. The particular conditions that are obviously required at the snow-soil interface explain the strong winter-to-winter variations in snow gliding.

Towards an improved soil moisture retrieval for organic-rich soils from SMOS passive microwave L-band observations

NASA Astrophysics Data System (ADS)

Bircher, Simone; Richaume, Philippe; Mahmoodi, Ali; Mialon, Arnaud; Fernandez-Moran, Roberto; Wigneron, Jean-Pierre; Demontoux, François; Jonard, François; Weihermüller, Lutz; Andreasen, Mie; Rautiainen, Kimmo; Ikonen, Jaakko; Schwank, Mike; Drusch, Mattias; Kerr, Yann H.

2017-04-01

From the passive L-band microwave radiometer onboard the Soil Moisture and Ocean Salinity (SMOS) space mission global surface soil moisture data is retrieved every 2 - 3 days. Thus far, the empirical L-band Microwave Emission of the Biosphere (L-MEB) radiative transfer model applied in the SMOS soil moisture retrieval algorithm is exclusively calibrated over test sites in dry and temperate climate zones. Furthermore, the included dielectric mixing model relating soil moisture to relative permittivity accounts only for mineral soils. However, soil moisture monitoring over the higher Northern latitudes is crucial since these regions are especially sensitive to climate change. A considerable positive feedback is expected if thawing of these extremely organic soils supports carbon decomposition and release to the atmosphere. Due to differing structural characteristics and thus varying bound water fractions, the relative permittivity of organic material is lower than that of the most mineral soils at a given water content. This assumption was verified by means of L-band relative permittivity laboratory measurements of organic and mineral substrates from various sites in Denmark, Finland, Scotland and Siberia using a resonant cavity. Based on these data, a simple empirical dielectric model for organic soils was derived and implemented in the SMOS Soil Moisture Level 2 Prototype Processor (SML2PP). Unfortunately, the current SMOS retrieved soil moisture product seems to show unrealistically low values compared to in situ soil moisture data collected from organic surface layers in North America, Europe and the Tibetan Plateau so that the impact of the dielectric model for organic soils cannot really be tested. A simplified SMOS processing scheme yielding higher soil moisture levels has recently been proposed and is presently under investigation. Furthermore, recalibration of the model parameters accounting for vegetation and roughness effects that were thus far only evaluated using the default dielectric model for mineral soils is ongoing for the "organic" L-MEB version. Additionally, in order to decide where a soil moisture retrieval using the "organic" dielectric model should be triggered, information on soil organic matter content in the soil surface layer has to be considered in the retrieval algorithm. For this purpose, SoilGrids (www.soilgrids.org) providing soil organic carbon content (SOCC) in g/kg is under study. A SOCC threshold based on the relation between the SoilGrids' SOCC and the presence of organic soil surface layers (relevant to alter the microwave L-band emissions from the land surface) in the SoilGrids' source soil profile information has to be established. In this communication, we present the current status of the above outlined studies with the objective to advance towards an improved soil moisture retrieval for organic-rich soils from SMOS passive microwave L-band observations.

Response of the microbial community to seasonal groundwater level fluctuations in petroleum hydrocarbon-contaminated groundwater.

PubMed

Zhou, Ai-xia; Zhang, Yu-ling; Dong, Tian-zi; Lin, Xue-yu; Su, Xiao-si

2015-07-01

The effects of seasonal groundwater level fluctuations on the contamination characteristics of total petroleum hydrocarbons (TPH) in soils, groundwater, and the microbial community were investigated at a typical petrochemical site in northern China. The measurements of groundwater and soil at different depths showed that significant TPH residue was present in the soil in this study area, especially in the vicinity of the pollution source, where TPH concentrations were up to 2600 mg kg(-1). The TPH concentration in the groundwater fluctuated seasonally, and the maximum variation was 0.8 mg L(-1). The highest TPH concentrations were detected in the silty clay layer and lied in the groundwater level fluctuation zones. The groundwater could reach previously contaminated areas in the soil, leading to higher groundwater TPH concentrations as TPH leaches into the groundwater. The coincident variation of the electron acceptors and TPH concentration with groundwater-table fluctuations affected the microbial communities in groundwater. The microbial community structure was significantly different between the wet and dry seasons. The canonical correspondence analysis (CCA) results showed that in the wet season, TPH, NO3(-), Fe(2+), TMn, S(2-), and HCO3(-) were the major factors correlating the microbial community. A significant increase in abundance of operational taxonomic unit J1 (97% similar to Dechloromonas aromatica sp.) was also observed in wet season conditions, indicating an intense denitrifying activity in the wet season environment. In the dry season, due to weak groundwater level fluctuations and low temperature of groundwater, the microbial activity was weak. But iron and sulfate-reducing were also detected in dry season at this site. As a whole, groundwater-table fluctuations would affect the distribution, transport, and biodegradation of the contaminants. These results may be valuable for the control and remediation of soil and groundwater pollution at this site and in other petrochemical-contaminated areas. Furthermore, they are probably helpful for reducing health risks to the general public from contaminated groundwater.

A streptavidin linker layer that functions after drying.

PubMed

Xia, Nan; Shumaker-Parry, Jennifer S; Zareie, M Hadi; Campbell, Charles T; Castner, David G

2004-04-27

The ability of streptavidin (SA) to simultaneously bind four biotins is often used in linker layers, where a biotinylated molecule is linked to a biotin-functionalized surface via SA. For biosensor and array applications, it is desirable that the SA linker layer be stable to drying and rehydration. In this study it was observed that a significant decrease in binding capacity of a SA layer occurred when that layer was dried. For this study a SA linker layer was constructed by binding SA to a biotin-containing alkylthiolate monolayer (BAT/OEG) self-assembled onto gold. Its stability after drying was investigated using surface plasmon resonance (SPR). Approximately a quarter of the SA layer was removed from the BAT/OEG surface upon drying and rehydration, suggesting disruption of SA-biotin binding when dry. This resulted in the dried SA layer losing approximately 40% of its biotinylated ferritin (BF) binding capacity. Coating the layer with trehalose before drying was found to inhibit the loss of SA from the BAT/OEG surface. SPR showed that the trehalose-protected SA linker layer retained approximately 91% of its original BF binding capacity after drying and rehydration. Atomic force microscopy, which was used to image individual surface-bound SA and BF molecules, qualitatively confirmed these observations.

Biopesticide effect of green compost against fusarium wilt on melon plants.

PubMed

Ros, M; Hernandez, M T; Garcia, C; Bernal, A; Pascual, J A

2005-01-01

The biopesticide effect of four green composts against fusarium wilt in melon plants and the effect of soil quality in soils amended with composts were assayed. The composts consisted of pruning wastes, with or without addition of coffee wastes (3/1 and 4/1, dry wt/dry wt) or urea (1000/1, dry wt/dry wt). In vitro experiments suggested the biopesticide effect of the composts against Fusarium oxysporum, while only the compost of pine bark and urea (1000/1dry wt/dry wt) had an abiotic effect. Melon plant growth with composts and F. oxysporum was one to four times greater than in the non-amended soil, although there was no significant decrease in the level of the F. oxysporum in the soil. The addition of composts to the soil also improved its biological quality, as assessed by microbiological and biochemical parameters: ATP and hydrolases involved in the P (phosphatase), C (beta-glucosidase) and N (urease) cycles. Green composts had greater beneficial characteristics, improved plant growth and controlled fusarium wilt in melon plants. These composts improve the soil quality of semi-arid agricultural soils. Biotic and abiotic factors from composts have been tested as responsible of their biopesticide activity against fusarium wilt.

Modeling the production, decomposition, and transport of dissolved organic carbon in boreal soils

USGS Publications Warehouse

Fan, Zhaosheng; Neff, Jason C.; Wickland, Kimberly P.

2010-01-01

The movement of dissolved organic carbon (DOC) through boreal ecosystems has drawn increased attention because of its potential impact on the feedback of OC stocks to global environmental change in this region. Few models of boreal DOC exist. Here we present a one-dimensional model with simultaneous production, decomposition, sorption/desorption, and transport of DOC to describe the behavior of DOC in the OC layers above the mineral soils. The field-observed concentration profiles of DOC in two moderately well-drained black spruce forest sites (one with permafrost and one without permafrost), coupled with hourly measured soil temperature and moisture, were used to inversely estimate the unknown parameters associated with the sorption/desorption kinetics using a global optimization strategy. The model, along with the estimated parameters, reasonably reproduces the concentration profiles of DOC and highlights some important potential controls over DOC production and cycling in boreal settings. The values of estimated parameters suggest that humic OC has a larger potential production capacity for DOC than fine OC, and most of the DOC produced from fine OC was associated with instantaneous sorption/desorption whereas most of the DOC produced from humic OC was associated with time-dependent sorption/desorption. The simulated DOC efflux at the bottom of soil OC layers was highly dependent on the component and structure of the OC layers. The DOC efflux was controlled by advection at the site with no humic OC and moist conditions and controlled by diffusion at the site with the presence of humic OC and dry conditions.

Nitrogen metabolism correlates with the acclimation of photosynthesis to short-term water stress in rice (Oryza sativa L.).

PubMed

Zhong, Chu; Cao, Xiaochuang; Bai, Zhigang; Zhang, Junhua; Zhu, Lianfeng; Huang, Jianliang; Jin, Qianyu

2018-04-01

Nitrogen metabolism is as sensitive to water stress as photosynthesis, but its role in plant under soil drying is not well understood. We hypothesized that the alterations in N metabolism could be related to the acclimation of photosynthesis to water stress. The features of photosynthesis and N metabolism in a japonica rice 'Jiayou 5' and an indica rice 'Zhongzheyou 1' were investigated under mild and moderate soil drying with a pot experiment. Soil drying increased non-photochemical quenching (NPQ) and reduced photon quantum efficiency of PSII and CO 2 fixation in 'Zhongzheyou 1', whereas the effect was much slighter in 'Jiayou 5'. Nevertheless, the photosynthetic rate of the two cultivars showed no significant difference between control and water stress. Soil drying increased nitrate reducing in leaves of 'Zhongzheyou 1', characterized by enhanced nitrate reductase (NR) activity and lowered nitrate content; whereas glutamate dehydrogenase (GDH), glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) were relative slightly affected. 'Jiayou 5' plants increased the accumulation of nitrate under soil drying, although its NR activity was increased. In addition, the activities of GDH, GOT and GPT were typically increased under soil drying. Besides, amino acids and soluble sugar were significantly increased under mild and moderate soil drying, respectively. The accumulation of nitrate, amino acid and sugar could serve as osmotica in 'Jiayou 5'. The results reveal that N metabolism plays diverse roles in the photosynthetic acclimation of rice plants to soil drying. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

Water Source Utilization of Hammock and Pine Rockland Plant Communities in the Everglades, USA.

NASA Astrophysics Data System (ADS)

Saha, A. K.; Sternberg, L.; Miralles-Wilhelm, F.

2007-12-01

South Florida has a mosaic of plant communities resulting from topographical differences, spatially varying hydroperiods and fire. The only plant communities not flooded in the wet season are hardwood hammocks and often pine rocklands. Natural fires burn off litter accumulated in pine rocklands, with the exception of organic matter in sinkholes in the limestone bedrock. This relative lack of soil is thought to constrain pineland plants in the Everglades to depend upon groundwater that is typically low in nutrients. In contrast, adjoining hardwood hammocks have accumulated an organic soil layer that traps rainwater and nutrients. Plants in hammocks may be able to utilize this water and thereby access nutrients present in the litter. Hammocks are thus viewed as localized areas of high nutrients and instances of vegetation feedback upon the oligotrophic everglades landscape enabling establishment and survival of flood-intolerant tropical hardwood species. This study examines water source use and couples it to foliar nutrient concentrations of plants found in hammocks and pinelands. We examined the δ2H and δ18O of stem waters in plants in Everglades National Park and compared those with the δ2H and δ18O of potential water sources. In the wet season hammock plants accessed both groundwater and water in the surface organic soil layer while in the dry season they relied more on groundwater. A similar seasonal shift was observed in pineland plants; however groundwater constituted a much higher proportion of total water uptake throughout the year under observation. Concomitant with differential water utilization by hammock and pineland plant communities, we observed hammock plants having a significantly higher annual mean foliar N and P concentration than pineland plants. Most hammock species are intolerant of flooded soils and are thus constrained by the high water table in the wet season, yet access the lowered groundwater table in the dry season due to drying up of surface soilwater. This dependence on a relatively narrow seasonal range of water table depth has important implications for South Florida water resource management that can affect these ecologically important upland communities in the Everglades. Being the only emergent areas in the wet season, hammocks provide habitat for a wide range of flora and fauna.

Influence of Dry Soil on the Ability of Formosan Subterranean Termites, Coptotermes formosanus, to Locate Food Sources

PubMed Central

Cornelius, Mary L.; Osbrink, Weste L.A.

2011-01-01

The effect of barriers of dry soil on the ability of Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), to construct tunnels and find food was evaluated. Termite movement and wood consumption in a three—chambered apparatus were compared between treatments with dry soil in the center container and treatments where the soil in the center container was moist. When a wood block was located in the release container, termites fed significantly more on that block, regardless of treatment or soil type. In the treatment with dry clay, none of the termites tunneled through the dry clay barrier to reach the distal container. When termites had to tunnel through a barrier of dry sand, topsoil, or clay to reach the sole wood block, there was no effect on wood consumption for the sand treatment, but there was significantly less feeding on wood in the treatments with dry topsoil or clay. When foraging arenas had a section of dry sand in the center, the dry sand significantly reduced tunneling in the distal section after 3 days, but not after 10 days. There was a highly significant effect on the ability of termites to colonize food located in dry sand. Only one feeding station located in dry sand was colonized by termites, compared with 11 feeding stations located in moist sand. PMID:22239343

The repeated drying-wetting and freezing-thawing cycles affect only the active pool of soil organic matter

NASA Astrophysics Data System (ADS)

Semenov, Vyacheslav; Zinyakova, Natalya; Tulina, Anastasiya

2016-04-01

The decrease in the content of soil organic carbon, particularly in active form, is one of the major problems of the 21st century, which is closely related to the disturbance of the biogeochemical carbon cycle and to the increase in the emission of carbon dioxide into the atmosphere. The main reasons for the SOM losses are the surplus of the SOM active pool losses due to mineralization, erosion, and infiltration over the input of fresh organic matter to the soil, as well as the changes in the soil conditions and processes due to natural and anthropogenic disturbing impacts. Experiments were carried out with mixed samples from the upper layers of soddy-podzolic soil, gray forest soil, and typical chernozems. Soil samples as controls were incubated after wetting for 150 days. The dynamics and cumulative production of C-CO2 under stable temperature (22°C) and moisture conditions were determined; the initial content of potentially mineralizable organic matter (C0) in the soil at the beginning of the incubation was then calculated to use these data as the control. Other soil samples were exposed in flasks to the following successive treatments: wetting →incubation → freezing → thawing → incubation →drying. Six repeated cycles of disturbing impacts were performed for 140 days of the experiment. After six cycles, the soil samples were incubated under stable temperature and moisture conditions for 150 days. The wetting of dried soils and the thawing of frozen soils are accompanied by the pulsed dynamics of the C-CO2 production with an abrupt increase in the rate of the C-CO2 emission within several days by 2.7-12.4 and 1.6-2.7 times, respectively, compared to the stable incubation conditions. The rate of the C-CO2 production pulses under each subsequent impact decreased compared to the preceding one similarly for all studied soils, which could be due to the depletion in potentially mineralizable soil organic matter (C0). The cumulative extra C-CO2 production by soils of the natural lands during six cycles of disturbing impacts composed 21-40% of that by soils incubated under stable conditions; the corresponding values for the cultivated soils, including soil under the continuous bare fallow, were in the range of 45-82%. The structure of the active organic matter pool in uncultivated soils after six incubation cycles became similar to those for soils under the continuous bare fallow, as well as under farming agrocenoses. Following from the obtained results that the organic matter mobilized by disturbing impacts was predominantly mineralized in arable soils with an initially low C0 content, while a part of the mobilized organic matter was stabilized in untreated soils with the high initial C0 content. This work was supported by RSF. Project number 14-14-00625

Changes in physical properties of sandy soil after long-term compost treatment

NASA Astrophysics Data System (ADS)

Aranyos, József Tibor; Tomócsik, Attila; Makádi, Marianna; Mészáros, József; Blaskó, Lajos

2016-07-01

Studying the long-term effect of composted sewage sludge application on chemical, physical and biological properties of soil, an experiment was established in 2003 at the Research Institute of Nyíregyháza in Hungary. The applied compost was prepared from sewage sludge (40%), straw (25%), bentonite (5%) and rhyolite (30%). The compost was ploughed into the 0-25 cm soil layer every 3rd year in the following amounts: 0, 9, 18 and 27 Mg ha-1 of dry matter. As expected, the compost application improved the structure of sandy soil, which is related with an increase in the organic matter content of soil. The infiltration into soil was improved significantly, reducing the water erosion under simulated high intensity rainfall. The soil compaction level was reduced in the first year after compost re-treatment. In accordance with the decrease in bulk density, the air permeability of soil increased tendentially. However, in the second year the positive effects of compost application were observed only in the plots treated with the highest compost dose because of quick degradation of the organic matter. According to the results, the sewage sludge compost seems to be an effective soil improving material for acidic sandy soils, but the beneficial effect of application lasts only for two years.

Microbial community dynamics induced by rewetting dry soil: summer precipitation matters

NASA Astrophysics Data System (ADS)

Barnard, Romain; Osborne, Catherine; Firestone, Mary

2015-04-01

The massive soil CO2 efflux associated with rewetting dry soils after the dry summer period significantly contributes to the annual carbon budget of Mediterranean grasslands. Rapid reactivation of soil heterotrophic activity and available carbon are both required to fuel the CO2 pulse. Better understanding of the effects of altered summer precipitation on the metabolic state of indigenous microorganisms may be important in predicting future changes in carbon cycling. We investigated the effects of a controlled rewetting event on the soil CO2 efflux pulse and on the present (DNA-based) and potentially active (rRNA-based) soil bacterial and fungal communities in intact soil cores previously subjected to three different precipitation patterns over four months (full summer dry season, extended wet season, and absent dry season). Phylogenetic marker genes for bacteria (16S) and fungi (28S) were sequenced before and after rewetting, and the abundance of these genes and transcripts was measured. Even after having experienced markedly different antecedent water conditions, the potentially active bacterial communities showed a consistent wet-up response, reflecting contrasting life-strategies for different groups. Moreover, we found a significant positive relation between the extent of change in the structure of the potentially active bacterial community and the magnitude of the CO2 pulse upon rewetting dry soils. We suggest that the duration of severe dry conditions (predicted to change under future climate) is important in conditioning the response potential of the soil bacterial community to wet-up as well as in framing the magnitude of the associated CO2 pulse.

Western US high June 2015 temperatures and their relation to global warming and soil moisture

NASA Astrophysics Data System (ADS)

Philip, Sjoukje Y.; Kew, Sarah F.; Hauser, Mathias; Guillod, Benoit P.; Teuling, Adriaan J.; Whan, Kirien; Uhe, Peter; Oldenborgh, Geert Jan van

2018-04-01

The Western US states Washington (WA), Oregon (OR) and California (CA) experienced extremely high temperatures in June 2015. The temperature anomalies were so extreme that they cannot be explained with global warming alone. We investigate the hypothesis that soil moisture played an important role as well. We use a land surface model and a large ensemble from the weather@home modelling effort to investigate the coupling between soil moisture and temperature in a warming world. Both models show that May was anomalously dry, satisfying a prerequisite for the extreme heat wave, and they indicate that WA and OR are in a wet-to-dry transitional soil moisture regime. We use two different land surface-atmosphere coupling metrics to show that there was strong coupling between temperature, latent heat flux and the effect of soil moisture deficits on the energy balance in June 2015 in WA and OR. June temperature anomalies conditioned on wet/dry conditions show that both the mean and extreme temperatures become hotter for dry soils, especially in WA and OR. Fitting a Gaussian model to temperatures using soil moisture as a covariate shows that the June 2015 temperature values fit well in the extrapolated empirical temperature/drought lines. The high temperature anomalies in WA and OR are thus to be expected, given the dry soil moisture conditions and that those regions are in the transition from a wet to a dry regime. CA is already in the dry regime and therefore the necessity of taking soil moisture into account is of lower importance.

A one- and two-layer model for estimating evapotranspiration with remotely sensed surface temperature and ground-based meteorological data over partial canopy cover

NASA Technical Reports Server (NTRS)

Kustas, William P.; Choudhury, Bhaskar J.; Kunkel, Kenneth E.

1989-01-01

Surface-air temperature differences are commonly used in a bulk resistance equation for estimating sensible heat flux (H), which is inserted in the one-dimensional energy balance equation to solve for the latent heat flux (LE) as a residual. Serious discrepancies between estimated and measured LE have been observed for partial-canopy-cover conditions, which are mainly attributed to inappropriate estimates of H. To improve the estimates of H over sparse canopies, one- and two-layer resistance models that account for some of the factors causing poor agreement are developed. The utility of the two models is tested with remotely sensed and micrometeorological data for a furrowed cotton field with 20 percent cover and a dry soil surface. It is found that the one-layer model performs better than the two-layer model when a theoretical bluff-body correction for heat transfer is used instead of an empirical adjustment; otherwise, the two-layer model is better.

Modelled hydraulic redistribution by sunflower (Helianthus annuus L.) matches observed data only after including night-time transpiration.

PubMed

Neumann, Rebecca B; Cardon, Zoe G; Teshera-Levye, Jennifer; Rockwell, Fulton E; Zwieniecki, Maciej A; Holbrook, N Michele

2014-04-01

The movement of water from moist to dry soil layers through the root systems of plants, referred to as hydraulic redistribution (HR), occurs throughout the world and is thought to influence carbon and water budgets and ecosystem functioning. The realized hydrologic, biogeochemical and ecological consequences of HR depend on the amount of redistributed water, whereas the ability to assess these impacts requires models that correctly capture HR magnitude and timing. Using several soil types and two ecotypes of sunflower (Helianthus annuus L.) in split-pot experiments, we examined how well the widely used HR modelling formulation developed by Ryel et al. matched experimental determination of HR across a range of water potential driving gradients. H. annuus carries out extensive night-time transpiration, and although over the last decade it has become more widely recognized that night-time transpiration occurs in multiple species and many ecosystems, the original Ryel et al. formulation does not include the effect of night-time transpiration on HR. We developed and added a representation of night-time transpiration into the formulation, and only then was the model able to capture the dynamics and magnitude of HR we observed as soils dried and night-time stomatal behaviour changed, both influencing HR. © 2013 John Wiley & Sons Ltd.

Modeled hydraulic redistribution by Helianthus annuus L. matches observed data only after model modification to include nighttime transpiration

NASA Astrophysics Data System (ADS)

Neumann, R. B.; Cardon, Z. G.; Rockwell, F. E.; Teshera-Levye, J.; Zwieniecki, M.; Holbrook, N. M.

2013-12-01

The movement of water from moist to dry soil layers through the root systems of plants, referred to as hydraulic redistribution (HR), occurs throughout the world and is thought to influence carbon and water budgets and ecosystem functioning. The realized hydrologic, biogeochemical, and ecological consequences of HR depend on the amount of redistributed water, while the ability to assess these impacts requires models that correctly capture HR magnitude and timing. Using several soil types and two eco-types of Helianthus annuus L. in split-pot experiments, we examined how well the widely used HR modeling formulation developed by Ryel et al. (2002) could match experimental determination of HR across a range of water potential driving gradients. H. annuus carries out extensive nighttime transpiration, and though over the last decade it has become more widely recognized that nighttime transpiration occurs in multiple species and many ecosystems, the original Ryel et al. (2002) formulation does not include the effect of nighttime transpiration on HR. We developed and added a representation of nighttime transpiration into the formulation, and only then was the model able to capture the dynamics and magnitude of HR we observed as soils dried and nighttime stomatal behavior changed, both influencing HR.

Aridity and plant uptake interact to make dryland soils hotspots for nitric oxide (NO) emissions

PubMed Central

Blankinship, Joseph C.; Marchus, Kenneth; Lucero, Delores M.; Sickman, James O.; Schimel, Joshua P.

2016-01-01

Nitric oxide (NO) is an important trace gas and regulator of atmospheric photochemistry. Theory suggests moist soils optimize NO emissions, whereas wet or dry soils constrain them. In drylands, however, NO emissions can be greatest in dry soils and when dry soils are rewet. To understand how aridity and vegetation interact to generate this pattern, we measured NO fluxes in a California grassland, where we manipulated vegetation cover and the length of the dry season and measured [δ15-N]NO and [δ18-O]NO following rewetting with 15N-labeled substrates. Plant N uptake reduced NO emissions by limiting N availability. In the absence of plants, soil N pools increased and NO emissions more than doubled. In dry soils, NO-producing substrates concentrated in hydrologically disconnected microsites. Upon rewetting, these concentrated N pools underwent rapid abiotic reaction, producing large NO pulses. Biological processes did not substantially contribute to the initial NO pulse but governed NO emissions within 24 h postwetting. Plants acted as an N sink, limiting NO emissions under optimal soil moisture. When soils were dry, however, the shutdown in plant N uptake, along with the activation of chemical mechanisms and the resuscitation of soil microbial processes upon rewetting, governed N loss. Aridity and vegetation interact to maintain a leaky N cycle during periods when plant N uptake is low, and hydrologically disconnected soils favor both microbial and abiotic NO-producing mechanisms. Under increasing rates of atmospheric N deposition and intensifying droughts, NO gas evasion may become an increasingly important pathway for ecosystem N loss in drylands. PMID:27114523

Soil moisture behavior in an experimental basin in Northeast of brazil - the case of Guaraira river basin

NASA Astrophysics Data System (ADS)

Moura Ramos Filho, Geraldo; das Neves Almeida, Cristiano; da Silva Freitas, Emerson

2017-04-01

In 2003, a hydrological network of the semiarid region (REHISA in Portuguese) was created in Brazil. Since then, experimental watersheds in this region have been providing hydro meteorological data collected in automatic gauges. One of these basins is the Guaraíra river basin, which is operated and maintained by the Federal University of Paraíba. This experimental watershed is located in the coastal region of Paraíba state, where the average annual rainfall is 1.700 mm. According to Köppen its climate is tropical with dry summer, and the drainage area is 5,84 km2. At this experimental basin four rainfall and one climate gauges were installed in 2003. In all of these gauges the soil moisture is monitored hourly with a Time Domain Reflectometry probe representing the 30 cm layer. According to previous analysis the spatial distribution of rainfall in the experimental basin is very low and also soil texture, which is sandy. However, the land use is different and the behavior of the soil moisture is also different. Thus, this paper present part of a study that tries to understand the difference between two gauges, in terms of soil moisture. In order to do this, two years data base were used of different gauges, gauges 2 and 4. In the first part of the study, just the descendent part of the soil moisture curve were used. Different data periods were select from a peak to a stabilization point and then the soil moisture Drying Rate (DR) was calculated to show the speed that a peak reaches the stabilization point. The data analysis was carried out considering the whole data together, then the data were shared into dry and wet periods. The results show that for the gauge 2 the DR range from 0.0335 to 2.772x10-3 kg/kg.h, with an average of 0.632x10-3 kg/kg.h. On the other hand, the gauge 4 present values that range from 0.0139 to 3.617x10-3 kg/kg.h, with an average of 0.375x10-3 kg/kg.h. As can be seen, both gauges presented different DR. When the data set is share into dry and wet period, it was found for both gauges that an exponential equation fits the dry period with determination coefficient equal to 0.68 for gauge 2 and 0.91 for gauge 4. However, for wet period it was not found a representative determination coefficient. The conclusions highlighted that in fact the soil moisture behavior is different in these gauges. Further studies will be carried to evaluate if this difference is related to the groundwater table or to the land use.

Sample storage-induced changes in the quantity and quality of soil labile organic carbon

PubMed Central

Sun, Shou-Qin; Cai, Hui-Ying; Chang, Scott X.; Bhatti, Jagtar S.

2015-01-01

Effects of sample storage methods on the quantity and quality of labile soil organic carbon are not fully understood even though their effects on basic soil properties have been extensively studied. We studied the effects of air-drying and frozen storage on cold and hot water soluble organic carbon (WSOC). Cold- and hot-WSOC in air-dried and frozen-stored soils were linearly correlated with those in fresh soils, indicating that storage proportionally altered the extractability of soil organic carbon. Air-drying but not frozen storage increased the concentrations of cold-WSOC and carbohydrate in cold-WSOC, while both increased polyphenol concentrations. In contrast, only polyphenol concentration in hot-WSOC was increased by air-drying and frozen storage, suggesting that hot-WSOC was less affected by sample storage. The biodegradability of cold- but not hot-WSOC was increased by air-drying, while both air-drying and frozen storage increased humification index and changed specific UV absorbance of both cold- and hot-WSOC, indicating shifts in the quality of soil WSOC. Our results suggest that storage methods affect the quantity and quality of WSOC but not comparisons between samples, frozen storage is better than air-drying if samples have to be stored, and storage should be avoided whenever possible when studying the quantity and quality of both cold- and hot-WSOC. PMID:26617054

Characteristics of organic soil in black spruce forests: Implications for the application of land surface and ecosystem models in cold regions

USGS Publications Warehouse

Yi, S.; Manies, K.; Harden, J.; McGuire, A.D.

2009-01-01

Soil organic layers (OL) play an important role in landatmosphere exchanges of water, energy and carbon in cold environments. The proper implementation of OL in land surface and ecosystem models is important for predicting dynamic responses to climate warming. Based on the analysis of OL samples of black spruce (Picea mariana), we recommend that implementation of OL for cold regions modeling: (1) use three general organic horizon types (live, fibrous, and amorphous) to represent vertical soil heterogeneity; (2) implement dynamics of OL over the course of disturbance, as there are significant differences of OL thickness between young and mature stands; and (3) use two broad drainage classes to characterize spatial heterogeneity, as there are significant differences in OL thickness between dry and wet sites. Implementation of these suggestions into models has the potential to substantially improve how OL dynamics influence variability in surface temperature and soil moisture in cold regions. Copyright 2009 by the American Geophys.ical Union.

An explanation of unstable wetting fronts in soils

NASA Astrophysics Data System (ADS)

Steenhuis, Tammo; Parlange, Jean-Yves; Kung, Samuel; Stoof, Cathelijne; Baver, Christine

2016-04-01

Despite the findings of Raats on unstable wetting front almost a half a century ago, simulating wetting fronts in soils is still an area of active research. One of the critical questions currently is whether Darcy law is valid at the wetting front. In this talk, we pose that in many cases for dry soils, Darcy's law does not apply because the pressure field across the front is not continuous. Consequently, the wetting front pressure is not dependent on the pressure ahead of the front but is determined by the radius of water meniscuses and the dynamic contact angle of the water. If we further assume since the front is discontinuous, that water flows at one pore at the time, then by using the modified Hoffman relationship - relating the dynamic contact angle to the pore water velocity - we find the elevated pressures at the wetting front typical for unstable flows that are similar to those observed experimentally in small diameter columns. The theory helps also explain the funnel flow phenomena observed in layered soils.

Responses of soil ammonia oxidizers to a short-term severe mercury stress.

