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Sample records for soil aggregates

  1. A whole soil stability index (WSSI) for evaluating soil aggregation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil aggregate stability is an indicator of soil quality. However, there is no standard methodology for measuring soil aggregation or aggregate stability, particularly for determining a whole soil stability index. A whole soil stability index (WSSI) was developed here which combined data from dry ...

  2. Seasonal variability of soil aggregate stability

    NASA Astrophysics Data System (ADS)

    Rohoskova, M.; Kodesova, R.; Jirku, V.; Zigova, A.; Kozak, J.

    2009-04-01

    Seasonal variability of soil properties measured in surface horizons of three soil types (Haplic Luvisol, Greyic Phaeozem, Haplic Cambisol) was studied in years 2007 and 2008. Undisturbed and disturbed soil samples were taken every month to evaluate field water content, bulk density, porosity, ration of gravitational and capillary pores, pHKCl and pHH2O, organic matter content and its quality, aggregate stability using WSA index. In addition, micromorphological features of soil aggregates were studied in thin soil sections that were made from undisturbed large soil aggregates. Results showed that soil aggregate stability depended on stage of the root zone development, soil management and climatic conditions. Larger aggregate stabilities and also larger ranges of measure values were obtained in the year 2007 then those measured in 2008. This was probably caused by lower precipitations and consequently lower soil water contents observed in 2007 than those measured in 2008. The highest aggregate stability was measured at the end of April in the years 2007 and 2008 in Haplic Luvisol and Greyic Phaeozem, and at the end of June in the year 2007 and at the beginning of June in 2008 in Haplic Cambisol. In all cases aggregate stability increased during the root growth and then gradually decreased due to summer rainfall events. Aggregate stability reflected aggregate structure and soil pore system development, which was documented on micromorphological images and evaluated using the ration of gravitational and capillary pores measured on the undisturbed sol samples. Acknowledgement: Authors acknowledge the financial support of the Grant Agency of the Czech Republic grant No. 526/08/0434, and the Ministry of Education, Youth and Sports grant No. MSM 6046070901.

  3. Surfactant effects on soil aggregate tensile strength

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Little is known regarding a soil aggregate's tensile strength response to surfactants that may be applied to alleviate soil water repellency. Two laboratory investigations were performed to determine surfactant effects on the tensile strength of 1) Ap horizons of nine wettable, agricultural soils co...

  4. Flow Partitioning in Fully Saturated Soil Aggregates

    SciTech Connect

    Yang, Xiaofan; Richmond, Marshall C.; Scheibe, Timothy D.; Perkins, William A.; Resat, Haluk

    2014-03-30

    Microbes play an important role in facilitating organic matter decomposition in soils, which is a major component of the global carbon cycle. Microbial dynamics are intimately coupled to environmental transport processes, which control access to labile organic matter and other nutrients that are needed for the growth and maintenance of microorganisms. Transport of soluble nutrients in the soil system is arguably most strongly impacted by preferential flow pathways in the soil. Since the physical structure of soils can be characterized as being formed from constituent micro aggregates which contain internal porosity, one pressing question is the partitioning of the flow among the “inter-aggregate” and “intra-aggregate” pores and how this may impact overall solute transport within heterogeneous soil structures. The answer to this question is particularly important in evaluating assumptions to be used in developing upscaled simulations based on highly-resolved mechanistic models. We constructed a number of diverse multi-aggregate structures with different packing ratios by stacking micro-aggregates containing internal pores and varying the size and shape of inter-aggregate pore spacing between them. We then performed pore-scale flow simulations using computational fluid dynamics methods to determine the flow patterns in these aggregate-of-aggregates structures and computed the partitioning of the flow through intra- and inter-aggregate pores as a function of the spacing between the aggregates. The results of these numerical experiments demonstrate that soluble nutrients are largely transported via flows through inter-aggregate pores. Although this result is consistent with intuition, we have also been able to quantify the relative flow capacity of the two domains under various conditions. For example, in our simulations, the flow capacity through the aggregates (intra-aggregate flow) was less than 2% of the total flow when the spacing between the aggregates

  5. Aggregate size distribution of the soil loss

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka; Józsa, Sándor; Szalai, Zoltán; Centeri, Csaba

    2016-04-01

    In agricultural areas the soil erosion and soil loss estimation is vital information in long-term planning. During the initial period of the erosion a part of the soil particles and aggregates get transportable and nutrients and organic matter could be transported due to the effect of water or wind. This preliminary phase was studied with laboratory-scale rainfall simulator. Developed surface crust and aggregate size composition of the runoff was examined in six different slope-roughness-moisture content combination of a Cambisol and a Regosol. The ratio of micro- and macro aggregates in the runoff indicate the stability of the aggregates and determine the transport capacity of the runoff. Both soil samples were taken from field where the water erosion is a potential hazard. During the experiment the whole amount of runoff and sediment was collected through sieve series to a bucket to separate the micro- and macro aggregates. In case of both samples the micro aggregates dominate in the runoff and the runoff rates are similar. Although the runoff of the Regosol - with dominant >1000μm macro aggregate content - contained almost nothing but <50μm sized micro aggregates. Meanwhile the runoff of the Cambisol - with more balanced micro and macro aggregate content - contained dominantly 50-250μm sized micro aggregates and in some case remarkable ratio 250-1000μm sized macro aggregates. This difference occurred because the samples are resistant against drop erosion differently. In case of both sample the selectivity of the erosion and substance matrix redistribution manifested in mineral crusts in the surface where the quartz deposited in place while the lighter organic matter transported with the sediment. The detachment of the aggregates and the redistribution of the particles highly effect on the aggregate composition of the runoff which is connected with the quality of the soil loss. So while the estimation of soil loss quantity is more or less is easy, measuring

  6. Aggregate stability in soils cultivated with eucalyptus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Eucalyptus cultivation has increased in many Brazilian regions. In order to recommend good management practices, it is necessary to understand changes in soil properties where eucalyptus is planted. Aggregate stability analyses have proved to be a useful tool to measure soil effects caused by change...

  7. Fire effects on soil aggregation: A review

    NASA Astrophysics Data System (ADS)

    Mataix-Solera, J.; Cerdà, A.; Arcenegui, V.; Jordán, A.; Zavala, L. M.

    2011-11-01

    Fire can affect soil properties depending on a number of factors including fire severity and soil type. Aggregate stability (AS) refers to soil structure resilience in response to external mechanical forces. Many authors consider soil aggregation to be a parameter reflecting soil health, as it depends on chemical, physical and biological factors. The response of AS to forest fires is complex, since it depends on how fire has affected other related properties such as organic matter content, soil microbiology, water repellency and soil mineralogy. Opinions differ concerning the effect of fire on AS. Some authors have observed a decrease in AS in soils affected by intense wildfire or severe laboratory heating. However, others have reported increases. We provide an up to date review of the research on this topic and an analysis of the causes for the different effects observed. The implications for soil system functioning and for the hydrology of the affected areas are also discussed. Generally, low severity fires do not produce notable changes in AS, although in some cases an increase has been observed and attributed to increased water repellency. In contrast, high severity fires can induce important changes in this property, but with different effects depending on the type of soil affected. The patterns observed can vary from a disaggregation as a consequence of the organic matter destruction, to a strong aggregation if a recrystallization of some minerals such as Fe and Al oxyhydroxides occurs when they are present in sufficient quantities in the soil, after exposure to high temperatures. Because of the complexity of the different possible effects and reasons for the potential changes in the fire-affected soil aggregates, the inclusion of other parameters in the studies is necessary to understand the results. The suggested parameters to include in the examination of AS are: soil organic matter, microbial biomass, water repellency, texture, aggregate size distribution

  8. Extraction of TNT from aggregate soil fractions.

    PubMed

    Williford, C W; Mark Bricka, R

    1999-04-23

    Past explosives manufacture, disposal, and training activities have contaminated soil at many military facilities, posing health and environmental risks through contact, potential detonation, and leaching into ground water. While methods have been confirmed for extraction and measuring explosives concentration in soil, no work has addressed aggregate size material (the >2 mm gravel and cobbles) that often occurs with the smaller soil fractions. This paper describes methods and results for extraction and measurement of TNT (2,4,6-trinitrotoluene) in aggregate material from 1/2 to 2-1/1 from a WWII era ammunition plant. TNT was extracted into acetonitrile by both Soxhlet and ultrasonic extraction methods. High pressure liquid chromatography analyses of extracts showed expected variation among samples. Also effective extraction and determination of TNT concentration for each aggregate size fraction was achieved.

  9. [Research methods of carbon sequestration by soil aggregates: a review].

    PubMed

    Chen, Xiao-Xia; Liang, Ai-Zhen; Zhang, Xiao-Ping

    2012-07-01

    To increase soil organic carbon content is critical for maintaining soil fertility and agricultural sustainable development and for mitigating increased greenhouse gases and the effects of global climate change. Soil aggregates are the main components of soil, and have significant effects on soil physical and chemical properties. The physical protection of soil organic carbon by soil aggregates is the important mechanism of soil carbon sequestration. This paper reviewed the organic carbon sequestration by soil aggregates, and introduced the classic and current methods in studying the mechanisms of carbon sequestration by soil aggregates. The main problems and further research trends in this study field were also discussed.

  10. Long term management practices influenced soil aggregation and carbon dynamics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil aggregation protects soil organic C (SOC) against rapid decomposition, improves soil quality, and reduces soil erosion potential. The objectives of this study are to evaluate the effects of long-term (21 yrs.) management practices on SOC, water stable aggregate (WSA), and aggregate-associated ...

  11. Biological framework for soil aggregation: Implications for ecological functions.

    NASA Astrophysics Data System (ADS)

    Ghezzehei, Teamrat; Or, Dani

    2016-04-01

    Soil aggregation is heuristically understood as agglomeration of primary particles bound together by biotic and abiotic cementing agents. The organization of aggregates is believed to be hierarchical in nature; whereby primary particles bond together to form secondary particles and subsequently merge to form larger aggregates. Soil aggregates are not permanent structures, they continuously change in response to internal and external forces and other drivers, including moisture, capillary pressure, temperature, biological activity, and human disturbances. Soil aggregation processes and the resulting functionality span multiple spatial and temporal scales. The intertwined biological and physical nature of soil aggregation, and the time scales involved precluded a universally applicable and quantifiable framework for characterizing the nature and function of soil aggregation. We introduce a biophysical framework of soil aggregation that considers the various modes and factors of the genesis, maturation and degradation of soil aggregates including wetting/drying cycles, soil mechanical processes, biological activity and the nature of primary soil particles. The framework attempts to disentangle mechanical (compaction and soil fragmentation) from in-situ biophysical aggregation and provides a consistent description of aggregate size, hierarchical organization, and life time. It also enables quantitative description of biotic and abiotic functions of soil aggregates including diffusion and storage of mass and energy as well as role of aggregates as hot spots of nutrient accumulation, biodiversity, and biogeochemical cycles.

  12. Soil aggregation and aggregating agents as affected by long term contrasting management of an Anthrosol

    NASA Astrophysics Data System (ADS)

    Zhang, Shulan; Wang, Renjie; Yang, Xueyun; Sun, Benhua; Li, Qinghui

    2016-12-01

    Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5–2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared.

  13. Soil aggregation and aggregating agents as affected by long term contrasting management of an Anthrosol

    PubMed Central

    Zhang, Shulan; Wang, Renjie; Yang, Xueyun; Sun, Benhua; Li, Qinghui

    2016-01-01

    Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5–2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared. PMID:27958366

  14. Distribution of chromium contamination and microbial activity in soil aggregates.

    PubMed

    Tokunaga, Tetsu K; Wan, Jiamin; Hazen, Terry C; Schwartz, Egbert; Firestone, Mary K; Sutton, Stephen R; Newville, Matthew; Olson, Keith R; Lanzirotti, Antonio; Rao, William

    2003-01-01

    Biogeochemical transformations of redox-sensitive chemicals in soils can be strongly transport-controlled and localized. This was tested through experiments on chromium diffusion and reduction in soil aggregates that were exposed to chromate solutions. Reduction of soluble Cr(VI) to insoluble Cr(II) occurred only within the surface layer of aggregates with higher available organic carbon and higher microbial respiration. Sharply terminated Cr diffusion fronts develop when the reduction rate increases rapidly with depth. The final state of such aggregates consists of a Cr-contaminated exterior, and an uncontaminated core, each having different microbial community compositions and activity. Microbial activity was significantly higher in the more reducing soils, while total microbial biomass was similar in all of the soils. The small fraction of Cr(VI) remaining unreduced resides along external surfaces of aggregates, leaving it potentially available to future transport down the soil profile. Using the Thiele modulus, Cr(VI) reduction in soil aggregates is shown to be diffusion rate- and reaction rate-limited in anaerobic and aerobic aggregates, respectively. Thus, spatially resolved chemical and microbiological measurements are necessary within anaerobic soil aggregates to characterize and predict the fate of Cr contamination. Typical methods of soil sampling and analyses that average over redox gradients within aggregates can erase important biogeochemical spatial relations necessary for understanding these environments.

  15. 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

  16. A Novel Method to Quantify Soil Aggregate Stability by Measuring Aggregate Bond Energies

    NASA Astrophysics Data System (ADS)

    Efrat, Rachel; Rawlins, Barry G.; Quinton, John N.; Watts, Chris W.; Whitmore, Andy P.

    2016-04-01

    Soil aggregate stability is a key indicator of soil quality because it controls physical, biological and chemical functions important in cultivated soils. Micro-aggregates are responsible for the long term sequestration of carbon in soil, therefore determine soils role in the carbon cycle. It is thus vital that techniques to measure aggregate stability are accurate, consistent and reliable, in order to appropriately manage and monitor soil quality, and to develop our understanding and estimates of soil as a carbon store to appropriately incorporate in carbon cycle models. Practices used to assess the stability of aggregates vary in sample preparation, operational technique and unit of results. They use proxies and lack quantification. Conflicting results are therefore drawn between projects that do not provide methodological or resultant comparability. Typical modern stability tests suspend aggregates in water and monitor fragmentation upon exposure to an un-quantified amount of ultrasonic energy, utilising a laser granulometer to measure the change in mean weight diameter. In this project a novel approach has been developed based on that of Zhu et al., (2009), to accurately quantify the stability of aggregates by specifically measuring their bond energies. The bond energies are measured operating a combination of calorimetry and a high powered ultrasonic probe, with computable output function. Temperature change during sonication is monitored by an array of probes which enables calculation of the energy spent heating the system (Ph). Our novel technique suspends aggregates in heavy liquid lithium heteropolytungstate, as opposed to water, to avoid exposing aggregates to an immeasurable disruptive energy source, due to cavitation, collisions and clay swelling. Mean weight diameter is measured by a laser granulometer to monitor aggregate breakdown after successive periods of calculated ultrasonic energy input (Pi), until complete dispersion is achieved and bond

  17. Impacts of Organic Farming on Soil Aggregate Stability

    NASA Astrophysics Data System (ADS)

    Petticrew, E. L.; Williams, N. D.

    2009-04-01

    Organic farming has expanded rapidly in the UK in recent years, amid increasing concerns for long term environmental and economic sustainability in agricultural systems. Much of the motivation for the shift away from conventional intensive agricultural practices has focused on soil nutrient management. Little attention has been directed toward the relative merits of organic farming for the physical structure of soils, despite aggregate structure and stability being of particular importance to soil erosion potential and sustainable soil quality. In this study, soil samples were collected from four arable sites within a small geographical area, in order to represent (1) an organic farm; (2) a conventional farm that only used artificial fertilizers; (3) a conventional farm that used artificial and cattle slurry fertilizers; and (4) a non-cultivated control site. Samples were analysed for living biomass and total organic content, bulk aggregate size and density distributions, bulk fragmentation fractal dimensions (which represent indices of soil erodibility), aggregate stability under simulated rainfall, and the stability of micro-aggregates that were mobilized in surface runoff generated by simulated rainfall. The relationships between the different soil properties were found to be complex. However, there were some significant differences between the samples, which were related to the different methods (or absence) of agriculture. The non-cultivated soil was determined to have the lowest erodibility and greatest aggregate stability. The conventional soil that was only fertilized by artificial means exhibited the lowest aggregate stability. There were few apparent differences between the organic soil and the conventional soil that received an input of organic fertilizer. The results of the physical analysis reflect the mining and replenishment of organic matter to each soil by the different management practices. This leads to the conclusion that the addition of organic

  18. Reduction in soil aggregation in response to dust emission processes

    NASA Astrophysics Data System (ADS)

    Swet, Nitzan; Katra, Itzhak

    2016-09-01

    Dust emission by aeolian (wind) soil erosion depends on the topsoil properties of the source area, especially on the nature of the aggregates where most dust particles are held. Although the key role of soil aggregates in dust emission, the response of soil aggregation to aeolian processes and its implications for dust emission remain unknown. This study focuses on aggregate size distribution (ASD) analyses before and after in-situ aeolian experiments in semiarid loess soils that are associated with dust emission. Wind tunnel simulations show that particulate matter (PM) emission and saltation rates depend on the initial ASD and shear velocity. Under all initial ASD conditions, the content of saltator-sized aggregates (63-250 μm) increased by 10-34% due to erosion of macro-aggregates (> 500 μm), resulting in a higher size ratio (SR) between the saltators and macro-aggregates following the aeolian erosion. The results revealed that the saltator production increases significantly for soils that are subjected to short-term (anthropogenic) disturbance of the topsoil. The findings highlight a decrease in soil aggregation for all initial ASD's in response to aeolian erosion, and consequently its influence on the dust emission potential. Changes in ASD should be considered as a key parameter in dust emission models of complex surfaces.

  19. Hydraulic and mechanical properties of soil aggregates under organic and conventional soil management

    NASA Astrophysics Data System (ADS)

    Wójciga, A.; Kuś, J.; Turski, M.; Lipiec, J.

    2009-04-01

    Variation in hydraulic and mechanical properties of soil aggregates is an important factor affecting water storage and infiltration because the large inter-aggregate pores are dewatered first and the transport of water and solutes is influenced by the properties of the individual aggregates and contacts between them. A high mechanical stability of soil aggregates is fundamental for the maintenance of proper tilth and provides stable traction for farm implements, but limit root growth inside aggregates. The aggregate properties are largely influenced by soil management practices. Our objective was to compare the effects of organic and conventional soil management on hydraulic and mechanical properties of soil aggregates. Experimental fields subjected to long-term organic (14 years) and conventional managements were located on loamy soil at the Institute of Soil Science and Plant Cultivation - National Research Institute in Pulawy, Poland. Soil samples were collected from two soil depths (0-10 cm and 10-20 cm). After air-drying, two size fractions of soil aggregates (15-20 and 30-35 mm) were manually selected and kept in the dried state in a dessicator in order to provide the same boundary conditions. Following properties of the aggregates were determined: porosity (%) using standard wax method, cumulative infiltration Q (mm3 s-1) and sorptivity S (mm s -1/2) of water and ethanol using a tube with a sponge inserted at the tip, wettability (by comparison of sorptivity of water and ethanol) using repellency index R, crushing strength q (MPa) using strength testing device (Zwick/Roell) and calculated by Dexter's formula. All properties were determined in 15 replicates for each treatment, aggregates size and depth. Organic management decreased porosity of soil aggregates and ethanol infiltration. All aggregates revealed rather limited wettability (high repellency index). In most cases the aggregate wettability was lower under conventional than organic soil management

  20. Fire effects on soil aggregate stability: a review and synthesis

    NASA Astrophysics Data System (ADS)

    Mataix-Solera, J.; Cerdà, A.; Arcenegui, V.; Jordán, A.; Zavala, L. M.

    2012-04-01

    Fire can affect soil properties depending on a number of factors including fire severity and soil type. Aggregate stability (AS) refers to soil structure resilience in response to external mechanical forces. Many authors consider soil aggregation to be a parameter reflecting soil health, as it depends on chemical, physical and biological factors. The response of AS to forest fires is complex, since it depends on how fire has affected other related properties such as organic matter content, soil microbiology, water repellency and soil mineralogy. Opinions differ concerning the effect of fire on AS. Some authors have observed a decrease in AS in soils affected by intense wildfire or severe laboratory heating. However, others have reported increases. We provide an up to date review of the research on this topic and an analysis of the causes for the different effects observed. The implications for soil system functioning and for the hydrology of the affected areas are also discussed. Generally, low severity fires do not produce notable changes in AS, although in some cases an increase has been observed and attributed to increased water repellency. In contrast, high severity fires can induce important changes in this property, but with different effects depending on the type of soil affected. The patterns observed can vary from a disaggregation as a consequence of the organic matter destruction, to a strong aggregation if a recrystallization of some minerals such as Fe and Al oxyhydroxides occurs when they are present in sufficient quantities in the soil, after exposure to high temperatures. Because of the complexity of the different possible effects and reasons for the potential changes in the fire-affected soil aggregates, the inclusion of other parameters in the studies is necessary to understand the results. The suggested parameters to include in the examination of AS are: soil organic matter, microbial biomass, water repellency, texture, aggregate size distribution

  1. Modeling the impact of soil aggregate size on selenium immobilization

    NASA Astrophysics Data System (ADS)

    Kausch, M. F.; Pallud, C. E.

    2013-03-01

    Soil aggregates are mm- to cm-sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-aggregate micropores. This can lead to mass transfer limitations and the formation of aggregate scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil aggregates are thought to promote this process in otherwise well-aerated soils. To evaluate the impact of soil aggregate size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se species. The spatial and temporal dynamics of the model were validated with data from experiments, and predictive simulations were performed covering aggregate sizes 1-2.5 cm in diameter. Simulations predict that selenium retention scales with aggregate size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4-23 times higher in 2.5 cm aggregates compared to 1 cm aggregates. Under oxic conditions, aggregate size and pyruvate concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on

  2. Evolution of unsaturated hydraulic conductivity of aggregated soils during compression

    NASA Astrophysics Data System (ADS)

    Berli, M.; Carminati, A.; Ghezzehei, T. A.; Or, D.

    2007-12-01

    Prediction of water flow and transport processes in soils susceptible to structural alteration such as compaction of tilled agricultural lands, or newly constructed landfills rely on accurate description of changes in soil unsaturated hydraulic conductivity. Recent studies have documented the critical impact of aggregate contact characteristics on water flow rates and pathways in unsaturated aggregated soils. We developed an analytical model for aggregate contact size evolution as a basis for quantifying effects of compression on unsaturated hydraulic conductivity of aggregated soil. Relating confined one-dimensional sample strain with aggregate deformation facilitates prediction of the increase in inter-aggregate contact area and concurrent decrease in macro-pore size with degree of sample compression. The hydrologic component of the model predicts unsaturated hydraulic conductivity of a pack of idealized aggregates (spheres) based on contact size and saturation conditions under prescribed sample deformation. Calculated contact areas and hydraulic conductivity for pairs of aggregates agreed surprisingly well with measured values, determined from compaction experiments employing Neutron- as well as X-ray-radiography and image analysis.

  3. Phosphorus content as a function of soil aggregate size and paddy cultivation in highly weathered soils.

    PubMed

    Li, Baozhen; Ge, Tida; Xiao, Heai; Zhu, Zhenke; Li, Yong; Shibistova, Olga; Liu, Shoulong; Wu, Jinshui; Inubushi, Kazuyuki; Guggenberger, Georg

    2016-04-01

    Red soils are the major land resource in subtropical and tropical areas and are characterized by low phosphorus (P) availability. To assess the availability of P for plants and the potential stability of P in soil, two pairs of subtropical red soil samples from a paddy field and an adjacent uncultivated upland were collected from Hunan Province, China. Analysis of total P and Olsen P and sequential extraction was used to determine the inorganic and organic P fractions in different aggregate size classes. Our results showed that the soil under paddy cultivation had lower proportions of small aggregates and higher proportions of large aggregates than those from the uncultivated upland soil. The portion of >2-mm-sized aggregates increased by 31 and 20 % at Taoyuan and Guiyang, respectively. The total P and Olsen P contents were 50-150 and 50-300 % higher, respectively, in the paddy soil than those in the upland soil. Higher inorganic and organic P fractions tended to be enriched in both the smallest and largest aggregate size classes compared to the middle size class (0.02-0.2 mm). Furthermore, the proportion of P fractions was higher in smaller aggregate sizes (<2 mm) than in the higher aggregate sizes (>2 mm). In conclusion, soils under paddy cultivation displayed improved soil aggregate structure, altered distribution patterns of P fractions in different aggregate size classes, and to some extent had enhanced labile P pools.

  4. Aggregate and soil organic carbon dynamics in South Chilean Andisols

    NASA Astrophysics Data System (ADS)

    Huygens, D.; Boeckx, P.; Van Cleemput, O.; Oyarzún, C.; Godoy, R.

    2005-06-01

    Extreme sensitivity of soil organic carbon (SOC) to climate and land use change warrants further research in different terrestrial ecosystems. The aim of this study was to investigate the link between aggregate and SOC dynamics in a chronosequence of three different land uses of a south Chilean Andisol: a second growth Nothofagus obliqua forest (SGFOR), a grassland (GRASS) and a Pinus radiata plantation (PINUS). Total carbon content of the 0-10cm soil layer was higher for GRASS (6.7 kg C m-2) than for PINUS (4.3 kg C m-2, while TC content of SGFOR (5.8 kg C m-2) was not significantly different from either one. High extractable oxalate and pyrophosphate Al concentrations (varying from 20.3-24.4 g kg-1, and 3.9-11.1 g kg-1, respectively) were found in all sites. In this study, SOC and aggregate dynamics were studied using size and density fractionation experiments of the SOC, δ13C and total carbon analysis of the different SOC fractions, and C mineralization experiments. The results showed that electrostatic sorption between and among amorphous Al components and clay minerals is mainly responsible for the formation of metal-humus-clay complexes and the stabilization of soil aggregates. The process of ligand exchange between SOC and Al would be of minor importance resulting in the absence of aggregate hierarchy in this soil type. Whole soil C mineralization rate constants were highest for SGFOR and PINUS, followed by GRASS (respectively 0.495, 0.266 and 0.196 g CO2-Cm-2d-1 for the top soil layer). In contrast, incubation experiments of isolated macro organic matter fractions gave opposite results, showing that the recalcitrance of the SOC decreased in another order: PINUS>SGFOR>GRASS. We deduced that electrostatic sorption processes and physical protection of SOC in soil aggregates were the main processes determining SOC stabilization. As a result, high aggregate carbon concentrations, varying from 148 till 48 g kg-1, were encountered for all land use sites. Al

  5. Soil aggregate stability within the morphologically diverse area

    NASA Astrophysics Data System (ADS)

    Jaksik, Ondrej; Kodesova, Radka; Kubis, Adam; Klement, Ales; Fer, Miroslav

    2013-04-01

    This study evaluates the effect of soil erosion on properties of topsoil especially on soil aggregate stability. Study was performed on morphologically diverse study site (6 ha area) in loess region of Southern Moravia, Czech Republic. The region has been under uninterrupted agricultural use since the middle of the Holocene. Haplic Chernozem is an original dominant soil unit in the area, nowadays progressively transformed into different soil units along with intensive soil erosion. There are eroded phases of Chernozem, Regosol (the steepest and heavily eroded parts of the study area), colluvial Chernozem and Colluvial soil (base slope). Sampling spots were selected in order to represent diverse soil units and morphological units. Soil samples were taken from the topsoil, carefully transported to the laboratory and consequently air dried. Following soil properties were measured: pH_KCl, pH_CaCl2, soil organic matter content (SOM), carbonate content (CO3), content of iron and manganese (in ammonium oxalate extract, Feo and Mn_o, and dithionite-citrate extract, Fed and Mn_d), and stability of soil aggregates using two different methods. The indexes of water stable aggregates (WSA) were determined using the procedure presented by Nimmo and Perkins (2002). The three methods proposed by Le Bissonnais (1996) were also used to study various destruction mechanisms. The fast wetting test (KV1) was applied to study aggregate slaking due to the compression of the entrapped air (mechanism similar to the WSA test). The slow wetting test (KV2) was used to evaluate aggregate disintegration caused by the micro cracking due to the different swelling, and physico-chemical dispersion due to the osmotic stress. The shaking after prewetting test (KV3) was utilized to study the mechanical aggregate breakdown. Terrain attributes were evaluated from digital terrain model. In general the lowest soil aggregate stability was observed on steep slopes, which were highly impacted by soil erosion

  6. Soil aggregation, erodibility, and erosion rates in mountain soils (NW Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Stanchi, S.; Falsone, G.; Bonifacio, E.

    2015-04-01

    Erosion is a relevant soil degradation factor in mountain agrosilvopastoral ecosystems that can be enhanced by the abandonment of agricultural land and pastures left to natural evolution. The on-site and off-site consequences of soil erosion at the catchment and landscape scale are particularly relevant and may affect settlements at the interface with mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates of soil erosion consider, among others, the soil erodibility factor (K), which depends on properties involved in structure and aggregation. A relationship between soil erodibility and aggregation should therefore be expected. However, erosion may limit the development of soil structure; hence aggregates should not only be related to erodibility but also partially mirror soil erosion rates. The aim of the research was to evaluate the agreement between aggregate stability and erosion-related variables and to discuss the possible reasons for discrepancies in the two kinds of land use considered (forest and pasture). Topsoil horizons were sampled in a mountain catchment under two vegetation covers (pasture vs. forest) and analyzed for total organic carbon, total extractable carbon, pH, and texture. Soil erodibility was computed, RUSLE erosion rate was estimated, and aggregate stability was determined by wet sieving. Aggregation and RUSLE-related parameters for the two vegetation covers were investigated through statistical tests such as ANOVA, correlation, and regression. Soil erodibility was in agreement with the aggregate stability parameters; i.e., the most erodible soils in terms of K values also displayed weaker aggregation. Despite this general observation, when estimating K from aggregate losses the ANOVA conducted on the regression residuals showed land-use-dependent trends (negative average residuals for forest soils, positive for pastures). Therefore, soil aggregation seemed to mirror the actual topsoil conditions better than soil

  7. Arbuscular mycorrhizal fungi make a complex contribution to soil aggregation

    NASA Astrophysics Data System (ADS)

    McGee, Peter; Daynes, Cathal; Damien, Field

    2013-04-01

    Soil aggregates contain solid and fluid components. Aggregates develop as a consequence of the organic materials, plants and hyphae of arbuscular mycorrhizal (AM) fungi acting on the solid phase. Various correlative studies indicate hyphae of AM fungi enmesh soil particles, but their impact on the pore space is poorly understood. Hyphae may penetrate between particles, remove water from interstitial spaces, and otherwise re-arrange the solid phase. Thus we might predict that AM fungi also change the pore architecture of aggregates. Direct observations of pore architecture of soil, such as by computer-aided tomography (CT), is difficult. The refractive natures of solid and biological material are similar. The plant-available water in various treatments allows us to infer changes in pore architecture. Our experimental studies indicate AM fungi have a complex role in the formation and development of aggregates. Soils formed from compost and coarse subsoil materials were planted with mycorrhizal or non-mycorrhizal seedlings and the resultant soils compared after 6 or 14 months in separate experiments. As well as enmeshing particles, AM fungi were associated with the development of a complex pore space and greater pore volume. Even though AM fungi add organic matter to soil, the modification of pore space is not correlated with organic carbon. In a separate study, we visualised hyphae of AM fungi in a coarse material using CT. In this study, hyphae appeared to grow close to the surfaces of particles with limited ramification across the pore spaces. Hyphae of AM fungi appear to utilise soil moisture for their growth and development of mycelium. The strong correlation between moisture and hyphae has profound implications for soil aggregation, plant utilisation of soil water, and the distribution of water as water availability declines.

  8. Soil aggregation, erodibility and erosion rates in mountain soils (NW-Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Stanchi, S.; Falsone, G.; Bonifacio, E.

    2015-01-01

    Erosion is a relevant soil degradation factor in mountain agrosilvopastoral ecosystems, and can be enhanced by the abandonment of agricultural land and pastures, then left to natural evolution. The on-site and off-site consequences of soil erosion at the catchment and landscape scale are particularly relevant and may affect settlements at the interface with mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates of soil erosion consider, among others, the soil erodibility factor (K), which depends on properties involved in structure and aggregation. A relationship between soil erodibility and aggregation is therefore expected. Erosion is however expected to limit the development of soil structure, hence aggregates should not only be related to erodibility but also mirror soil erosion rates. We investigated the relationships between aggregate stability and the RUSLE erodibility and erosion rate in a mountain watershed at the interface with settlements, characterized by two different land use types (pasture and forest). Soil erodibility was in agreement with the aggregate stability parameters, i.e. the most erodible soils in terms of K values also displayed weaker aggregation. However, estimating K from aggregate loss showed that forest soils always had negative residuals, while the opposite happened for pastures. A good relationship between RUSLE soil erosion rates and aggregate stability occurred in pastures, while no relationship was visible in forests. Several hypotheses for this behavior were discussed. A relevant effect of the physical protection of the organic matter by the aggregates that cannot be considered in K computation was finally hypothesized in the case of pastures, while in forests soil erodibility seemed to keep trace of past erosion and depletion of finer particles. In addition, in forests, the erosion rate estimate was particularly problematic likely because of a high spatial variability of litter properties. Considering the

  9. Soil aggregation and slope stability related to soil density, root length, and mycorrhiza

    NASA Astrophysics Data System (ADS)

    Graf, Frank; Frei, Martin

    2013-04-01

    Eco-engineering measures combine the use of living plants and inert mechanical constructions to protect slopes against erosion and shallow mass movement. Whereas in geotechnical engineering several performance standards and guidelines for structural safety and serviceability of construction exist, there is a lack of comparable tools in the field of ecological restoration. Various indicators have been proposed, including the fractal dimension of soil particle size distribution, microbiological parameters, and soil aggregate stability. We present results of an soil aggregate stability investigation and compare them with literature data of the angle of internal friction ?' which is conventionally used in slope stability analysis and soil failure calculation. Aggregate stability tests were performed with samples of differently treated moraine, including soil at low (~15.5 kN/m³) and high (~19.0 kN/m³) dry unit weight, soil planted with Alnus incana (White Alder) as well as the combination of soil planted with alder and inoculated with the mycorrhizal fungus Melanogaster variegatus s.l. After a 20 weeks growth period in a greenhouse, a total of 100 samples was tested and evaluated. Positive correlations were found between the soil aggregate stability and the three variables dry unit weight, root length per soil volume, and degree of mycorrhization. Based on robust statistics it turned out that dry unit weight and mycorrhization degree were strongest correlated with soil aggregate stability. Compared to the non-inoculated control plants, mycorrhized White Alder produced significantly more roots and higher soil aggregate stability. Furthermore, the combined biological effect of plant roots and mycorrhizal mycelia on aggregate stability on soil with low density (~15.5 kN/m³) was comparable to the compaction effect of the pure soil from 15.5 to ~19.0 kN/m³. Literature data on the effect of vegetation on the angle of internal friction ?' of the same moraine showed

  10. Compost incorporation, soil aggregates and organic C sequestration in two different Tuscan soils.

    NASA Astrophysics Data System (ADS)

    Pini, Roberto; Sparvoli, Enzo; Scatena, Manuele; Pucci, Amaranta; D'Acqui, Luigi P.

    2010-05-01

    Soil amendment with compost obtained from pre-selected urban food scraps together with green manure, reduced tillage, rotation of crops and other practices are generally considered as improving soil structure by increasing the levels of nutrient elements. The addition of well composted organic residues may increase the amount of organic C entangled within mineral particles and also stabilize soil aggregates and micro-aggregates. This consequently reduces carbon dioxide emissions and mitigates temperature increases. Our data refer to two soils, a clay soil and a sandy soil, subjected to a long term compost incorporation in order to ameliorate soil fertility. We measured the dynamic of pore size distribution and total porosity evolution together with water soil aggregates stability. We also developed our own procedure to assess the stabilization and protection of organic C in soil aggregates, by analyzing the dynamics of OM dry-oxidation by LTA (Low Temperature Ashing) cold oxygen plasma. Our results confirmed the beneficial effect of the compost on soil structure of both soils and that the potential sequestration of soil organic C is related to the granulometry and mineralogical features of the two soils. We propose an original methodological approach to assess the effective C sequestration in agricultural soil.

  11. Soil aggregate stability as affected by clay mineralogy and polyacrylamide addition

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The addition of polyacrylamide (PAM) to soil leads to stabilization of existing aggregates and improved bonding between, and aggregation of adjacent soil particles However, the dependence of PAM efficacy as an aggregate stabilizing agent on soil-clay mineralogy has not been studied. Sixteen soil sam...

  12. Polyacrylamide effects on aggregate and structure stability of soils with different clay mineralogy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples...

  13. Interaction of fecal coliforms with soil aggregates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Land-applied manures may contain various contaminants that cause water pollution and concomitant health problems. Some of these pollutants are bacteria, and fecal coliforms (FC) have been widely used as an indicator of bacterial contamination. Experiments on bacteria attachment to soil are tradition...

  14. Highly-resolved Imaging in aggregated soils

    NASA Astrophysics Data System (ADS)

    Rudolph, N.; Oswald, S.; Lazik, D.

    2009-04-01

    Dissolved oxygen is the primary electron acceptor in soil, and the concentration undergoes consumption reactions. Oxygen transition zones results from combined effect of soil structures, water flow, oxygen transport limitations and oxygen consuming reactions. In case of higher water saturation such oxygen transition zones will result from metabolic activity, but will in turn limit or enhance such activities. A prerequisite to precisely quantify the distribution of dissolved oxygen mass is to know the water content distribution, which is an important property affecting biogeochemical soil processes. We aim not only for detecting interfaces between fully-aerobic and oxygen-deficit regions with high spatial resolution, but even for determining the dissolved oxygen concentrations in the areas of the gradient and of oxygen depletion. Our approach to visualize and quantify water content and oxygen transition zones in soils is applying non-destructive imaging techniques to avoid the destruction of samples, which allows observations of temporal developments. The methodology is based on a combination of recently developed imaging approaches. The first is the possibility to detect dissolved oxygen concentrations via fluorescence of specific, dissolved photoluminescent molecules that act as oxygen probes when excited with UV light. Additionally we use the sodium fluorescein for imaging water content. In both setups the fluorescence light is detected with a camera, allowing for visualization of rapid changes. X-ray radiography, light transmission, and in some cases the highly sensitive and selective neutron radiography imaging, are possible alternatives to visualize water content. We are testing our set-up to estimate water content via fluorescence intensities (as shown by Bridge et al., 2007) and it was partly possible with a modulated imaging setup to visualize oxygen distributions in glass bead packs and sands.

  15. Accumulation of organic C components in soil and aggregates

    NASA Astrophysics Data System (ADS)

    Yu, Hongyan; Ding, Weixin; Chen, Zengming; Zhang, Huanjun; Luo, Jiafa; Bolan, Nanthi

    2015-09-01

    To explore soil organic carbon (SOC) accumulation mechanisms, the dynamics of C functional groups and macroaggregation were studied synchronously through aggregate fractionation and 13C NMR spectroscopy in sandy loam soil following an 18-year application of compost and fertilizer in China. Compared with no fertilizer control, both compost and fertilizer improved SOC content, while the application of compost increased macroaggregation. Fertilizer application mainly increased the levels of recalcitrant organic C components characterized by methoxyl/N-alkyl C and alkyl C, whereas compost application mainly promoted the accumulation of methoxyl/N-alkyl C, phenolic C, carboxyl C, O-alkyl C and di-O-alkyl C in bulk soil. The preferential accumulation of organic C functional groups in aggregates depended on aggregate size rather than nutrient amendments. These groups were characterized by phenolic C and di-O-alkyl C in the silt + clay fraction, carboxyl C in microaggregates and phenolic C, carboxyl C and methoxyl/N-alkyl C in macroaggregates. Thus, the differences in accumulated organic C components in compost- and fertilizer-amended soils were primarily attributable to macroaggregation. The accumulation of methoxyl/N-alkyl C in microaggregates effectively promoted macroaggregation. Our results suggest that organic amendment rich in methoxyl/N-alkyl C effectively improved SOC content and accelerated macroaggregation in the test soil.

  16. Accumulation of organic C components in soil and aggregates

    PubMed Central

    Yu, Hongyan; Ding, Weixin; Chen, Zengming; Zhang, Huanjun; Luo, Jiafa; Bolan, Nanthi

    2015-01-01

    To explore soil organic carbon (SOC) accumulation mechanisms, the dynamics of C functional groups and macroaggregation were studied synchronously through aggregate fractionation and 13C NMR spectroscopy in sandy loam soil following an 18-year application of compost and fertilizer in China. Compared with no fertilizer control, both compost and fertilizer improved SOC content, while the application of compost increased macroaggregation. Fertilizer application mainly increased the levels of recalcitrant organic C components characterized by methoxyl/N-alkyl C and alkyl C, whereas compost application mainly promoted the accumulation of methoxyl/N-alkyl C, phenolic C, carboxyl C, O-alkyl C and di-O-alkyl C in bulk soil. The preferential accumulation of organic C functional groups in aggregates depended on aggregate size rather than nutrient amendments. These groups were characterized by phenolic C and di-O-alkyl C in the silt + clay fraction, carboxyl C in microaggregates and phenolic C, carboxyl C and methoxyl/N-alkyl C in macroaggregates. Thus, the differences in accumulated organic C components in compost- and fertilizer-amended soils were primarily attributable to macroaggregation. The accumulation of methoxyl/N-alkyl C in microaggregates effectively promoted macroaggregation. Our results suggest that organic amendment rich in methoxyl/N-alkyl C effectively improved SOC content and accelerated macroaggregation in the test soil. PMID:26358660

  17. Indirect Contributions of AM Fungi and Soil Aggregation to Plant Growth and Protection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil ecological and biological engineering are processes by which soil organisms modify their physiochemical environment resulting indirectly to enhancements in plant growth. The formation and stabilization of soil aggregates is an example biologically-mediated engineering. For soil organisms, wate...

  18. Influence of urban land development and subsequent soil rehabilitation on soil aggregates, carbon, and hydraulic conductivity.

    PubMed

    Chen, Yujuan; Day, Susan D; Wick, Abbey F; McGuire, Kevin J

    2014-10-01

    Urban land use change is associated with decreased soil-mediated ecosystem services, including stormwater runoff mitigation and carbon (C) sequestration. To better understand soil structure formation over time and the effects of land use change on surface and subsurface hydrology, we quantified the effects of urban land development and subsequent soil rehabilitation on soil aggregate size distribution and aggregate-associated C and their links to soil hydraulic conductivity. Four treatments [typical practice (A horizon removed, subsoil compacted, A horizon partially replaced), enhanced topsoil (same as typical practice plus tillage), post-development rehabilitated soils (compost incorporation to 60-cm depth in subsoil; A horizon partially replaced plus tillage), and pre-development (undisturbed) soils] were applied to 24 plots in Virginia, USA. All plots were planted with five tree species. After five years, undisturbed surface soils had 26 to 48% higher levels of macroaggregation and 12 to 62% greater macroaggregate-associated C pools than those disturbed by urban land development regardless of whether they were stockpiled and replaced, or tilled. Little difference in aggregate size distribution was observed among treatments in subsurface soils, although rehabilitated soils had the greatest macroaggregate-associated C concentrations and pool sizes. Rehabilitated soils had 48 to 171% greater macroaggregate-associated C pool than the other three treatments. Surface hydraulic conductivity was not affected by soil treatment (ranging from 0.4 to 2.3 cm h(-1)). In deeper regions, post-development rehabilitated soils had about twice the saturated hydraulic conductivity (14.8 and 6.3 cm h(-1) at 10-25 cm and 25-40 cm, respectively) of undisturbed soils and approximately 6-11 times that of soils subjected to typical land development practices. Despite limited effects on soil aggregation, rehabilitation that includes deep compost incorporation and breaking of compacted

  19. Multiscale variability of soil aggregate stability: implications for rangeland hydrology and erosion

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Conservation of soil and water resources in rangelands is a crucial step in stopping desertification processes. The formation of water-stable soil aggregates reduces soil erodibility and can increase infiltration capacity in many soils. Soil aggregate stability is highly variable at scales ranging f...

  20. Recovery of MSWI and soil washing residues as concrete aggregates.

    PubMed

    Sorlini, Sabrina; Abbà, Alessandro; Collivignarelli, Carlo

    2011-02-01

    The aim of the present work was to study if municipal solid waste incinerator (MSWI) residues and aggregates derived from contaminated soil washing could be used as alternative aggregates for concrete production. Initially, chemical, physical and geometric characteristics (according to UNI EN 12620) of municipal solid waste incineration bottom ashes and some contaminated soils were evaluated; moreover, the pollutants release was evaluated by means of leaching tests. The results showed that the reuse of pre-treated MSWI bottom ash and washed soil is possible, either from technical or environmental point of view, while it is not possible for the raw wastes. Then, the natural aggregate was partially and totally replaced with these recycled aggregates for the production of concrete mixtures that were characterized by conventional mechanical and leaching tests. Good results were obtained using the same dosage of a high resistance cement (42.5R calcareous Portland cement instead of 32.5R); the concrete mixture containing 400 kg/m(3) of washed bottom ash and high resistance cement was classified as structural concrete (C25/30 class). Regarding the pollutants leaching, all concrete mixtures respected the limit values according to the Italian regulation.

  1. Do chemical gradients within soil aggregates reflect plant/soil interactions?

    NASA Astrophysics Data System (ADS)

    Krüger, Jaane; Hallas, Till; Kinsch, Lena; Stahr, Simon; Prietzel, Jörg; Lang, Friederike

    2016-04-01

    As roots and hyphae often accumulate at the surface of soil aggregates, their formation and turnover might be related to the bioavailability especially of immobile nutrients like phosphorus. Several methods have been developed to obtain specific samples from aggregate surfaces and aggregate cores and thus to investigate differences between aggregate shell and core. However, these methods are often complex and time-consuming; therefore most common methods of soil analysis neglect the distribution of nutrients within aggregates and yield bulk soil concentrations. We developed a new sequential aggregate peeling method to analyze the distribution of different nutrients within soil aggregates (4-20 mm) from four forest sites (Germany) differing in concentrations of easily available mineral P. Aggregates from three soil depths (Ah, BwAh, Bw) were isolated, air-dried, and peeled with a sieving machine performing four sieving levels with increasing sieving intensity. This procedure was repeated in quadruplicate, and fractions of the same sample and sieving level were pooled. Carbon and N concentration, citric acid-extractable PO4 and P, as well as total element concentrations (P, K, Mg, Ca, Al, Fe) were analyzed. Additionally, synchrotron-based P K-edge XANES spectroscopy was applied on selected samples to detect P speciation changes within the aggregates. The results reveal for most samples a significantly higher C and N concentration at the surface compared to the interior of the aggregates. Carbon and N gradients get more pronounced with increasing soil depth and decreasing P status of study sites. This might be explained by lower aggregate turnover rates of subsoil horizons and intense bioturbation on P-rich sites. This assumption is also confirmed by concentrations of citric acid-extractable PO4 and P: gradients within aggregates are getting more pronounced with increasing soil depth and decreasing P status. However, the direction of these gradients is site

  2. Effects of composite soil with feldspathic sandstone and sand on soil aggregates and organic carbon

    NASA Astrophysics Data System (ADS)

    Li, J.; Han, J. C.; Zhang, Y.; Lei, G. Y.; Wang, H. Y.; Zhu, D. W.

    2016-08-01

    The case was to study the effects of soils with different proportions of feldspathic sandstone and sand on soil stability and organic carbon at 0-30 cm soil depth with four different ratios(C1, C2, C3 and C4), They were used to prepare the composite soil in Fu Ping, Shaanxi Province of China, then the soil aggregates distribution, WASR, MWD, GMD, D valueand and organic carbon content were measured and analysed.The results showed : the soil stability of C1, C2 and C3 was better than C4, i.e., the composition could improve the soil stability. With the increasing of the planting years, the contents of soil aggregates with the size >0.25 mm and MWD, GMD and SOC increased for each treatment at 0- 30 cm soil depth, which was contrary to D values. WASR of C2 was significantly higher than others (p<0.05) after 3-year planting. The significant logarithmic relationships were found between the D values and the ratios in C1, C2 and C3. Besides C1 and C2 could increase the stability and content of large soil aggregates to improve soil structure; C2 could significantly increase the SOC than others at 0- 30 cm soil depth.

  3. Stability of Soil Carbon Fractions - from molecules to aggregates

    NASA Astrophysics Data System (ADS)

    Mueller, C. W.; Mueller, K. E.; Freeman, K. H.; Eissenstat, D.; Kögel-Knabner, I.

    2009-12-01

    The turnover of soil organic matter (SOM) is controlled both by its chemical composition, its spatial bioavailability and the association with the mineral phase. Separation by physical fractionation of bulk soils and subsequent chemical analysis of these fractions should give insights to how compositional differences in SOM drive turnover rates of different size-defined carbon pools. The main objective of the study was to elucidate the relative abundance and recalcitrance of lignin and plant lipids (e.g. cutin and suberin) in the course of SOM decomposition within aggregated bulk soils and SOM fractions. By the parallel incubation of physically-separated size fractions and bulk soils of the Ah horizon from a forested soil (Picea abies L.Karst) over a period of 400 days, a unique set of samples was created to study SOM dynamics. We used solid-state 13C-CPMAS NMR spectroscopy and GC-MS (after copper oxide oxidation and solvent extraction) to analyze the composition of the incubated samples. The abundance and isotopic composition (including 13C and 14C) of respired CO2 further enabled us to monitor the dynamics of SOM mineralization. This approach allowed for differentiating between C stabilization of soil fractions due to accessibility/aggregation and to recalcitrance at different scales of resolution (GC-MS, NMR). A relative enrichment of alkyl C and decreasing lignin contents in the order of sand < silt < clay were observed by 13C-NMR and GC-MS within soils and fractions before the incubation, resulting in increased lipid to lignin ratios with decreasing particle size. A relative enrichment of lignin in the incubated fractions compared to the incubated bulk soils clearly indicated the preferential mineralization of less recalcitrant C compounds that were spatially inaccessible in aggregates of the bulk soil. Differences in the abundance of various lignin, cutin, and suberin monomers measured by GC-MS before and after the incubation indicate selective degradation

  4. Litter Inputs and Soil Aggregation in Midwestern Biofuel Crops

    NASA Astrophysics Data System (ADS)

    Kantola, I. B.; Masters, M. D.; Smyth, E. M.; DeLucia, E. H.

    2014-12-01

    Perennial C4 grasses represent alternatives to corn for the production of ethanol because of low management costs and high biomass production. To evaluate the effects of perennial grasses on the agricultural soils of the Midwest, native switchgrass and a sterile hybrid of the Asian grass Miscanthus were planted at the University of Illinois Energy Farm in 2008. Through five years of growth, above and belowground plant biomass, litter, and soil were compared with soils in plots growing a corn-corn-soy rotation typical of the area. Above- and belowground plant biomass in Miscanthus and switchgrass averaged higher than corn/soy following two years of perennial establishment, with belowground biomass exceeding corn/soy by approximately 5-fold in the year after establishment (2010) and 25-fold by 2012. Measurements of root distribution and turnover rates indicate that roots are the primary contribution of new carbon to soils under perennial crops. Physical fractionation of the soils into water stable aggregates showed 4-14% increases in macroaggregate fractions under perennial crops; the large aggregates are adhered together by organic material and indicative of the increased presence of labile carbon forms like plant roots, fungi, and plant and microbial exudates. Carbon and nitrogen analyses of the fractions show that while overall carbon has not increased significantly in whole soil, soils under perennial grasses are concentrating carbon by 5-17% in the macroaggregates after just 5 years. Native switchgrass roots (buried) and litter (surface-applied) decompose faster than Miscanthus roots and litter, but slower than corn roots and litter buried to simulate incorporation by tillage. Switchgrass soil shows the highest degree of macroaggregate formation, pointing to a high rate of litter and root decomposition and incorporation into soil structure. While macroaggregates are relatively labile soil structures compared to microaggregates and free silt and clay, they offer

  5. Corn stover harvest changes soil hydrology and soil aggregation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the United States, commercial-scale cellulosic-ethanol production using corn (Zea Mays L.) stover has become a reality. As the industry matures and demand for stover increases, a clear understanding of how reducing the rate of stover remaining in the field impacts soil properties is critical. Sto...

  6. A quantitative investigation of the effect of pore morphology on soil aggregate stability

    NASA Astrophysics Data System (ADS)

    Papadopoulos, A.

    2009-04-01

    Soil structure determines the operating environment for all physical, chemical and biological processes within the soil. Soil aggregate stability is an important measure for assessing soil structure quality. Non-destructive tomography techniques such as X-ray Computed Tomography (CT) offer great opportunities to quantitatively investigate the soil porous architecture which can provide important information for understanding soil processes and function in a multi-scale manner. For instance, the intra-aggregate pore space is of great importance for microbial activity, the sequestration of organic carbon and water flow. This paper investigates the effect of pore morphology on soil aggregate stability. Apparent porosity, pore size distribution, average pore size and fractal perimeter dimension (pore roughness) were measured from the images of the reconstructed 2-D image stacks. A new theoretical concept of soil aggregate stability is proposed. A strong relationship was observed between soil aggregate stability and pore morphological complexity.

  7. Settling Velocity, Aggregate Stability, and Interrill Erodibility of Soils Varying in Clay Mineralogy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The relation of soil structural stability with soil erodibility depends on the mechanisms of aggregate disruption of different aggregate sizes and the measurement technique. In this study, we evaluated the relationship between settling velocity and stability of aggregates of different sizes, and int...

  8. Soil microbial parameters and stability of soil aggregate fractions under different grassland communities on the Loess Plateau, China

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Over-grazing and large scale monocultures on the Loess plateau in China have caused serious soil erosion by water and wind. Grassland revegetation has been reported as one of the most effective counter measures. Therefore, we investigated soil aggregation, aggregate stability and soil microbial ac...

  9. Changes in soil aggregation and dust emission potential in response to aeolian processes

    NASA Astrophysics Data System (ADS)

    swet, Nitzan; Katra, Itzhak

    2016-04-01

    Aeolian (wind) dust emission has high environmental and socioeconomic significances due to loss of natural soil and air pollution. Dust emission involves complex interactions between the airflow and the soil surface. The soil aggregates were dust particles are held determine the topsoil erodibility in aeolian erosion. Although the key role of soil aggregation in dust emission mechanisms, information on changes in soil aggregate size distribution (ASD) due to aeolian erosion is lucking. This study is focused on quantitative ASD analyses before and after aeolian processes (saltation). Aeolian experiments and soil analyses were conducted on semiarid loess topsoils with different initial conditions of aggregation. The results show that saltation rates and PM emissions depend on the initial ASD and shear velocity. In all initial soil conditions, the content of aggregates at saltator-sized 63-250 μm was increased by 10-34 % following erosion of macro-aggregates > 500 μm. It revealed that the aggregate-saltator production increases with the shear velocity (up to 0.61 m s-1) for soils with available macro-aggregates. The findings highlight the dynamics in soil aggregation in response to aeolian transport and therefore its significance for determining the mechanisms of dust emission from soil aggregates.

  10. Extraction of pores from microtomographic reconstructions of intact soil aggregates

    SciTech Connect

    Albee, P. B.; Stockman, G. C.; Smucker, A. J. M.

    2000-02-29

    Segmentation of features is often a necessary step in the analysis of volumetric data. The authors have developed a simple technique for extracting voids from irregular volumetric data sets. In this work they look at extracting pores from soil aggregates. First, they identify a threshold that gives good separability of the object from the background. They then segment the object, and perform connected components analysis on the pores within the object. Using their technique pores that break the surface can be segmented along with pores completely contained in the initially segmented object.

  11. Friability and aggregate stability of loamy soil after 5 years of biochar application

    NASA Astrophysics Data System (ADS)

    Utomo, Wani; Ganika, Shaory; Wisnubroto, Erwin; Islami, Titiek

    2016-04-01

    The effect of biochar application on soil friability and aggregate stability of loamy soil was studied at Brawijaya University field experimental station, Jatikerto, Malang, Indonesia. The soil has been planted with cassava for 4 years continuously and 1 year planted with maiz. The biochar applied was made from cassava stem and farm yard manure. It was found that biochar application, either made from cassava stem or farm yard manure improved soil qualities. Soil applied with biochar was more friable compared to that of the no biochar soil, although biochar application did not influence Atterberg limits. It seems that the higher friability of biochar applied soil was associated with the higher soil organic matter. It was found that until 5 years application, the biochar treated soil had a higher soil organic matter content. Soil applied with biochar possessed a better soil aggregate stability, both dry and wet stability. This was shown by the higher aggregate mean weight diameter (MWD) of biochar applied soil. The cassava biochar applied soil had MWD of 2.22 mm (dry stability) and 1.56 mm (wet stability), whereas the control soil had MWD of 1.45 mm (dry stability) and 1.25 (wet stability). There was a significant positive correlation between soil friability and dry aggregate stability. The biochar applied soils also had higher soil permeability. Key words: soil qualities, soil physical properties, Atterberg limits, hydraulic conductivity

  12. Detection of soil microarthropod aggregations in soybean fields, using a modified tullgren extractor

    SciTech Connect

    Farrar, F.P. Jr.; Crossley, D.A. Jr.

    1983-01-01

    The spatial distribution of soil microarthropods in soybean fields was investigated by use of a modified Tullgren extractor. Blocks of soil were extracted over a grid of collection cells from which microarthropod aggregations could be identified and measured. Aggregations in conventionally tilled soybeans were smaller than those in no tillage soybeans, and had less influence on population distributions. Population size was highly correlated with the area of soil microarthropod aggregations. 10 references, 5 figures, 3 tables.

  13. Land use effects on phosphorus sequestration in soil aggregates in western Iran.

    PubMed

    Sheklabadi, M; Mahmoudzadeh, H; Mahboubi, A A; Gharabaghi, B; Ahrens, B

    2014-10-01

    Cultivating native lands may alter soil phosphorus (P) distribution and availability. The present study aimed to determine the distribution of P in soil aggregates for different long-term land management practices. The partitioned P in labile (L), Fe/Al-bound, Ca-bound, organic pools, and total P in four aggregate size fractions were determined for five land uses (forest, vineyard after 30 years, wetland, alfalfa, and wheat cultivated soil after 20 years). Both native land uses (forest and wetland) were distinguished by high and low amounts of large macro- and micro-aggregates, respectively, compared with disturbed soils (vineyard, alfalfa, and wheat soils). Labile P in large macro-aggregates were higher in native land use when compared with the other land uses, which led to increasing lability of P and accelerated water pollution. Soils under native conditions sequestered more Ca-bound P in large macro-aggregates than the soils in disturbed conditions. Conversion of native lands to agricultural land caused enhanced organic P storage in aggregates smaller than the 2 mm from 31.0 to 54.3%. Soils under forest had 30% total P more than the vineyard for the aggregates >2 mm after 30 years land use change. However, the amount of P in smaller (<2 mm) sized aggregates was increased by 29% for the vineyard when compared with the forest. The P storage as bound Ca particles for the large macro-aggregates had negative correlation with the micro-aggregates.

  14. Effect of Organic Inputs on Strength and Stability of Soil Aggregates Under Rice-Wheat Rotation

    NASA Astrophysics Data System (ADS)

    Das, Bappa; Chakraborty, Debashis; Singh, Vinod K.; Aggarwal, Pramila; Singh, Ravender; Dwivedi, Brahm S.

    2014-04-01

    The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue- and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates <0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.

  15. Long-term manure amendments reduced soil aggregate stability via redistribution of the glomalin-related soil protein in macroaggregates.

    PubMed

    Xie, Hongtu; Li, Jianwei; Zhang, Bin; Wang, Lianfeng; Wang, Jingkuan; He, Hongbo; Zhang, Xudong

    2015-10-01

    Glomalin-related soil protein (GRSP) contributes to the formation and maintenance of soil aggregates, it is however remains unclear whether long-term intensive manure amendments alter soil aggregates stability and whether GRSP regulates these changes. Based on a three-decade long fertilization experiment in northeast China, this study examined the impact of long-term manure input on soil organic carbon (SOC), total and easily extractable GRSP (GRSPt and GRSPe) and their respective allocations in four soil aggregates (>2000 μm; 2000-250 μm; 250-53 μm; and <53 μm). The treatments include no fertilization (CK), low and high manure amendment (M1, M2), chemical nitrogen, phosphorus and potassium fertilizers (NPK), and combined manure and chemical fertilizers (NPKM1, NPKM2). Though SOC, GRSPe and GRSPt in soil and SOC in each aggregate generally increased with increasing manure input, GRSPt and GRSPe in each aggregate showed varying changes with manure input. Both GRSP in macroaggregates (2000-250 μm) were significantly higher under low manure input, a pattern consistent with changes in soil aggregate stability. Constituting 38~49% of soil mass, macroaggregates likely contributed to the nonlinear changes of aggregate stability under manure amendments. The regulatory process of GRSP allocations in soil aggregates has important implications for manure management under intensive agriculture.

  16. Field soil aggregate stability kit for soil quality and rangeland health evaluations

    USGS Publications Warehouse

    Herrick, J.E.; Whitford, W.G.; de Soyza, A. G.; Van Zee, J. W.; Havstad, K.M.; Seybold, C.A.; Walton, M.

    2001-01-01

    Soil aggregate stability is widely recognized as a key indicator of soil quality and rangeland health. However, few standard methods exist for quantifying soil stability in the field. A stability kit is described which can be inexpensively and easily assembled with minimal tools. It permits up to 18 samples to be evaluated in less than 10 min and eliminates the need for transportation, minimizing damage to soil structure. The kit consists of two 21??10.5??3.5 cm plastic boxes divided into eighteen 3.5??3.5 cm sections, eighteen 2.5-cm diameter sieves with 1.5-mm distance openings and a small spatula used for soil sampling. Soil samples are rated on a scale from one to six based on a combination of ocular observations of slaking during the first 5 min following immersion in distilled water, and the percent remaining on a 1.5-mm sieve after five dipping cycles at the end of the 5-min period. A laboratory comparison yielded a correlation between the stability class and percent aggregate stability based on oven dry weight remaining after treatment using a mechanical sieve. We have applied the method in a wide variety of agricultural and natural ecosystems throughout western North America, including northern Mexico, and have found that it is highly sensitive to differences in management and plant community composition. Although the field kit cannot replace the careful laboratory-based measurements of soil aggregate stability, it can clearly provide valuable information when these more intensive procedures are not possible.

  17. VARIATIONS IN SOIL AGGREGATE STABILITY AND ENZYME ACTIVITIES IN A TEMPERATE AGROFORESTRY PRACTICE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Agroforestry and grass buffers have been shown to improve soil properties and overall environmental quality. The objective of this study was to examine management and landscape effects on water stable soil aggregates (WSA), soil carbon, soil nitrogen, enzyme activity, and microbial community DNA co...

  18. Soil Aggregate Stability and Grassland Productivity Associations in a Northern Mixed-Grass Prairie

    PubMed Central

    Reinhart, Kurt O.; Vermeire, Lance T.

    2016-01-01

    Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25–1 and 1–2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0–10 or 0–30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land’s capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations. PMID:27467598

  19. Aggregate-associated carbon and nitrogen in reclaimed sandy loam soils

    SciTech Connect

    Wick, A.F.; Stahl, P.D.; Ingram, L.J.

    2009-11-15

    Minimal research has been conducted on aggregate, C, and N in coarse-textured soils used to reclaim surface coal mine lands. Furthermore, little is known about the contribution different plant communities make to the recovery of aggregation in these soils. Two chronosequences of semiarid reclaimed sites with sandy loam soils were sampled under shrub- and grass-dominated communities. Aggregation, aggregate fractions, and associated C and N were measured. No definitive trends of increasing macroaggregates between sites were observed undershrubs; however, macro- and microaggregation was greater in the 16-yr-old (0.20 and 0.23 kg aggregate kg{sup -1} soil, respectively) than in the 5-yr-old soils (0.02 and 0.08 kg aggregate kg{sup -1} soil, respectively) under grasses. Although C and N concentrations were drastically reduced (50-75%) with mining activity between the <1-yr-old and native soils, aggregate C and N concentrations tinder shrubs and grasses were similar to each other and to the native soils in the 5-yr-old site. Sods under grass in the 16-yr-old site had lower available and aggregate-occluded C and N concentrations than the 5-yr-old site, while C and N concentrations did not change between 5- and 16-yr-old soils under shrubs. Conversely, aggregate C and N pool sizes under shrubs and grasses both increased with site age to conditions similar to those observed in the native soil. Reclaimed shrub site soils had consistently higher C concentrations in the older reclaimed sites (10 and 16 yr old) than the soils under grasses, indicating greater accumulation and retention of C and N in organic material under shrub than grass communities in semiarid reclaimed sites.

