Function Of Soil Properties Research Articles

The relationship between the shear strength and water retention curve of unsaturated sand at different hydraulic phases

This technical paper focuses on evaluating the shear strength of unsaturated sand at drying, wetting and alternate drying–wetting cycles, as well as the correlation between the strength and the water retention curve (WRC) at different hydraulic phases. Results of stress–strain curves and WRCs were obtained from conducting numerous tests using suction-controlled triaxial test. Although the maximum shear strength was obtained from the specimens under drying conditions, the difference between the drying and wetting shear strength was relatively small for the tested soil. Based on analysis of the test results, a multi-surfaces envelope model was proposed to fit the experimental shear strength data under drying conditions and to predict the shear strength under wetting conditions (or any subsequent drying–wetting cycle) based on the drying fitting parameters. The fitting and prediction performance of the proposed equations were checked using experimental data from previous studies, and very good agreement was reported. Moreover, the WRC was found to be capable of not only estimating unsaturated soil property functions but also anticipating the soil shear strength behaviour under different hydraulic phases.

Evaluation of heavy metal phytotoxicity to Helianthus annuus L. using seedling vigor index-soil model

A mathematical model to estimate seedling vigor index (SVI) of sunflower (Helianthus annuus L.) seeds in soils contaminated with heavy metals was developed. This model was used to quantitatively describe the complex effects of heavy metal concentrations in soils (Cs) on seed germination and seedling growth. Negative linear regressions between relative seed germination percentage (GP), root length (Lr), and shoot length (Ls) versus log Cs varied as a function of soil properties and type and concentration of heavy metals. With an increase in the heavy metal concentration in soils, the predicted SVI values decreased and reasonably described the experimental SVI values within an 80% prediction band. This demonstrates that SVI values can be predicted, a priori, using SVI-soil models. Based on the sensitivity analysis, root elongation was more significantly affected by the external environment than shoot elongation. Consequently, the SVI-soil model developed in this study can explain heavy metal phytotoxicity to sunflower in complex soil systems. Further research using a diverse range of hyperaccumulator plants and soils is required to render SVI-soil model more available for complex systems in predictions of heavy metal phytotoxicity and hyperaccumulating behaviors of hyperaccumulator plants in various soil systems.

Assessment of Various Pedotransfer Functions for the Prediction of the Dry Bulk Density of Cultivated Soils in a Semiarid Environment

ABSTRACT Bulk density (BD) is a key soil indicator for the assessment of the sustainability of production from agricultural land. However, it is difficult to obtain data on BD from field studies because sampling is an extremely labor-intensive, time-consuming and expensive task at the large scale needed to generate meaningful amounts of data. Therefore, the purpose of this study was to evaluate different pedotransfer functions (PTFs) for their usefulness in the estimation of the BD values of an intensely cultivated area through the use of different geostatistical methods. PTFs are estimation functions of certain soil properties derived from raw data for other soil properties. Different approaches have been used for the development of PTFs, including regression methods and artificial neural networks. In this study, the multivariate analysis methods, general and stepwise regression, were used for BD estimation. In addition, different learning algorithms were evaluated with artificial neural networks (ANN) for their efficacy in estimating the BD. Seven basic soil properties, namely, sand, silt, clay, organic matter, pH, EC and CaCO3, were used in the development of models. The estimation power of the general regression model (normalized root mean square error (NRMSE): 7.10%) was higher than that of stepwise regression (NRMSE: 19.93%). Additionally, the lowest NRMSE (6.74%) and the highest R2 for BD estimation determined with different learning algorithms through artificial neural networks (ANN) were obtained with the Levenberg-Marguardt algorithm. Moreover, for BD estimation, ANN performed better than the multivariate regression equations. Spatial distribution maps of soil BD were generated with the commonly used ordinary kriging method by utilizing the real BD values in combination with BD values obtained from estimation models. Maps of BD values produced by stepwise regression estimation deviated significantly from maps generated with real values whereas ANN-II (Bayesian regularization algorithm) values were closest to the real values and that was reflected in the increased accuracy of mapping.

