Fine Soil Particles Research Articles

Partitioning, leachability, and speciation of chromium in the size-fractions of soil contaminated by chromate production

Soil particle size significantly affects the distribution and migration of chromium (Cr) in soil. Limited studies have investigated the impact of soil particle size on Cr partitioning at chromate contaminated sites. In this study, the physicochemical properties of coarse sand, medium sand, fine sand, and silt-clay were analyzed. And the particle size effects on partitioning, leachability, and bioaccessibility of total Cr and Cr(VI) were determined. The results showed the distribution factor (DF) of Cr(VI) in the coarse sand, medium sand, fine sand, and silt-clay fractions were 0.70, 0.79, 1.35, and 1.60, respectively. The total Cr DF values also had the similar result. The leached concentrations of total Cr and Cr(VI) in silt-clay (562.89 mg/L and 551.71 mg/L) was higher than in coarse sand (238.55 mg/L and 228.68 mg/L) fraction. The bioaccessibility of total Cr and Cr(VI) in silt-clay (77.72% and 88.58%) was higher than in fine sand (60.72% and 79.55%) fraction. The total Cr proportion of the exchangeable fraction (45.92%–73.67%) was relatively high in the four soil particle size fractions and gradually increased as soil particle size decreased. These implied that finer soil particles are more capable of enriching, mobilizing, and bioaccessibility of Cr and Cr(VI) than the coarse particles, which was related to the higher organic matter, cation exchange capacity, specific surface area, and clay components in smaller particles. The results suggested that higher environmental risk occurred in the finer fraction than in the coarser fraction for the chromate production contaminated soil.

Changes in mineral-associated carbon and nitrogen by long-term fertilization and sequestration potential with various cropping across China dry croplands

Mineral-associated organic carbon (MOC) and mineral-associated nitrogen (MN) are the major pools of total soil organic carbon (TSOC) and total nitrogen (TN) stocks. Thus, it is important to understand the impact of agricultural practices on MOC and MN stocks and capacities. The present study aimed to explore how the application of various fertilizers and crop rotation affect MOC and MN, and how improved management practices sequester carbon and nitrogen as MOC and MN to mitigate climate change. Twenty-one long-term experiments across China dry croplands with various soil types and crop rotations were involved to investigate the effects of the application of various fertilizers on MOC and MN. Results showed that mineral fertilizers combined with manure significantly increased TSOC (62 %) and TN (57 %), and MOC (33 %) and MN (32 %) concentrations, respectively, resulting in decreased ratios of MOC/TSOC (0.59) and MN/TN (0.47). Moreover, mineral fertilizers with straw significantly increased MOC/TSOC ratio, but had no effects on MN/TN ratio compared with mineral fertilizer application (0.72−0.77). Significantly positive linear correlations were observed between MOC (MN) concentrations and the mass proportion of fine soil particles (<20 μm). Further analysis suggested that TN, TSOC, crop rotation (e.g., wheat-maize, wheat-soybean, maize-soybean, maize-rape, and maize monoculture), and fine soil particle content were the key regulating factors, which accounted for about72 % of the variations of MOC and MN concentration. Boundary line analysis suggested that MOC and MN had the potential to increase by 48 % and 39 %, respectively. In conclusion, main dry croplands in China might sequester an additional 527 Tg for MOC and 37 Tg for MN with appropriate crop rotation and manure application.