  20. Microbial properties of soil aggregates created by earthworms and other factors: spherical and prismatic soil aggregates from unreclaimed post-mining sites.

    PubMed

    Frouz, J; Krištůfek, V; Livečková, M; van Loo, D; Jacobs, P; Van Hoorebeke, L

    2011-01-01

    Soil aggregates between 2 and 5 mm from 35- and 45-year-old unreclaimed post-mining sites near Sokolov (Czech Republic) were divided into two groups: spherical and prismatic. X-ray tomography indicated that prismatic aggregates consisted of fragments of claystone bonded together by amorphous clay and roots while spherical aggregates consisted of a clay matrix and organic fragments of various sizes. Prismatic aggregates were presumed to be formed by plant roots and physical processes during weathering of Tertiary mudstone, while earthworms were presumed to contribute to the formation of spherical aggregates. The effects of drying and rewetting and glucose addition on microbial respiration, microbial biomass, and counts of bacteria in these aggregates were determined. Spherical aggregates contained a greater percentage of C and N and a higher C-to-N ratio than prismatic ones. The C content of the particulate organic matter was also higher in the spherical than in the prismatic aggregates. Although spherical aggregates had a higher microbial respiration and biomass, the growth of microbial biomass in spherical aggregates was negatively correlated with initial microbial biomass, indicating competition between bacteria. Specific respiration was negatively correlated with microbial biomass. Direct counts of bacteria were higher in spherical than in prismatic aggregates. Bacterial numbers were more stable in the center than in the surface layers of the aggregates. Transmission electron microscopy indicated that bacteria often occurred as individual cells in prismatic aggregates but as small clusters of cells in spherical aggregates. Ratios of colony forming units (cultivatable bacteria) to direct counts were higher in spherical than in prismatic aggregates. Spherical aggregates also contained faster growing bacteria.

  1. Influence of sustainable management on aggregate stability and soil organic matter on agricultural soil of southern Spain

    NASA Astrophysics Data System (ADS)

    Morugan-Coronado, Alicia; Arcenegui, Victoria; Mataix-Solera, Jorge; Gomez-Lucas, Ignacio; Garcia-Orenes, Fuensanta

    2016-04-01

    Intensive agriculture has increased crop yields but also posed severe environmental problems. Unsustainable land management such as excessive tillage can lead to a loss of soil fertility and a drastic reduction in the aggregate stability and soil organic matter content. However sustainable agriculture can keep good crop yields with minimal impact on ecological factors conserving the soil quality and its ecosystem services. Sustainable agriculture management promotes the maintenance of soil organic matter levels providing plant nutrients through the microbial decomposition of organic materials. Also this management has a positive effect on soil structure with the improvement of stability of aggregates. The resistance of soil aggregates to the slaking and dispersive effects of water (aggregate stability) is important for maintaining the structure in arable soils. Our purpose was to investigate and compare the effects of sustainable agricultural practices versus intensive agriculture on aggregate stability and soil organic matter. Three agricultural areas are being monitored in the southern of Spain, two of them with citrus orchards (AL) and (FE) and one with grapevine(PA). In all of them two agricultural treatments are being developed, organic with no-tillage management(O) and inorganic fertilization with herbicide application and intensive tillage (I). The sustainable agricultural management (manure, no tillage and vegetation cover) contributed to the improve of soil conditions, increasing organic matter and aggregate stability. Meanwhile, herbicide treatment and intensive tillage with inorganic fertilization managements resulted in the decreasing of aggregate stability and low levels of soil organic carbon. Soil organic matter content is generally low in all unsustainable treatments plots and tends to decline in aggregate stability and soil physical condition. In both treatments the crop yield are comparable.

  2. Linking soil permeability and soil aggregate stability with root development: a pots experiment (preliminary results)

    NASA Astrophysics Data System (ADS)

    Vergani, Chiara; Graf, Frank; Gerber, Werner

    2015-04-01

    Quantifying and monitoring the contribution of vegetation to the stability of the slopes is a key issue for implementing effective soil bioengineering measures. This topic is being widely investigated both from the hydrological and mechanical point of view. Nevertheless, due to the high variability of the biological components, we are still far from a comprehensive understanding of the role of plants in slope stabilization, especially if the different succession phases and the temporal development of vegetation is considered. Graf et al., 2014, found within the scope of aggregate stability investigations that the root length per soil volume of alder specimen grown for 20 weeks under laboratory conditions is comparable to the one of 20 years old vegetation in the field. This means that already relatively short time scales can provide meaningful information at least for the first stage of colonization of soil bioengineering measures, which is also the most critical. In the present study we analyzed the effect of root growth on two soil properties critical to evaluate the performance of vegetation in restoring and re-stabilizing slopes: permeability and soil aggregate stability. We set up a laboratory experiment in order to work under controlled conditions and limit as much as possible the natural variability. Alnus incana was selected as the study species as it is widely used in restoration projects in the Alps, also because of its capacity to fix nitrogen and its symbiosis with both ecto and arbuscular mycorrhizal fungi. After the first month of growth in germination pots, we planted one specimen each in big quasi cylindrical pots of 34 cm diameter and 35 cm height. The pots were filled with the soil fraction smaller than 10 mm coming from an oven dried moraine collected in a subalpine landslide area (Hexenrübi catchment, central Switzerland). The targeted dry unit weight was 16 kN/m3. The plants have been maintained at a daily temperature of 25°C and relative

  3. Soil aggregation and glomalin in a soil quality management study in a cold, semi-arid region

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Global food insecurity and rapidly diminishing water, soil, and energy resources are putting pressure on agroecosystems to efficiently produce more food while maintaining or enhancing soil quality, particularly soil aggregation. A field study established in 1993 near Mandan, ND sought to evaluate im...

  4. Evolution of unsaturated hydraulic conductivity of aggregated soils due to compressive forces

    NASA Astrophysics Data System (ADS)

    Berli, M.; Carminati, A.; Ghezzehei, T. A.; Or, D.

    2008-05-01

    Prediction of water flow and transport processes in soils susceptible to structural alteration such as compaction of tilled agricultural lands or newly constructed landfills rely on accurate description of changes in soil unsaturated hydraulic conductivity. Recent studies have documented the critical impact of aggregate contact characteristics on water flow rates and pathways in unsaturated aggregated soils. We developed an analytical model for aggregate contact size evolution as a basis for quantifying effects of compression on saturated and unsaturated hydraulic conductivity of aggregated soil. Relating confined one-dimensional sample strain with aggregate deformation facilitates prediction of the increase in interaggregate contact area and concurrent decrease in macropore size with degree of sample compression. The hydrologic component of the model predicts unsaturated hydraulic conductivity of a pack of idealized aggregates (spheres) on the basis of contact size and saturation conditions under prescribed sample deformation. Calculated contact areas and hydraulic conductivity for pairs of aggregates agreed surprisingly well with measured values, determined from compaction experiments employing neutron and X-ray-radiography and image analysis. Model calculations for a unit cell of uniform spherical aggregates in cubic packing were able to mimic some of the differences in saturated and unsaturated hydraulic conductivity observed for aggregates and bulk soil.

  5. Soil 13C Dynamics in Aggregates Across a Soil Profile Under an Established Miscanthus System

    NASA Astrophysics Data System (ADS)

    Dondini, M.; Groenigen, K. J.; Jones, M.

    2008-12-01

    Soils are the largest pool of terrestrial organic carbon (C), containing nearly three times the amount of C as the atmosphere. Environmental changes that affect soil C dynamics could slow down the rise in atmospheric CO2 and associated warming by promoting soil C storage. Our capacity to predict the consequences for global change therefore depends on a better understanding of the distribution and controls of soil organic C and how vegetation change may affect SOC distributions. One land cover change of particular interest involves the establishment of bio energy crop stands. The full mitigation potential of bio energy crops cannot be considered without taking into account their effect on soil C dynamics. Miscanthus, a perennial C4 grass from Eastern Asia, has recently received considerable interest as a bio-energy crop. For that reason, we analyzed the C content and the 13C signatures across the soil profile in a 14 year old Miscanthus system, established on former arable land. We combined SOM fractionation techniques by size and density, allowing us to investigate small shifts in soil C stores that would be significant in the long term, but that might not be detected by conventional methodologies. The 13C signal of the various SOM fractions allowed us to distinguish between Miscanthus-derived vs. native soil organic C. Soils under Miscanthus contained 796 g C/m2 in the 0-15 cm layer, and 1233g C/m2 in the 15- 30 cm layer. These values are significantly higher than soil C contents in the arable land. Macroaggregates under Miscanthus contain more than twice as much C compared to arable land, showing a decrease in soil C content with decreasing aggregate size. These differences are largely caused by soil C storage in the microaggregate within macroaggregates fraction. Under Miscanthus, this fraction contains 440 g C/m2 and 488 g C/m2 at 0-15 cm and 15-30 cm respectively, while under the arable land it has mean values of 174 g C/m2 and 353 g C/m2. Our data suggest a

  6. Impact of Spatial Soil and Climate Input Data Aggregation on Regional Yield Simulations

    PubMed Central

    Hoffmann, Holger; Zhao, Gang; Asseng, Senthold; Bindi, Marco; Biernath, Christian; Constantin, Julie; Coucheney, Elsa; Dechow, Rene; Doro, Luca; Eckersten, Henrik; Gaiser, Thomas; Grosz, Balázs; Heinlein, Florian; Kassie, Belay T.; Kersebaum, Kurt-Christian; Klein, Christian; Kuhnert, Matthias; Lewan, Elisabet; Moriondo, Marco; Nendel, Claas; Priesack, Eckart; Raynal, Helene; Roggero, Pier P.; Rötter, Reimund P.; Siebert, Stefan; Specka, Xenia; Tao, Fulu; Teixeira, Edmar; Trombi, Giacomo; Wallach, Daniel; Weihermüller, Lutz; Yeluripati, Jagadeesh; Ewert, Frank

    2016-01-01

    We show the error in water-limited yields simulated by crop models which is associated with spatially aggregated soil and climate input data. Crop simulations at large scales (regional, national, continental) frequently use input data of low resolution. Therefore, climate and soil data are often generated via averaging and sampling by area majority. This may bias simulated yields at large scales, varying largely across models. Thus, we evaluated the error associated with spatially aggregated soil and climate data for 14 crop models. Yields of winter wheat and silage maize were simulated under water-limited production conditions. We calculated this error from crop yields simulated at spatial resolutions from 1 to 100 km for the state of North Rhine-Westphalia, Germany. Most models showed yields biased by <15% when aggregating only soil data. The relative mean absolute error (rMAE) of most models using aggregated soil data was in the range or larger than the inter-annual or inter-model variability in yields. This error increased further when both climate and soil data were aggregated. Distinct error patterns indicate that the rMAE may be estimated from few soil variables. Illustrating the range of these aggregation effects across models, this study is a first step towards an ex-ante assessment of aggregation errors in large-scale simulations. PMID:27055028

  7. Impact of Spatial Soil and Climate Input Data Aggregation on Regional Yield Simulations.

    PubMed

    Hoffmann, Holger; Zhao, Gang; Asseng, Senthold; Bindi, Marco; Biernath, Christian; Constantin, Julie; Coucheney, Elsa; Dechow, Rene; Doro, Luca; Eckersten, Henrik; Gaiser, Thomas; Grosz, Balázs; Heinlein, Florian; Kassie, Belay T; Kersebaum, Kurt-Christian; Klein, Christian; Kuhnert, Matthias; Lewan, Elisabet; Moriondo, Marco; Nendel, Claas; Priesack, Eckart; Raynal, Helene; Roggero, Pier P; Rötter, Reimund P; Siebert, Stefan; Specka, Xenia; Tao, Fulu; Teixeira, Edmar; Trombi, Giacomo; Wallach, Daniel; Weihermüller, Lutz; Yeluripati, Jagadeesh; Ewert, Frank

    2016-01-01

    We show the error in water-limited yields simulated by crop models which is associated with spatially aggregated soil and climate input data. Crop simulations at large scales (regional, national, continental) frequently use input data of low resolution. Therefore, climate and soil data are often generated via averaging and sampling by area majority. This may bias simulated yields at large scales, varying largely across models. Thus, we evaluated the error associated with spatially aggregated soil and climate data for 14 crop models. Yields of winter wheat and silage maize were simulated under water-limited production conditions. We calculated this error from crop yields simulated at spatial resolutions from 1 to 100 km for the state of North Rhine-Westphalia, Germany. Most models showed yields biased by <15% when aggregating only soil data. The relative mean absolute error (rMAE) of most models using aggregated soil data was in the range or larger than the inter-annual or inter-model variability in yields. This error increased further when both climate and soil data were aggregated. Distinct error patterns indicate that the rMAE may be estimated from few soil variables. Illustrating the range of these aggregation effects across models, this study is a first step towards an ex-ante assessment of aggregation errors in large-scale simulations.

  8. Soil Aggregates and Organic Carbon Distribution in Red Soils after Long-term Fertilization with Different Fertilizer Treatments

    NASA Astrophysics Data System (ADS)

    Tang, J.; Wang, Y.

    2013-12-01

    Red soils, a typical Udic Ferrosols, widespread throughout the subtropical and tropical region in southern China, support the majority of grain production in this region. The red soil is naturally low in pH values, cation exchange capacity, fertility, and compaction, resulting in low organic matter contents and soil aggregation. Application of chemical fertilizers and a combination of organic-chemical fertilizers are two basic approaches to improve soil structure and organic matter contents. We studied the soil aggregation and the distribution of aggregate-associated organic carbon in red soils with a long-term fertilization experiment during 1988-2009. We established treatments including 1) NPK and NK in the chemical fertilizer plots, 2) CK (Control), and 3) CK+ Peanut Straw (PS), CK+ Rice Straw (RS), CK+ Fresh Radish (FR), and CK + Pig Manure (PM) in the organic-chemical fertilizer plots. Soil samples were fractionated into 6 different sized aggregate particles through the dry-wet sieving method according to the hierarchical model of aggregation. Organic carbon in the aggregate/size classes was analyzed. The results showed that the distribution of mechanically stable aggregates in red soils after long-term fertilization decreased with the size, from > 5mm, 5 ~ 2 mm, 2 ~ 1 mm, 1~ 0.25 mm, to < 0.25 mm, but the distribution of water-stable aggregates did not follow this pattern. Compared with the chemical fertilizer application alone, the addition of pig manure and green manure can significantly improve the distribution of aggregates in the 5-2 mm, 2-1 mm and 1-0.25 mm classes. The organic carbon (OC) contents in red soils were all increased after the long-term fertilization. Compared with Treatment NK, soil OC in Treatment NPK was increased by 45.4%. Compared with Treatment CK (low chemical fertilizer), organic fertilizer addition increased soil OC. The OC in the different particle of water-stable aggregates were all significantly increased after long

  9. [Profile distribution of soil aggregates organic carbon in primary forests in Karst cluster-peak depression region].

    PubMed

    Lu, Ling-Xiao; Song, Tong-Qing; Peng, Wan-Xia; Zeng, Fu-Ping; Wang, Ke-Lin; Xu, Yun-Lei; Yu, Zi; Liu, Yan

    2012-05-01

    Soil profiles were collected from three primary forests (Itoa orientalis, Platycladus orientalis, and Radermachera sinica) in Karst cluster-peak depression region to study the composition of soil aggregates, their organic carbon contents, and the profile distribution of the organic carbon. In the three forests, >2 mm soil aggregates were dominant, occupying about 76% of the total. The content of soil total organic carbon ranged from 12.73 to 68.66 g x kg(-1), with a significant difference among the forests. The organic carbon content in <1 mm soil aggregates was slightly higher than that in >2 mm soil aggregates, but most of soil organic carbon was stored in the soil aggregates with greater particle sizes. About 70% of soil organic carbon came from >2 mm soil aggregates. There was a significant positive relationship between the contents of 2-5 and 5-8 mm soil aggregates and the content of soil organic carbon. To increase the contents of 2-8 mm soil aggregates could effectively improve the soil carbon sequestration in Karst region. In Itoa orientalis forest, 2-8 mm soil aggregates accounted for 46% of the total, and the content of soil total organic carbon reached to 37.62 g x kg(-1), which implied that Itoa orientalis could be the suitable tree species for the ecological restoration in Karst region.

  10. Applicability of recycled aggregates in concrete piles for soft soil improvement.

    PubMed

    Medeiros-Junior, Ronaldo A; Balestra, Carlos Et; Lima, Maryangela G

    2017-01-01

    The expressive generation of construction and demolition waste is stimulating several studies for reusing this material. The improvement of soft soils by concrete compaction piles has been widely applied for 40 years in some Brazilian cities. This technique is used to improve the bearing capacity of soft soils, allowing executing shallow foundations instead of deep foundations. The compaction piles use a high volume of material. This article explored the possibility of using recycled aggregates from construction waste to replace the natural aggregates in order to improve the bearing capacity of the soft soil, regarding its compressive strength. Construction wastes from different stages of a construction were used in order to make samples of concrete with recycled aggregates. The strength of concretes with natural aggregates was compared with the strength of concretes with recycled (fine and coarse) aggregates. Results show that all samples met the minimum compressive strength specified for compaction piles used to improve the bearing capacity of soft soils. The concrete with recycled aggregate from the structural stage had even higher resistances than the concrete with natural aggregates. This behaviour was attributed to the large amount of cementitious materials in the composition of this type of concrete. It was also observed that concrete with recycled fine aggregate has a superior resistance to concrete with recycled coarse aggregate.

  11. [Effects of Tillage on Distribution of Heavy Metals and Organic Matter Within Purple Paddy Soil Aggregates].

    PubMed

    Shi, Qiong-bin; Zhao, Xiu-lan; Chang, Tong-ju; Lu, Ji-wen

    2016-05-15

    A long-term experiment was utilized to study the effects of tillage methods on the contents and distribution characteristics of organic matter and heavy metals (Cu, Zn, Pb, Cd, Fe and Mn) in aggregates with different sizes (including 1-2, 0.25-1, 0.05-0.25 mm and < 0.05 mm) in a purple paddy soil under two tillage methods including flooded paddy field (FPF) and paddy-upland rotation (PR). The relationship between heavy metals and organic matter in soil aggregates was also analyzed. The results showed that the aggregates of two tillage methods were dominated by 0.05-0.25 mm and < 0.05 mm particle size, respectively. The contents of organic matter in each aggregate decreased with the decrease of aggregate sizes, however, compared to PR, FPF could significantly increase the contents of organic matter in soils and aggregates. The tillage methods did not significantly affect the contents of heavy metals in soils, but FPF could enhance the accumulation and distribution of aggregate, organic matter and heavy metals in aggregates with diameters of 1-2 mm and 0.25-1 mm. Correlation analysis found that there was a negative correlation between the contents of heavy metals and organic matter in soil aggregates, but a positive correlation between the amounts of heavy metal and organic matter accumulated in soil aggregates. From the slope of the correlation analysis equations, we could found that the sensitivities of heavy metals to the changes of soil organic matters followed the order of Mn > Zn > Pb > Cu > Fe > Cd under the same tillage. When it came to the same heavy metal, it was more sensitive in PR than in FPF.

  12. Organic carbon, water repellency and soil stability to slaking under different crops and managements: a case study at aggregate and intra-aggregate scales

    NASA Astrophysics Data System (ADS)

    Jordán, A.; García-Moreno, J.; Gordillo-Rivero, Á. J.; Zavala, L. M.; Cerdà, A.

    2014-08-01

    This research studies the distribution of organic C and intensity of water repellency in soil aggregates with different size and in the interior of aggregates from Mediterranean soils under different crops (apricot, citrus and wheat) and management (conventional tilling and no tilling/mulching). For this, undisturbed aggregates were sampled and carefully divided in size fractions (0.25-0.5, 0.5-1, 1-2, 2-5, 5-10 and 10-15 mm) or peeled to obtain separated aggregate layers (exterior, transitional and interior). Organic C 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 organic C content in aggregates with different size varied among soils under different crops, generally increasing with decreasing size. At the intra-aggregate level, organic C concentrated preferably in the exterior layer of aggregates 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 crops, 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 organic C in aggregate layers from conventionally tilled soils, great or significant differences in the distribution of water repellency at the intra-aggregate level were not found in any case. Finally, the intensity of water repellency was much more important than the concentration of organic C in the stability to slaking of aggregates.

  13. Stability and heavy metal distribution of soil aggregates affected by application of apatite, lime, and charcoal.

    PubMed

    Cui, Hongbiao; Ma, Kaiqiang; Fan, Yuchao; Peng, Xinhua; Mao, Jingdong; Zhou, Dongmei; Zhang, Zhongbin; Zhou, Jing

    2016-06-01

    Only a few studies have been reported on the stability and heavy metal distribution of soil aggregates after soil treatments to reduce the availability of heavy metals. In this study, apatite (22.3 t ha(-1)), lime (4.45 t ha(-1)), and charcoal (66.8 t ha(-1)) were applied to a heavy metal-contaminated soil for 4 years. The stability and heavy metal distribution of soil aggregates were investigated by dry and wet sieving. No significant change in the dry mean weight diameter was observed in any treatments. Compared with the control, three-amendment treatments significantly increased the wet mean weight diameter, but only charcoal treatment significantly increased the wet aggregate stability. The soil treatments increased the content of soil organic carbon, and the fraction 0.25-2 mm contained the highest content of soil organic carbon. Amendments' application slightly increased soil total Cu and Cd, but decreased the concentrations of CaCl2 -extractable Cu and Cd except for the fraction <0.053 mm. The fractions >2 and 0.25-2 mm contained the highest concentrations of CaCl2-extractable Cu and Cd, accounted for about 74.5-86.8 % of CaCl2-extractable Cu and Cd in soil. The results indicated that amendments' application increased the wet soil aggregate stability and decreased the available Cu and Cd. The distribution of available heavy metals in wet soil aggregates was not controlled by soil aggregate stability, but possibly by soil organic carbon.

  14. Aggregate formation and soil carbon sequestration by earthworms at the ORNL FACE experiment

    NASA Astrophysics Data System (ADS)

    Sanchez-de Leon, Y.; Gonzalez-Meler, M. A.; Lugo-Perez, J.; Wise, D. H.; Jastrow, J. D.

    2012-12-01

    Earthworms have an important role in soil carbon sequestration, but their contribution to carbon sequestration in soils exposed to elevated atmospheric CO2 concentrations has been largely overlooked. Previous studies at the Oak Ridge National Laboratory Free Air CO2 Experiment (ORNL FACE) site showed that the formation of soil aggregates is a key mechanism for soil carbon sequestration. We did a microcosm experiment to quantify earthworm-mediated aggregate formation and compare between two earthworm species with different feeding habits (endogeic vs. epi-edogeic). In addition, we wanted to identify the carbon source (soil, leaf litter or root litter) within aggregates formed by earthworms. We used 13C-depleted soil and 15N-enriched sweetgum (Liquidambar styraciflua) leaf and root litter collected from the ORNL FACE site to assess soil aggregate formation of the native, endogeic earthworm Diplocardia sp. and European, epi-endogeic earthworm Lumbricus rubellus. Both earthworm species are present at the ORNL FACE site. We crushed, sieved (< 250 μm) soil and prepared four treatments: (I) soil only; (II) soil and plant material; (III) soil, plant material and Diplocardia sp.; (IV) soil, plant material and L. rubellus. All treatments were at 30% water content and temperature was maintained at 20°C. The incubation period lasted 26 days. We measured aggregate size distribution, total aggregate carbon content and 13C and 15N to elucidate aggregate carbon source. Newly formed soil macroaggregates (> 250 μm) were higher in treatments with earthworms (III and IV) than in treatments without earthworms (I and II) (p = 0.02). Within macroaggregates, most of the carbon was soil-derived. Leaf and root-derived carbon was found in treatment IV only. Our results suggest that earthworms at the ORNL FACE site directly contribute to the formation of soil aggregates, thus contributing to soil carbon sequestration. Carbon source within macroaggregates correspond with earthworm feeding

  15. [Effects of gaps on distribution of soil aggregates and organic carbon in Pinus massoniana plantation].

    PubMed

    Song, Xiao-Yan; Zhang, Dan-Ju; Zhang, Jian; Li, Jian-Ping; Deng, Chang-Chun; Deng, Chao

    2014-11-01

    The effects of forest gap size on the distribution of soil aggregates, organic carbon and labile organic carbon were investigated in a 39-year-old Pinus massoniana plantation in Yibin, Sichuan Province. The results showed that the composition of soil aggregates was dominated by particles > 2 mm, which accounted for 51.7%-78.7% of the whole soil samples under different sized forest gaps and beneath P. massoniana plantation. Soil organic carbon content and labile organic carbon content in > 5 mm aggregates were significantly positively correlated with the soil organic carbon and labile organic carbon contents. Furthermore, the amounts of organic carbon and labile organic carbon storage > 5 mm particles were higher than those in other size particles. Therefore, particles > 5 mm of aggregates dominated the soil carbon pool. Compared with those P. massoniana plantations, the contents of organic carbon in aggregates and total topsoil decreased during the formation of forest gaps, whereas the soil organic carbon storage under 1225 m2 gap was higher. In addition, the soil labile organic carbon content under 225 and 400 m2 gaps and the labile organic carbon storage under 225, 400, 900 and 1225 m2 gaps were higher than those the plantations, but were lower than under the other gaps. It was suggested that an appropriate size of forest gap would increase the accumulation of soil organic carbon and labile organic carbon content. The size of forest gap had significant effects on the distribution of soil aggregates, organic carbon and labile organic carbon. The soil sample under 1225 m2 gap had the highest organic carbon content and storage and a better aggregate proportion, and the higher labile organic carbon storage. Therefore, it was suggested that 1225 m2 gap might be an optimal logging gap size.

  16. Fire induced changes in aggregate stability: the interacting effects of soil heating and ash leachate

    NASA Astrophysics Data System (ADS)

    Balfour, V.; Hatley, D.; Woods, S.

    2011-12-01

    Increases in runoff and erosion after wildfires are typically attributed to the combined effects of the loss of ground cover, water repellency and surface sealing. Surface sealing in burned areas is caused by raindrop compaction of mineral soils (structural seal formation), the clogging of soil pores by fine soil and ash, or the formation of low conductivity ash crusts (depositional seal formation). Structural sealing is more likely to occur if the fire reduces the aggregate stability of the mineral soil. Soil heating tends to reduce aggregate stability by combusting soil organic matter. Effects due to soil heating may be amplified or reduced by interactions between soil clays and ash leachate, but these effects are poorly understood. We are investigating the interacting effects of soil heating and exposure to ash leachate on the stability of soil aggregates in burned areas. During the 2011 fire season in the Rocky Mountains we collected soil samples (~1000g) from unburned areas adjacent to three recent wildfires. Soils were obtained from areas with sharply contrasting parent materials, leading to differences in the soil mineralogy. High severity ash was collected from within the burned areas. Each soil sample was divided into 6 subsamples with the first subsample acting as a control. The remaining five subsamples were heated to 100, 200, 300, 500, and 700C respectively. After heating, each subsample was split in two. Ash leachate was added to one half and DI water was added to the other half. The ash leachate was prepared by mixing 10 g of ash with 1000 mL of water in accordance with previous studies. All samples were then air dried and analyzed for porosity, bulk density, aggregate size distribution, aggregate stability and water repellency. Initial results suggest that there is an interacting effect of soil heating and exposure to ash leachate on the stability of soil aggregates, but the effect varies depending on the mineralogy of soil clays and the type of

  17. Nitrogen addition alters elemental stoichiometry within soil aggregates in a temperate steppe

    NASA Astrophysics Data System (ADS)

    Yin, Jinfei; Wang, Ruzhen; Liu, Heyong; Feng, Xue; Xu, Zhuwen; Jiang, Yong

    2016-11-01

    Ongoing increases in anthropogenic nitrogen (N) inputs have largely affected soil carbon (C) and nutrient cycling in most terrestrial ecosystems. Numerous studies have concerned the effects of elevated N inputs on soil dissolved organic carbon (DOC), dissolved inorganic N (DIN), available phosphorus (AP), exchangeable calcium (Ca) and magnesium (Mg), and available iron (Fe) and manganese (Mn). However, few have emphasized the stoichiometric traits of these soil parameters, especially within different soil aggregate fractions. In a semiarid grassland of Inner Mongolia, we studied the effect of N addition on the ratios of DOC : DIN, DOC : AP, DIN : AP, exchangeable Ca : Mg, available Fe : Mn within three soil aggregate classes of large macroaggregates (> 2000 µm), small macroaggregates (250-2000 µm), and microaggregates (< 250 µm). Elevated N inputs significantly decreased the DOC : DIN ratio within three soil aggregates. The soil DOC : AP ratio significantly decreased along with increasing N gradients within large macroaggregates and microaggregates. Nitrogen significantly decreased the ratio of exchangeable Ca : Mg within soil macroaggregates. The ratio of available Fe : Mn decreased with N addition within three soil aggregate classes. Alteration of elemental stoichiometry within soil fractions that are characterized by different nutrient retention capacity will influence the chemical composition of soil microorganisms and plant quality.

  18. Bacterial density and community structure associated with aggregate size fractions of soil-feeding termite mounds.

    PubMed

    Fall, S; Nazaret, S; Chotte, J L; Brauman, A

    2004-08-01

    The building and foraging activities of termites are known to modify soil characteristics such as the heterogeneity. In tropical savannas the impact of the activity of soil-feeding termites ( Cubitermes niokoloensis) has been shown to affect the properties of the soil at the aggregate level by creating new soil microenvironments (aggregate size fractions) [13]. These changes were investigated in greater depth by looking at the microbial density (AODC) and the genetic structure (automated rRNA intergenic spacer analysis: ARISA) of the communities in the different aggregate size fractions (i.e., coarse sand, fine sand, coarse silt, fine silt, and dispersible clays) separated from compartments (internal and external wall) of three Cubitermes niokoloensis mounds. The bacterial density of the mounds was significantly higher (1.5 to 3 times) than that of the surrounding soil. Within the aggregate size fractions, the termite building activity resulted in a significant increase in bacterial density within the coarser fractions (>20 mum). Multivariate analysis of the ARISA profiles revealed that the bacterial genetic structures of unfractionated soil and soil aggregate size fractions of the three mounds was noticeably different from the savanna soil used as a reference. Moreover, the microbial community associated with the different microenvironments in the three termite mounds revealed three distinct clusters formed by the aggregate size fractions of each mound. Except for the 2-20 mum fraction, these results suggest that the mound microbial genetic structure is more dependent upon microbial pool affiliation (the termite mound) than on the soil location (aggregate size fraction). The causes of the specificity of the microbial community structure of termite mound aggregate size fractions are discussed.

  19. Process-based reconstruction of sedimentary rocks, sandy soils and soil aggregates

    NASA Astrophysics Data System (ADS)

    Vasilyev, Roman; Gerke, Kirill; Čapek, Pavel; Karsanina, Marina; Korost, Dmitry

    2013-04-01

    There are three main approaches to model and reconstruct (using 2D cut(s), grain size distribution or some other limited information/properties) porous media: 1) statistical methods (correlation functions and simulated annealing, multi-point statistics, entropy methods), 2) sequential methods (sphere or other shapes granular packs), and 3) morphological methods. Each method has its own advantages and shortcomings, so there is no readily available solution and methods should be carefully chosen and tested for each particular media. Here we mainly focus on sequential process-based method due to its general simplicity and straightforward usability for different transformation modeling: diagenesis, mechanical compaction, erosion, etc. It is well known that process-based models for sandstone thin-sections give good transport properties after 3D reconstruction. This method is also useful for pore-network extraction validation. At first, polydisperse sphere packs are created using two different techniques: (1) modified Lubachevsky-Stillinger method, and (2) original Øren-Bakke method with global minimal or local minimal energy ballistic disposition rules. The latter are known to create anisotropic packs with kissing numbers different from real sedimentary materials. During the next step, the third phase (clay minerals for rocks and clay and organic matter for soils) is grown within pore space based on Voronoi tesselation to determine distances to the nearest grains. Input parameters, i.e., grain size distributions and porosities are determined using laboratory methods or image analysis for real porous media: sandstones, sandy soils and soil aggregates. To model soil aggregate structure a gravitational algorithm is used there a set of granules falls onto a gravity center in the middle of the aggregate. All further steps are similar to that of sedimentary rocks and soils. Resulted 3D reconstructions are compared with original 3D structures obtained using X

  20. 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.

  1. Soil type as factor controlling the effects of forest transformation to agricultural use in soil aggregation and related properties

    NASA Astrophysics Data System (ADS)

    Chrenková, Katarína; Mataix-Solera, Jorge; Dlapa, Pavel; Arcenegui, Victoria

    2014-05-01

    The stability of aggregates has an important role in soil functioning and its behavior to avoid erosion and degradation, the ability to transfer liquids and gases, which are important features for crop production and ecosystem health (Tisdall and Oades, 1982). It's also a property that is highly influenced by land use and management (Angers et al., 1993). The stability of aggregates provides key information about the capacity of soil functions that defines the soil quality. This study has aimed to identify the long-term effects of forest transformation on agricultural use on soil structure and related properties. For the research was chosen seven localities in the Alicante Province (E Spain) with different soil types in all cases to compare how the land use changes can affect as a function of soil type and characteristics. In every site, samples were collected from agricultural land use (dry crops with tillage management), and in forest areas close to them with similar soil type that are used as references. On the samples, selected physical and chemical properties were analyzed such as Soil aggregate stability (AS), Organic matter (OM), Mean weight diameter (MWD) of aggregates and Water repellency (WR). As expected, in all cases the AS was significant lower in agricultural sites than in forest. But in some cases the differences were much higher than in others. In forest sites the AS varied between 46 to 82% while in agricultural sites ranged between 14 to 45%. The results showed strong positive correlation of AS with OM. The lowest initial values of AS were found in wettable sandy soils. The agricultural land use lead to relative decrease in AS by 39 to 79% compared to forest soils, indicating that some soils are much more vulnerable to land use than others. These differences can be explained mainly because intrinsic soil properties, such as OM content, texture, and WR. Particularly, the decrease in OM content and absence of WR are responsible for the decrease in

  2. No tillage effect on water retention characteristics of soil aggregates in rainfed semiarid conditions.

    NASA Astrophysics Data System (ADS)

    Blanco-Moure, Nuria; López, M. Victoria; Moret, David

    2010-05-01

    The evaluation of changes in soil moisture retention characteristics associated to alterations in soil structure is of great interest in tillage studies. Most of these studies have evaluated soil properties in samples of total soil but not in individual aggregates. However, soil behavior at a macroscale level depends on the aggregate properties. A better knowledge of aggregate characteristics, as the water retention properties, will help to explain, for example, the response of soil to tillage, compaction and crop growth, and hence, to plan adequate soil management practices. In this study we determine the water retention curve of soil aggregates of different sizes from a soil under two tillage systems (conventional and no tillage). The study was carried out in a silty clay loam soil of semiarid Aragon (NE Spain). Two tillage systems were compared: no tillage (NT) and conventional tillage with mouldboard plough (CT). Water retention curves (WRC) were determined for soil surface aggregates (0-5 cm) of three different sizes (8-4, 4-2 and 2-1 mm in diameter) by using the TDR-pressure cell (Moret et al. 2008. Soil Till. Res, 100, 114-119). The TDR-pressure cell is a non-destructive method which permits determining WRC with the only one and same soil sample. Thus, the pressure cell was filled with aggregates up to 4 cm height, weighted and wetted to saturation from the bottom. Pressure steps were sequentially applied at -0.5, -1.5, -3, -5, -10, -33, -100, -300 kPa, and water content of each aggregate sample was measured gravimetrically and by TDR 24 h after starting each pressure head step. The volume of the sample within the cell was also determined at this moment in order to obtain the bulk density and thus calculate the volumetric water content. A good relationship was obtained between the volumetric water content calculated from the gravimetric water content and the corresponding values measured by TDR (r2=0.907; p≤0.05). Within the same tillage treatment, no

  3. Correlation of soil organic carbon and nutrients (NPK) to soil mineralogy, texture, aggregation, and land use pattern.

    PubMed

    Adhikari, Gopi; Bhattacharyya, Krishna G

    2015-11-01

    This work investigates the correlations existing among soil organic carbon (C), nitrogen (N), phosphorous (P), potassium (K), and physicochemical properties like clay mineralogy, textural components, soil aggregation, and land use pattern. Seven different locations were chosen in the tropical rainforest climate region of Assam, India, for the work. The soil texture classifications were clay, sandy clay loam, and sandy loam with mixed clay mineralogy consisting of tectosilicates and phylosilicates. Two distinct compositions of total Fe/Al oxides≥11.5 and <10.8% were observed along with two distinct groups of water stable soil aggregates of mean weight diameter≈6.42 and ≤3.26 mm. The soil clay and sand had positive and negative contributions respectively to the soil organic carbon (SOC) protection, which was observed to be dependent on lesser sand content, higher silt+clay content, and the presence of higher percentages of total Fe/Al oxides. Soil clay mineralogy suggested that the mineral, chlorite, favored retention of higher SOC content in a particular site. Under similar climatic and mineralogical conditions, both natural and anthropogenic soil disturbances destabilized SOC protection through SOM mineralization and soil aggregate destabilization as indicated by SOC protective capacity studies. Urbanization resulting in soil compaction contributed to enhanced SOC level through increased contact between the occluded organic carbon and the soil mineralogical constituents.

  4. Enzymatic activity inside and outside of water-stable aggregates in soils under different land use

    NASA Astrophysics Data System (ADS)

    Garbuz, S. A.; Yaroslavtseva, N. V.; Kholodov, V. A.

    2016-03-01

    A method is presented for assessing the distribution of enzymatic activity inside and outside of water-stable aggregates. Two samples of water-stable aggregates >1 mm have been isolated from dry aggregates of 1-2 mm. To determine the enzymatic activity, a substrate has been added to one of the samples without disaggregation; the other sample has been preliminarily disaggregated. Enzymatic activity within waterstable aggregates has been assessed from the difference between the obtained results under the supposition that the penetration of substrate within the water-saturated aggregates is hampered, and enzymatic reactions occur only at the periphery. The levels and distributions of enzymatic (peroxidase, polyphenol oxidase, and catalase) activities in water-stable aggregates of soddy-podzolic soils under forest and plowland and typical chernozems of long-term field experiments have been studied. The peroxidase, polyphenol oxidase, and catalase activities of water-stable aggregates vary from 6 to 23, from 7 to 30, and from 5 to 7 mmol/(g h), respectively. The ratio between the enzymatic activities inside and outside of soil aggregates showed a higher dependence on soil type and land use, as well as on the input of organic matter and the structural state, than the general activity level in water-stable aggregates.

  5. Ecology and function of culturable microbes in soil aggregation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil structure plays a dominant role in the physical protection of soil organic matter by controlling microbial access to substrate, microbial turnover processes, and food web interactions. Good soil structure results in soil productivity, a cornerstone of agricultural sustainability. While there is...

  6. Effect of aggregation on SOC transport: linking soil properties to sediment organic matter

    NASA Astrophysics Data System (ADS)

    Kuhn, Nikolaus J.

    2016-04-01

    Soils are an interface between the Earth's spheres and shaped by the nature of the interaction between them. The relevance of soil properties for the nature of the interaction between atmosphere, hydrosphere and biosphere is well-studied and accepted, on point- or ecotone-scale. However, this understanding of the largely vertical connections between spheres is not matched by a similar recognition of soil properties affecting processes acting largely in a lateral way across the land surface, such as erosion, transport and deposition of soil and the associated organic matter. Understanding the redistribution of eroded soil organic matter falls into several disciplines, most notably soil science, agronomy, hydrology and geomorphology, and recently into biogeochemistry. Accordingly, the way soil and sediment are described differs: in soil science, aggregation and structure are essential properties, while most process-based soil erosion models treat soil as a mixture of individual mineral grains, based on concepts derived in fluvial geomorphology or civil engineering. The actual behavior of aggregated sediment and the associated organic matter is not reflected by either approach and difficult to capture due to the dynamic nature of aggregation, especially in an environment such as running water. Still, a proxy to assess the uncertainties introduced by aggregation on the behavior of soil/sediment organic while moving in water across landscapes and into the aquatic system would represent a major step forward. To develop such a proxy, a database collating relevant soil, organic matter and sediment properties could serve as an initial step to identify which soil types and erosion scenarios are prone to generate a high uncertainty compared to the use of soil texture in erosion models. Furthermore, it could serve to develop standardized analytical procedures for appropriate description of soil and organic matter as sediment.

  7. Protection of soil carbon within macro-aggregates depends on intra-aggregate pore characteristics

    PubMed Central

    Kravchenko, Alexandra N.; Negassa, Wakene C.; Guber, Andrey K.; Rivers, Mark L.

    2015-01-01

    Soil contains almost twice as much carbon (C) as the atmosphere and 5–15% of soil C is stored in a form of particulate organic matter (POM). Particulate organic matter C is regarded as one of the most labile components of the soil C, such that can be easily lost under right environmental settings. Conceptually, micro-environmental conditions are understood to be responsible for protection of soil C. However, quantitative knowledge of the specific mechanisms driving micro-environmental effects is still lacking. Here we combined CO2 respiration measurements of intact soil samples with X-ray computed micro-tomography imaging and investigated how micro-environmental conditions, represented by soil pores, influence decomposition of POM. We found that atmosphere-connected soil pores influenced soil C’s, and especially POM’s, decomposition. In presence of such pores losses in POM were 3–15 times higher than in their absence. Moreover, we demonstrated the presence of a feed-forward relationship between soil C decomposition and pore connections that enhance it. Since soil hydrology and soil pores are likely to be affected by future climate changes, our findings indicate that not-accounting for the influence of soil pores can add another sizable source of uncertainty to estimates of future soil C losses. PMID:26541265

  8. A novel method for soil aggregate stability measurement by laser granulometry with sonication

    NASA Astrophysics Data System (ADS)

    Rawlins, B. G.; Lark, R. M.; Wragg, J.

    2012-04-01

    Regulatory authorities need to establish rapid, cost-effective methods to measure soil physical indicators - such as aggregate stability - which can be applied to large numbers of soil samples to detect changes of soil quality through monitoring. Limitations of sieve-based methods to measure the stability of soil macro-aggregates include: i) the mass of stable aggregates is measured, only for a few, discrete sieve/size fractions, ii) no account is taken of the fundamental particle size distribution of the sub-sampled material, and iii) they are labour intensive. These limitations could be overcome by measurements with a Laser Granulometer (LG) instrument, but this technology has not been widely applied to the quantification of aggregate stability of soils. We present a novel method to quantify macro-aggregate (1-2 mm) stability. We measure the difference between the mean weight diameter (MWD; μm) of aggregates that are stable in circulating water of low ionic strength, and the MWD of the fundamental particles of the soil to which these aggregates are reduced by sonication. The suspension is circulated rapidly through a LG analytical cell from a connected vessel for ten seconds; during this period hydrodynamic forces associated with the circulating water lead to the destruction of unstable aggregates. The MWD of stable aggregates is then measured by LG. In the next step, the aggregates - which are kept in the vessel at a minimal water circulation speed - are subject to sonication (18W for ten minutes) so the vast majority of the sample is broken down into its fundamental particles. The suspension is then recirculated rapidly through the LG and the MWD measured again. We refer to the difference between these two measurements as disaggregation reduction (DR) - the reduction in MWD on disaggregation by sonication. Soil types with more stable aggregates have larger values of DR. The stable aggregates - which are resistant to both slaking and mechanical breakdown by the

  9. Interaction between soil mineralogy and the application of crop residues on aggregate stability and hydraulic conductivity of the soil

    NASA Astrophysics Data System (ADS)

    Lado, M.; Kiptoon, R.; Bar-Tal, A.; Wakindiki, I. I. C.; Ben-Hur, M.

    2012-04-01

    One of the main goals of modern agriculture is to achieve sustainability by maintaining crop productivity while avoiding soil degradation. Intensive cultivation could lead to a reduction in soil organic matter that could affect the structure stability and hydraulic conductivity of the soil. Moreover, crops extract nutrients from the soil that are taken away from the field when harvested, and as a consequence, the addition of fertilizers to the soil is necessary to maintain crop productivity. One way to deal with these problems is to incorporate crop residues into the soil after harvest. Crop residues are a source of organic matter that could improve soil physical properties, such as aggregate stability and soil hydraulic conductivity. However, this effect could vary according to other soil properties, such as clay content, clay mineralogy, and the presence of other cementing materials in the soil (mainly carbonates and aluminum and iron oxides). In the present work, the interaction between the addition of chickpea crop residues to the soil and clay mineralogy on aggregate stability and saturated hydraulic conductivity were studied. Chickpea plant residues were added at a rate of 0.5% (w/w) to smectitic, kaolinitic, illitic and non-phyllosilicate soils from different regions. The soils without (control) and with chickpea residues were incubated for 0, 3, 7 and 30 days, and the saturated hydraulic conductivity of the soils was measured in columns after each incubation time. The response of hydraulic conductivity to the addition of residues and incubation time was different in the soils with various mineralogies, although in general, the addition of chickpea residues increased the saturated hydraulic conductivity as compared with the control soils. This positive effect of crop residues on hydraulic conductivity was mainly a result of improved aggregate stability and resistance to slaking during wetting.

  10. Effects of soil aggregates on debris-flow mobilization: Results from ring-shear experiments

    USGS Publications Warehouse

    Iverson, Neal R.; Mann, Janet E.; Iverson, Richard M.

    2010-01-01

    Rates and styles of landslide motion are sensitive to pore-water pressure changes caused by changes in soil porosity accompanying shear deformation. Soil may either contract or dilate upon shearing, depending upon whether its initial porosity is greater or less, respectively, than a critical-state porosity attained after sufficiently high strain. We observed complications in this behavior, however, during rate-controlled (0.02 m s−1) ring-shear experiments conducted on naturally aggregated dense loamy sand at low confining stresses (10.6 and 40 kPa). The aggregated soil first dilated and then contracted to porosities less than initial values, whereas the same soil with its aggregates destroyed monotonically dilated. We infer that aggregates persisted initially during shear and caused dilation before their eventual breakdown enabled net contraction. An implication of this contraction, demonstrated in experiments in which initial soil porosity was varied, is that the value of porosity distinguishing initially contractive from dilative behavior can be significantly larger than the critical-state porosity, which develops only after disaggregation ceases at high strains. In addition, post-dilative contraction may produce excess pore pressures, thereby reducing frictional strength and facilitating debris-flow mobilization. We infer that results of triaxial tests, which generally produce strains at least a factor of ∼ 4 smaller than those we observed at the inception of post-dilative contraction, do not allow soil contraction to be ruled out as a mechanism for debris-flow mobilization in dense soils containing aggregates.

  11. Differences in SOM decomposition and temperature sensitivity among soil aggregate size classes in a temperate grasslands.

    PubMed

    Wang, Qing; Wang, Dan; Wen, Xuefa; Yu, Guirui; He, Nianpeng; Wang, Rongfu

    2015-01-01

    The principle of enzyme kinetics suggests that the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is inversely related to organic carbon (C) quality, i.e., the C quality-temperature (CQT) hypothesis. We tested this hypothesis by performing laboratory incubation experiments with bulk soil, macroaggregates (MA, 250-2000 μm), microaggregates (MI, 53-250 μm), and mineral fractions (MF, <53 μm) collected from an Inner Mongolian temperate grassland. The results showed that temperature and aggregate size significantly affected on SOM decomposition, with notable interactive effects (P<0.0001). For 2 weeks, the decomposition rates of bulk soil and soil aggregates increased with increasing incubation temperature in the following order: MA>MF>bulk soil >MI(P <0.05). The Q10 values were highest for MA, followed (in decreasing order) by bulk soil, MF, and MI. Similarly, the activation energies (Ea) for MA, bulk soil, MF, and MI were 48.47, 33.26, 27.01, and 23.18 KJ mol-1, respectively. The observed significant negative correlations between Q10 and C quality index in bulk soil and soil aggregates (P<0.05) suggested that the CQT hypothesis is applicable to soil aggregates. Cumulative C emission differed significantly among aggregate size classes (P <0.0001), with the largest values occurring in MA (1101 μg g-1), followed by MF (976 μg g-1) and MI (879 μg g-1). These findings suggest that feedback from SOM decomposition in response to changing temperature is closely associated withsoil aggregation and highlights the complex responses of ecosystem C budgets to future warming scenarios.

  12. Monitoring soil aggregates dynamics at a plot scale using multitemporal image texture and colour analysis

    NASA Astrophysics Data System (ADS)

    Ymeti, Irena; van der Werff, Harald; van der Meer, Freek; Jetten, Victor

    2016-10-01

    Monitoring of soil aggregate breakdown remains, even at the micro-plot scale, a challenge. Remote sensing has shown its potential to assess many different soil properties and is a fast and non-destructive method to investigate soil susceptibility to water erosion. We designed an outdoor experiment to monitor soil aggregates breakdown under natural rainfall at a micro-plot scale using a regular camera. Five soils susceptible to detachment (silty loam with various organic matter content, loam and sandy loam) were photographed once per day. We collected images and rainfall data from November 2014 until February 2015. Considering that the soil surface roughness causes shadow cast, the blue/red band ratio is used to observe the soil aggregates changes. In addition, a Gray Level Co-occurrence Matrix (GLCM) is used to extract the image texture entropy which reflects the process of soil aggregates breakdown. In our research the entropy calculated at 135 degrees along the direction of shadows gives best results. Our results show that both entropy and shadow index follow the wetting and drying cycles with a decrease due to a rain event. This decrease is small due to low rainfall intensity (< 2.5 mmh-1) for the entire period that the experiment ran. However, the biggest rain event of 20 mmday-1 resulted in a decrease in entropy, meaning that sufficient rainfall energy was present to trigger the soil aggregates break down. This research concludes that both entropy and shadow index obtained with a regular camera enable the monitoring of soil aggregate breakdown at a high spatial resolution.

  13. Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China.

    PubMed

    Fang, Xiang-Min; Chen, Fu-Sheng; Wan, Song-Ze; Yang, Qing-Pei; Shi, Jian-Min

    2015-01-01

    The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0-15 cm) and deep soil (30-45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years.

  14. Beneath aggregate stability - quantifying thermodynamic properties that drive soil structure dynamics

    NASA Astrophysics Data System (ADS)

    Hallett, Paul; Ogden, Mike; Karim, Kamal; Schmidt, Sonja; Yoshida, Shuichiro

    2014-05-01

    Soil aggregates are a figment of your energy input and initial boundary conditions, so the basic thermodynamics that drive soil structure formation are needed to understand soil structure dynamics. Using approaches from engineering and materials science, it is possible quantify basic thermodynamic properties, but at present tests are generally limited to highly simplified, often remoulded, soil structures. Although this presents limitations, the understanding of underlying processes driving soil structure dynamics is poor, which could be argued is due to the enormity of the challenge of such an incredibly complex system. Other areas of soil science, particularly soil water physics, relied on simplified structures to develop theories that can now be applied to more complex pore structures. We argue that a similar approach needs to gain prominence in the study of soil aggregates. An overview will be provided of approaches adapted from other disciplines to quantify particle bonding, fracture resistance, rheology and capillary cohesion of soil that drive its aggregation and structure dynamics. All of the tests are limited as they require simplified soil structures, ranging from repacked soils to flat surfaces coated with mineral particles. A brief summary of the different approaches will demonstrate the benefits of collecting basic physical data relevant to soil structure dynamics, including examples where they are vital components of models. The soil treatments we have tested with these engineering and materials science approaches include field soils from a range of management practices with differing clay and organic matters contents, amendment and incubation of soils with a range of microorganisms and substrates in the laboratory, model clay-sand mixes and planar mineral surfaces with different topologies. In addition to advocating the wider adoption of these approaches, we will discuss limitations and hope to stimulate discussion on how approaches could be improved

  15. Effects of Polyacrylamide and Organic Matter on Microbes associated to Soil Aggregation of Norfolk Loamy Sand

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Polyacrylamide (PAM, anionic formulation of molecular size 12 MDa and 35% charge density) has been reported to increase aggregation and improve soil physical properties in United States southeastern Coastal Plain loamy sand soils, but nothing is known about the effects of PAM on microbes associated ...

  16. Vegetation effects on soil organic matter chemistry of aggregate fractions in a Hawaiian forest

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We examined chemical changes from live plant tissue to soil organic matter (SOM) to determine the persistence of individual plant compounds into soil aggregate fractions. We characterized the tissue chemistry of a slow- (Dicranopteris linearis) and fast-decomposing species (Cheirodendron trigynum) a...

  17. Development of Arsenic and Iron Biogeochemical Gradients upon Anaerobiosis at Soil Aggregate Scale

    NASA Astrophysics Data System (ADS)

    Masue-Slowey, Y.; Pallud, C.; Bedore, P.; Tufano, K.; Fendorf, S.

    2008-12-01

    In aerated soils, As release is limited due to the strong interaction between As(V) and soil minerals. However, under anaerobic conditions, As desorption is stimulated by As(V) reduction to As(III) and reductive dissolution/transformation of Fe (hydr)oxides, common hosts of As. The effect of As(V) and Fe(III) reduction on As release has been extensively studied in laboratory batch and column systems; correlation of apparent Fe and As reduction, with concomitant release to pore water, has also been noted under field conditions. What remains unresolved is the coupling of biogeochemical and physical processes that ultimately control As transport within structured media such as soils. Soils are heterogeneous porous media that are comprised of individual aggregates having pores that are dominated by diffusive (aggregate interiors) or advective (aggregate exteriors) transport. As a consequence of physical and chemical differences in the interior and the exterior of aggregates, As(III,V) and Fe(II,III) chemical gradients develop. Here, we examine As release from constructed aggregates exposed to fluctuating redox conditions. Artificial aggregates were made with As(V) adsorbed ferrihydrite-coated sand homogeneously inoculated with Shewanella sp. ANA-3 (model As(V) and Fe(III) reducer) and then fused using an agarose binder into spheres. Aggregates were placed in a flow reactor and saturated flow of aerobic or anaerobic artificial groundwater media was initiated. Redox fluctuated in select systems to examine changes in chemical gradient under changing aeration status. Our results show that within aerated solutions, oxidized aggregate exteriors provide a "gprotective barrier"h against As release despite anoxia within diffusively constrained aggregate interiors. During a transition to anaerobic conditions in advective zones, however, As is released and transport is promoted. Our study illustrates the microscale variation in biogeoechemical processes within soils and the

  18. Distribution of Two C Cycle Enzymes in Soil Aggregates of a Prairie Chronosequence

    SciTech Connect

    Fansler, Sarah J.; Smith, Jeffery L.; Bolton, Harvey; Bailey, Vanessa L.

    2005-11-01

    Recently attention has focused on the potential of using soil as a sink for atmospheric CO2. The objective of this study was to use soil enzymes and classical methods of soil aggregate fractionation to explore the relationship between microbial community function and soil structure of a tallgrass prairie chronosequence. The soils within the chronosequence were: (1) remnant native prairie, (2) agricultural soil, and (3, 4) tallgrass prairies restored from agriculture in 1979 and 1993. β-glucosidase (E.C. 3.2.1.21) and N-acetyl-β-glucosaminidase (NAGase, EC 3.2.1.30) assays were conducted on four different aggregate size fractions (>2 mm, 1 -2 mm, 250µm-1 mm, and 2 - 250 µm) from each soil. Specific activities for both enzymes (µg PNP g-1 soil h-1) were greatest in the microaggregate (2 µm -250 µm) fractions across the chronosequence; however, this size fraction makes up only a small proportion of the whole soil. Therefore, it is the larger macroaggregate-derived enzyme activities that have the greatest impact on the activity of the whole soil. Analyzing both enzymes and the physical structure, a reversion from an agricultural soil through the restored to more like the prairie soil, was not detected. It appears that the function of these microbial community systems in the native tallgrass prairie and agricultural soils of the chronosequence are in equilibria while the lands restored to tallgrass prairie are in an ongoing state of recovery.

  19. Adsorption behaviors of fungicide-derived copper onto various size fractions of aggregates from orchard soil.

    PubMed

    Wang, Quan-Ying; Hu, Bo; Yu, Hong-Wen

    2016-12-01

    Although the gradual accumulations of Cu in orchard soils due to the application of Cu-based fungicides have been widely reported, limited information is available about the retention characteristics of fungicide-derived Cu in soil, especially in various size soil aggregates. This study described the adsorption characteristics of Cu from commonly used fungicide, Bordeaux mixture (CuSO4 + Ca(OH)2), onto various aggregate fractions (2000-1000, 1000-500, 500-250, 250-106, and <106 μm) of orchard soil. The Cu(NO3)2 was selected as a comparison. Two different types of adsorption experiments were conducted as follows: variable pH and variable Cu concentration experiments. The adsorption processes of Bordeaux mixture and Cu(NO3)2 onto the studied soil samples followed well with the Freundlich isotherm, and the adsorption isotherms were the S shaped. The adsorption amounts of Cu from different Cu compounds differed, and Bordeaux mixture can result in more Cu retention in soil than Cu(NO3)2. The adsorption ability of different size soil aggregates varied, and it was mainly governed by soil properties. The findings of this study suggested that both the chemical compositions of Cu compounds and the soil physical structure should be taken into account when performing soil Cu retention experiments with fungicide-derived Cu.

  20. Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands.

    PubMed

    Wen, Ding; He, Nianpeng; Zhang, Jinjing

    2016-01-01

    Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250-2000 μm], microaggregates [53-250 μm], and mineral fraction [< 53 μm]) at 0-20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China.

  1. Enzymatic biofilm digestion in soil aggregates facilitates the release of particulate organic matter by sonication

    NASA Astrophysics Data System (ADS)

    Büks, Frederick; Kaupenjohann, Martin

    2016-10-01

    The stability of soil aggregates against shearing and compressive forces as well as water-caused dispersion is an integral marker of soil quality. High stability results in less compaction and erosion and has been linked to enhanced water retention, dynamic water transport and aeration regimes, increased rooting depth, and protection of soil organic matter (SOM) against microbial degradation. In turn, particulate organic matter is supposed to support soil aggregate stabilization. For decades the importance of biofilm extracellular polymeric substances (EPSs) regarding particulate organic matter (POM) occlusion and aggregate stability has been canonical because of its distribution, geometric structure and ability to link primary particles. However, experimental proof is still missing. This lack is mainly due to methodological reasons. Thus, the objective of this work is to develop a method of enzymatic biofilm detachment for studying the effects of EPSs on POM occlusion. The method combines an enzymatic pre-treatment with different activities of α-glucosidase, β-galactosidase, DNAse and lipase with a subsequent sequential ultrasonic treatment for disaggregation and density fractionation of soils. POM releases of treated samples were compared to an enzyme-free control. To test the efficacy of biofilm detachment the ratio of bacterial DNA from suspended cells and the remaining biofilm after enzymatic treatment were measured by quantitative real-time PCR. Although the enzyme treatment was not sufficient for total biofilm removal, our results indicate that EPSs may attach POM within soil aggregates. The tendency to additional POM release with increased application of enzymes was attributed to a slight loss in aggregate stability. This suggests that an effect of agricultural practices on soil microbial populations could influence POM occlusion/aggregate stability and thereby carbon cycle/soil quality.

  2. [Effects of straw mulching on the soil aggregates in dryland wheat field under no-tillage].

    PubMed

    Wang, Hai-Xia; Sun, Hong-Xia; Han, Qing-Fang; Wang, Min; Zhang, Rui; Jia, Zhi-Kuan; Nie, Jun-Feng; Liu, Ting

    2012-04-01

    A field experiment was conducted to study the effects of full period and growth period straw mulching with an amount of 3000, 6000, and 9000 kg x hm(-2) on the soil aggregates in a no-tillage dryland wheat field in Weibei Loess Pleateau of Shaanxi Province, taking no full period straw mulching as the control. In the 0-40 cm soil layer, the content of > 5 mm aggregates increased with depth, while that of <5 mm aggregates was in adverse. Under straw mulching, the total contents of > 0.25 mm mechanical stable aggregates (DR0.25) and of > 0.25 mm water stable aggregates (WR0.25) were significantly higher than the control, with an increase of 13.0%-26.4% and 18.6%-45.6%, respectively and the largest increment in the treatment 6000 kg x hm(-2) of straw mulching. Straw mulching increased the soil organic matter content, and the latter had a significant positive correlation with the WR0.25 content. All the straw mulching treatments decreased the soil unstable aggregate index (E(LT)) which was the lowest in treatment 6000 kg x hm(-2) of straw mulching. This study showed that straw mulching could increase the >0.25 mm aggregates and organic matter contents in 0-40 cm soil layer and improve the soil structural stability, and mulching with an amount of 6000 kg x hm(-2) had the best effect, being a reasonable straw mulching mode to be applied in the agricultural production in Weibei Loess Plateau.

  3. Effects of biodegradable plastics on the predominant culturable bacteria associated with soil aggregate formation and stability after 9 months of incubation in natural soil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An in vitro study of the effects of biodegradable plastics on the predominant soil aggregating bacteria associated to soil aggregate formation and stability after 9 months of incubation in soil. Caesar-TonThat TC, Fukui R*, Caesar AJ., Lartey, RT, and Gaskin, JF. USDA-Agricultural Research Service, ...

  4. Soil aggregate stability as an indicator for eco-engineering effectiveness?

    NASA Astrophysics Data System (ADS)

    Graf, Frank

    2015-04-01

    Eco-engineering aims at stabilising soil and slopes by applying technical and biological measures. Engineering structures are commonly well defined, immediately usable and operative, and their stability effects quantifiable and verifiable. Differently, the use of plants requires more restrictive boundary conditions and the protection potential is rarely easily calculable and develop-ing as a function of growth rate. Although the use of vegetation is widely appreciated and their stabilising effect recognised, there is an increasing demand on sound facts on its efficiency, in particular, in relation to time. Conclusively, a certain necessity has been recognised to monitor, assess and quantify the effectiveness of ecological restora-tion measures in order to facilitate the transfer of technology and knowledge. Recent theoretical models emphasize the im-portance of taking an integrated monitoring approach that considers multiple variables. However, limited financial and time resources often prevent such comprehensive assessments. A solution to this problem may be to use integrated indicators that reflect multiple aspects and, therefore, allow extensive information on ecosystem status to be gathered in a relatively short time. Among various other indicators, such as fractal dimension of soil particle size distribution or microbiological parameters, soil aggregate stability seems the most appropriate indicator with regard to protecting slopes from superficial soil failure as it is critical to both plant growth and soil structure. Soil aggregation processes play a crucial role in re-establishing soil structure and function and, conclusively, for successful and sustainable re-colonisation. Whereas the key role of soil aggregate stability in ecosystem functioning is well known concerning water, gas, and nutrient fluxes, only limited information is available with regard to soil mechanical and geotechnical aspects. Correspondingly, in the last couple of years several studies

  5. Cover cropping impacts on arbuscular mycorrhizal fungi and soil aggregation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cover crops are a management tool which can extend the period of time that a living plant is growing and conducting photosynthesis. This is critical for soil health, because most of the soil organisms, particularly the arbuscular mycorrhizal fungi, are limited by carbon. Research, on-farm, and demon...