PubMed

Zhou, Zhi-Feng; Liu, Yu-Rong; Sun, Guo-Xin; Zheng, Yuan-Ming

2015-12-01

The responses of soil ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to mercury (Hg) stress were investigated through a short-term incubation experiment. Treated with four different concentrations of Hg (CK, Hg25, Hg50, and Hg100, denoting 0, 25, 50, and 100mgHg/kg dry soil, respectively), samples were harvested after 3, 7, and 28day incubation. Results showed that the soil potential nitrification rate (PNR) was significantly inhibited by Hg stress during the incubation. However, lower abundances of AOA (the highest in CK: 9.20×10(7)copies/g dry soil; the lowest in Hg50: 2.68×10(7)copies/g dry soil) and AOB (the highest in CK: 2.68×10(7)copies/g dry soil; the lowest in Hg50: 7.49×10(6)copies/g dry soil) were observed only at day 28 of incubation (P<0.05). Moreover, only the community structure of soil AOB obviously shifted under Hg stress as seen through DGGE profiles, which revealed that 2-3 distinct AOB bands emerged in the Hg treatments at day 28. In summary, soil PNR might be a very useful parameter to assess acute Hg stress on soil ecosystems, and the community structure of soil AOB might be a realistic biological indicator for the assessment of heavy metal stress on soil ecosystems in the future. Copyright © 2015. Published by Elsevier B.V.

Quantification of Microbial Osmolytes in a Drought Impacted California Grassland

NASA Astrophysics Data System (ADS)

Boot, C. M.; Schaeffer, S. M.; Doyle, A. P.; Schimel, J. P.

2008-12-01

With drought frequency and severity likely increasing in the future, understanding its effect on terrestrial carbon (C) and nitrogen (N) cycling has become essential for accurately modeling ecosystem responses to climate change. Microbes respond to drought stress by accumulating internal solutes, or osmolytes, such as amino acids, betaines and polyols, to balance cell membrane water potential as the soil dries. However, when seasonal rains arrive, internal solutes are released and rapidly mineralized. We have been studying these processes in a California grassland. Beginning in summer 2007, we made monthly measurements of soil moisture, individual amino acid concentration in total soil and in microbial biomass, total dissolved organic carbon and nitrogen (DOC and DON), and microbial biomass carbon and nitrogen (MBC and MBN). We expected microbial concentrations of the known amino acid osmolytes glutamate (glu) and proline (pro) to fluctuate inversely with soil moisture. However, pro was only recovered in Mar 2008 (0.30 μg C g-1 dry soil) and the glu concentration varied proportionally with soil moisture: lowest during summer (0.06 g H2O g-1 dry soil, 2.22 μg glutamate-C g-1 dry soil) and highest in winter (0.27 g H2O g-1 dry soil, 4.43 μg glutamate-C g-1 dry soil). The trend from DOC, MBC, and DON measurements was opposite, however, with all concentrations decreasing as soil moisture shifted from dry to wet, (DOC: 64.61 to 32.49 μg C g-1 dry soil respectively). MBN was the exception to this trend, with concentrations staying nearly constant across seasons. These patterns suggest that the expected amino acids glu and pro are not being used for microbial osmoregulation in the CA grassland, and given the summer to winter decrease in MBC, the primary osmolyte source is likely to be either polyol-type compounds such as mannitol or betaines. The implications for terrestrial carbon cycle are considerable because as the frequency of drought increases, the accumulation and release of osmolytes in response to drought has potential to pump carbon out of the grassland ecosystem.

Soil aggregate and organic carbon distribution at dry land soil and paddy soil: the role of different straws returning.

PubMed

Huang, Rong; Lan, Muling; Liu, Jiang; Gao, Ming

2017-12-01

Agriculture wastes returning to soil is one of common ways to reuse crop straws in China. The returned straws are expected to improve the fertility and structural stability of soil during the degradation of straw it selves. The in situ effect of different straw (wheat, rice, maize, rape, and broad bean) applications for soil aggregate stability and soil organic carbon (SOC) distribution were studied at both dry land soil and paddy soil in this study. Wet sieving procedures were used to separate soil aggregate sizes. Aggregate stability indicators including mean weight diameter, geometric mean diameter, mean weight of specific surface area, and the fractal dimension were used to evaluate soil aggregate stability after the incubation of straws returning. Meanwhile, the variation and distribution of SOC in different-sized aggregates were further studied. Results showed that the application of straws, especially rape straw at dry land soil and rice straw at paddy soil, increased the fractions of macro-aggregate (> 0.25 mm) and micro-aggregate (0.25-0.053 mm). Suggesting the nutrients released from straw degradation promotes the growing of soil aggregates directly and indirectly. The application of different straws increased the SOC content at both soils and the SOC mainly distributed at < 0.53 mm aggregates. However, the contribution of SOC in macro- and micro-aggregates increased. Straw-applied paddy soil have a higher total SOC content but lower SOC contents at > 0.25 and 0.25-0.053 mm aggregates with dry land soil. Rape straw in dry land and rice straw in paddy field could stabilize soil aggregates and increasing SOC contents best.

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.

Estimating the spatial distribution of soil organic matter density and geochemical properties in a polygonal shaped Arctic Tundra using core sample analysis and X-ray computed tomography

NASA Astrophysics Data System (ADS)

Soom, F.; Ulrich, C.; Dafflon, B.; Wu, Y.; Kneafsey, T. J.; López, R. D.; Peterson, J.; Hubbard, S. S.

2016-12-01

The Arctic tundra with its permafrost dominated soils is one of the regions most affected by global climate change, and in turn, can also influence the changing climate through biogeochemical processes, including greenhouse gas release or storage. Characterization of shallow permafrost distribution and characteristics are required for predicting ecosystem feedbacks to a changing climate over decadal to century timescales, because they can drive active layer deepening and land surface deformation, which in turn can significantly affect hydrological and biogeochemical responses, including greenhouse gas dynamics. In this study, part of the Next-Generation Ecosystem Experiment (NGEE-Arctic), we use X-ray computed tomography (CT) to estimate wet bulk density of cores extracted from a field site near Barrow AK, which extend 2-3m through the active layer into the permafrost. We use multi-dimensional relationships inferred from destructive core sample analysis to infer organic matter density, dry bulk density and ice content, along with some geochemical properties from nondestructive CT-scans along the entire length of the cores, which was not obtained by the spatially limited destructive laboratory analysis. Multi-parameter cross-correlations showed good agreement between soil properties estimated from CT scans versus properties obtained through destructive sampling. Soil properties estimated from cores located in different types of polygons provide valuable information about the vertical distribution of soil and permafrost properties as a function of geomorphology.

Climate change reduces extent of temperate drylands and intensifies drought in deep soils

USGS Publications Warehouse

Schlaepfer, Daniel R.; Bradford, John B.; Lauenroth, William K.; Munson, Seth M.; Tietjen, Britta; Hall, Sonia A.; Wilson, Scott D.; Duniway, Michael C.; Jia, Gensuo; Pyke, David A.; Lkhagva, Ariuntsetseg; Jamiyansharav, Khishigbayar

2017-01-01

Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. While drylands as a whole are expected to increase in extent and aridity in coming decades, temperature and precipitation forecasts vary by latitude and geographic region suggesting different trajectories for tropical, subtropical, and temperate drylands. Uncertainty in the future of tropical and subtropical drylands is well constrained, whereas soil moisture and ecological droughts, which drive vegetation productivity and composition, remain poorly understood in temperate drylands. Here we show that, over the twenty first century, temperate drylands may contract by a third, primarily converting to subtropical drylands, and that deep soil layers could be increasingly dry during the growing season. These changes imply major shifts in vegetation and ecosystem service delivery. Our results illustrate the importance of appropriate drought measures and, as a global study that focuses on temperate drylands, highlight a distinct fate for these highly populated areas.

Climate change reduces extent of temperate drylands and intensifies drought in deep soils

PubMed Central

Schlaepfer, Daniel R.; Bradford, John B.; Lauenroth, William K.; Munson, Seth M.; Tietjen, Britta; Hall, Sonia A.; Wilson, Scott D.; Duniway, Michael C.; Jia, Gensuo; Pyke, David A.; Lkhagva, Ariuntsetseg; Jamiyansharav, Khishigbayar

2017-01-01

Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. While drylands as a whole are expected to increase in extent and aridity in coming decades, temperature and precipitation forecasts vary by latitude and geographic region suggesting different trajectories for tropical, subtropical, and temperate drylands. Uncertainty in the future of tropical and subtropical drylands is well constrained, whereas soil moisture and ecological droughts, which drive vegetation productivity and composition, remain poorly understood in temperate drylands. Here we show that, over the twenty first century, temperate drylands may contract by a third, primarily converting to subtropical drylands, and that deep soil layers could be increasingly dry during the growing season. These changes imply major shifts in vegetation and ecosystem service delivery. Our results illustrate the importance of appropriate drought measures and, as a global study that focuses on temperate drylands, highlight a distinct fate for these highly populated areas. PMID:28139649

[Research on characteristics of soil clay mineral evolution in paddy field and dry land by XRD spectrum].

PubMed

Zhang, Zhi-dan; Li, Qiao; Luo, Xiang-li; Jiang, Hai-chao; Zheng, Qing-fu; Zhao, Lan-po; Wang, Ji-hong

2014-08-01

The present paper took the typical saline-alkali soil in Jilin province as study object, and determinated the soil clay mineral composition characteristics of soil in paddy field and dry land. Then XRD spectrum was used to analyze the evolutionary mechanism of clay mineral in the two kinds of soil. The results showed that the physical and chemical properties of soil in paddy field were better than those in dry land, and paddy field would promote the weathering of mineral particles in saline-alkali soil and enhance the silt content. Paddy field soil showed a strong potassium-removal process, with a higher degree of clay mineral hydration and lower degree of illite crystallinity. Analysis of XRD spectrum showed that the clay mineral composition was similar in two kinds of soil, while the intensity and position of diffraction peak showed difference. The evolution process of clay mineral in dry land was S/I mixture-->vermiculite, while in paddy field it was S/I mixture-->vermiculite-->kaolinite. One kind of hydroxylated 'chlorite' mineral would appear in saline-alkali soil in long-term cultivated paddy field. Taking into account that the physical and chemical properties of soil in paddy field were better then those in dry land, we could know that paddy field could help much improve soil structure, cultivate high-fertility soil and improve saline-alkali soil. This paper used XRD spectrum to determine the characteristics of clay minerals comprehensively, and analyzed two'kinds of land use comparatively, and was a new perspective of soil minerals study.

Is the Pearl River basin, China, drying or wetting? Seasonal variations, causes and implications

NASA Astrophysics Data System (ADS)

Zhang, Qiang; Li, Jianfeng; Gu, Xihui; Shi, Peijun

2018-07-01

Soil moisture plays crucial roles in the hydrological cycle and is also a critical link between land surface and atmosphere. The Pearl River basin (PRb) is climatically subtropical and tropical and is highly sensitive to climate changes. In this study, seasonal soil moisture changes across the PRb were analyzed using the Variable Infiltration Capacity (VIC) model forced by the gridded 0.5° × 0.5° climatic observations. Seasonal changes of soil moisture in both space and time were investigated using the Mann-Kendall trend test method. Potential influencing factors behind seasonal soil moisture changes such as precipitation and temperature were identified using the Maximum Covariance Analysis (MCA) technique. The results indicated that: (1) VIC model performs well in describing changing properties of soil moisture across the PRb; (2) Distinctly different seasonal features of soil moisture can be observed. Soil moisture in spring decreased from east to west parts of the PRb. In summer however, soil moisture was higher in east and west parts but was lower in central parts of the PRb; (3) A significant drying trend was identified over the PRb in autumn, while no significant drying trends can be detected in other seasons; (4) The increase/decrease in precipitation can generally explain the wetting/drying tendency of soil moisture. However, warming temperature contributed significantly to the drying trends and these drying trends were particularly evident during autumn and winter; (5) Significant decreasing precipitation and increasing temperature combined to trigger substantially decreasing soil moisture in autumn. In winter, warming temperature is the major reason behind decreased soil moisture although precipitation is in slightly decreasing tendency. Season variations of soil moisture and related implications for hydro-meteorological processes in the subtropical and tropical river basins over the globe should arouse considerable human concerns.

Analysing the mechanisms of soil water and vapour transport in the desert vadose zone of the extremely arid region of northern China

NASA Astrophysics Data System (ADS)

Du, Chaoyang; Yu, Jingjie; Wang, Ping; Zhang, Yichi

2018-03-01

The transport of water and vapour in the desert vadose zone plays a critical role in the overall water and energy balances of near-surface environments in arid regions. However, field measurements in extremely dry environments face many difficulties and challenges, so few studies have examined water and vapour transport processes in the desert vadose zone. The main objective of this study is to analyse the mechanisms of soil water and vapour transport in the desert vadose zone (depth of ∼350 cm) by using measured and modelled data in an extremely arid environment. The field experiments are implemented in an area of the Gobi desert in northwestern China to measure the soil properties, daily soil moisture and temperature, daily water-table depth and temperature, and daily meteorological records from DOYs (Days of Year) 114-212 in 2014 (growing season). The Hydrus-1D model, which simulates the coupled transport of water, vapour and heat in the vadose zone, is employed to simulate the layered soil moisture and temperature regimes and analyse the transport processes of soil water and vapour. The measured results show that the soil water and temperatures near the land surface have visible daily fluctuations across the entire soil profile. Thermal vapour movement is the most important component of the total water flux and the soil temperature gradient is the major driving factor that affects vapour transport in the desert vadose zone. The most active water and heat exchange occurs in the upper soil layer (depths of 0-25 cm). The matric potential change from the precipitation mainly re-draws the spatio-temporal distribution of the isothermal liquid water in the soil near the land surface. The matric potential has little effect on the isothermal vapour and thermal liquid water flux. These findings offer new insights into the liquid water and vapour movement processes in the extremely arid environment.

Simulating ozone dry deposition at a boreal forest with a multi-layer canopy deposition model

NASA Astrophysics Data System (ADS)

Zhou, Putian; Ganzeveld, Laurens; Rannik, Üllar; Zhou, Luxi; Gierens, Rosa; Taipale, Ditte; Mammarella, Ivan; Boy, Michael

2017-01-01

A multi-layer ozone (O3) dry deposition model has been implemented into SOSAA (a model to Simulate the concentrations of Organic vapours, Sulphuric Acid and Aerosols) to improve the representation of O3 concentration and flux within and above the forest canopy in the planetary boundary layer. We aim to predict the O3 uptake by a boreal forest canopy under varying environmental conditions and analyse the influence of different factors on total O3 uptake by the canopy as well as the vertical distribution of deposition sinks inside the canopy. The newly implemented dry deposition model was validated by an extensive comparison of simulated and observed O3 turbulent fluxes and concentration profiles within and above the boreal forest canopy at SMEAR II (Station to Measure Ecosystem-Atmosphere Relations II) in Hyytiälä, Finland, in August 2010. In this model, the fraction of wet surface on vegetation leaves was parametrised according to the ambient relative humidity (RH). Model results showed that when RH was larger than 70 % the O3 uptake onto wet skin contributed ˜ 51 % to the total deposition during nighttime and ˜ 19 % during daytime. The overall contribution of soil uptake was estimated about 36 %. The contribution of sub-canopy deposition below 4.2 m was modelled to be ˜ 38 % of the total O3 deposition during daytime, which was similar to the contribution reported in previous studies. The chemical contribution to O3 removal was evaluated directly in the model simulations. According to the simulated averaged diurnal cycle the net chemical production of O3 compensated up to ˜ 4 % of dry deposition loss from about 06:00 to 15:00 LT. During nighttime, the net chemical loss of O3 further enhanced removal by dry deposition by a maximum ˜ 9 %. Thus the results indicated an overall relatively small contribution of airborne chemical processes to O3 removal at this site.

Deposition, Accumulation, and Alteration of Cl(-), NO3(-), ClO4(-) and ClO3(-) Salts in a Hyper-Arid Polar Environment: Mass Balance and Isotopic Constraints

NASA Technical Reports Server (NTRS)

Jackson, Andrew; Davila, Alfonso F.; Boehlke, J. K.; Sturchio, Neil C.; Sevanthi, Ritesh; Estrada, Nubia; Brundrette, Megan; Lacell, Denis; McKay, Christopher P.; Poghosyan, Armen;

Deposition, accumulation, and alteration of Cl-, NO3-, ClO4- and ClO3- salts in a hyper-arid polar environment: Mass balance and isotopic constraints

NASA Astrophysics Data System (ADS)

Jackson, Andrew; Davila, Alfonso F.; Böhlke, John Karl; Sturchio, Neil C.; Sevanthi, Ritesh; Estrada, Nubia; Brundrett, Maeghan; Lacelle, Denis; McKay, Christopher P.; Poghosyan, Armen; Pollard, Wayne; Zacny, Kris

2016-06-01

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl-, NO3-, ClO4- and ClO3- in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl- and NO3- isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO4-/NO3- ratios and NO3- isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO3-/ClO4- in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO3-, possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ∼10 to 30 kyr near the glacier to 70-200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization.

Influence of soil conditions on dissolved organic matter leached from forest and wetland soils: a controlled growth chamber study.

PubMed

Kim, Eun-Ah; Nguyen, Hang Vo-Minh; Oh, Hae Sung; Hur, Jin; Choi, Jung Hyun

2016-03-01

This study investigated the effects of various soil conditions, including drying-rewetting, nitrogen deposition, and temperature rise, on the quantities and the composition of dissolved organic matter leached from forest and wetland soils. A set of forest and wetland soils with and without the nitrogen deposition were incubated in the growth chambers under three different temperatures. The moisture contents were kept constant, except for two-week drying intervals. Comparisons between the original and the treated samples revealed that drying-rewetting was a crucial environmental factor driving changes in the amount of dissolved organic carbon (DOC). The DOC was also notably increased by the nitrogen deposition to the dry forest soil and was affected by the temperature of the dry wetland soil. A parallel factor (PARAFAC) analysis identified three sub-fractions of the fluorescent dissolved organic matter (FDOM) from the fluorescence excitation-emission matrices (EEMs), and their compositions depended on drying-rewetting. The data as a whole, including the DOC and PARAFAC components and other optical indices, were possibly explained by the two main variables, which were closely related with the PARAFAC components and DOC based on principal component analysis (PCA). Our results suggested that the DOC and PARAFAC component information could provide a comprehensive interpretation of the changes in the soil-leached DOM in response to the different environmental conditions.

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.

Assessing five evolving microbial enzyme models against field measurements from a semiarid savannah—What are the mechanisms of soil respiration pulses?

NASA Astrophysics Data System (ADS)

Zhang, Xia; Niu, Guo-Yue; Elshall, Ahmed S.; Ye, Ming; Barron-Gafford, Greg A.; Pavao-Zuckerman, Mitch

2014-09-01

Soil microbial respiration pulses in response to episodic rainfall pulses (the "Birch effect") are poorly understood. We developed and assessed five evolving microbial enzyme models against field measurements from a semiarid savannah characterized by pulsed precipitation to understand the mechanisms to generate the Birch pulses. The five models evolve from an existing four-carbon (C) pool model to models with additional C pools and explicit representations of soil moisture controls on C degradation and microbial uptake rates. Assessing the models using techniques of model selection and model averaging suggests that models with additional C pools for accumulation of degraded C in the dry zone of the soil pore space result in a higher probability of reproducing the observed Birch pulses. Degraded C accumulated in dry soil pores during dry periods becomes immediately accessible to microbes in response to rainstorms, providing a major mechanism to generate respiration pulses. Explicitly representing the transition of degraded C and enzymes between dry and wet soil pores in response to soil moisture changes and soil moisture controls on C degradation and microbial uptake rates improve the models' efficiency and robustness in simulating the Birch effect. Assuming that enzymes in the dry soil pores facilitate degradation of complex C during dry periods (though at a lower rate) results in a greater accumulation of degraded C and thus further improves the models' performance. However, the actual mechanism inducing the greater accumulation of labile C needs further experimental studies.

The Effect of Drying-Wetting Cycle’s Repetition to the Characteristic of Natural and Stabilization Residual Soils Jawa Timur - Indonesia

NASA Astrophysics Data System (ADS)

Muntaha, M.

2017-11-01

Indonesia, which located in tropical region, continuously undergoes wetting and drying cycles due to the changeable seasons. An important role in activating the clay minerals on tropical residual soils is the main factor that affects the static and dynamic properties, such as: volume change, soil suction and dynamic modulus. The purpose of this paper is to evaluate the effect of drying-wetting cycles repetition on volume change, soil suction and mechanical characteristics of natural and stabilization of residual soils from Jawa Timur - Indonesia. The natural undisturbed and stabilized residual soil sample was naturally and gradually dried up with air to 25%, 50%, 75%, and 100 % of the initial water content. The wetting processes were carried out with the gradual increment water content of 25 %(wsat - wi), 50 %(wsat - wi), 75 %(wsat - wi), up to 100 %(wsat - wi). The Direct Shear test is used to measure the mechanic properties, and Whatman filter paper No. 42 is used to measure the soil suction. The drying-wetting processes were carried out for 1, 2, 4, and 6 cycles. The laboratory test results showed that, the void ratio decreased, the unit weight, cohesion and the internal friction angle were increasing due to stabilization. Drying-wetting cycle repetition reduces void ratio, negative pore-water pressure, cohesion and internal friction angle of natural and stabilized soils. Briefly, the decreased of mechanical soil properties was proven from the physical properties change observation.

[Variation in soil Mn fractions as affected by long-term manure amendment using atomic absorption spectrophotometer in a typical grassland of inner Mongolia].

PubMed

Fu, Ming-ming; Jiang, Yong; Bai, Yong-fei; Zhang, Yu-ge; Xu, Zhu-wen; Li, Bo

2012-08-01

The effect of sheep manure amendment on soil manganese fractions was conducted in a 11 year experiment at inner Mongolia grassland, using sequential extraction procedure in modified Community Bureau of Reference, and determined by atomic absorption spectrophotometer. Five treatments with dry sheep manure addition rate 0, 50, 250, 750, and 1500 g x m(-2) x yr(-1), respectively, were carried out in this experiment. Results showed that the recovery rate for total Mn was 91.4%-105.9%, as the percentage recovered from the summation of the improved BCR results with aqua regia extractable contents, and it was 97.2%-102.9% from certified soil reference materials. Plant available exchangeable Mn could be enhanced by 47.89%, but reducible and total Mn contents decreased significantly under heavy application of manure at depth of 0-5 cm. The effect of manure amendment on Mn fractions was greater in 0-5 cm than in 5-10 cm soil layer. The results are benefit to micronutrient fractions determination and nutrient management in grassland soils.

Mass flow of a volatile organic liquid mixture in soils

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

Gerstl, Z.; Galin, Ts.; Yaron, B.

1994-05-01

The flow of kerosene, a volatile organic liquid mixture (VOLM), was studied in loam and clay soils and in a medium sand. The kerosene residual capacity and conductivity were determined for all three media at different initial moisture contents and with kerosene of different compositions. The kerosene conductivity of the soil was found to be strongly influenced by the soil texture and initial moisture content as well as by the kerosene composition. The kerosene conductivity of the sand was two orders of magnitude greater than that of the soils and was unaffected by initial moisture contents as high as fieldmore » capacity. The kerosene conductivity of the loam soil was similar in oven dry and air dry soils, but increased significantly in soils at 70% and fun field capacity due to the Yuster effect. In the clay soil the kerosene conductivity of the air dry sod was four times that of the oven dry sod and increased somewhat in the soil at 70% field capacity. No kerosene flow was observed in the oven dry soil at full field capacity. The differences in kerosene conductivity in these soils and the effect of moisture content were attributed to the different pore-sin distributions of the soil& Changes in the composition of the kerosene due to volatilization of the light fractions resulted in increased viscosity of the residual kerosene. This increased viscosity affected the fluid properties of kerosene, which resulted in decreased kerosene conductivity in the sand and the soils. 29 refs., 4 figs., 4 tabs.« less

Measured Two-Dimensional Ice-Wedge Polygon Thermal and Active Layer Dynamics

NASA Astrophysics Data System (ADS)

Cable, W.; Romanovsky, V. E.; Busey, R.

2016-12-01

Ice-wedge polygons are perhaps the most dominant permafrost related features in the arctic landscape. The microtopography of these features, that includes rims, troughs, and high and low polygon centers, alters the local hydrology. During winter, wind redistribution of snow leads to an increased snowpack depth in the low areas, while the slightly higher areas often have very thin snow cover, leading to differences across the landscape in vegetation communities and soil moisture between higher and lower areas. To investigate the effect of microtopographic caused variation in surface conditions on the ground thermal regime, we established temperature transects, composed of five vertical array thermistor probes (VATP), across four different development stages of ice-wedge polygons near Barrow, Alaska. Each VATP had 16 thermistors from the surface to a depth of 1.5 m, for a total of 80 temperature measurements per polygon. We found snow cover, timing and depth, and active layer soil moisture to be major controlling factors in the observed thermal regimes. In troughs and in the centers of low-centered polygons, the combined effect of typically saturated soils and increased snow accumulation resulted in the highest mean annual ground temperatures (MAGT) and latest freezeback dates. While the centers of high-centered polygons, with thinner snow cover and a dryer active layer, had the lowest MAGT, earliest freezeback dates, and shallowest active layer. Refreezing of the active layer initiated at nearly the same time for all locations and polygons however, we found large differences in the proportion of downward versus upward freezing and the length of time required to complete the refreezing process between polygon types and locations. Using our four polygon stages as a space for time substitution, we conclude that ice-wedge degradation resulting in surface subsidence and trough deepening can lead to overall drying of the active layer and increased skewedness of snow distribution. Which in turn leads to shallower active layers, earlier freezeback dates, and lower MAGT. We also find that the large variation in active layer dynamics (active layer depth, downward vs upward freezing, and freezeback date) are important considerations to understanding and scaling biological processes occurring in these landscapes.

[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.

Heavy Metals in Water Percolating Through Soil Fertilized with Biodegradable Waste Materials.

PubMed

Wierzbowska, Jadwiga; Sienkiewicz, Stanisław; Krzebietke, Sławomir; Bowszys, Teresa

The influence of manure and composts on the leaching of heavy metals from soil was evaluated in a model lysimeter experiment under controlled conditions. Soil samples were collected from experimental fields, from 0- to 90-cm layers retaining the layout of the soil profile layers, after the second crop rotation cycle with the following plant species: potatoes, spring barley, winter rapeseed, and winter wheat. During the field experiment, 20 t DM/ha of manure, municipal sewage sludge composted with straw (SSCS), composted sewage sludge (SSC), dried granular sewage sludge (DGSS), "Dano" compost made from non-segregated municipal waste (CMMW), and compost made from municipal green waste (CUGW) was applied, i.e., 10 t DM/ha per crop rotation cycle. The concentrations (μg/dm 3 ) of heavy metals in the leachate were as follows: Cd (3.6-11.5) < Mn (4.8-15.4) < Cu (13.4-35.5) < Zn (27.5-48.0) < Cr (36.7-96.5) < Ni (24.4-165.8) < Pb (113.8-187.7). Soil fertilization with organic waste materials did not contaminate the percolating water with manganese or zinc, whereas the concentrations of the other metals increased to the levels characteristic of unsatisfactory water quality and poor water quality classes. The copper and nickel content of percolating water depended on the concentration of those metals introduced into the soil with organic waste materials. The concentrations of Cd in the leachate increased, whereas the concentrations of Cu and Ni decreased with increasing organic C content of organic fertilizers. The widening of the C/N ratio contributed to Mn leaching. The concentrations of Pb, Cr, and Mn in the percolating water were positively correlated with the organic C content of soil.

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.

Grass mulching effect on infiltration, surface runoff and soil loss of three agricultural soils in Nigeria.

PubMed

Adekalu, K O; Olorunfemi, I A; Osunbitan, J A

2007-03-01

Mulching the soil surface with a layer of plant residue is an effective method of conserving water and soil because it reduces surface runoff, increases infiltration of water into the soil and retard soil erosion. The effectiveness of using elephant grass (Pennisetum purpureum) as mulching material was evaluated in the laboratory using a rainfall simulator set at rainfall intensities typical of the tropics. Six soil samples, two from each of the three major soil series representing the main agricultural soils in South Western Nigeria were collected, placed on three different slopes, and mulched with different rates of the grass. The surface runoff, soil loss, and apparent cumulative infiltration were then measured under each condition. The results with elephant grass compared favorably with results from previous experiments using rice straw. Runoff and soil loss decreased with the amount of mulch used and increased with slope. Surface runoff, infiltration and soil loss had high correlations (R = 0.90, 0.89, and 0.86, respectively) with slope and mulch cover using surface response analysis. The mean surface runoff was correlated negatively with sand content, while mean soil loss was correlated positively with colloidal content (clay and organic matter) of the soil. Infiltration was increased and soil loss was reduced greatly with the highest cover. Mulching the soils with elephant grass residue may benefit late cropping (second cropping) by increasing stored soil water for use during dry weather and help to reduce erosion on sloping land.

Drought and Winter Drying (Pest Alert)

Treesearch

USDA Forest Service

Drought and winter drying have periodically caused major damage to trees. Drought reduces the amount of water available in the soil. In the case of winter drying, the water may be in the soil, but freezing of the soil makes the water unavailable to the tree. In both cases, more water is lost through transpiration than is available to the plant. Symptoms of drought and...

Design of dry sand soil stratified sampler

NASA Astrophysics Data System (ADS)

Li, Erkang; Chen, Wei; Feng, Xiao; Liao, Hongbo; Liang, Xiaodong

2018-04-01

This paper presents a design of a stratified sampler for dry sand soil, which can be used for stratified sampling of loose sand under certain conditions. Our group designed the mechanical structure of a portable, single - person, dry sandy soil stratified sampler. We have set up a mathematical model for the sampler. It lays the foundation for further development of design research.

Organochlorine pesticides and polychlorinated biphenyls in surface soils of Novi Sad and bank sediment of the Danube River.

PubMed

Skrbic, Biljana; Cvejanov, Jelena; Durisic-Mladenovic, Natasa

2007-01-01

The contents of 16 organochlorine pesticides (OCPs) and six so-called indicator polychlorinated biphenyls (PCBs) were determined in the surface zone (0-5 cm) of soil and sediment samples, taken from different locations in the city of Novi Sad, capitol of Vojvodina Province (North of the Serbia) covering residential and commercial area, recreational and arable zone. The total organochlorine pesticides concentration in soil varied from 2.63 to 31.78 ng g(-1) dry weight, while the level in sediment was 10.35 ng g(-1) dry weight. Maximum content of identified individual organochlorine pesticide in soil samples was 10.40 ng g(-1) dry weight for p, p-DDE in the market garden and 6.31 ng g(-1) dry weight for p, p'-DDT in sediment of the Danube River, although their application is restricted in Serbia. Some of investigated PCBs were identified only in the soil samples from a park-school backyard in the city downtown (0.32 ng g(-1) dry weight) and market garden (0.22 ng g(-1) dry weight), and also in sediment sample from left bank of the Danube River (0.41 ng g(-1) dry weight). Data of the OCPs and PCBs present in this study were compared with the ones found for soils and river sediments throughout the world, and with limit values set by soil and sediment quality guidelines. Also, correlation between the levels of certain pesticides and soil characteristics (organic matter, pH and clay content) was investigated.