Determination of volumetric changes in cracked expansive clays

The main objective of this research was to determine volumetric changes in cracked expansive clays. The presence of soil discontinuities was captured by using appropriate soil property functions, namely: a bimodal water retention curve and a sigmoidal swell–shrink curve. Field measurements were used in empirical equations to predict volume changes, and the results were validated using published data (laboratory testing, numerical modeling, or site monitoring). The results indicated that the average swell potential and swell pressure of the expansive Regina clay are 18 ± 2% and 155 ± 15 kPa, respectively. Likewise, heave was found to be 20–30 mm at surface and gradually diminished at 1.75 m depth. The predicted results closely matched the ranges and trends as validated using published data of laboratory testing, numerical modeling, or site monitoring. It is concluded that for natural and compacted expansive soils, the bimodal water retention curve differentiates between flow through the cracks and through the soil matrix. Likewise, the proposed sigmoidal equation accurately describes the swell–shrink curve with most of the deformations between the shrinkage limit and the crack limit.

Simplified solutions for computing consolidation settlement of foundations embedded in a compressible finite stratum

Evaluation of one-dimensional consolidation settlement, which is a function of soil properties and loading profile, is an essential requirement for foundation design. This study presents novel solutions to determine the stress increment required to calculate the settlement of a compressible soil stratum. A systematic procedure is developed to compute the stress increment for different foundations and soil layouts by using the elastic methods available in literature. The solutions are presented in a series of charts and straightforward formulas. They are invaluable particularly when soil compressibility is variable or if loaded foundation is not directly over the compressible soil. Reliability of solutions is validated by comparing the results with those obtained by classical methods. Illustrative examples are included to demonstrate the effectiveness of the developed procedure in practice. The suggested solutions can be directly implemented into preliminary design of foundations allowing valid settlement estimation, or can be used for dimensioning footings under a certain allowable settlement.

Effect of biochars, biogenic, and inorganic amendments on dissolution and kinetic release of phytoavailable silicon in texturally different soils under submerged conditions

Extensive cropping leads to higher removal of silicon (Si) from the soils and makes it a limiting element for various crops. Application of silicic acid (H4SiO4) has limited scope due to high cost, low solubility, and high polymerization. The biogenic sources of Si are alternative to silicic acid (H4SiO4) and Si release from these sources is a function of different soil properties like pH, redox potential, texture etc. Kinetics release of plant available Si (PASi) from various organic and inorganic sources was evaluated in texturally different soils such as sandy loam (SL), sandy clay loam (SCL), and clay (CL) under a 60-day incubation study. Our findings suggest that the highest cumulative release of Si (cSi) was observed in SCL (47.6 mg/L) in control sets without any amendments. The highest cSi release among plant residue amendments was observed by bamboo leaves (340 mg/L) and rice husk (RH) (301 mg/L) in SL and SCL soils, respectively. Among biochar amendments, the rice husk biochar (RHB) released the maximum quantity (246.55 and 243.9 mg/L) of Si in SCL and CL soils respectively. Among the ashes, sugarcane bagasse ash had the highest release (316 mg/L) of Si in SCL and RHA which yielded 235.2 Si mg/L in CL soil for 60days. Silicon release kinetics for these sets of systems showed a diffusive behavior of Si being released from amendments primarily dependent on soil type.

Ecological criteria for zinc in Chinese soil as affected by soil properties.