Effects of soil surface electric field on aggregates breakdown and water erosion in black soil region of Northeast China

Through quantitatively adjust soil electric field, we investigated the effect of soil electric field on aggregate stability and soil erosion in black soil region of Northeast China with the experiments of wet sieving and rainfall simulation. Results showed that: 1) Soil surface potential absolute value and electric field strength increased with the decreases of electrolyte concentration in bulk solution. Soil electric field strength could reach to 108 V·m-1. 2) With the increase of soil electric field strength, the degree of fragmentation of soil aggregates increased and the mean weight diameter (MWD) decreased sharply first and then kept constant. 3) With decreasing electrolyte concentration and increasing surface potential, the amount of soil loss increased. As the electrolyte concentration was &lt;0.01 mol·L-1, the corresponding soil surface potential was &gt; 210 and 209 mV for Bin-xian and Keshan, respectively, the cumulative amounts of soil loss with rainfall time almost overlapped, suggesting that the electrolyte concentration of 0.01 mol·L-1 was the threshold for soil erosion. 4) There was a linear relationship between soil cumulative loss and MWD. Our results indicated that soil electric field strength increased as the rain enters into the soil, which could induce soil aggregate breakdown and release amounts of fine soil particles. Finally, soil erosion occurred under the driving of flowing water. Our results provided insights into the mechanism underlying soil erosion in the black soil region of Northeast China.

Experimental Study on the Effect of Additives on Drainage Consolidation in Vacuum Preloading Combined with Electroosmosis

Vacuum-electroosmosis is a common method of foundation treatment; however, it is disadvantaged by fine soil particles clogging the drainage plate. To overcome this issue, this study treated the dredged fill from vacuum-electroosmosis with different additives. The parameters of discharged water, current, water content, and shear strength of soils treated with different amounts of Ca(OH)2, FeCl3, and NaCl were analyzed. The results showed that different additives have different effects on the vacuum-electroosmosis method for reinforcing dredger filling. Excessive additive contents were found to have an adverse effect on vacuum-electroosmosis, and hence, optimum amounts are required for the three additives. On comparing the optimum dosage of these additives, FeCl3 was observed to be the most energy-saving. From the aspect of anode corrosion and the costs involved, Ca(OH)2 was the most economical. For practical engineering applications, Ca(OH)2 was the most preferable additive. The results of this study provide guidance and scientific criteria for similar dredging foundation treatments.

In situ undrained shear strength for cutting slopes erodibility estimation: case study in the Quadrilátero Ferrífero region, Brazil

Erosion is a natural relief modeling process that is influenced by several factors. Among these, we highlight the soil properties, designated by the specific concept of erodibility. Most of the existing methods for quantifying erodibility are based on field plots or indirect procedures developed from farmland approaches and methodologies limited to other study conditions such as slopes, where soil structure is different. Therefore, the objective of this study is to investigate the erodibility of cutting slopes in the Quadrilatero Ferrifero region, Brazil, and its relationship with soil properties, using the hand vane test to determine undrained shear strength (SU) and associating its values with the erodibility factor K. The results show that SU has significant correlation with the fine soil particles, especially clay and silt. In addition, properties responsible for the increase in SU decrease erodibility factor K. The mean weight diameter, geometric mean diameter, and aggregate stability index parameters show that aggregate diameter and stability are associated with higher SU and, conversely, lower K values. In addition, chemical properties, especially pH, also interfere in the results, however, in lower proportion when compared with the physical indexes. Finally, the undrained shear strength has a significant negative correlation with erodibility factor K, both in non-erodible (R2 = 0.6770, p value < 0.01) and erodible (R2 = 0.7885, p value < 0.01) soils, showing promising methods in the diagnosis of potentially erodible soils.

Testing Os Staining Approach for Visualizing Soil Organic Matter Patterns in Intact Samples via X-ray Dual-Energy Tomography Scanning.