Soil moisture-soil temperature interrelationships on a sandy-loam soil exposed to full sunlight

Treesearch

David A. Marquis

1967-01-01

In a study of birch regeneration in New Hampshire, soil moisture and temperature were found to be intimately related. Not only does low moisture lead to high temperature, but high temperature undoubtedly accelerates soil drying, setting up a vicious cycle of heating and drying that may prevent seed germination or kill seedlings.

Lanthanum toxicity to five different species of soil invertebrates in relation to availability in soil.

PubMed

Li, Jinxia; Verweij, Rudo A; van Gestel, Cornelis A M

2018-02-01

This study determined the toxicity of lanthanum, one of the most commonly used rare earth elements (REEs), to five representative soil invertebrates after 3-4 weeks exposure. Toxicity was related to total, 0.01 M CaCl 2 -extractable and porewater concentrations in the standard LUFA 2.2 soil, and for earthworms also to body concentrations. La sorption to LUFA 2.2 soil, estimated by relating total soil concentrations to CaCl 2 -extractable or porewater concentrations seemed to reach saturation at >1000 mg La/kg dry soil. Isopod (Porcellio scaber) growth was the most sensitive endpoint, followed by earthworm (Eisenia andrei), enchytraeid (Enchytraeus crypticus), springtail (Folsomia candida) and oribatid mite (Oppia nitens) reproduction, with EC 50 s of 312 (95% confidence interval: 5.6-619), 529 (295-762), 1010 ((>377 < 3133), 1220 (1180-1250) and 1500 (1250-1750) mg La/kg dry soil, respectively. EC 50 s related to CaCl 2 -extractable concentrations ranged between 1.3 (0.046-2.6) and 15.6 (5.6-25.7) mg La/kg dry soil, while porewater-based EC 50 s were 3.5 (-) and 10.2 (-) mg/L for the springtails and mites, respectively. La uptake in the earthworms linearly increased with increasing exposure concentration with bioaccumulation factors ranging between 0.04 and 0.53 (average ± SE: 0.24 ± 0.032). EC 50 for effects on earthworm reproduction related to internal concentrations was 184 (61-301) mg La/kg dry body weight. A risk assessment based on the available toxicity for soil invertebrates, bacteria and plants resulted in an HC 5 of approx. 50 mg La/kg dry soil, suggesting that La may affect soil ecosystems at concentrations slightly above natural background levels (6.6-50 mg La/kg dry soil) in non-polluted soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

Ammonia Volatilization from Urea-Application Influenced Germination and Early Seedling Growth of Dry Direct-Seeded Rice

PubMed Central

Qi, Xiaoli; Wu, Wei; Shah, Farooq; Peng, Shaobing; Huang, Jianliang; Cui, Kehui; Liu, Hongyan; Nie, Lixiao

2012-01-01

Poor seed germination and early seedling growth associated with urea-induced soil ammonia volatilization are major constraints in the adoption of dry direct-seeded rice. To directly examine soil ammonia volatilization and its damage to seed germination and early seedling growth of dry direct-seeded rice when urea is applied at seeding, two Petri-dish incubation experiments and a field experiment were conducted. Ammonia volatilization due to urea application significantly reduced seed germination and early seedling growth of dry direct-seedling rice. NBPT significantly reduced ammonia volatilization following urea application. The application of ammonium sulfate, instead of urea at seeding, may mitigate poor crop establishment of dry direct-seeded rice. Root growth of dry direct-seeded rice was more seriously inhibited by soil ammonia volatilization than that of shoot. Results suggest that roots are more sensitive to soil ammonia toxicity than shoots in dry direct-seeded rice system when N is applied as urea at seeding. PMID:22454611

Response of respiration and nutrient availability to drying and rewetting in soil from a semi-arid woodland depends on vegetation patch and a recent wild fire

NASA Astrophysics Data System (ADS)

Sun, Q.; Meyer, W. S.; Koerber, G.; Marschner, P.

2015-06-01

Semi-arid woodlands, which are characterised by patchy vegetation interspersed with bare, open areas, are frequently exposed to wild fire. During summer, long dry periods are occasionally interrupted by rainfall events. It is well-known that rewetting of dry soil induces a flush of respiration. However, the magnitude of the flush may differ between vegetation patches and open areas because of different organic matter content which could be further modulated by wild fire. Soils were collected from under trees, under shrubs or in open areas in unburnt and burnt sandy Mallee woodland, where part of the woodland experienced a wild fire which destroyed or damaged most of the aboveground plant parts four months before sampling. In an incubation experiment, the soils were exposed to two moisture treatments: constantly moist (CM) and drying and rewetting (DRW). In CM, soils were incubated at 80% of maximum water holding capacity for 19 days; In DRW, soils were dried for four days, kept dry for another five days, then rewet to 80% WHC and maintained at this water content until day 19. Soil respiration decreased during drying and was very low in the dry period; rewetting induced a respiration flush. Compared to soil under shrubs and in open areas, cumulative respiration per g soil in CM and DRW was greater under trees, but lower when expressed per g TOC. Organic matter content, available P, and microbial biomass C, but not available N were greater under trees than in open areas. Wild fire decreased the flush of respiration per g TOC in the open areas and under shrubs, and reduced TOC and MBC concentrations only under trees, but had little effect on available N and P concentrations. We conclude that of the impact wild fire and DRW events on nutrient cycling differ among vegetation patches of a native semiarid woodland which is related to organic matter amount and availability.

[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.

Quantifying the effects of wildfire on changes in soil properties by surface burning of soils from the Boulder Creek Critical Zone Observatory

USGS Publications Warehouse

Wieting, Celeste; Ebel, Brian A.; Singha, Kamini

2017-01-01

Study regionThis study used intact soil cores collected at the Boulder Creek Critical Zone Observatory near Boulder, Colorado, USA to explore fire impacts on soil properties.Study focusThree soil scenarios were considered: unburned control soils, and low- and high-temperature burned soils. We explored simulated fire impacts on field-saturated hydraulic conductivity, dry bulk density, total organic carbon, and infiltration processes during rainfall simulations.New hydrological insights for the regionSoils burned to high temperatures became more homogeneous with depth with respect to total organic carbon and bulk density, suggesting reductions in near-surface porosity. Organic matter decreased significantly with increasing soil temperature. Tension infiltration experiments suggested a decrease in infiltration rates from unburned to low-temperature burned soils, and an increase in infiltration rates in high-temperature burned soils. Non-parametric statistical tests showed that field-saturated hydraulic conductivity similarly decreased from unburned to low-temperature burned soils, and then increased with high-temperature burned soils. We interpret these changes result from the combustion of surface and near-surface organic materials, enabling water to infiltrate directly into soil instead of being stored in the litter and duff layer at the surface. Together, these results indicate that fire-induced changes in soil properties from low temperatures were not as drastic as high temperatures, but that reductions in surface soil water repellency in high temperatures may increase infiltration relative to low temperatures.

Effect of repeated drying-wetting-freezing-thawing cycles on the active soil organic carbon pool

NASA Astrophysics Data System (ADS)

Semenov, V. M.; Kogut, B. M.; Lukin, S. M.

2014-04-01

Samples of soddy-podzolic soil (long-term overgrown fallow and continuous bare fallow), gray forest soil (forest, farming agrocenosis), and a typical chernozem (virgin steppe, forest area, farming agrocenosis, continuous bare fallow) have been incubated under stable conditions; other samples of these soils have been subjected to six drying-wetting-incubation-freezing-thawing-incubation cycles during 136 days. The wetting of dried soils and the thawing of frozen soils result in an abrupt but short increase in the emission rate of C-CO2 by 2.7-12.4 and 1.6-2.7 times, respectively, compared to the stable incubation conditions. As the soil is depleted in potentially mineralizable organic matter, the rate of the C-CO2 emission pulses initiated by disturbing impacts decreases. The cumulative extra production of C-CO2 by soils of natural lands for six cycles makes up 21-40% of that in the treatments with stable incubation conditions; the corresponding value for cultivated soils, including continuous clean fallow, is in the range of 45-82%. The content of potentially mineralizable organic matter in the soils subjected to recurrent drying-wetting-freezingthawing cycles decreased compared to the soils without disturbing impacts by 1.6-4.4 times, and the mineralization constants decreased by 1.9-3.6 times. It has been emphasized that the cumulative effect of drying-wetting-freezing-thawing cycles is manifested not only in the decrease in the total Corg from the soil but also in the reduction of the mineralization potential of the soil organic matter.

Simulation of Dynamic Soil Crusting Processes and Vegetative Feedbacks in Semi-Arid Regions

NASA Astrophysics Data System (ADS)

Sivandran, G.; Bras, R. L.

2009-12-01

Many soils, especially those in arid and semi-arid regions, develop compacted surface layers with hydrologic properties different to those of the underlying layers. These layers, referred to as soil crusts when dry and soil seals when wet, may be only a few millimeters thick but can have a significant impact by altering the partitioning of rainfall, increasing surface runoff and reducing infiltration. This reduces the quantity of water entering the root zone, limiting the amount of water available for primary productivity, while increasing erosion and negatively impacting seedling establishment and growth. Vegetation significantly alters soil hydraulic properties in the immediate vicinity of a vegetation patch. Root action has been shown to create macropores, increasing infiltration capacity around the base of vegetation. Shading protects the soil from evaporation and the formation of soil seals/crusts. Experiments have confirmed large variations in infiltration rates in below canopy and bare soil patches. It is believed that a positive feedback may occur between seals/crusts and vegetation patches resulting in systems that exhibit ‘islands of fertility’. The bare soil patches act to increase the micro-catchment area of the vegetation patch, thereby collecting moisture from a far greater area than the immediate footprint of its rooting system. Vegetation then alters the soil conditions directly beneath it, allowing for increased infiltration of this extra moisture. A coupled, dynamic vegetation and hydrologic model, tRIBS+VEGGIE, was used to explore the role of dynamic soil properties on hydrologic and energy fluxes. Rather than assigning the hydraulic properties of the surface soils a priori, soil seals/crusts were allowed to develop in the model depending on vegetation cover, soil type and rainfall intensity. The effects of plant shading and root action on infiltration in the immediate vicinity of vegetation patches were also included. These changes introduced both spatial and temporal heterogeneity into soil hydraulic properties and allowed for simulation of plant-soil feedbacks. The semi-arid Lucky Hills basin in the Walnut Gulch Experimental Watershed in Arizona was used as a case study to investigate the role of dynamic soil properties, which occur at patch scales, on the larger basin scale hydrologic and energy fluxes (sensible and latent heats, net radiation and rainfall partitioning). The model was used to test the contribution of dynamic soil properties to the establishment of a positive feedback between vegetation and soils that leads to the ‘islands of fertility’ that have been observed in many semi-arid systems. The model was also used to investigate the role that plant-soil interactions play in providing both stability to the larger system during periods of consistent climate forcing and some resilience to disturbance during climate perturbations.

Degradation of Biochemical Activity in Soil Sterilized by Dry Heat and Gamma Radiation

NASA Technical Reports Server (NTRS)

Shih, K. L.; Souza, K. A.

1978-01-01

The effect of soil sterilization by dry heat (0.08% relative humidity), gamma radiation, or both on soil phosphatase, urease, and decarboxylase activity was studied. Soil sterilized by a long exposure to dry heat at relatively low temperatures (eight weeks at 100.5 C) retained higher activities than did soil exposed to a higher temperature (two weeks at 124.5 C), while all activity was destroyed by four days at 148.5 C. Sterilization with 7.5 Mrads destroyed less activity than did heat sterilization. The effect of several individually nonsterizing doses of heat radiation is described.

Soil water content plays an important role in soil-atmosphere exchange of carbonyl sulfide (OCS)

NASA Astrophysics Data System (ADS)

Yi, Zhigang; Behrendt, Thomas; Bunk, Rüdiger; Wu, Dianming; Kesselmeier, Jürgen

2016-04-01

Carbonyl sulfide (OCS) is a quite stable gas in the troposphere and is transported up to the stratosphere, where it contributes to the sulfate aerosol layer (Crutzen 1976). The tropospheric concentration seems to be quite constant, indicating a balance between sinks and sources. Recent work by Sandoval-Soto et al. (2005) demonstrated the enormous strength of the vegetation sink and the urgent needs to understand the sinks and sources. The role of soils is a matter of discussion (Kesselmeier et al., 1999; Van Diest and Kesselmeier, 2008; Maseyk et al., 2014; Whelan et al., 2015). To better understand the influence of soil water content and OCS mixing ratio on OCS fluxes, we used an OCS analyzer (LGR COS/CO Analyzer 907-0028, Los Gatos, CA, USA) coupled with automated soil chamber system (Behrendt et al., 2014) to measure the OCS fluxes with a slow drying of four different types of soil (arable wheat soil in Mainz, blueberry soil in Waldstein, spruce soil in Waldstein and needle forest soil in Finland). Results showed that OCS fluxes as well as the optimum soil water content for OCS uptake varied significantly for different soils. The net production rates changed significantly with the soil drying out from 100% to about 5% water holding capacity (WHC), implying that soil water content play an important role in the uptake processes. The production and uptake processes were distinguished by the regression of OCS fluxes under different OCS mixing ratios. OCS compensation points (CP) were found to differ significantly for different soil types and water content, with the lowest CP at about 20% WHC, implying that when estimating the global budgets of OCS, especially for soils fluxes, soil water content should be taken into serious consideration. References Crutzen, P. J. 1976, Geophys. Res. Lett., 3, 73-76. Sandoval-Soto, L. et al., 2005, Biogeosciences, 2, 125-132. Kesselmeier, J. et al., 1999, J. Geophys. Res., 104, 11577-11584. Van Diest, H. and Kesselmeier, J. 2008, Biogeosciences, 5, 475-483. Maseyk, K. et al., 2014, PNAS, 111, No 25, 9064-9069. Whelan, M. E., and Rhew, R., C. 2015, J. Geophys. Res., 120, 54-62. Behrendt, T. et al., 2014, Biogeosciences, 11, 5463-5492.

Rapid drying soils with microwave ovens.

DOT National Transportation Integrated Search

2002-07-01

Soils are normally dried in either a convection oven or stove. Inspections of field and laboratory moisture content testing indicated that the typical drying durations for a convection oven and stove were, 24 hours and 60 minutes, respectively. The o...

Continuing Measurements of CO2 Crystals with a Hand-Held 35 GHz Radiometer

NASA Technical Reports Server (NTRS)

Foster, J.; Chang, A.; Hall, D.; Tait, A.; Wergin, W.; Erbe, E.

2000-01-01

In order to increase our knowledge of the Martian polar caps, an improved understanding of the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum is needed. The thermal microwave part of the spectrum has received relatively little attention compared to the visible and infrared wavelengths. A simple experiment to measure the brightness temperature of frozen CO2 was first performed in the winter of 1998 using a 35 GHz radiometer. in experiments performed during the winter of 1999 and 2000, passive microwave radiation emanating from within layers of manufactured CO2 (dry ice) crystals was again measured with a 35 GHz handheld radiometer. Both large (0.8 cm) and small (0.3 cm) cylindrical-shaped dry ice pellets, at a temperature of 197 K (-76 C), were measured. A 1 sq m plate of aluminum sheet metal was positioned beneath the dry ice so that microwave emissions from the underlying soil layers would be minimized. Non-absorbing foam was positioned around the sides of the plate in order to keep the dry ice in place and to assure that the incremental deposits were level. Thirty-five GHz measurements of this plate were made through the dry ice deposits in the following way. Layers of dry ice were built up and measurements were repeated for the increasing CO2 pack. First, 7 cm of large CO2 pellets were poured onto the sheet metal plate, then an additional 7 cm were added, and finally, 12 cm were added on top of the 14 cm base. Hand-held 35 GHz measurements were made each time the thickness of the deposit was increased. The same process was repeated for the smaller grain pellets. Furthermore, during the past winter, 35 GHz measurements were taken of a 25 kg (27 cm x 27 cm x 27 cm) solid cube Of CO2, which was cut in half and then re-measured. Additional information is contained in the original extended abstract.

Emission of nitric oxide (NO) from tropical forest soils and exchange of NO between the forest canopy and atmospheric boundary layers

NASA Technical Reports Server (NTRS)

Bakwin, Peter S.; Wofsy, Steven C.; Fan, Song-Miao; Keller, Michael; Trumbore, Susan E.

1990-01-01

Emissions of NO from soils in the Amazon rain forest were measured at 66 locations using an enclosure technique, and continuous vertical profiles of NO and O3 were measured between the ground and 41-m altitude. Fluxes of NO averaged 8.9 (+ or - 1.5) x 10 to the 9th molecules/sq cm per sec from the dominant (yellow clay) soils of the region, with larger fluxes observed from adjacent white sand soils. Fluxes from clay soils were lower by more than a factor of 5 than fluxes observed during the dry season at a nearby site. Low soil emission rates were reflected in lower concentrations of NO at the top of the forest canopy in the wet season, only 30-50 parts per trillion by volume during the daytime. The measured fluxes are consistent with chemical mass balances for NO within the forest canopy, calculated from the NO and O3 profiles taken at night, and with observations of NO between 150 and 5000 m altitude. Measurements of NO emission rates from soil plots fertilized using NaNO3, NH4Cl, or sucrose indicated that a reductive pathway (denitrification) may have been primarily responsible for production of the NO released by both clay and sand soils.

Convergence of microbial assimilations of soil carbon, nitrogen, phosphorus, and sulfur in terrestrial ecosystems

DOE PAGES

Xu, Xiaofeng; Hui, Dafeng; King, Anthony Wayne; ...

2015-11-27

How soil microbes assimilate carbon-C, nitrogen-N, phosphorus-P, and sulfur-S is fundamental for understanding nutrient cycling in terrestrial ecosystems. We compiled a global database of C, N, P, and S concentrations in soils and microbes and developed relationships between them by using a power function model. The C:N:P:S was estimated to be 287:17:1:0.8 for soils, and 42:6:1:0.4 for microbes. We found a convergence of the relationships between elements in soils and in soil microbial biomass across C, N, P, and S. The element concentrations in soil microbial biomass follow a homeostatic regulation curve with soil element concentrations across C, N, Pmore » and S, implying a unifying mechanism of microbial assimilating soil elements. This correlation explains the well-constrained C:N:P:S stoichiometry with a slightly larger variation in soils than in microbial biomass. Meanwhile, it is estimated that the minimum requirements of soil elements for soil microbes are 0.8 mmol C Kg –1 dry soil, 0.1 mmol N Kg –1 dry soil, 0.1 mmol P Kg –1 dry soil, and 0.1 mmol S Kg –1 dry soil, respectively. Lastly, these findings provide a mathematical explanation of element imbalance in soils and soil microbial biomass, and offer insights for incorporating microbial contribution to nutrient cycling into Earth system models.« less

Impact assessment of intermediate soil cover on landfill stabilization by characterizing landfilled municipal solid waste.

PubMed

Qi, Guangxia; Yue, Dongbei; Liu, Jianguo; Li, Rui; Shi, Xiaochong; He, Liang; Guo, Jingting; Miao, Haomei; Nie, Yongfeng

2013-10-15

Waste samples at different depths of a covered municipal solid waste (MSW) landfill in Beijing, China, were excavated and characterized to investigate the impact of intermediate soil cover on waste stabilization. A comparatively high amount of unstable organic matter with 83.3 g kg(-1) dry weight (dw) total organic carbon was detected in the 6-year-old MSW, where toxic inorganic elements containing As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn of 10.1, 0.98, 85.49, 259.7, 530.4, 30.5, 84.0, and 981.7 mg kg(-1) dw, respectively, largely accumulated because of the barrier effect of intermediate soil cover. This accumulation resulted in decreased microbial activities. The intermediate soil cover also caused significant reduction in moisture in MSW under the soil layer, which was as low as 25.9%, and led to inefficient biodegradation of 8- and 10-year-old MSW. Therefore, intermediate soil cover with low permeability seems to act as a barrier that divides a landfill into two landfill cells with different degradation processes by restraining water flow and hazardous matter. Copyright © 2013 Elsevier Ltd. All rights reserved.

Carbon sequestration in a surface flow constructed wetland after 12 years of swine wastewater treatment.

PubMed

Reddy, Gudigopuram B; Raczkowski, Charles W; Cyrus, Johnsely S; Szogi, Ariel

2016-01-01

Constructed wetlands used for the treatment of swine wastewater may potentially sequester significant amounts of carbon. In past studies, we evaluated the treatment efficiency of wastewater in a marsh-pond-marsh design wetland system. The functionality of this system was highly dependent on soil carbon content and organic matter turnover rate. To better understand system performance and carbon dynamics, we measured plant dry matter, decomposition rates and soil carbon fractions. Plant litter decomposition rate was 0.0052 g day(-1) (±0.00119 g day(-1)) with an estimated half-life of 133 days. The detritus layer accumulated over the soil surface had much more humin than other C fractions. In marsh areas, soil C extracted with NaOH had four to six times higher amounts of humic acid, fulvic acid and humin than soil C extracted by cold and hot water, HCl/HF, and Na pyruvate. In the pond area, humic acid, fulvic acid and humin content were two to four times lower than in the marsh area. More soil C and N was found in the marsh area than in the pond area. These wetlands proved to be large sinks for stable C forms.

Disaster Management: Rapid Dry-Up of Rainwater on Land Surface Leading to the Santa Barbara Wildfire

NASA Image and Video Library

2009-05-08

Wildfires are a recurring natural hazard faced by Californians. In Santa Barbara County, a wildfire, called the Jesusita fire, ignited on May 5, 2009 in the Cathedral Peak area northwest of Mission Canyon. As of midday May 8, the fire, which was 10-percent contained, had scorched 3,500 acres, damaged or destroyed 75 structures, and had forced the evacuation of tens of thousands of residents. This image shows soil moisture change in the top soil layer (2-inches deep) on 2 and 3 May 2009, as measured by the NASA QuikSCAT satellite scatterometer (radar). Rainwater increased the amount of moisture in the soil by a moderate 4 percent (represented by the green color) on May 2, which rapidly dried up on the next day (0 percent, as depicted by the grey color on May 3). Son Nghiem of JPL is leading a science team to develop wildfire applications using QuikScat data. “Information critical to assessing the conditions leading to wildfires can be obtained from NASA’s SeaWinds scatterometer, a stable and accurate radar aboard the QuikScat satellite,” says Dr. Son Nghiem, a JPL scientist in remote sensing. This is accomplished by using QuikScat data to map moisture changes in the topsoil. As such, QuikScat can detect rainwater that actually reaches the land surface and accumulates on it, rather than raindrops in the air. While rain radars may detect a significant rain rate, rainwater may evaporate in part before reaching the surface. For example, in the case of dry thunderstorm (known as virga), raindrops disappear on the way down, leaving the land dry, while the associated lightning ignites fires. For the case of the current fire in Santa Barbara, QuikScat detected a moderate increase of 4 percent in soil moisture on May 2, while rain radar data seemed to indicate a significant and extensive rain. The next day, QuikScat revealed that whatever rainwater that had accumulated earlier quickly dried up over the whole area. The maximum temperature in Santa Barbara approached 90 degrees Fahrenheit and broke the record set in 1984. An important characteristic of QuikScat measurements is that they represent the average conditions over the whole area, rather than some disparate data collected at a few localized points. The rapid dry-up in Santa Barbara together with high temperatures and high winds led to the devastating Jesusita fire. http://photojournal.jpl.nasa.gov/catalog/PIA12006

Stochastic soil water balance under seasonal climates

PubMed Central

Feng, Xue; Porporato, Amilcare; Rodriguez-Iturbe, Ignacio

2015-01-01

The analysis of soil water partitioning in seasonally dry climates necessarily requires careful consideration of the periodic climatic forcing at the intra-annual timescale in addition to daily scale variabilities. Here, we introduce three new extensions to a stochastic soil moisture model which yields seasonal evolution of soil moisture and relevant hydrological fluxes. These approximations allow seasonal climatic forcings (e.g. rainfall and potential evapotranspiration) to be fully resolved, extending the analysis of soil water partitioning to account explicitly for the seasonal amplitude and the phase difference between the climatic forcings. The results provide accurate descriptions of probabilistic soil moisture dynamics under seasonal climates without requiring extensive numerical simulations. We also find that the transfer of soil moisture between the wet to the dry season is responsible for hysteresis in the hydrological response, showing asymmetrical trajectories in the mean soil moisture and in the transient Budyko's curves during the ‘dry-down‘ versus the ‘rewetting‘ phases of the year. Furthermore, in some dry climates where rainfall and potential evapotranspiration are in-phase, annual evapotranspiration can be shown to increase because of inter-seasonal soil moisture transfer, highlighting the importance of soil water storage in the seasonal context. PMID:25663808

[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.

Changing Summer Precipitation Pattern Alters Microbial Community Response to Fall Wet-up in a Mediterranean Soil

NASA Astrophysics Data System (ADS)

Barnard, R. L.; Osborne, C. A.; Firestone, M. K.

2014-12-01

The large soil CO2 efflux associated with rewetting dry soils after the dry summer period significantly contributes to the annual carbon budget of Mediterranean grasslands. Rapid reactivation of soil heterotrophic activity and a pulse of available carbon are both required to fuel the CO2 pulse. Better understanding of the effects of altered summer precipitation on the metabolic state of indigenous microorganisms may be important in predicting future changes in carbon cycling. Here, we investigated the effects of a controlled rewetting event on the soil CO2 efflux pulse and on the present (DNA-based) and potentially active (rRNA-based) soil bacterial and fungal communities in intact soil cores previously subjected to three different precipitation patterns over four months (full summer dry season, extended wet season, and absent dry season). Phylogenetic marker genes for bacteria (16S) and fungi (28S) were sequenced before and after rewetting, and the abundance of these genes and transcripts was measured. Even after having experienced markedly different antecedent water conditions, the potentially active bacterial communities showed a consistent wet-up response. Moreover, we found a significant positive relation between the extent of change in the structure of the potentially active bacterial community and the magnitude of the CO2 pulse upon rewetting dry soils. We suggest that the duration of severe dry conditions (predicted to change under future climate) is important in conditioning the response potential of the soil bacterial community to wet-up as well as in framing the magnitude of the associated CO2 pulse.

Changing precipitation pattern alters soil microbial community response to wet-up under a Mediterranean-type climate.

PubMed

Barnard, Romain L; Osborne, Catherine A; Firestone, Mary K

2015-03-17

A large soil CO2 pulse is associated with rewetting soils after the dry summer period under a Mediterranean-type climate, significantly contributing to grasslands' annual carbon budget. Rapid reactivation of soil heterotrophs and a pulse of available carbon are both required to fuel the CO2 pulse. Understanding of the effects of altered summer precipitation on the metabolic state of indigenous microorganisms may be important in predicting changes in carbon cycling. Here, we investigated the effects of extending winter rainfall into the normally dry summer period on soil microbial response to a controlled rewetting event, by following the present (DNA-based) and potentially active (rRNA-based) soil bacterial and fungal communities in intact soil cores (from a California annual grassland) previously subjected to three different precipitation patterns over 4 months (full summer dry season, extended wet season and absent dry season). Phylogenetic marker genes for bacteria and fungi were sequenced before and after rewetting, and the abundance of these genes and transcripts was measured. After having experienced markedly different antecedent water conditions, the potentially active bacterial communities showed a consistent wet-up response. We found a significant positive relation between the extent of change in the structure of the potentially active bacterial community and the magnitude of the CO2 pulse upon rewetting dry soils. We suggest that the duration of severe dry summer conditions characteristic of the Mediterranean climate is important in conditioning the response potential of the soil microbial community to wet-up as well as in framing the magnitude of the associated CO2 pulse.

The surface area of soil organic matter

USGS Publications Warehouse

Chiou, C.T.; Lee, J.-F.; Boyd, S.A.

1990-01-01

The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.The previously reported surface area for soil organic matter (SOM) of 560-800 m2/g as determined by the ethylene glycol (EG) retention method was reexamined by the standard BET method based on nitrogen adsorption at liquid nitrogen temperature. Test samples consisted of two high organic content soils, a freeze-dried soil humic acid, and an oven-dried soil humic acid. The measured BET areas for these samples were less than 1 m2/g, except for the freeze-dried humic acid. The results suggest that surface adsorption of nonionic organic compounds by SOM is practically insignificant in comparison to uptake by partition. The discrepancy between the surface areas of SOM obtained by BET and EG methods was explained in terms of the 'free surface area' and the 'apparent surface area' associated with these measurements.

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

Effect of dry spells and soil cracking on runoff generation in a semiarid micro watershed under land use change

NASA Astrophysics Data System (ADS)

dos Santos, Julio Cesar Neves; de Andrade, Eunice Maia; Guerreiro, Maria João Simas; Medeiros, Pedro Henrique Augusto; de Queiroz Palácio, Helba Araújo; de Araújo Neto, José Ribeiro

2016-10-01

Soil and water resources effective management and planning in a river basin rely on understanding of runoff generation processes, yield, and their relations to rainfall. This study analyzes the effects of antecedent soil moisture in an expansive soil and the influence of dry spells on soil cracking, runoff generation and yield in a semiarid tropical region in Brazil subject to land use change. Data were collected from 2009 to 2013 in a 2.8 ha watershed, totaling 179 natural rainfall events. In the first year of study (2009), the watershed maintained a typical dry tropical forest cover (arboreal-shrub Caatinga cover). Before the beginning of the second year of study, gamba grass (Andropogon gayanus Kunth) was cultivated after slash and burn of native vegetation. Gamba grass land use was maintained for the rest of the monitoring period. The occurrence of dry spells and the formation of cracks in the Vertisol soil were the most important factors controlling flow generation. Dry spells promoted crack formation in the expansive soil, which acted as preferential flow paths leading to high initial abstractions: average conditions for runoff to be generated included soil moisture content above 20%, rainfall above 70 mm, I30max above 60 mm h-1 and five continuous dry days at the most. The change of vegetation cover in the second year of study did not alter significantly the overall conditions for runoff initiation, showing similar cumulative flow vs. rainfall response, implying that soil conditions, such as humidity and cracks, best explain the flow generation process on the semiarid micro-scale watershed with Vertisol soil.

WISDOM GPR performance assessment in a cold artificial environment

NASA Astrophysics Data System (ADS)

Dechambre, M.; Ciarletti, V.; Biancheri-Astier, M.; Saintenoy, A.; Costard, F.; Hassen-Khodja, R.