The increasing accumulation of zinc (Zn) in agricultural soils has led to the need to assess the potential risk of this element for terrestrial organisms. However, the soil ecological criteria in agricultural soil as a function of soil properties have been sparsely reported. In the present study, we derived the ecological criteria (expressed as predicted no effect concentration (PNEC)) for Zn in soils, based on ecotoxicity data for 19 terrestrial species in Chinese soils, the effect of soil properties on Zn ecotoxicity, differences in species sensitivity, and differences between laboratory and realistic field conditions. First, all ecotoxicity data of Zn for terrestrial organisms in Chinese soils were collected and filtered with given criteria to obtain reliable database. Second, the ecotoxicity data were normalized using Zn ecotoxicity predictive models to eliminate the effect of soil properties on Zn ecotoxicity, and corrected with leaching and aging factors to minimize the differences in Zn ecotoxicity under laboratory and field conditions. Then, species sensitivity distribution (SSD) curves were generated with a Burr Ⅲ function based on corrected ecotoxicity data. The concentration of Zn in soil that provides ecological safety for (100-x)% of species (HCx), was calculated from the SSD curve and HC5 was used for estimation of PNEC. Finally, we developed the predictive models for HCx by quantifying the relationship between the Zn HCx and soil properties. Results showed that soil pH was the most crucial factor affecting Zn HCx values, with HC5 values varying from 38.3mg/kg in an acidic soil to 263.3mg/kg in an alkaline calcareous soil. Both the two-factor (soil pH and OC) and the three-factor (soil pH, OC and CEC) models predicted HCx values well, with determination coefficients (R2) of 0.941-0.959 and 0.978-0.982, respectively. This study provides a scientific and reliable basis for the improvement of ecological risk assessment and the establishment of soil environmental quality standards.

Hydro-mechanical properties of unsaturated residual soil from a flysch rock mass

Rainfall is a major triggering factor of landslides in flysch deposits along Europe. Physical and mechanical changes of flysch rock masses caused by the weathering process, result in a complex soil profile with residual soil typically present at the slope surface. The research encompasses residual soils from the Rječina River Valley in Croatia. Built in flysch deposits, the valley is known for several deep-seated and shallow historical landslides. This manuscript presents the hydro-mechanical properties of the soil existing in unsaturated zone of the slope that could play an important role in landslide activation on flysch slopes. Presented unsaturated soil property functions are essential for modelling of the transient rainfall infiltration process and how it affects the stability of flysch slopes in time. For the first time, shear strength and hydraulic conductivity determination were performed in saturated and unsaturated soil conditions, using both the intact as well as remolded samples of the residual soil form flysch rock mass. The results indicate that, in order to correctly define hydraulic and mechanical properties of the in-situ soil, measurements have to be performed on intact samples. Also, the presented results highlight the importance of hysteresis effects and hydraulic paths that fine-grained residual soil has been subjected to in the past.

Benefits and trade-offs of replacing synthetic fertilizers by animal manures in crop production in China: A meta-analysis.

Recycling of livestock manure to agricultural land may reduce the use of synthetic fertilizer and thereby enhance the sustainability of food production. However, the effects of substitution of fertilizer by manure on crop yield, nitrogen use efficiency (NUE), and emissions of ammonia (NH3 ), nitrous oxide (N2 O) and methane (CH4 ) as function of soil and manure properties, experimental duration and application strategies have not been quantified systematically and convincingly yet. Here, we present a meta-analysis of these effects using results of 143 published studies in China. Results indicate that the partial substitution of synthetic fertilizers by manure significantly increased the yield by 6.6% and 3.3% for upland crop and paddy rice, respectively, but full substitution significantly decreased yields (by 9.6% and 4.1%). The response of crop yields to manure substitution varied with soil pH and experimental durations, with relatively large positive responses in acidic soils and long-term experiments. NUE increased significantly at a moderate ratio (<40%) of substitution. NH3 emissions were significantly lower with full substitution (62%-77%), but not with partial substitution. Emissions of CH4 from paddy rice significantly increased with substitution ratio (SR), and varied by application rates and manure types, but N2 O emissions decreased. The SR did not significantly influence N2 O emissions from upland soils, and a relative scarcity of data on certain manure characteristic was found to hamper identification of the mechanisms. We derived overall mean N2 O emission factors (EF) of 0.56% and 0.17%, as well as NH3 EFs of 11.1% and 6.5% for the manure N applied to upland and paddy soils, respectively. Our study shows that partial substitution of fertilizer by manure can increase crop yields, and decrease emissions of NH3 and N2 O, but depending on site-specific conditions. Manure addition to paddy rice soils is recommended only if abatement strategies for CH4 emissions are also implemented.