  6. Soil aggregates in a collapsed chestnut grove and in an instable vineyard in Tuscany

    NASA Astrophysics Data System (ADS)

    Guastini, Enrico; Dani, Andrea

    2014-05-01

    Just like in agriculture the presence of stable macroaggregates is simptom of soil fecundity, in forestry the presence of stabe aggregates is index of stability for both the soil and the living communities settling there. Such formations, ascribable to organic matter and humic compound degree, can be present in better measure in a collapsed and recolonized soil than in non fallen area grown with the same species for long time. The mean stability in aggregates comes out to be very lower in farmed soil, yet foreseen by Tisdall and Oades (2006) wich wrote that farming generates a decline in the organic content of soil. The higher instability shown in the deepest soil, where the biotic contribution is lesser, and the higher infiltration found in superficial layers are in line with the empiric verification that the slip plane in shallow landslides doesn't intersect rhizosphere, but lays under it; the fragility zone is located where the organic matter degree is lower, both in humus and root and fungi exudates, or organism parts or remains. In other words, not only deep roots could sometimes anchor the shallow soil to the bedrock, but they can also improve the strenght characteristics of soil in presence of water. In soil with aggregates, moreover, seems to recognise an improvement in the shear strenght angle, accordingly with the results obtained by Graf et al. (2009) with triaxial tests on rooted soil samples. Roughly, the angle increase by 1 degree for every 5-7% in stable aggregates on the sample weigth, validating the better stability of a slope with a stable and mature community.

  7. Bacterial diversity of soil aggregates of different sizes in various land use conditions

    NASA Astrophysics Data System (ADS)

    Ivanova, Ekaterina; Azida, Thakahova; Olga, Kutovaya

    2014-05-01

    The patterns of soil microbiome structure may be a universal and very sensitive indicator of soil quality (soil "health") used for optimization and biologization of agricultural systems. The understanding of how microbial diversity influenses, and is influenced by, the environment can only be attained by analyses at scales relevant to those at which processes influencing microbial diversity actually operate. The basic structural and functional unit of the soil is a soil aggregate, which is actually a microcosm of the associative co-existing groups of microorganisms that form characteristic ecological food chains. It is known that many important microbial processes occur in spatially segregated microenvironments in soil leading to a microscale biogeography. The Metagenomic library of typical chernozem in conditions of different land use systems was created. Total genomic DNA was extracted from 0.5 g of the frozen soil after mechanical destruction. Sample preparation and sequencing was performed on a GS Junior ("Roche»", Switzerland) according to manufacturer's recommendations, using the universal primers to the variable regions V4 gene 16S - rRNA - F515 (GTGCCAGCMGCCGCGGTAA) and R806 (GGACT-ACVSGGGTATCTAAT). It is shown that the system of land use is a stronger determinant of the taxonomic composition of the soil microbial community, rather than the size of the structural units. In soil samples from different land use systems the presence of accessory components was revealed. They may be used as indicators of processes of soil recovery, soil degradation or soil exhaustion processes occuring in the agroecosystems. The comparative analysis of microbial communities of chernozem aggregates investigated demonstrates the statistically valuable differences in the amount of bacterial phyla and Archean domain content as well as the species richness in aggregates of various size fractions. The occurrence of specific components in the taxonomic structure of micro-and macro-aggregates

  8. Aggregation-induced reversal of transport distances of soil organic matter: are our balances correct?

    NASA Astrophysics Data System (ADS)

    Hu, Yaxian; Kuhn, Nikolaus

    2014-05-01

    The effect of soil erosion on global carbon cycling, especially as a source or sink of green-house gases (GHGs), is the subject of intense debate. The controversy arises mostly from the lack of information on the fate of eroded soil organic carbon (SOC) as it moves from the site of erosion to the site of longer-term deposition. This requires improved understanding the transport distances of eroded SOC, which is principally related to the settling velocities of sediment fractions that carry the eroded SOC. For aggregated soils, settling velocities are affected by their actual aggregate size rather than the mineral grain size distribution. Aggregate stability is, in turn, strongly influenced by soil organic matter. This study aims at identifying the effect of aggregation on the transport distances of eroded SOC and its susceptibility to mineralization after transport and deposition. A rainfall simulation was carried out on a silty loam soil. The eroded sediments were fractionated by a settling tube apparatus into six different size classes according to their settling velocities and likely transport distances. Weight, SOC concentration and instantaneous respiration rates of the fractions of the six classes were measured. Our results show that: 1) 41% of the eroded SOC was transported with coarse aggregates that would be likely re-distributed across landscapes; 2) erosion was prone to accelerate the mineralization of eroded organic carbon immediately after erosion, compared to undisturbed aggregates; 3) erosion might make a higher contribution to atmospheric CO2 than the estimation made without considering the effects of aggregation and extra SOC mineralization during transport.

  9. Aggregates dynamic in contrasting soils with different fertilizations and role of humic carbon as binding agent

    NASA Astrophysics Data System (ADS)

    Lugato, E.; Simonetti, G.; Nardi, S.; Berti, A.; Giardini, L.; Morari, F.

    2009-04-01

    In the last years aggregates fractionation has become a very common approach to study the close linkage between aggregate formation and SOM turnover. According to the hierarchical theory microaggregates are assumed to be stabilized by persisting binding agents whereas macroaggregates by transient or temporary organic materials. Humic substances, considered to be recalcitrant, should likely act as persistent binding agents but their role, also because of their heterogeneity and discussed origin, is still unclear. In a long-term experiment established in the early 1960s in north-eastern Italy, we wet-sieved large macroaggregates to separate three aggregate sizes (2000-250 mm, 250-53 mm and <53 mm) in contrasting soil (clay, sandy and peaty), fertilized with manure and mineral fertilizers. We analysed organic (OC) and humic (HC) carbon of each aggregate fraction, also investigating the molecular weight of the humic substances extracted (>60 KDa,60-30 KDa, <30 KDa). The aim were to evaluate the effect of the different fertilisations type in the aggregate and organic matter distribution and investigate the composition and role of HC as binding agent. The results evidenced that the addition of manure significantly increased the proportion of macroaggregates respect to the mineral fertilization but only in the clay soil. Aggregate hierarchy, according to which SOC concentration increase with increasing aggregates size, was generally supported by our data. The HC values followed the same pattern of the OC, with a very high correlation between these parameters (r >0.95). The HC/OC ratio, ranging narrowly among the aggregates fractions, indicated no hierarchical role of HC as persisting binding agents. However HC extracted in the silt-clay fraction showed higher proportion of low molecular weight fraction in peaty and clay soil, respect to HC of larger aggregates.

  10. Soil aggregate stabilization and carbon sequestration: Feedbacks through organomineral associations

    SciTech Connect

    Jastrow, J.D.; Miller, R.M.

    1996-12-31

    Primary production (specifically, the rate and quality of C transfer below ground) and soil microbial activity (specifically, the rates of C transformation and decay) are recognized as the overall biological processes governing soil organic C (SOC) dynamics. These two processes and, hence, SOC cycling and storage are controlled by complex underlying biotic and abiotic interactions and feedbacks, most of which can be tied in one way or another to the influences of the five state factors related to soil formation, and many of which are sensitive to management practices. Overall, C input rates and quality are largely dependent on climate (especially temperature and precipitation), vegetation type and landscape, soil type, and management practices. Decomposition processes and turnover rates, however, are greatly influenced by climate, the type and quality of organic matter (e.g., N content and the ratios of C:N and lignin:N), chemical or physicochemical associations of organic matter (OM) with soil mineral components, and the location of OM within the soil.

  11. Bacterial exopolysaccharide and biofilm formation stimulate chickpea growth and soil aggregation under salt stress

    PubMed Central

    Qurashi, Aisha Waheed; Sabri, Anjum Nasim

    2012-01-01

    To compensate for stress imposed by salinity, biofilm formation and exopolysaccharide production are significant strategies of salt tolerant bacteria to assist metabolism. We hypothesized that two previously isolated salt-tolerant strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) have an ability to improve plant growth, These strains can form biofilm and accumulate exopolysacharides at increasing salt stress. These results showed that bacteria might be involved in developing microbial communities under salt stress and helpful in colonizing of bacterial strains to plant roots and soil particles. Eventually, it can add to the plant growth and soil structure. We investigated the comparative effect of exopolysacharide and biofilm formation in two bacterial strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) in response to varying salt stress. We found that biofilm formation and exopolysaccharide accumulation increased at higher salinity. To check the effect of bacterial inoculation on the plant (Cicer arietinum Var. CM-98) growth and soil aggregation, pot experiment was conducted by growing seedlings under salt stress. Inoculation of both strains increased plant growth at elevated salt stress. Weight of soil aggregates attached with roots and present in soil were added at higher salt concentrations compared to untreated controls. Soil aggregation was higher at plant roots under salinity. These results suggest the feasibility of using above strains in improving plant growth and soil fertility under salinity. PMID:24031943

  12. [Characteristics of soil organic carbon and enzyme activities in soil aggregates under different vegetation zones on the Loess Plateau].

    PubMed

    Li, Xin; Ma, Rui-ping; An, Shao-shan; Zeng, Quan-chao; Li, Ya-yun

    2015-08-01

    In order to explore the distribution characteristics of organic carbon of different forms and the active enzymes in soil aggregates with different particle sizes, soil samples were chosen from forest zone, forest-grass zone and grass zone in the Yanhe watershed of Loess Plateau to study the content of organic carbon, easily oxidized carbon, and humus carbon, and the activities of cellulase, β-D-glucosidase, sucrose, urease and peroxidase, as well as the relations between the soil aggregates carbon and its components with the active soil enzymes were also analyzed. It was showed that the content of organic carbon and its components were in order of forest zone > grass zone > forest-grass zone, and the contents of three forms of organic carbon were the highest in the diameter group of 0.25-2 mm. The content of organic carbon and its components, as well as the activities of soil enzymes were higher in the soil layer of 0-10 cm than those in the 10-20 cm soil layer of different vegetation zones. The activities of cellulase, β-D-glucosidase, sucrose and urease were in order of forest zone > grass zone > forest-grass zone. The peroxidase activity was in order of forest zone > forest-grass zone > grass zone. The activities of various soil enzymes increased with the decreasing soil particle diameter in the three vegetation zones. The activities of cellulose, peroxidase, sucrose and urease had significant positive correlations with the contents of various forms of organic carbon in the soil aggregates.

  13. Monitoring aggregate disintegration with laser diffraction: A tool for studying soils as sediments

    NASA Astrophysics Data System (ADS)

    Mason, Joseph; Kasmerchak, Chase; Liang, Mengyu

    2016-04-01

    One of the more important characteristics of soil that becomes hillslope, fluvial, or aeolian sediment is the presences of aggregates, which disintegrate at varying rates and to varying degrees during transport. Laser diffraction particle size analyzers allow monitoring of aggregate disintegration as a sample of soil or sediment suspended in water is circulated continuously through the measurement cell (Bieganowski et al., 2010, Clay Minerals 45-23-34; Mason et al., Catena 87:107-118). Mason et al. (2011) applied this approach to aeolian sedimentary aggregates (e.g. clay pellets eroded from dry lakebeds), immersing dry samples in DI water and circulating them through a Malvern Mastersizer 2000 particle size analyzer for three hours while repeated size distribution (SD) measurements were made. A final measurement was made after sonication and treatment with Na-metaphosphate. In that study, most samples approached a steady SD within three hours, which included both primary mineral grains and persistent aggregates. The disintegration process could be modeled with a first-order rate law representing the disintegration of a single population of aggregates. A wide range of model parameters were observed among the samples studied, and it was suggested that they could be useful in predicting the behavior of these aggregates, under rainfall impact and during slopewash or fluvial transport. Addition of Ca++ to the suspension altered aggregate behavior in some but not all cases. We applied the same method to dry, unground material from upper horizons of soils sampled along a bioclimatic gradient in northern Minnesota, USA, all formed in lithologically similar glacigenic sediment. These ranged from Alfisols (Luvisols) formed under forest since the last deglaciation, to Alfisols under forest that more recently replaced grassland, and Mollisols (Chernozems) that formed entirely under grassland vegetation. Few of these soil samples approached a steady SD within three hours, and

  14. [Impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain].

    PubMed

    Li, Jian-Lin; Jiang, Chang-Sheng; Hao, Qing-Ju

    2014-12-01

    Soil aggregates have the important effect on soil fertility, soil quality and the sustainable utilization of soil, and they are the mass bases of water and fertilizer retention ability of soil and the supply or release of soil nutrients. In this paper, in order to study the impact of land use type on stability and organic carbon of soil aggregates in Jinyun Mountain, we separated four land use types of soil, which are woodland, abandoned land, orchard and sloping farmland by wet sieving method, then we got the proportion of large macroaggregates (> 2 mm), small macroaggregates (0.25-2 mm), microaggregates (53 μm-0.25 mm) and silt + clay (< 53 μm) and measured the content of organic carbon in each aggregate fraction in soil depth of 0-60 cm and calculated the total content of organic carbon of all aggregates fraction in each soil. The results showed that reclamation of woodland will lead to fragmentation of macroaggregates and deterioration of soil structure, and the proportion of macroaggrgates (> 0.25 mm) were 44.62% and 32.28% respectively in the soils of orchard and sloping farmland, which reduced 38.58% (P < 0.05) and 91.52% (P < 0.05) compared with woodland. While after changing the sloping farmland to abandoned land, which lead to the conversion of soil fraction from silt + clay to large macroaggregates and small macroaggregates, so it will improve the soil structure. MWD (mean weight diameter) and GMD (geometric mean diameter) are important indicators of evaluating the stability of soil aggregates. We found the MWD and GWD in soil depth of 0-60 cm in orchards and sloping farmland were significantly lower than those in woodland (P < 0.05), while after changing the sloping farmland to abandoned land, the MWD and GWD increased significantly (P < 0.05), which indicated that reclamation of woodland will lead to the decrease of stability of soil aggregates, and they will be separated more easily by water. However, after changing the sloping farmland to abandoned

  15. Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces.

    PubMed

    Wei, Yujie; Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

    2016-01-01

    The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate

  16. Variation of Soil Aggregation along the Weathering Gradient: Comparison of Grain Size Distribution under Different Disruptive Forces

    PubMed Central

    Wu, Xinliang; Xia, Jinwen; Shen, Xue; Cai, Chongfa

    2016-01-01

    The formation and stabilization of soil aggregates play a key role in soil functions. To date, few studies have been performed on the variation of soil aggregation with increasing soil weathering degree. Here, soil aggregation and its influencing factors along the weathering gradient were investigated. Six typical zonal soils (derived from similar parent materials) were sampled from temperate to tropical regions. Grain size distribution (GSD) in aggregate fragmentation with increasing disruptive forces (air-dried, water dispersion and chemical dispersion) was determined by laser diffraction particle size analyzer. Different forms of sesquioxides were determined by selective chemical extraction and their contributions to soil aggregation were identified by multiple stepwise regression analysis. The high variability of sesquioxides in different forms appeared with increasing free oxide content (Fed and Ald) from the temperate to tropical soils. The transformation of GSD peak to small size varied with increasing disruptive forces (p<0.05). Although in different weathering degrees, zonal soils showed a similar fragmentation process. Aggregate water stability generally increased with increasing soil weathering (p<0.01), with higher stability in eluvium (A) horizon than in illuvium (B) horizon (p<0.01). Crystalline oxides and amorphous iron oxides (Feo), especially (Fed-Feo) contributed to the formation of air-dried macroaggregates and their stability against slaking (R2 = 55%, p<0.01), while fine particles (<50μm) and Feo (excluding the complex form Fep) played a positive role in the formation of water stable aggregates (R2 = 93%, p<0.01). Additionally, water stable aggregates (including stability, size distribution and specific surface area) were closely related with pH, organic matter, cation exchange capacity (CEC), bulk density (BD), and free oxides (including various forms) (p<0.05). The overall results indicate that soil aggregation conforms to aggregate

  17. The influence of organic amendments on soil aggregate stability from semiarid sites

    NASA Astrophysics Data System (ADS)

    Hueso Gonzalez, Paloma; Francisco Martinez Murillo, Juan; Damian Ruiz Sinoga, Jose

    2016-04-01

    Restoring the native vegetation is the most effective way to regenerate soil health. Under these conditions, vegetation cover in areas having degraded soils may be better sustained if the soil is amended with an external source of organic matter. The addition of organic materials to soils also increases infiltration rates and reduces erosion rates; these factors contribute to an available water increment and a successful and sustainable land management. The goal of this study was to analyze the effect of various organic amendments on the aggregate stability of soils in afforested plots. An experimental paired-plot layout was established in southern of Spain (homogeneous slope gradient: 7.5%; aspect: N170). Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. The vegetation was planted in a grid pattern with 0.5 m between plants in each plot. During the afforestation process the soil was tilled to 25 cm depth from the surface. Soil from the afforested plots was sampled in: i) 6 months post-afforestation; ii) 12 months post-afforestation; iii) 18 months post-afforestation; and iv) 24 months post-afforestation. The sampling strategy for each plot involved collection of 4 disturbed soil samples taken from the surface (0-10 cm depth). The stability of aggregates was measured by wet-sieving. Regarding to soil aggregate stability, the percentage of stable aggregates has increased slightly in all the treatments in relation to control. Specifically, the differences were recorded in the fraction of macroaggregates (≥ 0.250 mm). The largest increases have been associated with straw mulch, pinus mulch and sludge. Similar results have been registered for the soil organic carbon content

  18. Nature and origin of the resistant carbonaceous polymorphs involved the fossilization of biogenic soil-aggregates

    NASA Astrophysics Data System (ADS)

    Courty, M.-A.

    2012-04-01

    The rare occurrence of organic-rich surface horizons in soil archives is widely accepted to resulting from their rapid degradation. We intend here to further elucidate how pedogenic signatures that initially formed at the soil surface could resist over long timescales to burial processes. We focus on the structural evolution of the biogenic soil aggregates that is controlled by the complex interaction of bioturbation, root colonization, microbial decomposition, chemical weathering and physical processes. The nature and origin of carbonaceous components that could possibly contribute to the long term preservation of biogenic soil-aggregates is particularly examined. The study is based on the comparison of pedogenic aggregated microfacies from present-day situations and the ones encountered in soil archives from contrasting edaphic conditions: Arctic Holocene soils from Spitsbergen, hyper-arid soils from the Moche valley (Peru), Holocene semi-arid Mediterranean soils from Northern Syria, late Pleistocene paleosols from lake Mungo (South Wales Australia) and late Pleistocene paleosols from the Ardeche valley (France). The assemblage and composition of biogenic soil-aggregated horizons has been characterized under the binocular microscope and in thin sections. The basic components have been separated by water sieving. A typology of carbonaceous polymorphs and associated composite materials has been established under the binocular. They have been characterized by SEM-EDS, Raman spectrometry, X-ray diffraction and TEM. The comparative study shows that all the biogenic soil-aggregates from the soil archives contain a high amount of similar exotic components that contrast from the parent materials by their fresh aspect and their hydrophobic properties. This exotic assemblage comprises various types of aliphatic carbonaceous polymorphs (filaments, agglutinates, spherules) and aromatic ones (vitrous char, graphite), carbon cenospheres, fine grained sandstones and rock clasts

  19. Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands

    PubMed Central

    Wen, Ding; He, Nianpeng; Zhang, Jinjing

    2016-01-01

    Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250–2000 μm], microaggregates [53–250 μm], and mineral fraction [< 53 μm]) at 0–20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China. PMID:26751370

  20. Estimating the collapse of aggregated fine soil structure in a mountainous forested catchment.

    PubMed

    Mouri, Goro; Shinoda, Seirou; Golosov, Valentin; Chalov, Sergey; Shiiba, Michiharu; Hori, Tomoharu; Oki, Taikan

    2014-06-01

    This paper describes the relationship of forest soil dryness and antecedent rainfall with suspended sediment (SS) yield due to extreme rainfall events and how this relationship affects the survival of forest plants. Several phenomena contribute to this relationship: increasing evaporation (amount of water vapour discharged from soil) due to increasing air temperature, decreasing moisture content in the soil, the collapse of aggregates of fine soil particles, and the resulting effects on forest plants. To clarify the relationships among climate variation, the collapse of soil particle aggregates, and rainfall-runoff processes, a numerical model was developed to reproduce such aggregate collapse in detail. The validity of the numerical model was confirmed by its application to the granitic mountainous catchment of the Nagara River basin in Japan and by comparison with observational data. The simulation suggests that important problems, such as the collapse of forest plants in response to decreases in soil moisture content and antecedent rainfall, will arise if air temperature continues to increase.

  1. Aggregate stratification assessment of soil bacterial communities and organic matter composition: Coupling pyrosequencing and mid-infrared spectroscopy techniques

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study integrated physical, chemical, and molecular techniques to assess relationships between soil bacterial communities and the quantity and quality of soil organic carbon (SOC) at the soil microenvironment scale (e.g., within different aggregate size-fractions). To accomplish this goal soil ...

  2. Linking Microbial Community Structure to β-Glucosidic Function in Soil Aggregates

    SciTech Connect

    Bailey, Vanessa L.; Fansler, Sarah J.; Stegen, James C.; McCue, Lee Ann

    2013-10-01

    To link microbial community 16S structure to a measured function in a natural soil we have scaled both DNA and β-glucosidase assays down to a volume of soil that may approach a unique microbial community. β-glucosidase activity was assayed in 450 individual aggregates which were then sorted into classes of high or low activities, from which groups of 10 or 11 aggregates were identified and grouped for DNA extraction and pyrosequencing. Tandem assays of ATP were conducted for each aggregate in order to normalize these small groups of aggregates for biomass size. In spite of there being no significant differences in the richness or diversity of the microbial communities associated with high β-glucosidase activities compared with the communities associated with low β-glucosidase communities, several analyses of variance clearly show that the communities of these two groups differ. The separation of these groups is partially driven by the differential abundances of members of the Chitinophagaceae family. It may be that observed functional differences in otherwise similar soil aggregates can be largely attributed to differences in resource availability, rather than to presence or absence of particular taxonomic groups.

  3. Geotechnical characteristics and stability analysis of rock-soil aggregate slope at the Gushui Hydropower Station, southwest China.

    PubMed

    Zhou, Jia-wen; Shi, Chong; Xu, Fu-gang

    2013-01-01

    Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope.

  4. Geotechnical Characteristics and Stability Analysis of Rock-Soil Aggregate Slope at the Gushui Hydropower Station, Southwest China

    PubMed Central

    Shi, Chong; Xu, Fu-gang

    2013-01-01

    Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope. PMID:24082854

  5. The specific role of fungal community structure on soil aggregation and carbon sequestration: results from long-term field study in a paddy soil

    NASA Astrophysics Data System (ADS)

    Murugan, Rajasekaran; Kumar, Sanjay

    2015-04-01

    Soil aggregate stability is a crucial soil property that affects soil biota, biogeochemical processes and C sequestration. The relationship between soil aggregate stability and soil C cycling is well known but the influence of specific fungal community structure on this relationship is largely unknown in paddy soils. The aim of the present study was to evaluate the long-term fertilisation (mineral fertiliser-MIN; farmyard manure-FYM; groundnut oil cake-GOC) effects on soil fungal community shifts associated with soil aggregates under rice-monoculture (RRR) and rice-legume-rice (RLR) systems. Fungal and bacterial communities were characterized using phospholipid fatty acids, and glucosamine and muramic acid were used as biomarkers for fungal and bacterial residues, respectively. Microbial biomass C and N, fungal biomass and residues were significantly higher in the organic fertiliser treatments than in the MIN treatment, for all aggregate sizes under both crop rotation systems. In general, fungal/bacterial biomass ratio and fungal residue C/bacterial residue C ratio were significantly higher in macroaggregate fractions (> 2000 and 250-2000 μm) than in microaggregate fractions (53-250 and <53 μm). In both crop rotation systems, the long-term application of FYM and GOC led to increased accumulation of saprotrophic fungi (SF) in aggregate fractions > 2000 μm. In contrast, we found that arbuscular mycorrhizal fungi (AMF) was surprisingly higher in aggregate fractions > 2000 μm than in aggregate fraction 250-2000 μm under MIN treatment. The RLR system showed significantly higher AMF biomass and fungal residue C/ bacterial residue C ratio in both macroaggregate fractions compared to the RRR system. The strong relationships between SF, AMF and water stable aggregates shows the specific contribution of fungi community on soil aggregate stability. Our results highlight the fact that changes within fungal community structure play an important role in shaping the soil

  6. Medium-term evolution of water repellency and aggregate stability in Mediterranean calcareous soils after wildfire

    NASA Astrophysics Data System (ADS)

    Gordillo-Rivero, Ángel; García-Moreno, Jorge; Zavala, Lorena M.; Jordán, Antonio; Granged, Arturo JP; Gil, Juan

    2013-04-01

    Wildfires are a common feature of Mediterranean ecosystems due to environmental factors and anthropic influence, especially in those areas where land use change and the development of touristic infrastructures are more intense. Wildfires induce a series of soil changes affecting their physical and chemical properties and the hydrological and erosive response. Two of the properties that are commonly affected by burning are soil water repellency (WR) and aggregate stability (AS). Both properties play an important role in the hydrological response of soils and other processes, and may be used as indices for assessing burn severity (Gordillo-Rivero et al., 2013). OBJECTIVES The field study was carried out between August 2006 (date of burning) and August 2011 with the following objectives: [i] to study the changes in SWR and AS immediately after fire and in the medium-term (6 years after burning) and its distribution within aggregate size fractions (<2, 1-2, 0.5-1 and 0.25-0.5 mm), [ii] to assess the relationships between postfire AS and WR, and [iii] to investigate interactions between AS and WR and different factors (site, time since burning, lithology and vegetation type) in calcareous Mediterranean soils. METHODS Five areas affected by wildfires during summer 2006 were selected for this research. Vegetation was characterized by grassland and Mediterranean shrubland. Soils were calcareous, with loam to clayey texture. As shown from adjacent areas, soils were wettable or slightly water-repellent immediately before burning. Soil WR and AS were measured in soil samples (0-15 mm deep) in fine earth (<2 mm) and aggregate sieve fractions (1-2, 0.5-1 and 0.25-0.5 mm). WR was assessed using the WDPT test, and AS was determined as the percentage of stable aggregates after laboratory rainfall simulation. RESULTS Both properties showed different tendencies in different aggregate size fractions. Results showed that soil WR was induced in wettable soils or enhanced in slightly or

  7. Changes in soil aggregate stability under different irrigation doses of waste water

    NASA Astrophysics Data System (ADS)

    Morugán, Alicia; García-Orenes, Fuensanta; Mataix-Solera, Jorge; Arcenegui, Victoria; Bárcenas, Gema

    2010-05-01

    Freshwater availability and soil degradation are two of the most important environmental problems in the Mediterranean area acerbated by incorrect agricultural use of irrigation in which organic matter is not correctly managed, the use of low quality water for irrigation, and the inefficiency of dose irrigation. For these reasons strategies for saving water and for the restoration of the mean properties of soil are necessary. The use of treated waste water for the irrigation of agricultural land could be a good solution to these problems, as it reduces the utilization of fresh water and could potentially improve key soil properties. In this work we have been studying, for more than three years, the effects on soil properties of different doses of irrigation with waste water. Here we show the results on aggregate stability. The study is located in an agricultural area at Biar (Alicante, SE of Spain), with a crop of grape (Vitis labrusca). Three types of waters are being used in the irrigation of the soil: fresh water (control) (TC), and treated waste water from secondary (T2) and tertiary treatment (T3). Three different doses of irrigation have been applied to fit the efficiency of the irrigation to the crop and soil type: D10 (10 L m-2 every week during 17 months), D50 (50 L m-2 every fifteen days during 14 moths) and D30 (30 L m-2 every week during 6 months up to present day). The results showed a clear decrease of aggregate stability during the period we used the second dose (D50) independent of the type of water used. That dose of irrigation and frequency produced strong wetting and drying cycles (WD) in the soil, and this is suspected to be the main factor responsible for the results. When we changed the dose of irrigation to D30, reducing the quantity per event and increasing the frequency, the soil aggregate stability started to improve. This dose avoids strong drying periods between irrigation events and the aggregate stability is confirmed to be slowly

  8. Study of soil aggregate breakdown dynamics under low dispersive ultrasonic energies with sedimentation and X-ray attenuation**

    PubMed Central

    Schomakers, Jasmin; Zehetner, Franz; Mentler, Axel; Ottner, Franz; Mayer, Herwig

    2016-01-01

    It has been increasingly recognized that soil organic matter stabilization is strongly controlled by physical binding within soil aggregates. It is therefore essential to measure soil aggregate stability reliably over a wide range of disruptive energies and different aggregate sizes. To this end, we tested high-accuracy ultrasonic dispersion in combination with subsequent sedimentation and X-ray attenuation. Three arable topsoils (notillage) from Central Europe were subjected to ultrasound at four different specific energy levels: 0.5, 6.7, 100 and 500 J cm−3, and the resulting suspensions were analyzed for aggregate size distribution by wet sieving (2 000-63 μm) and sedimentation/X-ray attenuation (63-2 μm). The combination of wet sieving and sedimentation technique allowed for a continuous analysis, at high resolution, of soil aggregate breakdown dynamics after defined energy inputs. Our results show that aggregate size distribution strongly varied with sonication energy input and soil type. The strongest effects were observed in the range of low specific energies (< 10 J cm−3), which previous studies have largely neglected. This shows that low ultrasonic energies are required to capture the full range of aggregate stability and release of soil organic matter upon aggregate breakdown. PMID:27099408

  9. Scale Model of a Soil Aggregate and Associated Organisms: A Teaching Tool for Soil Ecology

    ERIC Educational Resources Information Center

    Bruns, Mary Ann; Byrne, Loren B.

    2004-01-01

    Soil is a complex habitat for diverse biota. A significant challenge in teaching soil ecology is our inability to observe organisms as they live and interact in the soil. The objective of this article is to describe an interactive class project to help students visualize the sizes of different groups of soil organisms and to relate these to soil…

  10. Bacteria and fungi can contribute to nutrients bioavailability and aggregate formation in degraded soils.

    PubMed

    Rashid, Muhammad Imtiaz; Mujawar, Liyakat Hamid; Shahzad, Tanvir; Almeelbi, Talal; Ismail, Iqbal M I; Oves, Mohammad

    2016-02-01

    Intensive agricultural practices and cultivation of exhaustive crops has deteriorated soil fertility and its quality in agroecosystems. According to an estimate, such practices will convert 30% of the total world cultivated soil into degraded land by 2020. Soil structure and fertility loss are one of the main causes of soil degradation. They are also considered as a major threat to crop production and food security for future generations. Implementing safe and environmental friendly technology would be viable solution for achieving sustainable restoration of degraded soils. Bacterial and fungal inocula have a potential to reinstate the fertility of degraded land through various processes. These microorganisms increase the nutrient bioavailability through nitrogen fixation and mobilization of key nutrients (phosphorus, potassium and iron) to the crop plants while remediate soil structure by improving its aggregation and stability. Success rate of such inocula under field conditions depends on their antagonistic or synergistic interaction with indigenous microbes or their inoculation with organic fertilizers. Co-inoculation of bacteria and fungi with or without organic fertilizer are more beneficial for reinstating the soil fertility and organic matter content than single inoculum. Such factors are of great importance when considering bacteria and fungi inocula for restoration of degraded soils. The overview of presented mechanisms and interactions will help agriculturists in planning sustainable management strategy for reinstating the fertility of degraded soil and assist them in reducing the negative impact of artificial fertilizers on our environment.

  11. A physical scaling model for aggregation and disaggregation of field-scale surface soil moisture dynamics.

    PubMed

    Ojha, Richa; Govindaraju, Rao S

    2015-07-01

    Scaling relationships are needed as measurements and desired predictions are often not available at concurrent spatial support volumes or temporal discretizations. Surface soil moisture values of interest to hydrologic studies are estimated using ground based measurement techniques or utilizing remote sensing platforms. Remote sensing based techniques estimate field-scale surface soil moisture values, but are unable to provide the local-scale soil moisture information that is obtained from local measurements. Further, obtaining field-scale surface moisture values using ground-based measurements is exhaustive and time consuming. To bridge this scale mismatch, we develop analytical expressions for surface soil moisture based on sharp-front approximation of the Richards equation and assumed log-normal distribution of the spatial surface saturated hydraulic conductivity field. Analytical expressions for field-scale evolution of surface soil moisture to rainfall events are utilized to obtain aggregated and disaggregated response of surface soil moisture evolution with knowledge of the saturated hydraulic conductivity. The utility of the analytical model is demonstrated through numerical experiments involving 3-D simulations of soil moisture and Monte-Carlo simulations for 1-D renderings-with soil moisture dynamics being represented by the Richards equation in each instance. Results show that the analytical expressions developed here show promise for a principled way of scaling surface soil moisture.

  12. Influence of aggregate sizes and microstructures on bioremediation assessment of field-contaminated soils in pilot-scale biopiles

    NASA Astrophysics Data System (ADS)

    Chang, W.; Akbari, A.; Frigon, D.; Ghoshal, S.

    2011-12-01

    Petroleum hydrocarbon contamination of soils and groundwater is an environmental concern. Bioremediation has been frequently considered a cost-effective, less disruptive remedial technology. Formation of soil aggregate fractions in unsaturated soils is generally believed to hinder aerobic hydrocarbon biodegradation due to the slow intra-pore diffusion of nutrients and oxygen within the aggregate matrix and to the reduced bioavailability of hydrocarbons. On the other hand, soil aggregates may harbour favourable niches for indigenous bacteria, providing protective microsites against various in situ environmental stresses. The size of the soil aggregates is likely to be a critical factor for these processes and could be interpreted as a relevant marker for biodegradation assessment. There have been only limited attempts in the past to assess petroleum hydrocarbon biodegradation in unsaturated soils as a function of aggregate size. This study is aimed at investigating the roles of aggregate sizes and aggregate microstructures on biodegradation activity. Field-aged, contaminated, clayey soils were shipped from Norman Wells, Canada. Attempts were made to stimulate indigenous microbial activity by soil aeration and nutrient amendments in a pilot-scale biopile tank (1m L×0.65m W×0.3 m H). A control biopile was maintained without the nutrient amendment but was aerated. The initial concentrations of petroleum hydrocarbons in the field-contaminated soils increased with increasing aggregate sizes, which were classified in three fractions: micro- (<250 μm), meso- (>250-2000 μm) and macro-aggregates (>2000 μm). Compared to the TPH analyses at whole-soil level, the petroleum hydrocarbon analyses based on the aggregate-size levels demonstrated more clearly the extent of biodegradation of non-volatile, heavier hydrocarbons (C16-C34) in the soil. The removal of the C16-C34 hydrocarbons was 44% in macro-aggregates, but only 13% in meso-aggregates. The increased protein

  13. The fate of silver nanoparticles in soil solution--Sorption of solutes and aggregation.

    PubMed

    Klitzke, Sondra; Metreveli, George; Peters, Andre; Schaumann, Gabriele E; Lang, Friederike

    2015-12-01

    Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254 nm, and the absorption ratio α254/α410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca(2+) solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320 μg/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag(+) ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces.

  14. Non-native plants and soil microbes: potential contributors to the consistent reduction in soil aggregate stability caused by the disturbance of North American grasslands.

    PubMed

    Duchicela, Jessica; Vogelsang, Keith M; Schultz, Peggy A; Kaonongbua, Wittaya; Middleton, Elizabeth L; Bever, James D

    2012-10-01

    Soil aggregate stability is an important ecosystem property that is altered by anthropogenic disturbance. Yet, the generalization of these alterations and the identification of the main contributors are limited by the absence of cross-site comparisons and the application of inconsistent methodologies across regions. • We assessed aggregate stability in paired remnant and post-disturbance grasslands across California, shortgrass and tallgrass prairies, and in manipulative experiments of plant composition and soil microbial inoculation. • Grasslands recovering from anthropogenic disturbance consistently had lower aggregate stability than remnants. Across all grasslands, non-native plant diversity was significantly associated with reduced soil aggregate stability. A negative effect of non-native plants on aggregate stability was also observed in a mesocosm experiment comparing native and non-native plants from California grasslands. Moreover, an inoculation study demonstrated that the degradation of the microbial community also contributes to the decline in soil aggregate stability in disturbed grasslands. • Anthropogenic disturbance consistently reduced water-stable aggregates. The stability of aggregates was reduced by non-native plants and the degradation of the native soil microbial community. This latter effect might contribute to the sustained decline in aggregate stability following anthropogenic disturbance. Further exploration is advocated to understand the generality of these potential mechanisms.

  15. Pyrosequencing and mid-infrared spectroscopy techniques reveal distinct aggregate stratification of soil bacterial communities and organic matter composition

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study integrated physical, chemical, and molecular techniques to assess relationships between soil bacterial community structures and the quantity and quality of soil organic carbon (SOC) at the soil microenvironment scale (e.g., within different aggregate size-fractions). To accomplish this g...

  16. Geoenvironmental and engineering properties of rock, soil, and aggregate. Transportation research record

    SciTech Connect

    Not Available

    1992-01-01

    Partial Contents: Use of Waste Materials in Highway Construction: State of the Practice and Evaluation of the Selected Waste Products; Physical and Environmental Properties of Asphalt-Amended Bottom Ash; Use of Cement Kiln Dust, Fly Ash, and Recycling Technique in Low-Volume Road Rehabilitation; Use of By-Product Phosphogypsum in Road Construction; Stabilization of Water Treatment Plant Sludge for Possible Use as Embankment Material; Construction and Performance of a Shredded Waste Tire Test Embankment; Corrosion of Steel Piles in Some Waste Fills; Recycled Plastics for Highway Agencies; Effect of Chloride and Sulfate Contamination in Soils on Corrosion of Steel and Concrete; Permeability and Leaching Characteristics of Fly Ash Liner Materials; Evaluation of Recycled Concrete, Open-Graded Aggregate, and Large Top-Size Aggregate Bases; Engineering Properties of Phosphogypsum-Based Slag Aggregate.

  17. Input of 137Cs and 90Sr into plants from the surface of soil aggregates and the intraped space

    NASA Astrophysics Data System (ADS)

    Fokin, A. D.; Torshin, S. P.; Bebneva, Yu. M.; Gadzhiagaeva, R. A.; Zolotareva, Yu. I.; Umer, M. I.

    2014-12-01

    Soil aggregates with different localization of radionuclides—(a) only on the aggregate surface, (b) only in the intraped space, and (c) uniformly distributed throughout the aggregate volume—have been obtained under laboratory conditions, which has allowed separately assessing the roles of different aggregate parts in the uptake of radionuclides by plant roots and the reaggregation rate of the soil material. The uptake rate of the radionuclides localized on the surface of soil aggregates, especially 137Cs, by plants manifold exceeds their uptake observed at the localization of pollutants throughout the aggregate volume or only in their intraped material. The input rate of radionuclides into plants decreases with time. For 137Cs, this decrease is due to the strengthening of the sorption fixation of the radionuclide (about 15%) and the reaggregation of the soil material (85%). Under natural conditions, at a depth of 10 cm in the dark gray forest soil of a forest belt, aggregates 7-10 mm in size are subjected to 40-75% destruction and reaggregation on the average within a year, which corresponds, with consideration for the statistical dispersion of the initial data, to the aggregate lifetime of 1.5 to 3 years.

  18. Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China.

    PubMed

    Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S

    2016-01-01

    Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250-2000 μm), rather than within the microaggregates (53-250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions.

  19. Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China

    PubMed Central

    Li, Liguang; Vogel, Jason; He, Zhenli; Zou, Xiaoming; Ruan, Honghua; Huang, Wei; Wang, Jiashe; Bianchi, Thomas S.

    2016-01-01

    Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250–2000 μm), rather than within the microaggregates (53–250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions. PMID:26964101

  20. Transformations in soil organic matter and aggregate stability after conversion of Mediterranean forest to agriculture

    NASA Astrophysics Data System (ADS)

    Recio Vázquez, Lorena; Almendros, Gonzalo; Carral, Pilar; Knicker, Heike; González Pérez, José Antonio; González Vila, Francisco Javier

    2013-04-01

    Conversion of forest ecosystems into croplands often leads to severe decrease of the soil organic matter (SOM) levels with the concomitant deterioration of soil structure. The present research focuses on the effects of cultivation on the stability of soil macroaggregates, as well as on the total quantity and quality of SOM. Three representative soils from central Spain (i.e., Petric Calcisol, Cutanic Luvisol and Calcic Vertisol) were sampled. Each site had natural vegetation (NV) dominated either by characteristic Mediterranean forest (dehesa) or cereal crops (CC) under conventional tillage. For each site, three spatial replicates of the NV and CC were sampled. Soil aggregate stability was measured by the wet sieving method. The structural stability index was then calculated as the mass of aggregated soil (>250 μm) remaining after wet sieving, as a percent of total aggregate weight. The analytical characterization of the SOM was carried out after chemical fractionation for quantifying the different organic pools: free organic matter (FOM), humic acids (HA), fulvic acids (FA) and humin (H). Furthermore, whole soil samples pretreated with 10 % HF solution were analyzed by CP-MAS 13C NMR and the purified HA fraction was characterized by elementary analysis, visible and infrared spectroscopies and Py-GC/MS. A marked reduction in the proportion of stable aggregates when the natural ecosystem was converted to agriculture was observed. Values of the structural stability index (%) changed over from 96.2 to 38.1, 95.1 to 83.7 and 98.5 to 60.6 for the Calcisol, Luvisol and Vertisol respectively. Comparatively higher contents of SOM were found in the soils under NV (11.69 to 0.93, 3.29 to 2.72 and 9.51 to 0.79 g C100 g-1soil) even though a quantitative rearrangement of the SOM pools was noticed. In all sites, the relative contribution of the labile C (FOM) to the total SOM content decreased when the forest soils were converted into croplands, whereas the proportion of both

  1. The influence of different soil management practices on auxin herbicide interactions with organic carbon in soil aggregate fractions

    NASA Astrophysics Data System (ADS)

    Schnitzler, Frauke; Haupt, Nadine; Burauel, Peter; Berns, Anne E.

    2010-05-01

    The influence of changing organic carbon contents in soils on the sorption and/or sequestration mechanisms of xenobiotics and their bioavailability are still not understood precisely. The present work discusses the turnover of a crop residue interacting with processes like mobilisation, binding and metabolism of an auxin herbicide in soil. The soil type was a haplic chernozem, available in three crop production regimes (low, normal and high) due to three types of fertilisation (none, mineral and mineral & organic) [1]. Two sets of experiments were conducted with undisturbed soil columns under field-like conditions. In the first set 14C-labelled maize straw was incorporated into the top soil and after three months incubation the herbicide benazolin was applied. In the second set the unlabelled maize straw was incorporated first, then 14C-labelled benazolin was added. Soil layers of 0-5 cm and 5-10 cm were fractionated in according to a soil aggregate fractionation procedure [2]. The content of organic carbon and the distribution of benazolin and its metabolites were detected in the gained soil fractions. In general, the specific organic carbon content and the specific 14C-activity of benazolin and its metabolites increased in the order from sand-sized though silt-sized to clay fraction due to increasing specific surface areas and sorption sites of the mineral particles. The highest sorption capacity of benazolin and its metabolites was detected in the soil layers of 0-5 cm with mineral fertilisation. In the 5-10 cm soil layers the binding capacity increased with increasing crop production. It was shown that more than half of the residual 14C-activity was not extractable. LC-MS/MS analysis of the extracts showed that the major components were benazolin and the relatively non-mobile thiazolin. The amount of benazolin in the extracts increased with increasing crop production, but decreased with increasing soil depth. These results indicate that maize straw amendment

  2. The Relationship Between Carbon Input, Aggregation, and Soil Organic Carbon Stabilization in Sustainable Cropping Systems

    NASA Astrophysics Data System (ADS)

    Kong, A. Y.; Six, J.; Bryant, D. C.; Denison, R.; van Kessel, C.

    2003-12-01

    Approximately 10% of the earth's soil C is stored within agricultural soil ecosystems. Because farming systems hold promise for sequestering C, their sustainability, environmental impact, and potential role in mitigating rising atmospheric CO2 concentrations must be addressed. Our current challenges are to provide credible evidence that agricultural practices can sequester significant amounts of C and to quantify the mechanisms, capacity, and longevity of agricultural lands as C sinks. Agronomic practices that influence yield and, therefore, affect the proportion of crop residues returned to the soil (e.g. cover cropping, irrigation, fertilizer addition, and compost application) are likely to influence soil organic carbon (SOC). The objectives of this study were (1) to determine the influence of C input on C sequestration in SOC fractions and (2) to evaluate how aggregation (MWD) relates to SOC and cumulative C input, across 10 different cropping systems. Using SOM fractionation techniques, soil samples from 10 cropping systems at LTRAS (Long-term Research on Agricultural Systems, Davis, CA) were separated into four aggregate size classes (LM: >2000μ m, sM: 250-2000μ m, m: 53-250μ m, and silt&clay: <53μ m) and into three SOM fractions within LM and sM (cPOM:250-2000μ m, mM: 53-250μ m, and silt&clay: <53μ m). All fractions were analyzed for their C content. Empirically derived relationships between yield and aboveground biomass-C plus yield and belowground biomass-C were used to quantify C input from corn, wheat, and tomato residues as well as for legume cover crops and compost for the different cropping systems. We found a positive correlation between cumulative C input and SOC (R2=0.45, P<0.0001). After 9 years, MWD increased linearly with greater C input (R2=0.64, P<0.0001) and SOC (R2=0.61, P<0.0001), respectively. We observed that aggregate-C shifts from the microaggregate fraction (53-250μ m) in low C input systems to macroaggregate fractions (>2000

  3. Effects of fire on organic matter content and aggregate stability of soils in South of Spain.

    NASA Astrophysics Data System (ADS)

    Martínez-Murillo, Juan F.; Ruiz-Sinoga, José D.; Jiménez-Donaire, Virginia; Hueso-González, Paloma; Gabarrón-Galeote, Miguel A.

    2014-05-01

    Wildfires affect dramatically to soil physical, chemical and biological properties, which changes the hydrological and erosive soil response. The objectives of this study are to compare some soil properties affected by fire in field conditions. The experimental area is located in the South of Spain, 32 km western of the city of Málaga. In general, the area is characterized by a sub-humid Mediterranean climate (mean annual precipitation: 699 mm year-1; mean annual temperature: 17°C), with a substratum of alkaline metamorphic rocks. Vegetation cover consists on a mixed open wood of Quercus spp. and Pinus spp. with typical degraded Mediterranean scrub, where the dominant genus are Ulex spp. and Cistus spp. This area was partially affected by a wildfire on September 11th 2011. Soil samples were taken in burned and unburned areas: soil covered by shrubs, trees and bare soils. Unburned area was adjacent to the burned one and both of them had the same general conditions. On each microenvironment samples of the first 5 cm of soil were collected on September 19th 2011. The analyzed properties in the laboratory were organic matter (OM) and aggregate stability (AS). In general, fire affected mainly to OM (p<0.01). When we performed the analyses dividing the samples according to vegetal cover, the ANOVA showed that the wildfire only affected the OM content in soil covered by shrubs. In soil covered by trees and bare soil OM decreased, but it was insignificant. AS were not affected in any sampled environment.

  4. [Aluminum dissolution and changes of pH in soil solution during sorption of copper by aggregates of paddy soil].

    PubMed

    Xu, Hai-Bo; Zhao, Dao-Yuan; Qin, Chao; Li, Yu-Jiao; Dong, Chang-Xun

    2014-01-01

    Size fractions of soil aggregates in Lake Tai region were collected by the low-energy ultrasonic dispersion and the freeze-desiccation methods. The dissolution of aluminum and changes of pH in soil solution during sorption of Cu2+ and changes of the dissolution of aluminum at different pH in the solution of Cu2+ by aggregates were studied by the equilibrium sorption method. The results showed that in the process of Cu2+ sorption by aggregates, the aluminum was dissoluted and the pH decreased. The elution amount of aluminum and the decrease of pH changed with the sorption of Cu2+, both increasing with the increase of Cu2+ sorption. Under the same conditions, the dissolution of aluminum and the decrease of pH were in the order of coarse silt fraction > silt fraction > sand fraction > clay fraction, which was negatively correlated with the amount of iron oxide, aluminum and organic matter. It suggested that iron oxide, aluminum and organic matters had inhibitory and buffering effect on the aluminum dissolution and the decrease of pH during the sorption of Cu2+.

  5. Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

    PubMed Central

    Xiao, Shuangshuang; Zhang, Wei; Ye, Yingying; Zhao, Jie; Wang, Kelin

    2017-01-01

    Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25–2 mm), and micro- (0.053–0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types—enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields—were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics. PMID:28211507

  6. Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

    NASA Astrophysics Data System (ADS)

    Xiao, Shuangshuang; Zhang, Wei; Ye, Yingying; Zhao, Jie; Wang, Kelin

    2017-02-01

    Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25–2 mm), and micro- (0.053–0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types—enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields—were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics.

  7. Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem.

    PubMed

    Xiao, Shuangshuang; Zhang, Wei; Ye, Yingying; Zhao, Jie; Wang, Kelin

    2017-02-17

    Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25-2 mm), and micro- (0.053-0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types-enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields-were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics.

  8. Soil aggregates, organic matter turnover and carbon balance in a Mediterranean eroded vineyard

    NASA Astrophysics Data System (ADS)

    Novara, Agata; Lo Papa, Giuseppe; Dazzi, Carmelo; Gristina, Luciano; Cerdà, Artemi

    2014-05-01

    The carbon cycle is being affected by the human impacts (Novara et al., 2011; Yan-Gui et al., 2013), and one of those is the intensification in the soil erosion in agriculture land (Cerdà et al., 2009; García Orenes et al., 2009). Vineyards also are affected by the human activities (Fernández Calviño, 2012). Vineyards in Sicily are cultivated on 110.000 ha, 10% of which on >10% slope. Deficiencies of soil organic matter are typical of the semi arid Mediterranean environment especially where traditional intensive cropping practices are adopted (Novara et al., 2012; 2013). These practices in vineyards could lead soil to intensive erosion processes (Novara et al., 2011). The fate of SOC under erosion processes is difficult to understand because of the influence of the erosion impact on SOC pathway, which depends on the different features of the process involved (detachment, transport and/or deposition). Soil erosion must be considered a net C source (Lal, 2003), as eroded soils have lower net primary productivity (NPP) (Dick and Gregorich, 2004) caused by reduction in the effective rooting depth and all in all determining decline in soil quality. Breakdown of aggregates and soil dispersion expose SOM to microbial/enzymatic processes and chemical soil properties (Dimoyiannis, 2012; Kocyigit and Demirci, 2012). Moreover the light fraction, transported by runoff, is labile and easily mineralized determining CO2 emission in the atmosphere (Jacinthe and Lal, 2004). Therefore, the carbon pool is lower in eroded than in un-eroded soil scapes and the rate of mineralization of soil organic matter is higher in sediments than in original soil. In this survey we show a research conducted on a slope sequence of three soil profiles in an irrigated vineyard located in Sambuca di Sicilia, Italy (UTM33-WGS84: 4169367N; 325011E). The SOC content was measured at depth intervals of 10 cm up to a depth of 60 cm in each pedon. Wet aggregate-size fractions with no prior chemical

  9. Measuring ecosystem functioning of soil mega-aggregates produced by soil/litter mix-feeding animals

    NASA Astrophysics Data System (ADS)

    Kaneko, N.

    2009-04-01

    Some soil animals are soil/litter mix-feeders. They are known to produce long-lasting soil structures (e.g. casts and molting chamber), and these structures will modify resource availability and environmental conditions for plants and soil organisms. Good examples are epigeic Megascolecid earthworms (Uchida et al., 2004) and Xystodesmid millipeds (Toyota et al., 2006), both found in Japan. In this study we examined chemical, physical and biological properties of soil focusing on multi-functioning of aggregates made by these animals. Since 2003, we manipulated densities of epigeic earthworms in a field encloser (35 m2) (three replications) at a cool temperate forest in Japan. At a no-worm (NW) treatment, all the worms have been collected every year by hand. At the same place, we prepared a control treatment in an encloser (Closed control; CC) and outside the encloser (Open control; OC). We examined surface soil and plant growth after 5-years field manipulation of oak dominated forest. Growth of two Liliaceae forest floor herbs; Smilacina japonica and Polygonatum odoratum, and oak (Quercus crispula) seedlings and canopy oak trees were recorded. Reduction of aggregates after elimination of earthworms was observed in a field condition. The manipulation site showed decreased soil pH, Ca, Mg, and P concentration and total carbon storage was also reduced. There was a negative significant correlation between casts abundance and soil NH4-N, and a positive significance was observed between casts abundance and growth of S. japonica, and oak seedlings. Radial growth of canopy oak trees was decreased at NW treatment compared to CC and OC. Leaf N contents of oak seedling at NW were significantly lower in NW, but canopy oak trees did not show any difference in leaf-N. Although S. japonica and P. odoratum were both found in a same forest floor, S. japonica is known as nutrient limited plants in spring, whereas P. odoratum is light limited. Oak seedlings are depending early growth

  10. Effect of long-term combined application of organic and inorganic fertilizers on soil nematode communities within aggregates.

    PubMed

    Zhang, Zhiyong; Zhang, Xiaoke; Mahamood, Md; Zhang, Shuiqing; Huang, Shaomin; Liang, Wenju

    2016-08-09

    A long-term fertilization experiment was conducted to examine the effects of different fertilization practices on nematode community composition within aggregates in a wheat-maize rotation system. The study was a randomized complete block design with three replicates. The experiment involved the following four treatments: no fertilizer, inorganic N, P and K fertilizer (NPK), NPK plus manure (NPKM) and NPK plus maize straw (NPKS). Soil samples were taken at 0-20 cm depth during the wheat harvest stage. Based on our results, NPKS contributed to soil aggregation and moisture retention, with a positive effect on soil total nitrogen accumulation, particularly within small macroaggregates (0.25-1 mm) and microaggregates (<0.25 mm). The C/N ratio was correlated to the distribution of the soil nematode community. Both manure application and straw incorporation increased the nematode functional metabolic footprints within all aggregates. Additionally, the functional metabolic footprints decreased with a decline in aggregate size. The accumulation of total nitrogen within <1 mm aggregates under NPKS might play a key role in maintaining the survival of soil nematodes. In our study, both crop straw incorporation and inorganic fertilizer application effectively improved soil physicochemical properties and were also beneficial for nematode survival within small aggregate size fractions.

  11. Effect of long-term combined application of organic and inorganic fertilizers on soil nematode communities within aggregates

    PubMed Central

    Zhang, Zhiyong; Zhang, Xiaoke; Mahamood, Md.; Zhang, Shuiqing; Huang, Shaomin; Liang, Wenju

    2016-01-01

    A long-term fertilization experiment was conducted to examine the effects of different fertilization practices on nematode community composition within aggregates in a wheat-maize rotation system. The study was a randomized complete block design with three replicates. The experiment involved the following four treatments: no fertilizer, inorganic N, P and K fertilizer (NPK), NPK plus manure (NPKM) and NPK plus maize straw (NPKS). Soil samples were taken at 0–20 cm depth during the wheat harvest stage. Based on our results, NPKS contributed to soil aggregation and moisture retention, with a positive effect on soil total nitrogen accumulation, particularly within small macroaggregates (0.25–1 mm) and microaggregates (<0.25 mm). The C/N ratio was correlated to the distribution of the soil nematode community. Both manure application and straw incorporation increased the nematode functional metabolic footprints within all aggregates. Additionally, the functional metabolic footprints decreased with a decline in aggregate size. The accumulation of total nitrogen within <1 mm aggregates under NPKS might play a key role in maintaining the survival of soil nematodes. In our study, both crop straw incorporation and inorganic fertilizer application effectively improved soil physicochemical properties and were also beneficial for nematode survival within small aggregate size fractions. PMID:27502433

  12. Lignin from rice straw Kraft pulping: effects on soil aggregation and chemical properties.

    PubMed

    Xiao, C; Bolton, R; Pan, W L

    2007-05-01

    Lignin contained in pulping liquor that is generated during the pulping process for papermaking is a disposal problem for the pulp and paper industry. Separating lignin and other organic components from pulping liquor with inorganic acids may improve its applicability to fields as a beneficial soil amendment while offering a potential disposal alternative. Sulfuric acid-precipitated lignin from rice straw pulping liquor applied at rates of 1.67 and 3.34 g C kg(-1) soil was incubated to evaluate its effects on soil properties over 8 weeks of incubation. Addition of this acid-precipitated lignin at these rates decreased soil pH by 0.24-0.53 units over 8 weeks of incubation, suggesting that this sulfuric acid-precipitated lignin from pulping liquor may have potential as a soil acidifying agent. Soil electrical conductivity (EC) only increased by up to 0.36 d Sm(-1), but highest EC levels were less than 4 d Sm(-1), indicating that lignin applied at both rates would not cause salinity problems. Application of this lignin increased soil organic C by 1.46 and 3.13 g C kg(-1), and total soil N by 0.07 and 0.17 g N kg(-1) over the incubation period. Lignin improved the macroaggregation of >2mm size fraction, and increased wet microaggregate stability of >2mm and 0.5-0.25 mm aggregates compared to a nonamended control. The results of this study suggest that this acid-precipitated lignin from pulping liquor may have potential as a beneficial soil amendment.

  13. The dynamics of soil aggregate breakdown in water in response to landuse as measured with laser diffraction technique

    NASA Astrophysics Data System (ADS)

    Oyedele, D. J.; Pini, R.; Sparvoli, E.; Scatena, M.

    2012-04-01

    The Mastersizer 2000G (Malvern Instruments) Diffraction Instrument was used to assess and quantify the breakdown of soil aggregates and compute wet aggregate stability indices. The study was aimed at evolving a novel rapid method of determining soil aggregate stability. Bulk surface (0-15 cm) soil samples were collected under 5 different land uses in the Teaching and Resrach Farm of Obafemi Awolowo University, Ile-Ife, Nigeria. About 0.5g of the soils aggregates (0.5 -1 mm diameter) were evaluated in the laser diffractometer with the stirrer operated at 500 rpm and the pump at 1800 rpm. The different size aggregates and particles of sand silt and clay were quantified periodically. Water stable aggregates greater than 250 µm (WSA>250), water stable aggregates less than 250 µm (WSA<250), water dispersible clay index (WDI), and mean volume diameter (MVD) among others were computed from the laser diffraction data. The values were compared with the classical Yoder wet sieving technique. The WSA>250 was significantly higher on the soils under Forest (FR), Cacao (CC), Teak (TK) and Oil Palm (OP) plantations, while it was significantly lowest under no-tillage (NT) and continuous cultivation (CT). The pasture (PD) was not significantly different from either the cultivated and the non-cultivated soils. Conversely, the WSA<250 and water dispersible clay index was highest in the cultivated soils (CT and NT) and lowest in the non-cultivated soils (FR, TK, CC and OP) while the PD was in-between. The MVD also followed a similar trend as the WSA>250. The wet sieving water stable aggregates index (WSI>250) was significantly correlated with WSA>250 (r = 0.75), MVD (r = 0.75), WDI (r = -0.68) and WSA<250 (r = - 0.73). All the laser diffraction measured aggregation indices were significantly correlated with the organic matter contents of the soils. Thus the laser diffraction promises a rapid and comprehensive method of evaluation of soil aggregate stability.

  14. Soil Aggregates and Associated Organic Matter under Conventional Tillage, No-Tillage, and Forest Succession after Three Decades

    PubMed Central

    Devine, Scott; Markewitz, Daniel; Hendrix, Paul; Coleman, David

    2014-01-01

    Impacts of land use on soil organic C (SOC) are of interest relative to SOC sequestration and soil sustainability. The role of aggregate stability in SOC storage under contrasting land uses has been of particular interest relative to conventional tillage (CT) and no-till (NT) agriculture. This study compares soil structure and SOC fractions at the 30-yr-old Horseshoe Bend Agroecosystem Experiment (HSB). This research is unique in comparing NT and CT with adjacent land concurrently undergoing forest succession (FS) and in sampling to depths (15–28 cm) previously not studied at HSB. A soil moving experiment (SME) was also undertaken to monitor 1-yr changes in SOC and aggregation. After 30 years, enhanced aggregate stability under NT compared to CT was limited to a depth of 5 cm, while enhanced aggregate stability under FS compared to CT occurred to a depth of 28 cm and FS exceeded NT from 5–28 cm. Increases in SOC concentrations generally followed the increases in stability, except that no differences in SOC concentration were observed from 15–28 cm despite greater aggregate stability. Land use differences in SOC were explained equally by differences in particulate organic carbon (POC) and in silt-clay associated fine C. Enhanced structural stability of the SME soil was observed under FS and was linked to an increase of 1 Mg SOC ha−1 in 0–5 cm, of which 90% could be attributed to a POC increase. The crushing of macroaggregates in the SME soil also induced a 10% reduction in SOC over 1 yr that occurred under all three land uses from 5–15 cm. The majority of this loss was in the fine C fraction. NT and FS ecosystems had greater aggregation and carbon storage at the soil surface but only FS increased aggregation below the surface, although in the absence of increased carbon storage. PMID:24465460

  15. Effects of straw and biochar amendments on aggregate stability, soil organic carbon, and enzyme activities in the Loess Plateau, China.

