Modelling the Fate of Chromated Copper Arsenate in a sandy Soil

A pulse of chromated copper arsenate (CCA, a timber preservative) was applied in irrigation water to an undisturbed field soil in a laboratory column. Concentrations of various elements in the leachate from the column were measured during the experiment. Also, the remnants within the soil were measured at the end of the experiment. The geochemical modelling package, PHREEQC-2, was used to simulate the experimental data. Processes included in the CCA transport modelling were advection, dispersion, non-specific adsorption (cation exchange) and specific adsorption by clay minerals and organic matter, as well as other possible chemical reactions such as precipitation/dissolution. The modelling effort highlighted the possible complexities in CCA transport and reaction experiments. For example, the uneven dosing of CCA as well as incomplete knowledge of the soil properties resulted in simulations that gave only partial, although reasonable, agreement with the experimental data. Both the experimental data and simulations show that As and Cu are strongly adsorbed and therefore, will mostly remain at the top of the soil profile, with a small proportion appearing in leachate. On the other hand, Cr is more mobile and thus it is present in the soil column leachate. Further simulations show that both the quantity of CCA added to the soil and the pH of the irrigation water will influence CCA transport. Simulations suggest that application of larger doses of CCA to the soil will result in higher leachate concentrations, especially for Cu and As. Irrigation water with a lower pH will dramatically increase leaching of Cu. These results indicate that acidic rainfall or significant accidental spillage of CCA will increase the risk of groundwater pollution.     

Estimating the Fate of De-icing Salt in a Roadside Environment by Combining Modelling and Field Observations

Predicting the environmental effects of de-icing salt requires knowledge of the pathways taken by salt from on-road application through spread to the surroundings to deposition and fate in the roadside environment. This study described differences in chloride deposition and distribution in soil with increasing distance from the road by means of field observations and modelling. The dynamic modelling approach successfully represented the spread of de-icing salt from road to surroundings, deposition in the roadside environment and the subsequent infiltration into roadside soil. The general decrease in soil chloride content with distance from the road was described by differences in salt deposition, soil physical properties, vegetation properties and snow characteristics. The uncertainty in model predictions was highest in areas close to the road due to a complex combination of high salt deposition, snow-ploughed masses and road runoff. The exponential decline in salt deposition with distance from the road could not be justified close to the road. Different types of field investigations were applied in a calibration procedure to establish reasonable ranges for the most influential model parameters. Measured electrical resistivity reflected well the changes in simulated chloride content in soil during winter and spring when chloride concentrations were high. However, during summer or periods with low chloride concentrations the measured resistivity was substantially lower than simulated values, as it reflected the total contamination level in soil.     

Fate and Transport of Copper Applied in Channel Catfish Ponds

A pilot-scale study and field measurements at commercial ponds were conducted to investigate the environmental fate of copper (Cu) applied as an algaecide in commercial catfish ponds. In the pilot study, a total of 774 g Cu(II) was applied to an experimental catfish pond over a period of 16 summer weeks. More than 90% of Cu applied became associated with suspended sediment particles within a few minutes of addition, and then nearly all Cu applied was transferred to the sediment phase within about 2 days. At the end of the study, the peak Cu content in the sediment increased from an initial concentration of 25～35 mg kg^?1 to about 200 mg kg^?1, and the applied Cu was able to reach a sediment depth of about 16 cm. Meanwhile, Cu concentration in the catfish body decreased from 12.7 ± 2.81 mg kg^?1 to 6.15 ± 2.54 mg kg^?1. Copper mass balance indicated that virtually all Cu applied was retained in the sediment. Only 0.01% of the total Cu applied was taken up by fish and 0.1% remained in pond water. Data from 3 commercial fishponds of different ages (1–25 years) and with different sediment types (acidic, neutral and calcareous) supported the pilot-scale observation. Both pilot-testing results and field measurements revealed that Cu is predominantly accumulated within the top sediment layer and barely reached the bottom soil regardless of the pond age and the type of the sediments. Field monitoring of groundwater quality suggested that the copper leaching into the groundwater surrounding the ponds was insignificant.     

Environmental Controls on the Fate of Escherichia coli in Soil

An improved understanding of factors that influence the survival and/or growth of Escherichia coli (E. coli) in soil is essential to allow the formation of land management practices to control the spread of the pathogenic strains of the bacteria, whose transmission to fresh produce is a threat to food safety. Persistence of E. coli in soils held at different water potentials and with carbon additions then subjected to post-freezing incubation temperatures and in the presence of Klebsiella terrigena (K. terrigena) were investigated. Soil samples adjusted to different water potentials (?0.03, ?0.1 and ?1.5 MPa) were inoculated with a multi-antibiotic resistant strain of E. coli (E. coli 2+), which allowed recovery of the organism from soil samples. In addition to manipulation of water content, different C levels were added and samples were frozen for varying lengths of time, thawed and incubated. In freezing studies, initial soil moisture content significantly affected E. coil 2+ survival in soils following thawing, resulting in lower survival rate (k) at water potential of ?0.03 than at ?0.1 and ?1.5 MPa. The effect of length of freezing time was significant only at ?0.03 MPa. Glucose addition at 1.25 mg C g^?1 improved survival rate versus glucose at 0.125. The low level glucose increased die-off rate versus no addition, suggesting that unless amendments provide C above a certain threshold level, they might facilitate the death of the bacteria. E. coli 2+ survival improved in the presence of K. terrigena at 6°C but not at 23°C. Persistence of E. coli under the interactive influence of various environmental factors highlights the urgency and importance of understanding its potential for transmission to fresh produce and water bodies.     