Contribution of different catalytic types of peptidases to soil proteolytic activity

Soil organic nitrogen is largely composed of proteinaceous material, hence, the extracellular peptidases that are widely produced by microorganisms play a critical role in the recycling of soil organic nitrogen. But why do microbes produce such a variety of functionally different peptidases? In theory, this could be an adaptation to substrate heterogeneity, but it may also be an adaptation to variable soil conditions. Here we characterized the contribution of different catalytic types, or classes, of peptidases present in soil with the intent to determine if their relative contributions would vary as a function of soil properties. We screened specific peptidase inhibitors and optimized their concentrations to work effectively in soil. Total potential proteolytic activity was partitioned among several peptidase classes by adding class-specific inhibitors to the peptidase assay. Using Pepstatin A, EDTA (ethylenediaminetetraacetic acid), PMSF (phenylmethylsulfonyl fluoride), and E64 (epoxysuccinyl-L-leucylamido (4-guanidino) butane), we were able to discriminate among aspartic, metallo-, serine, and cysteine peptidases, respectively. We found that diverse peptidases were active and contributed to the proteolytic activity in soil. Extracellular peptidase profiles varied among different soils and were associated with soil chemical and microbial properties. Metallopeptidases contributed 30–50% of the soil proteolytic activity in all soils. A higher relative contribution of metallopeptidase activity was found in less acidic soils, reflecting its neutral pH optimum. Serine peptidases were only detected in soil from Douglas-fir (Pseudotsuga menziesii) stands (10–20% of total proteolytic activity) but not in soils under red alder (Alnus rubra). The relative activity of aspartic peptidase correlated positively with the fungal:bacterial ratios of the soils. Our results lend support to the view that microbial communities might modify their peptidase profile to optimize protein utilization in response to soil and other environmental factors.

State of practice for use of the soil-water characteristic curve (SWCC) in geotechnical engineering

Routine geotechnical engineering practice has witnessed a significant increase in the usage of unsaturated soil mechanics principles. Laboratory measurement of the soil-water characteristic curve (SWCC) for a soil has been labelled as a primary reason for the improved understanding of unsaturated soil behaviour. Laboratory measurement of the “shrinkage curve” has yielded further insight into the estimation of unsaturated soil property functions (USPFs). The USPFs provide the necessary information for the simultaneous numerical modeling of the saturated and unsaturated portions of the soil profile. This paper presents a state-of-practice summary of the engineering protocols that have emerged amidst the numerous research studies reported over the past couple of decades. It also introduces issues related to hysteresis associated with the SWCC and suggests a pathway forward.

Sources of soil dissolved organic carbon in a mixed agricultural and forested watershed in Rwanda

Dissolved organic carbon (DOC) plays a key role in linking terrestrial and aquatic carbon cycles. Most of the work on soil and water DOC has been conducted in temperate watersheds. There is still a gap in knowledge on DOC dynamics within the tropics. This study assesses water extractable organic carbon (WEOC) in topsoils and describes the relationship between WEOC and land use/land cover (LULC), slope position, curvature and soil properties using linear regression in the Rukarara River Watershed (RRW) in Rwanda. The study analyzes DOC concentration in soil percolation water (pDOC) and describes its relationship with antecedent precipitation index (API) and mean antecedent temperature (MAT) within the watershed using quadratic regression. Generalized linear model (GLM) and linear mixed effect model (LME) with site and/or LULC random effects are used to predict WEOC within the watershed. WEOC concentrations range from 124 to 855 mgC/L in the study area. The highest WEOC concentrations were observed in natural forest, followed by tree plantations, tea plantations and croplands. t-test results did not reveal a significant difference between concentrations of WEOC in valleys, upper slopes, ridges, flat, concave and convex areas in the Rukarara River Watershed (RRW). Considering the relationship between WEOC and soil properties, significant positive correlation coefficients were 0.60, 0.53, 0.50, and 0.36 respectively for the total organic carbon (TOC), the total nitrogen (TN), the cation exchange capacity (CEC), and the aluminum (Al). The best predictor WEOC as a function of soil properties was the generalized linear model (GLM) and indicated soil TOC as the overarching soil factor of WEOC in the RRW by 71%. The pDOC concentration ranges between 0.34 and 10.03 mgC/L and its relationship with both API and MAT was concave upward. APIs explained 12 to 17% of the pDOC variation in the RRW whereas MATs explained 8 to 25%, the natural forest site showing the highest values and the cropland site the lowest values. This result means that a conversion from forest to cropland within the RRW could decrease DOC in both soils and in percolation water. Also, an increase of precipitation and temperature up to respective optima in the RRW, could increase DOC in percolation water and consequently in streams. This increase of instream DOC can impact the water quality of the Rukarara River and its streams, with implications for their ecological function. Strategies of land management and water resources should be enhanced to preserve soil and water quality in the RRW.