Challenges with in situ visualization of nonparticulate organics in porous materials limit understanding and modeling processes of transport, decomposition, and storage of organic compounds. In particular, it impedes deciphering the mechanisms driving accumulation and protection of soil organic matter (SOM), processes crucial for sustaining soil fertility and mitigating effects of global climate change. A recently proposed method of staining soil organics by OsO4 vapors with subsequent dual-energy X-ray computed microtomography scanning (μCT) offers new opportunities to visualize SOM within intact soil matrix. Our objective was to test the method's performance in staining different organic materials located in media with contrasting pore characteristics: (1) roots of switchgrass (Panicum virgatum L.), either placed within fine and coarse sands or grown within soil microcores, (2) biochar fragments, and (3) soils with relatively low and high C contents. We found that the method was effective in staining organic materials of root origin and the organics associated with fine soil particles, but not the biochar. The estimated percent of total C that reacted with OsO4 vapors ranged from 0.7% in plant roots to 3.2% in sand-free fraction of the high C soil and was only 0.2% in the studied biochar. Total soil C and Os concentrations were strongly linearly related, suggesting a potential for future method development. However, we would recommend caution when interpreting the results in cases when gas diffusion through the soil matrix is limited.

Experimental Investigation on Suffusion Characteristics of Cohesionless Soils Along Horizontal Seepage Flow Under Controlled Vertical Stress

Suffusion is one of the main modes of internal erosion leading to selective erosion and gradual migration of fine soil particles through the voids of soil skeleton formed by coarse soil particles under seepage flow. Suffusion may induce deterioration and even failure of hydraulic geo-structures, such as embankment dams, dikes, levees, as well as landslide dams, if they are formed by gap-graded cohesionless soils. Soil mass in the hydraulic geo-structures is always subjected to overburden load and seepage through the soil mass generally has a large component along the horizontal direction. In the literature, however, little attention has been paid to the horizontal seepage-induced suffusion under controlled vertical stress. In this study, horizontal seepage-induced suffusion tests were carried out using a testing apparatus with controllable vertical stress and hydraulic gradient. The seepage flux and eroded fine particle mass, as well as local hydraulic gradients can be measured. The effects of initial dry density and initial fines content on suffusion characteristics of a cohesionless soil were investigated. Test results showed that after the initiation of suffusion, alternate decrease and increase in the coefficient of permeability occurred possibly due to alternate clogging and dredging of soil pores by the movable fine particles. Uneven distribution of local hydraulic gradients along the flow path was observed and this could be regarded as a sign of the initiation of suffusion. Both initiation and failure hydraulic gradients increased with initial dry density and initial fines content.

Linking soil macropores, subsurface flow and its hydrodynamic characteristics to the development of Benggang erosion

The increasing population in south China is exposed to Benggang erosion that deteriorates slope stability and agricultural production. However, the influence of subsurface flow, especially macropore flow, on the development of Benggang erosion and the collapse of Benggang remains inadequately studied. To address this issue, we measured the spatial distribution of soil macropores on an active Benggang-eroded slope in a subtropical region in China. During the experimental period of 20151221 to 20180116, two collapse events were observed on the study slope. In addition, the soil water content at the depths of 20, 40, 60, and 80 cm was monitored at a time interval of five minutes at six sites along the slope. The velocities of vertical subsurface flow traveling between measured soil depths were determined based on the difference in the response time of soil water content to rainfall along the depth. Further, the Reynolds number (Re) of subsurface flow in different water patterns, e.g., Darcy flow (DF) and preferential flow (PF) was calculated based on soil pore size and flow velocity. Results indicate that the number of macropores near the Benggang wall (i.e., the most active area of erosion on a Benggang slope) was almost twice that on the upper slope. The presence of abundant macropores near the Benggang wall facilitated faster subsurface flow and a greater variation in soil water content in time and space, which significantly influenced Benggang erosion and collapse. For both the DF and PF, the maximum Re was detected near the Benggang wall. The Re of PF was ten times higher than that of DF. The Re being greater than 3 was the threshold to initiate PF. Moreover, the larger Re of PF likely enhanced the leaching of fine soil particles and promoted the occurrence of Benggang erosion. This study confirms the key role of macropore flow in Benggang erosion, which helps better understanding, modeling and controlling of Benggang erosion.