2012-04-01

The WISDOM (Water Ice Subsurface Deposit Observation on Mars) GPR is one of the instruments that have been selected as part of the Pasteur payload of ESA's 2018 ExoMars Rover mission. WISDOM has been designed to obtain information about the nature of the subsurface along the rover path with the objective to explore the first ~ 3 m of the soil with a vertical resolution of a few centimetres. The sub-surface properties that can be addressed with WISDOM are variations in composition, texture, stratification (e.g., number, thickness and orientation of layers), the presence of unconformities and other structural characteristics (such as fractures and the deformation of strata). It is then essential to quantify the performances of WISDOM in controlled conditions, and several full polarimetric measurements have been carried out with the prototype in a cold artificial environment. The main objectives are the detection of different interface between homogeneous materials with WISDOM. The characterization of the material (porosity, % of water, dielectric properties, thickness and depth, temperature ...) is well-controlled. The cold room facility of IDES at Orsay (France) has been used, the ambient temperature ranged from -7° C to -10° C. A tank laying on the metallic floor (height: 0.5m, width: 0.80 m, length: 1.20m) in macrolon can contain liquid or frozen water or layers (dielectric contrasts) of home-maid permafrost (frozen saturated sand) with and without embedded objects or fractures. The temperature inside the medium (ice or permafrost) is controlled, the radar antennas are put on a sheet of polystyrene over the tank. Frequent measurements were performed (every 2cm) along a track from one side to the other side of the tank. The experimental conditions were: (1)dry cold sand (Fontainebleau sand) : porosity 35% density 2,67 (2) saturated wet sand : 35% of water (3) permafrost (frozen saturated sand) : 35% of ice content 1 layer: 3 consecutive experiments : 10cm dry sand ( 1) 10cm saturated sand (2) 10cm permafrost(3) 2 layers :previous 10cm permafrost in the bottom +3 consecutive experiments : 10cm dry sand ( 1) 10cm saturated sand (2) 10cm permafrost(3) . Basalt rocks and air fractures are or are not embedded in the layers Values of the permittivity of dry sand and permafrost were retrieve by two different ways. 1.Retrieval of the sand and permafrost permittivity from delay measurements knowing the layer thickness d ɛr = ct/2d = n2 2. Retrieval of the sand and permafrost permittivity from amplitude measurements knowing a calibration reference (reflection over a metallic plate), R is the Fresnel coefficient between the air and the medium. Aint/ = R = n- 1-,ɛ = 1+-R-= n2 Aair n +1 r 1- R Results : Internal layering is observed. The transition between dry sand and permafrost can be detected. The permittivity can be retrieved from delay or amplitude measurements as well from delay measurements : dry sand ɛr = 2.71 permafrost ɛr = 3.72 from amplitude measurements : dry sand ɛr = 2.73 permafrost ɛr = 3.35 Embedded objects are detected, Fracture and its orientation is detected.

Drying shrinkage problems in high PI subgrade soils.

DOT National Transportation Integrated Search

2014-01-01

The main objective of this study was to investigate the longitudinal cracking in pavements due to drying : shrinkage of high PI subgrade soils. The study involved laboartory soil testing and modeling. The : shrinkage cracks usually occur within the v...

Impact of a moderate/high-severity prescribed eucalypt forest fire on soil phosphorous stocks and partitioning.

PubMed

Santín, Cristina; Otero, Xose L; Doerr, Stefan H; Chafer, Chris J

2018-04-15

This study examines the direct impact of a moderate/high-severity prescribed fire on phosphorous (P) stocks and partitioning in oligotrophic soils of a dry eucalypt forest within Sydney's water supply catchments, Australia. We also quantify and characterize the P present in the ash produced in this fire, and explore its relationships with the maximum temperatures recorded in the litter layer during the burn. In these oligotrophic soils, P concentrations were already relatively low before the fire (<130mgkg -1 , mainly in organic forms). The fire consumed the entire litter layer and the thin Oa soil horizon, creating 6.3±3.1tha -1 of ash, and resulted into direct net P losses of ~7kgha -1 . The P lost was mostly organic and there was a moderate net gain of inorganic and non-reactive P forms. Importantly, only a small proportion of the post-fire P was bioavailable (equivalent to ~3% of the total P lost during fire). Higher total P concentrations in ash corresponded with higher maximum temperatures (>650°C) recorded in the burning litter layer, but effects of fire temperature on ash P partitioning were not significant. Fire not only transformed P chemically, but also physically. Our results show that, immediately after fire, up to 2kgha -1 of P was present in the ash layer and, therefore, highly erodible and susceptible to be transported off-site by wind- and water erosion. Even if most of this P was, initially, of low bioavailability, its transfer to depositional environments with different geochemical conditions (e.g. anoxic sediments in water reservoirs) can alter its geochemical forms and availability. Further investigation of potential P transformations off-site is therefore essential, particularly given that SE-Australian water supply catchments are subject to recurrent perturbation by prescribed fire and wildfires. The latter have already resulted in major algal blooms in water supply reservoirs. Copyright © 2017 Elsevier B.V. All rights reserved.

Effects of the Application of Digestates from Wet and Dry Anaerobic Fermentation to Japanese Paddy and Upland Soils on Short-Term Nitrification

PubMed Central

Sawada, Kozue; Toyota, Koki

2015-01-01

Wet and dry anaerobic fermentation processes are operated for biogas production from organic matter, resulting in wet and dry digestates as by-products, respectively. The application of these digestates to soil as fertilizer has increased in recent years. Therefore, we herein compared the effects of applying wet digestates (pH 8.2, C/N ratio 4.5), dry digestates (pH 8.8, C/N ratio 23.4), and a chemical fertilizer to Japanese paddy and upland soils on short-term nitrification under laboratory aerobic conditions. Chloroform-labile C, an indicator of microbial biomass, was only minimally affected by these applications, indicating that a small amount of labile N was immobilized by microbes. All applications led to rapid increases in NO3 -N contents in both soils, and ammonia-oxidizing bacteria, but not archaea may play a critical role in net nitrification in the amended soils. The net nitrification rates for both soils were the highest after the application of dry digestates, followed by wet digestates and then the chemical fertilizer in order of decreasing soil pH. These results suggest that the immediate effects of applying digestates, especially dry digestates with the highest pH, on nitrate leaching need to be considered when digestates are used as alternative fertilizers. PMID:25740173

Effects of the application of digestates from wet and dry anaerobic fermentation to Japanese paddy and upland soils on short-term nitrification.

PubMed

Sawada, Kozue; Toyota, Koki

2015-01-01

Wet and dry anaerobic fermentation processes are operated for biogas production from organic matter, resulting in wet and dry digestates as by-products, respectively. The application of these digestates to soil as fertilizer has increased in recent years. Therefore, we herein compared the effects of applying wet digestates (pH 8.2, C/N ratio 4.5), dry digestates (pH 8.8, C/N ratio 23.4), and a chemical fertilizer to Japanese paddy and upland soils on short-term nitrification under laboratory aerobic conditions. Chloroform-labile C, an indicator of microbial biomass, was only minimally affected by these applications, indicating that a small amount of labile N was immobilized by microbes. All applications led to rapid increases in NO3 -N contents in both soils, and ammonia-oxidizing bacteria, but not archaea may play a critical role in net nitrification in the amended soils. The net nitrification rates for both soils were the highest after the application of dry digestates, followed by wet digestates and then the chemical fertilizer in order of decreasing soil pH. These results suggest that the immediate effects of applying digestates, especially dry digestates with the highest pH, on nitrate leaching need to be considered when digestates are used as alternative fertilizers.

Do drying and rewetting cycles modulate effects of sulfadiazine spiked manure in soil?

PubMed

Jechalke, Sven; Radl, Viviane; Schloter, Michael; Heuer, Holger; Smalla, Kornelia

2016-05-01

Naturally occurring drying-rewetting events in soil have been shown to affect the dissipation of veterinary antibiotics entering soil by manure fertilization. However, knowledge of effects on the soil microbial community structure and resistome is scarce. Here, consequences of drying-rewetting cycles on effects of sulfadiazine (SDZ) in soil planted with Dactylis glomerata L. were investigated in microcosms. Manure containing SDZ or not was applied to the pregrown grass and incubated for 56 days in a climate chamber. Water was either added daily or reduced during two drying events of 7 days, each followed by a recovery phase. Total community DNA was analyzed to reveal the effects on the bacterial community structure and on the abundance of sul1, sul2, intI1 ,intI2, qacE+qacEΔ1, traN and korB genes relative to 16S rRNA genes. 16S rRNA gene-based DGGE fingerprints indicated that drying-rewetting cycles modulated the effects of SDZ on the bacterial community structure in the soil. Furthermore, the SDZ treatment increased the relative abundance of sulfonamide resistance and integrase genes compared to the control. However, this increase was not different between moisture regimes, indicating that drying-rewetting had only a negligible effect on the selection of the resistome by SDZ in the manured soil. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Mineralogy of Antarctica Dry Valley Soils: Implications for Pedogenic Processes on Mars

NASA Technical Reports Server (NTRS)

Quinn, J. E.; Ming, D. W.; Morris, R. V.; Douglas, S.; Kounaves, S. P.; McKay, C. P.; Tamppari, L, K.; Smith, P. H.; Zent, A. P.; Archer, P. D., Jr.

2010-01-01

The Antarctic Dry Valleys (ADVs) located in the Transantarctic Mountains are the coldest and driest locations on Earth. The mean annual air temperature is -20 C or less and the ADVs receive 100mm or less of precipitation annually in the form of snow. The cold and dry climate in the ADVs is one of the best terrestrial analogs for the climatic conditions on Mars [2]. The soils in the ADVs have been categorized into three soil moisture zones: subxerous, xerous and ultraxerous. The subxerous zone is a coastal region in which soils have ice-cemented permafrost relatively close to the surface. Moisture is available in relatively large amounts and soil temperatures are above freezing throughout the soil profile (above ice permafrost) in summer months. The xerous zone, the most widespread of the three zones, is an inland region with a climate midway between the subxerous and ultraxerous. The soils from this zone have dry permafrost at moderate depths (30-75cm) but have sufficient water in the upper soil horizons to allow leaching of soluble materials. The ultraxerous zone is a high elevation zone, where both temperature and precipitation amounts are very low resulting in dry permafrost throughout the soil profile. The three moisture regime regions are similar to the three microclimatic zones (coastal thaw, inland mixed, stable upland) defined by Marchant and Head.

Hydrologic regime controls soil phosphorus fluxes in restoration and undisturbed wetlands

USGS Publications Warehouse

Aldous, A.; McCormick, P.; Ferguson, C.; Graham, S.; Craft, C.

2005-01-01

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes - flooded, moist, and dry - for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron-bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence. ?? 2005 Society for Ecological Restoration International.

Influence of forest stands on soil and ecosystem carbon stocks in the conditions of the European part of Russia

NASA Astrophysics Data System (ADS)

Kaganov, Vladimir

2016-04-01

Forest stands are one of the most important components of ecosystems, both in Russia and around the world and at the same time forest vegetation is able to provide environment-modifying effect on the occupied landscape and, in particular, on the soil cover. Currently, due to the large interest in the carbon cycle, there is a question about the influence of forest vegetation on carbon stocks in ecosystems and in particular in the soil cover. To perform the study we selected 9 objects located in the European part of Russia from the area of the southern taiga to the semi-desert zone: Novgorod region, Kostroma region, Moscow region (2 objects), Penza region, Voronezh region, Volgograd region (2 objects) and Astrakhan region. For studying the influence of forest vegetation on the soil`s carbon, we organized the following experiment scheme: in each of the objects two key sites were selected, so that they originally were in the same soil conditions and the difference between them was only in a course development of vegetation - forest or grass. One part of the experimental sites, presenting forest vegetation, were the restored forests on abandoned lands with the age of 70-200 years. The second part of the experimental sites were artificial forest plantations aged from 60 to 112 years planted on the originally treeless forest-steppe or steppe landscapes. Perennial hayfields, perennial abandoned agricultural landscapes and virgin steppe areas were used as reference sites with grass vegetation. For each forest site we estimated the major carbon pools: phytomass, mortmass (dead wood, dry grass), debris, litter and soil. All data were recalculated using the conversion factors in carbon stocks in t C ha-1. We collected soil samples every 10 cm until the depth of 50 cm, and then at 50-75 and 75-100 cm soil layers. Bulk density and total organic carbon were determined by CHN analyzer. As a result, the soil`s carbon was also calculated into t C ha-1. We found out that the total carbon stocks were higher for the forestry vegetation than for the reference plots for all studied sites. Maximal values of carbon stocks (779±2 t C ha-1) were observed in forest sites of the forest-steppe zone (Voronezh region). These values decreased while moving both north and south and amounted for 236±1 t C ha-1 in south taiga (Novgorod region) and 104,5±7,4 t C ha-1 in semi-desert areas (Astrakhan region). The stock of total soil carbon significantly increased in 0-10 cm soil layer and decreased in 50-100 cm layer in the forest stands compared to the grass vegetation (T-test at significance level of 0.05). However, when considering the entire 100-cm layer of soil, there is no statistically significant difference in total carbon stock between forest and grass vegetation.

Experimental facility for testing nuclear instruments for planetary landing missions

NASA Astrophysics Data System (ADS)

Golovin, Dmitry; Mitrofanov, Igor; Litvak, Maxim; Kozyrev, Alexander; Sanin, Anton; Vostrukhin, Andrey

2017-04-01

The experimental facility for testing and calibration of nuclear planetology instruments has been built in the frame of JINR and Space Research Institute (Moscow) cooperation. The Martian soil model from silicate glass with dimensions 3.82 x 3.21 m and total weight near 30 tons has been assembled in the facility. The glass material was chosen for imitation of dry Martian regolith. The heterogeneous model has been proposed and developed to achieve the most possible similarity with Martian soil in part of the average elemental composition by adding layers of necessary materials, such as iron, aluminum, and chlorine. The presence of subsurface water ice is simulated by adding layers of polyethylene at different depths inside glass model assembly. Neutron generator was used as a neutron source to induce characteristic gamma rays for testing active neutron and gamma spectrometers to define elements composition of the model. The instrumentation was able to detect gamma lines attributed to H, O, Na, Mg, Al, Si, Cl, K, Ca and Fe. The identified elements compose up to 95 wt % of total mass of the planetary soil model. This results will be used for designing scientific instruments to performing experiments of active neutron and gamma ray spectroscopy on the surface of the planets during Russian and international missions Luna-Glob, Luna-Resource and ExoMars-2020.

Vertical profiles of ClNO2 at a remote terrestrial site: evidence of N2O5 dry deposition as a source of ClNO2?

NASA Astrophysics Data System (ADS)

McLaren, R.; Roberts, J. M.; Kercher, J. P.; Thornton, J. A.; Brown, S. S.; Edwards, P. M.; Young, C. J.; Dube, W. P.; Washenfelder, R. A.; Williams, E. J.; Holloway, J. S.; Bates, T. S.; Quinn, P.

2012-12-01

Recent observations of nitryl chloride (ClNO2) have suggested that this compound can accumulate to significant levels (several ppb) in the nocturnal boundary layer at night. Its photolytic loss the next day can be a significant source of chlorine atom radicals. The source of ClNO2 is largely thought to be the heterogeneous reaction of N2O5 with aerosol chloride, not just confined to coastal regions but also observed thousands of kilometers inland in urban areas. During the Uintah Basin Winter Ozone Study, we made measurements of ClNO2 by CIMS on a tower in a remote region of Utah. Levels of ClNO2 were surprisingly high at night (up to 2 ppb) even though sea salt aerosols were not present. Soils in the region were alkaline with high chloride content. To address the potential of N2O5 dry deposition as a source of ClNO2, we measured vertical profiles of ClNO2 from 1 to 12 m agl with a movable inlet. We observed negative gradients of ClNO2 and positive gradients of nitrate (a surrogate for N2O5), which suggests that dry deposition of N2O5 and reaction with Cl- in soils is a source of ClNO2 in this region.

Vertical profiles of ClNO2 measured in Utah: dry deposition of N2O5 as a source of ClNO2

NASA Astrophysics Data System (ADS)

McLaren, Robert; Roberts, James M.; Kercher, James P.; Thornton, Joel A.; Brown, Steven S.; Edwards, Peter M.; Young, Cora Y.; Dube, William P.; Washenfelder, Rebecca A.; Williams, Eric J.; Holloway, John S.; Bates, Timothy S.; Quinn, Patricia K.

2013-04-01

Several recent observations of nitryl chloride (ClNO2) have suggested that this compound can accumulate to significant levels (several ppb) in the nocturnal boundary layer at night. Its photolytic loss the next day can be a significant source of chlorine atom radicals. The source of ClNO2 is known to be the heterogeneous reaction of N2O5 with aerosol chloride, not just confined to coastal regions but also observed thousands of kilometers inland in urban areas. During the Uintah Basin Winter Ozone Study (2012), we made measurements of ClNO2 by CIMS on a tower in a remote region of Utah where intensive natural gas extraction operations via hydraulic fracturing were occurring. Levels of ClNO2 were surprisingly high at night (up to 2 ppb) even though coastal aerosols were not present. Soils in the region were alkaline with high chloride content. To address the potential of N2O5 dry deposition as a source of ClNO2, we measured vertical profiles of ClNO2 from 1 to 12 m agl with a movable inlet. We observed negative gradients of ClNO2 and positive gradients of N2O5, which suggest that dry deposition of N2O5 and reaction with soil chloride as a source of ClNO2.

Net ecosystem exchange of CO2 and CH4 in the high arctic (81°N) during the growing season

NASA Astrophysics Data System (ADS)

Barker, J. D.; St. Louis, V. L.; Graydon, J. A.; Lehnherr, I.

2009-12-01

The role of high arctic ecosystems in the global carbon budget has attracted scientific interest because a) arctic terrestrial ecosystems currently store significant amounts of organic carbon in permafrost and poorly drained tundra soils, and b) the arctic climate system is changing rapidly in response to global warming. The role of the high arctic terrestrial ecosystem as either a source or sink of atmospheric CO2 is unknown, although it is generally assumed that it will become a source of CO2 to the atmosphere as climate change continues to warm the region and previously sequestered organic matter in soils is mineralized as the active layer develops. We will present data on the net ecosystem exchange (NEE) of CO2 from high arctic tundra near Lake Hazen, Quittinirpaaq National Park (81°N) during the 2008 and 2009 growing seasons, collected using an eddy covariance flux tower. This is the first report of NEE from such a northerly latitude. We will also present data on the exchange of CH4 with tundra soils collected using static chambers. The tundra at Lake Hazen was a continuous CO2 sink during the growing season, and is carbon neutral during snow cover conditions in early spring. The CO2 flux correlated strongly with PAR and soil temperature. Despite active layer development at the site during our observation period (11 cm in 2008, 37 cm in 2009), no evidence of a corresponding CO2 pulse to the atmosphere was detected. Soil respiration rates, separately measured using a LiCOR 6400, indicated a correlation between soil respiration and plant cover corresponded. The strong correlation between NEE and vegetation parameters suggests that as vegetation cover increases in the high arctic in response to climate warming, the tundra at Lake Hazen may continue to function as a carbon sink despite continued active layer development. Dry tundra soils always consumed CH4 at our site, suggesting that parts of the high Arctic are actually sinks for this strong greenhouse gas.

Electrical resistivity characteristics of diesel oil-contaminated kaolin clay and a resistivity-based detection method.

PubMed

Liu, Zhibin; Liu, Songyu; Cai, Yi; Fang, Wei

2015-06-01

As the dielectric constant and conductivity of petroleum products are different from those of the pore water in soil, the electrical resistivity characteristics of oil-contaminated soil will be changed by the corresponding oil type and content. The contaminated soil specimens were manually prepared by static compaction method in the laboratory with commercial kaolin clay and diesel oil. The water content and dry density of the first group of soil specimens were controlled at 10 % and 1.58 g/cm(3). Corresponding electrical resistivities of the contaminated specimens were measured at the curing periods of 7, 14, and 28 and 90, 120, and 210 days on a modified oedometer cell with an LCR meter. Then, the electrical resistivity characteristics of diesel oil-contaminated kaolin clay were discussed. In order to realize a resistivity-based oil detection method, the other group of oil-contaminated kaolin clay specimens was also made and tested, but the initial water content, oil content, and dry density were controlled at 0~18 %, 0~18 %, 1.30~1.95 g/cm(3), respectively. Based on the test data, a resistivity-based artificial neural network (ANN) was developed. It was found that the electrical resistivity of kaolin clay decreased with the increase of oil content. Moreover, there was a good nonlinear relationship between electrical resistivity and corresponding oil content when the water content and dry density were kept constant. The decreasing velocity of the electrical resistivity of oil-contaminated kaolin clay was higher before the oil content of 12 % than after 12 %, which indicated a transition of the soil from pore water-controlled into oil-controlled electrical resistivity characteristics. Through microstructural analysis, the decrease of electrical resistivity could be explained by the increase of saturation degree together with the collapse of the electrical double layer. Environmental scanning electron microscopy (ESEM) photos indicated that the diesel oil in kaolin clay normally had three kinds of effects including oil filling, coating, and bridging. Finally, a resistivity-based ANN model was established based on the database collected from the experiment data. The performance of the model was proved to be reasonably accepted, which puts forward a possible simple, economic, and effective tool to detect the oil content in contaminated clayey soils just with four basic parameters: wet density, dry density, measured moisture content, and electrical resistivity.

Soil sorption of organic vapors and effects of humidity on sorptive mechanism and capacity

USGS Publications Warehouse

Chiou, C.T.; Shoup, T.D.

1985-01-01

Vapor sorption isotherms on dry Woodburn soil at 20-30??C were determined for benzene, chlorobenzene, p-dichlorobenzene, m-dichlorobenzene, 1,2,4-trichlorobenzene, and water as single vapors and for benzene, m-dichlorobenzene, and 1,2,4-trichlorobenzene as functions of relative humidity (RH). Isotherms for all compounds on dry soil samples are distinctively nonlinear, with water showing the greatest capacity. Water vapor sharply reduced the sorption capacities of organic compounds with the dry soil; on water-saturated soil, the reduction was about 2 orders of magnitude. The markedly higher sorption of organic vapors at subsaturation humidities is attributed to adsorption on the mineral matter, which predominates over the simultaneous uptake by partition into the organic matter. At about 90% RH, the sorption capacities of organic compounds become comparable to those in aqueous systems. The effect of humidity is attributed to adsorptive displacement by water of organics adsorbed on the mineral matter. A small residual uptake is attributed to the partition into the soil-organic phase that has been postulated in aqueous systems. The results are essentially in keeping with the model that was previously proposed for sorption on the soil from water and from organic solvents.Vapor sorption isotherms on dry Woodburn soil at 20-30 degree C were determined for benzene, chlorobenzene, p-dichlorobenzene, m-dichlorobenzene, 1,2,4-trichlorobenzene, and water as single vapors and for benzene, m-dichlorobenzene, and 1,2,4-trichlorobenzene as functions of relative humidity (RH). Isotherms for all compounds on dry soil samples are distinctively nonlinear, with water showing the greatest capacity. Water vapor sharply reduced the sorption capacities of organic compounds with the dry soil; on water-saturated soil, the reduction was about 2 orders of magnitude. The markedly higher sorption of organic vapors at subsaturation humidities is attributed to adsorption on the mineral matter. The results are essentially in keeping with the model that was previously proposed for sorption on the soil from water and from organic solvents.

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

USGS Publications Warehouse

Olefeldt, David; Turetsky, Merritt R.; Crill, Patrick M.; McGuire, A. David

2013-01-01

Methane (CH4) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH4 emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH4 emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near-surface permafrost had lower CH4 fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH4 emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost-free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high-latitude CH4 emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.

Arbuscular mycorrhizal fungi and associated microbial communities from dry grassland do not improve plant growth on abandoned field soil.

PubMed

Pánková, Hana; Lepinay, Clémentine; Rydlová, Jana; Voříšková, Alena; Janoušková, Martina; Dostálek, Tomáš; Münzbergová, Zuzana

2018-03-01

After abandonment of agricultural fields, some grassland plant species colonize these sites with a frequency equivalent to dry grasslands (generalists) while others are missing or underrepresented in abandoned fields (specialists). We aimed to understand the inability of specialists to spread on abandoned fields by exploring whether performance of generalists and specialists depended on soil abiotic and/or biotic legacy. We performed a greenhouse experiment with 12 species, six specialists and six generalists. The plants were grown in sterile soil from dry grassland or abandoned field inoculated with microbial communities from one or the other site. Plant growth, abundance of mycorrhizal structures and plant response to inoculation were evaluated. We focused on arbuscular mycorrhizal fungi (AMF), one of the most important parts of soil communities affecting plant performance. The abandoned field soil negatively affected plant growth, but positively affected plant response to inoculation. The AMF community from both sites differed in infectivity and taxa frequencies. The lower AMF taxa frequency in the dry grassland soil suggested a lack of functional complementarity. Despite the fact that dry grassland AMF produced more arbuscules, the dry grassland inoculum did not improve phosphorus nutrition of specialists contrary to the abandoned field inoculum. Inoculum origin did not affect phosphorus nutrition of generalists. The lower effectiveness of the dry grassland microbial community toward plant performance excludes its inoculation in the abandoned field soil as a solution to allow settlement of specialists. Still, the distinct response of specialists and generalists to inoculation suggested that they differ in AMF responsiveness.

The Inter-Valley Soil Comparative Survey: the ecology of Dry Valley edaphic microbial communities

PubMed Central

Lee, Charles K; Barbier, Béatrice A; Bottos, Eric M; McDonald, Ian R; Cary, Stephen Craig

2012-01-01

Recent applications of molecular genetics to edaphic microbial communities of the McMurdo Dry Valleys and elsewhere have rejected a long-held belief that Antarctic soils contain extremely limited microbial diversity. The Inter-Valley Soil Comparative Survey aims to elucidate the factors shaping these unique microbial communities and their biogeography by integrating molecular genetic approaches with biogeochemical analyses. Although the microbial communities of Dry Valley soils may be complex, there is little doubt that the ecosystem's food web is relatively simple, and evidence suggests that physicochemical conditions may have the dominant role in shaping microbial communities. To examine this hypothesis, bacterial communities from representative soil samples collected in four geographically disparate Dry Valleys were analyzed using molecular genetic tools, including pyrosequencing of 16S rRNA gene PCR amplicons. Results show that the four communities are structurally and phylogenetically distinct, and possess significantly different levels of diversity. Strikingly, only 2 of 214 phylotypes were found in all four valleys, challenging a widespread assumption that the microbiota of the Dry Valleys is composed of a few cosmopolitan species. Analysis of soil geochemical properties indicated that salt content, alongside altitude and Cu2+, was significantly correlated with differences in microbial communities. Our results indicate that the microbial ecology of Dry Valley soils is highly localized and that physicochemical factors potentially have major roles in shaping the microbiology of ice-free areas of Antarctica. These findings hint at links between Dry Valley glacial geomorphology and microbial ecology, and raise previously unrecognized issues related to environmental management of this unique ecosystem. PMID:22170424

The Foote House (10-AA-96), An Historic Archaeological Complex in the Boise River Canyon, Idaho.

DTIC Science & Technology

1982-01-01

into four or perhaps five basic rooms, three of which opened into one another (Paul 1972:293). The main front entrance faced west, and consisted of low...sediments were dry screened through 1/4 in. hardward mesh. Four areas in or adjacent to the Foote House were tested to provide structural and (if possible...down into the soil matrix through the first excavation level, to 10 cm depth. At this level, in the northwest quadrant of the unit, a thin layer of

[Abnormal of tear lipid layer and recent advances in clinical study of dry eye].

PubMed

Xiao, Xin-Ye; Liu, Zu-Guo

2012-03-01

Dry eye is a common disease in the ophthalmological clinic, which is related to the dysfunction of tear film. The tear film is composed of lipid layer, aqueous layer and mucin layer (or lipid layer, aqueous/mucin layer). The lipid of the outmost layer derived from Meibomian gland and distributed on the tear film after blinking can decrease the evaporation and stabilize the tear film. The thickness, quality, and distribution of lipid layer are impaired in many dry eye patients, hence restoring the physiological function of lipid layer may be crucial for the treatment of this kind of dry eye. The lipid artificial tears manifest great effects on increasing lipid layer thickness, stabilizing tear film, improving Meibomian gland dysfunction, and promoting tear film distribution.

Visible-near infrared spectroscopy as a tool to improve mapping of soil properties

NASA Astrophysics Data System (ADS)

Evgrafova, Alevtina; Kühnel, Anna; Bogner, Christina; Haase, Ina; Shibistova, Olga; Guggenberger, Georg; Tananaev, Nikita; Sauheitl, Leopold; Spielvogel, Sandra

2017-04-01

Spectroscopic measurements, which are non-destructive, precise and rapid, can be used to predict soil properties and help estimate the spatial variability of soil properties at the pedon scale. These estimations are required for quantifying soil properties with higher precision, identifying the changes in soil properties and ecosystem response to climate change as well as increasing the estimation accuracy of soil-related models. Our objectives were to (i) predict soil properties for nested samples (n = 296) using the laboratory-based visible-near infrared (vis-NIR) spectra of air-dried (<2 mm) soil samples and values of measured soil properties for gridded samples (n = 174) as calibration and validation sets; (ii) estimate the precision and predictive accuracy of an empirical spectral model using (a) our own spectral library and (b) the global spectral library; (iii) support the global spectral library with obtained vis-NIR spectral data on permafrost-affected soils. The soil samples were collected from three permafrost-affected soil profiles underlain by permafrost at various depths between 23 cm to 57.5 cm below the surface (Cryosols) and one soil profile with no presence of permafrost within the upper 100 cm layer (Cambisol) in order to characterize the spatial distribution and variability of soil properties. The gridded soil samples (n = 174) were collected using an 80 cm wide grid with a mesh size of 10 cm on both axes. In addition, 300 nested soil samples were collected using a grid of 12 cm by 12 cm (25 samples per grid) from a hole of 1 cm in a diameter with a distance from the next sample of 1 cm. Due to a small amount of available soil material (< 1.5 g), 296 nested soil samples were analyzed only using vis-NIR spectroscopy. The air-dried mineral gridded soil samples (n = 174) were sieved through a 2-mm sieve and ground with an agate mortar prior to the elemental analysis. The soil organic carbon and total nitrogen concentrations (in %) were determined using a dry combustion method on the Vario EL cube analyzer (Elementar Analysensysteme GmbH, Germany). Inorganic C was removed from the mineral soil samples with pH values higher than 7 prior to the elemental analysis using the volatilization method (HCl, 6 hours). The pH of soil samples was measured in 0.01 M CaCl2 using a 1:2 soil:solution ratio. However, for soil sample with a high in organic matter content, a 1:10 ratio was applied. We also measured oxalate and dithionite extracted iron, aluminum and manganese oxides and hydroxides using inductively coupled plasma optical emission spectroscopy (Varian Vista MPX ICP-OES, Agilent Technologies, USA). We predicted the above-mentioned soil properties for all nested samples using partial least squares regression, which was performed using R program. We can conclude that vis-NIR spectroscopy can be used effectively in order to describe, estimate and further map the spatial patterns of soil properties using geostatistical methods. This research could also help to improve the global soil spectral library taking into account that only few previous applications of vis-NIR spectroscopy were conducted on permafrost-affected soils of Northern Siberia. Keywords: Visible-near infrared spectroscopy, vis-NIR, permafrost-affected soils, Siberia, partial least squares regression.

[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.

AIR DRYING AND PRETREATMENT EFFECTS ON SOIL SULFATE SORPTION

EPA Science Inventory

Drying, freezing, and refrigeration are commonly employed to facilitate the handling and storage of soil samples on which chemical, biological and physical analyses are to be performed. hese laboratory protocol have the potential to alter soil chemical characteristics and may res...

A prelanding assessment of the ice table depth and ground ice characteristics in Martian permafrost at the Phoenix landing site

USGS Publications Warehouse

Mellon, M.T.; Boynton, W.V.; Feldman, W.C.; Arvidson, R. E.; Titus, Joshua T.N.; Bandfield, L.; Putzig, N.E.; Sizemore, H.G.