    PubMed

    Zhang, Man; Cheng, Gong; Feng, Hao; Sun, Benhua; Zhao, Ying; Chen, Haixin; Chen, Jing; Dyck, Miles; Wang, Xudong; Zhang, Jianguo; Zhang, Afeng

    2017-02-23

    Soil from the Loess Plateau of China is typically low in organic carbon and generally has poor aggregate stability. Application of organic amendments to these soils could help to increase and sustain soil organic matter levels and thus to enhance soil aggregate stability. A field experiment was carried out to evaluate the effect of the application of wheat straw and wheat straw-derived biochar (pyrolyzed at 350-550 °C) amendments on soil aggregate stability, soil organic carbon (SOC), and enzyme activities in a representative Chinese Loess soil during summer maize and winter wheat growing season from 2013 to 2015. Five treatments were set up as follows: no fertilization (CK), application of inorganic fertilizer (N), wheat straw applied at 8 t ha(-1) with inorganic fertilizer (S8), and wheat straw-derived biochar applied at 8 t ha(-1) (B8) and 16 t ha(-1) (B16) with inorganic fertilizer, respectively. Compared to the N treatment, straw and straw-derived biochar amendments significantly increased SOC (by 33.7-79.6%), microbial biomass carbon (by 18.9-46.5%), and microbial biomass nitrogen (by 8.3-38.2%), while total nitrogen (TN) only increased significantly in the B16 plot (by 24.1%). The 8 t ha(-1) straw and biochar applications had no significant effects on soil aggregation, but a significant increase in soil macro-aggregates (>2 mm) (by 105.8%) was observed in the B16 treatment. The concentrations of aggregate-associated SOC increased by 40.4-105.8% in macro-aggregates (>2 mm) under straw and biochar amendments relative to the N treatment. No significant differences in invertase and alkaline phosphatase activity were detected among different treatments. However, urease activity was greater in the biochar treatment than the straw treatment, indicating that biochar amendment improved the transformation of nitrogen in the soil. The carbon pool index and carbon management index were increased with straw and biochar amendments, especially in the B16

  16. Applying a new procedure to assess the controls on aggregate stability - including soil parent material and soil organic carbon concentrations - at the landscape scale

    NASA Astrophysics Data System (ADS)

    Turner, Gren; Rawlins, Barry; Wragg, Joanna; Lark, Murray

    2014-05-01

    Aggregate stability is an important physical indicator of soil quality and influences the potential for erosive losses from the landscape, so methods are required to measure it rapidly and cost-effectively. Previously we demonstrated a novel method for quantifying the stability of soil aggregates using a laser granulometer (Rawlins et al., 2012). We have developed our method further to mimic field conditions more closely by incorporating a procedure for pre-wetting aggregates (for 30 minutes on a filter paper) prior to applying the test. The first measurement of particle-size distribution is made on the water stable aggregates after these have been added to circulating water (aggregate size range 1000 to 2000 µm). The second measurement is made on the disaggregated material after the circulating aggregates have been disrupted with ultrasound (sonication). We then compute the difference between the mean weight diameters (MWD) of these two size distributions; we refer to this value as the disaggregation reduction (DR; µm). Soils with more stable aggregates, which are resistant to both slaking and mechanical breakdown by the hydrodynamic forces during circulation, have larger values of DR. We made repeated analyses of DR using an aggregate reference material (RM; a paleosol with well-characterised disaggregation properties) and used this throughout our analyses to demonstrate our approach was reproducible. We applied our modified technique - and also the previous technique in which dry aggregates were used - to a set of 60 topsoil samples (depth 0-15 cm) from cultivated land across a large region (10 000 km2) of eastern England. We wished to investigate: (i) any differences in aggregate stability (DR measurements) using dry or pre-wet aggregates, and (ii) the dominant controls on the stability of aggregates in water using wet aggregates, including variations in mineralogy and soil organic carbon (SOC) content, and any interaction between them. The sixty soil

  17. Effects of erosion in the fate of soil organic carbon and soil aggregation in a burned Mediterranean hill-slope

    NASA Astrophysics Data System (ADS)

    Campo, Julian; Cammeraat, Erik; Gimeno-García, Eugenia; Andreu, Vicente

    2016-04-01

    The Intergovernmental Panel on Climate Change indicated a higher degree of confidence that meteorological conditions associated to climate change will be propitious to increasing extreme events manifested, among others, in bigger and more frequent wildfires (IPCC, 2014). Wildfires contribute to shaping the landscape, and also the geomorphological and hydrological processes that operate on soil are affected (Bento-Gonçalves et al., 2012). Whereas, it is well documented that wildfires produce significant changes on erosion processes, the associated fate of soil organic carbon (SOC) has received less attention. This research assesses this gap by studying the loss, redistribution, and stabilization of SOC in a Mediterranean forest hill-slope burned the 28-08-2014, with high severity fire, at the Natural Park of Sierra de Espadán, Spain (39°50'45.11"N, 0°22'20.52"W). To this end, soil was sampled (19-9-2014) in the foot's slope (depositional), middle part (transport) and top (eroding) at two depths (<2 cm, 2-5 cm), and in two environments (under canopy soil: UC; bare soil: BS). Sediments were collected from four sediment fences constructed at the foot's slope, and together with soil samples, analysed with regard to SOC content and aggregate stability (AS). The main objective is to increase the understanding on the fate of SOC in Mediterranean burned areas experiencing soil erosion, transport and deposition, with special attention to the role of aggregation and disaggregation in redistribution processes. Immediately after the fire, SOC content was high (≈50 gC kg-1) as well as the AS (water drop test>146 drops). Significant differences (ANOVA, p<0.05) in SOC contents were observed between environments (UC>BS) and soil depths (topsoil>subsoil). However, no significant differences were observed among eroding (58.8+20.8 gC kg-1), transport (67.3+34.4 gC kg-1), and depositional zones (62.0+31.3 gC kg-1), which is not in agreement with other SOC redistribution studies

  18. The Aggregate Description of Semi-Arid Vegetation with Precipitation-Generated Soil Moisture Heterogeneity

    NASA Technical Reports Server (NTRS)

    White, Cary B.; Houser, Paul R.; Arain, Altaf M.; Yang, Zong-Liang; Syed, Kamran; Shuttleworth, W. James

    1997-01-01

    Meteorological measurements in the Walnut Gulch catchment in Arizona were used to synthesize a distributed, hourly-average time series of data across a 26.9 by 12.5 km area with a grid resolution of 480 m for a continuous 18-month period which included two seasons of monsoonal rainfall. Coupled surface-atmosphere model runs established the acceptability (for modelling purposes) of assuming uniformity in all meteorological variables other than rainfall. Rainfall was interpolated onto the grid from an array of 82 recording rain gauges. These meteorological data were used as forcing variables for an equivalent array of stand-alone Biosphere-Atmosphere Transfer Scheme (BATS) models to describe the evolution of soil moisture and surface energy fluxes in response to the prevalent, heterogeneous pattern of convective precipitation. The calculated area-average behaviour was compared with that given by a single aggregate BATS simulation forced with area-average meteorological data. Heterogeneous rainfall gives rise to significant but partly compensating differences in the transpiration and the intercepted rainfall components of total evaporation during rain storms. However, the calculated area-average surface energy fluxes given by the two simulations in rain-free conditions with strong heterogeneity in soil moisture were always close to identical, a result which is independent of whether default or site-specific vegetation and soil parameters were used. Because the spatial variability in soil moisture throughout the catchment has the same order of magnitude as the amount of rain failing in a typical convective storm (commonly 10% of the vegetation's root zone saturation) in a semi-arid environment, non-linearitv in the relationship between transpiration and the soil moisture available to the vegetation has limited influence on area-average surface fluxes.

  19. Dynamics of aggregate stability and soil organic C distribution as affected by climatic aggressiveness: a mesocosm approach

    NASA Astrophysics Data System (ADS)

    Pellegrini, Sergio; Elio Agnelli, Alessandro; Costanza Andrenelli, Maria; Barbetti, Roberto; Castelli, Fabio; Costantini, Edoardo A. C.; Lagomarsino, Alessandra; Pasqui, Massimiliano; Tomozeiu, Rodica; Razzaghi, Somayyeh; Vignozzi, Nadia

    2014-05-01

    In the framework of a research project aimed at evaluating the adaptation scenarios of the Italian agriculture to the current climate change, a mesocosm experiment under controlled conditions was set up for studying the dynamics of soil aggregate stability and organic C in different size fractions. Three alluvial loamy soils (BOV - Typic Haplustalfs coarse-loamy; CAS - Typic Haplustalfs fine-loamy; MED - Typic Hapludalfs fine-loamy) along a climatic gradient (from dryer to moister pedoclimatic conditions) in the river Po valley (northern Italy), under crop rotation for animal husbandry from more than 40 years, were selected. The Ap horizons (0-30cm) were taken and placed in 9 climatic chambers under controlled temperature and rainfall. Each soil was subjected to three different climate scenarios in terms of erosivity index obtained by combining Modified Fournier and Bagnouls-Gaussen indexes: i) typical (TYP), the median year of each site related to the 1961-1990 reference period; ii) maximum aggressive year (MAX) observed in the same period, and iii) the simulated climate (SIM), obtained by projections of climate change precipitation and temperature for the period 2021-2050 as provided by the IPCC-A1B emission scenario. In the climatic chambers the year climate was reduced to six months. The soils were analyzed for particle size distribution, aggregate stability by wet and dry sieving, and organic C content at the beginning and at the end of the trial. The soils showed different behaviour in terms of aggregate stability and dynamics of organic C in the diverse size fractions. The soils significantly differed in terms of initial mean weight diameter (MWD) (CAS>MED>BOV). A general reduction of MWD in all sites was observed at the end of the experiment, with the increase of the smallest aggregate fractions (0.250-0.05 mm). In particular, BOV showed the maximum decrease of the aggregate stability and MED the lowest. C distribution in aggregate fractions significantly

  20. Colonization of Wheat Roots by an Exopolysaccharide-Producing Pantoea agglomerans Strain and Its Effect on Rhizosphere Soil Aggregation

    PubMed Central

    Amellal, N.; Burtin, G.; Bartoli, F.; Heulin, T.

    1998-01-01

    The effect of bacterial secretion of an exopolysaccharide (EPS) on rhizosphere soil physical properties was investigated by inoculating strain NAS206, which was isolated from the rhizosphere of wheat (Triticum durum L.) growing in a Moroccan vertisol and was identified as Pantoea aglomerans. Phenotypic identification of this strain with the Biotype-100 system was confirmed by amplified ribosomal DNA restriction analysis. After inoculation of wheat seedlings with strain NAS206, colonization increased at the rhizoplane and in root-adhering soil (RAS) but not in bulk soil. Colonization further increased under relatively dry conditions (20% soil water content; matric potential, −0.55 MPa). By means of genetic fingerprinting using enterobacterial repetitive intergenic consensus PCR, we were able to verify that colonies counted as strain NAS206 on agar plates descended from inoculated strain NAS206. The intense colonization of the wheat rhizosphere by these EPS-producing bacteria was associated with significant soil aggregation, as shown by increased ratios of RAS dry mass to root tissue (RT) dry mass (RAS/RT) and the improved water stability of adhering soil aggregates. The maximum effect of strain NAS206 on both the RAS/RT ratio and aggregate stability was measured at 24% average soil water content (matric potential, −0.20 MPa). Inoculated strain NAS206 improved RAS macroporosity (pore diameter, 10 to 30 μm) compared to the noninoculated control, particularly when the soil was nearly water saturated (matric potential, −0.05 MPa). Our results suggest that P. agglomerans NAS206 can play an important role in the regulation of the water content (excess or deficit) of the rhizosphere of wheat by improving soil aggregation. PMID:9758793

  1. Biochar Improves Soil Aggregate Stability and Water Availability in a Mollisol after Three Years of Field Application

    PubMed Central

    Zhang, Yulan; Yang, Lijie; Yu, Chunxiao; Yin, Guanghua; Doane, Timothy A.; Wu, Zhijie; Zhu, Ping; Ma, Xingzhu

    2016-01-01

    A field experiment was carried out to evaluate the effect of organic amendments on soil organic carbon, total nitrogen, bulk density, aggregate stability, field capacity and plant available water in a representative Chinese Mollisol. Four treatments were as follows: no fertilization (CK), application of inorganic fertilizer (NPK), combined application of inorganic fertilizer with maize straw (NPK+S) and addition of biochar with inorganic fertilizer (NPK+B). Our results showed that after three consecutive years of application, the values of soil bulk density were significantly lower in both organic amendment-treated plots than in unamended (CK and NPK) plots. Compared with NPK, NPK+B more effectively increased the contents of soil organic carbon, improved the relative proportion of soil macro-aggregates and mean weight diameter, and enhanced field capacity as well as plant available water. Organic amendments had no obvious effect on soil C/N ratio or wilting coefficient. The results of linear regression indicated that the improvement in soil water retention could be attributed to the increases in soil organic carbon and aggregate stability. PMID:27191160

  2. Neutral hydrolysable sugars, OC and N content across soil aggregate size fractions, as an effect of two different crop rotations

    NASA Astrophysics Data System (ADS)

    Angeletti, Carlo; Giannetta, Beatrice; Kölbl, Angelika; Monaci, Elga; Kögel-Knabner, Ingrid; Vischetti, Costantino

    2016-04-01

    This paper presents the results regarding the effects of two 13 years long crop rotations, on the composition of mineral associated neutral sugars, organic carbon (OC) and N concentration, across different aggregate size fractions. The two cropping sequences were characterized by different levels of N input from plant residues and tillage frequency. We also analysed the changes that occurred in soil organic matter (SOM) chemical composition following the cultivation in the two soils of winter wheat and chickpea on the same soils. The analysis of OC and N content across soil aggregate fractions allowed getting an insight into the role played by SOM chemical composition in the formation of organo-mineral associations, while neutral sugars composition provided information on mineral associated SOM origin and decomposition processes, as pentoses derive mostly from plant tissues and hexoses are prevalently of microbial origin. Soil samples were collected from two adjacent fields, from the 0-10 cm layer, in November 2011 (T0). For 13 years before the beginning of the experiment, one soil was cultivated mostly with alfalfa (ALF), while a conventional cereal-sunflower-legume rotation (CON) was carried out on the other. Winter wheat and chickpea were sown on the two soils during the following 2 growing seasons and the sampling was repeated after 18 months (T1). A combination of aggregates size and density fractionation was used to isolate OM associated with mineral particles in: macro-aggregates (>212 μm), micro-aggregates (<200 μm, > 63 μm) and silt and clay size particles (<63 μm). For every fraction, OC and N contents were measured by means of elemental analysis, while the content of the following neutral hydrolysable sugar monomers was measured via GC-FID: rhamnose, fucose, ribose, arabinose, xylose, mannose, galactose, glucose. OC and N contents were higher in ALF as compared to CON for every aggregate fraction, both at T0 and T1. During the 18-months cultivation

  3. Modeling Soil Carbon Dynamics in Northern Forests: Effects of Spatial and Temporal Aggregation of Climatic Input Data.

    PubMed

    Dalsgaard, Lise; Astrup, Rasmus; Antón-Fernández, Clara; Borgen, Signe Kynding; Breidenbach, Johannes; Lange, Holger; Lehtonen, Aleksi; Liski, Jari

    2016-01-01

    Boreal forests contain 30% of the global forest carbon with the majority residing in soils. While challenging to quantify, soil carbon changes comprise a significant, and potentially increasing, part of the terrestrial carbon cycle. Thus, their estimation is important when designing forest-based climate change mitigation strategies and soil carbon change estimates are required for the reporting of greenhouse gas emissions. Organic matter decomposition varies with climate in complex nonlinear ways, rendering data aggregation nontrivial. Here, we explored the effects of temporal and spatial aggregation of climatic and litter input data on regional estimates of soil organic carbon stocks and changes for upland forests. We used the soil carbon and decomposition model Yasso07 with input from the Norwegian National Forest Inventory (11275 plots, 1960-2012). Estimates were produced at three spatial and three temporal scales. Results showed that a national level average soil carbon stock estimate varied by 10% depending on the applied spatial and temporal scale of aggregation. Higher stocks were found when applying plot-level input compared to country-level input and when long-term climate was used as compared to annual or 5-year mean values. A national level estimate for soil carbon change was similar across spatial scales, but was considerably (60-70%) lower when applying annual or 5-year mean climate compared to long-term mean climate reflecting the recent climatic changes in Norway. This was particularly evident for the forest-dominated districts in the southeastern and central parts of Norway and in the far north. We concluded that the sensitivity of model estimates to spatial aggregation will depend on the region of interest. Further, that using long-term climate averages during periods with strong climatic trends results in large differences in soil carbon estimates. The largest differences in this study were observed in central and northern regions with strongly

  4. Modeling Soil Carbon Dynamics in Northern Forests: Effects of Spatial and Temporal Aggregation of Climatic Input Data

    PubMed Central

    Dalsgaard, Lise; Astrup, Rasmus; Antón-Fernández, Clara; Borgen, Signe Kynding; Breidenbach, Johannes; Lange, Holger; Lehtonen, Aleksi; Liski, Jari

    2016-01-01

    Boreal forests contain 30% of the global forest carbon with the majority residing in soils. While challenging to quantify, soil carbon changes comprise a significant, and potentially increasing, part of the terrestrial carbon cycle. Thus, their estimation is important when designing forest-based climate change mitigation strategies and soil carbon change estimates are required for the reporting of greenhouse gas emissions. Organic matter decomposition varies with climate in complex nonlinear ways, rendering data aggregation nontrivial. Here, we explored the effects of temporal and spatial aggregation of climatic and litter input data on regional estimates of soil organic carbon stocks and changes for upland forests. We used the soil carbon and decomposition model Yasso07 with input from the Norwegian National Forest Inventory (11275 plots, 1960–2012). Estimates were produced at three spatial and three temporal scales. Results showed that a national level average soil carbon stock estimate varied by 10% depending on the applied spatial and temporal scale of aggregation. Higher stocks were found when applying plot-level input compared to country-level input and when long-term climate was used as compared to annual or 5-year mean values. A national level estimate for soil carbon change was similar across spatial scales, but was considerably (60–70%) lower when applying annual or 5-year mean climate compared to long-term mean climate reflecting the recent climatic changes in Norway. This was particularly evident for the forest-dominated districts in the southeastern and central parts of Norway and in the far north. We concluded that the sensitivity of model estimates to spatial aggregation will depend on the region of interest. Further, that using long-term climate averages during periods with strong climatic trends results in large differences in soil carbon estimates. The largest differences in this study were observed in central and northern regions with

  5. Measurement of particle size distribution of soil and selected aggregate sizes using the hydrometer method and laser diffractometry

    NASA Astrophysics Data System (ADS)

    Guzmán, G.; Gómez, J. A.; Giráldez, J. V.

    2010-05-01

    Soil particle size distribution has been traditionally determined by the hydrometer or the sieve-pipette methods, both of them time consuming and requiring a relatively large soil sample. This might be a limitation in situations, such as for instance analysis of suspended sediment, when the sample is small. A possible alternative to these methods are the optical techniques such as laser diffractometry. However the literature indicates that the use of this technique as an alternative to traditional methods is still limited, because the difficulty in replicating the results obtained with the standard methods. In this study we present the percentages of soil grain size determined using laser diffractometry within ranges set between 0.04 - 2000 μm. A Beckman-Coulter ® LS-230 with a 750 nm laser beam and software version 3.2 in five soils, representative of southern Spain: Alameda, Benacazón, Conchuela, Lanjarón and Pedrera. In three of the studied soils (Alameda, Benacazón and Conchuela) the particle size distribution of each aggregate size class was also determined. Aggregate size classes were obtained by dry sieve analysis using a Retsch AS 200 basic ®. Two hundred grams of air dried soil were sieved during 150 s, at amplitude 2 mm, getting nine different sizes between 2000 μm and 10 μm. Analyses were performed by triplicate. The soil sample preparation was also adapted to our conditions. A small amount each soil sample (less than 1 g) was transferred to the fluid module full of running water and disaggregated by ultrasonication at energy level 4 and 80 ml of sodium hexametaphosphate solution during 580 seconds. Two replicates of each sample were performed. Each measurement was made for a 90 second reading at a pump speed of 62. After the laser diffractometry analysis, each soil and its aggregate classes were processed calibrating its own optical model fitting the optical parameters that mainly depends on the color and the shape of the analyzed particle. As a

  6. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects.

    PubMed

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F; Carroll, Natalie J; Applegate, Bruce; Turco, Ronald F

    2016-06-16

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials.

  7. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects

    NASA Astrophysics Data System (ADS)

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F.; Carroll, Natalie J.; Applegate, Bruce; Turco, Ronald F.

    2016-06-01

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials.

  8. Influence of fullerene (C60) on soil bacterial communities: aqueous aggregate size and solvent co-introduction effects

    PubMed Central

    Tong, Zhong-Hua; Bischoff, Marianne; Nies, Loring F.; Carroll, Natalie J.; Applegate, Bruce; Turco, Ronald F.

    2016-01-01

    Fullerene C60 nanoparticles are being used in broad range of applications. It is important to assess their potential impacts in the environment. We evaluated the effects of C60 introduced as aqueous suspensions of nC60 aggregates of different particle size or via organic solvents on soils with different organic matter contents in this study. Impacts of the application were evaluated by measuring total microbial biomass, metabolic activity and bacterial community structure. Results show that nC60 aggregates, introduced as an aqueous suspension, had size-dependent effects on soil bacterial community composition in the low organic matter system, but induced minimal change in the microbial biomass and metabolic activity in soils with both high and low organic matter contents. Fullerene C60, co-introduced via an organic solvent, did not influence the response of soil microbes to the organic solvents. Our results suggest that nC60 aggregates of smaller size may have negative impact on soil biota and soil organic matter may play a key role in modulating the environmental effect of nanomaterials. PMID:27306076

  9. Contribution of arbuscular mycorrhizal fungi of sedges to soil aggregation along an altitudinal alpine grassland gradient on the Tibetan Plateau.

    PubMed

    Li, Xiaoliang; Zhang, Junling; Gai, Jingping; Cai, Xiaobu; Christie, Peter; Li, Xiaolin

    2015-08-01

    The diversity of arbuscular mycorrhizal fungi (AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of Kobresia pygmaea C.B. Clarke and Carex pseudofoetida Kük. in alpine Kobresia pastures along an elevational transect (4149-5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae (EMH) and total glomalin-related soil protein (T-GRSP). The influence of plant richness was mainly due to its indirect influence on T-GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co-occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands.

  10. Biotic interactions mediate the influence of bird colonies on vegetation and soil chemistry at aggregation sites.

    PubMed

    Natusch, Daniel James Deans; Lyons, Jessica Ann; Brown, Gregory P; Shine, Richard

    2017-02-01

    Colonial-nesting organisms can strongly alter the chemical and biotic conditions around their aggregation sites, with cascading impacts on other components of the ecosystem. In tropical Australia, Metallic Starlings (Aplonis metallica) nest in large colonies far above the forest canopy, in emergent trees. The ground beneath those trees is open, in stark contrast to the dense foliage all around. We surveyed the areas beneath 27 colony trees (and nearby randomly chosen trees lacking bird colonies) to quantify the birds' impacts on soil and vegetation characteristics, and to test alternative hypotheses about the proximate mechanisms responsible for the lack of live vegetation beneath colony trees. Nutrient levels were greatly elevated beneath colony trees (especially, those with larger colonies), potentially reaching levels toxic to older trees. However, seedlings thrived in the soil from beneath colony trees. The primary mechanism generating open areas beneath colony trees is disturbance by scavengers (feral pigs and native Turkeys) that are attracted in vast numbers to these nutrient hotspots. Seedlings flourished within exclosures inaccessible to vertebrate herbivores, but were rapidly consumed if unprotected. Our results contrast with previous studies of colonies of seabirds on remote islands, where a lack of large terrestrial herbivores results in bird colonies encouraging rather than eliminating vegetation in areas close to the nesting site. In our continental study system, scavengers may rapidly dilute the spatial heterogeneity generated by the massive nutrient subsidy from bird colonies.

  11. Positive evolution features in soil restoration assessed by means of glomalin and its relationship to aggregate stability

    NASA Astrophysics Data System (ADS)

    Luna Ramos, Lourdes; Miralles Mellado, Isabel; Gispert Negrell, María; Pardini, Giovanni; Solé Benet, Albert

    2014-05-01

    Restoration of limestone quarries in arid environments mainly consists of regenerating a highly degraded soil and/or creating a soil-like substrate with minimal physico-chemical and biological properties. In an experimental soil restoration in limestone quarries from Sierra de Gádor (Almería), SE Spain, with the aim to improve soil/substrate properties and to reduce evaporation and erosion, 18 plots 15 x 5 m were prepared to test organic amendments (sludge, compost, control) and different mulches (gravel, chopped forest residue, control). In order to evaluate the soil quality of the different treatments, their chemical, physical and biological properties were analyzed. Among the most efficient biological indicators are arbuscular mycorrhizal fungi (AMF). AMF play an important role in aggregate stability due to the production of a glycoprotein called glomalin. Therefore, the aim of this study was to quantify, 5 years after the start the experiment, the content of total glomalin (TG) and to analyze its relationship with other soil parameters such as organic matter (OM) and aggregate stability soil (AE). Results indicated a remarkable effect of organic amendments on glomalin content, which was higher in the treatments with compost (6.96 mg g -1) than in sludge and control (0.54 and 0.40 mg g-1, respectively). Amendments also significantly influenced aggregate stability: the highest values were recorded in treatments with sludge and compost (23.14 and 25.09%, respectively) compared to control (13.37%). The gravel mulch had a negative influenced on AE: an average of 16% compared to 23.4% for chopped forest residues and 23.1% of control. Data showed a positive and significant correlation between values of TG and OM content (r = 0.95). We also found a positive and significant correlation between abundance of TG and AE when OM contents were lower than 4% (r = 0.93), however, there was no significant correlation to higher OM when it was higher than 4% (r = 0.34). This

  12. Changes in Soil Aggregate, Carbon, and Nitrogen Storages Following the Conversion of Cropland to Alfalfa Forage Land in the Marginal Oasis of Northwest China

    NASA Astrophysics Data System (ADS)

    Su, Yong Zhong; Liu, Wen Jie; Yang, Rong; Chang, Xue Xiang

    2009-06-01

    Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa ( Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha-1 year-1 and 0.04 Mg N ha-1 year-1 following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2-0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25-0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with

  13. Effects of sandy desertified land rehabilitation on soil carbon sequestration and aggregation in an arid region in China.

    PubMed

    Su, Yong Zhong; Wang, Xue Fen; Yang, Rong; Lee, Jaehoon

    2010-11-01

    The rehabilitation of sandy desertified land in semi-arid and arid regions has a great potential to increase carbon sequestration and improve soil quality. Our objective was to investigate the changes in the soil carbon pool and soil properties of surface soil (0-15 cm) under different types of rehabilitation management. Our study was done in the short-term (7 years) and long-term (32 years) desertification control sites in a marginal oasis of northwest China. The different management treatments were: (1) untreated shifting sand land as control; (2) sand-fixing shrubs with straw checkerboards; (3) poplar (Populus gansuensis) shelter forest; and (4) irrigated cropland after leveling sand dune. The results showed that the rehabilitation of severe sandy desertified land resulted in significant increases in soil organic C (SOC), inorganic C, and total N concentrations, as well as enhanced soil aggregation. Over a 7-year period of revegetation and cultivation, SOC concentration in the recovered shrub land, forest land and irrigated cropland increased by 4.1, 14.6 and 11.9 times compared to the control site (shifting sand land), and increased by 11.2, 17.0 and 23.0 times over the 32-year recovery period. Total N, labile C (KMnO(4)-oxidation C), C management index (CMI) and inorganic C (CaCO(3)-C) showed a similar increasing trend as SOC. The increased soil C and N was positively related to the accumulation of fine particle fractions. The accumulation of silt and clay, soil C and CaCO(3) enhanced the formation of aggregates, which was beneficial to mitigate wind erosion. The percentage of >0.25 mm dry aggregates increased from 18.0% in the control site to 20.0-87.2% in the recovery sites, and the mean weight diameter (MWD) of water-stable aggregates significantly increased, with a range of 0.09-0.30 mm at the recovery sites. Long-term irrigation and fertilization led to a greater soil C and N accumulation in cropland than in shrub and forest lands. The amount of soil C

  14. Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Bol, R.; Willbold, S.; Vereecken, H.; Klumpp, E.

    2015-11-01

    To maximize crop productivity fertilizer P is generally applied to arable soils, a significant proportion of which becomes stabilized by mineral components and in part subsequently becomes unavailable to plants. However, little is known about the relative contributions of the different organic and inorganic P bound to Fe/Al oxides in the smaller soil particles. Alkaline (NaOH-Na2EDTA) extraction with solution 31P-nuclear magnetic resonance (31P-NMR) spectroscopy is considered a reliable method for extracting and quantifying organic P and (some) inorganic P. However, any so-called residual P after the alkaline extraction has remained unidentified. Therefore, in the present study, the amorphous (a) and crystalline (c) Fe/Al oxide minerals and related P in soil aggregate-sized fractions (> 20, 2-20, 0.45-2 and < 0.45 μm) were specifically extracted by oxalate (a-Fe/Al oxides) and dithionite-citrate-bicarbonate (DCB, both a- and c-Fe/Al oxides). These soil aggregate-sized fractions with and without the oxalate and DCB pre-treatments were then sequentially extracted by alkaline extraction prior to solution 31P-NMR spectroscopy. This was done to quantify the P associated with a- and c-Fe/Al oxides in both alkaline extraction and the residual P of different soil aggregate-sized fractions. The results showed that overall P contents increased with decreasing size of the soil aggregate-sized fractions. However, the relative distribution and speciation of varying P forms were found to be independent of soil aggregate-size. The majority of alkaline-extractable P was in the a-Fe/Al oxide fraction (42-47 % of total P), most of which was ortho-phosphate (36-41 % of total P). Furthermore, still significant amounts of particularly monoester P were bound to these oxides. Intriguingly, however, Fe/Al oxides were not the main bonding sites for pyrophosphate. Residual P contained similar amounts of total P associated with both a- (11-15 % of total P) and c-Fe oxides (7-13 % of total P

  15. Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Bol, R.; Willbold, S.; Vereecken, H.; Klumpp, E.

    2015-07-01

    To maximize crop productivity fertilizer P is generally applied to arable soils, a significant proportion of which becomes stabilized by mineral components and in part subsequently becomes unavailable to plants. However, little is known about the relative contributions of the different organic and inorganic P bound to Fe/Al oxides in the smaller soil particles. The alkaline (NaOH-Na2EDTA) extraction with solution 31P-nuclear magnetic resonance (31P-NMR) spectroscopy is considered as a reliable method for extracting and quantifying organic P and (some) inorganic P. However, any so-called residual P after the alkaline extraction has remained unidentified. Therefore, in the present study, the amorphous (a) and crystalline (c) Fe/Al oxide minerals and related P in soil aggregate-sized fractions (> 20, 2-20, 0.45-2 and < 0.45 μm) were specifically extracted by oxalate (a-Fe/Al oxides) and dithionite (DCB, both a- and c-Fe/Al oxides). These soil aggregate-sized fractions with and without the oxalate and DCB pre-treatments were then sequentially extracted by alkaline extraction prior to solution 31P-NMR spectroscopy. This was done to quantify the various chemical P forms which were associated with a- and c-Fe/Al oxides both in alkaline extraction and in the residual P of different soil aggregate-sized fractions. The results showed that overall P contents increased with decreasing size of the soil aggregate-sized fractions. However, the relative distribution and speciation of varying P forms were found to be independent of soil aggregate-size. The majority of alkaline extractable P was in the a-Fe/Al oxide fraction (42-47 % of total P), most of which was orthophosphate (36-41 % of total P). Furthermore, still significant amounts of particularly monoester P were bound to the oxides. Intriguingly, however, Fe/Al oxides were not the main bonding sites for pyrophosphate. Residual P contained similar amounts of total P associated with both a- (10-13 % of total P) and c

  16. Changes of microbial activities and soil aggregation in rhizosphere soil of lettuce plants by drought and the possible influence of inoculation with AM fungi and/or PGPR

    NASA Astrophysics Data System (ADS)

    Kohler, J.; Caravaca, F.; Roldán, A.

    2009-04-01

    The effect of different arbuscular mycorrhizal (AM) fungi, Glomus intraradices (Schenk & Smith) or Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and plant growth-promoting rhizobacteria (PGPR) (Pseudomonas mendocina Palleroni), alone or in combination, on structural stability and microbial activity in the rhizosphere soil of Lactuca sativa L. was assessed under well-watered conditions and two levels of drought. Desiccation caused an increase in aggregate stability and water-soluble and total carbohydrates but there were no significant differences among treated soils and the control soil. The glomalin-related soil protein (GRSP) levels in both the <2 mm and 0.2-4 mm soil fractions increased with medium water stress, whereas under severe water stress they did not differ with respect to those of well-watered soils. The values of GRSP in soils inoculated with PGPR and AM fungi were higher than in the control or fertilised soil under well-watered and severe-drought conditions, while under medium-drought conditions all soils showed similar GRSP values. Soils inoculated with AM fungi and PGPR generally presented higher dehydrogenase and phosphatase activities than the control soil, independent of the water regime.

  17. Field investigations of soils at TA-19, TA-26, TA-73 and TA-0, SWMU aggregate 0-D and 016

    SciTech Connect

    McFadden, L.D.

    1995-03-01

    Field based investigations of the general soil-geomorphic characteristics were carried out at TA-19, -26, -73, -0, Aggregate 0-D and -016 in order to provide information for utilization in ongoing and anticipated LANL ERP (Environmental Restoration Project) activities at these sites. These investigations show that soils exhibiting diverse morphologic character, varying ages, and relations to landforms characterize these sites. A review of recent and ongoing soils studies also shows that soil textural, chemical, and mineralogical characteristics may profoundly influence the migration and/or retardation of a variety of potential contaminants initially placed in direct contact with soils, or that encounter soils during subsurface percolation or discharge. Soil-geomorphic relations also provide important insights into recent site erosion, deposition or other surficial processes that must, be considered as part of environmental assessment of a given site and remediation; and, the planned geomorphic mapping activities at each site, as well as other associated activities (e.g, geophysical survey, site sampling) are accordingly appropriate and necessary with respect to identification of significant soil relations at each site. Specific and general recommendations in consideration of important findings regarding the possible impacts of soil development of the nature of contaminant behavior at various sites are provided to help guide sampling and analysis activities during ERP investigations outlined in the RFI Work Plan for Operational Unit-1071.

  18. Temporal dynamics of soil aggregates and microbial parameters in permanent and recently established grasslands in the temperate zone

    NASA Astrophysics Data System (ADS)

    Linsler, Deborah; Taube, Friedhelm; Geisseler, Daniel; Joergensen, Rainer Georg; Ludwig, Bernard

    2015-04-01

    While changes over time in soil aggregation or microbial parameters are well studied for arable soils, much less is known about such temporal variations in grassland soils. The objective of the present study was to determine the changes that occur within one year (between October 2010 and October 2011) for water-stable aggregate, microbial biomass carbon (Cmic) and ergosterol (as a proxy for fungal biomass) concentrations of a sandy soil under a permanent and recently established grasslands The analyzed treatments were (i) permanent grassland, (ii) grassland re-established after tillage of previous permanent grassland, and (iii) grassland established on arable land (both in September 2010). Temporal variations were found for the aggregate distribution and ergosterol concentration in the permanent grassland. For instance, the concentration of large macroaggregates (>2000 μm) in the surface soil (0-10 cm) varied strongly, with the highest concentration (mean ± standard error) in October 2011 (666 ± 12 g kg-1) and a 3.2-fold lower concentration in May 2011. An explanation could be less rainfall and decreasing soil moisture contents in May compared to October, which may have decreased the stability of this fraction. A multiple linear regression analysis showed that the large macroaggregate concentration was well described (R2=0.60) by the gravimetric moisture content, the Cmic concentration and the pH. After the tillage event in the grassland and the subsequent grassland renovation, the concentrations of large macroaggregate, Cmic and ergosterol decreased in the surface soil, while no difference was found in the soil profile (0-40 cm). In the first year after the conversion of arable land into grassland, the concentrations of Cmic and ergosterol increased by a factor of 1.4 and 3.3, respectively, in the surface soil layer, while the macroaggregate concentration was not affected. This study indicates that the aggregate dynamic in grassland is not only affected by

  19. Modelling the effect of aggregates on N2O emission from denitrification in an agricultural peat soil

    NASA Astrophysics Data System (ADS)

    Stolk, P. C.; Hendriks, R. F. A.; Jacobs, C. M. J.; Moors, E. J.; Kabat, P.

    2011-09-01

    Nitrous oxide (N2O) emissions are highly variable in time, with high peak emissions lasting a few days to several weeks and low background emissions. This temporal variability is poorly understood which hampers the simulation of daily N2O emissions. In structured soils, like clay and peat, aggregates hamper the diffusion of oxygen, which leads to anaerobic microsites in the soil, favourable for denitrification. Diffusion of N2O out of the aggregates is also hampered, which leads to delayed emissions and increased reduction of N2O to N2. In this model simulation study we investigate the effect of aggregates in soils on the N2O emissions. We present a parameterization to simulate the effects of aggregates on N2O production by denitrification and on N2O reduction. The parameterization is based on the mobile-immobile model concept. It was implemented in a field-scale hydrological-biogeochemical model combination. We compared the simulated fluxes with observed fluxes from a fertilized and drained peat soil under grass. The results of this study show that aggregates strongly affect the simulated N2O emissions: peak emissions are lower, whereas the background emissions are slightly higher. Including the effect of aggregates caused a 40% decrease in the simulated annual emissions relative to the simulations without accounting for the effects of aggregates. The new parameterization significantly improved the model performance regarding simulation of observed daily N2O fluxes; r2 and RMSE improved from 0.11 and 198 g N2O-N ha-1 d-1 to 0.41 and 40 g N2O-N ha-1 d-1, respectively. Our analyses of the model results show that aggregates have a larger impact on the reduction than on the production of N2O. Reduction of N2O is more sensitive to changes in the drivers than production of N2O and is in that sense the key to understanding N2O emissions from denitrification. The effects of changing environmental conditions on reduction of N2O relative to N2O production strongly depend on

  20. [Impact of Land Utilization Pattern on Distributing Characters of Labile Organic Carbon in Soil Aggregates in Jinyun Mountain].

    PubMed

    Li, Rui; Jiang, Chang-sheng; Hao, Qing-ju

    2015-09-01

    Four land utilization patterns were selected for this study in Jinyun mountain, including subtropical evergreen broad-leaved forest (abbreviation: forest), sloping farmland, orchard and abandoned land. Soil samples were taken every 10 cm in the depth of 60 cm soil and proportions of large macroaggregates (> 2 mm), small macroaggregates (0. 25-2 mm), microaggregates (0. 053 - 0. 25 mm) and silt + clay (<0. 053 mm) were obtained by wet sieving method to measure the content of organic carbon and labile organic carbon in each aggregate fraction and analyze impacts of land uses on organic carbon and labile organic carbon of soil aggregates. LOC content of four soil aggregates were significantly reduced with the increase of soil depth; in layers of 0-60 cm soil depth, our results showed that LOC contents of forest and abandoned land were higher than orchard and sloping farmland. Reserves of labile organic carbon were estimated by the same soil quality, it revealed that forest (3. 68 Mg.hm-2) > abandoned land (1. 73 Mg.hm-2) > orchard (1. 43 Mg.hm-2) >sloping farmland (0.54 Mg.hm-2) in large macroaggregates, abandoned land (7.77, 5. 01 Mg.hm-2) > forest (4. 96, 2.71 Mg.hm-2) > orchard (3. 33, 21. 10 Mg.hm-2) > sloping farmland (1. 68, 1. 35 Mg.hm-2) in small macroaggregates and microaggregates, and abandoned land(4. 32 Mg.hm-2) > orchard(4. 00 Mg.hm-2) > forest(3. 22 Mg.hm-2) > sloping farmland (2.37 Mg.hm-2) in silt + clay, forest and abandoned land were higher than orchard and sloping farmland in other three soil aggregates except silt + clay. It was observed that the level of organic carbon and labile organic carbon were decreased when bringing forest under cultivation to orchard or farmland, and augments on organic carbon and labile organic carbon were found after exchanging farmland to abandoned land. The most reverses of forest and abandoned land emerged in small macroaggregates, orchard and sloping farmland were in microaggregates. That was, during the

  1. Soil total carbon content, aggregation, bulk density, and penetration resistance of croplands and nearby grasslands

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Converting native grassland (NGL) to cropland (CL) decreases soil organic matter contents (components of soil total carbon contents, STCCs), which often leads to soil degradation. Reestablishing grass on CL generally increases soil organic matter, which improves soil conditions. This study was condu...

  2. Water stability of aggregates in subtropical and tropical soils (Georgia and China) and its relationships with the mineralogy and chemical properties

    NASA Astrophysics Data System (ADS)

    Alekseeva, T. V.; Sokolowska, Z.; Hajnos, M.; Alekseev, A. O.; Kalinin, P. I.

    2009-04-01

    Water-stable aggregates isolated from three subtropical and one tropical soil (Western Georgia and China) were studied for their organic carbon, cation exchange capacity (CEC), specific surface area, magnetic susceptibility, and total chemical elements. The soils were also studied for their particle-size distribution, mineralogy, and nonsilicate Fe and Al oxides. Describe the water stability, three indices have been used: the content of water-stable macroaggregates (>0.25 mm), the mean weighted diameter of the aggregates, and the numerical aggregation index. The yellow-cinnamonic soil (China) was neutral, and the three other soils were acid. The soils were degraded with a low content of organic matter. The yellow-cinnamonic soil was characterized by the lowest water stability due to the predominantly vermiculite composition of the clay. The high water stability of the Oxisol structure was determined by the kaolinites and high content of oxides. In three out of the four soils studied, the hierarchical levels of the soil structure organization were defined; they were identified by the content of organic matter and the Ca + Mg (in Oxisols). Iron oxides mainly participated in the formation of micro-aggregates; Al and Mn contributed to the formation of macroaggregates. The water-stable aggregates acted as sorption geochemical barriers and accumulated Pb, Zn, Cd, Cs, and other trace elements up to concentrations exceeding their levels in the soil by 5 times and more. The highest correlations were obtained with CEC, Mn, and P rather than with organic carbon and Fe.

  3. Effect of organic fertilizer and biochar application on soil macro-aggregate formation and organic carbon turnover

    NASA Astrophysics Data System (ADS)

    Grunwald, Dennis; Kaiser, Michael; Ludwig, Bernard

    2015-04-01

    Macro-aggregates are important for the organic matter dynamic and thus the productivity of sustainably managed soils. To date, less is known about the influence of biochar in comparison to other commonly used organic soil additives on the formation of macro-aggregates and organic carbon turnover. Here we aimed to analyze the effects of biochar applied individually and in combination with slurry versus the effects of the individual application of slurry and manure on macro-aggregate yield, the associated organic carbon concentration, and the organic carbon mineralization. For this, we crushed the macro-aggregate fraction (>250 μm) of two different soils that were then mixed with biochar (combustion temperature: 550° C, feedstock: woodchips) and/or cattle-slurry or cattle-manure and incubated within a microcosm experiment at 5° C, 15° C, and 25° C. We monitored the CO2 evolution during the incubation experiment. After four and eight weeks, we determined the dry mass and the carbon concentration of the newly formed macro-aggregates (>250 μm) and the microbial biomass carbon concentration. Carbon mineralization was modelled assuming first-order kinetics and using a rate modifying factor for the temperature (taken from the RothC-26.3 model). Two pools were considered (mineralization of the native organic matter from the control soils and mineralization of the substrates added) in each treatment and the models were calibrated to the C mineralization data at 25° C, whereas the data for 15° C and 5° C were used for validation. Independent from the incubation temperature and the duration of the experiment, the individual application of biochar did not show significant effects on the macro-aggregate yield, the associated carbon concentration, or the CO2 emission rate compared to the control sample receiving no amendments. For the application of biochar in combination with slurry, we observed only for the 15° C treatment higher CO2 emission rates in combination with

  4. Tillage and liming effects on aggregate distribution and associated carbon and nitrogen in acid soils of SW Spain

    NASA Astrophysics Data System (ADS)

    Gómez-Paccard, Clara; Zabaleta, Javier; Benito, Marta; León, Paloma; Mariscal-Sancho, Ignacio; Espejo, Rafael; Hontoria, Chiquinquirá

    2013-04-01

    Beneficial effects of conservation tillage are well known on a wide variety of environmental aspects. The lack of ploughing in no till systems conserves soil structure, enhances the accumulation of organic carbon in the surface layer and promotes the development of soil microorganisms. On the other hand, liming is a common practice in acid soils. Lime raises the pH, reduces Al toxicity enhancing root development, but controversial results have been found about the effects of liming on soil structure. Ultisols from SW of Spain present severe chemical constraints as poor nutrient availability and high Al contents in the exchange complex. On the other hand, traditional practices as conventional tillage led to a dramatic decrease on soil organic carbon and a degraded soil structure. No till plus liming might be recommendable to achieve a sustainable and productive agriculture in these particular soils, but little is known about the effect of these practices on soil structure when applied together. The aim of this study was to evaluate the effect of traditional tillage (TT) versus no tillage (NT), and liming versus no liming on aggregate size distribution and associated carbon and nitrogen. The study was conducted on a Plinthic Palexerult (Soil Survey Staff, 1999) in the Cañamero's Raña (SW Spain) under Mediterranean climate (mean annual temperature: 15.0° C; mean annual precipitation: 869 mm). The experimental design was a split-plot with four replications. The main factor was tillage (no till versus traditional till) while the second was the inclusion or not of Ca-amendment (sugar foam plus red gypsum). Samples were collected in 2011 after six years of treatment at a 0-5, 5-10 and 10-25 cm depths. The aggregate distribution was determined by wet sieving method to separate four aggregate size classes: (i) >2000 µm (large macroaggregates), (ii) 250-2000 µm (small macroaggregates), (iii) 53-250 µm (microaggregates), (iv) <53 µm (silt and clay fraction). Soil

  5. Use of morphometric soil aggregates parameters to evaluate the reclamation process in mined areas located at amazon forest - Brazil

    NASA Astrophysics Data System (ADS)

    Ribeiro, A. I.; Fengler, F. H.; Longo, R. M.; Mello, G. F.; Damame, D. B.; Crowley, D. E.

    2015-12-01

    Brazil has a high mineral potential that have been explored over the years. A large fraction of these mineral resources are located in Amazon region, which is known for its large biodiversity and world climate importance. As the policies that control the Amazon preservation are relatively new, several mining activities have been exploring the Amazon territory, promoting a large process of degradation. Once the mining activities have a high potential of environmental changes the government created polices to restrain the mining in Amazon forests and obligate mining companies to reclaim theirs minded areas. However, the measurement of reclamation development still is a challenging task for the Professionals involved. The volume and complexity of the variables, allied to the difficulty in identifying the reclamation of ecosystem functionalities are still lack to ensure the reclamation success. In this sense this work aims to investigate the representativeness of morphometric soil aggregates parameters in the understanding of reclamation development. The study area is located in the National Forest of Jamari, State of Rondônia. In the past mining companies explored the region producing eight closed mines that are now in reclamation process. The soil aggregates morphometric measurements: geometric mean diameter (GMD), aggregate circularity index, and aggregate roundness, were choose based in its obtaining facility, and their association to biological activity. To achieve the proposed objective the aggregates of eight sites in reclamation, from different closed mines, where chosen and compared to Amazon forest and open mine soil aggregates. The results were analyzed to one way ANOVA to identifying differences between areas in reclamation, natural ecosystem, and open mine. It was obtained differences for GMD and circularity index. However, only the circularity index allowed to identifying differences between the reclamation sites. The results allowed concluding: (1

  6. Using fourier-transform mid-infrared spectroscopy to distinguish soil organic matter composition dynamics in aggregate fractions of two agroecosystems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The relationship between soil organic carbon (SOC) content and quality of SOC as impacted by land management is not well understood and may influence long-term storage of SOC. To better understand the potential for SOC storage in specific aggregate pools (i.e. physically protected intra-aggregate C)...

  7. Aggregating available soil water holding capacity data for crop yield models

    NASA Technical Reports Server (NTRS)

    Seubert, C. E.; Daughtry, C. S. T.; Holt, D. A.; Baumgardner, M. F.

    1984-01-01

    The total amount of water available to plants that is held against gravity in a soil is usually estimated as the amount present at -0.03 MPa average water potential minus the amount present at -1.5 MPa water potential. This value, designated available water-holding capacity (AWHC), is a very important soil characteristic that is strongly and positively correlated to the inherent productivity of soils. In various applications, including assessing soil moisture status over large areas, it is necessary to group soil types or series as to their productivity. Current methods to classify AWHC of soils consider only total capacity of soil profiles and thus may group together soils which differ greatly in AWHC as a function of depth in the profile. A general approach for evaluating quantitatively the multidimensional nature of AWHC in soils is described. Data for 902 soil profiles, representing 184 soil series, in Indiana were obtained from the Soil Characterization Laboratory at Purdue University. The AWHC for each of ten 150-mm layers in each soil was established, based on soil texture and parent material. A multivariate clustering procedure was used to classify each soil profile into one of 4, 8, or 12 classes based upon ten-dimensional AWHC values. The optimum number of classes depends on the range of AWHC in the population of oil profiles analyzed and on the sensitivity of a crop to differences in distribution of water within the soil profile.

  8. C and N accumulations in soil aggregates determine nitrous oxide emissions from cover crop treated rice paddy soils during fallow season.

    PubMed

    Pramanik, Prabhat; Haque, Md Mozammel; Kim, Sang Yoon; Kim, Pil Joo

    2014-08-15

    Combination of leguminous and non-leguminous plant residues are preferably applied in rice paddy soils to increase the rate of organic matter mineralization and to improve plant growth. However, organic matter addition facilitates methane (CH4) emission from rice paddy soil. Mineralization of organic nitrogen (N) increases NO3-N concentrations in soil, which are precursors for the formation of nitrous oxide (N2O). However, N2O is a minor greenhouse gas emitted from submerged rice field and hence is not often considered during calculation of total global warming potential (GWP) during rice cultivation. The hypothesis of this study was that fluxes of N2O emissions might be changed after removal of flooded water from rice field and the effect of cover crops on N2O emissions in the fallow season might be interesting. However, the effects of N-rich plant residues on N2O emission rates in the fallow season and its effect on annual GWP were not studied before. In this experiment, combination of barley (non-leguminous) and hairy vetch (leguminous) biomasses were applied at 9 Mg ha(-1) and 27 Mg ha(-1) rates in rice paddy soil. Cover crop application significantly increased CH4 emission flux while decreased N2O emissions during rice cultivation. The lowest N2O emission was observed in 27 Mg ha(-1) cover crop treated plots. Cover crop applications increased N contents in soil aggregates especially in smaller aggregates (<250 μm), and that proportionately increased the N2O emission potentials of these soil aggregates. Fluxes of N2O emissions in the fallow season were influenced by the N2O emission potentials of soil aggregates and followed opposite trends as those observed during rice cultivation. Therefore, it could be concluded that the doses of cover crop applications for rice cultivation should not be optimized considering only CH4, but N2O should also be considered especially for fallow season to calculate total GWP.

  9. Synchrotron-based Infrared-microspectroscopy reveals the impact of land management on carbon storage in soil micro-aggregates

    NASA Astrophysics Data System (ADS)

    Hernandez-Soriano, Maria C.; Dalal, Ram C.; Menzies, Neal W.; Kopittke, Peter M.

    2015-04-01

    Carbon stabilization in soil microaggregates results from chemical and biological processes that are highly sensitive to changes in land use. Indeed, such processes govern soil capability to store carbon, this being essential for soil health and productivity and to regulate emissions of soil organic carbon (SOC) as CO2. The identification of carbon functionalities using traditional mid-infrared analysis can be linked to carbon metabolism in soil but differences associated to land use are generally limited. The spatial resolution of synchrotron-based Infrared-microspectroscopy allows mapping microaggregate-associated forms of SOC because it has 1000 times higher brightness than a conventional thermal globar source. These maps can contribute to better understand molecular organization of SOC, physical protection in the soil particles and co-localization of carbon sources with microbial processes. Spatially-resolved analyses of carbon distribution in micro-aggregates (<200 μm diameter) have been conducted using FTIR microspectroscopy (Infrared Microspectroscopy beamline, Australian Synchrotron). Two soil types (Ferralsol and Vertisol, World Reference Base 2014) were collected from undisturbed areas and from a location(s) immediately adjacent which has a long history of agricultural use (>20 years). Soils were gently screened (250 μm) to obtain intact microaggregates which were humidified and frozen at -20°C, and sectioned (200 μm thickness) using a diamond knife and a cryo-ultramicrotome. The sections were placed between CaF2 windows and the spectra were acquired in transmission mode. The maps obtained (5 µm step-size over ca. 150 × 150 µm) revealed carbon distribution in microaggregates from soils under contrasting land management, namely undisturbed and cropping land. Accumulation of aromatic and carboxylic functions on specific spots and marginal co-localization with clays was observed, which suggests processes other than organo-mineral associations being

  10. Vapor-pressure osmometric study of the molecular weight and aggregation tendency of a reference-soil fulvic acid

    USGS Publications Warehouse

    Marinsky, J.A.; Reddy, M.M.

    1990-01-01

    The molecular weight and aggregation tendency of a reference-soil fulvic acid in Armadale horizon Bh were determined by vapor-pressure osmometry using tetrahydrofuran and water as solvents. With tetrahydrofuran, number-average molecular weight values of 767 ?? 34 and 699 ?? 8 daltons were obtained from two separate sets of measurements. Two sets of measurements with water also yielded values within this range (754 ?? 70 daltons) provided that the fulvic acid concentration in water did not exceed 7 mg ml-1; at higher concentrations (9.1-13.7 mg ml-1) a number-average molecular weight of 956 ?? 25 daltons was resolved, providing evidence of molecular aggregation. Extension of these studies to 80% neutralized fulvic acid showed that a sizeable fraction of the sodium counter ion is not osmotically active.

  11. Effects of agaricus lilaceps fairy rings on soil aggregation and microbial community structure in relation to growth stimulation of western wheatgrass (pascopyrum smithii) in Eastern Montana rangeland

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stimulation of plant productivity caused by Agaricus fairy rings has been reported, but nothing is known about soil aggregation and the microbial community structure of the stimulated zone, particularly the communities that can bind to soil particles. We studied three concentric zones of Agaricus li...

  12. Soil aggregate stability and wind erodible fraction in a semi-arid environment of White Nile State, Sudan

    NASA Astrophysics Data System (ADS)

    Elhaja, Mohamed Eltom; Ibrahim, Ibrahim Saeed; Adam, Hassan Elnour; Csaplovics, Elmar

    2014-11-01

    One of the most important recent issues facing White Nile State, Sudan, as well as Sub Saharan Africa, is the threat of continued land degradation and desertification as a result of climatic factors and human activities. Remote sensing and satellites imageries with multi-temporal and spectral and GIS capability, plays a major role in developing a global and local operational capability for monitoring land degradation and desertification in dry lands, as well as in White Nile State. The process of desertification in form of sand encroachment in White Nile State has increased rapidly, and much effort has been devoted to define and study its causes and impacts. This study depicts the capability afforded by remote sensing and GIS to analyze and map the aggregate stability as indicator for the ability of soil to wind erosion process in White Nile State by using Geo-statistical techniques. Cloud-free subset Landsat; Enhance Thematic Mapper plus (ETM +) scenes covering the study area dated 2008 was selected in order to identify the different features covering the study area as well as to make the soil sampling map. Wet-sieving method was applied to determine the aggregate stability. The geo-statistical methods in EARDAS 9.1 software was used for mapping the aggregate stability. The results showed that the percentage of aggregate stability ranged from (0 to 61%) in the study area, which emphasized the phenomena of sand encroachment from the western part (North Kordofan) to the eastern part (White Nile State), following the wind direction. The study comes out with some valuable recommendations and comments, which could contribute positively in reducing sand encroachments

  13. Effect of soil surface conditions on runoff velocity and sediment mean aggregate diameter

    NASA Astrophysics Data System (ADS)

    César Ramos, Júlio; Bertol, Ildegardis; Paz González, Antonio; de Souza Werner, Romeu; Marioti, Juliana; Henrique Bandeira, Douglas; Andrighetti Leolatto, Lidiane

    2013-04-01

    Soil cover and soil management are the factors that most influence soil erosion by water, because they directly affect soil surface roughness and surface cover. The main effect of soil cover by crop residues consists in dissipation of kinetic energy of raindrops and also partly kinetic energy of runoff, so that the soil disaggregation is considerably reduced but, in addition, soil cover captures detached soil particles, retains water on its surface and decreases runoff volume and velocity. In turn, soil surface roughness, influences soil surface water storage and infiltration and also runoff volume and velocity, sediment retention and subsequently water and sediment losses. Based on the above rationale, we performed a field experiment to assess the influence of soil cover and soil surface roughness on decay of runoff velocity as well as on mean diameter of transported sediments (D50 index). The following treatments were evaluated: SRR) residues of Italian ryegrass (Lolium multiflorum) on a smooth soil surfcace, SRV) residues of common vetch (Vicia sativa) on a smooth soil surface, SSR) scarification after cultivation of Italian ryegrass resulting in a rough surface, SSV) scarification after cultivation of common vetch resulting in a rough surface, and SBS) scarified bare soil with high roughness as a control. The field experiments was performed on an Inceptisol in South Brazil under simulated rainfall conditions during 2012. Experimental plots were 11 m long and 3.5 m wide with an area of 38.5 m2. Six successive simulated rainfall tests were applied using a rotating-boom rain simulator. During each test, rain intensity was 60 mmhr-1, whereas rain duration was 90 minutes. Runoff velocity showed no significant differences between cultivated treatments. However, when compared to bare soil treatment, SBS (0.178 m s-1) and irrespective of the presence of surface crop residues or scarification operations, cultivated soil treatments significantly reduced runoff velocity

  14. Effects of Agaricus lilaceps fairy rings on soil aggregation and microbial community structure in relation to growth stimulation of western wheatgrass (Pascopyrum smithii) in Eastern Montana rangeland.

    PubMed

    Caesar-Tonthat, The Can; Espeland, Erin; Caesar, Anthony J; Sainju, Upendra M; Lartey, Robert T; Gaskin, John F

    2013-07-01

    Stimulation of plant productivity caused by Agaricus fairy rings has been reported, but little is known about the effects of these fungi on soil aggregation and the microbial community structure, particularly the communities that can bind soil particles. We studied three concentric zones of Agaricus lilaceps fairy rings in Eastern Montana that stimulate western wheatgrass (Pascopyrum smithii): outside the ring (OUT), inside the ring (IN), and stimulated zone adjacent to the fungal fruiting bodies (SZ) to determine (1) soil aggregate proportion and stability, (2) the microbial community composition and the N-acetyl-β-D-glucosaminidase activity associated with bulk soil at 0-15 cm depth, (3) the predominant culturable bacterial communities that can bind to soil adhering to wheatgrass roots, and (4) the stimulation of wheatgrass production. In bulk soil, macroaggregates (4.75-2.00 and 2.00-0.25 mm) and aggregate stability increased in SZ compared to IN and OUT. The high ratio of fungal to bacteria (fatty acid methyl ester) and N-acetyl-β-D-glucosaminidase activity in SZ compared to IN and OUT suggest high fungal biomass. A soil sedimentation assay performed on the predominant isolates from root-adhering soil indicated more soil-binding bacteria in SZ than IN and OUT; Pseudomonas fluorescens and Stenotrophomonas maltophilia isolates predominated in SZ, whereas Bacillus spp. isolates predominated in IN and OUT. This study suggests that growth stimulation of wheatgrass in A. lilaceps fairy rings may be attributed to the activity of the fungus by enhancing soil aggregation of bulk soil at 0-15 cm depth and influencing the amount and functionality of specific predominant microbial communities in the wheatgrass root-adhering soil.

  15. Effects of Combined Application of Biogas Slurry and Chemical Fertilizer on Soil Aggregation and C/N Distribution in an Ultisol

    PubMed Central

    Zheng, Xuebo; Fan, Jianbo; Xu, Lei; Zhou, Jing

    2017-01-01

    Unreasonable use of chemical fertilizer (CF) on agricultural soil leads to massive losses of soil organic carbon (SOC) and total nitrogen (TN) in tropical and subtropical areas, where soil conditions are unfavorable for aggregate formation. This study evaluated the effects of combined application of biogas slurry (BS) plus CF on soil aggregation and aggregate—associated C/N concentration and storage in an Ultisol. Six treatments included: no fertilizer (T1), CF only (T2), partial (15% (T3), 30% (T4) and 45% (T5)) substitution of TN with BS and BS only (T6). Soil mechanical—stable aggregates (MSAs) formation and stability as well as MSAs—associated C/N concentration and storage were observed in different aggregate sizes (>5, 5–2, 2–1, 1.0–0.5, 0.50–0.25 and <0.25 mm). The proportion of MSAs >5 mm significantly increased with BS substitution (T5), while the proportions of MSAs 1.0–0.5 mm, MSAs 0.50–0.25 mm and MSAs <0.25 mm significantly decreased. Both mean weight diameter and geometric mean diameter were highest in T5, which improved soil aggregation stability as well as resulted in significantly higher SOC and TN concentrations and storage in MSAs >0.5 mm that constituted 72–82% of MSAs. Stepwise regression analysis showed that MSAs >5 mm, SOC in MSAs >5 mm and TN in MSAs >5 mm were the dominant variables affecting aggregate stability. Meanwhile SOC in MSAs <0.25 mm and TN in MSAs 2–1 mm were independent variables affecting SOC and TN concentrations in bulk soils. Therefore, certain rate of combined application of BS plus CF is an effective, eco—friendly way to improve soil quality in an Ultisol. PMID:28125647

  16. Effect of sustainable land management practices on soil aggregation and stabilization of organic carbon in semiarid mediterranean ecosystems

    NASA Astrophysics Data System (ADS)

    Garcia-Franco, Noelia; Albaladejo, Juan; Almagro, María; Wiesmeier, Martin; Martínez-Mena, María

    2016-04-01

    Arid and semiarid regions represent about 47% of the total land area of the world (UNEP, 1992). At present, there is a priority interest for carbon (C) sequestration in drylands. These areas are considered as very fragile ecosystems with low organic carbon (OC) saturation, and potentially, high capacity for soil OC sequestration. In addition, the restoration of these areas is one of the major challenges for scientists, who will be able to identify and recommended the best land uses and sustainable land management (SLM) practices for soil conservation and mitigation of climate change in these environments. In this regard, in semiarid Mediterranean ecosystems there is an urgent need for the implementation of SLM practices regardless of land-use type (forest, agricultural and shrubland) to maintain acceptable levels of soil organic matter (SOM) and the physico-chemical protection of the OC. Long- and short-term effects of SLM practices on soil aggregation and SOC stabilization were studied in two land uses. The long-term experiment was conducted in a reforestation area with Pinus halepensis Mill., where two afforestation techniques were implemented 20 years ago: a) mechanical terracing with a single application of organic waste of urban soil refuse, and b) mechanical terracing without organic amendment. An adjacent shrubland was considered as the reference plot. The short-term experiment was conducted in a rain-fed almond (Prunus dulcis Mill., var. Ferragnes) orchard where two SLM practices were introduced 4 years ago: a) reduced tillage plus green manure, and b) no tillage. Reduced tillage was considered as the reference plot given that it is the habitual management practice. Four aggregate size classes were differentiated by sieving (large and small macroaggregates, microaggregates, and the silt plus clay fraction), and the microaggregates occluded within small macroaggregates (SMm) were isolated. In addition, different organic C fractions corresponding with active

  17. Stimulation of nitrogen turnover due to nutrients release from aggregates affected by freeze-thaw in wetland soils

    NASA Astrophysics Data System (ADS)

    Song, Yang; Zou, Yuanchun; Wang, Guoping; Yu, Xiaofei

    2017-02-01

    The freeze-thaw phenomenon will occur more frequently in mid-high latitude ecosystems under climate change which has a remarkable effect on biogeochemical processes in wetland soils. Here, we used a wet sieving procedure and a barometric process separation (BaPS) technique to examine the responses of wetland soil aggregates and related carbon and nitrogen turnover affected by the freeze-thaw treatment. Wetland soil samples were divided into a treatment group and a control group. The treatment group was incubated at temperatures fluctuating from 10 °C to -10 °C, whereas the control group was incubated at the constant temperature of 10 °C. A 24 h process was set as the total freeze-thaw cycle, and the experiment had 20 continuous freeze-thaw cycles. In our results, the freeze-thaw process caused great destruction to the >2 mm water-stable aggregates (WSA) fraction and increased the <0.053 mm WSA fraction. The dissolved organic carbon (DOC) content was stimulated during the initial freeze-thaw cycles followed by a rapid decline, and then still increased during subsequent freeze-thaw cycles, which was mainly determined by the soil organic carbon (SOC). The NH4+ and NO3- content, respiration rate and gross nitrification rate were all significantly improved by the freeze-thaw effect. Because the amount of NH4+ and NO3- expressed prominent negative responses to the content of >2 mm WSA fraction and the gross nitrification rate can be stimulated at the initial freeze-thaw cycles, nutrients and substrates may play a leading role in the freeze-thaw treatment regardless of the minimal influences on microbial biomass pools.

  18. Changes in carbon stability and microbial activity in size fractions of micro-aggregates in a rice soil chronosequence under long term rice cultivation

    NASA Astrophysics Data System (ADS)

    Pan, Genxing; Liu, Yalong; Wang, Ping; Li, Lianqinfg; Cheng, Kun; Zheng, Jufeng; Zhang, Xuhui; Zheng, Jinwei; Bian, Rongjun; Ding, Yuanjun; Ma, Chong

    2016-04-01

    Recent studies have shown soil carbon sequestration through physical protection of relative labile carbon intra micro-aggregates with formation of large sized macro-aggregates under good management of soil and agricultural systems. While carbon stabilization had been increasingly concerned as ecosystem properties, the mechanisms underspin bioactivity of soil carbon with increased carbon stability has been still poorly understood. In this study, topsoil samples were collected from rice soils derived from salt marsh under different length of rice cultivation up to 700 years from eastern China. Particle size fractions (PSF) of soil aggregates were separated using a low energy dispersion protocol. Carbon fractions in the PSFs were analyzed either with FTIR spectroscopy. Soil microbial community of bacterial, fungal and archaeal were analyzed with molecular fingerprinting using specific gene primers. Soil respiration and carbon gain from amended maize as well as enzyme activities were measured using lab incubation protocols. While the PSFs were dominated by the fine sand (200-20μm) and silt fraction (20-2μm), the mass proportion both of sand (2000-200μm) and clay (<2μm) fraction increased with prolonged rice cultivation, giving rise to an increasing trend of mean weight diameter of soil aggregates (also referred to aggregate stability). Soil organic carbon was found most enriched in coarse sand fraction (40-60g/kg), followed by the clay fraction (20-24.5g/kg), but depleted in the silt fraction (~10g/kg). Phenolic and aromatic carbon as recalcitrant pool were high (33-40% of total SOC) in both coarse sand and clay fractions than in both fine sand and silt fractions (20-29% of total SOC). However, the ratio of LOC/total SOC showed a weak decreasing trend with decreasing size of the aggregate fractions. Total gene content in the size fractions followed a similar trend to that of SOC. Bacterial and archaeal gene abundance was concentrated in both sand and clay fractions

  19. Chemical Composition of Soil Horizons and Aggregate Size Fractions Under the Hawaiian Fern Dicranopteris and Angiosperm Cheirodendrom

    NASA Astrophysics Data System (ADS)

    Stewart, C. E.; Amatangelo, K.; Neff, J.