Spatial distribution, mobility and potential health risks of arsenic and lead concentrations in semiarid fine top-soils of Durango City, Mexico

Significant amounts of mining wastes containing Fe-oxide rich phases (i.e., hard rock dumps, tailing impoundments) have been historically deposited in semiarid soils within Durango City. Urban mapping along with mineralogical and geostatistical analyses were carried out to determine levels of concentration, spatial distribution, and relationships between As-bearing and Pb-bearing phases and their mobilities for different sites around this city. It was found that fine As-bearing particles (<5–10 μm) comprised of Pb3(AsO4)2-like, FeAsS, and complex structures were the main phases in urban sprawl soil, while PbO2-like, PbS, and (Ba, Pb)SO4-like were the main Pb-bearing phases (<5 μm). Levels of As and Pb vary in urban sprawl soil from 4.37 to 42 and 8.3 to 82.5 mg kg−1, respectively, and are higher in the soil adjacent to Cerro de Mercado, where the mining area is conurbated, from 55.1 to 221 and 21.6 to 107.3 mg kg−1, respectively. Most of these concentrations were associated with the finest soil fraction (<10–250 μm), enhancing health risks due to inhalation or incidental intake. The spatial distribution patterns of these elements were mainly related to high traffic density and mining waste for Pb, and eolic dispersion of fine soil particles for As. A low mobility was found for Pb (up to 3%), indicating a low environmental risk if released, whereas As mobility changes from a low to a medium risk level (0.1–37.1%). Geostatistical analysis suggested correlations between soil pollution and distance regarding hard rock and tailing impoundment sources.

Effect of Clay on Internal Erosion of Clay‐Sand‐Gravel Mixture

In this study, a one‐dimensional seepage test apparatus was used to investigate the effect of clay on the critical hydraulic gradient, hydraulic conductivity, migration of fine particles in soil, and percentage of fine particle loss during the internal erosion of clay‐sand‐gravel mixture, compared with clean gravel. The critical hydraulic gradient and fine sand loss percentage of the clay‐sand‐gravel mixture decreased, and critical flow velocity and the hydraulic conductivity increased. Six clay‐sand‐gravel mixture samples with different clay contents were used to evaluate the effect of different clay contents on internal erosion. As the percentage of clay mass to fine particle mass increases from 0% to 25%, the critical hydraulic gradient of soil samples decreases by nearly half and the fine sand loss percentage decreases from 13.73% to 3.48%. Overall, clay has a significant effect on the development of internal erosion of clay‐sand‐gravel mixture. And attention should be paid in engineering project; clay‐sand‐gravel mixture with a small amount of clay is more likely to be damaged than clean gravel.

Long-term fertilization and intensive cropping enhance carbon and nitrogen accumulated in soil clay-sized particles of red soil in South China

Understanding the underlying mechanism of soil carbon (C) and nitrogen (N) accumulation is of great significance for soil C sequestration and climate change mitigation, as well as soil fertility improvement. The objective of this study was to evaluate the response of C and N accumulation in aggregates and fine soil particles to long-term mineral fertilizer and manure application. Five treatments from a long-term experiment with double maize cropping were examined in this study, i.e., (1) no fertilizer (control); (2) mineral nitrogen, phosphorus, and potassium application (NPK); (3) doubled application rate of the NPK (2NPK); (4) pig manure alone (M); and (5) mineral NPK fertilizers and manure combination (NPKM). By using physical particle-sized fractionation, we analyzed soil organic carbon (OC) and total nitrogen (N), and δ13C of OC in bulk soil and aggregates (53–2000 μm) and, coarse silt-sized fraction (5–53 μm), fine silt-sized fraction (2–5 μm), and clay-sized fraction (< 2 μm) under those five treatments. Fertilizer application for 24 years, particularly M and NPKM treatments, significantly increased the concentration and proportion of OC and total N associated with aggregates and clay-sized fraction as compared with control. Manure application significantly increased the proportion of OC by 6.6–7.8 points in aggregates, whereas it was by 22.6–25.0 points in clay-sized fraction. Clay-sized fraction-associated C and N showed a non-linear response to C and N accumulation in bulk soil, contributing approximately 47% and 69% to soil OC and total N, respectively. Moreover, the mass proportion of aggregates and the mass ratio of aggregates to fine soil particles increased significantly with C accumulation in fine silt-sized and clay-sized fraction. Organic carbon and total nitrogen accumulation in soil clay-sized particles play important role in soil C and N sequestration in red soil. Our results also suggested that C accumulation in fine soil particles might benefit soil aggregation in intensive cropping system of South China.