2009-01-01

We review multiple estimates of the ice table depth at potential Phoenix landing sites and consider the possible state and distribution of subsurface ice. A two-layer model of ice-rich material overlain by ice-free material is consistent with both the observational and theoretical lines of evidence. Results indicate ground ice to be shallow and ubiquitous, 2-6 cm below the surface. Undulations in the ice table depth are expected because of the thermodynamic effects of rocks, slopes, and soil variations on the scale of the Phoenix Lander and within the digging area, which can be advantageous for analysis of both dry surficial soils and buried ice-rich materials. The ground ice at the ice table to be sampled by the Phoenix Lander is expected to be geologically young because of recent climate oscillations. However, estimates of the ratio of soil to ice in the ice-rich subsurface layer suggest that that the ice content exceeds the available pore space, which is difficult to reconcile with existing ground ice stability and dynamics models. These high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity, initially high-porosity soils, or the migration of water along thin films. Measurement of the D/H ratio within the ice at the ice table and of the soil-to-ice ratio, as well as imaging ice-soil textures, will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable. Copyright 2008 by the American Geophysical Union.

Advances in understanding, models and parameterisations of biosphere-atmosphere ammonia exchange

NASA Astrophysics Data System (ADS)

Flechard, C. R.; Massad, R.-S.; Loubet, B.; Personne, E.; Simpson, D.; Bash, J. O.; Cooter, E. J.; Nemitz, E.; Sutton, M. A.

2013-03-01

Atmospheric ammonia (NH3) dominates global emissions of total reactive nitrogen (Nr), while emissions from agricultural production systems contribute about two thirds of global NH3 emissions; the remaining third emanates from oceans, natural vegetation, humans, wild animals and biomass burning. On land, NH3 emitted from the various sources eventually returns to the biosphere by dry deposition to sink areas, predominantly semi-natural vegetation, and by wet and dry deposition as ammonium (NH4+) to all surfaces. However, the land/atmosphere exchange of gaseous NH3 is in fact bi-directional over unfertilized as well as fertilized ecosystems, with periods and areas of emission and deposition alternating in time (diurnal, seasonal) and space (patchwork landscapes). The exchange is controlled by a range of environmental factors, including meteorology, surface layer turbulence, thermodynamics, air and surface heterogeneous-phase chemistry, canopy geometry, plant development stage, leaf age, organic matter decomposition, soil microbial turnover, and, in agricultural systems, by fertilizer application rate, fertilizer type, soil type, crop type, and agricultural management practices. We review the range of processes controlling NH3 emission and uptake in the different parts of the soil-canopy-atmosphere continuum, with NH3 emission potentials defined at the substrate and leaf levels by different [NH4+] / [H+] ratios (Γ). Surface/atmosphere exchange models for NH3 are necessary to compute the temporal and spatial patterns of emissions and deposition at the soil, plant, field, landscape, regional and global scales, in order to assess the multiple environmental impacts of air-borne and deposited NH3 and NH4+. Models of soil/vegetation/atmosphereem NH3 exchange are reviewed from the substrate and leaf scales to the global scale. They range from simple steady-state, "big leaf" canopy resistance models, to dynamic, multi-layer, multi-process, multi-chemical species schemes. Their level of complexity depends on their purpose, the spatial scale at which they are applied, the current level of parameterisation, and the availability of the input data they require. State-of-the-art solutions for determining the emission/sink Γ potentials through the soil/canopy system include coupled, interactive chemical transport models (CTM) and soil/ecosystem modelling at the regional scale. However, it remains a matter for debate to what extent realistic options for future regional and global models should be based on process-based mechanistic versus empirical and regression-type models. Further discussion is needed on the extent and timescale by which new approaches can be used, such as integration with ecosystem models and satellite observations.

Advances in understanding, models and parameterizations of biosphere-atmosphere ammonia exchange

NASA Astrophysics Data System (ADS)

Flechard, C. R.; Massad, R.-S.; Loubet, B.; Personne, E.; Simpson, D.; Bash, J. O.; Cooter, E. J.; Nemitz, E.; Sutton, M. A.

2013-07-01

Atmospheric ammonia (NH3) dominates global emissions of total reactive nitrogen (Nr), while emissions from agricultural production systems contribute about two-thirds of global NH3 emissions; the remaining third emanates from oceans, natural vegetation, humans, wild animals and biomass burning. On land, NH3 emitted from the various sources eventually returns to the biosphere by dry deposition to sink areas, predominantly semi-natural vegetation, and by wet and dry deposition as ammonium (NH4+) to all surfaces. However, the land/atmosphere exchange of gaseous NH3 is in fact bi-directional over unfertilized as well as fertilized ecosystems, with periods and areas of emission and deposition alternating in time (diurnal, seasonal) and space (patchwork landscapes). The exchange is controlled by a range of environmental factors, including meteorology, surface layer turbulence, thermodynamics, air and surface heterogeneous-phase chemistry, canopy geometry, plant development stage, leaf age, organic matter decomposition, soil microbial turnover, and, in agricultural systems, by fertilizer application rate, fertilizer type, soil type, crop type, and agricultural management practices. We review the range of processes controlling NH3 emission and uptake in the different parts of the soil-canopy-atmosphere continuum, with NH3 emission potentials defined at the substrate and leaf levels by different [NH4+] / [H+] ratios (Γ). Surface/atmosphere exchange models for NH3 are necessary to compute the temporal and spatial patterns of emissions and deposition at the soil, plant, field, landscape, regional and global scales, in order to assess the multiple environmental impacts of airborne and deposited NH3 and NH4+. Models of soil/vegetation/atmosphere NH3 exchange are reviewed from the substrate and leaf scales to the global scale. They range from simple steady-state, "big leaf" canopy resistance models, to dynamic, multi-layer, multi-process, multi-chemical species schemes. Their level of complexity depends on their purpose, the spatial scale at which they are applied, the current level of parameterization, and the availability of the input data they require. State-of-the-art solutions for determining the emission/sink Γ potentials through the soil/canopy system include coupled, interactive chemical transport models (CTM) and soil/ecosystem modelling at the regional scale. However, it remains a matter for debate to what extent realistic options for future regional and global models should be based on process-based mechanistic versus empirical and regression-type models. Further discussion is needed on the extent and timescale by which new approaches can be used, such as integration with ecosystem models and satellite observations.

Root distribution of Nitraria sibirica with seasonally varying water sources in a desert habitat.

PubMed

Zhou, Hai; Zhao, Wenzhi; Zheng, Xinjun; Li, Shoujuan

2015-07-01

In water-limited environments, the water sources used by desert shrubs are critical to understanding hydrological processes. Here we studied the oxygen stable isotope ratios (δ (18)O) of stem water of Nitraria sibirica as well as those of precipitation, groundwater and soil water from different layers to identify the possible water sources for the shrub. The results showed that the shrub used a mixture of soil water, recent precipitation and groundwater, with shallow lateral roots and deeply penetrating tap (sinker) roots, in different seasons. During the wet period (in spring), a large proportion of stem water in N. sibirica was from snow melt and recent precipitation, but use of these sources declined sharply with the decreasing summer rain at the site. At the height of summer, N. sibirica mainly utilized deep soil water from its tap roots, not only supporting the growth of shoots but also keeping the shallow lateral roots well-hydrated. This flexibility allowed the plants to maintain normal metabolic processes during prolonged periods when little precipitation occurs and upper soil layers become extremely dry. With the increase in precipitation that occurs as winter approaches, the percentage of water in the stem base of a plant derived from the tap roots (deep soil water or ground water) decreased again. These results suggested that the shrub's root distribution and morphology were the most important determinants of its ability to utilize different water sources, and that its adjustment to water availability was significant for acclimation to the desert habitat.

Snow Water Equivalent Retrieval By Markov Chain Monte Carlo Based on Memls and Hut Snow Emission Model

NASA Astrophysics Data System (ADS)

Pan, J.; Durand, M. T.; Vanderjagt, B. J.

2014-12-01

The Markov chain Monte Carlo (MCMC) method had been proved to be successful in snow water equivalent retrieval based on synthetic point-scale passive microwave brightness temperature (TB) observations. This method needs only general prior information about distribution of snow parameters, and could estimate layered snow properties, including the thickness, temperature, density and snow grain size (or exponential correlation length) of each layer. In this study, the multi-layer HUT (Helsinki University of Technology) model and the MEMLS (Microwave Emission Model of Layered Snowpacks) will be used as observation models to assimilate the observed TB into snow parameter prediction. Previous studies had shown that the multi-layer HUT model tends to underestimate TB at 37 GHz for deep snow, while the MEMLS does not show sensitivity of model bias to snow depth. Therefore, results using HUT model and MEMLS will be compared to see how the observation model will influence the retrieval of snow parameters. The radiometric measurements at 10.65, 18.7, 36.5 and 90 GHz at Sodankyla, Finland will be used as MCMC input, and the statistics of all snow property measurement will be used to calculate the prior information. 43 dry snowpits with complete measurements of all snow parameters will be used for validation. The entire dataset are from NorSREx (Nordic Snow Radar Experiment) experiments carried out by Juha Lemmetyinen, Anna Kontu and Jouni Pulliainen in FMI in 2009-2011 winters, and continued two more winters from 2011 to Spring of 2013. Besides the snow thickness and snow density that are directly related to snow water equivalent, other parameters will be compared with observations, too. For thin snow, the previous studies showed that influence of underlying soil is considerable, especially when the soil is half frozen with part of unfrozen liquid water and part of ice. Therefore, this study will also try to employ a simple frozen soil permittivity model to improve the performance of retrieval. The behavior of the Markov chain in soil parameters will be studied.

Stomatal Conductance, Plant Hydraulics, and Multilayer Canopies: A New Paradigm for Earth System Models or Unnecessary Uncertainty

NASA Astrophysics Data System (ADS)

Bonan, G. B.

2016-12-01

Soil moisture stress is a key regulator of canopy transpiration, the surface energy budget, and land-atmosphere coupling. Many land surface models used in Earth system models have an ad-hoc parameterization of soil moisture stress that decreases stomatal conductance with soil drying. Parameterization of soil moisture stress from more fundamental principles of plant hydrodynamics is a key research frontier for land surface models. While the biophysical and physiological foundations of such parameterizations are well-known, their best implementation in land surface models is less clear. Land surface models utilize a big-leaf canopy parameterization (or two big-leaves to represent the sunlit and shaded canopy) without vertical gradients in the canopy. However, there are strong biometeorological and physiological gradients in plant canopies. Are these gradients necessary to resolve? Here, I describe a vertically-resolved, multilayer canopy model that calculates leaf temperature and energy fluxes, photosynthesis, stomatal conductance, and leaf water potential at each level in the canopy. In this model, midday leaf water stress manifests in the upper canopy layers, which receive high amounts of solar radiation, have high leaf nitrogen and photosynthetic capacity, and have high stomatal conductance and transpiration rates (in the absence of leaf water stress). Lower levels in the canopy become water stressed in response to longer-term soil moisture drying. I examine the role of vertical gradients in the canopy microclimate (solar radiation, air temperature, vapor pressure, wind speed), structure (leaf area density), and physiology (leaf nitrogen, photosynthetic capacity, stomatal conductance) in determining above canopy fluxes and gradients of transpiration and leaf water potential within the canopy.

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.

A toxicity test in artificial soil based on the life-history strategy of the nematode Plectus acuminatus

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

Kammenga, J.E.; Van Koert, P.H.G.; Riksen, J.A.G.

1996-05-01

The ecological risk assessment of toxicants in soil requires reproducible and relevant test systems using a wide range of species. To supplement present test methods from the Organisation of Economic Cooperation and Development (OECD) in artificial soil with earthworms and springtails, a toxicity test in OECD artificial soil has been developed using the bacterivorous nematode Plectus acuminatus (Bastian, 1865) (Nematoda; Plectidae). The juvenile to adult ratio was used as a test parameter since previous life-cycle studies pointed out that fitness of P. acuminatus was strongly determined by changes in both reproduction and juvenile survival. Optimal conditions for the performance ofmore » nematodes in OECD artificial soil were determined (pH{sub KCl} = 5.5, temperature = 20C, and a moisture content of 70% dry wt. artificial soil), and tests were conducted with cadmium, copper, and pentachlorophenol. After an exposure period of 3 weeks the EC50 for cadmium was 321.0 {+-} 1.7 mg/kg dry wt., and the no-observed-effect concentration (NOEC) was 32 mg/kg dry wt. The EC50 for pentachlorophenol was 47.9 {+-} 1.2 mg/kg dry wt., and the NOEC was <10 mg/kg dry wt. For copper the EC50 was 162 {+-} 0.2 mg/kg dry wt., and the NOEC was 32 mg/kg dry wt. It is concluded that the nematode test may well supplement current coil test systems using earthworms and springtails.« less

Soil water storage, rainfall and runoff relationships in a tropical dry forest catchment

NASA Astrophysics Data System (ADS)

Farrick, Kegan K.; Branfireun, Brian A.

2014-12-01

In forested catchments, the exceedance of rainfall and antecedent water storage thresholds is often required for runoff generation, yet to our knowledge these threshold relationships remain undescribed in tropical dry forest catchments. We, therefore, identified the controls of streamflow activation and the timing and magnitude of runoff in a tropical dry forest catchment near the Pacific coast of central Mexico. During a 52 day transition phase from the dry to wet season, soil water movement was dominated by vertical flow which continued until a threshold soil moisture content of 26% was reached at 100 cm below the surface. This satisfied a 162 mm storage deficit and activated streamflow, likely through lateral subsurface flow pathways. High antecedent soil water conditions were maintained during the wet phase but had a weak influence on stormflow. We identified a threshold value of 289 mm of summed rainfall and antecedent soil water needed to generate >4 mm of stormflow per event. Above this threshold, stormflow response and magnitude was almost entirely governed by rainfall event characteristics and not antecedent soil moisture conditions. Our results show that over the course of the wet season in tropical dry forests the dominant controls on runoff generation changed from antecedent soil water and storage to the depth of rainfall.

Differential response of ammonia-oxidizing archaea and bacteria to the wetting of salty arid soil.

PubMed

Sher, Yonatan; Ronen, Zeev; Nejidat, Ali

2016-08-01

Ammonia-oxidizing archaea and bacteria (AOA, AOB) catalyze the first and rate-limiting step of nitrification. To examine their differential responses to the wetting of dry and salty arid soil, AOA and AOB amoA genes (encoding subunit A of the ammonia monooxygenase) and transcripts were enumerated in dry (summer) and wet (after the first rainfall) soil under the canopy of halophytic shrubs and between the shrubs. AOA and AOB were more abundant under shrub canopies than between shrubs in both the dry and wetted soil. Soil wetting caused a significant decrease in AOB abundance under the canopy and an increase of AOA between the shrubs. The abundance of the archaeal amoA gene transcript was similar for both the wet and dry soil, and the transcript-to-gene ratios were < 1 independent of niche or water content. In contrast, the bacterial amoA transcript-to-gene ratios were between 78 and 514. The lowest ratio was in dry soil under the canopy and the highest in the soil between the shrubs. The results suggest that the AOA are more resilient to stress conditions and maintain a basic activity in arid ecosystems, while the AOB are more responsive to changes in the biotic and abiotic conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Soil greenhouse gas flux, soil moisture, and soil temperature variability among three plant communities from 2015 to 2017 in a High-Arctic lake basin, Northwest Greenland

NASA Astrophysics Data System (ADS)

Konkel, J. M.; Welker, J. M.; Schaeffer, S. M.

2017-12-01

Soil greenhouse gas flux rates are known to vary with plant community and soil environment. Increases in temperature and precipitation are likely to affect the distribution of vegetation and soil conditions in High Arctic ecosystems. In coastal tundra landscapes in northwest Greenland, vegetation, soil organic matter, and greenhouse gas fluxes are thought to be controlled primarily by water availability. In this study, we measured greenhouse gas flux rates, soil moisture, and soil temperature over three summer seasons along a soil moisture gradient in a High Arctic lake basin represented by dry tundra, moist tundra, and wet grassland plant communities. Preliminary results for trace gas fluxes showed N2O production from all three plant communities ranged from 0.03±0.03 to 0.48±0.12 g N ha-1d-1. While wet grassland was a CH4 source up to 5.2±1.1 g C ha-1d-1, dry tundra and moist tundra were CH4 sinks up to -10.4±1.7 and -2.2±0.9 g C ha-1d-1, respectively. For all three seasons, the highest and lowest mean soil CO2 flux rates were measured in wet grassland and moist tundra (up to 18.3±1.1 and 8.7±0.6 kg C ha-1 d-1, respectively). A lab incubation study showed that, with frequent wetting events, soil CO2 flux remained relatively high in wet grassland, was consistently higher in dry tundra than in moist tundra, and dry tundra CO2 flux significantly increased with wetting events. We show that while soil CO2 flux in all three vegetation zones was influenced by soil moisture variability, soil temperature clearly influenced the timing of flux rate increases and decreases over the course of each season. Colder air and soil temperatures in 2017 corresponded with decreased mean soil CO2 flux rates in dry tundra and wet grassland, yet CO2 flux rates remained consistent in moist tundra among all three seasons. These results suggest that climate-induced warmer and wetter soil environmental conditions may increase rates of soil CO2 flux from wet grassland and dry tundra. Further, changes in the distribution of plant communities under future climate scenarios may significantly alter the function of High Arctic lake basins as CH4 sinks or sources, which will be dependent upon the ground area of wet grassland relative to that of dry tundra and moist tundra.

Response of respiration and nutrient availability to drying and rewetting in soil from a semi-arid woodland depends on vegetation patch and a recent wildfire

NASA Astrophysics Data System (ADS)

Sun, Q.; Meyer, W. S.; Koerber, G. R.; Marschner, P.

2015-08-01

Semi-arid woodlands, which are characterised by patchy vegetation interspersed with bare, open areas, are frequently exposed to wildfire. During summer, long dry periods are occasionally interrupted by rainfall events. It is well known that rewetting of dry soil induces a flush of respiration. However, the magnitude of the flush may differ between vegetation patches and open areas because of different organic matter content, which could be further modulated by wildfire. Soils were collected from under trees, under shrubs or in open areas in unburnt and burnt sandy mallee woodland, where part of the woodland experienced a wildfire which destroyed or damaged most of the aboveground plant parts 4 months before sampling. In an incubation experiment, the soils were exposed to two moisture treatments: constantly moist (CM) and drying and rewetting (DRW). In CM, soils were incubated at 80 % of maximum water holding capacity (WHC) for 19 days; in DRW, soils were dried for 4 days, kept dry for another 5 days, then rewetted to 80 % WHC and maintained at this water content until day 19. Soil respiration decreased during drying and was very low in the dry period; rewetting induced a respiration flush. Compared to soil under shrubs and in open areas, cumulative respiration per gram of soil in CM and DRW was greater under trees, but lower when expressed per gram of total organic carbon (TOC). Organic matter content, available P, and microbial biomass C, but not available N, were greater under trees than in open areas. Wild fire decreased the flush of respiration per gram of TOC in the open areas and under shrubs, and reduced TOC and microbial biomass C (MBC) concentrations only under trees, but had little effect on available N and P concentrations. We conclude that the impact of wildfire and DRW events on nutrient cycling differs among vegetation patches of a native semi-arid woodland which is related to organic matter amount and availability.

[Contribution of soil water at various depths to water consumption of rainfed winter wheat in the Loess tableland, China].

PubMed

Cheng, Li Ping; Liu, Wen Zhao

2017-07-18

Soil water and stem water were collected in jointing and heading stages of the rainfed winter wheat in the Changwu Loess tableland, and the stable isotopic compositions of hydrogen and oxygen in water samples were measured to analyze the contribution of soil water at various depths to water consumption of winter wheat. The results showed that the isotopes were enriched in soil and wheat stem water in comparison with that in precipitation. Under the condition of no dry layer in soil profile, the contributions to wheat water consumption in jointing and heading stages were 5.4% and 2.6% from soil water at 0-30 cm depth, 73.4% and 67.3% at 60-90 cm depth (the main water source for winter wheat), and 7.9% and 13.5% below 120 cm depth, respectively. With the wheat growth, the contribution of soil water below the depth of 90 cm increased. It was concluded that soil evaporation mainly consumed soil water in 0-30 cm depth and wheat transpiration mainly consumed soil water below 60 cm depth in the experimental period. In the production practice, it is necessary to increase rainwater storage ratio during the summer fallow period, and apply reasonable combination of nitrogen and phosphorus fertilizers in order to increase soil moisture before wheat sowing, promote the wheat root developing deep downwards and raise the deep soil water utilization ratio.

Mineralization of carbon and nitrogen from freeze- and over-dried plant material added to soil

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

Moorhead, K.K.; Graetz, D.A.; Reddy, K.R.

Drying organic material before soil incorporation is a common procedure used in mineralization or decomposition studies. A laboratory study was conducted to determine the effect of drying methods on plant C and N and associated mineralization patterns in soil. Freeze- and oven-dried water hyacinth (Eichhornia crassipes (Mart) Solms) was added to a Kendrick soil (loamy, siliceous, hyperthermic Arenic Paleudults) at a rate of 5 g kg{sup {minus}1} and incubated in the dark at 27{degree}C for 90 d. Oven drying in paper bags significantly increased the lignin content and decreased the mineral content of the plant material compared to freeze drying.more » The total C and N was not significantly different for the two materials. The mineralization of C from freeze-dried plant material was more rapid during the initial stage of decomposition and remained significantly higher throughout the incubation. At 90 d, 50, and 41% of the plant C had evolved as CO{sub 2} for the freeze- and oven-dried plant material, respectively. Mineralization of {sup 15}N from the plant material accounted for 33% of the applied N of the freeze-dried material and 23% of the applied N of the oven-dried material. Nitrogen mineralization and CO{sub 2} evolution were linearly correlated (r=0.998) for the oven-dried plant material, but less correlated (r=0.770) for the freeze-dried material.« less

Uncovering the effects of Arundo invasion & forest restoration on riparian soils: Plant controls on microbial processes & trace gas flux in a California watershed

NASA Astrophysics Data System (ADS)

Dowdy, K. L.; Dudley, T.; Schimel, J.

2016-12-01

The opportunistic reed Arundo donax has invaded riparian zones in many California watersheds, altering hydrological and ecological processes. There have been intense efforts to restore these watersheds to native vegetation. How the shifts in communities—native to invaded to restored—affect soil conditions and processes, however, remains unclear. Because riparian zones are hotspots of nutrient cycling and greenhouse gas flux, it is critical to understand how plant community composition (and associated litter contributions) governs riparian biogeochemistry. How do organic matter inputs in invaded and restored plant communities alter soil microbial processes and trace gas dynamics? In this study, we use laboratory incubations to compare microbial cycling of C and nitrogen (N) and trace gas flux between the soils and litter of the invasive Arundo and three native riparian species: Populus tricocarpa, Salix laevigata, and Baccharis salicifolia (or, black cotton wood, red willow, and mulefat). Soils beneath Arundo and Salix produced CO2 at a similar rate ( 250 ug CO2 g dry soil-1 hour-1), while Populus and Baccharis produced less ( 170 ug CO2 g dry soil-1 hour-1). All soils consumed CH4; however, Arundo soils consumed more than native-restored species, which consumed similar quantities (-0.013 CH4 g dry soil-1 hour-1 in Arundo vs. -0.009 CH4 g dry soil-1 hour-1 in native). Arundo soils also produced less N2O (0.02 ug N2O g dry soil-1 hour-1) than all native species ( 0.09 ug N2O g dry soil-1 hour-1). Arundo contributed far less litter inputs than native-restored species, as Arundo leaves senesce and remain on the stalk; furthermore, Arundo litter has been shown to have a higher C:N (40.2) than Salix and Baccharis (30.9). Greater CH4 consumption and lower N2O production in Arundo soils may be the result of enhanced porosity compared to restored soils, leading to more aeration and less methanogenesis and denitrification, or it may be that there is lower N availability in Arundo soils suppressing nitrification and reducing NH4- inhibition of methanotrophs.

Impact of biochar amendment on soil water soluble carbon in the context of extreme hydrological events.

PubMed

Wang, Daoyuan; Griffin, Deirdre E; Parikh, Sanjai J; Scow, Kate M

2016-10-01

Biochar amendments to soil have been promoted as a low cost carbon (C) sequestration strategy as well as a way to increase nutrient retention and remediate contaminants. If biochar is to become part of a long-term management strategy, it is important to consider its positive and negative impacts, and their trade-offs, on soil organic matter (SOM) and soluble C under different hydrological conditions such as prolonged drought or frequent wet-dry cycles. A 52-week incubation experiment measuring the influence of biochar on soil water soluble C under different soil moisture conditions (wet, dry, or wet-dry cycles) indicated that, in general, dry and wet-dry cycles increased water soluble C, and biochar addition further increased release of water soluble C from native SOM. Biochar amendment appeared to increase transformation of native SOM to water soluble C, based on specific ultraviolet absorption (SUVA) and C stable isotope composition; however, the increased amount of water soluble C from native SOM is less than 1% of total biochar C. The impacts of biochar on water soluble C need to be carefully considered when applying biochar to agricultural soil. Copyright © 2016 Elsevier Ltd. All rights reserved.

In-filled reservoirs serving as sediment archives to analyse soil organic carbon erosion - A case study from the Karoo rangelands

NASA Astrophysics Data System (ADS)

Krenz, Juliane; Greenwood, Philip; Heckrath, Goswin; Kuhn, Brigitte; Kuhn, Nikolaus

2017-04-01

Covering about 41 % of the Earth's Land Surface drylands provide a range of ecosystem services for more than one third of the world population. Threatened by climate change and incorrect land use their natural land cover is changing and land degradation is one of their major problems. The semi-arid rangelands of the Great Karoo region in South Africa are just one example of a region that has experienced a number of environmental changes. After European farmers settled in the late 18th century agricultural activities increased, leading to overgrazing and probably representing a trigger to land degradation. As a consequence of a higher water demand and shifting rainfall patterns many dams and small reservoirs have been constructed to provide drinking water for cattle or to facilitate irrigation during dry periods. High erosion rates lead to a fast filling-up of reservoirs and thereby reduced their storage capacities. Thus, most of the dams are nowadays dry (filled with sediment) or even breached. In this ongoing project, a combination of analytical methods that include drone imagery, landscape mapping, erosion modelling and sediment analysis have been employed to determine whether land degradation in the Karoo has resulted in the reversion from a net sink of C to a net source of C. Sediment deposits from three silted-up reservoirs were analysed for varying physicochemical parameters, in order to analyse and reconstruct erosional and depositional patterns. A sharp decrease in total carbon content with decreasing depth for two reservoirs suggests that land degradation during and after the post-European settlement most likely triggered erosion of the relatively fertile surface soils, which presumably in-filled the reservoirs. It is assumed that the carbon-rich bottom layers of the dam deposits originate from these eroded surface soils. Low organic Carbon (OC) content in the top layers of the reservoir in-fill, and in the eroded source areas, supports the assumption that the eroded material was transported from the degraded areas down into the reservoir, where it settled. This raises a crucial question of whether the decline of C sinks in degraded rangelands due to exacerbated soil erosion may have had a greater attenuating effect on GHG emissions than modelled scenarios of present emissions suggest. The slight decrease of TOC with increasing depth for the third reservoir might imply differences in geochemical cycling between dried out dams and reservoirs with continuous throughflow.

Controls on the distribution of productivity and organic resources in Antarctic Dry Valley soils.

PubMed

Hopkins, D W; Sparrow, A D; Novis, P M; Gregorich, E G; Elberling, B; Greenfield, L G

2006-11-07

The Antarctic Dry Valleys are regarded as one of the harshest terrestrial habitats on Earth because of the extremely cold and dry conditions. Despite the extreme environment and scarcity of conspicuous primary producers, the soils contain organic carbon and heterotrophic micro-organisms and invertebrates. Potential sources of organic compounds to sustain soil organisms include in situ primary production by micro-organisms and mosses, spatial subsidies from lacustrine and marine-derived detritus, and temporal subsidies ('legacies') from ancient lake deposits. The contributions from these sources at different sites are likely to be influenced by local environmental conditions, especially soil moisture content, position in the landscape in relation to lake level oscillations and legacies from previous geomorphic processes. Here we review the abiotic factors that influence biological activity in Dry Valley soils and present a conceptual model that summarizes mechanisms leading to organic resources therein.

Short and Long-Term Soil Moisture Effects of Liana Removal in a Seasonally Moist Tropical Forest

PubMed Central

Reid, Joseph Pignatello; Schnitzer, Stefan A.; Powers, Jennifer S.

2015-01-01

Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increasing in the neotropics. Lianas can compete intensely with trees for above- and belowground resources, including water. As tropical forests experience longer and more intense dry seasons, competition for water is likely to intensify. However, we lack an understanding of how liana abundance affects soil moisture and hence competition with trees for water in tropical forests. To address this critical knowledge gap, we conducted a large-scale liana removal experiment in a seasonal tropical moist forest in central Panama. We monitored shallow and deep soil moisture over the course of three years to assess the effects of lianas in eight 0.64 ha removal plots and eight control plots. Liana removal caused short-term effects in surface soils. Surface soils (10 cm depth) in removal plots dried more slowly during dry periods and accumulated water more slowly after rainfall events. These effects disappeared within four months of the removal treatment. In deeper soils (40 cm depth), liana removal resulted in a multi-year trend towards 5–25% higher soil moisture during the dry seasons with the largest significant effects occurring in the dry season of the third year following treatment. Liana removal did not affect surface soil temperature. Multiple and mutually occurring mechanisms may be responsible for the effects of liana removal on soil moisture, including competition with trees, and altered microclimate, and soil structure. These results indicate that lianas influence hydrologic processes, which may affect tree community dynamics and forest carbon cycling. PMID:26545205

Physical and ecological controllers of the microbial responses to drying and rewetting in soil

NASA Astrophysics Data System (ADS)

Leizeaga, Ainara; Meisner, Annelein; Bååth, Erland; Rousk, Johannes

2017-04-01

Soil moisture is one of the most powerful factors that regulate microbial activity in soil. The variation of moisture leads to drying-rewetting (DRW) events which are known to induce enormous dynamics in soil biogeochemistry; however, the microbial underpinnings are mostly unknown. Rewetting a dry soil can result in two response patterns of bacterial growth. In the Type 1 response, bacteria start growing immediately after rewetting with rates that increase in a linear fashion to converge with those prior to the DRW within hours. This growth response coincides with respiration rates that peak immediately after rewetting to then exponentially decrease. In the Type 2 response, bacterial growth remains very low after rewetting during a lag period of up to 20 hours. Bacteria then increase their growth rates exponentially to much higher rates than those before the DRW event. This growth response coincides with respiration rates that increase to high rates immediately after rewetting that then remain elevated and sometimes even increase further in sync with the growth increase. Previous studies have shown that (i) extended drying (ii) starving before DRW and (iii) inhibitors combined with drought could change the bacterial response from Type 1 to Type 2. This suggested that the response of bacteria upon rewetting could be related to the harshness of the disturbance as experienced by the microbes. In the present study, we set out to study if reduced harshness could change a Type 2 response into a Type 1 response. We hypothesized that (1) a reduced physical harshness of drying and (2) induced tolerance to drying in microbial communities could change a Type 2 response into a Type 1 growth response upon rewetting. To address this, two experiments were performed. First, soils were partially dried to different water contents and bacterial response upon rewetting was measured. Second, soils were exposed to repeated DRW cycles (< 9 cycles) and the bacterial response was followed after rewetting. A less harsh drying (partial drying) of a soil could change the growth responses to rewetting. The lag period decreased with less complete drying to eventually became 0, transitioning from a Type 2 to a Type 1. Even after a Type 1 response was induced, further reduction of harshness could also lead to a faster recovery of growth rates. Our results support the hypothesis: the physical harshness of drying can determine the microbial survival and thus the type of bacterial growth response. Subjecting soil to DRW cycles could also induce a change from a Type 2 to Type 1 growth response. This suggested that there was a community shift towards higher drought-tolerance. Thus, identical physical disturbance was less harsh for a community that has been subjected to more drying rewetting cycles. To predict how the microbial community's control of the soil C budget of ecosystems is affected warming-induced drought, our results demonstrate that both the physical characteristics of the disturbance and the community's tolerance to drought need to be considered.