    2007-12-01

    Soil organic matter (SOM) inherits much of its chemical nature from the dominant vegetation, including phenolic (lignin-derived), aromatic, and aliphatic (cutin and wax-derived) compounds. However, relatively stable recalcitrant compounds may also be formed as a result of condensation and complexation reactions through decomposition and protected with association with mineral particles. The Hawaiian fern species Dicranopteris decomposes more slowly than the angiosperm, Cheirodendrom due to high concentrations of recalcitrant C compounds. These aliphatic fern leaf waxes are well-preserved and may comprise a large portion of the recalcitrant organic matter in these soils. Our objective was to determine the chemical composition of the SOM under the O- (litter-dominated) and the A- (mineral) horizons formed under fern and angiosperm vegetation. To determine the effect of mineral-association, we fractioned the soil into four size classes; 850-590 μm, 590-180 μm, 180-53 μm and <53 μm and characterized the SOM via pyrolysis-gas chromatography-mass spectrometry (py-GC/MS). As the soils developed from the O- to the A-horizon, there was a decrease of lignin-derived phenolic compounds and an increase in more recalcitrant, aromatic and aliphatic C. Soils under ferns had greater relative concentrations of phenolic compounds, while the angiosperms had greater concentrations of fatty-acid methyl esters and furans (some polysaccharide-derived). Differences between size fractions were most evident in the O-horizon of both species. Recalcitrant fern-derived cutin and leaf waxes (alkene and alkanes structures) occurred in the 180-53 μm fraction, which has been shown to be the most stable of the aggregate-size fractions. Soils developed under fern versus angiosperm vegetation have distinct chemical signatures, which likely determine the recalcitrance of the SOM.

  20. Soil wind erodibility based on dry aggregate-size distribution in the Tarim Basin

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Tarim Basin is an important source of airborne particulate matter that contributes to poor air quality in China. However, little attention has been given to estimating wind erodibility of soils in the region. The objective of this study was to determine the soil wind erodibility for six land use...

  1. Nitrogen-mediated effects of elevated CO2 on intra-aggregate soil pore structure

    Technology Transfer Automated Retrieval System (TEKTRAN)

    While previous elevated atmospheric CO2 research has addressed changes in belowground processes, its effects on soil structure remain virtually undescribed. This study examined the long-term effects of elevated CO2 and N fertilization on soil structural changes in a bahiagrass pasture grown on a san...

  2. Influence of tillage practices and straw incorporation on soil aggregates, organic carbon, and crop yields in a rice-wheat rotation system

    PubMed Central

    Song, Ke; Yang, Jianjun; Xue, Yong; Lv, Weiguang; Zheng, Xianqing; Pan, Jianjun

    2016-01-01

    In this study, a fixed-site field experiment was conducted to study the influence of different combinations of tillage and straw incorporation management on carbon storage in different-sized soil aggregates and on crop yield after three years of rice-wheat rotation. Compared to conventional tillage, the percentages of >2 mm macroaggregates and water-stable macroaggregates in rice-wheat double-conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0–15 cm soil layer and 28.93% and 66.34% in the 15–30 cm soil layer, respectively. Zero tillage and straw incorporation also increased the mean weight diameter and stability of the soil aggregates. In surface soil (0–15 cm), the maximum proportion of total aggregated carbon was retained with 0.25–0.106 mm aggregates, and rice-wheat double-conservation tillage had the greatest ability to hold the organic carbon (33.64 g kg−1). However, different forms occurred at higher levels in the 15–30 cm soil layer under the conventional tillage. In terms of crop yield, the rice grown under conventional tillage and the wheat under zero tillage showed improved equivalent rice yields of 8.77% and 6.17% compared to rice-wheat double-cropping under zero tillage or conventional tillage, respectively. PMID:27812038

  3. Influence of tillage practices and straw incorporation on soil aggregates, organic carbon, and crop yields in a rice-wheat rotation system

    NASA Astrophysics Data System (ADS)

    Song, Ke; Yang, Jianjun; Xue, Yong; Lv, Weiguang; Zheng, Xianqing; Pan, Jianjun

    2016-11-01

    In this study, a fixed-site field experiment was conducted to study the influence of different combinations of tillage and straw incorporation management on carbon storage in different-sized soil aggregates and on crop yield after three years of rice-wheat rotation. Compared to conventional tillage, the percentages of >2 mm macroaggregates and water-stable macroaggregates in rice-wheat double-conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0–15 cm soil layer and 28.93% and 66.34% in the 15–30 cm soil layer, respectively. Zero tillage and straw incorporation also increased the mean weight diameter and stability of the soil aggregates. In surface soil (0–15 cm), the maximum proportion of total aggregated carbon was retained with 0.25–0.106 mm aggregates, and rice-wheat double-conservation tillage had the greatest ability to hold the organic carbon (33.64 g kg‑1). However, different forms occurred at higher levels in the 15–30 cm soil layer under the conventional tillage. In terms of crop yield, the rice grown under conventional tillage and the wheat under zero tillage showed improved equivalent rice yields of 8.77% and 6.17% compared to rice-wheat double-cropping under zero tillage or conventional tillage, respectively.

  4. Influence of tillage practices and straw incorporation on soil aggregates, organic carbon, and crop yields in a rice-wheat rotation system.

    PubMed

    Song, Ke; Yang, Jianjun; Xue, Yong; Lv, Weiguang; Zheng, Xianqing; Pan, Jianjun

    2016-11-04

    In this study, a fixed-site field experiment was conducted to study the influence of different combinations of tillage and straw incorporation management on carbon storage in different-sized soil aggregates and on crop yield after three years of rice-wheat rotation. Compared to conventional tillage, the percentages of >2 mm macroaggregates and water-stable macroaggregates in rice-wheat double-conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0-15 cm soil layer and 28.93% and 66.34% in the 15-30 cm soil layer, respectively. Zero tillage and straw incorporation also increased the mean weight diameter and stability of the soil aggregates. In surface soil (0-15 cm), the maximum proportion of total aggregated carbon was retained with 0.25-0.106 mm aggregates, and rice-wheat double-conservation tillage had the greatest ability to hold the organic carbon (33.64 g kg(-1)). However, different forms occurred at higher levels in the 15-30 cm soil layer under the conventional tillage. In terms of crop yield, the rice grown under conventional tillage and the wheat under zero tillage showed improved equivalent rice yields of 8.77% and 6.17% compared to rice-wheat double-cropping under zero tillage or conventional tillage, respectively.

  5. Effects of earthworms and plants on the soil structure, the physical stabilization of soil organic matter and the microbial abundance and diversity in soil aggregates in a long term study

    NASA Astrophysics Data System (ADS)

    Zangerlé, Anne; Hissler, Christophe; Lavelle, Patrick

    2014-05-01

    Earthworms and plant roots, as ecosystem engineers, have large effects on biotic and abiotic properties of the soil system. They create biogenic soil macroaggregates (i.e. earthworm casts and root macroaggregates) with specific physical, chemical and microbiological properties. Research to date has mainly considered their impacts in isolation thereby ignoring potential interactions between these organisms. On the other hand, most of the existing studies focused on short to midterm time scale. We propose in this study to consider effect of earthworms and plants on aggregate dynamics at long time scale. A 24 months macrocosm experiment, under semi-controlled conditions, was conducted to assess the impacts of corn and endogeic plus anecic earthworms (Apporectodea caliginosa and Lumbricus terrestris) on soil structure, C stabilization and microbial abundance and biodiversity. Aggregate stability was assessed by wet-sieving. Macroaggregates (>2 mm) were also visually separated according to their biological origin (e.g., earthworms, roots). Total C and N contents were measured in aggregates of all size classes and origins. Natural abundances of 13C of corn, a C4 plant, were used as a supplemental marker of OM incorporation in aggregates. The genetic structure and the abundance of the bacterial and fungal communities were characterized by using respectively the B- and F-ARISA fingerprinting approach and quantitative PCR bacteria (341F/515R) and fungi (FF330/FR1). They significantly impacted the soil physical properties in comparison to the other treatments: lower bulk density in the first 10cm of the soil with 0.95 g/cm3 in absence of corn plants and 0.88 g/cm3 in presence of corn plants compared to control soil (1.21g/cm3). The presence of earthworms increased aggregate stability (mean weight diameter) by 7.6 %, while plants alone had no simple impacts on aggregation. A significant interaction revealed that earthworms increased aggregate stability in the presence of

  6. Relationship between chemical structure of soil organic matter and intra-aggregate pore structure: evidence from X-ray computed micro-tomography

    NASA Astrophysics Data System (ADS)

    Kravchenko, Alexandra; Grandy, Stuart A.

    2014-05-01

    Understanding chemical structure of soil organic matter (SOM) and factors that affect it are vital for gaining understanding of mechanisms of C sequestration by soil. Physical protection of C by adsorption to mineral particles and physical disconnection between C sources and microbial decomposers is now regarded as the key component of soil C sequestration. Both of the processes are greatly influenced by micro-scale structure and distribution of soil pores. However, because SOM chemical structure is typically studied in disturbed (ground and sieved) soil samples the experimental evidence of the relationships between soil pore structure and chemical structure of SOM are still scarce. Our study takes advantage of the X-ray computed micro-tomography (µ-CT) tools that enable non-destructive analysis of pore structure in intact soil samples. The objective of this study is to examine the relationship between SOM chemical structure and pore-characteristics in intact soil macro-aggregates from two contrasting long-term land uses. The two studied land use treatments are a conventionally tilled corn-soybean-wheat rotation treatment and a native succession vegetation treatment removed from agricultural use >20 years ago. The study is located in southwest Michigan, USA, on sandy-loam Typic Hapludalfs. For this study we used soil macro-aggregates 4-6 mm in size collected at 0-15 cm depth. The aggregate size was selected so as both to enable high resolution of µ-CT and to provide sufficient amount of soil for C measurements. X-ray µ-CT scanning was conducted at APS Argonne at a scanning resolution of 14 µm. Two scanned aggregates (1 per treatment) were used in this preliminary study. Each aggregate was cut into 7 "geo-referenced" sections. Analyses of pore characteristics in each section were conducted using 3DMA and ImageJ image analysis tools. SOM chemistry was analyzed using pyrolysis/gas chromatography-mass spectroscopy. Results demonstrated that the relationships

  7. Do aggregate stability and soil organic matter content increase following organic inputs?

    NASA Astrophysics Data System (ADS)

    Lehtinen, Taru; Gísladóttir, Guðrún; van Leeuwen, Jeroen P.; Bloem, Jaap; Steffens, Markus; Vala Ragnarsdóttir, Kristin

    2014-05-01

    Agriculture is facing several challenges such as loss of soil organic matter (SOM); thus, sustainable farming management practices are needed. Organic farming is growing as an alternative to conventional farming; in Iceland approximately 1% and in Austria 16% of utilized agricultural area is under organic farming practice. We analyzed the effect of different farming practices (organic, and conventional) on soil physicochemical and microbiological properties in grassland soils in Iceland and cropland soils in Austria. Organic farms differed from conventional farms by absence of chemical fertilizers and pesticide use. At these farms, we investigated soil physicochemical (e.g. soil texture, pH, CAL-extractable P and K) and microbiological properties (fungal and bacterial biomass and activity). The effects of farming practices on soil macroaggregate stability and SOM quantity, quality and distribution between different fractions were studied following a density fractionation. In Iceland, we sampled six grassland sites on Brown (BA) and Histic (HA) Andosols; two sites on extensively managed grasslands, two sites under organic and two sites under conventional farming practice. In Austria, we sampled four cropland sites on Haplic Chernozems; two sites under organic and two sites under conventional farming practice. We found significantly higher macroaggregate stability in the organic compared to the conventional grasslands in Iceland. In contrast, slightly higher macroaggregation in conventional compared to the organic farming practice was found in croplands in Austria, although the difference was not significant. Macroaggregates were positively correlated with fungal biomass in Iceland, and with Feo and fungal activity in Austria. In Austria, SOM content and nutrient status (except for lower CAL-extractable P at one site) were similar between organic and conventional farms. Our results show that the organic inputs may have enhanced macroaggregation in organic farming

  8. Influence of 20-year organic and inorganic fertilization on organic carbon accumulation and microbial community structure of aggregates in an intensively cultivated sandy loam soil.

    PubMed

    Zhang, Huanjun; Ding, Weixin; He, Xinhua; Yu, Hongyan; Fan, Jianling; Liu, Deyan

    2014-01-01

    To evaluate the long-term effect of compost (CM) and inorganic fertilizer (NPK) application on microbial community structure and organic carbon (OC) accumulation at aggregate scale, soils from plots amended with CM, NPK and no fertilizer (control) for 20 years (1989-2009) were collected. Soil was separated into large macroaggregate (>2,000 μm), small macroaggregate (250-2,000 μm), microaggregate (53-250 μm), silt (2-53 μm) and clay fraction (<2 μm) by wet-sieving, and their OC concentration and phospholipid fatty acids (PLFA) were measured. The 20-year application of compost significantly (P<0.05) increased OC by 123-134% and accelerated the formation of macroaggregates, but decreased soil oxygen diffusion coefficient. NPK mainly increased OC in macroaggregates and displayed weaker influence on aggregation. Bacteria distributed in all aggregates, while fungi and actinobacteria were mainly in macroaggregates and microaggregates. The ratio of monounsaturated to branched (M/B) PLFAs, as an indicator for the ratio of aerobic to anaerobic microorganisms, increased inversely with aggregate size. Both NPK and especially CM significantly (P<0.05) decreased M/B ratios in all aggregates except the silt fraction compared with the control. The increased organic C in aggregates significantly (P<0.05) negatively correlated with M/B ratios under CM and NPK. Our study suggested that more efficient OC accumulations in aggregates under CM-treated than under NPK-treated soil was not only due to a more effective decrease of actinobacteria, but also a decrease of monounsaturated PLFAs and an increase of branched PLFAs. Aggregations under CM appear to alter micro-habitats to those more suitable for anaerobes, which in turn boosts OC accumulation.

  9. STOCK AND DISTRIBUTION OF TOTAL AND CORN-DERIVED SOIL ORGANIC CARBON IN AGGREGATE AND PRIMARY PARTICLE FRACTIONS FOR DIFFERENT LAND USE AND SOIL MANAGEMENT PRACTICES

    SciTech Connect

    Puget, P; Lal, Rattan; Izaurralde, R Cesar C.; Post, M; Owens, Lloyd

    2005-04-01

    Land use, soil management, and cropping systems affect stock, distribution, and residence time of soil organic carbon (SOC). Therefore, SOC stock and its depth distribution and association with primary and secondary particles were assessed in long-term experiments at the North Appalachian Experimental Watersheds near Coshocton, Ohio, through *13C techniques. These measurements were made for five land use and soil management treatments: (1) secondary forest, (2) meadow converted from no-till (NT) corn since 1988, (3) continuous NT corn since 1970, (4) continuous NT corn-soybean in rotation with ryegrass since 1984, and (5) conventional plow till (PT) corn since 1984. Soil samples to 70-cm depth were obtained in 2002 in all treatments. Significant differences in soil properties were observed among land use treatments for 0 to 5-cm depth. The SOC concentration (g C kg*1 of soil) in the 0 to 5-cm layer was 44.0 in forest, 24.0 in meadow, 26.1 in NT corn, 19.5 in NT corn-soybean, and 11.1 i n PT corn. The fraction of total C in corn residue converted to SOC was 11.9% for NT corn, 10.6% for NT corn-soybean, and 8.3% for PT corn. The proportion of SOC derived from corn residue was 96% for NT corn in the 0 to 5-cm layer, and it decreased gradually with depth and was 50% in PT corn. The mean SOC sequestration rate on conversion from PT to NT was 280 kg C ha*1 y*1. The SOC concentration decreased with reduction in aggregate size, and macro-aggregates contained 15 to 35% more SOC concentration than microaggregates. In comparison with forest, the magnitude of SOC depletion in the 0 to 30-cm layer was 15.5 Mg C/ha (24.0%) in meadow, 12.7 Mg C/ha (19.8%) in NT corn, 17.3 Mg C/ha (26.8%) in NT corn-soybean, and 23.3 Mg C/ha (35.1%) in PT corn. The SOC had a long turnover time when located deeper in the subsoil.

  10. Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse-grained soil in an alpine eco-engineering field experiment?

    NASA Astrophysics Data System (ADS)

    Bast, A.; Wilcke, W.; Graf, F.; Lüscher, P.; Gärtner, H.

    2016-08-01

    Steep vegetation-free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco-engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small-scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotal = 1248) and soil core (ntotal = 108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5 mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long-term field experimental monitoring before transferring laboratory results to the field.

  11. Mapping of monthly soil erosion risk of mainland Mauritius and its aggregation with delineated basins

    NASA Astrophysics Data System (ADS)

    Nigel, Rody; Rughooputh, Soonil

    2010-01-01

    This paper reports the mapping of monthly soil erosion risk on Mauritius which was carried out using GIS, decision rules and readily available data namely, monthly rainfall depth, soil types, slope and land cover. Slope and soil were first combined to produce soil erosion susceptibility followed by land cover to produce erosion sensitivity, and then rainfall to produce erosion risk. The high erosion areas of the Island have been extracted from the soil erosion risk maps, whereby these areas can face land degradation problems and can be responsible for sediment discharge into wetlands located at the outlet of drainage basins. As such, drainage basins have been delineated using automatic catchment delineation tools and their percentage of high erosion areas computed. Basins with the greatest percentage of high erosion areas and particularly those that directly have a wetland at the outlet can be given priority for soil and water conservation efforts. The mapping reported in this paper can be adapted to other countries which need an erosion assessment for the identification of high erosion areas and priority action areas.

  12. Soil aggregation as mechanism for understanding the roles of soil biota in the sustainable usage of natural resources

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Global food insecurity and rapidly diminishing water, soil, and energy resources resulting from increases in population numbers and wealth are putting pressure on agroecosystems to efficiently produce the most nutrient dense food while maintaining or enhancing natural resources. To address these ne...

  13. Influence of humic acid applications on modulus of rupture, aggregate stability, electrical conductivity, carbon and nitrogen content of a crusting problem soil

    NASA Astrophysics Data System (ADS)

    Gümüş, İ.; Şeker, C.

    2015-11-01

    Soil structure is often said to be the key to soil productivity since a fertile soil, with desirable soil structure and adequate moisture supply, constitutes a productive soil. Soil structure influences soil water movement and retention, erosion, crusting, nutrient recycling, root penetration and crop yield. The objective of this work is to study humic acid (HA) application on some physical and chemical properties in weakly structured soils. The approach involved establishing a plot experiment in laboratory conditions. Different rates of HA (control, 0.5, 1, 2 and 4 %) were applied to soil during three incubation periods (21, 42 and 62 days). At the end of the each incubation period, the changes in physicochemical properties were measured. Generally, HA addition increased electrical conductivity values during all incubation periods. HA applications decreased soil modulus of rupture. Application of HA at the rate of 4 % significantly increased soil organic carbon contents. HA applications at the rate of 4 % significantly increased both mean soil total nitrogen content and aggregate stability after three incubation periods (p < 0.05). Therefore, HA has the potential to improve the structure of soil in the short term.

  14. The SAWO (Small And Well Organized) avatar teaches the importance of the aggregates on the soil system and how to determine their stability

    NASA Astrophysics Data System (ADS)

    Mataix-Solera, Jorge; Cerdà, Artemi; Jordán, Antonio; Úbeda, Xavier; Pereira, Paulo

    2015-04-01

    Soil structure is the key factor that determine the soil quality as control the organic matter turnnover, soil biology and soil erodibility (Cerdà, 1996; 1998; Wick et al., 2014; Gelaw, 2015). There is a need to understand better the factors and the processes that act on the soil aggregation and the dynamics of the soil aggregation, which will make easier to understand the soil system functioning (Jordán et al., 2011; Jordán et al., 2012; Pulido Moncada et al., 2013). Fire, mines, grazing and agricultura (Cerdà, 2000; Mataix Solera et al., 2011; Cerdà et al., 2012; Hallett et al., 2014; Lozano et al., 2013) determines how the soil structure is highly affected by the humankind. And this determines the sustainability of the land managements (García Orenes et al., 2012; K¨ropfl et al., 2013; Mekuria and Aynekulu, 2013; Taguas et al., 2013; Zhao et al., 2013). Aggregates are Small And Well Organized (SAWO) structures that allow the water to flow, the air fill the porous and the life to be diverse and abundant in the soil. The SAWO avatar will teach the importance of the functions and the services of the aggregates to students and other scientists, but also to any audience. This means that the experiments and the vocabulary to be used by SAWO will be very wide and rich. The Avatar SAWO will use different strategies and skills to teach the soil aggregation properties and characteristics. And also, how to measure. Easy to carry out experiments will be shown by SAWO to measure the aggregate stability in the field and in the laboratory, and the soil sampling in the field. The SAWO avatar will play a special attention to the impact of forest fires on aggregate stability changes and how to measure. The SAWO avatar will teach how to take samples in the field, how to transport and manage in the laboratory, and finally which measurements and test can be done to determine the aggregate stability. Acknowledgements To the "Ministerio de Economía and Competitividad" of

  15. Aggregates: Waste and recycled materials; new rapid evaluation technology. Soils, geology, and foundations; materials and construction. Transportation research record

    SciTech Connect

    Not Available

    1994-01-01

    ;Contents: Engineering Properties of Shredded Tires in Lightweight Fill Applications; Using Recovered Glass as Construction Aggregate Feedstock; Utilization of Phosphogypsum-Based Slag Aggregate in Portland Cement Concrete Mixtures; Waste Foundry Sand in Asphalt Concrete; Toward Automating Size-Gradation Analysis of Mineral Aggregate; Evaluation of Fine Aggregate Angularity Using National Aggregate Association Flow Test; Siliceous Content Determination of Sands Using Automatic Image Analysis; and Methodology for Improvement of Oxide Residue Models for Estimation of Aggregate Performance Using Stoichiometric Analysis.

  16. Cropping Intensity Impacts on Soil Aggregation and Carbon Sequestration in the Central Great Plains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The predominant cropping system in the Central Great Plains is conventional tillage (CT) winter wheat–summer fallow. We investigated the effect 15 yrs of variable cropping intensity, fallow frequency, and tillage (CT and no-till [NT]) had on soil organic C (SOC) sequestration, particulate organic ma...

  17. Aggregate Carbon Pools after 13 Years of Integrated Crop-Livestock Management in Semiarid Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Semi-arid regions have the potential to sequester soil organic carbon (SOC) but the magnitude and rate of sequestration is highly management specific. Integrated crop-livestock (ICL) systems that utilize perennial or high-residue no-till annual forage crops as part of the overall agronomic system ma...

  18. Soil aggregates stability was an uncertain predictor of ecosystem functioning in a temperate and semiarid grassland

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Science-based information is needed to identify indicators of ecosystem health that may then be used to monitor natural resources and guide management decisions. We conducted a local gradient study to elucidate correlative associations between vegetation and multiple soil properties for rangelands ...

  19. Increases in soil aggregation following phosphorus additions in a tropical premontane forest are not driven by root and arbuscular mycorrhizal fungal abundances

    NASA Astrophysics Data System (ADS)

    Camenzind, Tessa; Papathanasiou, Helena; Foerster, Antje; Dietrich, Karla; Hertel, Dietrich; Homeier, Juergen; Oelmann, Yvonne; Olsson, Pål Axel; Suárez, Juan; Rillig, Matthias

    2015-12-01

    Tropical ecosystems have an important role in global change scenarios, in part because they serve as a large terrestrial carbon pool. Carbon protection is mediated by soil aggregation processes, whereby biotic and abiotic factors influence the formation and stability of aggregates. Nutrient additions may affect soil structure indirectly by simultaneous shifts in biotic factors, mainly roots and fungal hyphae, but also via impacts on abiotic soil properties. Here, we tested the hypothesis that soil aggregation will be affected by nutrient additions primarily via changes in arbuscular mycorrhizal fungal (AMF) hyphae and root length in a pristine tropical forest system. Therefore, the percentage of water-stable macroaggregates (> 250µm) (WSA) and the soil mean weight diameter (MWD) was analyzed, as well as nutrient contents, pH, root length and AMF abundance. Phosphorus additions significantly increased the amount of WSA, which was consistent across two different sampling times. Despite a positive effect of phosphorus additions on extraradical AMF biomass, no relationship between WSA and extra-radical AMF nor roots was revealed by regression analyses, contrary to the proposed hypothesis. These findings emphasize the importance of analyzing soil structure in understudied tropical systems, since it might be affected by increasing nutrient deposition expected in the future.

  20. [Effects of selective microbial inhibitors on the microbial transformation of phosphorous in aggregates of highly weathered red soil with rice straw amendment].

    PubMed

    Ding, Long-jun; Xiao, He-ai; Wu, Jin-shui; Ge, Ti-da

    2010-07-01

    In order to further understand the mechanisms of microbial immobilization of phosphorous (P) in highly weathered red soil with organic amendment, an incubation test was conducted to investigate the roles of microbial functional groups in the transformation of P in 0.2-2 mm soil aggregates. Throughout the 90-day incubation period, amendment with rice straw induced a substantial increase in the amounts of microbial biomass C and P, Olsen-P, and organic P in the aggregates. Comparing with rice straw amendment alone, the amendment with rice straw plus fungal inhibitor actidione decreased the amount of microbial biomass C in the aggregates by 10.5%-31.8% in the first 30 days. Such a decrement was significantly larger than that (6.8%-11.6%) in the treatment amended with rice straw plus bacterial inhibitors tetracycline and streptomycin sulphate (P<0.01). After the first 30 days, the microbial biomass C remained constant. In the first 20 days, the amount of microbial biomass P in the aggregates was 10.0%-28.8% higher in the treatment amended with bacterial inhibitors than in the treatment amended with fungal inhibitor (P<0.01). All the results suggested that that both the fungal and the bacterial groups were involved in the microbial immobilization of P in the soil aggregates, and the fungal group played a relatively larger role.

  1. Leaching characteristics of EDTA-enhanced phytoextraction of Cd and Pb by Zea mays L. in different particle-size fractions of soil aggregates exposed to artificial rain.

    PubMed

    Lu, Yayin; Luo, Dinggui; Lai, An; Liu, Guowei; Liu, Lirong; Long, Jianyou; Zhang, Hongguo; Chen, Yongheng

    2017-01-01

    Chelator-assisted phytoextraction is an alternative and effective technique for the remediation of heavy metal-contaminated soils, but the potential for heavy metal leaching needs to be assessed. In the present study, a soil column cultivation-leaching experiment was conducted to investigate the Cd and Pb leaching characteristics during assisted phytoextraction of metal-contaminated soils containing different particle-size soil aggregates. The columns were planted with Zea mays "Zhengdan 958" seedlings and treated with combined applications of EDTA and simulated rainfall (pH 4.5 or 6.5). The results were as follows: (1) The greatest uptake of Cd and Pb by Z. mays was observed after treatment with EDTA (2.5 mmol kg(-1) soil) and soil aggregates of <1 mm; uptake decreased as the soil aggregate size increased. (2) Simulated rainfall, especially acid rain (pH 4.5), after EDTA applications led to the increasing metal concentrations in the leachate, and EDTA significantly increased the concentrations of both Cd and Pb in the leachate, especially with soil aggregates of <1 mm; metal leachate concentrations decreased as soil particle sizes increased. (3) Concentrations of Cd and Pb decreased with each continuing leachate collection, and data were fit to linear regression models with coefficients of determination (R (2)) above 0.90 and 0.87 for Cd and Pb, respectively. The highest total amounts of Cd (22.12%) and Pb (19.29%) were observed in the leachate of soils treated with EDTA and artificial acid rain (pH 4.5) with soil aggregates of <1 mm. The application of EDTA during phytoextraction method increased the leaching risk in the following order: EDTA2.5-1 (pH 4.5) > EDTA2.5-1 (pH 6.5) > EDTA2.5-2 (pH 4.5) > EDTA2.5-4 (pH 4.5) > EDTA2.5-2 (pH 6.5) > EDTA2.5-4 (pH 6.5).

  2. Mineral associated and aggregate-occluded soil carbon decreased with increasing nitrogen and residue input for three decades

    NASA Astrophysics Data System (ADS)

    Shahbaz, Muhammad; Kuzyakov, Yakov; Heitkamp, Felix

    2016-04-01

    Cropland soils may be a source or sink for atmospheric CO2. Therefore, effects of cropland management and fertilization on soil organic carbon (SOC) can be assessed best in long-term experiments. Generally, it is assumed that change in SOC is linearly related to C-input into the soil. However, recently it has been shown that residue incorporation resulted to only small extents in the increase of SOC levels. This gives rise to environmental concerns regarding the efficient use of crop residue. Such concerns are also applicable for the well designed and documented long-term experiment of Puch, Germany, in a silt-loam soil. The crop rotation is winter barley - winter wheat - silage maize. Five organic amendments were combined with N-fertiliser rates. The levels of organic amendments are unamended control (CON), straw was removed; farmyard manure (FYM), straw was removed; straw incorporation (STR); slurry application (SLU), straw was removed; and straw incorporation combined with slurry application (STSL). Three levels of mineral fertilizer application were selected: no nitrogen (N0); medium, 100 kg N ha-1year-1 (N2); and high, 200 kg N ha-1 year-1 (N4). These treatments resulted in a wide range of mean annual carbon input (1 - 5 t C ha-1 year-1). We hypothesize that the amount of soil carbon stored in different fractions will increase with C-input, but the effect will decrease in the order free light fraction (f-LF), occluded light fraction (o-LF) and heavy mineral-associated fraction (HF). Soil samples were fractionated by density using sodium polytungstate (1.6 g cm-3). Compared to the starting value SOC was lost in STR and CON and increased in SLU and STSL, whereas FYM showed no differences to initial carbon stocks. However, N additions resulted in only slightly increase in SOC contents with reference to C-input. The lower amount of o-LF carbon in CON and STR demonstrated the low ability of crop residue in comparison to animal manures to build up SOC contents

  3. Response of microbial extracellular enzyme activities and r- vs. K- selected microorganisms to elevated atmospheric CO2 depends on soil aggregate size

    NASA Astrophysics Data System (ADS)

    Dorodnikov, Maxim; Blagodatskaya, Evgenia; Blagodatskiy, Sergey; Kuzyakov, Yakov

    2014-05-01

    Increased belowground carbon (C) transfer by plant roots under elevated atmospheric CO2 and the contrasting environment in soil macro- and microaggregates could affect properties of the microbial community in the rhizosphere. We evaluated the effect of 5 years of elevated CO2 (550 ppm) on four extracellular enzymes: ß-glucosidase, chitinase, phosphatase, and sulfatase along with the contribution of fast- (r-strategists) and slow-growing microorganisms (K-strategists) in soil aggregates. We fractionated the bulk soil from the ambient and elevated CO2 treatments of FACE-Hohenheim (Stuttgart) into large macro- (>2 mm), small macro- (0.25-2.00 mm), and microaggregates (<0.25 mm) using a modified dry sieving. Microbial biomass (C-mic by SIR), the maximal specific growth rate (µ), growing microbial biomass (GMB) and lag-period (t-lag) were estimated by the kinetics of CO2 emission from bulk soil and aggregates amended with glucose and nutrients. In the bulk soil and isolated aggregates before and after activation with glucose, the actual and the potential enzyme activities were measured. Although C-org and C-mic as well as the activities of ß-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO2, significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO2 were 1.2-1.9-fold higher than under ambient CO2. In addition, µ values were significantly higher under elevated than ambient CO2 for bulk soil, small macroaggregates, and microaggregates. Based on changes in µ, GMB, and lag-period, we conclude that elevated atmospheric CO2 stimulated the r-selected microorganisms, especially in soil microaggregates. In contrast, significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO2 revealed an increased contribution of fungi to turnover processes. We conclude that quantitative and

  4. A Conceptual Approach to Assimilating Remote Sensing Data to Improve Soil Moisture Profile Estimates in a Surface Flux/Hydrology Model. 2; Aggregation

    NASA Technical Reports Server (NTRS)

    Schamschula, Marius; Crosson, William L.; Inguva, Ramarao; Yates, Thomas; Laymen, Charles A.; Caulfield, John

    1998-01-01

    This is a follow up on the preceding presentation by Crosson. The grid size for remote microwave measurements is much coarser than the hydrological model computational grids. To validate the hydrological models with measurements we propose mechanisms to aggregate the hydrological model outputs for soil moisture to allow comparison with measurements. Weighted neighborhood averaging methods are proposed to facilitate the comparison. We will also discuss such complications as misalignment, rotation and other distortions introduced by a generalized sensor image.

  5. Grazing cessation changes quantity, quality and distribution of soil organic matter and (micro-)aggregates in a semiarid steppe ecosystem in Inner Mongolia

    NASA Astrophysics Data System (ADS)

    Steffens, M.; Wiesmeier, M.; Koelbl, A.; Kogel-Knabner, I.

    2012-12-01

    Grazing is one of the most important factors that may reduce soil organic carbon (SOC) stocks and subsequently deteriorate aggregate stability in grassland soils. Improvements to land use management, e.g. grazing reduction, are assumed to increase the carbon sequestration of steppe ecosystems which may act as one of the big global carbon sinks. The central aims of this study were to investigate the effects of grazing on semiarid steppe ecosystems and to evaluate the benefits and potentials of grazing management to mitigate the detrimental effects of grazing. Special emphasize was placed on changes in the amount, composition and turnover of soil organic matter (SOM) and its effects on soil structure and aggregation. We sampled 5 differently grazed plots (ungrazed since 1979 = Ug79, ungrazed since 1999 = Ug99, winter grazing = Wg, continuously grazed = Cg, heavily grazed = Hg) and a 7-year grazing experiment with regular orthogonal grids and representative soil pits in a semiarid steppe ecosystem in Inner Mongolia, China. Topsoil and vegetation samples from grids were analysed statistically and geostatistically. Differently sized grids allowed the exploration of scale effects. Pit samples were taken from three horizons and were analysed for aggregate stability and physically fractionated according to aggregate size, density and particle size. Statistical analyses showed that physical and chemical parameters of bulked steppe topsoils deteriorated significantly following heavy grazing, remained stable if grazing was reduced or excluded for five years and recovered significantly after 25 years of grazing exclusion. Spatial heterogeneity of topsoil properties increased with decreasing grazing intensity from a homogeneous to a patchy distribution. This is attributed to vegetation recovery/succession and deposition of windblown material in ungrazed areas. On the large scale (>50 m) spatial variability of topsoil and vegetation was controlled by topography or soil erosion

  6. The impact of long-term irrigation on the degree of aggregation and the mineralogical composition of the clay fraction in dark chestnut soils of the Transvolga region

    NASA Astrophysics Data System (ADS)

    Chizhikova, N. P.; Baranovskaya, V. A.; Khitrov, N. B.

    2011-08-01

    Dark chestnut soils of the Ershov Experimental Station in the Transvolga region are characterized by the even distribution and aggregation of clay minerals in the profile. Hydromica, chlorite, kaolinite, and smectitic minerals predominate in the clay (<1 μm) fraction. The smectitic phase consists of randomly ordered mixed-layered minerals of the following types: mica-smectite with a low (<50%) content of smectite layers, mica-smectite with a high (>50%) content of smectite layers, and chlorite-smectite. In some horizons, the smectitic phase occurs in the superdispersed state. The long-term irrigation of these soils with fresh water of the Volga River has led to certain changes in the composition and properties of the clay particles. The weakening of bonds between them has taken place. As a result, the content of water-peptizable clay has increased by two times, and the content of aggregated clay of the first category (AC1) has increased by 1.5 times at the expense of a decrease in the contents of tightly bound clay (TBC) and aggregated clay of the second category (AC2). Also, the redistribution of organic matter bound with clay particles has taken place: its content in the AC1 fraction has decreased, whereas its content in the AC2 and TBC fractions has increased. In the topsoil horizon, the amount of the smectitic phase has lowered, whereas the contents of hydromica, kaolinite, and fine-dispersed quartz in the clay fraction have increased. In general, some amorphization of the clay material has occurred. The periodic alkalization of the soil solutions upon irrigation has led to the conversion of the smectitic phase into the superdispersed state in the entire soil profile.

  7. Polycyclic aromatic hydrocarbons (PAHs) in wetland soils under different land uses in a coastal estuary: toxic levels, sources and relationships with soil organic matter and water-stable aggregates.

    PubMed

    Xiao, Rong; Bai, Junhong; Wang, Junjing; Lu, Qiongqiong; Zhao, Qingqing; Cui, Baoshan; Liu, Xinhui

    2014-09-01

    The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the soils from industrial, wharf, cropland, milldam and natural wetland sites to characterize their distributions, toxic levels and possible sources in the Pearl River Estuary and identify their relationships with soil organic matter (SOM) and water-stable aggregates (WSAs). Our results indicate that the average concentration of total PAHs in this region reached a moderate pollution level, which was higher than that in other larger estuaries in Asia. The average level of total PAHs in industrial soils was 1.2, 1.5, 1.6 and 2.3 times higher than those in soils from wharf, cropland, milldam and natural wetland sites, respectively. Greater accumulation of PAHs occurred in the middle and/or bottom soil layers where 3-ring PAHs were dominant. Industrial soils also exhibited the highest toxic levels with the highest toxic equivalent concentrations of PAHs, followed by wharf and milldam soils, and the cropland and wetland soils had the lowest toxicity. The diagnostic ratios suggested that PAHs primarily originated from biomass and coal combustion at industrial and milldam sites, and petroleum combustion was determined to be the primary source of PAHs at the wharf, cropland and wetland sites. Both 3-ring and 4-ring PAHs in the milldam and wharf soils were significantly positively correlated with the SOM, whereas the 4,5,6-ring PAHs and total PAHs in industrial soils and the 2-ring PAHs in cropland soils were significantly negatively correlated with the SOM. In addition, large WSAs also exhibited a significant positive correlation with PAHs.

  8. Biodegradation of petroleum hydrocarbons in contaminated clayey soils from a sub-arctic site: the role of aggregate size and microstructure.

    PubMed

    Chang, Wonjae; Akbari, Ali; Snelgrove, Jessica; Frigon, Dominic; Ghoshal, Subhasis

    2013-06-01

    This study investigates the extent of biodegradation of non-volatile petroleum hydrocarbons (C16-C34) and the associated microbial activity in predominant aggregate sizes during a pilot-scale biopile experiment conducted at 15 °C, with a clayey soil, from a crude oil-impacted site in northern Canada. The in situ aggregate microstructure was characterized by N2 adsorption and X-ray CT scanning. The soils in the nutrient (N)-amended and unamended biopile tanks were comprised of macroaggregates (>2 mm) and mesoaggregates (0.25-2 mm). Nutrient addition significantly enhanced petroleum hydrocarbon biodegradation in macroaggregates, but not in mesoaggregates. At the end of 65-d biopile experiment, 42% of the C16-C34 hydrocarbons were degraded in the nutrient-amended macroaggregates, compared to 13% in the mesoaggregates. Higher microbial activity in the macroaggregates of the nutrient amended biopile was inferred from a larger increase in extractable protein concentrations, compared to the other aggregates. Terminal Restriction Fragment Length Polymorphism (T-RFLP) of 16S rRNA genes showed that there was no selection of bacterial populations in any of the aggregates during biopile treatment, suggesting that the enhanced biodegradation in nutrient-amended macroaggregates was likely due to metabolic stimulation. X-ray micro CT scanning revealed that the number of pores wider than 4 μm, which would be easily accessible by bacteria, were an order of magnitude higher in macroaggregates. Also, N2 adsorption analyses showed that pore surface areas and pore volumes per unit weight were four to five-times larger, compared to the mesoaggregates. Thus the higher porosity microstructure in macroaggregates allowed greater hydrocarbon degradation upon biostimulation by nutrient addition and aeration.

  9. Micro-arthropod communities under human disturbance: is taxonomic aggregation a valuable tool for detecting multivariate change? Evidence from Mediterranean soil oribatid coenoses

    NASA Astrophysics Data System (ADS)

    Caruso, Tancredi; Migliorini, Massimo

    2006-07-01

    Animal communities are sensitive to environmental disturbance, and several multivariate methods have recently been developed to detect changes in community structure. The complex taxonomy of soil invertebrates constrains the use of the community level in monitoring environmental changes, since species identification requires expertise and time. However, recent literature data on marine communities indicate that little multivariate information is lost in the taxonomic aggregation of species data to high rank taxa. In the present paper, this hypothesis was tested on two oribatid mite (Oribatida, Acari) assemblages under two different kinds of disturbance: metal pollution and fires. Results indicate that data sets built at the genus and family systematic rank can detect the effects of disturbance with little loss of information. This is an encouraging result in view of the use of the community level as a preliminary tool for describing patterns of human-disturbed soil ecosystems.

  10. Long-term tillage and drainage influences on soil organic carbon dynamics, aggregate stability, and corn yield

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Labile pools of soil organic carbon (SOC) and nitrogen (N) affect the carbon (C) and N fluxes from terrestrial soils, whereas, long-term C and N storage is determined by the long-lived recalcitrant fractions. Tillage influences these labile pools, however effect of the tillage systems may be differe...

  11. EnKF with closed-eye period - towards a consistent aggregation of information in soil hydrology

    NASA Astrophysics Data System (ADS)

    Bauser, Hannes H.; Jaumann, Stefan; Berg, Daniel; Roth, Kurt

    2016-12-01

    The representation of soil water movement exposes uncertainties in all model components. We assess the key uncertainties for the specific hydraulic situation of a 1-D soil profile with TDR (time domain reflectometry)-measured water contents. The uncertainties addressed are initial condition, soil hydraulic parameters, small-scale heterogeneity, upper boundary condition, and the local equilibrium assumption by the Richards equation. We employ an ensemble Kalman filter (EnKF) with an augmented state to represent and estimate all key uncertainties, except for the intermittent violation of the local equilibrium assumption. For the latter, we introduce a closed-eye EnKF to bridge the gap. Due to an iterative approach, the EnKF was capable of estimating soil parameters, Miller scaling factors and upper boundary condition based on TDR measurements during a single rain event. The introduced closed-eye period ensured constant parameters, suggesting that they resemble the believed true material properties. This closed-eye period improves predictions during periods when the local equilibrium assumption is met, but requires a description of the dynamics during local non-equilibrium phases to be able to predict them. Such a description remains an open challenge. Finally, for the given representation our results show the necessity of including small-scale heterogeneity. A simplified representation with Miller scaling already yielded a satisfactory description.

  12. Long-term combined chemical and manure fertilizations increase soil organic carbon and total nitrogen in aggregate fractions at three typical cropland soils in China.

    PubMed

    He, Y T; Zhang, W J; Xu, M G; Tong, X G; Sun, F X; Wang, J Z; Huang, S M; Zhu, P; He, X H

    2015-11-01

    Soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) are important factors of soil fertility. However, effects of the combined chemical fertilizer and organic manure or straw on these factors and their relationships are less addressed under long-term fertilizations. This study addressed changes in SOC, TN, MBC and MBN at 0-20 cm soil depth under three 17 years (September 1990-September 2007) long-term fertilization croplands along a heat and water gradient in China. Four soil physical fractions (coarse free and fine free particulate organic C, cfPOC and ffPOC; intra-microaggregate POC, iPOC; and mineral associated organic C, MOC) were examined under five fertilizations: unfertilized control, chemical nitrogen (N), phosphorus (P) and potassium (K) (NPK), NPK plus straw (NPKS, hereafter straw return), and NPK plus manure (NPKM and 1.5NPKM, hereafter manure). Compared with Control, manure significantly increased all tested parameters. SOC and TN in fractions distributed as MOC > iPOC > cfPOC > ffPOC with the highest increase in cfPOC (329.3%) and cfPTN (431.1%), and the lowest in MOC (40.8%) and MTN (45.4%) under manure. SOC significantly positively correlated with MBC, cfPOC, ffPOC, iPOC and MOC (R(2) = 0.51-0.84, P < 0.01), while TN with cfPTN, ffPTN, iPTN and MTN (R(2) = 0.45-0.79, P < 0.01), but not with MBN, respectively. Principal component analyses explained 86.9-91.2% variance of SOC, TN, MBC, MBN, SOC and TN in each fraction. Our results demonstrated that cfPOC was a sensitive SOC indicator and manure addition was the best fertilization for improving soil fertility while straw return should take into account climate factors in Chinese croplands.

  13. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1995-01-01

    Part of the 1994 Industrial Minerals Review. The production, consumption, and applications of construction aggregates are reviewed. In 1994, the production of construction aggregates, which includes crushed stone and construction sand and gravel combined, increased 7.7 percent to 2.14 Gt compared with the previous year. These record production levels are mostly a result of funding for highway construction work provided by the Intermodal Surface Transportation Efficiency Act of 1991. Demand is expected to increase for construction aggregates in 1995.

  14. The impact of agriculture terraces on soil organic matter, aggregate stability, water repellency and bulk density. A study in abandoned and active farms in the Sierra de Enguera, Eastern Spain.

    NASA Astrophysics Data System (ADS)

    Cerdà, Artemi; Burguet, Maria; Keesstra, Saskia; Prosdocimi, Massimo; Di Prima, Simone; Brevik, Erik; Novara, Agata; Jordan, Antonio; Tarolli, Paolo

    2016-04-01

    Soil erosion, land degradation, lack of organic matter, erodible soils, rock outcrops… are a consequence of the human abuse and misuse of the soil resources. And this is a worldwide environmental issue (Novara et al., 2011; Vanlauwe et al., 2015; Musinguzi et al., 2015; Pereira et al., 2015; Mwagno et al., 2016). Agriculture terraces are a strategy to reduce the soil erosion, improve the soil fertility and allow the ploughing (Cerdà et al., 2010; Li et al., 2014). Although this idea is well accepted there are few scientific evidences that demonstrate that soils in the terraced areas are more stable, fertile and sustainable that the soil in non terraced areas. In fact, the ploughing in comparison to the abandoned or not ploughed land results in the soil degradation (Lieskovský and Kenderessy, 2014; Gao et al., 2015; Parras-Alcántara et al., 2014). This is mainly due to the lack of vegetation that increase the surface runoff (Cerdà et al., 1998; Keesstra et al., 2007). And why is necessary to develop also in terraced landscapes soil erosion control strategies (Mekonnen et al., 2015a; Mekonnen et al., 2015b; Prosdocimi et al., 2016). Our objective was to assess the soil organic matter content (Walkley and Black, 1934), the soil bulk density (ring method), the aggregate stabilility (drop impact) and the water repellency (Water Drop Penetration Time test) in four study sites in the Sierra de Enguera. Two sites were terraced: one abandoned 40 years before the measurements and the other still active with olive crops. And two control sites non-terraced. We used the paired plot strategy to compare the impact of terracing and abandonment. At each site we collected randomly 50 soil samples at 0-2 cm, 4-6 and 8-10 cm depth. At each sampling point 100 WDPT measurements where carried out, and one sample for the bulk density, and one for the organic matter, and one for the soil aggregate stability were collected. The soil surface samples shown the largest differences. The

  15. Molecular aggregation of humic substances

    USGS Publications Warehouse

    Wershaw, R. L.

    1999-01-01

    Humic substances (HS) form molecular aggregates in solution and on mineral surfaces. Elucidation of the mechanism of formation of these aggregates is important for an understanding of the interactions of HS in soils arid natural waters. The HS are formed mainly by enzymatic depolymerization and oxidation of plant biopolymers. These reactions transform the aromatic and lipid plant components into amphiphilic molecules, that is, molecules that consist of separate hydrophobic (nonpolar) and hydrophilic (polar) parts. The nonpolar parts of the molecules are composed of relatively unaltered segments of plant polymers and the polar parts of carboxylic acid groups. These amphiphiles form membrane-like aggregates on mineral surfaces and micelle-like aggregates in solution. The exterior surfaces of these aggregates are hydrophilic, and the interiors constitute separate hydrophobic liquid-like phases.

  16. Spatial and temporal distribution of 13C labelled plant residues in soil aggregates and Lumbricus terrestris surface casts: A combination of Transmission Electron Microscopy and Nanoscale Secondary Ion Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Vidal, Alix; Remusat, Laurent; Watteau, Françoise; Derenne, Sylvie; Quenea, Katell

    2016-04-01

    Earthworms play a central role in litter decomposition, soil structuration and carbon cycling. They ingest both organic and mineral compounds which are mixed, complexed with mucus and dejected in form of casts at the soil surface and along burrows. Bulk isotopic or biochemical technics have often been used to study the incorporation of litter in soil and casts, but they could not reflect the complex interaction between soil, plant and microorganisms at the microscale. However, the heterogeneous distribution of organic carbon in soil structures induces contrasted microbial activity areas. Nano-scale secondary ion mass spectrometry (NanoSIMS), which is a high spatial resolution method providing elemental and isotopic maps of organic and mineral materials, has recently been applied in soil science (Herrmann et al., 2007; Vogel et al., 2014). The combination of Nano-scale secondary ion mass spectrometry (NanoSIMS) and Transmission Electron Microscopy (TEM) has proven its potential to investigate labelled residues incorporation in earthworm casts (Vidal et al., 2016). In line of this work, we studied the spatial and temporal distribution of plant residues in soil aggregates and earthworm surface casts. This study aimed to (1) identify the decomposition states of labelled plant residues incorporated at different time steps, in casts and soil, (2) identify the microorganisms implied in this decomposition (3) relate the organic matter states of decomposition with their 13C signature. A one year mesocosm experiment was set up to follow the incorporation of 13C labelled Ryegrass (Lolium multiflorum) litter in a soil in the presence of anecic earthworms (Lumbricus terrestris). Soil and surface cast samples were collected after 8 and 54 weeks, embedded in epoxy resin and cut into ultra-thin sections. Soil was fractionated and all and analyzed with TEM and NanoSIMS, obtaining secondary ion images of 12C, 16O, 12C14N, 13C14N and 28Si. The δ13C maps were obtained using the 13C14

  17. Construction aggregates

    USGS Publications Warehouse

    Nelson, T.I.; Bolen, W.P.

    2007-01-01

    Construction aggregates, primarily stone, sand and gravel, are recovered from widespread naturally occurring mineral deposits and processed for use primarily in the construction industry. They are mined, crushed, sorted by size and sold loose or combined with portland cement or asphaltic cement to make concrete products to build roads, houses, buildings, and other structures. Much smaller quantities are used in agriculture, cement manufacture, chemical and metallurgical processes, glass production and many other products.

  18. Construction aggregates

    USGS Publications Warehouse

    Tepordei, V.V.

    1996-01-01

    Part of the Annual Commodities Review 1995. Production of construction aggregates such as crushed stone and construction sand and gravel showed a marginal increase in 1995. Most of the 1995 increases were due to funding for highway construction work. The major areas of concern to the industry included issues relating to wetlands classification and the classification of crystalline silica as a probable human carcinogen. Despite this, an increase in demand is anticipated for 1996.

  19. Aggregated and complementary: symmetric proliferation, overyielding, and mass effects explain fine-root biomass in soil patches in a diverse temperate deciduous forest landscape.

    PubMed

    Valverde-Barrantes, Oscar J; Smemo, Kurt A; Feinstein, Larry M; Kershner, Mark W; Blackwood, Christopher B

    2015-01-01

    Few studies describe root distributions at the species level in diverse forests, although belowground species interactions and traits are often assumed to affect fine-root biomass (FRB). We used molecular barcoding to study how FRB of trees relates to soil characteristics, species identity, root diversity, and root traits, and how these relationships are affected by proximity to ecotones in a temperate forest landscape. We found that soil patch root biomass increased in response to soil resources across all species, and there was little belowground vertical or horizontal spatial segregation among species. Root traits and species relative abundance did not explain significant variation in FRB after correcting for soil fertility. A positive relationship between phylogenetic diversity and FRB indicated significant belowground overyielding attributable to local root diversity. Finally, variation in FRB explained by soil fertility and diversity was reduced near ecotones, but only because of a reduction in biomass in periodically anoxic areas. These results suggest that symmetric responses to soil properties are coupled with complementary species traits and interactions to explain variation in FRB among soil patches. In addition, landscape-level dispersal among habitats and across ecotones helps explain variation in the strength of these relationships in complex landscapes.

  20. Aggregate stability in citrus plantations. The impact of drip irrigation

    NASA Astrophysics Data System (ADS)

    Cerdà, A.; Mataix-Solera, J.; Arcenegui, V.

    2012-04-01

    Soil aggregate stability is a key property for soil and water conservation, and a synthetic parameter to quantify the soil degradation. Aggregation is relevant in soils where vegetation cover is scarce (Cerdà, 1996). Most of the research carried out to determine the soil aggregate stability was done in forest soils (Mataix-Solera et al., 2011) and little is done on farms (Cerdà, 2000). The research have show the effect of vegetation cover on soil aggregate stability (Cerdà, 1998) but little is known when vegetation is scarce, rare or not found such it can be seeing in agriculture soils. Then, aggregation is the main factor to control the soil losses and to improve the water availability. Moreover, agriculture management can improve the soil aggregate characteristics and the first step in this direction should be to quantify the aggregate stability. There is no information about the aggregate stability of soils under citrus production, although the research did show that the soil losses in the farms with citrus plantations is very high (Cerdà et al., 2009), and that aggregation should play a key role as the soils are bare due to the widespread use of herbicides. From 2009 to 2011, samples were collected in summer and winter in a chemically managed farm in Montesa, Eastern Iberian Peninsula. Ten irrigated patches and ten non-irrigated patches were selected to compare the effect of the drip irrigation on the soil aggregate stability. The Ten Drop Impacts (TDI) and the Counting the number of drops (CND) tests were applied at 200 aggregates (10 samples x 10 aggregates x 2 sites) in winter and summer in 2009, 2010 and 2011. The results show that the irrigated patches had TDI values that ranged from 43 to 56 % and that the non-irrigated reached values of 41 to 54 %. The CND samples ranged from 29 to 38 drops in the non-irrigated patches to 32 to 42 drop-impacts in the irrigated soil patches. No trends were found from winter to summer during the three years time period

  1. Liquid chromatography-atmospheric pressure photoionization-Orbitrap analysis of fullerene aggregates on surface soils and river sediments from Santa Catarina (Brazil).

    PubMed

    Sanchís, Josep; Oliveira, Luis Felipe Silva; de Leão, Felipe Baptista; Farré, Marinella; Barceló, Damià

    2015-02-01

    In the present work, a new analytical approach is proposed for the analysis of seven fullerenes (C₆₀, C₇₀, N-methylfulleropyrrolidine, [6,6]-phenyl C₆₁ butyric acid methyl ester, [6,6]-thienyl C61 butyric acid methyl ester, C60 pyrrolidine tris-acid ethyl ester and [6,6]-phenyl C₇₁ butyric acid methyl ester fullerenes) in soils and sediments. This procedure combines an ultrasound-assisted solvent extraction (UAE) with toluene followed by liquid chromatography (LC), using a pyrenylpropyl group bonded silica based column, coupled to a high-resolution mass spectrometer (HRMS) using atmospheric pressure photoionisation (APPI) in negative ion mode. The analytical performance for fullerene separation of the pyrenylpropyl group bonded silica column was compared to the C18 column. For the ultra-trace analysis of fullerenes in complex environmental samples, the use of the APPI source and the use of the electrospray ionisation (ESI) source were compared. Using this approach for the analysis of fullerenes in complex matrices, a series of advantages, in terms of sensitivity and specificity, have been demonstrated. The method limits of detection (MLOD) and the method limits of quantification (MLOQ) in soils and sediments ranged from 0.022 to 0.39 pg/g and from 0.072 to 1.3 pg/g, respectively. Recoveries were between 68 and 106%. The analytical method was applied in order to assess the occurrence of selected fullerenes in 45 soils of Sul Catarinense (Santa Catalina State, Brazil) and 15 sediments from the Tubarão River, presenting different pressures of contamination: a coal-combustion power plant, car exhaust, coal mining industry and wastewater effluents. C₆₀ and C₇₀ fullerenes have been detected at concentrations ranging from the MLOD to 0.150 ng/g. None of the functionalised fullerenes were detected in any of the samples. Combustion processes, in particular car exhaust, were identified as the main source of fullerenes. However, the potential

  2. Relating soil biochemistry to sustainable crop production

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Amino acids, amino sugars, carbohydrates, phenols, and fatty acids together comprise appreciable proportions of soil organic matter (SOM). Their cycling contribute to soil processes, including nitrogen availability, carbon sequestration and aggregation. For example, soil accumulation of phenols has ...

  3. Environmentalism and natural aggregate mining

    USGS Publications Warehouse

    Drew, L.J.; Langer, W.H.; Sachs, J.S.

    2002-01-01

    Sustaining a developed economy and expanding a developing one require the use of large volumes of natural aggregate. Almost all human activity (commercial, recreational, or leisure) is transacted in or on facilities constructed from natural aggregate. In our urban and suburban worlds, we are almost totally dependent on supplies of water collected behind dams and transported through aqueducts made from concrete. Natural aggregate is essential to the facilities that produce energy-hydroelectric dams and coal-fired powerplants. Ironically, the utility created for mankind by the use of natural aggregate is rarely compared favorably with the environmental impacts of mining it. Instead, the empty quarries and pits are seen as large negative environmental consequences. At the root of this disassociation is the philosophy of environmentalism, which flavors our perceptions of the excavation, processing, and distribution of natural aggregate. The two end-member ideas in this philosophy are ecocentrism and anthropocentrism. Ecocentrism takes the position that the natural world is a organism whose arteries are the rivers-their flow must not be altered. The soil is another vital organ and must not be covered with concrete and asphalt. The motto of the ecocentrist is "man must live more lightly on the land." The anthropocentrist wants clean water and air and an uncluttered landscape for human use. Mining is allowed and even encouraged, but dust and noise from quarry and pit operations must be minimized. The large volume of truck traffic is viewed as a real menace to human life and should be regulated and isolated. The environmental problems that the producers of natural aggregate (crushed stone and sand and gravel) face today are mostly difficult social and political concerns associated with the large holes dug in the ground and the large volume of heavy truck traffic associated with quarry and pit operations. These concerns have increased in recent years as society's demand for

  4. Thermodynamics of Protein Aggregation

    NASA Astrophysics Data System (ADS)

    Osborne, Kenneth L.; Barz, Bogdan; Bachmann, Michael; Strodel, Birgit

    Amyloid protein aggregation characterizes many neurodegenerative disorders, including Alzheimer's, Parkinson's, and Creutz- feldt-Jakob disease. Evidence suggests that amyloid aggregates may share similar aggregation pathways, implying simulation of full-length amyloid proteins is not necessary for understanding amyloid formation. In this study we simulate GNNQQNY, the N-terminal prion-determining domain of the yeast protein Sup35 to investigate the thermodynamics of structural transitions during aggregation. We use a coarse-grained model with replica-exchange molecular dynamics to investigate the association of 3-, 6-, and 12-chain GNNQQNY systems and we determine the aggregation pathway by studying aggregation states of GN- NQQNY. We find that the aggregation of the hydrophilic GNNQQNY sequence is mainly driven by H-bond formation, leading to the formation of /3-sheets from the very beginning of the assembly process. Condensation (aggregation) and ordering take place simultaneously, which is underpinned by the occurrence of a single heat capacity peak only.

  5. Soil and Water: Some Teaching Suggestions.

    ERIC Educational Resources Information Center

    Fischer, Richard B.

    1987-01-01

    Outlines six soil and water investigations that students can pursue outdoors, in nature centers, or in classrooms: soil characteristics; relationship between soil ph and plant life; what aggregates tell us; differences in soil structure; differences in rate of water absorption by soil; and soil exploration with a Berlesi funnel. (NEC)

  6. On mean type aggregation.

    PubMed

    Yager, R R

    1996-01-01

    We introduce and define the concept of mean aggregation of a collection of n numbers. We point out that the lack of associativity of this operation compounds the problem of the extending mean of n numbers to n+1 numbers. The closely related concepts of self identity and the centering property are introduced as one imperative for extending mean aggregation operators. The problem of weighted mean aggregation is studied. A new concept of prioritized mean aggregation is then introduced. We next show that the technique of selecting an element based upon the performance of a random experiment can be considered as a mean aggregation operation.

  7. Active matter model of Myxococcus xanthus aggregation

    NASA Astrophysics Data System (ADS)

    Patch, Adam; Bahar, Fatmagul; Liu, Guannan; Thutupalli, Shashi; Welch, Roy; Yllanes, David; Shaevitz, Joshua; Marchetti, M. Cristina

    Myxococcus xanthus is a soil-dwelling bacterium that exhibits several fascinating collective behaviors including streaming, swarming, and generation of fruiting bodies. A striking feature of M. xanthus is that it periodically reverses its motility direction. The first stage of fruiting body formation is characterized by the aggregation of cells on a surface into round mesoscopic structures. Experiments have shown that this aggregation relies heavily on regulation of the reversal rate and local mechanical interactions, suggesting motility-induced phase separation may play an important role. We have adapted self-propelled particle models to include cell reversal and motility suppression resulting from sporulation observed in aggregates. Using 2D molecular dynamics simulations, we map the phase behavior in the space of Péclet number and local density and examine the kinetics of aggregation for comparison to experiments.

  8. Aggregations in Flatworms.

    ERIC Educational Resources Information Center

    Liffen, C. L.; Hunter, M.

    1980-01-01

    Described is a school project to investigate aggregations in flatworms which may be influenced by light intensity, temperature, and some form of chemical stimulus released by already aggregating flatworms. Such investigations could be adopted to suit many educational levels of science laboratory activities. (DS)

  9. Unbonded Aggregate Surface Roads

    DTIC Science & Technology

    2006-12-01

    are sufficiently angular and rough in texture, thus ensuring mixture stability. A popular asphalt mixture design method called Superpave Level 1...would not pass either of the Superpave aggregate requirements. Table 18 Additional Characteristics for the Fine Fraction Abbreviated Common Name...CBR values when compacted wet of optimum. This is likely attributable to their relatively high permeabilities . For soaked CBR tests, the aggregates

  10. Erosion of dust aggregates

    NASA Astrophysics Data System (ADS)

    Seizinger, A.; Krijt, S.; Kley, W.

    2013-12-01

    Aims: The aim of this work is to gain a deeper insight into how much different aggregate types are affected by erosion. Especially, it is important to study the influence of the velocity of the impacting projectiles. We also want to provide models for dust growth in protoplanetary disks with simple recipes to account for erosion effects. Methods: To study the erosion of dust aggregates we employed a molecular dynamics approach that features a detailed micro-physical model of the interaction of spherical grains. For the first time, the model has been extended by introducing a new visco-elastic damping force, which requires a proper calibration. Afterwards, different sample generation methods were used to cover a wide range of aggregate types. Results: The visco-elastic damping force introduced in this work turns out to be crucial to reproduce results obtained from laboratory experiments. After proper calibration, we find that erosion occurs for impact velocities of 5 ms-1 and above. Though fractal aggregates as formed during the first growth phase are most susceptible to erosion, we observe erosion of aggregates with rather compact surfaces as well. Conclusions: We find that bombarding a larger target aggregate with small projectiles results in erosion for impact velocities as low as a few ms-1. More compact aggregates suffer less from erosion. With increasing projectile size the transition from accretion to erosion is shifted to higher velocities. This allows larger bodies to grow through high velocity collisions with smaller aggregates.