Effect of water content on lime additive content in vacuum preloading with PVDs

Dredged slurry is composed of a great quantity of fine soil particles, which accumulate around prefabricated vertical drains during vacuum preloading. The addition of hydrated lime as a flocculent can improve the permeability and vane shear strength of dredged slurry. A series of experiments showed that lime exists in the lime modification optimum as a flocculent. This study was aimed at analyzing the relationship between a given amount of lime additive and different water contents according to lime flocculation combined with a vacuum preloading test. For this, parameters, including the pore water pressure, discharged water, post-test water content, and vane shear strength, were monitored. Based on a given amount of lime additive in optimum water content, a function was derived, which could provide theoretical guidance for similar studies in the future.

The recovery rates of secondary savannas in abandoned pastures are poorly explained by environmental and landscape factors

AbstractQuestionAssessing the natural regeneration potential of degraded savannas is a crucial step in restoration planning, since that assessment will define the need for and costs of active intervention. Predicting natural regeneration, however, depends on the mechanistic understanding of ecosystem resilience. Here, we searched for the factors modulating plant communities spontaneously regenerating in abandoned pastures.LocationTropical savanna (cerrado), Brazil.MethodsOver two years, we quantified changes in the structure, richness and species composition of plant communities in 29 secondary savannas resulting from pasture abandonment. We then investigated the influence of soil and landscape attributes, exotic grass cover and time since pasture abandonment on the recovery rate and species composition of these communities.ResultsThe wide variation among sites was not explained by time since abandonment or distance to the nearest remnant native vegetation. Soil attributes, exotic grasses and native vegetation cover around a pasture explained a small fraction of the variation in the recovery rate. We did not find an isolated factor or a robust set of factors explaining the variation in the recovery rate for all vegetation attributes. Species composition was slightly influenced by exotic grasses, soil penetration resistance, proportion of fine soil particles and time since abandonment. Colonization and resprouting by savanna specialists over the two‐year period were hindered by exotic grasses.ConclusionThe use of predictive models based on soil properties, exotic grasses, landscape attributes or time since abandonment is unfeasible for inferring the recovery rate of savanna structure and richness after pasture abandonment. Case‐by‐case monitoring is required to support decisions on restoration intervention. Other factors, which are almost impossible to obtain, such as land‐use practices and history and the taxonomic or functional composition of pre‐existing vegetation, can potentially influence the recovery rate. Exotic grasses must be controlled to favour colonization and resprouting by savanna specialists.

Characterization of Soil Moisture Distribution and Movement Under the Influence of Watering-dewatering Using AHFO and BOTDA Technologies

ABSTRACT The infiltration and distribution of water through unsaturated soil determine its mechanical and hydrological properties. However, there are few methods that can accurately capture the spatial distribution of moisture inside soil. This study aims to demonstrate the use of actively heated fiber optic (AHFO) and Brillouin optical time domain analysis (BOTDA) technologies for monitoring soil moisture distribution as well as strain distribution. In addition to a laboratory model test, finite element analyses were conducted to interpret the measurements. During the experiment, the fine particle migration was also measured to understand its influence on soil hydraulic conductivity. The results of the experiment indicate that (i) for a soil that has never experienced a watering-dewatering cycle, water infiltration can be accurately calculated using the Richards’ equation; (ii) migration of fine soil particles caused by the watering-dewatering cycle significantly increases the hydraulic conductivity; and (iii) two critical zones (drainage and erosion) play significant roles in determining the overall hydraulic conductivity of the entire soil. This study provides a new method for monitoring the changes in soil moisture, soil strain, and hydraulic conductivity. The observations suggest that the effect of fine particles migration should be considered while evaluating soil moisture distribution and water movement.