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.

Thin Layer Drying Model of Bacterial Cellulose Film

NASA Astrophysics Data System (ADS)

Hadi Jatmiko, Tri; Taufika Rosyida, Vita; Wheni Indrianingsih, Anastasia; Apriyana, Wuri

2017-12-01

The bacterial cellulose film produced by Acetobacter xylinum using coconut water as a carbon source was dried at a temperature of 60 to 100 C. The drying process of bacterial cellulose film occur at falling rate drying period. Increasing drying temperature will shorten the drying time. The drying data fitted with thin layer drying models that widely used, Newton, Page and Henderson and Pabis models. All thin layer drying models describe the experimental data well, but Page model is better than the other models on all various temperature with coefficients of determination (R2) range from 0.9908 to 0.9979, chi square range from 0.000212 to 0.000851 and RMSE range from 0.014307 to 0.0289458.

Tracking nitrogen losses in a greenhouse crop rotation experiment in North China using the EU-Rotate_N simulation model.

PubMed

Guo, Ruiying; Nendel, Claas; Rahn, Clive; Jiang, Chunguang; Chen, Qing

2010-06-01

Vegetable production in China is associated with high inputs of nitrogen, posing a risk of losses to the environment. Organic matter mineralisation is a considerable source of nitrogen (N) which is hard to quantify. In a two-year greenhouse cucumber experiment with different N treatments in North China, non-observed pathways of the N cycle were estimated using the EU-Rotate_N simulation model. EU-Rotate_N was calibrated against crop dry matter and soil moisture data to predict crop N uptake, soil mineral N contents, N mineralisation and N loss. Crop N uptake (Modelling Efficiencies (ME) between 0.80 and 0.92) and soil mineral N contents in different soil layers (ME between 0.24 and 0.74) were satisfactorily simulated by the model for all N treatments except for the traditional N management. The model predicted high N mineralisation rates and N leaching losses, suggesting that previously published estimates of N leaching for these production systems strongly underestimated the mineralisation of N from organic matter. Copyright 2010 Elsevier Ltd. All rights reserved.

Heavy metal speciation and risk assessment in dry land and paddy soils near mining areas at Southern China.

PubMed

Liu, Guannan; Wang, Juan; Zhang, Erxi; Hou, Jing; Liu, Xinhui

2016-05-01

Heavy metal contamination of soils has been a long-standing environmental problem in many parts of the world, and poses enormous threats to ecosystem and human health. Speciation of heavy metals in soils is crucial to assessing environmental risks from contaminated soils. In this study, total concentrations and speciation of As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn were measured for agricultural soils near mines along the Diaojiang River in Guangxi Zhuang Autonomy Region, China. The sources of heavy metals in soils also were identified to assess their effect on speciation distribution of soil heavy metals. Furthermore, the speciation distribution of Cd and Zn, main soil heavy metal pollutants, in dry land and paddy soils were compared. Results showed that there were two severely polluted regions near mine area reaching alarming pollution level. As, Cd, Pb, and Zn were more affected by mining activities, showing very strong pollution level in soils. The mean percentage of exchangeable and carbonate fraction was highest and up to 46.8 % for Cd, indicating a high environmental risk. Greater bioavailable fractions of As, Cd, Cu, Mn, Pb, and Zn were found in soils heavily polluted by mining activities, whereas Cr and Ni as geogenic elements in the stable residual fraction. In addition, in the dry land soils, reducible fraction proportion of Cd was higher than that in the paddy soils, whereas exchangeable and carbonate fraction of Cd was lower than that in the paddy soils. Oxidizable fraction of Zn was higher in the paddy soils than that in the dry land soils. The results indicate that the sources of soil heavy metals and land types affect heavy metal speciation in the soil and are significant for environmental risk assessment of soil heavy metal pollutions.

Effect of biochar addition on short-term N2O and CO2 emissions during repeated drying and wetting of an anthropogenic alluvial soil.

PubMed

Yang, Fang; Lee, Xinqing; Theng, Benny K G; Wang, Bing; Cheng, Jianzhong; Wang, Qian

2017-06-01

Agricultural soils are an important source of greenhouse gases (GHG). Biochar application to such soils has the potential of mitigating global anthropogenic GHG emissions. Under irrigation, the topsoils in arid regions experience repeated drying and wetting during the crop growing season. Biochar incorporation into these soils would change the soil microbial environment and hence affect GHG emissions. Little information, however, is available regarding the effect of biochar addition on carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) emissions from agricultural soils undergoing repeated drying and wetting. Here, we report the results of a 49-day aerobic incubation experiment, incorporating biochar into an anthropogenic alluvial soil in an arid region of Xinjiang Province, China, and measuring CO 2 and N 2 O emissions. Under both drying-wetting and constantly moist conditions, biochar amendment significantly increased cumulative CO 2 emission. At the same time, there was a significant reduction (up to ~20 %) in cumulative N 2 O emission, indicating that the addition of biochar to irrigated agricultural soils may effectively slow down global warming in arid regions of China.

The Influence of Processing Soil With a Coffee Grinder on Soil Classification

DTIC Science & Technology

2015-01-20

shaker, sieves , coffee grinder, plastic limit tool, bowls, spatulas, and scoops. To classify soils, a dry sieve analysis is performed, as is a Plastic...processed with the coffee grinder for 90 seconds as described above. Sieve analysis using the wet preparation method was used to test and classify the soils...one 90 second cycle of Elevator Soil Figure 3: The blades after three 90 second cycles of Elevator Soil 71Page 4.2 Ottawa Sand Dry Sieve Analysis

Roots bridge water to nutrients: a study of utilizing hydraulic redistribution through root systems to extract nutrients in the dry soils

NASA Astrophysics Data System (ADS)

Yan, J.; Ghezzehei, T. A.

2017-12-01

The rhizosphere is the region of soil that surrounds by individual plant roots. While its small volume and narrow region compared to bulk soil, the rhizosphere regulates numerous processes that determine physical structure, nutrient distribution, and biodiversity of soils. One of the most important and distinct functions of the rhizosphere is the capacity of roots to bridge and redistribute soil water from wet soil layers to drier layers. This process was identified and defined as hydraulic lift or hydraulic redistribution, a passive process driven by gradients in water potentials and it has attracted much research attention due to its important role in global water circulation and agriculture security. However, while previous studies mostly focused on the hydrological or physiological impacts of hydraulic redistribution, limited research has been conducted to elucidate its role in nutrient cycling and uptake. In this study, we aim to test the possibility of utilizing hydraulic redistribution to facilitate the nutrient movement and uptake from resource segregated zone. Our overarching hypothesis is that plants can extract nutrients from the drier but nutrient-rich regions by supplying sufficient amounts of water from the wet but nutrient-deficient regions. To test our hypothesis, we designed split-root systems of tomatoes with unequal supply of water and nutrients in different root compartments. More specifically, we transplanted tomato seedlings into sand or soil mediums, and grew them under conditions with alternate 12-h lightness and darkness. We continuously monitored the temperature, water and nutrient content of soils in these separated compartments. The above and below ground biomass were also quantified to evaluate the impacts on the plant growth. The results were compared to a control with evenly supply of water and nutrients to assess the plant growth, nutrient leaching and uptake without hydraulic redistribution.

[Effects of deep plowing time during the fallow period on water storage-consumption characteristics and wheat yield in dry-land soil.

PubMed

Dang, Jian You; Pei, Xue Xia; Zhang, Ding Yi; Wang, Jiao Ai; Zhang, Jing; Wu, Xue Ping

2016-09-01

Through a three-year field trail, effects of deep plowing time during the fallow period on water storage of 0-200 cm soil before sowing, water consumption of growth period, and growth and development of wheat were investigated. Results demonstrated that soil water storage (SWS) of the fallow period was influenced by deep plowing time, precipitation, and rainfall distribution. With postponing the time of deep plowing in the fallow period, SWS was increased firstly, and then decreased. SWS with deep plowing in early or middle of August was 23.9-45.8 mm more than that with deep plowing in mid-July. It would benefit SWS when more precipitation occurred in the fallow period or more rainfall was distributed in August and September. Deep plowing at a proper time could facilitate SWS, N and P absorption of wheat, and the number of stems before winter and the spike number. The yield of wheat with deep plowing in early or middle August was 3.67%-18.2% higher than that with deep plowing in mid-July, and it was positively correlated with water storage of 0-200 cm soil during the fallow period and SWS of each soil layer during the wheat growth period. However, this correlation coefficient would be weakened by adequate rainfall in spring, the critical growing period for wheat. The time of deep plowing mainly affected the water consumption at soil layer of 60-140 cm during wheat growth. Under current farming conditions of south Shanxi, the increased grain yield of wheat could be achieved by combining the measures of high wheat stubble and wheat straw covering for holding soil water and deep plowing between the Beginning of Autumn (August 6th) and the Limit of Heat (August 21st) for promoting soil water penetration characteristics to improve the number of stems before winter and spike.

Observational Constraints on Ephemeral Wind Gusts that MobilizeSoil Dust Aerosols

NASA Astrophysics Data System (ADS)

Miller, R. L.; Leung, M. F.

2017-12-01

Dust aerosol models resolve the planetary scale winds that disperse particles throughout the globe, but the winds raising dust are often organized on smaller scales that are below the resolution of the model. These winds, including ephemeral wind gusts associated with boundary layer mixing, are typically parameterized. For example, gusts by dry convective eddies are related to the sensible heat flux. What remains is to constrain the magnitude of the wind gusts using boundary layer measurements, so that dust emission has the correct sensitivity to these gusts, relative to the resolved wind. Here, we use a year of ARM measurements with high temporal resolution from Niamey, Niger in the Sahel to evaluate our parameterization. This evaluation is important for dust aerosol models that use 'nudging' to reproduce observed transport patterns.

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.

Modulation of Soil Initial State on WRF Model Performance Over China

NASA Astrophysics Data System (ADS)

Xue, Haile; Jin, Qinjian; Yi, Bingqi; Mullendore, Gretchen L.; Zheng, Xiaohui; Jin, Hongchun

2017-11-01

The soil state (e.g., temperature and moisture) in a mesoscale numerical prediction model is typically initialized by reanalysis or analysis data that may be subject to large bias. Such bias may lead to unrealistic land-atmosphere interactions. This study shows that the Climate Forecast System Reanalysis (CFSR) dramatically underestimates soil temperature and overestimates soil moisture over most parts of China in the first (0-10 cm) and second (10-25 cm) soil layers compared to in situ observations in July 2013. A correction based on the global optimal dual kriging is employed to correct CFSR bias in soil temperature and moisture using in situ observations. To investigate the impacts of the corrected soil state on model forecasts, two numerical model simulations—a control run with CFSR soil state and a disturbed run with the corrected soil state—were conducted using the Weather Research and Forecasting model. All the simulations are initiated 4 times per day and run 48 h. Model results show that the corrected soil state, for example, warmer and drier surface over the most parts of China, can enhance evaporation over wet regions, which changes the overlying atmospheric temperature and moisture. The changes of the lifting condensation level, level of free convection, and water transport due to corrected soil state favor precipitation over wet regions, while prohibiting precipitation over dry regions. Moreover, diagnoses indicate that the remote moisture flux convergence plays a dominant role in the precipitation changes over the wet regions.

Integration of Satellite, Global Reanalysis Data and Macroscale Hydrological Model for Drought Assessment in Sub-Tropical Region of India

NASA Astrophysics Data System (ADS)

Pandey, V.; Srivastava, P. K.

2018-04-01

Change in soil moisture regime is highly relevant for agricultural drought, which can be best analyzed in terms of Soil Moisture Deficit Index (SMDI). A macroscale hydrological model Variable Infiltration Capacity (VIC) was used to simulate the hydro-climatological fluxes including evapotranspiration, runoff, and soil moisture storage to reconstruct the severity and duration of agricultural drought over semi-arid region of India. The simulations in VIC were performed at 0.25° spatial resolution by using a set of meteorological forcing data, soil parameters and Land Use Land Cover (LULC) and vegetation parameters. For calibration and validation, soil parameters obtained from National Bureau of Soil Survey and Land Use Planning (NBSSLUP) and ESA's Climate Change Initiative soil moisture (CCI-SM) data respectively. The analysis of results demonstrates that most of the study regions (> 80 %) especially for central northern part are affected by drought condition. The year 2001, 2002, 2007, 2008 and 2009 was highly affected by agricultural drought. Due to high average and maximum temperature, we observed higher soil evaporation that reduces the surface soil moisture significantly as well as the high topographic variations; coarse soil texture and moderate to high wind speed enhanced the drying upper soil moisture layer that incorporate higher negative SMDI over the study area. These findings can also facilitate the archetype in terms of daily time step data, lengths of the simulation period, various hydro-climatological outputs and use of reasonable hydrological model.

Land surface energy budget during dry spells: global CMIP5 AMIP simulations vs. satellite observations

NASA Astrophysics Data System (ADS)

Gallego-Elvira, Belen; Taylor, Christopher M.; Harris, Phil P.; Ghent, Darren; Folwell, Sonja S.

2015-04-01

During extended periods without rain (dry spells), the soil can dry out due to vegetation transpiration and soil evaporation. At some point in this drying cycle, land surface conditions change from energy-limited to water-limited evapotranspiration, and this is accompanied by an increase of the ground and overlying air temperatures. Regionally, the characteristics of this transition determine the influence of soil moisture on air temperature and rainfall. Global Climate Models (GCMs) disagree on where and how strongly the surface energy budget is limited by soil moisture. Flux tower observations are improving our understanding of these dry down processes, but typical heterogeneous landscapes are too sparsely sampled to ascertain a representative regional response. Alternatively, satellite observations of land surface temperature (LST) provide indirect information about the surface energy partition at 1km resolution globally. In our study, we analyse how well the dry spell dynamics of LST are represented by GCMs across the globe. We use a spatially and temporally aggregated diagnostic to describe the composite response of LST during surface dry down in rain-free periods in distinct climatic regions. The diagnostic is derived from daytime MODIS-Terra LST observations and bias-corrected meteorological re-analyses, and compared against the outputs of historical climate simulations of seven models running the CMIP5 AMIP experiment. Dry spell events are stratified by antecedent precipitation, land cover type and geographic regions to assess the sensitivity of surface warming rates to soil moisture levels at the onset of a dry spell for different surface and climatic zones. In a number of drought-prone hot spot regions, we find important differences in simulated dry spell behaviour, both between models, and compared to observations. These model biases are likely to compromise seasonal forecasts and future climate projections.

Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying

PubMed Central

Puértolas, Jaime; Conesa, María R.; Ballester, Carlos; Dodd, Ian C.

2015-01-01

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0–10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm3 cm–3 for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction. PMID:25547916

Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying.

PubMed

Puértolas, Jaime; Conesa, María R; Ballester, Carlos; Dodd, Ian C

2015-04-01

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0-10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm(3) cm(-3) for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Potential fate of SOC eroded from natural crusted soil surface under simulated wind driven storm

NASA Astrophysics Data System (ADS)

Xiao, Liangang; Fister, Wolfgang; Greenwood, Philip; Hu, Yaxian; Kuhn, Nikolaus J.

2016-04-01

Improving the assessment of the impact of soil erosion on carbon (C) cycling requires a better understanding of the redistribution of eroded sediment and associated soil organic carbon (SOC) across agricultural landscapes. Recent studies conducted on dry-sieved aggregates in the laboratory demonstrated that aggregation can profoundly skew SOC redistribution and its subsequent fate by accelerating settling velocities of aggregated sediment compared to mineral grains, which in turn can increase SOC mineralization into greenhouse gases. However, the erodibility of the soil in the field is more variable than in the laboratory due to tillage, crus formation, drying-wetting and freeze-thaw cycles, and biological effects. This study aimed to investigate the potential fate of the SOC eroded from naturally developed soil surface and to compare the observations with those made in the laboratory. Simulated, short, high intensity wind driven storms were conducted on a crusted loam in the field. The sediments were fractionated with a settling tube according to their potential transport distances. The soil mass, SOC concentration and cumulative 80-day CO2 emission of each fraction were identified. The results show: 1) 53% of eroded sediment and 62% of eroded SOC from the natural surface in the field would be deposited across landscapes, which is six times and three times higher compared to that implied by mineral grains, respectively; 2) the preferential deposition of SOC-rich fast-settling sediment potentially releases approximately 50% more CO2 than the same layer of the non-eroded soil; 3) the respiration of the slow-settling fraction that is potentially transported to the aquatic systems was much more active compared to the other fractions and the bulk soil. Our results confirm in general the conclusions drawn from laboratory and thus demonstrate that aggregation can affect the redistribution of sediment associated SOC under field conditions, including an increase in emissions compared to bulk soil. Overall, this confirms that terrestrial SOC redistribution and the mineralization play an important role in erosion induced C cycling, with major uncertainties to be addressed.

Deposition, accumulation, and alteration of Cl−, NO3−, ClO4− and ClO3− salts in a hyper-arid polar environment: Mass balance and isotopic constraints

USGS Publications Warehouse

Jackson, Andrew; Davila, Alfonso F.; Böhlke, John Karl; Sturchio, Neil C.; Sevanthi, Ritesh; Estrada, Nubia; Brundrett, Maeghan; Lacelle, Denis; McKay, Christopher P.; Poghosyan, Armen; Pollard, Wayne; Zacny, Kris

2016-01-01

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl−, NO3−, ClO4− and ClO3− in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl− and NO3−isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO4−/NO3− ratios and NO3− isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO3−/ClO4− in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO3−, possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ∼10 to 30 kyr near the glacier to 70–200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization.

Survival of rhizobia in two soils as influenced by storage conditions.

PubMed

Martyniuk, Stefan; Oroń, Jadwiga

2008-01-01

Two soils were kept moist at 4 degrees C, -20 degrees C or air-dried at 20-22 degrees C and after one week, one month, two months and six months of storage at these conditions changes in soil populations of Rhizobium leguminosarum bv. trifolii (Rlt) and Rhizobium leguminosarum bv. viciae (Rlv) were examined. In one air-dried soil (from Grab6w) markedly lower numbers of both Rlt and Rlv., as compared to the refrigerated or frozen samples, were found already after 1 week of storage. In the case of the second soil (from Osiny) air-drying significantly reduced numbers of the rhizobia after 2 and 6 months of storage. The soil from Osiny contained higher amounts of C org, total N and clay than the Grabów soil. Both soils stored moist in a refrigerator (4 degrees C) or frozen (-20 degrees C) retained similar populations of the examined rhizobia throughout the entire storage period, indicating that soil freezing is not detrimental for the examined rhizobia.

Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

NASA Astrophysics Data System (ADS)

Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan

2016-04-01

The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric layers in different configurations. With a Thru Reflect Line calibration (TRL) the influences of connectors and adapters at the coaxial line sample holder were removed. The combination of the full two port calibration procedure and broadband modeling approach turns out to achieve a good accordance of modeling and experimental results. The next step is the implementation of an inversion to calculate the material parameters of every layer out of the s-parameters of the layered sample.

Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

NASA Astrophysics Data System (ADS)

Schmidt, Felix; Wagner, Norman; Lünenschloß, Peter; Toepfer, Hannes; Dietrich, Peter; Kaliorias, Andreas; Bumberger, Jan

2015-04-01

The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric layers in different configurations. With a Thru Reflect Line calibration (TRL) the influences of connectors and adapters at the coaxial line sample holder were removed. The combination of the full two port calibration procedure and broadband modeling approach turns out to achieve a good accordance of modeling and experimental results. The next step is the implementation of an inversion to calculate the material parameters of every layer out of the s-parameters of the layered sample.

Effects of long-term simulated martian conditions on a freeze-dried and homogenized bacterial permafrost community.

PubMed

Hansen, Aviaja A; Jensen, Lars L; Kristoffersen, Tommy; Mikkelsen, Karina; Merrison, Jonathan; Finster, Kai W; Lomstein, Bente Aa

2009-03-01

Indigenous bacteria and biomolecules (DNA and proteins) in a freeze-dried and homogenized Arctic permafrost were exposed to simulated martian conditions that correspond to about 80 days on the surface of Mars with respect to the accumulated UV dose. The simulation conditions included UV radiation, freeze-thaw cycles, the atmospheric gas composition, and pressure. The homogenized permafrost cores were subjected to repeated cycles of UV radiation for 3 h followed by 27 h without irradiation. The effects of the simulation conditions on the concentrations of biomolecules; numbers of viable, dead, and cultured bacteria; as well as the community structure were determined. Simulated martian conditions resulted in a significant reduction of the concentrations of DNA and amino acids in the uppermost 1.5 mm of the soil core. The total number of bacterial cells was reduced in the upper 9 mm of the soil core, while the number of viable cells was reduced in the upper 15 mm. The number of cultured aerobic bacteria was reduced in the upper 6 mm of the soil core, whereas the community structure of cultured anaerobic bacteria was relatively unaffected by the exposure conditions. As explanations for the observed changes, we propose three causes that might have been working on the biological material either individually or synergistically: (i) UV radiation, (ii) UV-generated reactive oxygen species, and (iii) freeze-thaw cycles. Currently, the production and action of reactive gases is only hypothetical and will be a central subject in future investigations. Overall, we conclude that in a stable environment (no wind-/pressure-induced mixing) biological material is efficiently shielded by a 2 cm thick layer of dust, while it is relatively rapidly destroyed in the surface layer, and that biomolecules like proteins and polynucleotides are more resistant to destruction than living biota.

Effects of Long-Term Simulated Martian Conditions on a Freeze-Dried and Homogenized Bacterial Permafrost Community

NASA Astrophysics Data System (ADS)

Hansen, Aviaja A.; Jenson, Lars L.; Kristoffersen, Tommy; Mikkelsen, Karina; Merrison, Jonathan; Finster, Kai W.; Lomstein, Bente Aa.

2009-03-01

Indigenous bacteria and biomolecules (DNA and proteins) in a freeze-dried and homogenized Arctic permafrost were exposed to simulated martian conditions that correspond to about 80 days on the surface of Mars with respect to the accumulated UV dose. The simulation conditions included UV radiation, freeze-thaw cycles, the atmospheric gas composition, and pressure. The homogenized permafrost cores were subjected to repeated cycles of UV radiation for 3 h followed by 27 h without irradiation. The effects of the simulation conditions on the concentrations of biomolecules; numbers of viable, dead, and cultured bacteria; as well as the community structure were determined. Simulated martian conditions resulted in a significant reduction of the concentrations of DNA and amino acids in the uppermost 1.5 mm of the soil core. The total number of bacterial cells was reduced in the upper 9 mm of the soil core, while the number of viable cells was reduced in the upper 15 mm. The number of cultured aerobic bacteria was reduced in the upper 6 mm of the soil core, whereas the community structure of cultured anaerobic bacteria was relatively unaffected by the exposure conditions. As explanations for the observed changes, we propose three causes that might have been working on the biological material either individually or synergistically: (i) UV radiation, (ii) UV-generated reactive oxygen species, and (iii) freeze-thaw cycles. Currently, the production and action of reactive gases is only hypothetical and will be a central subject in future investigations. Overall, we conclude that in a stable environment (no wind-/pressure-induced mixing) biological material is efficiently shielded by a 2 cm thick layer of dust, while it is relatively rapidly destroyed in the surface layer, and that biomolecules like proteins and polynucleotides are more resistant to destruction than living biota.

Brominated flame retardants and dechlorane plus on a remote high mountain of the eastern Tibetan Plateau: implications for regional sources and environmental behaviors.

PubMed

Liu, Xin; Bing, Haijian; Chen, Yanzhi; Li, Jun; Wu, Yanhong; Zhang, Gan

2017-04-10

We investigated the occurrence of halogenated flame retardants (HFRs) including polybrominated diphenyl ethers (PBDEs), six novel brominated flame retardants (NBFRs) and dechlorane plus in air and soils on the eastern slope of Mt. Gongga on the eastern Tibetan Plateau. We detected all of the NBFR except bis(2-ethylhexyl)-tetrabromophthalate and pentabromoethyl benzene. NBFRs constituted the most prevalent group. BDE-28 and BDE-47 dominated among the PBDE congeners. Decabromodiphenyl ethane was detected at relatively high levels up to 171 pg/m 3 and 1450 pg/g dry weight in air and soils, respectively; however, it appeared to be easily degraded in the environment. A general decreasing trend was observed among the HFR concentrations with increasing altitude, and this was due to the prominent contribution of source emissions over possible influence of environmental conditions. This study also suggests that HFRs are supplied to forest soils mainly in the form of precipitation and retained in the O horizon layers.

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...

Phosphorus retention and fractionation in an eutrophic wetland: A one-year mesocosms experiment under fluctuating flooding conditions.

PubMed

Tercero, María Del Carmen; Álvarez-Rogel, José; Conesa, Héctor Miguel; Párraga-Aguado, Isabel; González-Alcaraz, María Nazaret

2017-04-01

This study aimed to evaluate the response of salt marshes to pulses of PO 4 3- -enriched water, with and without the presence of Phragmites australis. A one-year mesocosms experiment was performed in simulated soil profiles (fine-textured surface layers and sandy subsurface layers) from a coastal salt marsh of the Mar Menor lagoon under alternating flooding-drying conditions with eutrophic water, under low (1.95 mg L -1 P-PO 4 3- ) and high (19.5 mg L -1 P-PO 4 3- ) P load, and with the presence/absence of Phragmites. The PO 4 3- concentrations in soil porewater and drainage water were regularly measured, and P accumulated in soils (including a fractionation procedure) and plants (roots, rhizomes, stems and leaves) were analyzed. The experimental mesocosms were highly effective in the removal of P from the eutrophic flooding water (>90% reduction of the P added to the system both in the soil pore water and drainage water), regardless of the nutrient load, the season of the year and the presence/absence of Phragmites. The soil was the main sink of the P added to the system, while Phragmites had a minor role in P removal. The biomass of Phragmites accumulated ∼27% of the P added with the flooding water in the treatment with water of low P load while ∼12% of P in that of high P load; the rhizomes were the organs that contributed the most (∼67-72% of the total P retained by the plants). Ca/Mg compounds were the main contributors to the retention of P in the soil compartment, especially in the fine-textured surface soil layers (∼34-53% of the total P in the soil was present in this fraction). Phragmites favored the retention of P onto metal oxides (∼12% increase of the P retained in the metal oxides fraction in the treatment with water of high P load). Hence, the use of constructed wetlands to ameliorate the negative impacts of P-enriched waters in the Mar Menor lagoon and similar areas is recommended. We propose the incorporation of fine-textured carbonated materials, with high content of Ca/Mg compounds, and the use of Phragmites to favor the retention of P by these systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Roles of Arbuscular Mycorrhizal Fungi and Soil Abiotic Conditions in the Establishment of a Dry Grassland Community.

PubMed

Knappová, Jana; Pánková, Hana; Münzbergová, Zuzana

2016-01-01

The importance of soil biota in the composition of mature plant communities is commonly acknowledged. In contrast, the role of soil biota in the early establishment of new plant communities and their relative importance for soil abiotic conditions are still poorly understood. The aim of this study was to understand the effects of soil origin and soil fungal communities on the composition of a newly established dry grassland plant community. We used soil from two different origins (dry grassland and abandoned field) with different pH and nutrient and mineral content. Grassland microcosms were established by sowing seeds of 54 species of dry grassland plants into the studied soils. To suppress soil fungi, half of the pots were regularly treated with fungicide. In this way, we studied the independent and combined effects of soil origin and soil community on the establishment of dry grassland communities. The effect of suppressing the soil fungal community on the richness and composition of the plant communities was much stronger than the effect of soil origin. Contrary to our expectations, the effects of these two factors were largely additive, indicating the same degree of importance of soil fungal communities in the establishment of species-rich plant communities in the soils from both origins. The negative effect of suppressing soil fungi on species richness, however, occurred later in the soil from the abandoned field than in the soil from the grassland. This result likely occurred because the negative effects of the suppression of fungi in the field soil were caused mainly by changes in plant community composition and increased competition. In contrast, in the grassland soil, the absence of soil fungi was limiting for plants already at the early stages of their establishment, i.e., in the phases of germination and early recruitment. While fungicide affects not only arbuscular mycorrhizal fungi but also other biota, our data indicate that changes in the AMF communities are the most likely drivers of the observed changes. The effects of other soil biota, however, cannot be fully excluded. These results suggest that the availability of soil fungi may not be the most important limiting factor for the establishment of grassland species in abandoned fields if we manage to reduce the intensity of competition at these sites e.g., by mowing or grazing.

Response of Carbon Fluxes to Soil Moisture Variability across an Alaskan Tundra Landscape

NASA Astrophysics Data System (ADS)

Melton, S.; Natali, S.; Schade, J. D.; Holmes, R. M.; Mann, P. J.; Fiske, G. J.

2017-12-01

Soils in arctic and sub-arctic permafrost regions store large amounts of carbon (C), which is becoming more biologically available as soils warm and permafrost thaws. Microbial decay of organic forms of C can result in the production and emission of carbon dioxide (CO2) and methane (CH4), and the amount and form of C released into the atmosphere depend on organic matter composition and soil conditions. Soil moisture, which is a strong driver of microbial processes, varies spatially and temporally across tundra landscapes and may change dramatically as a result of permafrost thaw. The Yukon-Kuskokwim Delta (YKD) of Alaska is underlain by discontinuous permafrost and is particularly vulnerable to permafrost thaw and soil moisture changes associated with thaw. As permafrost thaws, some areas may dry as drainage increases with increasing thaw depth. Alternatively, permafrost thaw may lead to ground subsidence and saturation of previously dry soils. Our objective was to investigate patterns in C storage and processing across the landscape and in response to changes in soil moisture in the YKD. We analyzed soil C pools (0-30 cm) and CO2 and CH4 concentrations in soils from sites of different land cover and landscape position, including moist and dry peat plateaus, high and low intensity burned plateaus, fens, and drained lakes. We also conducted aerobic and anaerobic soil incubations to determine changes in CO2 and CH4 production under a range of soil moisture conditions. Soils from burned plateaus, which were drier and had lower C content than unburned soils, had higher CO2 production (per g soil) than unburned soils during aerobic incubations. Both increased and decreased moisture reduced CO2 production from soils. Soil drying increased net CH4 uptake in all aerobically-incubated burned soils, and wetting resulted in CH4 emissions from low intensity burn soils. CO2 and CH4 production from fen soils were higher than from the other landscape positions analyzed here. Our results suggest that soil drying could lead to decreased microbial respiration, whereas subsidence may result in increased methanogenesis. Additionally, amplified CH4 release from burned soils after rainfall events or subsidence may accompany the increased fire frequency projected in tundra regions.

Estimating the impact of seawater on the production of soil water-extractable organic carbon during coastal erosion.