  11. Low aggregation state diminishes ferrihydrite reactivity

    NASA Astrophysics Data System (ADS)

    Braunschweig, Juliane; Heister, Katja; Meckenstock, Rainer U.

    2013-04-01

    Ferrihydrite is an abundant iron(oxy)hydroxide in soils and sediments and plays an important role in microbial iron cycling due to its high reactivity. Therefore, it is often synthesized and used in geomicrobiological and mineralogical studies. The reactivities of synthetic ferrihydrites vary between different studies and synthesis protocols. Hence, we synthesized five different ferrihydrites and characterized them with XRD, FTIR, XPS, and BET specific surface area. The reactivity of the ferrihydrite samples towards ascorbic acid was examined and compared with microbial reduction rates by Geobacter sulfurreducens. FTIR and XRD results show the presence of secondary, higher crystalline iron oxide phases like goethite and akaganeite for two samples. Consequently, those samples revealed lower biotic and abiotic reduction rates compared to pure ferrihydrite. Comparison of reduction rates with the specific surface area of all ferrihydrites showed neither correlation with abiotic reductive dissolution nor with microbial reduction. Especially one sample, characterized by a very low aggregation state and presence of secondary minerals, revealed a poor reactivity. We speculate that apart from the occurring secondary minerals also the low aggregation state played an important role. Decreasing aggregation diminishes the amount of kinks and edges on the surfaces, which are produced at contact sites in aggregates. According to dissolution theories, dissolution mainly starts at those surface defects and slows down with decreasing amount of defects. Furthermore, the non-aggregated ferrihydrite is free of micropores, a further stimulant for dissolution. Independent repetitions of experiments and syntheses according to the same protocol but without formation of secondary minerals, confirmed the low reactivity of the non-aggregated ferrihydrite. In summary, our results indicate that a decreasing aggregation state of ferrihydrite to a certain size does increase the reactivity

  12. Charged Dust Aggregate Interactions

    NASA Astrophysics Data System (ADS)

    Matthews, Lorin; Hyde, Truell

    2015-11-01

    A proper understanding of the behavior of dust particle aggregates immersed in a complex plasma first requires a knowledge of the basic properties of the system. Among the most important of these are the net electrostatic charge and higher multipole moments on the dust aggregate as well as the manner in which the aggregate interacts with the local electrostatic fields. The formation of elongated, fractal-like aggregates levitating in the sheath electric field of a weakly ionized RF generated plasma discharge has recently been observed experimentally. The resulting data has shown that as aggregates approach one another, they can both accelerate and rotate. At equilibrium, aggregates are observed to levitate with regular spacing, rotating about their long axis aligned parallel to the sheath electric field. Since gas drag tends to slow any such rotation, energy must be constantly fed into the system in order to sustain it. A numerical model designed to analyze this motion provides both the electrostatic charge and higher multipole moments of the aggregate while including the forces due to thermophoresis, neutral gas drag, and the ion wakefield. This model will be used to investigate the ambient conditions leading to the observed interactions. This research is funded by NSF Grant 1414523.

  13. Aggregate and the environment

    USGS Publications Warehouse

    Langer, William H.; Drew, Lawrence J.; Sachs, J.S.

    2004-01-01

    This book is designed to help you understand our aggregate resources-their importance, where they come from, how they are processed for our use, the environmental concerns related to their mining and processing, how those concerns are addressed, and the policies and regulations designed to safeguard workers, neighbors, and the environment from the negative impacts of aggregate mining. We hope this understanding will help prepare you to be involved in decisions that need to be made-individually and as a society-to be good stewards of our aggregate resources and our living planet.

  14. Marine aggregate dynamics

    NASA Astrophysics Data System (ADS)

    The direction and scope of the Office of Naval Research's Marine Aggregate Dynamics Accelerated Research Initiative will be the topic of an open-house style meeting February 14, 7:30-10:00 P.M. in Ballroom D of the Hyatt Regency New Orleans at the Louisiana Superdome. This meeting is scheduled during the AGU/American Society of Limnology and Oceanography Ocean Sciences Meeting February 12-16 in New Orleans.The critical focus of the ARI is the measurement and modeling of the dynamics of the biological, physical, chemical and molecular processes that drive aggregation and produce aggregates. This new ARI will provide funding in Fiscal Years 1991-1995 to identify and quantify mechanisms that determine the distribution, abundance and size spectrum of aggregated particulate matter in the ocean.

  15. Protein Colloidal Aggregation Project

    NASA Technical Reports Server (NTRS)

    Oliva-Buisson, Yvette J. (Compiler)

    2014-01-01

    To investigate the pathways and kinetics of protein aggregation to allow accurate predictive modeling of the process and evaluation of potential inhibitors to prevalent diseases including cataract formation, chronic traumatic encephalopathy, Alzheimer's Disease, Parkinson's Disease and others.

  16. Aggregation and Averaging.

    ERIC Educational Resources Information Center

    Siegel, Irving H.

    The arithmetic processes of aggregation and averaging are basic to quantitative investigations of employment, unemployment, and related concepts. In explaining these concepts, this report stresses need for accuracy and consistency in measurements, and describes tools for analyzing alternative measures. (BH)

  17. Soil-Structural Stability as Affected by Clay Mineralogy, Soil Texture and Polyacrylamide Application

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil-structural stability (expressed in terms of aggregate stability and pore size distribution) depends on (i) soil inherent properties, (ii) extrinsic condition prevailing in the soil that may vary temporally and spatially, and (iii) addition of soil amendments. Different soil management practices...

  18. Fibronectin Aggregation and Assembly

    PubMed Central

    Ohashi, Tomoo; Erickson, Harold P.

    2011-01-01

    The mechanism of fibronectin (FN) assembly and the self-association sites are still unclear and contradictory, although the N-terminal 70-kDa region (I1–9) is commonly accepted as one of the assembly sites. We previously found that I1–9 binds to superfibronectin, which is an artificial FN aggregate induced by anastellin. In the present study, we found that I1–9 bound to the aggregate formed by anastellin and a small FN fragment, III1–2. An engineered disulfide bond in III2, which stabilizes folding, inhibited aggregation, but a disulfide bond in III1 did not. A gelatin precipitation assay showed that I1–9 did not interact with anastellin, III1, III2, III1–2, or several III1–2 mutants including III1–2KADA. (In contrast to previous studies, we found that the III1–2KADA mutant was identical in conformation to wild-type III1–2.) Because I1–9 only bound to the aggregate and the unfolding of III2 played a role in aggregation, we generated a III2 domain that was destabilized by deletion of the G strand. This mutant bound I1–9 as shown by the gelatin precipitation assay and fluorescence resonance energy transfer analysis, and it inhibited FN matrix assembly when added to cell culture. Next, we introduced disulfide mutations into full-length FN. Three disulfide locks in III2, III3, and III11 were required to dramatically reduce anastellin-induced aggregation. When we tested the disulfide mutants in cell culture, only the disulfide bond in III2 reduced the FN matrix. These results suggest that the unfolding of III2 is one of the key factors for FN aggregation and assembly. PMID:21949131

  19. Aggregate distribution and associated organic carbon influenced by cover crops

    NASA Astrophysics Data System (ADS)

    Barquero, Irene; García-González, Irene; Benito, Marta; Gabriel, Jose Luis; Quemada, Miguel; Hontoria, Chiquinquirá

    2013-04-01

    Replacing fallow with cover crops during the non-cropping period seems to be a good alternative to diminish soil degradation by enhancing soil aggregation and increasing organic carbon. The aim of this study was to analyze the effect of replacing fallow by different winter cover crops (CC) on the aggregate distribution and C associated of an Haplic Calcisol. The study area was located in Central Spain, under semi-arid Mediterranean climate. A 4-year field trial was conducted using Barley (Hordeum vulgare L.) and Vetch (Vicia sativa L.) as CC during the intercropping period of maize (Zea mays L.) under irrigation. All treatments were equally irrigated and fertilized. Maize was directly sown over CC residues previously killed in early spring. Composite samples were collected at 0-5 and 5-20 cm depths in each treatment on autumn of 2010. Soil samples were separated by wet sieving into four aggregate-size classes: large macroaggregates ( >2000 µm); small macroaggregates (250-2000 µm); microaggregates (53-250 µm); and < 53 µm (silt + clay size). Organic carbon associated to each aggregate-size class was measured by Walkley-Black Method. Our preliminary results showed that the aggregate-size distribution was dominated by microaggregates (48-53%) and the <53 µm fraction (40-44%) resulting in a low mean weight diameter (MWD). Both cover crops increased aggregate size resulting in a higher MWD (0.28 mm) in comparison with fallow (0.20 mm) in the 0-5 cm layer. Barley showed a higher MWD than fallow also in 5-20 cm layer. Organic carbon concentrations in aggregate-size classes at top layer followed the order: large macroaggregates > small macroaggregates > microaggregates > silt + clay size. Treatments did not influence C concentration in aggregate-size classes. In conclusion, cover crops improved soil structure increasing the proportion of macroaggregates and MWD being Barley more effective than Vetch at subsurface layer.

  20. The capacity of soil particles for spontaneous formation of macroaggregates after a wetting-drying cycle

    NASA Astrophysics Data System (ADS)

    Kholodov, V. A.

    2013-06-01

    The capacity of soil particles for spontaneous formation of aggregates >0.25 mm was studied in a laboratory experiment. The particles from soil aggregates (3-1 mm) (initially aggregated particles, APs) and initially free particles (FPs) of <0.25 mm in size were isolated from the soddy-podzolic and chernozemic soils under fallow and from the arable soddy-podzolic soil. The aggregates of 3-1 mm were ground and passed through a 0.25-mm sieve. Then, the aggregates and free particles were poured with water and dried, and the content of the formed aggregates and their water stability were determined; in the samples from the arable soddy-podzolic soil, the organic carbon content was also determined in the newly formed aggregates. The FPs from the untilled soils formed almost no aggregates. At the same time, the APs from these soils manifested the ability for the spontaneous formation of aggregates, including water-stable aggregates. In the arable soddy-podzolic soil, on the contrary, both FPs and APs demonstrated the capacity for spontaneous self-organization into aggregates. The water stability of the self-organized aggregates from the arable soil was similar regardless of their source (APs or FPs). It was supposed that the ability of the FPs from the arable soil to form macroaggregates reflects the mechanical degradation of the aggregates in the soil: tillage results in the degradation of the aggregates, and the particles capable of spontaneously aggregation temporarily fall in the fraction of <0.25 mm. The water-stable aggregates produced from the APs or FPs of the arable soil contained more organic carbon (1.89%) in comparison with the water-stable aggregates separated from the initial 3- to 1-mm aggregates of this soil (1.31%).

  1. The Influence of Biochar on Soil Processes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biochar may be a good soil amendment with the potential to sequester Carbon (C) for long periods of time. In addition, biochar added to soils could increase water infiltration and retention, increase cation exchange capacity and perhaps soil aggregation. However the effects of biochar on soil biol...

  2. Technology meets aggregate

    SciTech Connect

    Wilson, C.; Swan, C.

    2007-07-01

    New technology carried out at Tufts University and the University of Massachusetts on synthetic lightweight aggregate has created material from various qualities of fly ash from coal-fired power plants for use in different engineered applications. In pilot scale manufacturing tests an 'SLA' containing 80% fly ash and 20% mixed plastic waste from packaging was produced by 'dry blending' mixed plastic with high carbon fly ash. A trial run was completed to produce concrete masonry unit (CMU) blocks at a full-scale facility. It has been shown that SLA can be used as a partial substitution of a traditional stone aggregate in hot asphalt mix. 1 fig., 2 photos.

  3. Reconciling opposing soil processes in row-crop agroecosystems via soil functional zone management

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sustaining soil productivity in agroecosystems presents a fundamental ecological challenge: nutrient provisioning depends upon aggregate turnover and microbial decomposition of organic matter (SOM); yet to prevent soil depletion these processes must be balanced by those that restore nutrients and SO...

  4. Soil structural changes caused by agricultural machinery

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Effects of tractor traffic with high axle load on the aggregate size distribution, the total soil porosity, and the aggregate porosity were studied in a field experiment on a silty clay loam Greyzem soil. One and three tractors passes were made at pre-irrigated and non-irrigated 10x10 m plots. The v...

  5. Aggregates, broccoli and cauliflower

    NASA Astrophysics Data System (ADS)

    Grey, Francois; Kjems, Jørgen K.

    1989-09-01

    Naturally grown structures with fractal characters like broccoli and cauliflower are discussed and compared with DLA-type aggregates. It is suggested that the branching density can be used to characterize the growth process and an experimental method to determine this parameter is proposed.

  6. Comparison of soil amendments to decrease high strength in SE USA Coastal Plain soils using fuzzy decision-making analyses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cemented subsurface layers restrict root growth in many southeastern USA Coastal Plain soils. Though cementation is usually reduced by tillage, soil amendments can offer a more permanent solution if they develop aggregation. To increase aggregation, we amended 450 g of a Norfolk soil blend of 90% E ...

  7. Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region

    NASA Astrophysics Data System (ADS)

    Tang, F. K.; Cui, M.; Lu, Q.; Liu, Y. G.; Guo, H. Y.; Zhou, J. X.

    2015-08-01

    Changes in soil utilization significantly affect aggregate stability and aggregate-associated soil organic carbon (SOC). A field investigation and indoor analysis were conducted in order to study the soil aggregate stability and organic carbon distribution in the water-stable aggregates (WSA) of the bare land (BL), grassland (GL), shrubland (SL), and woodland (WL) in a typical karst gorge region. The results indicated that the BL, GL, SL, and WL were dominated by particles with sizes > 5 mm under dry sieving treatment, and that the soil aggregate contents of various sizes decreased as the particle size decreased. In addition, the BL, GL, SL, and WL were predominantly comprised of WSA < 0.25 mm under wet sieving treatment, and that the WSA contents initially increased, then decreased, and then increased again as the particle size decreased. Furthermore, at a soil depth of 0-60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSA > 0.25 mm, MWD and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. The results of this study indicated that, as the SOC contents increased after vegetation restoration, the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. The total SOC and SOC associated in WSA of various sizes were the highest at a soil depth of 0-20 cm. In addition, the SOC contents of the WSA increased as the soil aggregate sizes decreased. The SOC contents of the WSA < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm, which ranged from 18.85 to 41.08 %, comprised the majority of the total aggregate SOC contents. The woodland and

  8. Structure of soil microarthropod communities in agroecosystems

    SciTech Connect

    Farrar, F.P. Jr.; Crossley, D.A. Jr.

    1982-09-01

    By employing a simple modification of the Tullgren extractor it is possible to examine directly the spatial distribution of individual microarthropods within a thin square soil sample. The technique was applied to measure the area and population of soil microarthropod aggregations in conventional tillage and non-tillage soybean plots. Aggregations in the tilled soil were smaller and seemed to be less influential in determining the population distribution pattern, in comparison with the no-tillage plot. Population size was highly correlated with the map area of soil microarthropod aggregations.

  9. Stratification of soil organic matter and its importance on soil and water quality

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil organic matter is a key component of soil quality that sustains many important soil functions by providing the energy, substrates, and biological diversity to support biological activity, which affects aggregation (important for habitat space, oxygen supply, and preventing soil erosion), infilt...

  10. Tracking protein aggregate interactions

    PubMed Central

    Bartz, Jason C; Nilsson, K Peter R

    2011-01-01

    Amyloid fibrils share a structural motif consisting of highly ordered β-sheets aligned perpendicular to the fibril axis.1, 2 At each fibril end, β-sheets provide a template for recruiting and converting monomers.3 Different amyloid fibrils often co-occur in the same individual, yet whether a protein aggregate aids or inhibits the assembly of a heterologous protein is unclear. In prion disease, diverse prion aggregate structures, known as strains, are thought to be the basis of disparate disease phenotypes in the same species expressing identical prion protein sequences.4–7 Here we explore the interactions reported to occur when two distinct prion strains occur together in the central nervous system. PMID:21597336

  11. Zooplankton Aggregations Near Sills

    DTIC Science & Technology

    2003-09-30

    frequency echo-sounder system. This data were supplemented with multi-net (BIONESS) trawls, bongo nets, and otter trawls (operated by D. Mackas and group...side. The general composition of the zooplankton aggregations can be deduced from the relative levels of the three echo-sounder frequencies; krill ...Nov. 20th, 2002. Krill layer is evident at 66 – 90 m, coincident with BIONESS trawl through the region. 3 Figure 2 shows a comparison between

  12. Proteins aggregation and human diseases

    NASA Astrophysics Data System (ADS)

    Hu, Chin-Kun

    2015-04-01

    Many human diseases and the death of most supercentenarians are related to protein aggregation. Neurodegenerative diseases include Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), frontotemporallobar degeneration, etc. Such diseases are due to progressive loss of structure or function of neurons caused by protein aggregation. For example, AD is considered to be related to aggregation of Aβ40 (peptide with 40 amino acids) and Aβ42 (peptide with 42 amino acids) and HD is considered to be related to aggregation of polyQ (polyglutamine) peptides. In this paper, we briefly review our recent discovery of key factors for protein aggregation. We used a lattice model to study the aggregation rates of proteins and found that the probability for a protein sequence to appear in the conformation of the aggregated state can be used to determine the temperature at which proteins can aggregate most quickly. We used molecular dynamics and simple models of polymer chains to study relaxation and aggregation of proteins under various conditions and found that when the bending-angle dependent and torsion-angle dependent interactions are zero or very small, then protein chains tend to aggregate at lower temperatures. All atom models were used to identify a key peptide chain for the aggregation of insulin chains and to find that two polyQ chains prefer anti-parallel conformation. It is pointed out that in many cases, protein aggregation does not result from protein mis-folding. A potential drug from Chinese medicine was found for Alzheimer's disease.

  13. Changes on aggregation in mine waste amended with biochar and marble mud

    NASA Astrophysics Data System (ADS)

    Ángeles Muñoz, María; Guzmán, Jose; Zornoza, Raúl; Moreno-Barriga, Fabián; Faz, Ángel; Lal, Rattan

    2016-04-01

    Mining activities have produced large amounts of wastes over centuries accumulated in tailing ponds in Southeast Spain. Applications of biochar may have a high potential for reclamation of degraded soils. Distribution, size and stability of aggregates are important indices of soil physical quality. However, research data on aggregation processes at amended mining tailings with biochar are scanty. Therefore, the aim of this study was to determine the effects of seven different treatments involving biochar and marble mud (MM) on the aggregation in mine waste (MW). Seven different treatments were tested after 90 days of incubation in the laboratory. These treatments were the mix of MW and: biochar from solid pig manure (PM), biochar from cotton crop residues (CR), biochar from municipal solid waste (MSW), marble mud (MM), PM+MM, CR+MM, MSW+MM and control without amendment. High sand percentages were identified in the MW. The biochars made from wastes (PM, CR, MSW) were obtained through pyrolysis of feedstocks. The water stability of soil aggregates was studied. The data on total aggregation were corrected for the primary particles considering the sandy texture of the MW. Moreover, partial aggregation was determined for each fraction and the mean weight diameter (MWD) of aggregates was computed. Soil bulk density and total porosity were also determined. No significant differences were observed in total aggregation and MWD among treatments including the control. For the size range of >4.75 mm, there were significant differences in aggregates > 4.75 mm between CR+MM in comparison with that for CT. There were also significant differences between MSW and PM+MM for the 1-0.425 mm fraction, and between CT and MM and CR for 0.425-0.162 mm aggregate size fractions. Therefore, CR-derived biochar applied with MM enhanced stability of macro-aggregates. Furthermore, soil bulk density was also the lowest bulk density and total porosity the highest for the CR-derived biochar

  14. Roles of Reversible and Irreversible Aggregation in Sugar Processing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Colloids (1-1000 nm particles) in sugar cane/beet juice originate from non-sucrose impurities (polyphenolic colorants, residual soil, polysaccharides) of the plant materials; additional colloids form during the high temperature processing. Colloids are reactive towards aggregation, sorption, desorp...

  15. Aggregate structure and stability linked to carbon dynamics in a south Chilean Andisol

    NASA Astrophysics Data System (ADS)

    Huygens, D.; Boeckx, P.; van Cleemput, O.; Godoy, R.; Oyarzún, C.

    2005-02-01

    The extreme vulnerability of soil organic carbon to climate and land use change emphasizes the need for further research in different terrestrial ecosystems. We have studied the aggregate stability and carbon dynamics in a chronosequence of three different land uses in a south Chilean Andisols: a second growth Nothofagus obliqua forest (SGFOR), a grassland (GRASS) and a Pinus radiata plantation (PINUS). The aim of this study was to investigate the role of Al as soil organic matter stabilizing agent in this Andisol. In a case study, we linked differences in carbon dynamics between the three land use treatments to physical protection and recalcitrance of the soil organic matter (SOM). In this study, C aggregate stability and dynamics were studied using size and density fractionation experiments of the SOM, δ13C and total carbon analysis of the different SOM fractions, and mineralization measurements. The results showed that electrostatic attractions between and among Al-oxides and clay minerals are mainly responsible for the stabilization of soil aggregates and the physical protection of the enclosed soil organic carbon. Whole soil C mineralization rate constants were highest for SGFOR and PINUS, followed by GRASS. In contrast, incubation experiments of isolated macro organic matter fractions showed that the recalcitrance of the SOM decreased in another order: PINUS > SGFOR > GRASS. We concluded that physical protection of soil aggregates was the main process determining whole soil C mineralization. Land use changes affected soil organic carbon dynamics in this south Chilean Andisol by altering soil pH and consequently available Al.

  16. Biological and physical factors controlling aggregate stability under different climatic conditions in Southern Spain.

    NASA Astrophysics Data System (ADS)

    Ángel Gabarrón-Galeote, Miguel; Damián Ruiz-Sinoga, Jose; Francisco Martinez-Murillo, Juan; Lavee, Hanoch

    2013-04-01

    Soil aggregation is a key factor determining the soil structure. The presence of stable aggregates is essential to maintain a good soil structure, that in turn plays an important role in sustaining agricultural productivity and preserving environmental quality. A wide range of physical and biological soil components are involved in the aggregate formation and stabilization, namely clay mineral content; the quantity and quality of organic matter, that can be derived from plants, fungal hyphae, microorganism and soil animals; and the soil water content. Climatic conditions, through their effect on soil water content, vegetation cover and organic matter content, are supposed to affect soil aggregation. Thus the main objective of this research is to analyse the effect of organic matter, clay content and soil water content on aggregate stability along a climatic transect in Southern Spain. This study was conducted in four catchments along a pluviometric gradient in the South of Spain (rainfall depth decreases from west to east from more than 1000 mm year-1 to less than 300 mm year-1) and was based on a methodology approximating the climatic gradient in Mediterranean conditions. The selected sites shared similar conditions of geology, topography and soil use, which allowed making comparisons among them and relating the differences to the pluviometric conditions. In February 2007, 250 disturbed and undisturbed samples from the first 5cm of the soil were collected along the transect. We measured the aggregate stability, organic matter, clay content and bulk density of every sample. In the field we measured rainfall, air temperature, relative humidity, wind speed, wind direction, solar radiation, potential evapotranspiration, soil water content, vegetation cover and presence of litter. Our results suggest that aggregate stability is a property determined by a great number of highly variable factors, which can make extremely difficult to predict its behavior taking in

  17. Properties of concrete blocks prepared with low grade recycled aggregates.

    PubMed

    Poon, Chi-Sun; Kou, Shi-cong; Wan, Hui-wen; Etxeberria, Miren

    2009-08-01

    Low grade recycled aggregates obtained from a construction waste sorting facility were tested to assess the feasibility of using these in the production of concrete blocks. The characteristics of the sorted construction waste are significantly different from that of crushed concrete rubbles that are mostly derived from demolition waste streams. This is due to the presence of higher percentages of non-concrete components (e.g. >10% soil, brick, tiles etc.) in the sorted construction waste. In the study reported in this paper, three series of concrete block mixtures were prepared by using the low grade recycled aggregates to replace (i) natural coarse granite (10mm), and (ii) 0, 25, 50, 75 and 100% replacement levels of crushed stone fine (crushed natural granite <5mm) in the concrete blocks. Test results on properties such as density, compressive strength, transverse strength and drying shrinkage as well as strength reduction after exposure to 800 degrees C are presented below. The results show that the soil content in the recycled fine aggregate was an important factor in affecting the properties of the blocks produced and the mechanical strength deceased with increasing low grade recycled fine aggregate content. But the higher soil content in the recycled aggregates reduced the reduction of compressive strength of the blocks after exposure to high temperature due probably to the formation of a new crystalline phase. The results show that the low grade recycled aggregates obtained from the construction waste sorting facility has potential to be used as aggregates for making non-structural pre-cast concrete blocks.

  18. The influence of erythrocyte aggregation on induced platelet aggregation.

    PubMed

    Ott, C; Lardi, E; Schulzki, T; Reinhart, W H

    2010-01-01

    Red blood cells (RBCs) affect platelet aggregation in flowing blood (primary hemostasis). We tested the hypothesis that RBC aggregation could influence platelet aggregation. RBC aggregation was altered in vitro by: (i) changing plasma aggregatory properties with 3.7 g% dextran 40 (D40), 3.0 g% dextran 70 (D70) or 1.55 g% dextran 500 (D500); (ii) changing RBC aggregatory properties by incubating RBCs in 50 mU/ml neuraminidase for 60 min (reduction of the surface sialic acid content, thus reducing electrostatic repulsion) and subsequent RBC resuspension in platelet rich plasma (PRP) containing 1 g% dextran 70. RBC aggregation was assessed with the sedimentation rate (ESR). Platelet aggregation was measured: (i) in flowing whole blood with a platelet function analyzer PFA-100(R), which simulates in vivo conditions with RBCs flowing in the center and platelets along the wall, where they adhere to collagen and aggregate; and (ii) in a Chrono-log 700 Aggregometer, which measures changes of impedance by platelet aggregation in whole blood or changes in light transmission in PRP. We found that RBC aggregation increased with increasing molecular weight of dextran (ESR: 4 +/- 3 mm/h, 34 +/- 14 mm/h and 89 +/- 23 mm/hfor D40, D70 and D500, respectively, p < 0.0001) and with neuraminidase-treated RBCs (76 +/- 27 mm/h vs 27 +/- 8 mm/h, respectively, p < 0.0001). Platelet aggregation measured in whole blood under flow conditions (PFA-100) and without flow (Chronolog Aggregometer) was not affected by RBC aggregation. Our data suggest that RBC aggregation does not affect platelet aggregation in vitro and plays no role in primary hemostasis.

  19. Impact of disturbance on soil microbial activity in the Northern Chihuahuan Desert

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cryptobiotic soil crusts in arid regions contribute to ecosystem stability through increased water infiltration, soil aggregate stability, and nutrient cycling between the soil community and vascular plants. These crusts are particularly sensitive to compaction/fracturing disturbances such as livest...

  20. Structure of Viral Aggregates

    NASA Astrophysics Data System (ADS)

    Barr, Stephen; Luijten, Erik

    2010-03-01

    The aggregation of virus particles is a particular form of colloidal self-assembly, since viruses of a give type are monodisperse and have identical, anisotropic surface charge distributions. In small-angle X-ray scattering experiments, the Qbeta virus was found to organize in different crystal structures in the presence of divalent salt and non-adsorbing polymer. Since a simple isotropic potential cannot explain the occurrence of all observed phases, we employ computer simulations to investigate how the surface charge distribution affects the virus interactions. Using a detailed model of the virus particle, we find an asymmetric ion distribution around the virus which gives rise to the different phases observed.

  1. Soil Structure and Saturated Hydraulic Conductivity

    NASA Astrophysics Data System (ADS)

    Houskova, B.; Nagy, V.

    The role of soil structure on saturated hydraulic conductivity changes is studied in plough layers of texturally different soils. Three localities in western part of Slovakia in Zitny ostrov (Corn Island) were under investigation: locality Kalinkovo with light Calcaric Fluvisol (FAO 1970), Macov with medium heavy Calcari-mollic Fluvisol and Jurova with heavy Calcari-mollic Fluvisol. Soil structure was determined in dry as well as wet state and in size of macro and micro aggregates. Saturated hydraulic conductivity was measured by the help of double ring method. During the period of ring filling the soil surface was protected against aggregates damage by falling water drops. Spatial and temporal variability of studied parameters was evaluated. Cultivated crops were ensilage maize at medium heavy and heavy soil and colza at light soil. Textural composition of soil and actual water content at the beginning of measurement are one of major factor affecting aggregate stability and consequently also saturated hydraulic conductivity.

  2. Long-term Differences in Tillage and Land Use Affect Intra-aggregate Pore Heterogeneity

    SciTech Connect

    Kravchenko, A.N.; Wang, A.N.W.; Smucker, A.J.M.; Rivers, M.L.

    2012-10-25

    Recent advances in computed tomography provide measurement tools to study internal structures of soil aggregates at micrometer resolutions and to improve our understanding of specific mechanisms of various soil processes. Fractal analysis is one of the data analysis tools that can be helpful in evaluating heterogeneity of the intra-aggregate internal structures. The goal of this study was to examine how long-term tillage and land use differences affect intra-aggregate pore heterogeneity. The specific objectives were: (i) to develop an approach to enhance utility of box-counting fractal dimension in characterizing intra-aggregate pore heterogeneity; (ii) to examine intra-aggregate pores in macro-aggregates (4-6 mm in size) using the computed tomography scanning and fractal analysis, and (iii) to compare heterogeneity of intra-aggregate pore space in aggregates from loamy Alfisol soil subjected to 20 yr of contrasting management practices, namely, conventional tillage (chisel plow) (CT), no-till (NT), and native succession vegetation (NS). Three-dimensional images of the intact aggregates were obtained with a resolution of 14.6 {micro}m at the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. Proposed box-counting fractal dimension normalization was successfully implemented to estimate heterogeneity of pore voxel distributions without bias associated with different porosities in soil aggregates. The aggregates from all three studied treatments had higher porosity associated with large (>100 {micro}m) pores present in their centers than in their exteriors. Pores 15 to 60 {micro}m were equally abundant throughout entire aggregates but their distributions were more heterogeneous in aggregate interiors. The CT aggregates had greater numbers of pores 15 to 60 {micro}m than NT and NS. Distribution of pore voxels belonging to large pores was most heterogeneous in the aggregates from NS, followed by NT and by CT. This result was consistent with presence of

  3. Holographic characterization of protein aggregates

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Zhong, Xiao; Ruffner, David; Stutt, Alexandra; Philips, Laura; Ward, Michael; Grier, David

    Holographic characterization directly measures the size distribution of subvisible protein aggregates in suspension and offers insights into their morphology. Based on holographic video microscopy, this analytical technique records and interprets holograms of individual aggregates in protein solutions as they flow down a microfluidic channel, without requiring labeling or other exceptional sample preparation. The hologram of an individual protein aggregate is analyzed in real time with the Lorenz-Mie theory of light scattering to measure that aggregate's size and optical properties. Detecting, counting and characterizing subvisible aggregates proceeds fast enough for time-resolved studies, and lends itself to tracking trends in protein aggregation arising from changing environmental factors. No other analytical technique provides such a wealth of particle-resolved characterization data in situ. Holographic characterization promises accelerated development of therapeutic protein formulations, improved process control during manufacturing, and streamlined quality assurance during storage and at the point of use. Mrsec and MRI program of the NSF, Spheryx Inc.

  4. Roles of biology, chemistry, and physics in soil macroaggregate formation and stabilization

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil functions or ecosystem services depend on the distribution of macro- (= 0.25 mm) and micro- (< 0.25 mm) aggregates and open space between aggregates. It is the arrangement of the aggregates and pore space which allows air and water movement in and out of soil; reduces compaction; and stimulates...

  5. Fractal structure of asphaltene aggregates.

    PubMed

    Rahmani, Nazmul H G; Dabros, Tadeusz; Masliyah, Jacob H

    2005-05-15

    A photographic technique coupled with image analysis was used to measure the size and fractal dimension of asphaltene aggregates formed in toluene-heptane solvent mixtures. First, asphaltene aggregates were examined in a Couette device and the fractal-like aggregate structures were quantified using boundary fractal dimension. The evolution of the floc structure with time was monitored. The relative rates of shear-induced aggregation and fragmentation/restructuring determine the steady-state floc structure. The average floc structure became more compact or more organized as the floc size distribution attained steady state. Moreover, the higher the shear rate is, the more compact the floc structure is at steady state. Second, the fractal dimensions of asphaltene aggregates were also determined in a free-settling test. The experimentally determined terminal settling velocities and characteristic lengths of the aggregates were utilized to estimate the 2D and 3D fractal dimensions. The size-density fractal dimension (D(3)) of the asphaltene aggregates was estimated to be in the range from 1.06 to 1.41. This relatively low fractal dimension suggests that the asphaltene aggregates are highly porous and very tenuous. The aggregates have a structure with extremely low space-filling capacity.

  6. Aggregation dynamics of rigid polyelectrolytes

    NASA Astrophysics Data System (ADS)

    Tom, Anvy Moly; Rajesh, R.; Vemparala, Satyavani

    2016-01-01

    Similarly charged polyelectrolytes are known to attract each other and aggregate into bundles when the charge density of the polymers exceeds a critical value that depends on the valency of the counterions. The dynamics of aggregation of such rigid polyelectrolytes are studied using large scale molecular dynamics simulations. We find that the morphology of the aggregates depends on the value of the charge density of the polymers. For values close to the critical value, the shape of the aggregates is cylindrical with height equal to the length of a single polyelectrolyte chain. However, for larger values of charge, the linear extent of the aggregates increases as more and more polymers aggregate. In both the cases, we show that the number of aggregates decrease with time as power laws with exponents that are not numerically distinguishable from each other and are independent of charge density of the polymers, valency of the counterions, density, and length of the polyelectrolyte chain. We model the aggregation dynamics using the Smoluchowski coagulation equation with kernels determined from the molecular dynamics simulations and justify the numerically obtained value of the exponent. Our results suggest that once counterions condense, effective interactions between polyelectrolyte chains short-ranged and the aggregation of polyelectrolytes are diffusion-limited.

  7. Pore size distribution of soil near saturation as affected by soil type, land use, and soil amendments

    NASA Astrophysics Data System (ADS)

    Mamedov, A. I.; Wagner, L. E.; Levy, G. J.

    2008-12-01

    Storage and flow of water in soil voids, which are related to the size and geometry of the voids and flow rate are usually controlled by the void of the smallest size. Another reason for the complexity of water flow in soils is the intricate nature and change of the soil pores due to the modification of soil structure under different agricultural management and climatic conditions. Shrinking and swelling stresses enhance breakdown of aggregates and to subsequent collapse of pores, thus adversely affecting the movement of water and solutes in the soil. Our objective was to study the role of soil type, nature of cultivation, waste and soil stabilizers application, and soil condition on disturbed soil pore-size distribution, drainable porosity and water holding capacity at near saturation (infiltration porosity) using the high energy moisture characteristic method. In this method, the wetting process of the aggregates is accurately controlled, and the energy of hydration and entrapped air are the main forces responsible for aggregate breakdown. We studied a large number (> 300) of soil samples from different climatic regions varying (i) in their inherent properties (clay mineralogy, dispersion potential, texture, organic matter, Fe and Al oxides content), and; (ii) the conditions prevailing in the soil (water quality, salinity, sodicity, redox potential, type of tillage); and finally that were subjected to the addition of different soil amendments (polymers, gypsum, manure, sludge). The results showed that structural stability and pore size distribution strongly depended on soil type, conditions prevailing in the soil and the type of amendment used. Detailed analyses of the results provided valuable information on inter- and intra- aggregate porosities that may have vital bearing on the understanding of (i) solution transport processes in different soil types under different treatments or with different solute concentration, and (ii) down-profile transport of soil

  8. Insights into asphaltene aggregation in the Na-montmorillonite interlayer.

    PubMed

    Zhu, Xinzhe; Chen, Daoyi; Wu, Guozhong

    2016-10-01

    This study aimed to provide insights into the diffusion and aggregation of asphaltenes in the Na-montmorillonite (MMT) interlayer with different water saturation, salinity, interlayer space and humic substances. The molecular configuration, density profile, diffusion coefficient and aggregation intensity were determined by molecular dynamic simulation, while the 3D topography and particle size of the aggregates were characterized by atomic force microscopy. Results indicated that the diffusivity of asphaltenes was up to 5-fold higher in the MMT interlayer filled with fresh water than with saline water (salinity: 35‰). However, salinity had little impact on the asphaltene aggregation. This study also showed a marked decrease in the mobility of asphaltenes with decrease in the pore water content and the interlayer space of MMT. This was more pronounced in the organo-MMT where the humic substances were present. The co-aggregation process resulted in the sequestration of asphaltenes in the hollow cone-shaped cavity of humic substances in the MMT interlayer, which decreased the asphaltene diffusion by up to one-order of magnitude and increased the asphaltene aggregation by about 33%. These findings have important ramifications for evaluating the fate and transport of heavy fractions of the residual oil in the contaminated soils.

  9. Impact of spatial and temporal aggregation of input parameters on the assessment of irrigation scheme performance

    NASA Astrophysics Data System (ADS)

    Lorite, I. J.; Mateos, L.; Fereres, E.

    2005-01-01

    SummaryThe simulations of dynamic, spatially distributed non-linear models are impacted by the degree of spatial and temporal aggregation of their input parameters and variables. This paper deals with the impact of these aggregations on the assessment of irrigation scheme performance by simulating water use and crop yield. The analysis was carried out on a 7000 ha irrigation scheme located in Southern Spain. Four irrigation seasons differing in rainfall patterns were simulated (from 1996/1997 to 1999/2000) with the actual soil parameters and with hypothetical soil parameters representing wider ranges of soil variability. Three spatial aggregation levels were considered: (I) individual parcels (about 800), (II) command areas (83) and (III) the whole irrigation scheme. Equally, five temporal aggregation levels were defined: daily, weekly, monthly, quarterly and annually. The results showed little impact of spatial aggregation in the predictions of irrigation requirements and of crop yield for the scheme. The impact of aggregation was greater in rainy years, for deep-rooted crops (sunflower) and in scenarios with heterogeneous soils. The highest impact on irrigation requirement estimations was in the scenario of most heterogeneous soil and in 1999/2000, a year with frequent rainfall during the irrigation season: difference of 7% between aggregation levels I and III was found. Equally, it was found that temporal aggregation had only significant impact on irrigation requirements predictions for time steps longer than 4 months. In general, simulated annual irrigation requirements decreased as the time step increased. The impact was greater in rainy years (specially with abundant and concentrated rain events) and in crops which cycles coincide in part with the rainy season (garlic, winter cereals and olive). It is concluded that in this case, average, representative values for the main inputs of the model (crop, soil properties and sowing dates) can generate results

  10. Topics in Probabilistic Judgment Aggregation

    ERIC Educational Resources Information Center

    Wang, Guanchun

    2011-01-01

    This dissertation is a compilation of several studies that are united by their relevance to probabilistic judgment aggregation. In the face of complex and uncertain events, panels of judges are frequently consulted to provide probabilistic forecasts, and aggregation of such estimates in groups often yield better results than could have been made…

  11. Mineral of the month: aggregates

    USGS Publications Warehouse

    Tepordei, Valentin V.

    2005-01-01

    Natural aggregates, consisting of crushed stone, and sand and gravel, are a major contributor to economic health, and have an amazing variety of uses. Aggregates are among the most abundant mineral resources and are major basic raw materials used by construction, agriculture and other industries that employ complex chemical and metallurgical processes.

  12. Premature red blood cells have decreased aggregation and enhanced aggregability.

    PubMed

    Arbell, D; Orkin, B; Bar-Oz, B; Barshtein, G; Yedgar, S

    2008-06-01

    Preterm infants are highly susceptible to ischemic damage. This damage is most obvious in the brain, retina, and gastrointestinal tract. Studies focusing on the rheological properties of premature red blood cells (pRBCs) have consistently shown minimal or no RBC aggregation. Previously, measurements of pRBC aggregation kinetics indicated that specific plasma properties are responsible for the decreased RBC aggregation observed in the neonates, but that their specific RBC properties do not affect it. However, the strength of interaction in the pRBC aggregates as a function of medium composition has not been tested. In our previous research, we described clinically relevant parameters, that is, the aggregate resistance to disaggregation by flow. With the help of a cell flow property analyzer (CFA), we can monitor RBC aggregation by direct visualization of its dynamics during flow. We used the CFA to examine pRBC (from 9 premature babies) in the natural plasma and in PBS buffer supplemented with dextran (500 kDa) to distinguish between RBC intrinsic-cellular and plasma factors. pRBCs suspended in the native plasma showed minimal or no aggregation in comparison to normal adult RBC. When we transferred pRBCs from the same sample to the dextran solution, enhanced resistance to disaggregation by flow was apparent.

  13. Orthogonal flexible Rydberg aggregates

    NASA Astrophysics Data System (ADS)

    Leonhardt, K.; Wüster, S.; Rost, J. M.

    2016-02-01

    We study the link between atomic motion and exciton transport in flexible Rydberg aggregates, assemblies of highly excited light alkali-metal atoms, for which motion due to dipole-dipole interaction becomes relevant. In two one-dimensional atom chains crossing at a right angle adiabatic exciton transport is affected by a conical intersection of excitonic energy surfaces, which induces controllable nonadiabatic effects. A joint exciton-motion pulse that is initially governed by a single energy surface is coherently split into two modes after crossing the intersection. The modes induce strongly different atomic motion, leading to clear signatures of nonadiabatic effects in atomic density profiles. We have shown how this scenario can be exploited as an exciton switch, controlling direction and coherence properties of the joint pulse on the second of the chains [K. Leonhardt et al., Phys. Rev. Lett. 113, 223001 (2014), 10.1103/PhysRevLett.113.223001]. In this article we discuss the underlying complex dynamics in detail, characterize the switch, and derive our isotropic interaction model from a realistic anisotropic one with the addition of a magnetic bias field.

  14. Kinetics of Aggregation with Choice

    DOE PAGES

    Ben-Naim, Eli; Krapivsky, Paul

    2016-12-01

    Here we generalize the ordinary aggregation process to allow for choice. In ordinary aggregation, two random clusters merge and form a larger aggregate. In our implementation of choice, a target cluster and two candidate clusters are randomly selected and the target cluster merges with the larger of the two candidate clusters.We study the long-time asymptotic behavior and find that as in ordinary aggregation, the size density adheres to the standard scaling form. However, aggregation with choice exhibits a number of different features. First, the density of the smallest clusters exhibits anomalous scaling. Second, both the small-size and the large-size tailsmore » of the density are overpopulated, at the expense of the density of moderate-size clusters. Finally, we also study the complementary case where the smaller candidate cluster participates in the aggregation process and find an abundance of moderate clusters at the expense of small and large clusters. Additionally, we investigate aggregation processes with choice among multiple candidate clusters and a symmetric implementation where the choice is between two pairs of clusters.« less

  15. Kinetics of Aggregation with Choice

    SciTech Connect

    Ben-Naim, Eli; Krapivsky, Paul

    2016-12-01

    Here we generalize the ordinary aggregation process to allow for choice. In ordinary aggregation, two random clusters merge and form a larger aggregate. In our implementation of choice, a target cluster and two candidate clusters are randomly selected and the target cluster merges with the larger of the two candidate clusters.We study the long-time asymptotic behavior and find that as in ordinary aggregation, the size density adheres to the standard scaling form. However, aggregation with choice exhibits a number of different features. First, the density of the smallest clusters exhibits anomalous scaling. Second, both the small-size and the large-size tails of the density are overpopulated, at the expense of the density of moderate-size clusters. Finally, we also study the complementary case where the smaller candidate cluster participates in the aggregation process and find an abundance of moderate clusters at the expense of small and large clusters. Additionally, we investigate aggregation processes with choice among multiple candidate clusters and a symmetric implementation where the choice is between two pairs of clusters.

  16. Carbon dynamics and aggregation in a Vicia faba crop: influence of management practice and cultivar

    NASA Astrophysics Data System (ADS)

    Sánchez-Navarro, Virginia; Zornoza, Raúl; Faz, Ángel; Fernández, Juan

    2016-04-01

    In this study, we assessed the influence of a legume crop (Vicia faba) on the soil properties related to the carbon (C) cycle and soil aggregation, taking into account two cultivars (Muchamiel and Palenca) and two different management practices (conventional and organic). The study was randomly designed in blocks with four replications, in plots of 10 m2. Faba bean crop spanned from 24 November 2014 to 2 March 2015. We took a soil sampling (0-30 cm) from each plot at the end of the cycle to measure soil organic C, recalcitrant C, labile C fractions, microbial biomass C (MBC), aggregate stability and the enzyme activities β-glucosidase, β-glucosaminidase, dehydrogenase, cellulose and arylesterase. Results showed that the cultivar and the management practice had no significant effect on any of the analyzed properties. Significant positive correlations were only observed between soil organic C and arylesterase activity, recalcitrant C and labile C fractions, and recalcitrant C with arylesterase and cellulase activities. So, it seems that the selected cultivars and management practices had similar effects on C dynamics and aggregation. Both management practices maintain the same levels of soil organic C, the different organic C pools, and aggregate stability. In addition, soil microorganisms are responding to the recalcitrant fraction of the organic carbon by release of cellulases and arylesterases. Acknowledgements: This research was financed by the FP7 European Project Eurolegume (FP7-KBBE- 613781).

  17. Fractal aggregates in Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Cabane, M.; Rannou, P.; Chassefiere, E.; Israel, G.

    1993-04-01

    The cluster structure of Titan's atmosphere was modeled by using an Eulerian microphysical model with the specific formulation of microphysical laws applying to fractal particles. The growth of aggregates in the settling phase was treated by introducing the fractal dimension as a parameter of the model. The model was used to obtain a vertical distribution of size and number density of the aggregates for different production altitudes. Results confirm previous estimates of the formation altitude of photochemical aerosols. The vertical profile of the effective radius of aggregates was calculated as a function of the visible optical depth.

  18. Increased physical protection of soil carbon in the mineral soil of a poplar plantation after five years of free atmospheric CO2 enrichment (FACE)

    NASA Astrophysics Data System (ADS)

    Hoosbeek, M. R.; Vos, J. M.; Scarascia-Mugnozza, G. E.

    2006-07-01

    Free air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the existence of protection offered by the soil matrix and minerals. Fresh litter entering the soil enhances microbial activity which induces the binding of organic matter and soil particles into macro-aggregates. As the enclosed organic matter is decomposed, microbial and decomposition products become associated with mineral particles. This association results in the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the micro- and small macro-aggregates weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions. This study reveals that: 1) Species has an effect on the formation of macro-aggregates. The choice of species in a plantation or the effect of global change on species diversity, may therefore affect the stabilization and protection of soil C in aggregates. And 2) Increased atmospheric CO2 concentration increases the stabilization and protection of soil C in micro-aggregates formed within macro-aggregates. This mechanism increases the C sink of forest soils

  19. Surface fractals in liposome aggregation.

    PubMed

    Roldán-Vargas, Sándalo; Barnadas-Rodríguez, Ramon; Quesada-Pérez, Manuel; Estelrich, Joan; Callejas-Fernández, José

    2009-01-01

    In this work, the aggregation of charged liposomes induced by magnesium is investigated. Static and dynamic light scattering, Fourier-transform infrared spectroscopy, and cryotransmission electron microscopy are used as experimental techniques. In particular, multiple intracluster scattering is reduced to a negligible amount using a cross-correlation light scattering scheme. The analysis of the cluster structure, probed by means of static light scattering, reveals an evolution from surface fractals to mass fractals with increasing magnesium concentration. Cryotransmission electron microscopy micrographs of the aggregates are consistent with this interpretation. In addition, a comparative analysis of these results with those previously reported in the presence of calcium suggests that the different hydration energy between lipid vesicles when these divalent cations are present plays a fundamental role in the cluster morphology. This suggestion is also supported by infrared spectroscopy data. The kinetics of the aggregation processes is also analyzed through the time evolution of the mean diffusion coefficient of the aggregates.

  20. Cell aggregation: Packing soft grains

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Karttunen, M.

    2006-06-01

    Cellular aggregates may be considered as collections of membrane enclosed units with a pressure difference between the internal and external liquid phases. Cells are kept together by membrane adhesion and/or confined space compression. Pattern formation and, in particular, intercellular spacing have important roles in controlling solvent diffusion within such aggregates. A physical approach is used to study generic aspects of cellular packings in a confined space. Average material properties are derived from the free energy. The appearance of penetrating intercellular void channels is found to be critically governed by the cell wall adhesion mechanisms during the formation of dense aggregates. A fully relaxed aggregate efficiently hinders solvent diffusion at high hydrostatic pressures, while a small fraction (˜0.1) of adhesion related packing frustration is sufficient for breaking such a blockage even at high a pressure.

  1. Soil cultivation in vineyards alters interactions between soil biota and soil physical and hydrological properties

    NASA Astrophysics Data System (ADS)

    Zaller, Johann G.; Buchholz, Jacob; Querner, Pascal; Winter, Silvia; Kratschmer, Sophie; Pachinger, Bärbel; Strauss, Peter; Bauer, Thomas; Stiper, Katrin; Potthoff, Martin; Guernion, Muriel; Scimia, Jennifer; Cluzeau, Daniel

    2016-04-01

    Several ecosystem services provided by viticultural landscapes result from interactions between soil organisms and soil parameters. However, to what extent different soil cultivation intensities in vineyards compromise soil organisms and their interactions between soil physical and hydrological properties is not well understood. In this study we examined (i) to what extent different soil management intensities affect the activity and diversity of soil biota (earthworms, Collembola, litter decomposition), and (ii) how soil physical and hydrological properties influence these interactions, or vice versa. Investigating 16 vineyards in Austria, earthworms were assessed by hand sorting, Collembola via pitfall trapping and soil coring, litter decomposition by using the tea bag method. Additionally, soil physical (water infiltration, aggregate stability, porosity, bulk density, soil texture) and chemical (pH, soil carbon content, cation exchange capacity, potassium, phosphorus) parameters were assessed. Results showed complex ecological interactions between soil biota and various soil characteristics altered by management intensity. These investigations are part of the transdisciplinary BiodivERsA project VineDivers and will ultimately lead into management recommendations for various stakeholders.

  2. Aggregate breakdown of nanoparticulate titania

    NASA Astrophysics Data System (ADS)

    Venugopal, Navin

    Six nanosized titanium dioxide powders synthesized from a sulfate process were investigated. The targeted end-use of this powder was for a de-NOx catalyst honeycomb monolith. Alteration of synthesis parameters had resulted principally in differences in soluble ion level and specific surface area of the powders. The goal of this investigation was to understand the role of synthesis parameters in the aggregation behavior of these powders. Investigation via scanning electron microscopy of the powders revealed three different aggregation iterations at specific length scales. Secondary and higher order aggregate strength was investigated via oscillatory stress rheometry as a means of simulating shear conditions encountered during extrusion. G' and G'' were measured as a function of the applied oscillatory stress. Oscillatory rheometry indicated a strong variation as a function of the sulfate level of the particles in the viscoelastic yield strengths. Powder yield stresses ranged from 3.0 Pa to 24.0 Pa of oscillatory stress. Compaction curves to 750 MPa found strong similarities in extrapolated yield point of stage I and II compaction for each of the powders (at approximately 500 MPa) suggesting that the variation in sulfate was greatest above the primary aggregate level. Scanning electron microscopy of samples at different states of shear in oscillatory rheometry confirmed the variation in the linear elastic region and the viscous flow regime. A technique of this investigation was to approach aggregation via a novel perspective: aggregates are distinguished as being loose open structures that are highly disordered and stochastic in nature. The methodology used was to investigate the shear stresses required to rupture the various aggregation stages encountered and investigate the attempt to realign the now free-flowing constituents comprising the aggregate into a denser configuration. Mercury porosimetry was utilized to measure the pore size of the compact resulting from

  3. Effect of cover crops management in aggregate stability of a vineyard in Central Spain.

    NASA Astrophysics Data System (ADS)

    Ruiz-Colmenero, Marta; Bienes, Ramon; Marques, Maria-Jose

    2010-05-01

    Our research focuses in cover crop treatments used to avoid soil degradation in hillsides. The soil-plant interaction can influence the soil structure. In this study we pay special attention to the soil aggregates in a hillside vineyard (average slope of 14%), under Mediterranean semiarid climatic conditions (average annual temperature 14°C, annual rainfall around 400 mm), in the South East of Madrid located at an altitude of 800 masl. The soil classification according to USDA (2006) is Calcic Haploxeralf. Its particle size yields 58% sand, 18% silt and 24% clay, so that according to USDA classification it is a sandy clay loam soil. The bulk density of the first 10 cm of topsoil is 1.2 g cm-3 and its real density is 2.4 g cm-3. It has low organic matter content: 1.3 ± 0.1% (Walkley and Black, 1934). Three treatments were tested: i) traditional tillage ii) soil covered by Brachypodium distachyon allowing self-sowing, and iii) soil covered by Secale cereale, mown in early spring. In each treatment the aggregate stability was measured. These cover crops were established in a 2m wide strip at the center of the rows. We have collected samples of soil for each treatment along 2 years and we analyzed the aggregates, trying to find changes in their stability. Aggregates of 4 to 4.75 mm diameter were selected by dry sieving. The stability was measured with Drop-test: CND and TDI (Imeson and Vis, 1984). An improvement in the stability of aggregates was observed after two years of cover crop treatment. There are significant differences among the treatments analyzed with Kolmogorov-Smirnov test, being Brachypodium distachyon the treatment with more stable aggregates, it is necessary a mean higher than 8 drops to disintegrate every aggregate completely. Organic carbon was also measured by Loss on Ignition method (Schulte and Hopkins, 1996). This method can lead to an overestimation of the organic matter in soil samples but is considered suitable for aggregates. Again, those

  4. Glycation precedes lens crystallin aggregation

    SciTech Connect

    Swamy, M.S.; Perry, R.E.; Abraham, E.C.

    1987-05-01

    Non-enzymatic glycosylation (glycation) seems to have the potential to alter the structure of crystallins and make them susceptible to thiol oxidation leading to disulfide-linked high molecular weight (HMW) aggregate formation. They used streptozotocin diabetic rats during precataract and cataract stages and long-term cell-free glycation of bovine lens crystallins to study the relationship between glycation and lens crystallin aggregation. HMW aggregates and other protein components of the water-soluble (WS) and urea-soluble (US) fractions were separated by molecular sieve high performance liquid chromatography. Glycation was estimated by both (/sup 3/H)NaBH/sub 4/ reduction and phenylboronate agarose affinity chromatography. Levels of total glycated protein (GP) in the US fractions were about 2-fold higher than in the WS fractions and there was a linear increase in GP in both WS and US fractions. This increase was parallelled by a corresponding increase in HMW aggregates. Total GP extracted by the affinity method from the US fraction showed a predominance of HMW aggregates and vice versa. Cell-free glycation studies with bovine crystallins confirmed the results of the animals studies. Increasing glycation caused a corresponding increase in protein insolubilization and the insoluble fraction thus formed also contained more glycated protein. It appears that lens protein glycation, HMW aggregate formation, and protein insolubilization are interrelated.

  5. Model for amorphous aggregation processes

    NASA Astrophysics Data System (ADS)

    Stranks, Samuel D.; Ecroyd, Heath; van Sluyter, Steven; Waters, Elizabeth J.; Carver, John A.; von Smekal, Lorenz

    2009-11-01

    The amorphous aggregation of proteins is associated with many phenomena, ranging from the formation of protein wine haze to the development of cataract in the eye lens and the precipitation of recombinant proteins during their expression and purification. While much literature exists describing models for linear protein aggregation, such as amyloid fibril formation, there are few reports of models which address amorphous aggregation. Here, we propose a model to describe the amorphous aggregation of proteins which is also more widely applicable to other situations where a similar process occurs, such as in the formation of colloids and nanoclusters. As first applications of the model, we have tested it against experimental turbidimetry data of three proteins relevant to the wine industry and biochemistry, namely, thaumatin, a thaumatinlike protein, and α -lactalbumin. The model is very robust and describes amorphous experimental data to a high degree of accuracy. Details about the aggregation process, such as shape parameters of the aggregates and rate constants, can also be extracted.

  6. Ash Aggregates in Proximal Settings

    NASA Astrophysics Data System (ADS)

    Porritt, L. A.; Russell, K.

    2012-12-01

    Ash aggregates are thought to have formed within and been deposited by the eruption column and plume and dilute density currents and their associated ash clouds. Moist, turbulent ash clouds are considered critical to ash aggregate formation by facilitating both collision and adhesion of particles. Consequently, they are most commonly found in distal deposits. Proximal deposits containing ash aggregates are less commonly observed but do occur. Here we describe two occurrences of vent proximal ash aggregate-rich deposits; the first within a kimberlite pipe where coated ash pellets and accretionary lapilli are found within the intra-vent sequence; and the second in a glaciovolcanic setting where cored pellets (armoured lapilli) occur within <1 km of the vent. The deposits within the A418 pipe, Diavik Diamond Mine, Canada, are the residual deposits within the conduit and vent of the volcano and are characterised by an abundance of ash aggregates. Coated ash pellets are dominant but are followed in abundance by ash pellets, accretionary lapilli and rare cored pellets. The coated ash pellets typically range from 1 - 5 mm in diameter and have core to rim ratios of approximately 10:1. The formation and preservation of these aggregates elucidates the style and nature of the explosive phase of kimberlite eruption at A418 (and other pipes?). First, these pyroclasts dictate the intensity of the kimberlite eruption; it must be energetic enough to cause intense fragmentation of the kimberlite to produce a substantial volume of very fine ash (<62 μm). Secondly, the ash aggregates indicate the involvement of moisture coupled with the presence of dilute expanded eruption clouds. The structure and distribution of these deposits throughout the kimberlite conduit demand that aggregation and deposition operate entirely within the confines of the vent; this indicates that aggregation is a rapid process. Ash aggregates within glaciovolcanic sequences are also rarely documented. The

  7. Modeling Tritium and Chloride 36 Transport Through an Aggregated Oxisol

    NASA Astrophysics Data System (ADS)

    Nkedi-Kizza, P.; Biggar, J. W.; van Genuchten, M. Th.; Wierenga, P. J.; Selim, H. M.; Davidson, J. M.; Nielsen, D. R.

    1983-06-01

    Breakthrough curves (BTC's) of 3H2O and 36Cl simultaneously displaced through columns of various-sized aggregates of an Ione Oxisol soil were measured under water-saturated steady flow conditions. The data were simulated using two conceptual models. In model I, all soil water was assumed to be mobile with a physical equilibrium existing in the system. For model II, soil water was partitioned into mobile and immobile regions. Convective diffusive solute transport was limited to the mobile water region. Transfer of a tracer between the two soil water regions was assumed to occur at a rate proportional to the difference in tracer concentration between the two regions. Sorption Of 3H2O and 36Cl was considered to be an instantaneous linear and reversible process. The two unknown parameters in model I and the four unknown parameters in model II were estimated by fitting model predictions to the experimental data. Model I could only describe BTC's obtained from columns packed with small aggregates (0.5-1 mm) and for displacements run at small fluxes (0.2 cm/h), whereas model II described all the BTC's well. Peclet numbers P in model II, as measured on each separate column, were essentially constant, indicating a linear relationship between the apparent diffusion coefficient D and the mobile pore water velocity vm. The fraction of soil water that is mobile, Φ, and the mass transfer coefficient α were found to be a function of the physical and chemical properties of the porous medium (aggregate size, pore water velocity, and solution concentration).

  8. Labile aggregation stimulating substance, free fatty acids, and platelet aggregation.

    PubMed

    Gerrard, J M; White, J G; Krivit, W

    1976-01-01

    Labile aggregation stimulating substance (LASS), an intermediate produced during platelet biosynthesis of PGE2 and PGF2alpha, acts as a physiologic intercellular messenger to promote platelet aggregation and the release reaction. The activity is formed by intact cells after physiologic stimulation or can be generated from platelet membrane fractions after combination with arachidonate. In the present investigation, small amounts of polyunsaturated fatty acids added to an incubation mixture of platelet microsomes and arachidonate were found to significantly inhibit subsequent platelet aggregation. Saturated and mono-unsaturated fatty acids in the same concentrations were without effect. However, in higher concentrations mono-unsaturated fatty acids were found to be inhibitory and stearic acid was found to enhance subsequent platelet aggregation. The inhibition caused by the polyunsaturated fatty acid, linoleate, was shown to be the result of an effect on the production of LASS through an interaction with the platelet enzyme responsible for conversion of arachidonate to LASS. In contrast, stearic acid was found to enhance platelet aggregation by acting on the platelets and not directly on LASS production. The results suggest that small changes in the fatty acid composition of platelet phospholipids could significantly influence platelet reactivity.

  9. Impacts of Cropping Systems on Aggregates Associated Organic Carbon and Nitrogen in a Semiarid Highland Agroecosystem

    PubMed Central

    Chu, Jiashu; Zhang, Tianzhe; Chang, Weidong; Zhang, Dan; Zulfiqar, Saman; Fu, Aigen; Hao, Yaqi

    2016-01-01

    The effect of cropping system on the distribution of organic carbon (OC) and nitrogen (N) in soil aggregates has not been well addressed, which is important for understanding the sequestration of OC and N in agricultural soils. We analyzed the distribution of OC and N associated with soil aggregates in three unfertilized cropping systems in a 27-year field experiment: continuously cropped alfalfa, continuously cropped wheat and a legume-grain rotation. The objectives were to understand the effect of cropping system on the distribution of OC and N in aggregates and to examine the relationships between the changes in OC and N stocks in total soils and in aggregates. The cropping systems increased the stocks of OC and N in total soils (0–40 cm) at mean rates of 15.6 g OC m-2 yr-1 and 1.2 g N m-2 yr-1 relative to a fallow control. The continuous cropping of alfalfa produced the largest increases at the 0–20 cm depth. The OC and N stocks in total soils were significantly correlated with the changes in the >0.053 mm aggregates. 27-year of cropping increased OC stocks in the >0.053 mm size class of aggregates and N stocks in the >0.25 mm size class but decreased OC stocks in the <0.053 mm size class and N stocks in the <0.25 mm size class. The increases in OC and N stocks in these aggregates accounted for 99.5 and 98.7% of the total increases, respectively, in the continuous alfalfa system. The increases in the OC and N stocks associated with the >0.25 mm aggregate size class accounted for more than 97% of the total increases in the continuous wheat and the legume-grain rotation systems. These results suggested that long-term cropping has the potential to sequester OC and N in soils and that the increases in soil OC and N stocks were mainly due to increases associated with aggregates >0.053 mm. PMID:27764209

  10. Radon exhalation from sub-slab aggregate used in home construction in Canada.

    PubMed

    Bergman, Lauren; Lee, Jaeyoung; Sadi, Baki; Chen, Jing

    2015-06-01

    Exposure to elevated levels of radon in homes has been shown to result in an increased risk of developing lung cancer. The two largest contributors to indoor radon are radon in soil gas, formed from the rocks and soil surrounding the home, and building materials such as aggregate. This study measured the surface radon exhalation rates for 35 aggregate samples collected from producers across Canada. The radon exhalation rates ranged from 2.3 to 479.9 Bq m(-2) d(-1), with a mean of 80.7±112 Bq m(-2) d(-1). Using a simple, conservative analysis, the aggregate contribution to radon concentrations in an unfinished basement was determined. The maximum estimated radon concentration was 32.5±2.7 Bq m(-3), or ~16 % of the Canadian Radon Guideline. It can be concluded that under normal conditions radon exhalation from aggregate contributes very little to the total radon concentration in indoor air.

  11. Soils as Sediment database: closing a gap between soil science and geomorphology

    NASA Astrophysics Data System (ADS)

    Kuhn, Nikolaus J.