Change in Characteristics of Soil Carbon and Nitrogen during the Succession of Nitraria Tangutorum in an Arid Desert Area

The shrub Nitraria tangutorum is distributed widely in arid desert areas, and plays a critical role in the desert–oasis ecosystem. This study quantified varying characteristics of carbon (C) and nitrogen (N) in the soil at four stages—the initial stage (IS), stable stage (SS), degradation stage (DS), and severe degradation stage (SDS)—in a steppe ecosystem in the desert of northwestern China. The results indicated that N. tangutorum experienced both expansion and deterioration as a decline of 50.7% occurred in the available soil water due to agricultural utilization, and the plant community transformed from being shrub-dominated to annual herb-dominated. At soil layer depths between 0–100 cm in the N. tangutorum nebkha dune ecosystem, organic C and total N storage was 1195.84 g/m2 and 115.01 g/m2 during the SDS, respectively, with an increase of 11.13% and 12.59% from the IS. In addition, the storage of C and N in the soil increased during the IS as well as the SS, when most of the C and N were accumulated, and the storage decreased during the DS and SDS, as the N. tangutorum communities declined. At soil layer depths between 0–100 cm in the desert steppe ecosystem, the highest storage levels of C and N were 8465.97 g/m2 and 749.29 g/m2 during the SS, and the lowest were 1076.12 g/m2 and 102.15 g/m2 during the IS, respectively. The changes and accumulation of C and N were greater in the deeper (40–100 cm) layer than in the surface layer of soil (0–40 cm). Lastly, changes in soil organic carbon (SOC) as well as in the total nitrogen (TN) were strongly related to the coverage degree, water content in soil, and the ratio of fine soil particles (silt and clay). To sum up, the intensive development of water resources has vastly reduced the ability of N. tangutorum vegetation to sequester C and N in the desert of Minqin. Efforts to perform ecological restoration and reverse desertification in the Minqin Desert should focus on preventing the unreasonable exploitation of water resources in order to maintain stable N. tangutorum communities.

Soil particle composition, fractal dimension and their effects on soil properties following sand-binding revegetation within straw checkerboard in Tengger Desert, China