PubMed

Dou, Fugen; Ping, Chien-Lu; Guo, Laodong; Jorgenson, Torre

2008-01-01

The production of water-extractable organic carbon (WEOC) during arctic coastal erosion and permafrost degradation may contribute significantly to C fluxes under warming conditions, but it remains difficult to quantify. A tundra soil collected near Barrow, AK, was selected to evaluate the effects of soil pretreatments (oven drying vs. freeze drying) as well as extraction solutions (pure water vs. seawater) on WEOC yields. Both oven drying and freeze drying significantly increased WEOC release compared with the original moist soil samples; dried samples released, on average, 18% more WEOC than did original moist samples. Similar results were observed for the production of low-molecular-weight dissolved organic C. However, extractable OC released from different soil horizons exhibited differences in specific UV absorption, suggesting differences in WEOC quality. Furthermore, extractable OC yields were significantly less in samples extracted with seawater compared with those extracted with pure water, likely due to the effects of major ions on extractable OC flocculation. Compared with samples from the active horizons, upper permafrost samples released more WEOC, suggesting that continuously frozen samples were more sensitive than samples that had experienced more drying-wetting cycles in nature. Specific UV absorption of seawater-extracted OC was significantly lower than that of OC extracted using pure water, suggesting more aromatic or humic substances were flocculated during seawater extraction. Our results suggest that overestimation of total terrestrial WEOC input to the Arctic Ocean during coastal erosion could occur if estimations were based on WEOC extracted from dried soil samples using pure water.

Effect of prescribed fire on soil properties and N transformation in two vegetation types in South China.

PubMed

Wang, Faming; Li, Jian; Zou, Bi; Xu, Xin; Li, Zhian

2013-06-01

Prescribed fire is a common site preparation practice in forest management in southern China. However, the effect of fire on soil properties and N transformations is still poorly understood in this region. In this study, soil properties and N transformations in burned and unburned site of two vegetation types (Eucalyptus plantation and shrubland) were compared in rainy and dry seasons after 2 years' prescribed fire. Soil pH and soil NH4-N were all higher in the burned site compared to the unburned control. Furthermore, burned sites had 30-40 % lower of soil total phosphorus than conspecific unburned sites. There was no difference in soil organic matter, total N, soil exchangeable cations, available P or NO3-N. Nitrogen mineralization rate of 0-5 cm soil in the unburned site ranged from 8.24 to 11.6 mg N kg(-1) soil month(-1) in the rainy season, compared to a lower level of 4.82-5.25 mg N kg(-1) soil month(-1) in the burned sites. In contrast, 0-5 cm layer nitrification rate was overall 2.47 mg N kg(-1) soil month(-1) in the rainy season, and was not significantly affected by burning. The reduced understory vegetation coverage after burning may be responsible for the higher soil NH4-N in the burned site. This study highlights that a better understanding the effect of prescribed burning on soil nutrients cycling would provide a critical foundation for management decision and be beneficial to afforestation in southern China.

Using Artificial Soil and Dry-Column Flash Chromatography to Simulate Organic Substance Leaching Process: A Colorful Environmental Chemistry Experiment

ERIC Educational Resources Information Center

de Avellar, Isa G. J.; Cotta, Tais A. P. G.; Neder, Amarilis de V. Finageiv

2012-01-01

Soil is an important and complex environmental compartment and soil contamination contributes to the pollution of aquifers and other water basins. A simple and low-cost experiment is described in which the mobility of three organic compounds in an artificial soil is examined using dry-column flash chromatography. The compounds were applied on top…

Soil erosion transport through multiple rainfall events in the presence of stone cover: Laboratory flume experiments and analysis with the Hairsine-Rose model

NASA Astrophysics Data System (ADS)

Jomaa, S.; Barry, D. A.; Brovelli, A.; Heng, B. P.; Sander, G. C.; Parlange, J.

2011-12-01

Soil erosion is a major environmental problem that can lead to loss of fertility and degradation of agricultural fields. In order to develop efficient strategies to mitigate the impact of precipitation and reduce the erosion rate, a process-based understanding of the mechanisms that govern sediment transport and delivery is necessary. Soil state and physical properties prior to a precipitation event can affect significantly the erosion rate. Among the most important soil variables are moisture content, compaction and infiltration capacity. Additionally, the presence of stones on the topsoil surface retards the overland flow discharge, reduces runoff generation as well as the sediment delivery and prevents the development of a surface seal, which in turn maintains the infiltration rate. The aim of this study was to examine in detail the effect of surface stones, soil compaction and sealing for a sequence of rainfall events on soil erosion. Experiments were conducted using the EPFL erosion flume, which was divided into two identical flumes (one with stone and one without). The experiment involved four rainfall events with the precipitation rates: 28, 74, 74 and 28 mm h-1. After each 2-h event, the soil was allowed to air dry for 22 h. The total sediment concentration, the concentration of seven sediment size classes and the flow discharge were measured during each event at the outlet of each flume. Experimental results were analyzed using the Hairsine and Rose (H-R) soil erosion model. Results showed that (i) within each precipitation event, the proportion of each size class for the bare/stone-covered flume pairs at steady state were similar, whereas the initial response differed significantly; (ii) in all cases the effluent was enriched in finer particles relative to the original soil; and (iii) the effluent sediment composition was different from that of the original soil, and there was no clear trend towards the parent soil sediment size composition with time. The H-R model was able to reproduce well the events with high precipitation rate (events 2 and 3) with the same parameter set, while the match was less satisfactory for the low precipitation events. A possible explanation for this is that the initial soil compaction/sealing/development of the deposited layer combined to yield a surface that eroded similarly for identical rainfall conditions. Changes in the precipitation rate modifies the soil surface (the deposited layer in particular) and thus the erosion rates. Model application further suggested that over the course of the rainfall events, the contribution of the original soil to the eroded sediment decreased gradually, while that of the deposited layer increased.

Plants as sources of airborne bacteria, including ice nucleation-active bacteria.

PubMed

Lindemann, J; Constantinidou, H A; Barchet, W R; Upper, C D

1982-11-01

Vertical wind shear and concentration gradients of viable, airborne bacteria were used to calculate the upward flux of viable cells above bare soil and canopies of several crops. Concentrations at soil or canopy height varied from 46 colony-forming units per m over young corn and wet soil to 663 colony-forming units per m over dry soil and 6,500 colony-forming units per m over a closed wheat canopy. In simultaneous samples, concentrations of viable bacteria in the air 10 m inside an alfalfa field were fourfold higher than those over a field with dry, bare soil immediately upwind. The upward flux of viable bacteria over alfalfa was three- to fourfold greater than over dry soil. Concentrations of ice nucleation-active bacteria were higher over plants than over soil. Thus, plant canopies may constitute a major source of bacteria, including ice nucleation-active bacteria, in the air.

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.

The influence of land use on the abundance and diversity of ammonia oxidizers.

PubMed

Zhao, Dayong; Luo, Juan; Wang, Jianqun; Huang, Rui; Guo, Kun; Li, Yi; Wu, Qinglong L

2015-02-01

Nitrification plays a significant role in soil nitrogen cycling, a process in which the first step can be catalyzed by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). In this study, six soil samples with distinct land-use regimes (forestland soil, paddy soil, wheat-planted soil, fruit-planted soil, grassland soil, and rape-planted soil) were collected from Chuzhou city in the Anhui province to elucidate the effects of land use on the abundance and diversity of AOA and AOB. The abundance of the archaeal amoA gene ranged from 2.12 × 10(4) copies per gram of dry soil to 2.57 × 10(5) copies per gram of dry soil, while the abundance of the bacterial amoA gene ranged from 5.58 × 10(4) copies per gram of dry soil to 1.59 × 10(8) copies per gram of dry soil. The grassland and the rape-planted soil samples maintained the highest abundance of the bacterial and archaeal amoA genes, respectively. The abundance of the archaeal amoA gene was positively correlated with the pH (P < 0.05). The ammonia concentrations exhibited a significantly positive relation with the abundance of the bacterial amoA gene (P < 0.01) and the number of OTUs of AOB (P < 0.05). The community composition of AOB was more sensitive to the land-use regimes than that of AOA. The data obtained in this study may be useful to better understand the nitrification process in soils with different land-use regimes.

CeO2 nanoparticles induce no changes in phenanthrene toxicity to the soil organisms Porcellionides pruinosus and Folsomia candida.

PubMed

Tourinho, Paula S; Waalewijn-Kool, Pauline L; Zantkuijl, Irene; Jurkschat, Kerstin; Svendsen, Claus; Soares, Amadeu M V M; Loureiro, Susana; van Gestel, Cornelis A M

2015-03-01

Cerium oxide nanoparticles (CeO2 NPs) are used as diesel fuel additives to catalyze oxidation. Phenanthrene is a major component of diesel exhaust particles and one of the most common pollutants in the environment. This study aimed at determining the effect of CeO2 NPs on the toxicity of phenanthrene in Lufa 2.2 standard soil for the isopod Porcellionides pruinosus and the springtail Folsomia candida. Toxicity tests were performed in the presence of CeO2 concentrations of 10, 100 or 1000mg Ce/kg dry soil and compared with results in the absence of CeO2 NPs. CeO2 NPs had no adverse effects on isopod survival and growth or springtail survival and reproduction. For the isopods, LC50s for the effect of phenanthrene ranged from 110 to 143mg/kg dry soil, and EC50s from 17.6 to 31.6mg/kg dry soil. For the springtails, LC50s ranged between 61.5 and 88.3mg/kg dry soil and EC50s from 52.2 to 76.7mg/kg dry soil. From this study it may be concluded that CeO2 NPs have a low toxicity and do not affect toxicity of phenanthrene to isopods and springtails. Copyright © 2014 Elsevier Inc. All rights reserved.

Rhizosphere bacteria containing 1-aminocyclopropane-1-carboxylate deaminase increase yield of plants grown in drying soil via both local and systemic hormone signalling.

PubMed

Belimov, Andrey A; Dodd, Ian C; Hontzeas, Nikos; Theobald, Julian C; Safronova, Vera I; Davies, William J

2009-01-01

Decreased soil water availability can stimulate production of the plant hormone ethylene and inhibit plant growth. Strategies aimed at decreasing stress ethylene evolution might attenuate its negative effects. An environmentally benign (nonchemical) method of modifying crop ethylene relations - soil inoculation with a natural root-associated bacterium Variovorax paradoxus 5C-2 (containing the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase that degrades the ethylene precursor ACC), was assessed with pea (Pisum sativum) plants grown in drying soil. Inoculation with V. paradoxus 5C-2, but not with a transposome mutant with massively decreased ACC deaminase activity, improved growth, yield and water-use efficiency of droughted peas. Systemic effects of V. paradoxus 5C-2 included an amplified soil drying-induced increase of xylem abscisic acid (ABA) concentration, but an attenuated soil drying-induced increase of xylem ACC concentration. A local bacterial effect was increased nodulation by symbiotic nitrogen-fixing bacteria, which prevented a drought-induced decrease in nodulation and seed nitrogen content. Successfully deploying a single bacterial gene in the rhizosphere increased yield and nutritive value of plants grown in drying soil, via both local and systemic hormone signalling. Such bacteria may provide an easily realized, economic means of sustaining crop yields and using irrigation water more efficiently in dryland agriculture.

Moisture and substrate availability constrain soil trace gas fluxes in an eastern Amazonian regrowth forest

NASA Astrophysics Data System (ADS)

Vasconcelos, Steel S.; Zarin, Daniel J.; Capanu, Marinela; Littell, Ramon; Davidson, Eric A.; Ishida, Francoise Y.; Santos, Elisana B.; Araújo, Maristela M.; AragãO, DéBora V.; Rangel-Vasconcelos, LíVia G. T.; de Assis Oliveira, Francisco; McDowell, William H.; de Carvalho, Claudio José R.

2004-06-01

Changes in land-use and climate are likely to alter moisture and substrate availability in tropical forest soils, but quantitative assessment of the role of resource constraints as regulators of soil trace gas fluxes is rather limited. The primary objective of this study was to quantify the effects of moisture and substrate availability on soil trace gas fluxes in an Amazonian regrowth forest. We measured the efflux of carbon dioxide (CO2), nitric oxide (NO), nitrous oxide (N2O), and methane (CH4) from soil in response to two experimental manipulations. In the first, we increased soil moisture availability during the dry season by irrigation; in the second, we decreased substrate availability by continuous removal of aboveground litter. In the absence of irrigation, soil CO2 efflux decreased during the dry season while irrigation maintained soil CO2 efflux levels similar to the wet season. Large variations in soil CO2 efflux consistent with a significant moisture constraint on respiration were observed in response to soil wet-up and dry-down events. Annual soil C efflux for irrigated plots was 27 and 13% higher than for control plots in 2001 and 2002, respectively. Litter removal significantly reduced soil CO2 efflux; annual soil C efflux in 2002 was 28% lower for litter removal plots compared to control plots. The annual soil C efflux:litterfall C ratio for the control treatment (4.0-5.2) was consistent with previously reported values for regrowth forests that indicate a relatively large belowground C allocation. In general, fluxes of N2O and CH4 were higher during the wet season and both fluxes increased during dry-season irrigation. There was no seasonal effect on NO fluxes. Litter removal had no significant impact on N oxide or CH4 emissions. Net soil nitrification did not respond to dry-season irrigation, but was somewhat reduced by litter removal. Overall, these results demonstrate significant soil moisture and substrate constraints on soil trace gas emissions, particularly for CO2, and suggest that climate and land-use changes that alter moisture and substrate availability are therefore likely to have an impact on atmosphere chemistry.

[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.

Thin layer drying of cassava starch using continuous vibrated fluidized bed dryer

NASA Astrophysics Data System (ADS)

Suherman, Trisnaningtyas, Rona

2015-12-01

This paper present the experimental work and thin layer modelling of cassava starch drying in continuous vibrated fluidized bed dryer. The experimental data was used to validate nine thin layer models of drying curve. Cassava starch with 0.21 initial moisture content was dried in different air drying temperature (50°C, 55°C, 60°C, 65°C, 70°C), different weir height in bed (0 and 1 cm), and different solid feed flow (10 and 30 gr.minute-1). The result showed air dryer temperature has a significant effect on drying curve, while the weir height and solid flow rate are slightly. Based on value of R2, χ2, and RMSE, Page Model is the most accurate simulation for thin layer drying model of cassava starch.

Mitigation of water repellency in burned soils applying hydrophillic polymers

NASA Astrophysics Data System (ADS)

Neris, Jonay; de la Torre, Sara; Vidal-Vazquez, Eva; Lado, Marcos

2017-04-01

In this study, the effect of fire on water repellency was analyzed in soils from different parent materials, as well as the suitability of anionic polyacrylamide (PAM) to reduce water repellency in these soils. Samples were collected in four different sites where wildfires took place: two in the Canary Islands, with soils developed on volcanic materials, and two in Galicia (NW Spain), with soils developed on plutonic rocks. In Galicia, two soil samples were collected in each site, one in the burnt area and one in an adjacent unburnt area. In the Canary Islands, four samples were collected from each site, three inside the burnt area where the soils were affected by different fire intensities, and one in an unburnt adjacent area. Samples were air-dried and sieved by a 2-mm mesh sieve. Water repellency was measured using the Water Drop Penetration Time test. An amount of 10 g of soil was placed in a tray. Five drops of deionized water were place on the soil surface with a pipette, and the time for each drop to fully penetrate into the soil was recorded. PAM solution was applied to the burnt soils simulating a field application rate of 1gm-2. The polymer used was Superfloc A-110 (Kemira Water Solutions BV, Holland) with 1x107 Da molecular weigth and 15% hydrolysis. PAM was sprayed on the soil surface as solution with a concentration 0.2 g/L. After the application, the samples were dried and the WDPT test was performed. Three replicates for each treatment and soil were used, and the treatments included: dry soil, dry soil after a wetting treatment, dry PAM-treated soil. The results showed that water repellency was modified by fire differently in the various soils. In hydrophilic soils and soils with low water repellency, water repellency was increased after the action of fire. In soils with noticeable initial water repellency, this was reduced or eliminated after the fire. Wetting repellent soils caused a decrease in water repellency most probably because of the spatial redistribution of hydrophobic organic compounds that caused water repellency. The addition of PAM further reduced in all of the cases. The application of PAM could be an effective method for mitigation of water repellency in burnt soils.

Seasonal dynamics of soil CO2 efflux and soil profile CO2 concentrations in arboretum of Moscow botanical garden

NASA Astrophysics Data System (ADS)

Goncharova, Olga; Udovenko, Maria; Matyshak, Georgy

2016-04-01

To analyse and predict recent and future climate change on a global scale exchange processes of greenhouse gases - primarily carbon dioxide - over various ecosystems are of rising interest. In order to upscale land-use dependent sources and sinks of CO2, knowledge of the local variability of carbon fluxes is needed. Among terrestrial ecosystems, urban areas play an important role because most of anthropogenic emissions of carbon dioxide originate from these areas. On the other hand, urban soils have the potential to store large amounts of soil organic carbon and, thus, contribute to mitigating increases in atmospheric CO2 concentrations. Research objectives: 1) estimate the seasonal dynamics of carbon dioxide production (emission - closed chamber technique and profile concentration - soil air sampling tubes method) by soils of Moscow State University Botanical Garden Arboretum planted with Picea obovata and Pinus sylvestris, 1) identification the factors that control CO2 production. The study was conducted with 1-2 weeks intervals between October 2013 and November 2015 at two sites. Carbon dioxide soil surface efflux during the year ranged from 0 to 800 mgCO2/(m2hr). Efflux values above 0 mgCO2/(m2hr) was observed during the all cold period except for only 3 weeks. Soil CO2 concentration ranged from 1600-3000 ppm in upper 10-cm layer to 10000-40000 ppm at a depth of 60 cm. The maximum concentrations of CO2 were recorded in late winter and late summer. We associate it with high biological activity (both heterotrophic and autotrophic) during the summer, and with physical gas jamming in the winter. The high value of annual CO2 production of the studied soils is caused by high organic matter content, slightly alkaline reaction, good structure and texture of urban soils. Differences in soil CO2 production by spruce and pine urban forest soils (in the pine forest 1.5-2.0 times higher) are caused by urban soil profiles construction, but not temperature regimes. Seasonal dynamics of CO2 production are the same for both soils and associated with seasonal changes in climatic parameters (temperature and moisture). CO2 efflux in the annual cycle correlates well with the soil temperature at a depth of 10 cm (r2 = 0.7). In the dry summer months, efflux largely depends on soil moisture. Soil CO2 efflux decreased by 1.5 - 2 times during the dry season.

Wet-dry seasonal and vertical geochemical variations in soil water and their driving forces under different land covers in southwest China karst

NASA Astrophysics Data System (ADS)

Wang, Peng; Hu, Bill X.; Wu, Chuanhao; Xu, Kai

2017-04-01

Karst aquifers supply drinking water for 25% of the world's population, and they are, however, vulnerable to climate change. Bimonthly hydrochemical data in karst soil water samples from July 2010 to July 2011 were obtained to reveal the seasonal and vertical geochemical variations in soil water under five vegetation types in Qingmuguan, a small karst catchment in southwest China. Soil water chemistry was dominated by Ca2+, HCO3-, and SO42- because of the dissolution of limestone, dolomite, and gypsum minerals in the strata. The predominant hydrochemical types in soil water were Ca2+-HCO3-, Ca2+-SO42-, and mixed Ca2+-HCO3-SO42-. Ca2+ and HCO3- concentrations ranked in the following order: shrub land > dry land > afforestation farmland > bamboo land > grassland. In warm and wet seasons, the main ion concentrations in soil water from grasslands were low. Na+, K+, Ca2+, Mg2+, HCO3-, SO42-, and Cl- concentrations in soil water from other lands were high. An opposite trend was observed in cold and dry seasons. Marked seasonal variations were observed in Ca2+, HCO3-, and NO3- in soil water from dry land. The main ion concentrations in soil water from bamboo lands decreased as soil depth increased. By contrast, the chemistry of soil water from other lands increased as soil depth increased. Their ions were accumulated in depth. A consistent high and low variation between the main ions in soil water and the contents of carbonate and CO2 was found in the soil. Hydrochemical changes in soil water were regulated by the effects of dilution and soil CO2.

A Physically-based Model for Predicting Soil Moisture Dynamics in Wetlands

NASA Astrophysics Data System (ADS)

Kalin, L.; Rezaeianzadeh, M.; Hantush, M. M.

2017-12-01

Wetlands are promoted as green infrastructures because of their characteristics in retaining and filtering water. In wetlands going through wetting/drying cycles, simulation of nutrient processes and biogeochemical reactions in both ponded and unsaturated wetland zones are needed for an improved understanding of wetland functioning for water quality improvement. The physically-based WetQual model can simulate the hydrology and nutrient and sediment cycles in natural and constructed wetlands. WetQual can be used in continuously flooded environments or in wetlands going through wetting/drying cycles. Currently, WetQual relies on 1-D Richards' Equation (RE) to simulate soil moisture dynamics in unponded parts of the wetlands. This is unnecessarily complex because as a lumped model, WetQual only requires average moisture contents. In this paper, we present a depth-averaged solution to the 1-D RE, called DARE, to simulate the average moisture content of the root zone and the layer below it in unsaturated parts of wetlands. DARE converts the PDE of the RE into ODEs; thus it is computationally more efficient. This method takes into account the plant uptake and groundwater table fluctuations, which are commonly overlooked in hydrologic models dealing with wetlands undergoing wetting and drying cycles. For verification purposes, DARE solutions were compared to Hydrus-1D model, which uses full RE, under gravity drainage only assumption and full-term equations. Model verifications were carried out under various top boundary conditions: no ponding at all, ponding at some point, and no rain. Through hypothetical scenarios and actual atmospheric data, the utility of DARE was demonstrated. Gravity drainage version of DARE worked well in comparison to Hydrus-1D, under all the assigned atmospheric boundary conditions of varying fluxes for all examined soil types (sandy loam, loam, sandy clay loam, and sand). The full-term version of DARE offers reasonable accuracy compared to the full RE solutions from Hydrus-1D, with a significant reduction in computational time. The full-term version of DARE estimated the moisture content with better accuracy for the root zone by considering zero pressure head at a fixed groundwater depth as the bottom boundary condition. The accuracy of this model is lower for the second layer.

Influence of hydraulic hysteresis on the mechanical behavior of unsaturated soils and interfaces

NASA Astrophysics Data System (ADS)

Khoury, Charbel N.

Unsaturated soils are commonly widespread around the world, especially at shallow depths from the surface. The mechanical behavior of this near surface soil is influenced by the seasonal variations such as rainfall or drought, which in turn may have a detrimental effect on many structures (e.g. retaining walls, shallow foundations, mechanically stabilized earth walls, soil slopes, and pavements) in contact with it. Thus, in order to better understand this behavior, it is crucial to study the complex relationship between soil moisture content and matric suction (a stress state variable defined as pore air pressure minus pore water pressure) known as the Soil Water Characteristic Curve (SWCC). In addition, the influence of hydraulic hysteresis on the behavior of unsaturated soils, soil-structure interaction (i.e. rough and smooth steel interfaces, soil-geotextile interfaces) and pavement subgrade (depicted herein mainly by resilient modulus, Mr) was also studied. To this end, suction-controlled direct shear tests were performed on soils, rough and smooth steel interfaces and geotextile interface under drying (D) and wetting after drying (DW). The shearing behavior is examined in terms of the two stress state variables, matric suction and net normal stress. Results along the D and DW paths indicated that peak shear strength increased with suction and net normal stress; while in general, the post peak shear strength was not influenced by suction for rough interfaces and no consistent trend was observed for soils and soil-geotextiles interfaces. Contrary to saturated soils, results during shearing at higher suction values (i.e. 25 kPa and above) showed a decrease in water content eventhough the sample exhibited dilation. A behavior postulated to be related to disruption of menisci and/or non-uniformity of pore size which results in an increase in localized pore water pressures. Interestingly, wetting after drying (DW) test results showed higher peak and post peak shear strength than that of the drying (D) tests. This is believed to be the result of many factors such as: (1) cyclic suction stress loading, (2) water content (less on wetting than drying), and (3) type of soil. The cyclic suction loading may have induced irrecoverable plastic strains, resulting in stiffer samples for wetting tests as compared to drying. Additionally, water may be acting as a lubricant and thus resulting in lower shear strength for test samples D with higher water contents than DW samples. Furthermore, various shear strength models were investigated for their applicability to the experimental data. Models were proposed for the prediction of shear strength with suction based on the SWCC. The models are able to predict the shear strength of unsaturated soil and interfaces due to drying and wetting (i.e. hydraulic hysteresis) by relating directly to the SWCC. The proposed models were used and partly validated by predicting different test results from the literature. In addition, an existing elastoplastic constitutive model was investigated and validated by comparing the predicted and experimental (stress-displacement, volume change behavior) results obtained from rough and geotextile interface tests. This study also explores the effect of hydraulic hysteresis on the resilient modulus (Mr) of subgrade soils. Suction-controlled Mr tests were performed on compacted samples along the primary drying, wetting, secondary drying and wetting paths. Two test types were performed to check the effect of cyclic deviatoric stress loading on the results. First, M r tests were performed on the same sample at each suction (i.e. 25, 50, 75, 100 kPa) value along all the paths (drying, wetting etc.). A relationship between resilient modulus (Mr) and matric suction was obtained and identified as the resilient modulus characteristic curve (MRCC). MRCC results indicated that Mr increased with suction along the drying curve. On the other hand, results on the primary wetting indicated higher Mr than that of the primary drying and the secondary drying. The second type of test was performed at selected suction without subjecting the sample to previous Mr tests. Results indicated that Mr compared favorably with the other type of test (i.e. with previous M r testing), which indicates that the cyclic deviatoric stress loading influence was not as significant as the hydraulic hysteresis (i.e. cyclic suction stress loading). A new model to predict the MRCC results during drying and wetting (i.e., hydraulic hysteresis) is proposed based on the SWCC hysteresis. The model predicted favorably the drying and then the wetting results using the SWCC at all stress levels. (Abstract shortened by UMI.)

Effect of phosphoric fertilizer and starter rates of nitrogen fertilizers on the phosphatase activity in the rhizosphere soil and nonlignified soybean roots under drought conditions

NASA Astrophysics Data System (ADS)

Emnova, E. E.; Daraban, O. V.; Bizgan, I. V.; Toma, S. I.

2014-02-01

In a small-plot field experiment, two soybean ( Glycine max L.) cultivars were grown on a calcareous chernozem under the drought conditions of 2012 with the preplanting application of simple superphosphate (Ps) at 60 kg/ha, urea (Nu) at 10 and 20 kg/ha, and ammonium nitrate (Nan) at 20 kg/ha. The phosphatase activity was measured in the rhizosphere soil (0- to 20-cm layer) and the fine nonlignified roots of soybean plants at the blossoming and pod-formation stages (the soil water content was 19 and 33% of the total water capacity, respectively). The maximum content of available phosphorus in the rhizosphere of both soybean cultivars (4.3-4.8 mg/100 g dry soil) was found at the simultaneous application of Ps and Nu20. Higher activities of the predominant phosphatases (alkaline phosphatase in the rhizosphere and acid phosphatase in the roots) were observed in the root-inhabited zone of the soil under the Indra cultivar compared to the Aura cultivar, which correlated with the lower content of available phosphorus in the rhizosphere soil (especially at the simultaneous application of Ps and Nu20) and the higher productivity of this cultivar in this treatment.

Using 13C labeled glucose to determine soil microbial and physical controls of new C incorporation under drying-rewetting cycles and conservation agricultural management

NASA Astrophysics Data System (ADS)

Li, L.; Schaeffer, S. M.

2017-12-01

Drying-rewetting cycles can induce carbon (C) depletion in soil, while conservation agricultural management aims at soil C sequestration. Understanding the combined effect of drying-rewetting cycles and conservation management is critical for sustaining agricultural soil under climate change. Soil organic C can be stored in a relatively rapidly cycling active pool, or a more slowly cycling passive pool. We conducted a 24-days mesocosm incubation using an agricultural soil from western Tennessee under 35-years of conservation management. Different lengths of drought period before rewetting of 0, 3, 6, and 24 days were applied on the mesocosms. To trace the fate of newly added C, 13C labeled glucose was added to the mesocosms at the beginning of the incubation. After 24 days, dissolvable organic C, microbial biomass C, accumulative microbial respiration, and extracellular enzyme activity were analyzed to evaluate the active C pool; hydrogen peroxide oxidation and aggregate size fractionation were used to examine the passive C pool. The highest cumulative microbial respiration was found in the 6-days treatment combining a N-fixing cover crop with no-tillage, and the lowest in the 24-day treatment with a wheat cover crop combined with conventional-tillage (1000.0±20.5 and 106.8±17.5 µg C-CO2 g-1 dry soil, respectively). The 6-days treatment induced 0.5-4.3 times higher cumulative C-CO2 emission than the 3-days treatment. The proportion of macroaggregates in bulk soil varied between 97.2% and 76.7%, and it was negatively correlated with drying-rewetting frequency. The proportion of microaggregates in bulk soil varied between 21.9% and 2.1%, and it was positively correlated with drying-rewetting frequency. 13C recovery rate in bulk soil varied between 11-53%. The vetch-cover-crop-with-no-tillage treatment facilitated 13C accumulation the most. Our results show that the N fixing cover crops combined with no-tillage treatment induced the highest C accumulation in bulk soil, while the no cover crop combined with conventional tillage induced the lowest C concentration. Our results show that frequent drying-rewetting cycles disrupt macroaggregates and release the microaggregates within macroaggregates, and favor greater C loss combined with greater C storage in less stable aggregate fractions.

Effect of Drying on Heavy Metal Fraction Distribution in Rice Paddy Soil

PubMed Central

Qi, Yanbing; Huang, Biao; Darilek, Jeremy Landon

2014-01-01

An understanding of how redox conditions affect soil heavy metal fractions in rice paddies is important due to its implications for heavy metal mobility and plant uptake. Rice paddy soil samples routinely undergo oxidation prior to heavy metal analysis. Fraction distribution of Cu, Pb, Ni, and Cd from paddy soil with a wide pH range was investigated. Samples were both dried according to standard protocols and also preserved under anaerobic conditions through the sampling and analysis process and heavy metals were then sequentially extracted for the exchangeable and carbonate bound fraction (acid soluble fraction), iron and manganese oxide bound fraction (reducible fraction), organic bound fraction (oxidizable fraction), and residual fraction. Fractions were affected by redox conditions across all pH ranges. Drying decreased reducible fraction of all heavy metals. Curesidual fraction, Pboxidizable fraction, Cdresidual fraction, and Niresidual fraction increased by 25%, 33%, 35%, and >60%, respectively. Pbresidual fraction, Niacid soluble fraction, and Cdoxidizable fraction decreased 33%, 25%, and 15%, respectively. Drying paddy soil prior to heavy metal analysis overestimated Pb and underestimated Cu, Ni, and Cd. In future studies, samples should be stored after injecting N2 gas to maintain the redox potential of soil prior to heavy metal analysis, and investigate the correlation between heavy metal fraction distribution under field conditions and air-dried samples. PMID:24823670

Modelling the Response of Energy, Water and CO2 Fluxes Over Forests to Climate Variability

NASA Astrophysics Data System (ADS)

Ju, W.; Chen, J.; Liu, J.; Chen, B.