Iodine bioavailability in acidic soils of Northern Ireland

Iodine is an essential trace element for humans and grazing animals and is often deficient. Our aim was to investigate the role of soil properties in retaining and ‘fixing' iodine in soils and thereby controlling its phyto-availability to grass. Soils were spiked with labelled 129IO3− and rye grass (Lolium perenne L.) was grown to measure iodine uptake by grass as a function of yield, soil properties and continuous 127I inputs from irrigation water. Iodine-129 added at the start of the uptake trial was rapidly fixed (t1/2 c. 40 h) into non-labile humus-bound forms in soil. The 129I/127I isotopic ratio in grass, compared to the ratio in soil, declined over time confirming progressive 129I fixation into the soil solid phase. The rate of fixation was controlled by soil properties. A model describing iodine dynamics and uptake accounted for c. 75% of the variation in iodine concentration in grass. For most of the soils studied, the main source of iodine in herbage probably arises from the transient availability of periodic rainfall inputs rather than from soil sources. This is expected to improve biofortification strategies.

Lead and antimony from bullet weathering in newly constructed target berms: Chemical speciation, mobilization, and remediation strategies

Understanding lead (Pb) and antimony (Sb) speciation associated with the weathering of bullets at shooting ranges is essential for identifying species migration potential to local watersheds and for assessing the overall toxicity of shooting range soils. In the present study, we fired 2000 5.56 mm bullets into newly constructed and instrumented target berms composed of well-characterized test soils (sand, sandy loam, loamy sand, silt loam) and collected berm pore water runoff and soil samples over five summers (2011 to 2015). We tracked the chemical transformations of Pb and Sb released during bullet weathering as a function of time and soil properties. During 2014 summer, an amendment of ferrous chloride (FeCl2) with a calcium carbonate (CaCO3) buffer was added to a subset of the berms of each soil type to test this remediation strategy.Bulk speciation analysis coupled with micro-scale spectroscopic methods show that both Sb(III) and Sb(V) species are present in soil solution depending on the soil matrix type, but Sb(III) was not observed after 9 months of weathering. In general, Sb was found to be more mobile than Pb, attributable to the relatively low solubility of the dominant Pb phases present in the crust forming around bullet fragments and within soil. The oxidation of Pb(0) resulted in a mixture of lead oxide, lead carbonate, and lead sorbed onto iron(III) oxides. We found a higher degree of metal(loid) mobilization (higher dissolved metal concentrations) in the berms made from the sandy soils. In contrast, silt loam soil was found to be more effective at immobilizing metal(loid)s. Furthermore, we observed that an iron-oxide type amendment may be effective at further reducing Pb and Sb runoff. Results from this study provide insight into the fate and transport of metal(loid)s within small arms target ranges and address a potential method for metal(loid) immobilization.