This study aims to elucidate the effects of soil particle composition and fractal dimension on soil physical and chemical properties following sand-binding revegetation within straw checkerboard in south-eastern Tengger Desert. Three afforested plantations in the year of 2016 (i.e., 1 year), 2013 (i.e., 4 years) and 1987 (i.e., 30 years) were selected as study sites, with the adjacent mobile sand land as control (CK). We measured soil particle composition, soil fractal dimension, and the changes of soil physical and chemical properties. The relationship between soil particle composition, soil fractal dimension, and soil properties was analyzed. The results showed that contents of soil particle with the size of both 100-250 μm and 250-500 μm were greater than that of 50-100 μm, ranging from 42.5% to 80.1% and from 12.5% to 42.2% relative to that ranging from 0.2% to 20.8%. Contents of soil particle with the size of <2 μm and 2-50 μm were remarka-bly lower than that of 100-250 μm, 250-500 μm and 50-100 μm, ranging from 0 to 1.3% and from 0 to 22.7%, respectively. However, contents of soil particle at the size of 500-1000 μm was the lowest occupying <0.3% of soil particle composition. Soil particle with the size of <2 μm and 2-50 μm were found in the 30-year sites only. Soil particle distribution at the size of 50-100 μm, 100-250 μm, and 250-500 μm followed the order of 30 a>1 a>4 a＞CK, 4 a>1 a>CK>30 a, and CK>1 a>4 a> 30a, respectively. Soil particle with the size of 500-1000 μm occupied little of soil particle composition, with no significant difference between each site. The fractal dimension of soil particles ranged from 0.54 to 2.59. There was significantly greater soil fractal dimension in 30 a in comparison to 4 a, 1 a and CK, with the intermediate values in 4 a and 1 a, and the lowest values in CK. There was a significantly positive correlation of fractal dimension of soil particles with soil particle content of clay, silt, very fine sand, and a significantly negative correlation of fractal dimension of soil particles with soil particle content of medium sand. Fractal dimension of soil particles was positively correlated with soil electrical conductivity, organic carbon, total nitrogen, and carbon-nitrogen ratio, but with no correlation with soil pH and soil water content. Soil particle content at the size of <2 μm, 2-50 μm, and 50-100 μm had a significant positive correlation with soil electrical conductivity, organic carbon, total nitrogen, and carbon-nitrogen ratio, whereas soil particle content at the size of 250-500 μm had a negative correlation with the former four soil indices and soil water content. In addition, there was a significant negative correlation of soil particle content at the size of 500-1000 μm with soil water content. It was concluded that the sand-binding reve-getation within straw checkerboard in Tengger Desert could facilitate the fine soil particles by ameli-orating stressful soil conditions. Long-term succession of revegetation on mobile sand land could enhance soil clay and silt content as well as soil fractal dimension, thus be beneficial for the improvement of soil physical and chemical properties and desertification control.

Spatial and temporal dynamics of nutrients in riparian soils after nine years of operation of the Three Gorges Reservoir, China

The construction and operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has had significant consequences for the hydrology of riparian zones along the Yangtze river. Little is known about how such changes in hydrology might affect the levels of nutrients and organic matter (OM) in riparian soils. We conducted a nine-year study on the spatio-temporal dynamics and dominant environmental correlates of nutrients and OM in riparian soils along a 600 km section of the Yangtze. These soils have been exposed to a disrupted hydrological regime since the TGR's establishment in 2008. Vegetation surveys were also conducted from 2012 to 2016 to assess relationships between soil chemical properties and vegetation community properties under altered hydrology. Across the stream gradient, concentrations of total potassium (K) increased by 54% since the TGR's establishment. The opposite occurred for SOM and available K, concentrations of which were 35% and 33% lower in 2016, respectively, than those of 2008. The rate of increase in total K tended to be more rapid at the middle section of the stream gradient. Moreover, concentrations of SOM, total N, total K, and available phosphorus (P) and K tended to be particularly high at the middle section. The spatio-temporal distributions of nutrients were strongly positively related to the contents of fine soil particles (i.e., silt and clay). Moreover, the aboveground biomass was negatively correlated with the nutrient dynamics. Our results indicate that the control of the nutrient release in the middle reaches and lower elevations where fine particles tend to accumulate, will be essential for maintaining the health of aquatic and riparian ecosystems upstream of the TGR.

Occurrence of organophosphate flame retardants in farmland soils from Northern China: Primary source analysis and risk assessment

Ninety-eight soil samples were collected from farmland soils from Beijing-Tianjin-Hebei core area, Northern China, where agricultural lands were subjected to contamination from intense urban and industrial activities. Twelve organophosphates flame retardants (OPFRs) were analyzed with total soil concentrations ranging from 0.543 μg/kg to 54.9 μg/kg. Chlorinated OPFRs were dominating at mean level of 3.64 μg/kg and Tris(2-chloroisopropyl) phosphate contributed the most (mean 3.36 ± 5.61 μg/kg, 98.0%). Tris(2-ethylhexyl) phosphate was fully detected at levels of 0.041–1.95 μg/kg. Generally, tris(2-butoxyethyl) phosphate and triphenyl phosphate contributed the most to alkyl- (53.6%) and aryl-OPFRs (54.3%), respectively. The levels of ∑OPFRs close to the core urban areas were significantly higher than those from background sites. The occurrence and fate of OPFRs in soil were significantly associated with total organic carbon content and mostly with fine soil particles (<0.005 mm), and a transfer potential from the atmosphere was predicted with logKSA values. Comparable soil levels with poly brominated diphenyl ethers s in other studies suggested that the contamination of OPFRs occurred in farmland soil with an increasing trend but currently showed no significant environmental risk based on risk quotient estimation (<1). This investigation warrants further study on behaviors of OPFRs in a soil system and a continual monitoring for their risk assessment.