2004-05-01

Understanding the response of energy, water and CO2 fluxes of terrestrial ecosystems to climate variability at various temporal scales is of interest to climate change research. To simulate carbon (C) and water dynamics and their interactions at the continental scale with high temporal and spatial resolutions, the remote sensing driven BEPS (Boreal Ecosystem Productivity Simulator) model was updated to couple with the soil model of CENTURY and a newly developed biophysical model. This coupled model separates the whole canopy into two layers. For the top layer, the leaf-level conductance is scaled up to canopy level using a sunlit and shaded leaf separation approach. Fluxes of water, and CO{2} are simulated as the sums of those from sunlit and shaded leaves separately. This new approach allows for close coupling in modeling these fluxes. The whole profile of soil under a seasonal snowpack is split into four layers for estimating soil moisture and temperature. Long-term means of the vegetation productivity and climate are employed to initialize the carbon pools for the computation of heterotrophic respiration. Validated against tower data at four forested sites, this model is able to describe these fluxes and their response to climate variability. The model captures over 55% of year-round half/one hourly variances of these fluxes. The highest agreement of model results with tower data was achieved for CO2 flux at Southern Old Aspen (SOA) (R2>0.85 and RMSE<2.37 μ mol C m-2 s-1, N=17520). However, the model slightly overestimates the diurnal amplitude of sensible heat flux in winter and sometimes underestimates that of CO2 flux in the growing season. Model simulations suggest that C uptakes of forests are controlled by climate variability and the response of C cycle to climate depends on forest type. For SOA, the annual NPP (Net Primary Productivity) is more sensitive to temperature than to precipitation. This forest usually has higher NPP in warm years than in cool years. Interannual variability of heterotrophic respiration, however, is strongly related to precipitation. The soil releases more CO2 in wet years than in dry years. Warm and relatively dry climate enhances the C uptake in this forest stand. Compared with SOA, a temperate deciduous forest in the southern part of the temperate deciduous forest biome in eastern United States responds to climate variability differently. High temperature and low precipitation in the growing season reduces NPP and consequently NEP (Net Ecosystem Productivity). In warm years, the Southern Old Jack Pine forest uptakes less C than in cool years. The modeled heterotrophic respiration and NEP are very sensitive to soil moisture and the empirical equation used to describe the effect of soil moisture on decomposition. This suggests that hydrological modelling is critical in C budget estimation. Next step, this model will be validated against more tower data and used for upscaling from site to region.

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.

Influence of dry soil on the ability of Formosan Subterranean Termites, Coptotermes formosanus, to locate food sources.

USDA-ARS?s Scientific Manuscript database

The effect of barriers of dry soil on the ability of Formosan subterranean termites, Coptotermes formosanus Shiraki, to construct tunnels and find food was evaluated. Termite movement and wood consumption in a three-chambered apparatus were compared for treatments where the soil in the center contai...

Influence of Dry Soil on the Ability of Formosan Subterranean Termites (Coptotermes formosanus) to Locate Food Sources

USDA-ARS?s Scientific Manuscript database

The effect of barriers of dry soil on the ability of Formosan subterranean termites, Coptotermes formosanus Shiraki, to construct tunnels and find food was evaluated. Termite movement and wood consumption in a three-chambered apparatus were compared for treatments where the soil in the center contai...

Timing of seed dispersal generates a bimodal seed bank depth distribution

USGS Publications Warehouse

Espinar, J.L.; Thompson, K.; Garcia, L.V.

2005-01-01

The density of soil seed banks is normally highest at the soil surface and declines monotonically with depth. Sometimes, for a variety of reasons, peak density occurs below the surface but, except in severely disturbed soils, it is generally true that deeper seeds are older. In seasonally dry habitats that develop deep soil cracks during the dry season, it is possible that some seeds fall down cracks and rapidly become deeply buried. We investigated this possibility for three dominant clonal perennials (Scirpus maritimus, S. litoralis, and Juncus subulatus) in the Don??ana salt marsh, a nontidal marsh with a Mediterranean climate located in southwest Spain. Two species, which shed most of their seed during the dry season and have seeds with low buoyancy, had bimodal viable seed depth distributions, with peak densities at the surface and at 16-20 cm. A third species, which shed most seeds after soil cracks had closed and had seeds with high buoyancy, had viable seeds only in surface soil. Bimodal seed bank depth distributions may be relatively common in seasonally dry habitats with fine-textured soils, but their ecological significance has not been investigated.

Individual contributions of climate and vegetation change to soil moisture trends across multiple spatial scales.

PubMed

Feng, Huihui

2016-09-07

Climate and vegetation change are two dominating factors for soil moisture trend. However, their individual contributions remain unknown due to their complex interaction. Here, I separated their contributions through a trajectory-based method across the global, regional and local scales. Our results demonstrated that climate change accounted for 98.78% and 114.64% of the global drying and wetting trend. Vegetation change exhibited a relatively weak influence (contributing 1.22% and -14.64% of the global drying and wetting) because it occurred in a limited area on land. Regionally, the impact of vegetation change cannot be neglected, which contributed -40.21% of the soil moisture change in the wetting zone. Locally, the contributions strongly correlated to the local environmental characteristics. Vegetation negatively affected soil moisture trends in the dry and sparsely vegetated regions and positively in the wet and densely vegetated regions. I conclude that individual contributions of climate and vegetation change vary at the global, regional and local scales. Climate change dominates the soil moisture trends, while vegetation change acts as a regulator to drying or wetting the soil under the changing climate.

Dry deposition and soil-air gas exchange of polychlorinated biphenyls (PCBs) in an industrial area.

PubMed

Bozlaker, Ayse; Odabasi, Mustafa; Muezzinoglu, Aysen

2008-12-01

Ambient air and dry deposition, and soil samples were collected at the Aliaga industrial site in Izmir, Turkey. Atmospheric total (particle+gas) Sigma(41)-PCB concentrations were higher in summer (3370+/-1617 pg m(-3), average+SD) than in winter (1164+/-618 pg m(-3)), probably due to increased volatilization with temperature. Average particulate Sigma(41)-PCBs dry deposition fluxes were 349+/-183 and 469+/-328 ng m(-2) day(-1) in summer and winter, respectively. Overall average particulate deposition velocity was 5.5+/-3.5 cm s(-1). The spatial distribution of Sigma(41)-PCB soil concentrations (n=48) showed that the iron-steel plants, ship dismantling facilities, refinery and petrochemicals complex are the major sources in the area. Calculated air-soil exchange fluxes indicated that the contaminated soil is a secondary source to the atmosphere for lighter PCBs and as a sink for heavier ones. Comparable magnitude of gas exchange and dry particle deposition fluxes indicated that both mechanisms are equally important for PCB movement between air and soil in Aliaga.

Mitigation of Prion Infectivity and Conversion Capacity by a Simulated Natural Process—Repeated Cycles of Drying and Wetting

PubMed Central

Yuan, Qi; Eckland, Thomas; Telling, Glenn; Bartz, Jason; Bartelt-Hunt, Shannon

2015-01-01

Prions enter the environment from infected hosts, bind to a wide range of soil and soil minerals, and remain highly infectious. Environmental sources of prions almost certainly contribute to the transmission of chronic wasting disease in cervids and scrapie in sheep and goats. While much is known about the introduction of prions into the environment and their interaction with soil, relatively little is known about prion degradation and inactivation by natural environmental processes. In this study, we examined the effect of repeated cycles of drying and wetting on prion fitness and determined that 10 cycles of repeated drying and wetting could reduce PrPSc abundance, PMCA amplification efficiency and extend the incubation period of disease. Importantly, prions bound to soil were more susceptible to inactivation by repeated cycles of drying and wetting compared to unbound prions, a result which may be due to conformational changes in soil-bound PrPSc or consolidation of the bonding between PrPSc and soil. This novel finding demonstrates that naturally-occurring environmental process can degrade prions. PMID:25665187

Influence of summer marine fog and low cloud stratus on water relations of evergreen woody shrubs (Arctostaphylos: Ericaceae) in the chaparral of central California.

PubMed

Vasey, Michael C; Loik, Michael E; Parker, V Thomas

2012-10-01

Mediterranean-type climate (MTC) regions around the world are notable for cool, wet winters and hot, dry summers. A dominant vegetation type in all five MTC regions is evergreen, sclerophyllous shrubland, called chaparral in California. The extreme summer dry season in California is moderated by a persistent low-elevation layer of marine fog and cloud cover along the margin of the Pacific coast. We tested whether late dry season water potentials (Ψ(min)) of chaparral shrubs, such as Arctostaphylos species in central California, are influenced by this coast-to-interior climate gradient. Lowland coastal (maritime) shrubs were found to have significantly less negative Ψ(min) than upland interior shrubs (interior), and stable isotope (δ(13)C) values exhibited greater water use efficiency in the interior. Post-fire resprouter shrubs (resprouters) had significantly less negative Ψ(min) than co-occurring obligate seeder shrubs (seeders) in interior and transitional chaparral, possibly because resprouters have deeper root systems with better access to subsurface water than shallow-rooted seeders. Unexpectedly, maritime resprouters and seeders did not differ significantly in their Ψ(min), possibly reflecting more favorable water availability for shrubs influenced by the summer marine layer. Microclimate and soil data also suggest that maritime habitats have more favorable water availability than the interior. While maritime seeders constitute the majority of local Arctostaphylos endemics, they exhibited significantly greater vulnerability to xylem cavitation than interior seeders. Because rare seeders in maritime chaparral are more vulnerable to xylem cavitation than interior seeders, the potential breakdown of the summer marine layer along the coast is of potential conservation concern.

Vegetation Coverage Mapping and Soil Effect Correction in Estimating Vegetation Water Content and Dry Biomass from Satellites

NASA Astrophysics Data System (ADS)

Huang, J.; Chen, D.

2005-12-01

Vegetation water content (VWC) attracts great research interests in hydrology research in recent years. As an important parameter describing the horizontal expansion of vegetation, vegetation coverage is essential to implement soil effect correction for partially vegetated fields to estimate VWC accurately. Ground measurements of corn and soybeans in SMEX02 resulted in an identical expolinear relationship between vegetation coverage and leaf area index (LAI), which is used for vegetation coverage mapping. Results illustrated two parts of LAI growth quantitatively: the horizontal expansion of leaf coverage and the vertical accumulation of leaf layers. It is believed that the former part contributes significantly to LAI growth at initial vegetation growth stage and the latter is more dominant after vegetation coverage reaches a certain level. The Normalized Difference Water Index (NDWI) using short-wave infrared bands is convinced for its late saturation at high LAI values, in contrast to the Normalized Difference Vegetation Index (NDVI). NDWI is then utilized to estimate LAI, via another expolinear relationship, which is evidenced having vegetation species independency in study of corn and soybeans in SMEX02 sites. It is believed that the surface reflectance measured at satellites spectral bands are the mixed results of signals reflected from vegetation and bare soil, especially at partially vegetated fields. A simple linear mixture model utilizing vegetation coverage information is proposed to correct soil effect in such cases. Surface reflectance fractions for -rpure- vegetation are derived from the model. Comparing with ground measurements, empirical models using soil effect corrected vegetation indices to estimate VWC and dry biomass (DB) are generated. The study enhanced the in-depth understanding of the mechanisms how vegetation growth takes effect on satellites spectral reflectance with and without soil effect, which are particularly useful for modeling in hydrology, agriculture, forestry and meteorology etc.

Effect of soil water content on spatial distribution of root exudates and mucilage in the rhizosphere

NASA Astrophysics Data System (ADS)

Holz, Maire; Zarebanadkouki, Mohsen; Kuzyakov, Yakov; Carminati, Andrea

2016-04-01

Water and nutrients are expected to become the major factors limiting food production. Plant roots employ various mechanisms to increase the access to these limited soil resources. Low molecular root exudates released into the rhizosphere increase nutrient availability, while mucilage improves water availability under low moisture conditions. However, studies on the spatial distribution and quantification of exudates in soil are scarce. Our aim was therefore to quantify and visualize root exudates and mucilage distribution around growing roots using neutron radiography and 14C imaging at different levels of water stress. Maize plants were grown in rhizotrons filled with a silty soil and were exposed to varying soil conditions, from optimal to dry. Mucilage distribution around the roots was estimated from the profiles of water content in the rhizosphere - note that mucilage increases the soil water content. The profiles of water content around different root types and root ages were measured with neutron radiography. Rhizosphere extension was approx. 0.7 mm and did not differ between wet and dry treatments. However, water content (i.e. mucilage concentration) in the rhizosphere of plants grown in dry soils was higher than for plants grown under optimal conditions. This effect was particularly pronounced near the tips of lateral roots. The higher water contents near the root are explained as the water retained by mucilage. 14C imaging of root after 14CO2 labeling of shoots (Pausch and Kuzyakov 2011) was used to estimate the distribution of all rhizodeposits. Two days after labelling, 14C distribution was measured using phosphor-imaging. To quantify 14C in the rhizosphere a calibration was carried out by adding given amounts of 14C-glucose to soil. Plants grown in wet soil transported a higher percentage of 14C to the roots (14Croot/14Cshoot), compared to plants grown under dry conditions (46 vs. 36 %). However, the percentage of 14C allocated from roots to rhizosphere (14Crhizosphere/14Croot) was double in plants grown under dry conditions (0.43 vs. 0.75 %). Plants grown in wet soils showed a faster root growth (1.4 cm d-1) compared to plants in dry soil (1 cm d-1). Compared to the results with neutron radiography, rhizosphere extension of 14C was generally higher and strongly depended on root type: it was 2 mm for main roots and 1 mm for lateral roots. This indicates that low molecular exudates diffuse further into the soil than mucilage. As for mucilage, concentration of 14C was higher in the rhizosphere of plants grown under dry conditions. This observation can be explained by: (a) higher allocation of 14C from roots to rhizosphere in dry soils, (b) a fast diffusion of exudates in wet soils, and (c) faster root growth in wet soils, which results in lower exudation per root length. In summary, the combination of neutron radiography and 14C imaging was successfully used to visualize and to quantify the distribution of mucilage and root exudates in the rhizosphere of plants grown in soil. The high concentration of root exudates in rhizosphere under dry conditions might be strategy of plants to increase their water and nutrient availability unfavorable conditions.

Sources of nitric oxide and nitrous oxide following wetting of dry soil

NASA Technical Reports Server (NTRS)

Davidson, Eric A.

1992-01-01

A study is presented which is aimed at distinguishing among autotrophic nitrification, denitrification, and abiological processes as sources of NO and N2O production following wetting of dry soil. To distinguish among these processes, combinations of treatments in laboratory incubations of soil were used which included varying soil water content, autoclaving, C2H2 inhibition, and NO2(-) addition. Biological sources of NO and N2O commenced within minutes of wetting dry soil. Acetylene inhibition revealed that emissions of NO were dependent on nitrification, although a combination of NO2(-) production by nitrifiers and abiological reduction of NO2(-) to NO is also possible. NO emissions exceeded N2O emissions, and nitrification was the dominant source of both gases when soil water was below field capacity. It is concluded that NO emissions appear to be more important when good soil aeration favors nitrification, whereas N2O emissions appear more important when elevated soil water favors denitrification.

Subsurface Salts in Antarctic Dry Valley Soils

NASA Technical Reports Server (NTRS)

Englert, P.; Bishop, J. L.; Gibson, E. K.; Koeberl, C.

2013-01-01

The distribution of water-soluble ions, major and minor elements, and other parameters were examined to determine the extent and effects of chemical weathering on cold desert soils. Patterns at the study sites support theories of multiple salt forming processes, including marine aerosols and chemical weathering of mafic minerals. Periodic solar-mediated ionization of atmospheric nitrogen might also produce high nitrate concentrations found in older sediments. Chemical weathering, however, was the major contributor of salts in Antarctic Dry Valleys. The Antarctic Dry Valleys represent a unique analog for Mars, as they are extremely cold and dry desert environments. Similarities in the climate, surface geology, and chemical properties of the Dry Valleys to that of Mars imply the possible presence of these soil formation mechanisms on Mars, other planets and icy satellites.

An Experimental Study on the Impact of Different-frequency Elastic Waves on Water Retention Curve

NASA Astrophysics Data System (ADS)

Deng, J. H.; Dai, J. Y.; Lee, J. W.; Lo, W. C.

2017-12-01

ABSTEACTOver the past few decades, theoretical and experimental studies on the connection between elastic wave attributes and the physical properties of a fluid-bearing porous medium have attracted the attention of many scholars in fields of porous medium flow and hydrogeology. It has been previously determined that the transmission of elastic waves in a porous medium containing two immiscible fluids will have an effect on the water retention curve, but it has not been found that the water retention curve will be affected by the frequency of elastic vibration waves or whether the effect on the soil is temporary or permanent. This research is based on a sand box test in which the soil is divided into three layers (a lower, middle, and upper layer). In this case, we discuss different impacts on the water retention curve during the drying process under sound waves (elastic waves) subject to three frequencies (150Hz, 300Hz, and 450Hz), respectively. The change in the water retention curve before and after the effect is then discussed. In addition, how sound waves affect the water retention curve at different depths is also observed. According to the experimental results, we discover that sound waves can cause soil either to expand or to contract. When the soil is induced to expand due to sound waves, it can contract naturally and return to the condition it was in before the influence of the sound waves. On the contrary, when the soil is induced to contract, it is unable to return to its initial condition. Due to the results discussed above, it is suggested that sound waves causing soil to expand have a temporary impact while those causing soil to contract have a permanent impact. In addition, our experimental results show how sound waves affect the water retention curve at different depths. The degree of soil expansion and contraction caused by the sound waves will differ at various soil depths. Nevertheless, the expanding or contracting of soil is only subject to the frequency of sound waves. Key words: Elastic waves, Water retention curve, Sand box test.

Comparison of organochlorine pesticides and polychlorinated biphenyls residues in vegetables, grain and soil from organic and conventional farming in Poland.

PubMed

Witczak, Agata; Abdel-Gawad, Hassan

2012-01-01

Organic and conventional crops were studied by identifying the relationship between persistent organic pollutants in cereals, vegetables and soil. The residues of organochlorine pesticides and polychlorinated biphenyls (PCBs) were determined in grains (rye and wheat), vegetables (carrots and beets) and soil collected from the fields. PCB residues recorded in the beets from organic farming were as high as 3.71 ppb dry weight (dry wt.), while in the soil from conventional farming of beets 0.53 ppb dry wt. Among vegetables, higher concentrations of pesticides were detected in organically grown beets (190.63 ppb dry wt.). Soil samples from the organic farming contained lower levels of organochlorine pesticide residues compared to the conventional farming. Taking into account toxicity equivalent (TEQ), the conventionally grown carrots accumulated the most toxic PCBs. Non-ortho and mono-ortho PCBs were also noted in the grain of conventionally grown rye and amounted to 3.05 pg-TEQ/g wet wt.

Chemical and Mineralogical Characterization of Arsenic, Lead, Chromium, and Cadmium in a Metal-contaminated Histosol

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

Gao, X.; Schulze, D

2010-01-01

The chemical and mineralogical forms of As, Pb, Cr, and Cd were studied in a metal-contaminated organic soil (Histosol) that received runoff and seepage water from a site that was once occupied by a lead smelter. Soil samples were collected from different depth intervals during both wet and dry seasons and analyzed using bulk powder X-ray diffraction (XRD), synchrotron-based micro X-ray diffraction ({mu}-XRD), and micro X-ray fluorescence ({mu}-SXRF) spectroscopy. There was a clear pattern of mineral distribution with depth that indicated the presence of an intense redox gradient. The oxidized reddish brown surface layer (0-10 cm) was dominated by goethitemore » ({alpha}-FeOOH) and poorly crystalline akaganeite ({beta}-FeOOH). Lead and arsenic were highly associated with these Fe oxides, possibly by forming inner-sphere surface complexes. Gypsum (CaSO{sub 4} {center_dot} 2H{sub 2}O) was abundant in the layer as well, particularly for samples collected during dry periods. Fe(II)-containing minerals, such as magnetite (Fe{sub 3}O{sub 4}) and siderite (FeCO{sub 3}), were identified in the intermediate layers (10-30 cm) where the reductive dissolution of Fe(III) oxides occurred. A number of high-temperature minerals, such as mullite (3Al{sub 2}O{sub 3} {center_dot} 2Si{sub 2}O), corundum ({alpha}-Al{sub 2}O{sub 3}), hematite ({alpha}-Fe{sub 2}O{sub 3}), and wustite (FeO) were identified in the subsurface and they probably formed as a result of a burning event. Several sulfide minerals were identified in the most reduced layers at depths > 30 cm. They included realgar (AsS), alacranite (As{sub 4}S{sub 4}), galena (PbS), and sphalerite (Zn, Fe{sup 2+})S, and a series of Fe sulfides, including greigite (Fe{sup 2+}Fe{sub 2}{sup 3+} S{sub 4}), pyrrhotite (Fe{sub 1-x}S), mackinawite (FeS), marcasite (FeS{sub 2}), and pyrite (FeS{sub 2}). Most of these minerals occurred as almost pure phases in sub-millimeter aggregates and appeared to be secondary phases that had precipitated from solution. Despite the elevated levels of Cd in the soil, no specific Cd phases were identified. The complex mineralogy has important implications for risk assessment and the design of in-situ remediation strategies for this and similar metal-contaminated sites.« less

[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.

Hydrological Responses of Weather Conditions and Crop Change of Agricultural Area in the Rincon Valley, New Mexico

NASA Astrophysics Data System (ADS)

Ahn, S.; Sheng, Z.; Abudu, S.

2017-12-01

Hydrologic cycle of agricultural area has been changing due to the impacts of climate and land use changes (crop coverage changes) in an arid region of Rincon Valley, New Mexico. This study is to evaluate the impacts of weather condition and crop coverage change on hydrologic behavior of agricultural area in Rincon Valley (2,466km2) for agricultural watershed management using a watershed-scale hydrologic model, SWAT (Soil and Water Assessment Tool). The SWAT model was developed to incorporate irrigation of different crops using auto irrigation function. For the weather condition and crop coverage change evaluation, three spatial crop coverages including a normal (2008), wet (2009), and dry (2011) years were prepared using USDA crop data layer (CDL) for fourteen different crops. The SWAT model was calibrated for the period of 2001-2003 and validated for the period of 2004-2006 using daily-observed streamflow data. Scenario analysis was performed for wet and dry years based on the unique combinations of crop coverages and releases from Caballo Reservoir. The SWAT model simulated the present vertical water budget and horizontal water transfer considering irrigation practices in the Rincon Valley. Simulation results indicated the temporal and spatial variability for irrigation and non-irrigation seasons of hydrologic cycle in agricultural area in terms of surface runoff, evapotranspiration, infiltration, percolation, baseflow, soil moisture, and groundwater recharge. The water supply of the dry year could not fully cover whole irrigation period due to dry weather conditions, resulting in reduction of crop acreage. For extreme weather conditions, the temporal variation of water budget became robust, which requires careful irrigation management of the agricultural area. The results could provide guidelines for farmers to decide crop patterns in response to different weather conditions and water availability.

Biogeochemical Relationships of a Subtropical Dry Forest on Karst

Treesearch

E. Medina; E. Cuevas; H. Marcano-Vega; E. Meléndez-Ackerman; E.H. Helmer

2017-01-01

Tropical dry forests on calcareous substrate constitute the main vegetation cover in many islands of the Caribbean. Dry climate and nutrient scarcity in those environments are ideal to investigate the potential role of high levels of soil calcium (Ca) in regulating plant selection and productivity. We analyzed the elemental composition of soil, loose litter, and leaf...

Active layer thermal monitoring of a Dry Valley of the Ellsworth Mountains, Continental Antarctica

NASA Astrophysics Data System (ADS)

Schaefer, Carlos Ernesto; Michel, Roberto; Souza, Karoline; Senra, Eduardo; Bremer, Ulisses

2015-04-01

The Ellsworth Mountains occur along the southern edge of the Ronne-Filchner Ice Shelf and are subdivided by the Minnesota Glacier into the Heritage Range to the east and the Sentinel Range to the West. The climate of the Ellsworth Mountains is strongly controlled by proximity to the Ronne-Filchner Ice Shelf and elevation. The mean annual air temperature at the 1,000 m level is estimated to be -25°C, and the average annual accumulation of water-equivalent precipitation likely ranges from 150 to 175 mm yr-1 (Weyant, 1966). The entire area is underlain by continuous permafrost of unknown thickness. Based on data collected from 22 pits, 41% of the sites contained dry permafrost below 70 cm, 27% had ice-cemented permafrost within 70 cm of the surface, 27% had bedrock within 70 cm, and 5% contained an ice-core (Bockheim, unpublished; Schaefer et al., 2015). Dry-frozen permafrost, which may be unique to Antarctica, appears to form from sublimation of moisture in ice-cemented permafrost over time. Active-layer depths in drift sheets of the Ellsworth Mountains range from 15 to 50 cm (Bockheim, unpublished); our understanding of Antarctic permafrost is poor, especially at the continent. The active layer monitoring sites were installed at Edson Hills, Ellsworth_Mountains, in the summer of 2012, and consist of thermistors (accuracy ± 0.2 °C) installed at 1 m above ground for air temperature measurements at two soil profiles on quartzite drift deposits, arranged in a vertical array (Lithic Haplorthel 886 m asl, 5 cm, 10 cm, 30 cm and Lithic Anyorthel 850 m asl, 5 cm, 10 cm, 30 cm). All probes were connected to a Campbell Scientific CR 1000 data logger recording data at hourly intervals from January 2nd 2012 until December 29th 2013. We calculated the thawing days (TD), freezing days (FD); isothermal days (ID), freeze thaw days (FTD), thawing degree days (TDD) and freezing degree days (FDD); all according to Guglielmin et al. (2008). Temperature at 5 cm reaches a maximum daily average in late December 2012, reaching a minimum in mid July 2013 on P1 (10.9 °C, -37.9 °C, ± 11.1) and P2 (6.9 °C, -37.1 °C, ± 10.2). The active layer thickness reaches a maximum of 48.4 cm at P1 on January 17th 2013 and 47.8 cm at P2 on January 7th 2012. No ID were recorded for the studied period, one TD was recorded at 5 cm on P2, 143 FTD were recorded at 5 cm, 81 at 10 cm and 46 days at 30 cm on P1, on P2 118 FTD were recorded at 5 cm, 80 at 10 cm and 42 days at 30 cm. The majority of the days were classified as FD for both sites; 585 at 5 cm, 647 at 10 cm and 684 days at 30 cm on P1, on P2 611 FD were recorded at 5 cm, 650 at 10 cm and 688 days at 30 cm. Only 17 FTD were recorded for the air temperature and 713 FD. Over the 728 days of the studied period the sum of all positive daily average temperatures was 166.3 TDD at 5 cm and 23.8 TDD at 10 cm on P1, 45.0 TDD at 5 cm and 5.2 TDD at 10 cm on P2. No positive daily average was recorded at 30 cm for both sites. The sum of all negative daily average temperatures was -13504.5 FDD at 5 cm, -13389.9 FDD at 10 cm and -13381.0 FDD at 30 cm on P1, -13508.0 FDD at 5 cm, -13486.6 FDD at 10 cm and -13398.9 FDD at 30 cm on P2. Only 0.28 TDD were summed for the air temperature and -14430.7 FDD. The soil thermal regime at the dry valley of Edson Hill, Ellsworth Mountains is characteristic of polar desert affected by Dry-frozen permafrost. Although air temperature does not reach high positive values, variations in soil temperature are more intense during the year, showing the soil's response to solar radiation.

Quantifying the influence of deep soil moisture on ecosystem albedo: the role of vegetation Zulia M. Sánchez-Mejía 1 and Shirley A. Papuga1 1School of Natural Resources and the Environment, University of Arizona, Tucson, AZ

NASA Astrophysics Data System (ADS)

Sanchez-Mejia, Z. M.; Papuga, S. A.

2012-12-01

Water limited ecosystems in arid and semiarid regions are characterized by sparse vegetation and a relatively large fraction of bare soil. Importantly, the land surface in these dryland regions is highly sensitive to pulses of moisture that affect the vegetation canopy in density and color, as well as the soil color. Changes in surface conditions due to these pulses have been shown to affect the surface energy fluxes and atmospheric processes in these regions. For instance, previous studies have shown that shallow soil moisture ( < 20 cm below the surface) significantly changes surface albedo (a= SWup/ SWin). Recent studies have highlighted the importance of deep soil moisture ( > 20 cm below the surface) for vegetation dynamics in these regions. We hypothesize that deep soil moisture will change vegetation canopy density and color enough that changes in albedo will be observable at the surface, therefore linking deep soil moisture and albedo. We adopt a conceptual framework to address this hypothesis, where at any point in time the soil profile falls into one of four cases: (1) dry shallow soil and dry deep soil; (2) wet shallow soil and dry deep soil; (3) wet shallow soil and wet deep soil; and (4) dry shallow soil and wet deep soil. At a creosotebush dominated ecosystem of the Santa Rita Experimental Range, southern Arizona during summers of 2011 and 2012, we took albedo measurements during these cases at multiple bare and vegetated patches within the footprint of an eddy covariance tower. We found that when the soil is completely dry (Case 1) albedo is highest in both bare and vegetated patches. Likewise, when the soil is wet in both the shallow and deep regions (Case 3), albedo is lowest in both bare and vegetated patches. Interestingly, we also found that albedo is significantly lower for vegetated patches when the deep soil is wet and shallow soil is dry (Case 4). These results imply that deep soil moisture can be important in altering ecosystem level albedo. We note that ecosystems with higher percent vegetative cover are likely to be more sensitive to deep soil moisture driven changes in albedo. To quantify the influence of percent cover on ecosystem albedo, we populate a 100 x 100 cell grid randomly with bare and vegetated cells. For each case, we assign an albedo value to each cell based on probability distribution functions (PDFs) of soil moisture and albedo created from our field campaign data. Using this technique we can identify for each soil moisture case at which point the percent vegetative cover will significantly influence ecosystem albedo. Quantitative analyses of these ecosystem interactions help identify the unique role of deep soil moisture in land surface - atmosphere interactions.

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.

Improving Numerical Weather Predictions of Summertime Precipitation Over the Southeastern U.S. Through a High-Resolution Initialization of the Surface State

NASA Technical Reports Server (NTRS)

Case, Jonathan L.; Kumar, Sujay V.; Krikishen, Jayanthi; Jedlovec, Gary J.

2011-01-01

It is hypothesized that high-resolution, accurate representations of surface properties such as soil moisture and sea surface temperature are necessary to improve simulations of summertime pulse-type convective precipitation in high resolution models. This paper presents model verification results of a case study period from June-August 2008 over the Southeastern U.S. using the Weather Research and Forecasting numerical weather prediction model. Experimental simulations initialized with high-resolution land surface fields from the NASA Land Information System (LIS) and sea surface temperature (SST) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) are compared to a set of control simulations initialized with interpolated fields from the National Centers for Environmental Prediction 12-km North American Mesoscale model. The LIS land surface and MODIS SSTs provide a more detailed surface initialization at a resolution comparable to the 4-km model grid spacing. Soil moisture from the LIS spin-up run is shown to respond better to the extreme rainfall of Tropical Storm Fay in August 2008 over the Florida peninsula. The LIS has slightly lower errors and higher anomaly correlations in the top soil layer, but exhibits a stronger dry bias in the root zone. The model sensitivity to the alternative surface initial conditions is examined for a sample case, showing that the LIS/MODIS data substantially impact surface and boundary layer properties.