Latitudinal variation in soil biota: testing the biotic interaction hypothesis with an invasive plant and a native congener

Soil biota community structure can change with latitude, but the effects of changes on native plants, invasive plants, and their herbivores remain unclear. Here, we examined latitudinal variation in the soil biota community associated with the invasive plant Alternanthera philoxeroides and its native congener A. sessilis, and the effects of soil biota community variation on these plants and the beetle Agasicles hygrophila. We characterized the soil bacterial and fungal communities and root-knot nematodes of plant rhizospheres collected from 22 °N to 36.6 °N in China. Soil biota community structure changed with latitude as a function of climate and soil properties. Root-knot nematode abundance and potential soil fungal pathogen diversity (classified with FUNGuild) decreased with latitude, apparently due to higher soil pH and lower temperatures. A greenhouse experiment and lab bioassay showed native plant mass, seed production, and mass of beetles fed native foliage increased with soil collection latitude. However, there were no latitudinal patterns for the invasive plant. These results suggest that invasive and native plants and, consequently, their herbivores have different responses to latitudinal changes in soil-borne enemies, potentially creating spatial variation in enemy release or biotic resistance. This highlights the importance of linking above- and below-ground multitrophic interactions to explore the role of soil biota in non-native plant invasions with a biogeographic approach.

Long-term Trends in Corn Yields and Soil Carbon under Diversified Crop Rotations.

Agricultural practices such as including perennial alfalfa ( L.), winter wheat ( L.), or red clover ( L.) in corn ( L.) rotations can provide higher crop yields and increase soil organic C (SOC) over time. How well process-based biogeochemical models such as DeNitrification-DeComposition (DNDC) capture the beneficial effects of diversified cropping systems is unclear. To calibrate and validate DNDC for simulation of observed trends in corn yield and SOC, we used long-term trials: continuous corn (CC) and corn-oats ( L.)-alfalfa-alfalfa (COAA) for Woodslee, ON, 1959 to 2015; and CC, corn-corn-soybean [ (L.) Merr.]-soybean (CCSS), corn-corn-soybean-winter wheat (CCSW), corn-corn-soybean-winter wheat + red clover (CCSW+Rc), and corn-corn-alfalfa-alfalfa (CCAA) for Elora, ON, 1981 to 2015. Yield and SOC under 21st century conditions were projected under future climate scenarios from 2016 to 2100. The DNDC model was calibrated to improve crop N stress and was revised to estimate changes in water availability as a function of soil properties. This improved yield estimates for diversified rotations at Elora (mean absolute prediction error [MAPE] decreased from 13.4-15.5 to 10.9-14.6%) with lower errors for the three most diverse rotations. Significant improvements in yield estimates were also simulated at Woodslee for COAA, with MAPE decreasing from 24.0 to 16.6%. Predicted and observed SOC were in agreement for simpler rotations (CC or CCSS) at both sites (53.8 and 53.3 Mg C ha for Elora, 52.0 and 51.4 Mg C ha for Woodslee). Predicted SOC increased due to rotation diversification and was close to observed values (58.4 and 59 Mg C ha for Elora, 63 and 61.1 Mg C ha for Woodslee). Under future climate scenarios the diversified rotations mitigated crop water stress resulting in trends of higher yields and SOC content in comparison to simpler rotations.

Development of analytical models to estimate the increase in pile capacity with time (pile setup) from soil properties

This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different bridge construction projects of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile setup. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers, pressure cells that were monitored during the whole testing period. Several static load tests (SLTs) and dynamic load tests were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program was performed on the restrikes data and was used along with the load distribution plots from the SLTs to evaluate the increase in skin friction capacity of individual soil layers along the length of the piles. The logarithmic linear setup parameter “A” for unit skin friction was calculated of the 70 individual clayey soil layers and was correlated with different soil properties such as undrained shear strength (Su), plasticity index, vertical coefficient of consolidation (cv), over consolidation ratio and sensitivity (St). Nonlinear multivariable regression analyses were performed, and three different empirical models are proposed to predict the pile setup parameter “A” as a function of soil properties. For verification, the subsurface soil conditions and setup information for additional 18 PSC piles collected from local database were used to compare the measured versus predicted “A” parameters from the proposed models, which showed good agreement.