    2016-04-01

    Soils are an interface between the Earth's spheres and shaped by the nature of the interaction between them. The relevance of soil properties for the nature of the interaction between atmosphere, hydrosphere and biosphere is well-studied and accepted, on point- or ecotone-scale. However, this understanding of the largely vertical connections between spheres is not matched by a similar recognition of soil properties affecting processes acting largely in a lateral way across the land surface, such as erosion, transport and deposition of soil. Key areas where such an understanding is essential are all issues related to the lateral movement of soil-bound substances that affect the nature of soils itself, as well as water or vegetation downslope from the source area. The redistribution of eroded soil falls several disciplines, most notably soil science, agronomy, hydrology and geomorphology. Accordingly, the way sediment is described differs: in soil science, aggregation and structure are essential properties, while most process-based soil erosion models treat soil as a mixture of individual mineral grains, based on concepts derived in fluvial geomorphology or civil engineering. The actual behavior of aggregated sediment is not reflected by either approach and difficult to capture due to the dynamic nature of aggregation, especially in an environment such as running water. Still, a proxy to assess the uncertainties introduced by aggregation on the behavior of soil as sediment would represent a step forward. To develop such a proxy, a database collating relevant soil and sediment properties could serve as an initial step to identify which soil types and erosion scenarios are prone to generate a high uncertainty compared to the use of soil texture in erosion models. Furthermore, it could serve to develop standardized analytical procedures for appropriate description of soil as sediment.

  12. Fractal Aggregates in Tennis Ball Systems

    ERIC Educational Resources Information Center

    Sabin, J.; Bandin, M.; Prieto, G.; Sarmiento, F.

    2009-01-01

    We present a new practical exercise to explain the mechanisms of aggregation of some colloids which are otherwise not easy to understand. We have used tennis balls to simulate, in a visual way, the aggregation of colloids under reaction-limited colloid aggregation (RLCA) and diffusion-limited colloid aggregation (DLCA) regimes. We have used the…

  13. Thermodynamic modeling of asphaltene aggregation.

    PubMed

    Rogel, E

    2004-02-03

    A new molecular thermodynamic model for the description of the aggregation behavior of asphaltenes in different solvents is presented. This new model is relatively simple and strictly predictive and does not use any experimental information from asphaltene solutions. In this model, asphaltene aggregates are described as composed of an aromatic core formed by stacked aromatic sheets surrounded by aliphatic chains. The proposed model qualitatively predicts the asphaltene aggregation behavior in a series of different solvents. In particular, the experimental trends observed for the variation of aggregate size with (1) asphaltene molecular characteristics (condensation index, aromaticity, and chain length), (2) asphaltene concentration, (3) solvent characteristics, and (4) temperature have been successfully reproduced by the proposed model. The model also provides a plausible explanation for the existence or absence of a critical micelle concentration (cmc) for asphaltene solutions. Specifically, the model predicted that the asphaltenes with low aromaticities and low aromatic condensations do not exhibit cmc behavior. Finally, the obtained results clearly support the classical model for asphaltene aggregates.

  14. Spatial aggregation: Language and applications

    SciTech Connect

    Bailey-Kellogg, C.; Zhao, F.; Yip, K.

    1996-12-31

    Spatial aggregation is a framework for organizing computations around image-like, analogue representations of physical processes in data interpretation and control tasks. It conceptualizes common computational structures in a class of implemented problem solvers for difficult scientific and engineering problems. It comprises a mechanism, a language, and a programming style. The spatial aggregation mechanism transforms a numerical input field to successively higher-level descriptions by applying a small, identical set of operators to each layer given a metric, neighborhood relation and equivalence relation. This paper describes the spatial aggregation language and its applications. The spatial aggregation language provides two abstract data types - neighborhood graph and field - and a set of interface operators for constructing the transformations of the field, together with a library of component implementations from which a user can mix-and-match and specialize for a particular application. The language allows users to isolate and express important computational ideas in different problem domains while hiding low-level details. We illustrate the use of the language with examples ranging from trajectory grouping in dynamics interpretation to region growing in image analysis. Programs for these different task domains can be written in a modular, concise fashion in the spatial aggregation language.

  15. Leaching behaviour of synthetic aggregates.

    PubMed

    van der Sloot, H A; Hoede, D; Cresswell, D J; Barton, J R

    2001-01-01

    In the framework of EU project "Utilising innovative kiln technology to recycle waste into synthetic aggregate" (BRST-CT98-5234), the leaching behaviour of synthetic aggregates has been studied to assess its environmental compatibility in the various stages of its use. Since the conditions are very different for the different uses, the assessment calls for a variety of different leaching conditions. The pH dependence test is used to cover important differences in pH environment to which the materials are exposed to as well as for an assessment of the buffering capacity of the material. Synthetic aggregate features a low buffer capacity, which makes it sensitive to externally imposed pH conditions. Utilisation and storage exposed to acidic conditions needs to be avoided. The results of the pH dependence test and column leaching test are mutually consistent. The CEN TC 154 method appears to provide systematically low values due to the arbitrary selection of test conditions. Synthetic aggregate studied to date will not adversely affect the concrete in its service life. The main issue for aggregate use is the recycling and the "end of life" condition, when the material becomes construction debris. Not metals, but oxyanions, such as Cr VI and Mo are most relevant under these conditions. A concise test has been applied to assess crucial aspects of leaching for different production mixes.

  16. Novel insights into amylin aggregation

    PubMed Central

    Pillay, Karen; Govender, Patrick

    2014-01-01

    Amylin is a peptide that aggregates into species that are toxic to pancreatic beta cells, leading to type II diabetes. This study has for the first time quantified amylin association and dissociation kinetics (association constant (ka) = 28.7 ± 5.1 L mol−1 s−1 and dissociation constant (kd) = 2.8 ± 0.6 ×10−4 s−1) using surface plasmon resonance (SPR). Thus far, techniques used for the sizing of amylin aggregates do not cater for the real-time monitoring of unconstrained amylin in solution. In this regard we evaluated recently innovated nanoparticle tracking analysis (NTA). In addition, both SPR and NTA were used to study the effect of previously synthesized amylin derivatives on amylin aggregation and to evaluate their potential as a cell-free system for screening potential inhibitors of amylin-mediated cytotoxicity. Results obtained from NTA highlighted a predominance of 100–300 nm amylin aggregates and correlation to previously published cytotoxicity results suggests the toxic species of amylin to be 200–300 nm in size. The results seem to indicate that NTA has potential as a new technique to monitor the aggregation potential of amyloid peptides in solution and also to screen potential inhibitors of amylin-mediated cytotoxicity. PMID:26019498

  17. Aggregated Recommendation through Random Forests

    PubMed Central

    2014-01-01

    Aggregated recommendation refers to the process of suggesting one kind of items to a group of users. Compared to user-oriented or item-oriented approaches, it is more general and, therefore, more appropriate for cold-start recommendation. In this paper, we propose a random forest approach to create aggregated recommender systems. The approach is used to predict the rating of a group of users to a kind of items. In the preprocessing stage, we merge user, item, and rating information to construct an aggregated decision table, where rating information serves as the decision attribute. We also model the data conversion process corresponding to the new user, new item, and both new problems. In the training stage, a forest is built for the aggregated training set, where each leaf is assigned a distribution of discrete rating. In the testing stage, we present four predicting approaches to compute evaluation values based on the distribution of each tree. Experiments results on the well-known MovieLens dataset show that the aggregated approach maintains an acceptable level of accuracy. PMID:25180204

  18. Aggregate stability in mine residues after reclamation with biochar

    NASA Astrophysics Data System (ADS)

    Moreno-Barriga, Fabián; Díaz, Vicente; Acosta, José; Faz, Ángel; Zornoza, Raúl

    2016-04-01

    This study aims to assess how the addition of biochar and marble waste to acidic mine residues affected aggregate stability (AS) and contributed to the improvement of soil texture. For this purpose, a lab incubation was carried out for 90 days. Biochars derived from pig manure (PM), crop residues (CR) and municipal solid waste (MSW) were added to the soil at a rate of 20 g kg-1. The marble waste (MW) was added at a rate of 200 g kg-1, with the aim of increasing pH from 3 to 8 (pH of the native soils of the area). Biochars and MW were applied independently and combined. A control treatment was used without application of amendments. The evolution of AS was periodically monitored at 2, 4, 7, 15, 30 and 90 days by the method of artificial rainfall. Results showed, at the end of the incubation, that the addition of MW alone did not significantly increased AS with comparison to CT (30%). However, the biochar, alone or together with MW, significantly increased AS, the treatment receiving CR derived biochar being the one with the highest values (46%). Increments in AS were significant from the day 30 of incubation. AS showed a significant correlation with the total organic carbon content, but was not correlated with organic carbon fractions (soluble, labile, recalcitrant), inorganic carbon, microbial biomass carbon, enzyme activities, exchangeable fraction of heavy metals (As, Cd, Cu, Pb, Zn), pH, electrical conductivity nor greenhouse gas emissions (NO₂, CH₄). Thus, the application of biochar (alone or in combination with MW as a source of calcium carbonate) significantly increased the formation of stable aggregates in former acidic mine residues, favoring the development of soil structure, essential to create a soil from residues. It seems that the total content of organic carbon is directly controlling aggregation, rather than other labile organic sources. Moreover, pH, salinity or the presence of exchangeable metals did not seem to affect soil aggregation

  19. [Nitrogen Fraction Distributions and Impacts on Soil Nitrogen Mineralization in Different Vegetation Restorations of Karst Rocky Desertification].

    PubMed

    Hu, Ning; Ma, Zhi-min; Lan, Jia-cheng; Wu, Yu-chun; Chen, Gao-qi; Fu, Wa-li; Wen, Zhi-lin; Wang, Wen-jing

    2015-09-01

    In order to illuminate the impact on soil nitrogen accumulation and supply in karst rocky desertification area, the distribution characteristics of soil nitrogen pool for each class of soil aggregates and the relationship between aggregates nitrogen pool and soil nitrogen mineralization were analyzed in this study. The results showed that the content of total nitrogen, light fraction nitrogen, available nitrogen and mineral nitrogen in soil aggregates had an increasing tendency along with the descending of aggregate-size, and the highest content was occurred in < 0. 25 mm. The content of nitrogen fractions for all aggregate-classes followed in the order of abandoned land < grass land < brush land < brush-arbor land < arbor land in different sample plots. Artificial forest lands had more effects on the improvement of the soil nitrogen than honeysuckle land. In this study it also showed the nitrogen stockpiling quantity of each aggregate-size class was differed in all aggregate-size classes, in which the content of nitrogen fraction in 5-10 mm and 2-5 mm classes of soil aggregate-size were the highest. And it meant that soil nutrient mainly was stored in large size aggregates. Large size aggregates were significant to the storage of soil nutrient. For each class of soil aggregate-size, the contribution of the nitrogen stockpiling quantity of 0. 25-1 mm class to soil net nitrogen mineralization quantity was the biggest, and following >5mm and 2-5 mm classes, and the others were the smallest. With the positive vegetation succession, the weight percentage of > 5 mm aggregate-size classes was improved and the nitrogen storage of macro-aggregates also was increased. Accordingly, the capacity of soil supply mineral nitrogen and storage organic nitrogen were intensified.

  20. Customer Aggregation: An Opportunity for Green Power?

    SciTech Connect

    Holt, E.; Bird, L.

    2001-02-26

    We undertook research into the experience of aggregation groups to determine whether customer aggregation offers an opportunity to bring green power choices to more customers. The objectives of this report, therefore, are to (1) identify the different types of aggregation that are occurring today, (2) learn whether aggregation offers an opportunity to advance sales of green power, and (3) share these concepts and approaches with potential aggregators and green power advocates.

  1. Equilibrium structure of ferrofluid aggregates.

    PubMed

    Yoon, Mina; Tománek, David

    2010-11-17

    We study the equilibrium structure of large but finite aggregates of magnetic dipoles, representing a colloidal suspension of magnetite particles in a ferrofluid. With increasing system size, the structural motif evolves from chains and rings to multi-chain and multi-ring assemblies. Very large systems form single- and multi-wall coils, tubes and scrolls. These structural changes result from a competition between various energy terms, which can be approximated analytically within a continuum model. We also study the effect of external parameters such as magnetic field on the relative stability of these structures. Our results may give insight into experimental data obtained during solidification of ferrofluid aggregates at temperatures where thermal fluctuations become negligible in comparison to inter-particle interactions. These data may also help to experimentally control the aggregation of magnetic particles.

  2. Equilibrium structure of ferrofluid aggregates

    SciTech Connect

    Yoon, Mina; Tomanek, David

    2010-01-01

    We study the equilibrium structure of large but finite aggregates of magnetic dipoles, representing a colloidal suspension of magnetite particles in a ferrofluid. With increasing system size, the structural motif evolves from chains and rings to multi-chain and multi-ring assemblies. Very large systems form single- and multi-wall coils, tubes and scrolls. These structural changes result from a competition between various energy terms, which can be approximated analytically within a continuum model. We also study the effect of external parameters such as magnetic field on the relative stability of these structures. Our results may give insight into experimental data obtained during solidification of ferrofluid aggregates at temperatures where thermal fluctuations become negligible in comparison to inter-particle interactions. These data may also help to experimentally control the aggregation of magnetic particles.

  3. A specialist's audit of aggregated occurrence records: An 'aggregator's' perspective.

    PubMed

    Belbin, Lee; Daly, Joanne; Hirsch, Tim; Hobern, Donald; Salle, John La

    2013-01-01

    A recent ZooKeys' paper (Mesibov, 2013: http://www.pensoft.net/journal_home_page.php?journal_id=1&page=article&SESID=df7bcb35b02603283dcb83ee0e0af0c9&type=show&article_id=5111) has highlighted data quality issues in aggregated data sets, but did not provide a realistic way to address these issues. This paper provides an aggregator's perspective including ways that the whole community can help to address data quality issues. The establishment of GBIF and national nodes (national aggregators) such as the Atlas of Living Australia (ALA) have integrated and exposed a huge diversity of biological observations along with many associated issues. Much of the admirable work by Mesibov (2013) was enabled by having the data exposed. Data quality, one of the highest priorities for GBIF, the national nodes and other aggregators, depends on both automatic methods and community experts to detect and correct data issues. Not all issues can however be automatically detected or corrected, so community assistance is needed to help improve the quality of exposed biological data. We do need to improve the infrastructure and associated processes to more easily identify data issues and document all changes to ensure a full record is permanently and publicly available.

  4. Hydrodynamic behavior of fractal aggregates

    NASA Astrophysics Data System (ADS)

    Wiltzius, Pierre

    1987-02-01

    Measurements of the radius of gyration RG and the hydrodynamic radius RH of colloidal silica aggregates are reported. These aggregates have fractal geometry and RH is proportional to RG for 500 Å<=RH<=7000 Å, with a ratio RH/RG=0.72+/-0.02. The results are compared with predictions for macromolecules of various shapes. The proportionality of the two radii can be understood with use of the pair correlation function of fractal objects and hydrodynamic interactions on the Oseen level. The value of the ratio remains to be explained.

  5. Markov Modeling with Soft Aggregation for Safety and Decision Analysis

    SciTech Connect

    COOPER,J. ARLIN

    1999-09-01

    Sensitivity measures for soil aggregation, for developing dependence methodology, for constructing early alert logic, for tracking trends, for relating the Markov model to other (e.g., Reason) models, for developing and demonstrating rudimentary laptop software, and for developing an input/output display methodology.

  6. Can biosolids reduce wind erosion of agricultural soils?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The application of biosolids to agricultural land has the potential to improve soil health and crop production. In addition, organic material contained in biosolids may enhance biological activity, retention of soil water, and soil aggregation. Thus, there is a likelihood that biosolids applied to s...

  7. Estimation of soil saturated hydraulic conductivity by artificial neural networks ensemble in smectitic soils

    NASA Astrophysics Data System (ADS)

    Sedaghat, A.; Bayat, H.; Safari Sinegani, A. A.

    2016-03-01

    The saturated hydraulic conductivity ( K s ) of the soil is one of the main soil physical properties. Indirect estimation of this parameter using pedo-transfer functions (PTFs) has received considerable attention. The Purpose of this study was to improve the estimation of K s using fractal parameters of particle and micro-aggregate size distributions in smectitic soils. In this study 260 disturbed and undisturbed soil samples were collected from Guilan province, the north of Iran. The fractal model of Bird and Perrier was used to compute the fractal parameters of particle and micro-aggregate size distributions. The PTFs were developed by artificial neural networks (ANNs) ensemble to estimate K s by using available soil data and fractal parameters. There were found significant correlations between K s and fractal parameters of particles and microaggregates. Estimation of K s was improved significantly by using fractal parameters of soil micro-aggregates as predictors. But using geometric mean and geometric standard deviation of particles diameter did not improve K s estimations significantly. Using fractal parameters of particles and micro-aggregates simultaneously, had the most effect in the estimation of K s . Generally, fractal parameters can be successfully used as input parameters to improve the estimation of K s in the PTFs in smectitic soils. As a result, ANNs ensemble successfully correlated the fractal parameters of particles and micro-aggregates to K s .

  8. Studies on recycled aggregates-based concrete.

    PubMed

    Rakshvir, Major; Barai, Sudhirkumar V

    2006-06-01

    Reduced extraction of raw materials, reduced transportation cost, improved profits, reduced environmental impact and fast-depleting reserves of conventional natural aggregates has necessitated the use of recycling, in order to be able to conserve conventional natural aggregate. In this study various physical and mechanical properties of recycled concrete aggregates were examined. Recycled concrete aggregates are different from natural aggregates and concrete made from them has specific properties. The percentages of recycled concrete aggregates were varied and it was observed that properties such as compressive strength showed a decrease of up to 10% as the percentage of recycled concrete aggregates increased. Water absorption of recycled aggregates was found to be greater than natural aggregates, and this needs to be compensated during mix design.

  9. Mesoscale Simulation of Asphaltene Aggregation.

    PubMed

    Wang, Jiang; Ferguson, Andrew L

    2016-08-18

    Asphaltenes constitute a heavy aromatic crude oil fraction with a propensity to aggregate and precipitate out of solution during petroleum processing. Aggregation is thought to proceed according to the Yen-Mullins hierarchy, but the molecular mechanisms underlying mesoscopic assembly remain poorly understood. By combining coarse-grained molecular models parametrized using all-atom data with high-performance GPU hardware, we have performed molecular dynamics simulations of the aggregation of hundreds of asphaltenes over microsecond time scales. Our simulations reveal a hierarchical self-assembly mechanism consistent with the Yen-Mullins model, but the details are sensitive and depend on asphaltene chemistry and environment. At low concentrations asphaltenes exist predominantly as dispersed monomers. Upon increasing concentration, we first observe parallel stacking into 1D rod-like nanoaggregates, followed by the formation of clusters of nanoaggregates associated by offset, T-shaped, and edge-edge stacking. Asphaltenes possessing long aliphatic side chains cannot form nanoaggregate clusters due to steric repulsions between their aliphatic coronae. At very high concentrations, we observe a porous percolating network of rod-like nanoaggregates suspended in a sea of interpenetrating aliphatic side chains with a fractal dimension of ∼2. The lifetime of the rod-like aggregates is described by an exponential distribution reflecting a dynamic equilibrium between coagulation and fragmentation.

  10. RAGG - R EPISODIC AGGREGATION PACKAGE

    EPA Science Inventory

    The RAGG package is an R implementation of the CMAQ episodic model aggregation method developed by Constella Group and the Environmental Protection Agency. RAGG is a tool to provide climatological seasonal and annual deposition of sulphur and nitrogen for multimedia management. ...

  11. Sequence-dependent internalization of aggregating peptides.

    PubMed

    Couceiro, José R; Gallardo, Rodrigo; De Smet, Frederik; De Baets, Greet; Baatsen, Pieter; Annaert, Wim; Roose, Kenny; Saelens, Xavier; Schymkowitz, Joost; Rousseau, Frederic

    2015-01-02

    Recently, a number of aggregation disease polypeptides have been shown to spread from cell to cell, thereby displaying prionoid behavior. Studying aggregate internalization, however, is often hampered by the complex kinetics of the aggregation process, resulting in the concomitant uptake of aggregates of different sizes by competing mechanisms, which makes it difficult to isolate pathway-specific responses to aggregates. We designed synthetic aggregating peptides bearing different aggregation propensities with the aim of producing modes of uptake that are sufficiently distinct to differentially analyze the cellular response to internalization. We found that small acidic aggregates (≤500 nm in diameter) were taken up by nonspecific endocytosis as part of the fluid phase and traveled through the endosomal compartment to lysosomes. By contrast, bigger basic aggregates (>1 μm) were taken up through a mechanism dependent on cytoskeletal reorganization and membrane remodeling with the morphological hallmarks of phagocytosis. Importantly, the properties of these aggregates determined not only the mechanism of internalization but also the involvement of the proteostatic machinery (the assembly of interconnected networks that control the biogenesis, folding, trafficking, and degradation of proteins) in the process; whereas the internalization of small acidic aggregates is HSF1-independent, the uptake of larger basic aggregates was HSF1-dependent, requiring Hsp70. Our results show that the biophysical properties of aggregates determine both their mechanism of internalization and proteostatic response. It remains to be seen whether these differences in cellular response contribute to the particular role of specific aggregated proteins in disease.

  12. Precipitation Aggregation and the Local Environment

    NASA Astrophysics Data System (ADS)

    Smalley, Mark

    The details of large-scale spatial structures of precipitation have only recently become apparent with the advent of high-resolution near-global observations from space-borne radars. As such, the relationships between these structures and the local environment and global climate are just beginning to emerge in the scientific community. Precipitation aggregates on a wide variety of scales, from individual boundary layer instabilities to extra-tropical cyclones. Separate aggregation states have been associated with widely varying precipitation rates and atmospheric states, motivating the inclusion of spatial information in hydrologic and climate models. This work adds to the body of knowledge surrounding large-scale precipitation aggregation and its driving factors by describing and demonstrating a new method of defining the spatial characteristics of precipitation events. The analysis relies on the high sensitivity and high resolution of the CloudSat Cloud Profiling Radar for the identification of precipitation with near-global coverage. The method is based on the dependence of the probability of precipitation on search area, or spatial resolution. Variations in this relationship are caused by variations in the principal characteristics of event spatial patterns: the relative spacing between events, the number density of events, and the overall fraction of precipitating scenes at high resolution. Here, this relationship is modeled by a stretched exponential containing two coefficients, that are shown to depict seasonal general circulation patterns as well as local weather. NASA's Modern-Era Retrospective analysis for Research and Applications is then used to place those spatial characteristics in the context of the local and large-scale environment. At regional scale, precipitation event density during the Amazon wet season is shown to be dependent on zonal wind speed. On a global scale, the relative spacing of shallow oceanic precipitation depends on the

  13. Stabilities of ant nests and their adjacent soils

    NASA Astrophysics Data System (ADS)

    Echezona, B. C.; Igwe, C. A.

    2012-10-01

    Nests habour ants and termites and protect them from harsh environmental conditions. The structural stabilities of nests were studied to ascertain their relative vulnerability to environmental stresses. Arboreal-ant nests were pried from different trees, while epigeous-termite nests were excavated from soil surface within the sample area. Soils without any visible sign of ant or termite activity were also sampled 6 m away from the nests as control. Laboratory analysis result showed that irrespective of the tree hosts, the aggregate stabilities of the ant nests were lower than those of the ground termite, with nests formed on Cola nitida significantly showing lower aggregate stability (19.7%) than other antnest structures. Clay dispersion ratio, moisture content, water stable aggregate class <0.25mm and sand mass were each negatively correlated with aggregate stability, while water stable aggregate class1.00-0.50 mm gave a positive correlation. Nest structures were dominated more by water stable aggregate class >2.00 mm but path analysis demonstrated that water stable aggregate class <0.25 mm contributed most to the higher aggregate stability of the termite nest than the other nest. Nest aggregates had greater structural stability compared to the control soil. The higher structural stability of termite nests over other nest and soil was considered a better adaptive mechanism against body desiccation.

  14. Soil property effects on wind erosion of organic soils

    NASA Astrophysics Data System (ADS)

    Zobeck, Ted M.; Baddock, Matthew; Scott Van Pelt, R.; Tatarko, John; Acosta-Martinez, Veronica

    2013-09-01

    Histosols (also known as organic soils, mucks, or peats) are soils that are dominated by organic matter (OM > 20%) in half or more of the upper 80 cm. Forty two states have a total of 21 million ha of Histosols in the United States. These soils, when intensively cropped, are subject to wind erosion resulting in loss of crop productivity and degradation of soil, air, and water quality. Estimating wind erosion on Histosols has been determined by USDA-Natural Resources Conservation Service (NRCS) as a critical need for the Wind Erosion Prediction System (WEPS) model. WEPS has been developed to simulate wind erosion on agricultural land in the US, including soils with organic soil material surfaces. However, additional field measurements are needed to understand how soil properties vary among organic soils and to calibrate and validate estimates of wind erosion of organic soils using WEPS. Soil properties and sediment flux were measured in six soils with high organic contents located in Michigan and Florida, USA. Soil properties observed included organic matter content, particle density, dry mechanical stability, dry clod stability, wind erodible material, and geometric mean diameter of the surface aggregate distribution. A field portable wind tunnel was used to generate suspended sediment and dust from agricultural surfaces for soils ranging from 17% to 67% organic matter. The soils were tilled and rolled to provide a consolidated, friable surface. Dust emissions and saltation were measured using an isokinetic vertical slot sampler aspirated by a regulated suction source. Suspended dust was sampled using a Grimm optical particle size analyzer. Particle density of the saltation-sized material (>106 μm) was inversely related to OM content and varied from 2.41 g cm-3 for the soil with the lowest OM content to 1.61 g cm-3 for the soil with highest OM content. Wind erodible material and the geometric mean diameter of the surface soil were inversely related to dry clod

  15. Physical properties of soils in Rostov agglomeration

    NASA Astrophysics Data System (ADS)

    Gorbov, S. N.; Bezuglova, O. S.; Abrosimov, K. N.; Skvortsova, E. B.; Tagiverdiev, S. S.; Morozov, I. V.

    2016-08-01

    Physical properties of natural and anthropogenically transformed soils of Rostov agglomeration were examined. The data obtained by conventional methods and new approaches to the study of soil physical properties (in particular, tomographic study of soil monoliths) were used for comparing the soils of different functional zones of the urban area. For urban territories in the steppe zone, a comparison of humus-accumulative horizons (A, Asod, Ap, and buried [A] horizons) made it possible to trace tendencies of changes in surface soils under different anthropogenic impacts and in the buried and sealed soils. The microtomographic study demonstrated differences in the bulk density and aggregation of urban soils from different functional zones. The A horizon in the forest-park zone is characterized by good aggregation and high porosity, whereas buried humus-accumulative horizons of anthropogenically transformed soils are characterized by poor aggregation and low porosity. The traditional parameters of soil structure and texture also proved to be informative for the identification of urban pedogenesis.

  16. Key soil functional properties affected by soil organic matter - evidence from published literature

    NASA Astrophysics Data System (ADS)

    Murphy, Brian

    2015-07-01

    The effect of varying the amount of soil organic matter on a range of individual soil properties was investigated using a literature search of published information largely from Australia, but also included relevant information from overseas. Based on published pedotransfer functions, soil organic matter was shown to increase plant available water by 2 to 3 mm per 10 cm for each 1% increase in soil organic carbon, with the largest increases being associated with sandy soils. Aggregate stability increased with increasing soil organic carbon, with aggregate stability decreasing rapidly when soil organic carbon fell below 1.2 to 1.5 5%. Soil compactibility, friability and soil erodibility were favourably improved by increasing the levels of soil organic carbon. Nutrient cycling was a major function of soil organic matter. Substantial amounts of N, P and S become available to plants when the soil organic matter is mineralised. Soil organic matter also provides a food source for the microorganisms involved in the nutrient cycling of N, P, S and K. In soils with lower clay contents, and less active clays such as kaolinites, soil organic matter can supply a significant amount of the cation exchange capacity and buffering capacity against acidification. Soil organic matter can have a cation exchange capacity of 172 to 297 cmol(+)/kg. As the cation exchange capacity of soil organic matter varies with pH, the effectiveness of soil organic matter to contribute to cation exchange capacity below pH 5.5 is often minimal. Overall soil organic matter has the potential to affect a range of functional soil properties.

  17. Role of streams in myxobacteria aggregate formation

    NASA Astrophysics Data System (ADS)

    Kiskowski, Maria A.; Jiang, Yi; Alber, Mark S.

    2004-10-01

    Cell contact, movement and directionality are important factors in biological development (morphogenesis), and myxobacteria are a model system for studying cell-cell interaction and cell organization preceding differentiation. When starved, thousands of myxobacteria cells align, stream and form aggregates which later develop into round, non-motile spores. Canonically, cell aggregation has been attributed to attractive chemotaxis, a long range interaction, but there is growing evidence that myxobacteria organization depends on contact-mediated cell-cell communication. We present a discrete stochastic model based on contact-mediated signaling that suggests an explanation for the initialization of early aggregates, aggregation dynamics and final aggregate distribution. Our model qualitatively reproduces the unique structures of myxobacteria aggregates and detailed stages which occur during myxobacteria aggregation: first, aggregates initialize in random positions and cells join aggregates by random walk; second, cells redistribute by moving within transient streams connecting aggregates. Streams play a critical role in final aggregate size distribution by redistributing cells among fewer, larger aggregates. The mechanism by which streams redistribute cells depends on aggregate sizes and is enhanced by noise. Our model predicts that with increased internal noise, more streams would form and streams would last longer. Simulation results suggest a series of new experiments.

  18. Soil microstructure and factors of its formation

    NASA Astrophysics Data System (ADS)

    Alekseeva, T. V.

    2007-06-01

    The microstructural stability of soils of different geneses (steppe soils, tropical soils, and subtropical soils) developed from marine clay, loess, and weathering crusts was studied by the method of successive treatments with chemical reagents destroying the particular clay-aggregating components. The following dispersing agents were used: (1) H2O (pH 5.5), (2) 0.1 N NaCl (pH 6), (3) 0.002% Na2CO3 (pH 8.7), (4) 0.1 N NaOH (pH 11.5), (5) the Tamm reagent (pH 3.2), and (6) 0.1 N NaOH (pH 11.5). The properties of the clay subfractions obtained in the course of these treatments were studied by a set of analytical methods, including X-ray diffractometry, Mössbauer spectroscopy, and magnetic measurements. It was shown that soil microaggregates are formed under the impact of a number of physicochemical processes; the content and properties of inorganic components (clay minerals in soils with a high CEC and iron oxides in soils with a low CEC) are the controlling factors. The structure of the parent materials is transformed to different degrees to form the soil structure. For example, autonomous nondifferentiated soils inherit, to some extent, the specific microorganization of the parent material. At the same time, the redistribution of substances in the soil profile and in the landscape may exert a substantial influence on the soil structure and microstructure. This is particularly true for autonomous differentiated soils, turbated soils, accumulative soils, polylithogenic soils, and polygenetic soils. The properties of the obtained subfractions of the clay (the mineralogical composition, the Fe2+/(Fe2+ + Fe3+) ratio, the magnetic susceptibility, and the Cha/Cfa ratio) attest to the spatial heterogeneity of the composition and properties of the mineral and organic aggregated compounds in soils.

  19. Assessment of Soil Quality for Grazed Pastures with Agroforestry Buffers and Row Crop Systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Incorporation of trees and establishment of buffers are believed to enhance soil quality. Soil enzyme activities and water stable aggregates have been identified as good indices for assessing soil quality to evaluate early responses to changes in soil management. However, studies comparing these p...

  20. Soil quality parameters for row-crop and grazed pasture systems with agroforestry buffers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Incorporation of trees and establishment of buffers are practices that can improve soil quality. Soil enzyme activities and water stable aggregates are sensitive indices for assessing soil quality by detecting early changes in soil management. However, studies comparing grazed pasture and row crop...

  1. Depth stratification of soil organic matter as an indicator of multiple ecosystem services

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil organic matter is a key component of soil quality that sustains many key soil functions by providing the energy, substrates, and biological diversity to support biological activity, which affects aggregation (important for habitat space, oxygen supply, and preventing soil erosion), infiltration...

  2. Stratification of soil organic matter as an indicator of ecosystem services

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil organic matter is a key component of soil quality that sustains many key soil functions by providing the energy, substrates, and biological diversity to support biological activity, which affects aggregation (important for habitat space, oxygen supply, and preventing soil erosion), infiltration...

  3. Soil quality indicator responses to row crop, grazed pasture, and agroforestry buffer management

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Incorporation of trees and establishment of grass buffers within agroecosystems are management practices shown to enhance soil quality. Soil enzyme activities and water stable aggregates (WSA) have been identified as sensitive soil quality indicators to evaluate early responses to soil management. ...

  4. Oligomeric baroeffect and gas aggregation states

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1992-01-01

    The baroeffect is analyzed to include a gas that aggregates into higher-order polymers or oligomers. The resulting pressure change is found to vary independently of the molecular weight of the gas components and to depend only on the aggregation or oligomeric order of the gas. With increasing aggregation, diffusive slip velocities are found to increase. The calculations are extended to include general counterdiffusion of two distinct aggregation states (k-, j-mer) for the gas, and the pressure change is derived as a function that is independent of both molecular weight and the absolute aggregation. The only parameter that determines the baroeffect is the ratio of aggregated states, beta = k/j. For gases that reversibly aggregate, possible oscillatory behavior and complex dynamics for pressure are discussed. Gas aggregation may play a role for low-temperature crystal-growth conditions in which vapor concentrations of one (or more) species are high.

  5. Virus-induced aggregates in infected cells.

    PubMed

    Moshe, Adi; Gorovits, Rena

    2012-10-17

    During infection, many viruses induce cellular remodeling, resulting in the formation of insoluble aggregates/inclusions, usually containing viral structural proteins. Identification of aggregates has become a useful diagnostic tool for certain viral infections. There is wide variety of viral aggregates, which differ by their location, size, content and putative function. The role of aggregation in the context of a specific virus is often poorly understood, especially in the case of plant viruses. The aggregates are utilized by viruses to house a large complex of proteins of both viral and host origin to promote virus replication, translation, intra- and intercellular transportation. Aggregated structures may protect viral functional complexes from the cellular degradation machinery. Alternatively, the activation of host defense mechanisms may involve sequestration of virus components in aggregates, followed by their neutralization as toxic for the host cell. The diversity of virus-induced aggregates in mammalian and plant cells is the subject of this review.

  6. Protein aggregation in salt solutions

    PubMed Central

    Kastelic, Miha; Kalyuzhnyi, Yurij V.; Hribar-Lee, Barbara; Dill, Ken A.; Vlachy, Vojko

    2015-01-01

    Protein aggregation is broadly important in diseases and in formulations of biological drugs. Here, we develop a theoretical model for reversible protein–protein aggregation in salt solutions. We treat proteins as hard spheres having square-well-energy binding sites, using Wertheim’s thermodynamic perturbation theory. The necessary condition required for such modeling to be realistic is that proteins in solution during the experiment remain in their compact form. Within this limitation our model gives accurate liquid–liquid coexistence curves for lysozyme and γ IIIa-crystallin solutions in respective buffers. It provides good fits to the cloud-point curves of lysozyme in buffer–salt mixtures as a function of the type and concentration of salt. It than predicts full coexistence curves, osmotic compressibilities, and second virial coefficients under such conditions. This treatment may also be relevant to protein crystallization. PMID:25964322

  7. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size.

  8. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32 Project aggregation. (a) A responsible entity must group together and evaluate as a single project...

  9. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32 Project aggregation. (a) A responsible entity must group together and evaluate as a single project...

  10. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32 Project aggregation. (a) A responsible entity must group together and evaluate as a single project...

  11. 24 CFR 58.32 - Project aggregation.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Project aggregation. 58.32 Section... Environmental Review Process: Documentation, Range of Activities, Project Aggregation and Classification § 58.32 Project aggregation. (a) A responsible entity must group together and evaluate as a single project...

  12. Mineral resource of the month: aggregates

    USGS Publications Warehouse

    Willett, Jason C.

    2012-01-01

    Crushed stone and construction sand and gravel, the two major types of natural aggregates, are among the most abundant and accessible natural resources on the planet. The earliest civilizations used aggregates for various purposes, mainly construction. Today aggregates provide the basic raw materials for the foundation of modern society.

  13. 78 FR 68945 - Aggregation of Positions

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-15

    ... the aggregation provisions of part 150 of the Commission's regulations that are substantially similar... modifications proposed here to the aggregation provisions of part 150 would apply to the position limits regimes... position limits because it believes that these proposed amendments regarding aggregation of...

  14. Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

    PubMed Central

    Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

    2015-01-01

    Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability. PMID:25874864

  15. Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

    PubMed

    Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

    2015-01-01

    Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

  16. Gaussian multiscale aggregation applied to segmentation in hand biometrics.

    PubMed

    de Santos Sierra, Alberto; Avila, Carmen Sánchez; Casanova, Javier Guerra; del Pozo, Gonzalo Bailador

    2011-01-01

    This paper presents an image segmentation algorithm based on Gaussian multiscale aggregation oriented to hand biometric applications. The method is able to isolate the hand from a wide variety of background textures such as carpets, fabric, glass, grass, soil or stones. The evaluation was carried out by using a publicly available synthetic database with 408,000 hand images in different backgrounds, comparing the performance in terms of accuracy and computational cost to two competitive segmentation methods existing in literature, namely Lossy Data Compression (LDC) and Normalized Cuts (NCuts). The results highlight that the proposed method outperforms current competitive segmentation methods with regard to computational cost, time performance, accuracy and memory usage.

  17. Aggregate tensile strength and friability characteristics of furrow and sprinkler irrigated fields in Southern Idaho

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Agricultural crops grown in southern Idaho are furrow or sprinkler irrigated. Therefore, the soil experiences several wetting and drying cycles each growing season that can contribute to changes in aggregate tensile strength and friability. The objective of the research was to evaluate the influence...

  18. [Lysophosphatidic acid and human erythrocyte aggregation].

    PubMed

    Sheremet'ev, Iu A; Popovicheva, A N; Levin, G Ia

    2014-01-01

    The effects of lysophosphatidic acid on the morphology and aggregation of human erythrocytes has been studied. Morphology of erythrocytes and their aggregates were studied by light microscopy. It has been shown that lysophosphatidic acid changes the shape of red blood cells: diskocyte become echinocytes. Aggregation of red blood cells (rouleaux) was significantly reduced in autoplasma. At the same time there is a strong aggregation of echinocytes. This was accompanied by the formation of microvesicles. Adding normal plasma to echinocytes restores shape and aggregation of red blood cells consisting of "rouleaux". A possible mechanism of action of lysophosphatidic acid on erythrocytes is discussed.

  19. [AGGREGATION OF METABOLICALLY DEPLETED HUMAN ERYTHROCYTES].

    PubMed

    Sheremet'ev, Yu A; Popovicheva, A N; Rogozin, M M; Levin, G Ya

    2016-01-01

    An aggregation of erythrocytes in autologous plasma after blood storage for 14 days at 4 °C was studied using photometry and light microscopy. The decrease of ATP content, the formation of echinocytes and spheroechinocytes, the decrease of rouleaux form of erythrocyte aggregation were observed during the storage. On the other hand the aggregates of echinocytes were formed in the stored blood. The addition of plasma from the fresh blood didn't restore the normal discocytic shape and aggregation of erythrocytes in the stored blood. The possible mechanisms of erythrocytes and echinocytes aggregation are discussed.

  20. Beneficiation of natural aggregates by polymer impregnation

    SciTech Connect

    Webster, R.P.; Fontana, J.J.

    1980-09-01

    The use of polymer impregnation as a means of upgrading natural aggregates has been investigated. The effect of polymer impregnation on the physical and mechanical properties was evaluated in a series of tests performed using four aggregates of varying quality. The strength of concrete cast with polymer impregnated coarse aggregate was also tested. Two monomer systems were used in the investigation; a methyl methacrylate-based system and a styrene-based system. In general, significant improvements in the physical and mechanical properties of each of the four aggregates resulted from polymer impregnation. The strength of concrete cast with impregnated aggregates varied, being increased in some cases and decreased in others.

  1. Erythrocyte aggregation: basic aspects and clinical importance.

    PubMed

    Baskurt, Oguz K; Meiselman, Herbert J

    2013-01-01

    Red blood cell (RBC) aggregate to form two- and three-dimensional structures when suspended in aqueous solutions containing large plasma proteins or polymers; this aggregation is reversible and shear dependent (i.e., dispersed at high shear and reformed at low or stasis). The extent of aggregation is the main determinant of low shear blood viscosity, thus predicting an inverse relationship between aggregation and in vivo blood flow. However, the effects of aggregation on hemodynamic mechanisms (e.g., plasma skimming, Fåhraeus Effect, microvascular hematocrit) may promote rather than impede vascular blood flow. The impact of enhanced RBC aggregation on endothelial function and hemostatic mechanisms adds further complexity, thereby requiring specific attention to the nature, extent and time course of aggregation when considering its overall influence on tissue perfusion. A detailed understanding of aggregation effects is important from a clinical point of view since it may be enhanced during a variety of pathophysiological processes, including infections, circulatory and metabolic disorders, hematological pathologies and several other disease states. Altered RBC aggregation may be an indicator of disease as well as a factor affecting the course of the clinical condition; the prognostic value of RBC aggregation indices has been demonstrated in various diseases. Currently, RBC aggregation is an easily and accurately measurable parameter, and therefore may be expected to have broader clinical usage in the future.

  2. Dynamics and mechanisms of asbestos-fiber aggregate growth in water

    NASA Astrophysics Data System (ADS)

    Wu, L.; Ortiz, C. P.; Jerolmack, D. J.

    2015-12-01

    Most colloidal particles including asbestos fibers form aggregates in water, when solution chemistry provides favorable conditions. To date, the growth of colloidal aggregates has been observed in many model systems under optical and scanning electron microscopy; however, all of these studies have used near-spherical particles. The highly elongated nature of asbestos fibers may cause anomalous aggregate growth and morphology, but this has never been examined. Although the exposure pathway of concern for asbestos is through the air, asbestos particles typically reside in soil that is at least partially saturated, and aggregates formed in the aqueous phase may influence the mobility of particles in the environment. Here we study solution-phase aggregation kinetics of asbestos fibers using a liquid-cell by in situ microscopy, over micron to centimeter length scales and from a tenth of a second to hours. We employ an elliptical particle tracking technique to determine particle trajectories and to quantify diffusivity. Experiments reveal that diffusing fibers join by cross linking, but that such linking is sometimes reversible. The resulting aggregates are very sparse and non-compact, with a fractal dimension that is lower than any previously reported value. Their morphology, growth rate and particle size distribution exhibit non-classical behavior that deviates significantly from observations of aggregates composed of near-spherical particles. We also perform experiments using synthetic colloidal particles, and compare these to asbestos in order to separate the controls of particle shape vs. material properties. This direct method for quantitatively observing aggregate growth is a first step toward predicting asbestos fiber aggregate size distributions in the environment. Moreover, many emerging environmental contaminants - such as carbon nanotubes - are elongated colloids, and our work suggests that theories for aggregate growth may need to be modified in order to

  3. Simulation of J-aggregate microcavity photoluminescence

    NASA Astrophysics Data System (ADS)

    Michetti, Paolo; La Rocca, Giuseppe C.

    2008-05-01

    We have developed a model in order to account for the photoexcitation dynamics of J-aggregate films and strongly coupled J-aggregate microcavities. The J aggregates are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. The correspondence between the photophysics in J-aggregate films and that in J-aggregate microcavities is obtained by introducing a model polariton wave function mixing cavity photon modes and J-aggregate super-radiant excitons. With the same description of the material properties, we have calculated both absorption and luminescence spectra for the J-aggregate film and the photoluminescence of strongly coupled organic microcavities. The model is able to account for the fast relaxation dynamics in organic microcavities following nonresonant pumping and explains the temperature dependence of the ratio between the upper polariton and the lower polariton luminescence.

  4. Microwave extinction characteristics of nanoparticle aggregates

    NASA Astrophysics Data System (ADS)

    Wu, Y. P.; Cheng, J. X.; Liu, X. X.; Wang, H. X.; Zhao, F. T.; Wen, W. W.

    2016-07-01

    Structure of nanoparticle aggregates plays an important role in microwave extinction capacity. The diffusion-limited aggregation model (DLA) for fractal growth is utilized to explore the possible structures of nanoparticle aggregates by computer simulation. Based on the discrete dipole approximation (DDA) method, the microwave extinction performance by different nano-carborundum aggregates is numerically analyzed. The effects of the particle quantity, original diameter, fractal structure, as well as orientation on microwave extinction are investigated, and also the extinction characteristics of aggregates are compared with the spherical nanoparticle in the same volume. Numerical results give out that proper aggregation of nanoparticle is beneficial to microwave extinction capacity, and the microwave extinction cross section by aggregated granules is better than that of the spherical solid one in the same volume.

  5. Aggregation Kinetics of Interrupted Polyglutamine Peptides

    PubMed Central

    Walters, Robert H.; Murphy, Regina M.

    2011-01-01

    Abnormally expanded polyglutamine domains are associated with at least nine neurodegenerative diseases, including Huntington’s disease. Expansion of the glutamine region facilitates aggregation of the impacted protein, and aggregation has been linked to neurotoxicity. Studies of synthetic peptides have contributed substantially to our understanding of the mechanism of aggregation, because the underlying biophysics of polyglutamine-mediated association can be probed independent of their context within a larger protein. In this report, interrupting residues were inserted into polyglutamine peptides (Q20), and the impact on conformational and aggregation properties was examined. A peptide with 2 alanine residues formed laterally-aligned fibrillar aggregates which were similar to the uninterrupted Q20 peptide. Insertion of 2 proline residues resulted in soluble, nonfibrillar aggregates, which did not mature into insoluble aggregates. In contrast, insertion of a β-turn template DPG rapidly accelerated aggregation and resulted in a fibrillar aggregate morphology with little lateral alignment between fibrils. These results are interpreted to indicate that (a) long-range nonspecific interactions lead to the formation of soluble oligomers, while maturation of oligomers into fibrils requires conformational conversion, and (b) that soluble oligomers dynamically interact with each other, while insoluble aggregates are relatively inert. Kinetic analysis revealed that the increase in aggregation caused by the DPG insert is inconsistent with the nucleation-elongation mechanism of aggregation featuring a monomeric β-sheet nucleus. Rather, the data support a mechanism of polyglutamine aggregation by which monomers associate into soluble oligomers, which then undergo slow structural rearrangement to form sedimentable aggregates. PMID:21821045

  6. Role of organic matter on aggregate stability and related mechanisms through organic amendments

    NASA Astrophysics Data System (ADS)

    Zaher, Hafida

    2010-05-01

    To date, only a few studies have tried to simultaneously compare the role of neutral and uronic sugars and lipids on soil structural stability. Moreover, evidence for the mechanisms involved has often been established following wetting of moist aggregates after various pre-treatments thus altering aggregate structure and resulting in manipulations on altered aggregates on which the rapid wetting process may not be involved anymore. To the best of our knowledge, the objective of this work was to study the role of neutral and uronic sugars and lipids in affecting key mechanisms (swelling rate, pressure evolution) involved in the stabilization of soil structure. A long-term incubation study (48-wk) was performed on a clay loam and a silty-clay loam amended with de-inking-secondary sludge mix at three rates (8, 16 and 24 Mg dry matter ha-1), primary-secondary sludge mix at one rate (18 Mg oven-dry ha-1) and composted de-inking sludge at one rate (24 Mg ha-1). Different structural stability indices (stability of moist and dry aggregates, the amount of dispersible clay and loss of soil material following sudden wetting) were measured on a regular basis during the incubation, along with CO2 evolved, neutral and uronic sugar, and lipid contents. During the course of the incubations, significant increases in all stability indices were measured for both soil types. In general, the improvements in stability were proportional to the amount of C added as organic amendments. These improvements were linked to a very intense phase of C mineralization and associated with increases in neutral and uronic sugars as well as lipid contents. The statistical relationships found between the different carbonaceous fractions and stability indices were all highly significant and indicated no clear superiority of one fraction over another. Paper sludge amendments also resulted in significant decreases in maximum internal pressure of aggregate and aggregate swelling following immersion in water

  7. Investigating the mechanisms leading to protein aggregation

    NASA Astrophysics Data System (ADS)

    McNamara, Ruth; McManus, Jennifer J.

    2014-03-01

    The formation of protein aggregates is a feature of several diseases and is a problem during the manufacture of biopharmaceutical and protein based food products. During processing, stability may become compromised leading to the condensation of proteins to form non-native aggregates. The aim of this work is to induce aggregation on model proteins by the imposition of a particular stress to evaluate the extent of aggregation and to assess the degree of structural change to the protein. Aggregation of two proteins, lysozyme and bovine serum albumin has been induced by several mechanisms. Using various techniques (electrophoresis, HPLC, spectroscopic analysis, and microscopic techniques) both the level of aggregation extent of protein unfolding has been investigated for a range of solution conditions. Our results show that the amount of aggregation depends strongly on the mechanism by which non-native aggregation proceeds, and within each mechanism, solution conditions are an important factor. With the exception of aggregation by self-association (which is concentration dependent), the appearance of aggregation is driven by structural changes induced by the applied stress (heat, chemical denaturant, oxidation or contact with a surface). Author would like to acknowledge support from Science Foundation Ireland (SFI), National University of Maynooth John and Pat Hume Scholarship.

  8. Applications of aggregation theory to sustainability assessment

    DOE PAGES

    Pollesch, N.; Dale, V. H.

    2015-04-01

    In order to aid in transition towards operations that promote sustainability goals, researchers and stakeholders use sustainability assessments. Although assessments take various forms, many utilize diverse sets of indicators that can number anywhere from two to over 2000. Indices, composite indicators, or aggregate values are used to simplify high dimensional and complex data sets and to clarify assessment results. Although the choice of aggregation function is a key component in the development of the assessment, there are few examples to be found in literature to guide appropriate aggregation function selection. This paper develops a connection between the mathematical study ofmore » aggregation functions and sustainability assessment in order to aid in providing criteria for aggregation function selection. Relevant mathematical properties of aggregation functions are presented and interpreted. Lastly, we provide cases of these properties and their relation to previous sustainability assessment research. Examples show that mathematical aggregation properties can be used to address the topics of compensatory behavior and weak versus strong sustainability, aggregation of data under varying units of measurements, multiple site multiple indicator aggregation, and the determination of error bounds in aggregate output for normalized and non-normalized indicator measures.« less

  9. Applications of aggregation theory to sustainability assessment

    SciTech Connect

    Pollesch, N.; Dale, V. H.

    2015-04-01

    In order to aid in transition towards operations that promote sustainability goals, researchers and stakeholders use sustainability assessments. Although assessments take various forms, many utilize diverse sets of indicators that can number anywhere from two to over 2000. Indices, composite indicators, or aggregate values are used to simplify high dimensional and complex data sets and to clarify assessment results. Although the choice of aggregation function is a key component in the development of the assessment, there are few examples to be found in literature to guide appropriate aggregation function selection. This paper develops a connection between the mathematical study of aggregation functions and sustainability assessment in order to aid in providing criteria for aggregation function selection. Relevant mathematical properties of aggregation functions are presented and interpreted. Lastly, we provide cases of these properties and their relation to previous sustainability assessment research. Examples show that mathematical aggregation properties can be used to address the topics of compensatory behavior and weak versus strong sustainability, aggregation of data under varying units of measurements, multiple site multiple indicator aggregation, and the determination of error bounds in aggregate output for normalized and non-normalized indicator measures.

  10. Sectoral shifts and aggregate unemployment

    SciTech Connect

    Loungani, P.

    1986-01-01

    Some recent research has taken the view that sectoral or industry-specific shocks significantly affect aggregate unemployment by increasing the amount of inter-industry labor reallocation required. The empirical evidence for this view rests on the finding that during the 1950s - and again during the 1970s - there was a positive correlation between aggregate unemployment and the dispersion of employment growth rates. This thesis demonstrates that this correlation arises largely because oil price shocks affect both unemployment and the dispersion of employment growth. Once the dispersion due to oil shocks is accounted for, the residual dispersion in employment has very low explanatory power for unemployment. Since the dispersion index does not measure pure sectoral shifts, an alternate measure of dispersion is developed that serves as a better proxy for the amount of inter-industry labor reallocation required each period. Estimates using this measure suggest that, during the 1950s, temporary increases in the relative price of oil were responsible for generating the observed correlation. On the other hand, sectoral shifts were important during the 1970s; in particular, the 1973 oil price increase has had significant reallocative effects on the economy. This contention is subjected to further tests by looking at the time-series behavior of employment in durable-goods industries and also by following the inter-industry movements of workers over time through the use of panel data.

  11. Asphaltene aggregation in organic solvents.

    PubMed

    Oh, Kyeongseok; Ring, Terry A; Deo, Milind D

    2004-03-01

    Asphaltenic solids formed in the Rangely field in the course of a carbon dioxide flood and heptane insolubles in the oil from the same field were used in this study. Four different solvents were used to dissolve the asphaltenes. Near-infrared (NIR) spectroscopy was used to determine the onset of asphaltene precipitation by heptane titration. When the onset values were plotted versus asphaltene concentrations, distinct break points (called critical aggregation concentrations (CAC) in this paper) were observed. CACs for the field asphaltenes dissolved in toluene, trichloroethylene, tetrahydrofuran, and pyridine occurred at concentrations of 3.0, 3.7, 5.0, and 8.2 g/l, respectively. CACs are observed at similar concentrations as critical micelle concentrations (CMC) for the asphaltenes in the solvents employed and can be interpreted to be the points at which rates of asphaltene aggregations change. CMC values of asphaltenes determined from surface tension measurements (in pyridine and TCE) were slightly higher than the CAC values measured by NIR onset measurements. The CAC for heptane-insoluble asphaltenes in toluene was 3.1 g/l. Thermal gravimetric analysis (TGA) and elemental compositions of the two asphaltenes showed that the H/C ratio of the heptane-insoluble asphaltenes was higher and molecular weight (measured by vapor pressure osmometry) was lower.

  12. Detergent-mediated protein aggregation.

    PubMed

    Neale, Chris; Ghanei, Hamed; Holyoake, John; Bishop, Russell E; Privé, Gilbert G; Pomès, Régis

    2013-04-01

    Because detergents are commonly used to solvate membrane proteins for structural evaluation, much attention has been devoted to assessing the conformational bias imparted by detergent micelles in comparison to the native environment of the lipid bilayer. Here, we conduct six 500-ns simulations of a system with >600,000 atoms to investigate the spontaneous self assembly of dodecylphosphocholine detergent around multiple molecules of the integral membrane protein PagP. This detergent formed equatorial micelles in which acyl chains surround the protein's hydrophobic belt, confirming existing models of the detergent solvation of membrane proteins. In addition, unexpectedly, the extracellular and periplasmic apical surfaces of PagP interacted with the headgroups of detergents in other micelles 85 and 60% of the time, respectively, forming complexes that were stable for hundreds of nanoseconds. In some cases, an apical surface of one molecule of PagP interacted with an equatorial micelle surrounding another molecule of PagP. In other cases, the apical surfaces of two molecules of PagP simultaneously bound a neat detergent micelle. In these ways, detergents mediated the non-specific aggregation of folded PagP. These simulation results are consistent with dynamic light scattering experiments, which show that, at detergent concentrations ≥600 mM, PagP induces the formation of large scattering species that are likely to contain many copies of the PagP protein. Together, these simulation and experimental results point to a potentially generic mechanism of detergent-mediated protein aggregation.

  13. Role of Multicellular Aggregates in Biofilm Formation

    PubMed Central

    Kragh, Kasper N.; Hutchison, Jaime B.; Melaugh, Gavin; Rodesney, Chris; Roberts, Aled E. L.; Irie, Yasuhiko; Jensen, Peter Ø.; Diggle, Stephen P.; Allen, Rosalind J.

    2016-01-01

    ABSTRACT In traditional models of in vitro biofilm development, individual bacterial cells seed a surface, multiply, and mature into multicellular, three-dimensional structures. Much research has been devoted to elucidating the mechanisms governing the initial attachment of single cells to surfaces. However, in natural environments and during infection, bacterial cells tend to clump as multicellular aggregates, and biofilms can also slough off aggregates as a part of the dispersal process. This makes it likely that biofilms are often seeded by aggregates and single cells, yet how these aggregates impact biofilm initiation and development is not known. Here we use a combination of experimental and computational approaches to determine the relative fitness of single cells and preformed aggregates during early development of Pseudomonas aeruginosa biofilms. We find that the relative fitness of aggregates depends markedly on the density of surrounding single cells, i.e., the level of competition for growth resources. When competition between aggregates and single cells is low, an aggregate has a growth disadvantage because the aggregate interior has poor access to growth resources. However, if competition is high, aggregates exhibit higher fitness, because extending vertically above the surface gives cells at the top of aggregates better access to growth resources. Other advantages of seeding by aggregates, such as earlier switching to a biofilm-like phenotype and enhanced resilience toward antibiotics and immune response, may add to this ecological benefit. Our findings suggest that current models of biofilm formation should be reconsidered to incorporate the role of aggregates in biofilm initiation. PMID:27006463

  14. Pattern Effects of Soil on Photovoltaic Surfaces

    DOE PAGES

    Burton, Patrick D.; Hendrickson, Alex; Ulibarri, Stephen Seth; ...

    2016-06-06

    The texture or patterning of soil on PV surfaces may influence light capture at various angles of incidence (AOI). Accumulated soil can be considered a microshading element, which changes with respect to AOI. Laboratory deposition of simulated soil was used to prepare test coupons for simultaneous AOI and soiling loss experiments. A mixed solvent deposition technique was used to consistently deposit patterned test soils onto glass slides. Transmission decreased as soil loading and AOI increased. Dense aggregates significantly decreased transmission. But, highly dispersed particles are less prone to secondary scattering, improving overall light collection. In order to test AOI losses on relevant systems, uniform simulated soil coatings were applied to split reference cells to further examine this effect. Finally, the measured optical transmission and area coverage correlated closely to the observedmore » $$I_{{rm SC}}$$. Angular losses were significant at angles as low as 25°.« less

  15. Pattern Effects of Soil on Photovoltaic Surfaces

    SciTech Connect

    Burton, Patrick D.; Hendrickson, Alex; Ulibarri, Stephen Seth; Riley, Daniel; Boyson, William E.; King, Bruce H.

    2016-06-06

    The texture or patterning of soil on PV surfaces may influence light capture at various angles of incidence (AOI). Accumulated soil can be considered a microshading element, which changes with respect to AOI. Laboratory deposition of simulated soil was used to prepare test coupons for simultaneous AOI and soiling loss experiments. A mixed solvent deposition technique was used to consistently deposit patterned test soils onto glass slides. Transmission decreased as soil loading and AOI increased. Dense aggregates significantly decreased transmission. But, highly dispersed particles are less prone to secondary scattering, improving overall light collection. In order to test AOI losses on relevant systems, uniform simulated soil coatings were applied to split reference cells to further examine this effect. Finally, the measured optical transmission and area coverage correlated closely to the observed $I_{{rm SC}}$. Angular losses were significant at angles as low as 25°.

  16. Threshold velocities for input of soil particles into the air by desert soils

    SciTech Connect

    Gillette, D.A.; Adams, J.; Endo, A.; Smith, D.; Kihl, R.

    1980-10-20

    Desert soils mostly from the Mojave Desert were tested for threshold friction velocity (the friction velocity above which soil erosion takes place) with an open-bottomed portable wind tunnel. Several geomorphological settings were chosen to be representative of much of the surface of the Mojave Desert, for example, playas, alluvial fans, and aeolian features. Variables which increase threshold velocity are decreasing proportion of sand, increasing size of dry aggregates of the soil, and increasing fraction of the soil mass larger than 1 mm. Threshold velocity increases with different types of soil surfaces in the following order: disturbed soils (except disturbed heavy clay soils), sand dunes, alluvial and aeolian sand deposits, disturbed playa soils, skirts of playas, playa centers, and desert pavement (alluvial deposits). 21 references, 5 figures, 6 tables.

  17. Threshold velocities for input of soil particles into the air by desert soils

    NASA Astrophysics Data System (ADS)

    Gillette, Dale A.; Adams, John; Endo, Albert; Smith, Dudley; Kihl, Rolf

    1980-10-01

    Desert soils mostly from the Mojave Desert were tested for threshold friction velocity (the friction velocity above which soil erosion takes place) with an open-bottomed portable wind tunnel. Several geomorphological settings were chosen to be representative of much of the surface of the Mojave Desert, for example, playas, alluvial fans, and aeolian features. Variables which increase threshold velocity are decreasing proportion of sand, increasing size of dry aggregates of the soil, and increasing fraction of the soil mass larger than 1 mm. Threshold velocity increases with different types of soil surfaces in the following order: distrubed soils (except disturbed heavy clay soils), sand dunes, alluvial and aeolian sand deposits, disturbed playa soils, skirts of playas, playa centers, and desert pavements (alluvial deposits).

  18. Natural aggregates of the conterminous United States

    USGS Publications Warehouse

    Langer, William H.

    1988-01-01

    Crushed stone and sand and gravel are the two main sources of natural aggregates. These materials are commonly used construction materials and frequently can be interchanged with one another. They are widely used throughout the United States, with every State except two producing crushed stone. Together they amount to about half the mining volume in the United States. Approximately 96 percent of sand and gravel and 77 percent of the crushed stone produced in the United States are used in the construction industry. Natural aggregates are widely distributed throughout the United States in a variety of geologic environments. Sand and gravel deposits commonly are the results of the weathering of bedrock and subsequent transportation and deposition of the material by water or ice (glaciers). As such, they commonly occur as river or stream deposits or in glaciated areas as glaciofluvial and other deposits. Crushed stone aggregates are derived from a wide variety of parent bedrock materials. Limestone and other carbonates account for approximately three quarters of the rocks used for crushed stone, with granite and other igneous rocks making up the bulk of the remainder. Limestone deposits are widespread throughout the Central and Eastern United States and are scattered in the West. Granites are widely distributed in the Eastern and Western United States, with few exposures in the Midwest. Igneous rocks (excluding granites) are largely concentrated in the Western United States and in a few isolated localities in the East. Even though natural aggregates are widely distributed throughout the United States, they are not universally available for consumptive use. Some areas are devoid of sand and gravel, and potential sources of crushed stone may be covered with sufficient unconsolidated material to make surface mining impractical. In some areas many aggregates do not meet the physical property requirements for certain uses, or they may contain mineral constituents that react

  19. Role of Soil Microstructure in Microbially-mediated Drying Resistance

    NASA Astrophysics Data System (ADS)

    Cruz, B. C.; Shor, L. M.; Gage, D. J.

    2015-12-01

    The retention of soil moisture between rainfall or irrigation events is imperative to the productivity of terrestrial ecosystems. Amplified weather conditions are expected to result in widespread reduction in soil moisture. Extracellular polysaccharides (EPS) produced by soil bacteria have the ability to influence soil moisture by (i) retaining water directly within the hydrogel matrix, and (ii) promoting an aggregated soil structure. We have developed microfluidic devices that emulate realistic soil microstructures and enable direct observation of EPS production and drying resistance. The objective of this study was to compare moisture retention in emulated soil micromodels containing different soil microstructures. "Aggregated" devices contain a greater number of small (<30 μm) and large (>100 μm) pores, while "non-aggregated" devices contained more intermediate-sized (30-100 μm) pores. Particle-size distributions, similar to a sandy loam, were identical in both cases. Dilute suspensions of either of two strains of Sinorhizobium meliloti were introduced into replicate micromodels: one strain produced EPS ("EPS+") and the other did not produce EPS ("EPS-"). Loaded micromodels were equilibrated at saturated conditions, then dried at 83% RH for several days. Direct observation showed micro-scale patterns of air infiltration. The rate and extent of moisture loss was determined as a function of bacterial strain and microstructure aggregation state. Results showed devices loaded with EPS+ bacteria retained moisture longer than devices loaded with EPS- bacteria. Moisture retention by EPS+ bacteria was enhanced in aggregated versus non-aggregated microstructures. This work illustrates how moisture retention in soil is the result of microbial processes acting within pore-scale soil microstructures. Validated microfluidics-based approaches may help quantitatively link pore-scale phenomena to ecosystem function.