Soil nutrient loss through erosion: Impact of different cropping systems and soil amendments in Ghana.

Soil erosion is a multifactor threat to crop production and the environment. Most studies on soil erosion characterization have not focused on soil nutrient loss associated with erosion. The aim of this study was therefore to quantify the magnitude of nutrient loss through soil erosion under different cropping systems and amendments to inform agronomic practices in sub-Saharan Africa (SSA). A field experiment was carried out on runoff plots with different cropping systems (sole maize, sole cowpea, sole maize and maize intercropped with soybean) as main plots and soil amendments (biochar, NPK (Nitrogen +Phosphorus +Potassium) fertilizer, NPK + biochar and a control (no amendment)) constituting the subplots in a randomized complete block design. For each block, a bare plot was included to assess the efficiency of the different crop and soil management practices on soil erosion. The study was carried out in three consecutive cropping seasons in the semi-deciduous forest zone of Ghana. The bare plots had the highest amounts of nitrogen (N), phosphorus (P), and potassium (K) eroded: 33.88, 12.35 and 12.75 kg ha-1 respectively followed by the control plots with magnitude of 20.43, 8.42 and 7.87 kg ha-1 respectively for N, P and K. Sole maize had the highest amounts of nutrient loss: 19.71, 8.12 and 7.27 for N, P and K respectively compared to all the other cropping systems where the losses varied respectively from 12.38 to 17.12, 6.67 to 7.49 and 5.81 to 6.75 kg ha-1 The legume-based cropping systems under inorganic fertilizer and biochar management effectively reduced nutrient loss more than all other treatment combinations. The off-site effect of soil erosion expressed as enrichment ratio (ER) was higher for all plots, which received inorganic fertilizer inputs varying from 1.93 to 3.06 while the other treatments had ERs of 1.51 to 2.03. The ERs of fine soil particles were greater than 1 (ranging from 1.14 to 3.6) being relatively higher than that of coarse particles (sand) with values below 1 (ranging from 0.62 to 0.88). The least cumulative monetary value of nutrient loss (30.82 US$ ha-1) was observed under cowpea cropping system which received NPK + BC treatment. Soil erosion affected directly soil nutrient depletion through nutrient loss; however, integrated soil fertility management associated with legume-based cropping systems can be alternative options to reducing its effects on croplands in SSA.

Changes in Particle Size Composition under Seepage Conditions of Reclaimed Soil in Xinjiang, China

The distribution of reclaimed soil particle size under seepage conditions after the management period will directly determine the success or failure of reclamation work. The geotechnical experimental method was used in this paper to study the changes in the granulometric composition of soil. The results show that the granulometric composition of the reclaimed soil varied obviously at different depths. The granulometric composition of the soil at a depth of 10 cm was not much different from undisturbed reclaimed soil (URS). At a depth of 30 cm, as the sharp decrease of the content of fine particles resulted in coarser reclaimed soil, the soil became more uniform, with an increase in porosity and water content. At a depth of 50 cm, the fine particle content was generally slightly lower than that of URS. At a depth of 70 cm, the fine particle content of the soil greatly exceeded that of the URS, with the finest soil particles and lowest porosity. The main reason for the above-mentioned changes of granulometric composition in the reclaimed soil was the seepage in soil caused by irrigation during the management period. The research results can provide a reference for management after land reclamation at non-metallic mines in Xinjiang, China.