CORRELATION OF CBR VALUE WITH PARTICLES SIZE AND COMPACTION CHARACTERISTICS OF COHESIONLESS SOIL

Coarse grains of soil particles play an important role in the geotechnical problems. Therefore, it is necessary to predict of CBR value from some physical properties that easy, low time consume, and limited facility for laboratory experiments. In this paper, an attempt has been conducted to correlate CBR value of coarse-grained soils based on some physical properties such as grain size analysis (percentage finer sieves 25, 9.5, 4.75, 2.36, 1.18, 0.3, and 0.075mm), particles fraction as Gravel (G), Sand (S), and Fines (F). Other parameters taken into consideration are Compaction Characteristics namely optimum moisture content (OMC) and maximum dry density (MDD). The tests conducted for determining grain size, MDD and OMC are easy cheaper and less time to consume than soaking CBR test. The correlation established was in the form of an equation of soaked CBR value as a function of different soil properties using regression analysis.

Soil ecological criteria for nickel as a function of soil properties.

Scientific information for the chemistry and ecotoxicology of metals in soils has been obtained in the research conducted in recent years. However, the latest "science" obtained from this research has not yet been translated into "regulations" in China. In the present study, the predicted no effect concentrations (PNECs) for Ni which denoted as soil ecological criteria for Ni were derived based on the effects of soil properties on bioavailability/ecotoxicity of Ni, incorporating the differences in species sensitivity as well as in laboratory and field conditions. First, collected all ecotoxicity data of Ni from bioassays in Chinese soils and filtered with given criteria to obtain reliable data. Second, corrected the compiled data with either aging factor or leaching and aging factors simultaneously to eliminate the discrepancy caused by difference between laboratory and realistic field conditions. Prior to being put into a species sensitivity distribution (SSD) method to fit SSD curves, the corrected Ni ecotoxicity data were normalized with Ni ecotoxicity predictive models to modify the variation in Ni ecotoxicity caused by different soil properties. Then, the hazardous concentration for x% of the species (HCx) was figured out from the Ni SSD curve and the ecological criterion of Ni (PNEC) was set equal to HCx. Finally, predictive models for HCx were developed by quantifying the relationship between the Ni HCx and soil properties. Soil pH was the major factor controlling the values of HCx for Ni, with HC5 varying from 6.5mg/kg in an acidic soil (pH 5.0) to 218.8mg/kg in an alkaline soil (pH 8.5). The predictive models with parameters of soil pH and organic carbon (%) could calculate HCx with determination coefficients (R2) of 0.90-0.95. When soil cation exchange capacity was taken into account the third parameter, the predictive models could predict HCx more accurate with R2 values of 0.94-0.99.

Relationships between physical‐geochemical soil properties and erodibility of streambanks among different physiographic provinces of Tennessee, USA

AbstractErosion of cohesive soils in fluvial environments is dependent on physical, geochemical and biological properties, which govern inter‐particle attraction forces and control detachment rates from stream beds and banks. Most erosion rate models are based on the excess shear stress equation where the soil erodibility coefficient (kd) is multiplied by the difference between the boundary hydraulic shear stress (τb) and the soil critical shear stress (τc). Both kd and τc are a function of soil properties and must be obtained through in situ field or laboratory testing. Many studies have generated predictive relationships for kd and τc derived from various soil properties. These studies typically were conducted in watersheds within a single physiographic region with a common surficial geology and/or investigated a limited number of soil properties, particularly geochemical properties. With widely reported differences in relationships between τc and soil properties, this study investigated differences in predictive relationships for τc among different physiographic provinces in Tennessee, USA. Erodibility parameters were determined in the field using a mini‐jet test device. Among these provinces, statistically four unique clusters were identified from a dataset of 128 observations and these data clusters were used to develop predictive models for τc to identify dominant properties governing erosion. In these clusters, 16 significant physical and geochemical soil properties were identified for τc prediction. Among these soil properties, water content and passing #200 sieve (percentage soil less than 75 μm) were the dominant controlling parameters to predict τc in addition to clay percentage (&lt; 2 μm), bulk density, and soil pore water chemistry. This study suggests that unique relationships exist for physiographic provinces that are likely due to soil physical‐geochemical processes associated with surficial geology that determine minerology of the cohesive soil. Copyright © 2017 John Wiley &amp; Sons, Ltd.