  20. 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.

  1. Tubular aggregates: their association with myalgia.

    PubMed Central

    Niakan, E; Harati, Y; Danon, M J

    1985-01-01

    Three thousand consecutive muscle biopsies were reviewed for the presence of tubular aggregates and their association with clinical symptomatology. Tubular aggregates were detected in 19 patients (0.6%). Twelve of these nineteen patients had severe myalgia, and the most abundant tubular aggregates were found in biopsies of patients with myalgia. Seven patients had only myalgia as their clinical symptomatology with normal physical examination. An additional five patients with tubular aggregates and myalgia had concomitant amyotrophic lateral sclerosis (2) or neuropathy (3). The high incidence of myalgia associated with tubular aggregates in our patients and the fact that tubular aggregates originate from sarcoplasmic reticulum suggest a role played by this structure in the pathogenesis of myalgia. Images PMID:2995591

  2. Aggregation server for grid-integrated vehicles

    DOEpatents

    Kempton, Willett

    2015-05-26

    Methods, systems, and apparatus for aggregating electric power flow between an electric grid and electric vehicles are disclosed. An apparatus for aggregating power flow may include a memory and a processor coupled to the memory to receive electric vehicle equipment (EVE) attributes from a plurality of EVEs, aggregate EVE attributes, predict total available capacity based on the EVE attributes, and dispatch at least a portion of the total available capacity to the grid. Power flow may be aggregated by receiving EVE operational parameters from each EVE, aggregating the received EVE operational parameters, predicting total available capacity based on the aggregated EVE operational parameters, and dispatching at least a portion of the total available capacity to the grid.

  3. Multiscale simulation of red blood cell aggregation

    NASA Astrophysics Data System (ADS)

    Bagchi, P.; Popel, A. S.

    2004-11-01

    In humans and other mammals, aggregation of red blood cells (RBC) is a major determinant to blood viscosity in microcirculation under physiological and pathological conditions. Elevated levels of aggregation are often related to cardiovascular diseases, bacterial infection, diabetes, and obesity. Aggregation is a multiscale phenomenon that is governed by the molecular bond formation between adjacent cells, morphological and rheological properties of the cells, and the motion of the extra-cellular fluid in which the cells circulate. We have developed a simulation technique using front tracking methods for multiple fluids that includes the multiscale characteristics of aggregation. We will report the first-ever direct computer simulation of aggregation of deformable cells in shear flows. We will present results on the effect of shear rate, strength of the cross-bridging bonds, and the cell rheological properties on the rolling motion, deformation and subsequent breakage of an aggregate.

  4. Protein Aggregation Profile of the Bacterial Cytosol

    PubMed Central

    de Groot, Natalia S.; Ventura, Salvador

    2010-01-01

    Background Protein misfolding is usually deleterious for the cell, either as a consequence of the loss of protein function or the buildup of insoluble and toxic aggregates. The aggregation behavior of a given polypeptide is strongly influenced by the intrinsic properties encoded in its sequence. This has allowed the development of effective computational methods to predict protein aggregation propensity. Methodology/Principal Findings Here, we use the AGGRESCAN algorithm to approximate the aggregation profile of an experimental cytosolic Escherichia coli proteome. The analysis indicates that the aggregation propensity of bacterial proteins is associated with their length, conformation, location, function, and abundance. The data are consistent with the predictions of other algorithms on different theoretical proteomes. Conclusions/Significance Overall, the study suggests that the avoidance of protein aggregation in functional environments acts as a strong evolutionary constraint on polypeptide sequences in both prokaryotic and eukaryotic organisms. PMID:20195530

  5. Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange.

    PubMed

    Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

    2014-07-25

    To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00-4.00, 0.50-1.00, and 0.25-0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere.

  6. Nanoarchitectonics of Molecular Aggregates: Science and Technology

    SciTech Connect

    Ramanathan, Nathan Muruganathan; Hong, Kunlun; Ji, Dr. Qingmin; Hill, Dr. Jonathan P; Ariga, Katsuhiko; Yusuke, Yonamine

    2014-01-01

    The field of making, studying and using molecular aggregates, in which the individual molecules (monomers) are arranged in a regular fashion, has come a long way. Taking control over the aggregation of small molecules and polymers in bulk, on surfaces and at interfaces pose a considerable challenge for their utilization in modern high tech applications. In this review we provide a detailed insight into recent trends in molecular aggregates from the perspectives of nanoarchitectonics.

  7. Aggregates in the Temporal Query Language TQuel,

    DTIC Science & Technology

    1987-07-27

    makes it possible to define both standard and unique aggregates in a rigorous way. Ceri and Gottlob present 43 prVPW t TW WRJR V P P V * a translation...from a subset of SQL that includes aggregates into relational algebra, thereby defining an operational semantics for SQL aggregates [Ceri & Gottlob ...Zvi, J. The Time Relational Model. Ph). Diss. Computer Science Department, UCLA, 1982. (Ceri & Gotlob 19851 Ceri, S. and G. Gottlob . Translating SQL

  8. Whey utilization in furrow irrigation: effects on aggregate stability and erosion.

    PubMed

    Lehrsch, Gary A; Robbins, Charles W; Brown, Melvin J

    2008-11-01

    Improving soil structure often reduces furrow erosion and maintains adequate infiltration. Cottage cheese whey, the liquid byproduct from cottage cheese manufacture, was utilized to stabilize soil aggregates and reduce sediment losses from furrow irrigation. We applied either 2.4 or 1.9L of whey per meter of furrow (3.15 or 2.49Lm(-2), respectively) by gravity flow without incorporation to two fields of Portneuf silt loam (Durinodic Xeric Haplocalcid) near Kimberly, ID. Furrows were irrigated with water beginning four days later. We measured sediment losses with furrow flumes during each irrigation and measured aggregate stability by wet sieving about 10 days after the last irrigation. Overall, whey significantly increased aggregate stability 25% at the 0-15mm depth and 14% at 15-30mm, compared to controls. On average, whey reduced sediment losses by 75% from furrows sloped at 2.4%. Whey increased the aggregate stability of structurally degraded calcareous soil in irrigation furrows.

  9. Stabilized fiber-reinforced pavement base course with recycled aggregate

    NASA Astrophysics Data System (ADS)

    Sobhan, Khaled

    This study evaluates the benefits to be gained by using a composite highway base course material consisting of recycled crushed concrete aggregate, portland cement, fly ash, and a modest amount of reinforcing fibers. The primary objectives of this research were to (a) quantify the improvement that is obtained by adding fibers to a lean concrete composite (made from recycled aggregate and low quantities of Portland cement and/or fly ash), (b) evaluate the mechanical behavior of such a composite base course material under both static and repeated loads, and (c) utilize the laboratory-determined properties with a mechanistic design method to assess the potential advantages. The split tensile strength of a stabilized recycled aggregate base course material was found to be exponentially related to the compacted dry density of the mix. A lean mix containing 4% cement and 4% fly ash (by weight) develops sufficient unconfined compressive, split tensile, and flexural strengths to be used as a high quality stabilized base course. The addition of 4% (by weight) of hooked-end steel fibers significantly enhances the post-peak load-deformation response of the composite in both indirect tension and static flexure. The flexural fatigue behavior of the 4% cement-4% fly ash mix is comparable to all commonly used stabilized materials, including regular concrete; the inclusion of 4% hooked-end fibers to this mix significantly improves its resistance to fatigue failure. The resilient moduli of stabilized recycled aggregate in flexure are comparable to the values obtained for traditional soil-cement mixes. In general, the fibers are effective in retarding the rate of fatigue damage accumulation, which is quantified in terms of a damage index defined by an energy-based approach. The thickness design curves for a stabilized recycled aggregate base course, as developed by using an elastic layer approach, is shown to be in close agreement with a theoretical model (based on Westergaard

  10. Quantifying aggregation dynamics during Myxococcus xanthus development.

    PubMed

    Zhang, Haiyang; Angus, Stuart; Tran, Michael; Xie, Chunyan; Igoshin, Oleg A; Welch, Roy D

    2011-10-01

    Under starvation conditions, a swarm of Myxococcus xanthus cells will undergo development, a multicellular process culminating in the formation of many aggregates called fruiting bodies, each of which contains up to 100,000 spores. The mechanics of symmetry breaking and the self-organization of cells into fruiting bodies is an active area of research. Here we use microcinematography and automated image processing to quantify several transient features of developmental dynamics. An analysis of experimental data indicates that aggregation reaches its steady state in a highly nonmonotonic fashion. The number of aggregates rapidly peaks at a value 2- to 3-fold higher than the final value and then decreases before reaching a steady state. The time dependence of aggregate size is also nonmonotonic, but to a lesser extent: average aggregate size increases from the onset of aggregation to between 10 and 15 h and then gradually decreases thereafter. During this process, the distribution of aggregates transitions from a nearly random state early in development to a more ordered state later in development. A comparison of experimental results to a mathematical model based on the traffic jam hypothesis indicates that the model fails to reproduce these dynamic features of aggregation, even though it accurately describes its final outcome. The dynamic features of M. xanthus aggregation uncovered in this study impose severe constraints on its underlying mechanisms.

  11. Population balance modeling of antibodies aggregation kinetics.

    PubMed

    Arosio, Paolo; Rima, Simonetta; Lattuada, Marco; Morbidelli, Massimo

    2012-06-21

    The aggregates morphology and the aggregation kinetics of a model monoclonal antibody under acidic conditions have been investigated. Growth occurs via irreversible cluster-cluster coagulation forming compact, fractal aggregates with fractal dimension of 2.6. We measured the time evolution of the average radius of gyration, , and the average hydrodynamic radius, , by in situ light scattering, and simulated the aggregation kinetics by a modified Smoluchowski's population balance equations. The analysis indicates that aggregation does not occur under diffusive control, and allows quantification of effective intermolecular interactions, expressed in terms of the Fuchs stability ratio (W). In particular, by introducing a dimensionless time weighed on W, the time evolutions of measured under various operating conditions (temperature, pH, type and concentration of salt) collapse on a single master curve. The analysis applies also to data reported in the literature when growth by cluster-cluster coagulation dominates, showing a certain level of generality in the antibodies aggregation behavior. The quantification of the stability ratio gives important physical insights into the process, including the Arrhenius dependence of the aggregation rate constant and the relationship between monomer-monomer and cluster-cluster interactions. Particularly, it is found that the reactivity of non-native monomers is larger than that of non-native aggregates, likely due to the reduction of the number of available hydrophobic patches during aggregation.

  12. A competitive aggregation model for flash nanoprecipitation.

    PubMed

    Cheng, Janine Chungyin; Vigil, R D; Fox, R O

    2010-11-15

    Flash NanoPrecipitation (FNP) is a novel approach for producing functional nanoparticles stabilized by amphiphilic block copolymers. FNP involves the rapid mixing of a hydrophobic active (organic) and an amphiphilic di-block copolymer with a non-solvent (water) and subsequent co-precipitation of nanoparticles composed of both the organic and copolymer. During this process, the particle size distribution (PSD) is frozen and stabilized by the hydrophilic portion of the amphiphilic di-block copolymer residing on the particle surface. That is, the particle growth is kinetically arrested and thus a narrow PSD can be attained. To model the co-precipitation process, a bivariate population balance equation (PBE) has been formulated to account for the competitive aggregation of the organic and copolymer versus pure organic-organic or copolymer-copolymer aggregation. Aggregation rate kernels have been derived to account for the major aggregation events: free coupling, unimer insertion, and aggregate fusion. The resulting PBE is solved both by direct integration and by using the conditional quadrature method of moments (CQMOM). By solving the competitive aggregation model under well-mixed conditions, it is demonstrated that the PSD is controlled primarily by the copolymer-copolymer aggregation process and that the energy barrier to aggregate fusion plays a key role in determining the PSD. It is also shown that the characteristic aggregation times are smaller than the turbulent mixing time so that the FNP process is always mixing limited.

  13. Microbial aggregates in anaerobic wastewater treatment.

    PubMed

    Kosaric, N; Blaszczyk, R

    1990-01-01

    The phenomenon aggregation of anaerobic bacteria gives an opportunity to speed up the digestion rate during methanogenesis. The aggregates are mainly composed of methanogenic bacteria which convert acetate and H2/CO2 into methane. Other bacteria are also included in the aggregates but their concentration is rather small. The aggregates may also be formed during acetogenesis or even hydrolysis but such aggregates are not stable and disrupt quickly when not fed. A two stage process seems to be suitable when high concentrated solid waste must be treated. Special conditions are necessary to promote aggregate formation from methanogenic bacteria but aggregates once formed are stable without feeding even for a few years. The structure, texture and activity of bacterial aggregates depend on several parameters: (1)--temperature and pH, (2)--wastewater composition and (3)--hydrodynamic conditions within the reactor. The common influence of all these parameters is still rather unknown but some recommendations may be given. Temperature and pH should be maintained in the range which is optimal for methanogenic bacteria e.g. a temperature between 32 and 50 degrees C and a value pH between 6.5 and 7.5. Wastewaters should contain soluble wastes and the specific loading rate should be around one kgCOD(kgVSS)-1 d-1. The concentration of the elements influences aggregate composition and probably structure and texture. At high calcium concentration a change in the colour of the granules has been observed. Research is necessary to investigate the influence of other elements and organic toxicants on maintenance of the aggregates. Hydrodynamic conditions seem to influence the stability of the granules over long time periods. At low liquid stream rates, aggregates may starve and lysis within the aggregates is possible which results in hollowing of aggregates and their floating. At high liquid stream rates the aggregates may be disrupted and washed out of the reactor as a flocculent

  14. Familial aggregation analysis of gene expressions

    PubMed Central

    Rao, Shao-Qi; Xu, Liang-De; Zhang, Guang-Mei; Li, Xia; Li, Lin; Shen, Gong-Qing; Jiang, Yang; Yang, Yue-Ying; Gong, Bin-Sheng; Jiang, Wei; Zhang, Fan; Xiao, Yun; Wang, Qing K

    2007-01-01

    Traditional studies of familial aggregation are aimed at defining the genetic (and non-genetic) causes of a disease from physiological or clinical traits. However, there has been little attempt to use genome-wide gene expressions, the direct phenotypic measures of genes, as the traits to investigate several extended issues regarding the distributions of familially aggregated genes on chromosomes or in functions. In this study we conducted a genome-wide familial aggregation analysis by using the in vitro cell gene expressions of 3300 human autosome genes (Problem 1 data provided to Genetic Analysis Workshop 15) in order to answer three basic genetics questions. First, we investigated how gene expressions aggregate among different types (degrees) of relative pairs. Second, we conducted a bioinformatics analysis of highly familially aggregated genes to see how they are distributed on chromosomes. Third, we performed a gene ontology enrichment test of familially aggregated genes to find evidence to support their functional consensus. The results indicated that 1) gene expressions did aggregate in families, especially between sibs. Of 3300 human genes analyzed, there were a total of 1105 genes with one or more significant (empirical p < 0.05) familial correlation; 2) there were several genomic hot spots where highly familially aggregated genes (e.g., the chromosome 6 HLA genes cluster) were clustered; 3) as we expected, gene ontology enrichment tests revealed that the 1105 genes were aggregating not only in families but also in functional categories. PMID:18466548

  15. Single molecule force spectroscopy of asphaltene aggregates.

    PubMed

    Long, Jun; Xu, Zhenghe; Masliyah, Jacob H

    2007-05-22

    Asphaltene aggregation and deposition cause severe problems in nearly all phases of petroleum processing. To resolve those problems, understanding the aggregation mechanisms is a prerequisite and has attracted the interest of a great number of investigators. However, to date, the nature and extent of asphaltene aggregation remain widely debated. In the present study, we attempt to investigate asphaltene aggregation from a completely new perspective. The technique of single molecule force spectroscopy (SMFS) was used to investigate the response of single asphaltene aggregates under an external pulling force. Force curves representing the stretching of single asphaltene aggregates were obtained in simple electrolyte solutions (KCl and calcium) and organic solvents (toluene and heptane). These force curves were well-fitted by the modified worm-like chain model, indicating that those asphaltene aggregates acted like long-chain polymers under pulling by an external force. It was found that lower solution pH values and the presence of divalent cations resulted in a lower bending rigidity of the formed aggregates. The information retrieved from the force curves suggests that asphaltene molecules with a structure featuring small aromatic clusters connected by aliphatic chains do exist and that asphaltene aggregation could occur through a linear polymerization mechanism. The current study extends the application scope of SMFS.

  16. Macroeconomic susceptibility, inflation, and aggregate supply

    NASA Astrophysics Data System (ADS)

    Hawkins, Raymond J.

    2017-03-01

    We unify aggregate-supply dynamics as a time-dependent susceptibility-mediated relationship between inflation and aggregate economic output. In addition to representing well various observations of inflation-output dynamics this parsimonious formalism provides a straightforward derivation of popular representations of aggregate-supply dynamics and a natural basis for economic-agent expectations as an element of inflation formation. Our formalism also illuminates questions of causality and time-correlation that challenge central banks for whom aggregate-supply dynamics is a key constraint in their goal of achieving macroeconomic stability.

  17. Neuronal aggregates: formation, clearance and spreading

    PubMed Central

    Lim, Junghyun; Yue, Zhenyu

    2015-01-01

    Summary Proteostasis is maintained by multiple cellular pathways, including protein synthesis, quality control and degradation. An imbalance of neuronal proteostasis, associated with protein misfolding and aggregation, leads to proteinopathies or neurodegeneration. While genetic variations and protein modifications contribute to aggregate formation, components of the proteostasis network dictate the fate of protein aggregates. Here we provide an overview of proteostasis pathways and their interplay (particularly autophagy) with the metabolism of disease-related proteins. We review recent studies on neuronal activity-mediated regulation of proteostasis and transcellular propagation of protein aggregates in the nervous system. Targeting proteostasis pathways therapeutically remains an attractive but challenging task. PMID:25710535

  18. RBC aggregation: laboratory data and models.

    PubMed

    Meiselman, H J; Neu, B; Rampling, M W; Baskurt, O K

    2007-01-01

    The reversible aggregation of red blood cells (RBC) into linear and three-dimensional structures continues to be of basic science and clinical interest: RBC aggregation affects low shear blood viscosity and microvascular flow dynamics, and can be markedly enhanced in several clinical states. Until fairly recently, most research efforts were focused on relations between suspending medium composition (i.e., protein levels, polymer type and concentration) and aggregate formation. However, there is now an increasing amount of experimental evidence indicating that RBC cellular properties can markedly affect aggregation, with the term "RBC aggregability" coined to describe the cell's intrinsic tendency to aggregate. Variations of aggregability can be large, with some changes of aggregation substantially greater than those resulting from pathologic states. The present review provides a brief overview of this topic, and includes such areas as donor-to-donor variations, polymer-plasma correlations, effects of RBC age, effects of enzymatic treatment, and current developments related to the mechanisms involved in RBC aggregation.

  19. Hemodynamic effects of red blood cell aggregation.

    PubMed

    Baskurt, Oguz K; Meiselman, Herbert J

    2007-01-01

    The influence of red blood cell (RBC) aggregation on blood flow in vivo has been under debate since early 1900's, yet a full understanding has still has not been reached. Enhanced RBC aggregation is well known to increase blood viscosity measured in rotational viscometers. However, it has been demonstrated that RBC aggregation may decrease flow resistance in cylindrical tubes, due to the formation of a cell-poor zone near the tube wall which results from the enhanced central accumulation of RBC. There is also extensive discussion regarding the effects of RBC aggregation on in vivo blood flow resistance. Several groups have reported increased microcirculatory flow resistance with enhanced RBC aggregation in experiments that utilized intravital microscopy. Alternatively, whole organ studies revealed that flow resistance may be significantly decreased if RBC aggregation is enhanced. Recently, new techniques have been developed to achieve well-controlled, graded alterations in RBC aggregation without influencing suspending phase properties. Studies using this technique revealed that the effects of RBC aggregation are determined by the degree of aggregation changes, and that this relationship can be explained by different hemodynamic mechanisms.

  20. Aggregate growth in a protoplanetary disk

    NASA Astrophysics Data System (ADS)

    Xiang, Chuchu; Carballido, Augusto; Matthews, Lorin; Hyde, Truell

    2017-01-01

    We present a method to model the growth of neutral and charged dusts in a turbulent protoplanetary disk, and analyze their collision probabilities. Coagulation of dust aggregates plays an important role in the formation of planets and is of key importance to the evolution of protoplanetary disks. In our method, the temporal evolution of the dusts is followed by Monte Carlo algorithm, and the inter-particle interactions are calculated by Aggregate_Builder (AB), which is a code used to model the collision process of aggregates. First an aggregate library is built and all the aggregates are binned according to their sizes. In each iteration, the collision rate for aggregates from any two bins are computed, which determines the time it takes for the next collision to happen and which two aggregates are selected for collision. Then the AB codes are used to calculate the interaction of the two aggregates. The relative velocity between the two aggregates is the vector sum of Brownian velocity and the turbulent velocity. The latter is calculated by ATHENA, which is a grid-based code for astrophysical magnetohydrodynamics. In each iteration, it’s determined whether the two aggregates hit or miss. In the case of hit, it either sticks or bounces as determined by the critical velocity. As a result, the neutral aggregates are more porous than the charged ones. For a certain size of incoming aggregates, the neutral ones have a higher collision probability than the charged ones. Also, similarly-sized aggregates have lower collision probabilities than aggregates with large size dispersions. This research enables us to determine which physical properties have a greater impact on the collision rate. By tracing the dust size distribution, we can identify the stage when they settle out to the mid-plane and how long it takes to develop to that stage. In the hit-stick regime, our results are consistent with the experiments which shows that when the velocity is smaller than the

  1. Collisional Aggregation Due to Turbulence

    NASA Astrophysics Data System (ADS)

    Pumir, Alain; Wilkinson, Michael

    2016-03-01

    Collisions between particles suspended in a fluid play an important role in many physical processes. As an example, collisions of microscopic water droplets in clouds are a necessary step in the production of macroscopic raindrops. Collisions of dust grains are also conjectured to be important for planet formation in the gas surrounding young stars and to play a role in the dynamics of sand storms. In these processes, collisions are favored by fast turbulent motions. Here we review recent advances in the understanding of collisional aggregation due to turbulence. We discuss the role of fractal clustering of particles and caustic singularities of their velocities. We also discuss limitations of the Smoluchowski equation for modeling such processes. These advances lead to a semiquantitative understanding on the influence of turbulence on collision rates and point to deficiencies in the current understanding of rainfall and planet formation.

  2. Swarms: Optimum aggregations of spacecraft

    NASA Technical Reports Server (NTRS)

    Mayer, H. L.

    1980-01-01

    Swarms are aggregations of spacecraft or elements of a space system which are cooperative in function, but physically isolated or only loosely connected. For some missions the swarm configuration may be optimum compared to a group of completely independent spacecraft or a complex rigidly integrated spacecraft or space platform. General features of swarms are induced by considering an ensemble of 26 swarms, examples ranging from Earth centered swarms for commercial application to swarms for exploring minor planets. A concept for a low altitude swarm as a substitute for a space platform is proposed and a preliminary design studied. The salient design feature is the web of tethers holding the 30 km swarm in a rigid two dimensional array in the orbital plane. A mathematical discussion and tutorial in tether technology and in some aspects of the distribution of services (mass, energy, and information to swarm elements) are included.

  3. [Influence of double rice cropping system innovation on paddy soil profile form and soil characteristics].

    PubMed

    Zeng, Xi-Bai; Sun, Nan; Gao, Ju-Sheng; Li, Lian-Fang; Wang, Bo-Ren; Bai, Ling-Yu

    2008-05-01

    Field experiments were conducted on the double rice cropping paddy field in red soil area to evaluate the influence of cropping system innovation on soil profile form and related soil characteristics. Four cropping systems of rice-rice-Chinese Milkvetch (Astragalus sinicus Linn.), forage, paddy-upland rotation, and upland were substituted for the double rice cropping system. The results indicated that compared with those under double rice cropping system, the thickness of cultivated horizon under upland cropping system increased by 4 cm, that of plow pan declined by 2 cm, > 2 mm aggregates in wet-sieved particle-size fractions increased by 6.94%, wet-sieved mean-mass diameter increased by 0.37 mm, contents of humic acid carbon and fulvic acid carbon increased by 0.15 and 0.49 g kg(-1), respectively, and quotient of aggregates water stability was 0.78 times higher. Under paddy-upland rotation, the quotient of aggregates water stability was higher (95.86), while soil nutrient contents changed a little. Under rice-rice-Chinese Milkvetch system, soil organic matter content increased by 1.3 g kg(-1), quotient of aggregates water stability declined by 8.82, but other parameters had less changes. Under forage system, the thickness of cultivated and transitional horizons increased by 2 cm and 9 cm, respectively, quotient of aggregates water stability increased by 1.39, while the contents of soil organic matter and total potassium decreased by 5.6 and 2.8 g kg(-1), respectively. Among all test cropping systems, forage system had the greatest changes in soil characteristics. It was completely feasible to substitute the local double rice cropping system for paddy-upland rotation or upland cropping, particularly in the areas where full irrigation was not available. However, attention should be paid to the decrease of soil potassium content when the cropping system innovation was practiced.

  4. Thrombolytic therapy reduces red blood cell aggregation in plasma without affecting intrinsic aggregability.

    PubMed

    Ben-Ami, R; Sheinman, G; Yedgar, S; Eldor, A; Roth, A; Berliner, A S; Barshtein, G

    2002-03-15

    Red blood cell (RBC) aggregation may contribute to occlusion of the coronary microcirculation during myocardial infarction. We studied the effect of thrombolytic therapy on RBC aggregation in patients with acute myocardial infarction (AMI). Compared with patients with myocardial infarction who did not receive thrombolytic therapy, those treated with systemic thrombolysis exhibited significantly reduced RBC aggregation, reduced plasma fibrinogen levels and increased plasma D-dimer levels. Using measurement of RBC aggregation in a standardized dextran-500 solution, reduction in RBC aggregation after thrombolysis was shown to be plasma dependent. Thrombolytic therapy had no direct effect on intrinsic RBC aggregability in patients with AMI. We conclude that thrombolytic therapy has rheologic consequences that may contribute to its overall efficacy. Inhibition of RBC aggregation by thrombolytic therapy may result from the degradation of fibrinogen, a key factor in the formation of RBC aggregates, and from the generation of fibrinogen degradation products capable of disaggregating RBCs.

  5. Conserving Soil.

    ERIC Educational Resources Information Center

    Soil Conservation Service (USDA), Washington, DC.

    Designed as enrichment materials for grades six through nine, this program is an interdisciplinary study of soils. As part of the program students: (1) examine soil organisms; (2) research history of local Native Americans to see how they and others have used the land and its soils; (3) investigate how soils are degraded and how they are conserved…

  6. Soil organic carbon dynamics under long-term fertilization in a black soil of China: Evidence from stable C isotopes

    NASA Astrophysics Data System (ADS)

    Dou, Xiaolin; He, Ping; Zhu, Ping; Zhou, Wei

    2016-02-01

    Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 μm, 2000–250 μm, 250–53 μm, and <53 μm), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m2) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM.

  7. Soil organic carbon dynamics under long-term fertilization in a black soil of China: Evidence from stable C isotopes

    PubMed Central

    Dou, Xiaolin; He, Ping; Zhu, Ping; Zhou, Wei

    2016-01-01

    Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 μm, 2000–250 μm, 250–53 μm, and <53 μm), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m2) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM. PMID:26898121

  8. Acetal phosphatidic acids: novel platelet aggregating agents.

    PubMed

    Brammer, J P; Maguire, M H; Walaszek, E J; Wiley, R A

    1983-05-01

    1 Palmitaldehyde, olealdehyde and linolealdehyde acetal phosphatidic acids induced rapid shape change and dose-dependent biphasic aggregation of human platelets in platelet-rich plasma; aggregation was reversible at low doses and irreversible at high doses of the acetal phosphatidic acids. The palmitaldehyde congener elicited monophasic dose-dependent aggregation of sheep platelets in platelet-rich plasma.2 The threshold concentration for palmitaldehyde acetal phosphatidic acid (PGAP)-induced platelet aggregation was 2.5-5 muM for human platelets and 0.25-0.5 muM for sheep platelets. PGAP was 4-5 times as potent versus human platelets as the olealdehyde and linolealdehyde acetal phosphatidic acids, which were equipotent.3 PGAP-induced irreversible aggregation of [(14)C]-5-hydroxytryptamine ([(14)C]-5-HT)-labelled human platelets in platelet-rich plasma was accompanied by release of 44.0+/-2.4% (s.e.) of the platelet [(14)C]-5-HT; reversible aggregation was not associated with release. In contrast, PGAP-induced release of [(14)C]-5-HT-labelled sheep platelets was dose-dependent.4 The adenosine diphosphate (ADP) antagonist, 2-methylthio-AMP, and the cyclo-oxygenase inhibitor, aspirin, abolished PGAP-induced second phase aggregation and release in human platelets but did not affect the first, reversible, phase of aggregation. Both the first and second phases of PGAP-induced aggregation were abolished by chlorpromazine, by the phospholipase A(2) inhibitor, mepacrine, and by nmolar concentrations of prostaglandin E(1) (PGE(1)); these agents abolished the second, but not the first phase of ADP-induced aggregation.5 The related phospholipids, lecithin, lysolecithin and phosphatidic acid, at <100 muM, neither induced aggregation of human platelets in platelet-rich plasma, nor modified PGAP-induced aggregation; 1-palmityl lysophosphatidic acid elicited aggregation of human platelets at a threshold concentration of 100 muM.6 It is concluded that the acetal phosphatidic acids

  9. Morphological properties of atmospheric aerosol aggregates

    PubMed Central

    Xiong, C.; Friedlander, S. K.

    2001-01-01

    Ultrafine particles (smaller than about 0.1 μm) are often emitted from combustion and other high-temperature processes in the form of fractal-like aggregates composed of solid nanoparticles. Results of a study of atmospheric aggregates are reported. Particles were collected on transmission electron microscope grids fitted on the last two stages of a single-jet eight-stage low-pressure impactor for periods of a few minutes. Photomicrographs of transmission electron microscope grids from the impactor stages were analyzed to obtain the fractal dimension (Df) and prefactor (A) for aggregates. Df increased from near 1 to above 2 as the number of primary particles making up the aggregates increased from 10 to 180. Total particle concentrations in size ranges roughly equivalent to the low-pressure impactor stages were measured with a mobility analyzer and condensation particle counter. In one set of measurements, the fraction of the particles present as aggregates was about 60% for particles with aerodynamic diameters between 50 and 75 nm and 34% for the range 75 to 120 nm. The total aggregate concentration in the 50- to 120-nm size range was about 400 ml−1. The primary particles that make up atmospheric aggregates are more polydisperse than soot aggregates generated from a single laboratory source, an ethane/oxygen flame. Most measurements were made in the Los Angeles area, where the aggregates may represent a signature for diesel emissions. Rural aggregate concentrations in the size range 50 to 120 nm were less than 1% of the concentrations at urban sites. The data will permit better estimates of atmospheric aggregate residence times, transport, and deposition in the lung, optical extinction, and heterogenous nucleation. PMID:11592995

  10. Morphological properties of atmospheric aerosol aggregates.

    PubMed

    Xiong, C; Friedlander, S K

    2001-10-09

    Ultrafine particles (smaller than about 0.1 microm) are often emitted from combustion and other high-temperature processes in the form of fractal-like aggregates composed of solid nanoparticles. Results of a study of atmospheric aggregates are reported. Particles were collected on transmission electron microscope grids fitted on the last two stages of a single-jet eight-stage low-pressure impactor for periods of a few minutes. Photomicrographs of transmission electron microscope grids from the impactor stages were analyzed to obtain the fractal dimension (D(f)) and prefactor (A) for aggregates. D(f) increased from near 1 to above 2 as the number of primary particles making up the aggregates increased from 10 to 180. Total particle concentrations in size ranges roughly equivalent to the low-pressure impactor stages were measured with a mobility analyzer and condensation particle counter. In one set of measurements, the fraction of the particles present as aggregates was about 60% for particles with aerodynamic diameters between 50 and 75 nm and 34% for the range 75 to 120 nm. The total aggregate concentration in the 50- to 120-nm size range was about 400 ml(-1). The primary particles that make up atmospheric aggregates are more polydisperse than soot aggregates generated from a single laboratory source, an ethane/oxygen flame. Most measurements were made in the Los Angeles area, where the aggregates may represent a signature for diesel emissions. Rural aggregate concentrations in the size range 50 to 120 nm were less than 1% of the concentrations at urban sites. The data will permit better estimates of atmospheric aggregate residence times, transport, and deposition in the lung, optical extinction, and heterogeneous nucleation.

  11. Selectivity of aggregation-determining interactions.

    PubMed

    Ganesan, Ashok; Debulpaep, Maja; Wilkinson, Hannah; Van Durme, Joost; De Baets, Greet; Jonckheere, Wim; Ramakers, Meine; Ivarsson, Ylva; Zimmermann, Pascale; Van Eldere, Johan; Schymkowitz, Joost; Rousseau, Frederic

    2015-01-30

    Protein aggregation is sequence specific, favoring self-assembly over cross-seeding with non-homologous sequences. Still, as the majority of proteins in a proteome are aggregation prone, the high level of homogeneity of protein inclusions in vivo both during recombinant overexpression and in disease remains surprising. To investigate the selectivity of protein aggregation in a proteomic context, we here compared the selectivity of aggregation-determined interactions with antibody binding. To that purpose, we synthesized biotin-labeled peptides, corresponding to aggregation-determining sequences of the bacterial protein β-galactosidase and two human disease biomarkers: C-reactive protein and prostate-specific antigen. We analyzed the selectivity of their interactions in Escherichia coli lysate, human serum and human seminal plasma, respectively, using a Western blot-like approach in which the aggregating peptides replace the conventional antibody. We observed specific peptide accumulation in the same bands detected by antibody staining. Combined spectroscopic and mutagenic studies confirmed accumulation resulted from binding of the peptide on the identical sequence of the immobilized target protein. Further, we analyzed the sequence redundancy of aggregating sequences and found that about 90% of them are unique within their proteome. As a result, the combined specificity and low sequence redundancy of aggregating sequences therefore contribute to the observed homogeneity of protein aggregation in vivo. This suggests that these intrinsic proteomic properties naturally compartmentalize aggregation events in sequence space. In the event of physiological stress, this might benefit the ability of cells to respond to proteostatic stress by allowing chaperones to focus on specific aggregation events rather than having to face systemic proteostatic failure.

  12. Preformed Seeds Modulate Native Insulin Aggregation Kinetics.

    PubMed

    Dutta, Colina; Yang, Mu; Long, Fei; Shahbazian-Yassar, Reza; Tiwari, Ashutosh

    2015-12-10

    Insulin aggregates under storage conditions via disulfide interchange reaction. It is also known to form aggregates at the site of repeated injections in diabetes patients, leading to injection amyloidosis. This has fueled research in pharmaceutical and biotechnology industry as well as in academia to understand factors that modulate insulin stability and aggregation. The main aim of this study is to understand the factors that modulate aggregation propensity of insulin under conditions close to physiological and measure effect of "seeds" on aggregation kinetics. We explored the aggregation kinetics of insulin at pH 7.2 and 37 °C in the presence of disulfide-reducing agent dithiothreitol (DTT), using spectroscopy (UV-visible, fluorescence, and Fourier transform infrared spectroscopy) and microscopy (scanning electron microscopy, atomic force microscopy) techniques. We prepared insulin "seeds" by incubating disulfide-reduced insulin at pH 7.2 and 37 °C for varying lengths of time (10 min to 12 h). These seeds were added to the native protein and nucleation-dependent aggregation kinetics was measured. Aggregation kinetics was fastest in the presence of 10 min seeds suggesting they were nascent. Interestingly, intermediate seeds (30 min to 4 h incubation) resulted in formation of transient fibrils in 4 h that converted to amorphous aggregates upon longer incubation of 24 h. Overall, the results show that insulin under disulfide reducing conditions at pH and temperature close to physiological favors amorphous aggregate formation and seed "maturity" plays an important role in nucleation dependent aggregation kinetics.

  13. Measurements of microbial community activities in individual soil macroaggregates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The functional potential of single soil aggregates may provide insights into the localized distribution of microbial activities better than traditional assays conducted on bulk quantities of soil. Thus, we scaled down enzyme assays for ß-glucosidase, N-acetyl-ß-D-glucosaminidase, lipase, and leucine...

  14. Impact of Particle Aggregation on Nanoparticle Reactivity

    NASA Astrophysics Data System (ADS)

    Jassby, David

    2011-12-01

    The prevalence of nanoparticles in the environment is expected to grow in the coming years due to their increasing pervasiveness in consumer and industrial applications. Once released into the environment, nanoparticles encounter conditions of pH, salinity, UV light, and other solution conditions that may alter their surface characteristics and lead to aggregation. The unique properties that make nanoparticles desirable are a direct consequence of their size and increased surface area. Therefore, it is critical to recognize how aggregation alters the reactive properties of nanomaterials, if we wish to understand how these properties are going to behave once released into the environment. The size and structure of nanoparticle aggregates depend on surrounding conditions, including hydrodynamic ones. Depending on these conditions, aggregates can be large or small, tightly packed or loosely bound. Characterizing and measuring these changes to aggregate morphology is important to understanding the impact of aggregation on nanoparticle reactive properties. Examples of decreased reactivity due to aggregation include the case where tightly packed aggregates have fewer available surface sites compared to loosely packed ones; also, photocatalytic particles embedded in the center of large aggregates will experience less light when compared to particles embedded in small aggregates. However, aggregation also results in an increase in solid-solid interfaces between nanoparticles. This can result in increased energy transfer between neighboring particles, surface passivation, and altered surface tension. These phenomena can lead to an increase in reactivity. The goal of this thesis is to examine the impacts of aggregation on the reactivity of a select group of nanomaterials. Additionally, we examined how aggregation impacts the removal efficiency of fullerene nanoparticles using membrane filtration. The materials we selected to study include ZnS---a metal chalcogenide

  15. Impact of varying soil structure on transport processes in different diagnostic horizons of three soil types.

    PubMed

    Kodesová, Radka; Vignozzi, Nadia; Rohosková, Marcela; Hájková, Tereza; Kocárek, Martin; Pagliai, Marcello; Kozák, Josef; Simůnek, Jirka

    2009-02-16

    When soil structure varies in different soil types and the horizons of these soil types, it has a significant impact on water flow and contaminant transport in soils. This paper focuses on the effect of soil structure variations on the transport of pesticides in the soil above the water table. Transport of a pesticide (chlorotoluron) initially applied on soil columns taken from various horizons of three different soil types (Haplic Luvisol, Greyic Phaeozem and Haplic Cambisol) was studied using two scenarios of ponding infiltration. The highest infiltration rate and pesticide mobility were observed for the Bt(1) horizon of Haplic Luvisol that exhibited a well-developed prismatic structure. The lowest infiltration rate was measured for the Bw horizon of Haplic Cambisol, which had a poorly developed soil structure and a low fraction of large capillary pores and gravitational pores. Water infiltration rates were reduced during the experiments by a soil structure breakdown, swelling of clay and/or air entrapped in soil samples. The largest soil structure breakdown and infiltration decrease was observed for the Ap horizon of Haplic Luvisol due to the low aggregate stability of the initially well-aggregated soil. Single-porosity and dual-permeability (with matrix and macropore domains) flow models in HYDRUS-1D were used to estimate soil hydraulic parameters via numerical inversion using data from the first infiltration experiment. A fraction of the macropore domain in the dual-permeability model was estimated using the micro-morphological images. Final soil hydraulic parameters determined using the single-porosity and dual-permeability models were subsequently used to optimize solute transport parameters. To improve numerical inversion results, the two-site sorption model was also applied. Although structural changes observed during the experiment affected water flow and solute transport, the dual-permeability model together with the two-site sorption model proved to be

  16. Processing Protocol for Soil Samples Potentially ...

    EPA Pesticide Factsheets

    Method Operating Procedures This protocol describes the processing steps for 45 g and 9 g soil samples potentially contaminated with Bacillus anthracis spores. The protocol is designed to separate and concentrate the spores from bulk soil down to a pellet that can be used for further analysis. Soil extraction solution and mechanical shaking are used to disrupt soil particle aggregates and to aid in the separation of spores from soil particles. Soil samples are washed twice with soil extraction solution to maximize recovery. Differential centrifugation is used to separate spores from the majority of the soil material. The 45 g protocol has been demonstrated by two laboratories using both loamy and sandy soil types. There were no significant differences overall between the two laboratories for either soil type, suggesting that the processing protocol would be robust enough to use at multiple laboratories while achieving comparable recoveries. The 45 g protocol has demonstrated a matrix limit of detection at 14 spores/gram of soil for loamy and sandy soils.

  17. Communicating soil property variability in heterogeneous soil mapping units

    NASA Astrophysics Data System (ADS)

    Farewell, Timothy

    2014-05-01

    . For categorical data, the choice of the property of the spatially dominant soil series may provide the 'most likely' answer, but this may not be the most helpful answer for the end user. Additionally, when aggregating to select the dominant property or class, rather than the dominant taxonomic soil series, it is not uncommon for the 'dominant' class to change. One example of our new approach is to communicate the attributes of the soil associations on the basis of the worst-case scenario at various confidence levels, based on the percentage of the soil series of the association. As an example, when soil maps are used to help underwriters understand the vulnerability of an area to soil related subsidence, the maximum subsidence rating can be chosen from soils which comprise, for example, more than 5% or more than 30% of the soil association in question. Developing an understanding of end-user requirements allows optimization of soil datasets to suit their needs, and encourages engagement between soil scientists and industry.

  18. 7 CFR 1.6 - Aggregating requests.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 1 2010-01-01 2010-01-01 false Aggregating requests. 1.6 Section 1.6 Agriculture Office of the Secretary of Agriculture ADMINISTRATIVE REGULATIONS Official Records § 1.6 Aggregating requests. When an agency reasonably believes that a requester, or a group of requesters acting in...

  19. 7 CFR 1.6 - Aggregating requests.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 1 2013-01-01 2013-01-01 false Aggregating requests. 1.6 Section 1.6 Agriculture Office of the Secretary of Agriculture ADMINISTRATIVE REGULATIONS Official Records § 1.6 Aggregating requests. When an agency reasonably believes that a requester, or a group of requesters acting in...

  20. Biomass round bales infield aggregation logistic scenarios

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biomass bales often need to be aggregated (collected into groups and transported) to a field-edge stack for temporary storage for feedlots or processing facilities. Aggregating the bales with the least total distance involved is a goal of producers and bale handlers. Several logistics scenarios for ...

  1. The Aggregate Demand Curve: A Reply.

    ERIC Educational Resources Information Center

    Hansen, Richard B.; And Others

    1987-01-01

    Responds to claims about the instructional value of the downward-sloping aggregate demand curve in teaching principles of macroeconomics. Examines the effects of interest-rates and the role of money on demand curves. Concludes by arguing against the use of downward-sloping aggregate demand curves in textbooks. (RKM)

  2. 42 CFR 411.106 - Aggregation rules.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 42 Public Health 2 2014-10-01 2014-10-01 false Aggregation rules. 411.106 Section 411.106 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES MEDICARE PROGRAM... Under Group Health Plans: General Provisions § 411.106 Aggregation rules. The following rules apply...

  3. 42 CFR 411.106 - Aggregation rules.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 42 Public Health 2 2010-10-01 2010-10-01 false Aggregation rules. 411.106 Section 411.106 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES MEDICARE PROGRAM... Under Group Health Plans: General Provisions § 411.106 Aggregation rules. The following rules apply...

  4. Marine particle aggregate breakup in turbulent flows

    NASA Astrophysics Data System (ADS)

    Rau, Matthew; Ackleson, Steven; Smith, Geoffrey

    2016-11-01

    The dynamics of marine particle aggregate formation and breakup due to turbulence is studied experimentally. Aggregates of clay particles, initially in a quiescent aggregation tank, are subjected to fully developed turbulent pipe flow at Reynolds numbers of up to 25,000. This flow arrangement simulates the exposure of marine aggregates in coastal waters to a sudden turbulent event. Particle size distributions are measured by in-situ sampling of the small-angle forward volume scattering function and the volume concentration of the suspended particulate matter is quantified through light attenuation measurements. Results are compared to measurements conducted under laminar and turbulent flow conditions. At low shear rates, larger sized particles indicate that aggregation initially governs the particle dynamics. Breakup is observed when large aggregates are exposed to the highest levels of shear in the experiment. Models describing the aggregation and breakup rates of marine particles due to turbulence are evaluated with the population balance equation and results from the simulation and experiment are compared. Additional model development will more accurately describe aggregation dynamics for remote sensing applications in turbulent marine environments.

  5. Choosing Aggregation Rules for Composite Indicators

    ERIC Educational Resources Information Center

    Munda, Giuseppe

    2012-01-01

    From a formal point of view, a composite indicator is an aggregate of all dimensions, objectives, individual indicators and variables used for its construction. This implies that what defines a composite indicator is the set of properties underlying its mathematical aggregation convention. In this article, I try to revise the theoretical debate on…

  6. Molecular dynamics simulation of fractal aggregate diffusion

    NASA Astrophysics Data System (ADS)

    Pranami, Gaurav; Lamm, Monica H.; Vigil, R. Dennis

    2010-11-01

    The diffusion of fractal aggregates constructed with the method by Thouy and Jullien [J. Phys. A 27, 2953 (1994)10.1088/0305-4470/27/9/012] comprised of Np spherical primary particles was studied as a function of the aggregate mass and fractal dimension using molecular dynamics simulations. It is shown that finite-size effects have a strong impact on the apparent value of the diffusion coefficient (D) , but these can be corrected by carrying out simulations using different simulation box sizes. Specifically, the diffusion coefficient is inversely proportional to the length of a cubic simulation box, and the constant of proportionality appears to be independent of the aggregate mass and fractal dimension. Using this result, it is possible to compute infinite dilution diffusion coefficients (Do) for aggregates of arbitrary size and fractal dimension, and it was found that Do∝Np-1/df , as is often assumed by investigators simulating Brownian aggregation of fractal aggregates. The ratio of hydrodynamic radius to radius of gyration is computed and shown to be independent of mass for aggregates of fixed fractal dimension, thus enabling an estimate of the diffusion coefficient for a fractal aggregate based on its radius of gyration.

  7. Oxygen limitation within a bacterial aggregate.

    PubMed

    Wessel, Aimee K; Arshad, Talha A; Fitzpatrick, Mignon; Connell, Jodi L; Bonnecaze, Roger T; Shear, Jason B; Whiteley, Marvin

    2014-04-15

    ABSTRACT Cells within biofilms exhibit physiological heterogeneity, in part because of chemical gradients existing within these spatially structured communities. Previous work has examined how chemical gradients develop in large biofilms containing >10(8) cells. However, many bacterial communities in nature are composed of small, densely packed aggregates of cells (≤ 10(5) bacteria). Using a gelatin-based three-dimensional (3D) printing strategy, we confined the bacterium Pseudomonas aeruginosa within picoliter-sized 3D "microtraps" that are permeable to nutrients, waste products, and other bioactive small molecules. We show that as a single bacterium grows into a maximally dense (10(12) cells ml(-1)) clonal population, a localized depletion of oxygen develops when it reaches a critical aggregate size of ~55 pl. Collectively, these data demonstrate that chemical and phenotypic heterogeneity exists on the micrometer scale within small aggregate populations. IMPORTANCE Before developing into large, complex communities, microbes initially cluster into aggregates, and it is unclear if chemical heterogeneity exists in these ubiquitous micrometer-scale aggregates. We chose to examine oxygen availability within an aggregate since oxygen concentration impacts a number of important bacterial processes, including metabolism, social behaviors, virulence, and antibiotic resistance. By determining that oxygen availability can vary within aggregates containing ≤ 10(5) bacteria, we establish that physiological heterogeneity exists within P. aeruginosa aggregates, suggesting that such heterogeneity frequently exists in many naturally occurring small populations.

  8. Teaching Aggregate Demand and Supply Models

    ERIC Educational Resources Information Center

    Wells, Graeme

    2010-01-01

    The author analyzes the inflation-targeting model that underlies recent textbook expositions of the aggregate demand-aggregate supply approach used in introductory courses in macroeconomics. He shows how numerical simulations of a model with inflation inertia can be used as a tool to help students understand adjustments in response to demand and…

  9. Ovine colostrum nanopeptide affects amyloid beta aggregation.

    PubMed

    Janusz, Maria; Woszczyna, Mirosław; Lisowski, Marek; Kubis, Adriana; Macała, Józefa; Gotszalk, Teodor; Lisowski, Józef

    2009-01-05

    A colostral proline-rich polypeptide complex (PRP) consisting of over 30 peptides shows beneficial effects in Alzheimer's disease (AD) patients when administered in the form of sublinqual tablets called Colostrinin. The aim of the present studies was to investigate whether nanopeptide fragment of PRP (NP) - one of the PRP complex components can affect aggregation of amyloid beta (Abeta1-42). The effect of NP on Abeta aggregation was studied using Thioflavin T (ThT) binding, atomic force microscopy, and analyzing circular dichroism spectra. Results presented suggest that NP can directly interact with amyloid beta, inhibit its aggregation and disrupt existing aggregates acting as a beta sheet breaker and reduce toxicity induced by aggregated forms of Abeta.

  10. Aggregation of sodium alkylbenzenesulfonates in aqueous solution

    SciTech Connect

    Magid, L.J.; Shaver, R.J.; Gulari, E.; Bedwell, B.; Alkhafaji, S.

    1981-01-01

    The surfactant 6 phenyl C/sub 12/SNa forms small spherical micelles in aqueous solution, having an aggregation number of 20 to 30 and a fractional charge of 0.45. These micelles are hydrated to the extent of approximately 18 moles H/sub 2/O per moles of surfactant. A second larger aggregate is also present in 6 phenyl C/sub 12/SNa solutions; its importance increases with solution age. Addition of NaCl causes both aggregates to apparently increase modestly in size. The surfactant 8 phenyl C/sub 16/SNa also contains both aggregates in its solutions; the larger one is relatively more important here. The larger aggregate does not correspond to dispersed bits of a liquid crystalline mesophase.

  11. Multicandidate Elections: Aggregate Uncertainty in the Laboratory*

    PubMed Central

    Bouton, Laurent; Castanheira, Micael; Llorente-Saguer, Aniol

    2015-01-01

    The rational-voter model is often criticized on the grounds that two of its central predictions (the paradox of voting and Duverger’s Law) are at odds with reality. Recent theoretical advances suggest that these empirically unsound predictions might be an artifact of an (arguably unrealistic) assumption: the absence of aggregate uncertainty about the distribution of preferences in the electorate. In this paper, we propose direct empirical evidence of the effect of aggregate uncertainty in multicandidate elections. Adopting a theory-based experimental approach, we explore whether aggregate uncertainty indeed favors the emergence of non-Duverger’s law equilibria in plurality elections. Our experimental results support the main theoretical predictions: sincere voting is a predominant strategy under aggregate uncertainty, whereas without aggregate uncertainty, voters massively coordinate their votes behind one candidate, who wins almost surely. PMID:28298811

  12. Blood platelet aggregation and personality traits.

    PubMed

    Jenkins, C D; Thomas, G; Olewine, D; Zyzanski, S J; Simpson, M T; Hames, C G

    1975-12-01

    Changes in blood platelet aggregation may precipitate episodes of arterial occlusive diseases. Little is known, however, regarding the influence of psychological traits, emotional states and other behavioral stressors on platelet aggregation phenomena. This study examined 46 healthy college men at rest and after submaximal treadmill exercise. Associations were found between the duration of platelet aggregation and a number of scores from the California Psychological Inventory and self-administered anxiety scales. The more socially adequate, poised and dominant persons--those with more mature ego development and less overt anxiety--had platelets with more prolonged aggregation reactions to the in vitro introduction of noradrenalin. Irreversible aggregation of platelets occurred more regularly to lower in vitro concentrations of noradrenalin in platelet samples drawn from subjects who were less anxious and tended to be more rigidly defensive. It is premature to attempt to derive clinical implications from this exploratory work, but some implications for the design of future research are discussed.

  13. Effects of soil tillage on the microwave emission of soils

    NASA Technical Reports Server (NTRS)

    Jackson, T. J.; Koopman, G. J.; Oneill, P. E.; Wang, J. R.

    1985-01-01

    In order to understand the interactions of soil properties and microwave emission better, a series of field experiments were conducted in 1984. Small plots were measured with a truck-mounted passive microwave radiometer operating at 1.4 GHz. These data were collected concurrent with ground observations of soil moisture and bulk density. Treatment effects studied included different soil moisture contents and bulk densities. Evaluations of the data have shown that commonly used models of the dielectric properties of wet soils do not explain the observations obtained in these experiments. This conclusion was based on the fact that the roughness parameters determined through optimization were significantly larger than those observed in similar investigations. These discrepancies are most likely due to the soil structure. Commonly used models assume a homogeneous three phase mixture of soil solids, air and water. Under tilled conditions the soil is actually a two phase mixture of aggregates and voids. Appropriate dielectric models for this tilled condition were evaluated and found to explain the observations. These results indicate that previous conclusions concerning the effects of surface roughness in tilled fields may be incorrect, and they may explain some of the inconsistencies encountered in roughness modeling.

  14. Production of mineral aggregates in quartz tumbling experiments

    NASA Astrophysics Data System (ADS)

    Nørnberg, Per; Finster, Kai; Pall Gunnlaugsson, Haraldur; Knak Jensen, Svend; Merrison, Jonathan Peter

    2013-04-01

    Introduction Tumbling experiments with quartz sand with the purpose of tracing the effect of broken bonds in mineral surfaces resulted in an unexpected production of aggregates. These aggregates are a few microns in diameter, spherical and resembling tiny white "snowballs." Particle comminution by aeolian and other natural weathering processes are known in soil science and is often seen as an increase of fine particles towards the top of soil profiles (Nørnberg, P. 1987, 1988, 2002, J.S. Wright 2007). When mineral grains collide in aeolian processes they break up along weakness zones in the crystal lattice. This mechanism causes broken bonds between atoms in the crystal lattice and results in reactive groups in the mineral surface. This mechanism provides the background for experiments to investigate the oxidation processes of magnetite on the planet Mars. The primary magnetic iron oxide phase on Mars is to day known to be magnetite and the colour of the dust on Mars is most likely due to hematite. To investigate if the oxidation process could take place without going over dissolution and precipitation in water, experiments with tumbling of quartz grains in sealed glass containers along with magnetite were started. The idea was that activated bonds at the surface of quartz could oxidize magnetite and convert it to hematite over time. This proved to be the case (Merrison, J.P. et al. 2010). However, in these experiments we observed the formation of the white aggregates which has been the subject of the study that we present here. Results of tumbling experiments Commercially available quarts (Merck) was sieved to obtain the fraction between 125 and 1000 µm. This fraction was tumbled in glass containers for months and resulted in production of a significant amount of fine grained material (Merrison, J.P et al. 2010). A part of this fine fraction consists of the "snowball"-like aggregates which is a fragile element with relatively high specific surface. The physical

  15. Human land-use and soil change

    USGS Publications Warehouse

    Wills, Skye A.; Williams, Candiss O.; Duniway, Michael C.; Veenstra, Jessica; Seybold, Cathy; Pressley, DeAnn

    2017-01-01

    Soil change refers to the alteration of soil and soil properties over time in one location, as opposed to soil variability across space. Although soils change with pedogensis, this chapter focuses on human caused soil change. Soil change can occur with human use and management over long or short time periods and small or large scales. While change can be negative or positive; often soil change is observed when short-term or narrow goals overshadow the other soil’s ecosystem services. Many soils have been changed in their chemical, physical or biological properties through agricultural activities, including cultivation, tillage, weeding, terracing, subsoiling, deep plowing, manure and fertilizer addition, liming, draining, and irrigation. Assessing soil change depends upon the ecosystem services and soil functions being evaluated. The interaction of soil properties with the type and intensity of management and disturbance determines the changes that will be observed. Tillage of cropland disrupts aggregates and decreases soil organic carbon content which can lead to decreased infiltration, increased erosion, and reduced biological function. Improved agricultural management systems can increase soil functions including crop productivity and sustainability. Forest management is most intensive during harvesting and seedling establishment. Most active management in forests causes disturbance of the soil surface which may include loss of forest floor organic materials, increases in bulk density, and increased risk of erosion. In grazing lands, pasture management often includes periods of biological, chemical and physical disturbance in addition to the grazing management imposed on rangelands. Grazing animals have both direct and indirect impacts on soil change. Hoof action can lead to the disturbance of biological crusts and other surface features impairing the soil’s physical, biological and hydrological function. There are clear feedbacks between vegetative systems

  16. Classification and Characterization of Therapeutic Antibody Aggregates

    PubMed Central

    Joubert, Marisa K.; Luo, Quanzhou; Nashed-Samuel, Yasser; Wypych, Jette; Narhi, Linda O.

    2011-01-01

    A host of diverse stress techniques was applied to a monoclonal antibody (IgG2) to yield protein particles with varying attributes and morphologies. Aggregated solutions were evaluated for percent aggregation, particle counts, size distribution, morphology, changes in secondary and tertiary structure, surface hydrophobicity, metal content, and reversibility. Chemical modifications were also identified in a separate report (Luo, Q., Joubert, M. K., Stevenson, R., Narhi, L. O., and Wypych, J. (2011) J. Biol. Chem. 286, 25134–25144). Aggregates were categorized into seven discrete classes, based on the traits described. Several additional molecules (from the IgG1 and IgG2 subtypes as well as intravenous IgG) were stressed and found to be defined with the same classification system. The mechanism of protein aggregation and the type of aggregate formed depends on the nature of the stress applied. Different IgG molecules appear to aggregate by a similar mechanism under the same applied stress. Aggregates created by harsh mechanical stress showed the largest number of subvisible particles, and the class generated by thermal stress displayed the largest number of visible particles. Most classes showed a disruption of the higher order structure, with the degree of disorder depending on the stress process. Particles in all classes (except thermal stress) were at least partially reversible upon dilution in pH 5 buffer. High copper content was detected in isolated metal-catalyzed aggregates, a stress previously shown to produce immunogenic aggregates. In conclusion, protein aggregates can be a very heterogeneous population, whose qualities are the result of the type of stress that was experienced. PMID:21454532

  17. Soil fungal community and fuctional diversity assessments of agroecosystems in the Southern High Plains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil fungi perform a variety of ecosystem functions that are crucial to maintaining agroecosystem sustainability including aggregate stability and soil carbon storage. The purpose of this study was to compare soil fungal communities and functional diversity in integrated crop and livestock (ICL) sy...

  18. Polyacrylamide Molecular Weight and Phosphogypsum Effects on Infiltration and Erosion in Semi-Arid Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seal formation at the surface of semi-arid soils during rainstorms reduces soil infiltration rate (IR) and causes runoff and erosion. Surface application of dry anionic polyacrylamide (PAM) with high molecular weight (MW) has been found to be effective in stabilizing soil aggregates, and decreasing ...

  19. Polyacrylamide molecular weight and phosphogypsum effects on infiltration and erosion in semi-arid soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seal formation at the surface of semi-arid soils during rainstorms reduces soil infiltration rate (IR) and causes runoff and erosion. Surface application of dry anionic polyacrylamide (PAM) with high molecular weight (MW) has been found to be effective in stabilizing soil aggregates, and decreasing ...

  20. Ridge tillage concentrates potentially mineralizable soil N in the crop row, facilitating maize N uptake

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ridge tillage (RT) has been shown to promote increases in soil carbon and aggregation at greater rates than conventional tillage, but less is known about the soil N provisioning capacity of this system. Using a spatially intensive sampling design, we monitored soil potentially mineralizable nitrogen...

  1. Fractionation of soil organic matter following long-term laboratory incubation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil organic matter (SOM) in agricultural soils comprises a significant part of the global terrestrial C pool. It has often been characterized by utilizing a combination of chemical dispersion of the soil followed by physical separation. These fractions include a non aggregate protected, light fra...

  2. PM2.5 and PM10 Emission from agricultural soils by wind erosion

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil tillage and wind erosion are a major source of particulate matter less than 2.5 and 10 µm (PM2.5 and PM10) emission from cultivated soil. Fifteen cultivated soils collected from 5 states were tested as crushed (<2.0 mm) and uncrushed (natural aggregation) at 8, 10, and 13 m s-1 wind velocity in...

  3. Experimental investigations on aggregate-aggregate collisions in the early solar nebula

    NASA Astrophysics Data System (ADS)

    Blum, Jürgen; Münch, Michael

    1993-11-01

    An experimental setup has been devised to study the low-velocity aggregate-aggregate collisions that play a role in determining aggregate sizes in the preplanetary nebula; both central and grazing collisions are in this way studied for both ZrSiO4 and Aerosil 200. Fragment-mass distributions for catastrophic collisions between equal-sized aggregates are extrapolated according to several assumptions of the simple fragmentation model chosen. The model predicts a complete disintegration of the ZrSiO4 equal-size aggregates.

  4. Soil experiment

    NASA Technical Reports Server (NTRS)

    Hutcheson, Linton; Butler, Todd; Smith, Mike; Cline, Charles; Scruggs, Steve; Zakhia, Nadim

    1987-01-01

    An experimental procedure was devised to investigate the effects of the lunar environment on the physical properties of simulated lunar soil. The test equipment and materials used consisted of a vacuum chamber, direct shear tester, static penetrometer, and fine grained basalt as the simulant. The vacuum chamber provides a medium for applying the environmental conditions to the soil experiment with the exception of gravity. The shear strength parameters are determined by the direct shear test. Strength parameters and the resistance of soil penetration by static loading will be investigated by the use of a static cone penetrometer. In order to conduct a soil experiment without going to the moon, a suitable lunar simulant must be selected. This simulant must resemble lunar soil in both composition and particle size. The soil that most resembles actual lunar soil is basalt. The soil parameters, as determined by the testing apparatus, will be used as design criteria for lunar soil engagement equipment.

  5. Sans study of asphaltene aggregation

    SciTech Connect

    Overfield, R.E.; Sheu, E.Y.; Sinha, S.K.; Liang, K.S. )

    1988-06-01

    The colloidal properties of asphaltenes have long been recognized from peculiarities in their solubility and colligative properties. A layered micellar model or asphaltenes was proposed by others in which a highly condensed alkyl aromatic formed the central part, and molecules of decreasingly aromatic character (resins) clustered around them. Numerous studies, based on a variety of techniques such as ultracentrifugation and electron microscopy indicated a particulate nature for asphaltenes with size 20-40 A diameter. Others have proposed a refined model based on x-ray diffraction and small angle scattering. In this model, interactions between flat sheets of condensed aromatic rings form the central ''crystallite'' part of a spherical particle with the outer part being comprised of the aliphatic positions of the same molecules. These particles are bunched together with some degree of entanglement into ''micelles''. Concentration and solvent dependent radii of gyration, ranging from 30-50 A were reported. The aggregation creates a good deal of uncertainty as to the true molecular size or weight of asphaltenes. Neutron scattering offers novel contrast relative to light scattering (refractive index) and x-ray scattering (electron density). This is because the scattering length of proton is negative, whereas that from deuterium and other nuclei such as C, S, O, and N are positive. Thus by replacing hydrogen with deuterium in either the solvent or the scatterer the contrast can be varied, and different parts of the molecule can be highlighted.

  6. Aggregate Models of Climate Change

    NASA Astrophysics Data System (ADS)

    Hooss, G.; Voss, R.; Hasselmann, K.; Maier-Reimer, E.; Joos, F.

    Integrated assessment of climate change generally requires the evaluation of many transient scenario simulations of century-timescale changes in atmospheric compo- sition and climate, desirably with the accuracy of state-of-the-art three-dimensional (3D) coupled a