Effects of Low Molecular Weight Organic Anions on the Release of Arsenite and Arsenate from a Contaminated Soil

Low-molecular-weight-organic-anions (LMWOAs) are important exudates of plants and may influence the mobility and bioavailability of metals or metalloids. In the present study the effects of selected LMWOAs, citrate, malate and oxalate, on the release of arsenite (As(III)) and arsenate (As(V)) in a contaminated soil were investigated. The organic anions have significant influence upon the release of arsenic from the soil, and a linear relationship exits between the released arsenic and the concentration of LMWOAs in the extractants. pH effects on the arsenite and arsenate adsorption were not significant over the range from 3 to 7. The amounts of arsenite and arsenate released were significantly correlated with the release of Fe, Mn and Al, suggesting that arsenic was mainly released from Fe-, Mn- and Al-oxides or hydroxides in soil. The ratio of released arsenite to arsenate was not influenced by LMWOAs.     

浑善达克沙地人工植被覆盖下土壤蒸发的模拟研究

应用自制的微型蒸渗仪(Micro-Lysimeter)测定了2005年浑善达克沙地人工牧草区的日棵间土壤蒸发量。对影响土壤蒸发的主要因子进行了回归分析,并比较了以6因子[日平均气温(T)、净辐射(Rn)、相对湿度(RH)、2m处风速(U2)、0~30cm土壤含水率(θ)及叶面积指数(LAI)]和4因子[日平均气温(T)、净辐射(Rn)、0~30cm土壤含水率(θ)及叶面积指数(LAI)]为输入样本,以日棵间土壤蒸发量为输出样本的BP网络模拟预报模型。研究表明,BP网络可以用于日棵间土壤蒸发量的预报,6因子法和4因子法均简便可行,能满足生产的需要。相比之下,6因子法的精度更高。此研究是对传统棵间土壤蒸发量计算的补充。     

Soil properties following cultivation and non-grazing of a semi-arid sandy grassland in northern China

Cultivation and overgrazing are widely recognized as the primary causes of desertification of sandy grassland in the semi-arid region of northern China. Very little is known about the effect of cultivation and overgrazing on soil physical, chemical and biological properties in this region. The objective of this study was to quantitatively evaluate the magnitude of changes in soil properties due to 3 years of cultivation (3CGS) and 5 years of ungrazed exclosure (5RGS) in a degraded grassland ecosystem of the semi-arid Horqin sandy steppe. Short-term cultivation resulted in a 18–38% reduction in concentration of soil organic C, and total N and P in the 0–15 cm plow layer. Cultivation had a significant influence on N and P availability and soil biological properties, with lower basal soil respiration (BSR) and enzyme activities than the grassland soils. This was mostly due to strong wind erosion when sandy grassland was cultivated. Data indicated a considerable difference in soil particle size distribution between the cultivated and grassland soils, and fine fraction (<0.1 mm) in the cultivated soil was lower than that in the grassland soils. Moreover, grassland vegetation recovery in the 5RGS resulted in significant improvement in soil properties measured at the 0–7.5 cm depth. From the perspective of soil resource management and environmental conservation, a viable option for these sandy grasslands would be to stop conversion of grassland to cropland and adopt proper fencing practices to limit overgrazing.     

土壤钝化剂对黑土中铜的原位固定作用

采用盆栽试验研究3种钝化剂(粉煤灰、磷灰石和膨润土)对黑土中铜(Cu)的化学形态、生物积累和有效性的影响。结果表明:3种钝化剂能显著降低Cu污染黑土中水提取态(DW)、TCLP提取态和二乙基三胺五乙酸-三乙醇胺(DTPA-TEA)提取态Cu含量,其中以膨润土的效果最为明显;Tessier连续提取测定发现,3种钝化剂显著降低非残留态Cu(水溶态和交换态、碳酸盐结合态、铁锰氧化物结合态和有机结合态)含量(p<0.01),增加残留态Cu含量,表明3种钝化剂通过改变黑土中Cu的化学形态,降低了黑土中Cu的可淋失性和生物有效性;与对照相比,添加钝化剂能显著降低水稻地上部分的Cu含量(p<0.01),如在400Cu mg/kg处理的土壤上,添加2.5%的粉煤灰、磷灰石和膨润土使米粉中的Cu含量分别降低21.8%,22.7%和31.9%。土壤中可淋失态和生物有效态Cu的分析表明,钝化剂主要是通过改变土壤中Cu的化学形态,降低土壤中Cu的生物有效性,以降低Cu在水稻中的积累;试验表明,Cu污染土壤中施用钝化剂可以修复Cu污染,降低水稻Cu污染风险。     

Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping

Long‐term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse‐textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle‐size fractions. Long‐term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi‐exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt‐ and clay‐sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation.     

Fate of Microelements Applied to a Tropical Peat Soil: Column Experiment

Lack of microelements is a major problem in crop production in tropical peatland. For their efficient application, the fate of copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) in a Histosol was investigated in a 3-month column experiment. Leaching of Cu, Fe, Mn, and Zn accounted for 2, –2 to 7, 28 to 32, and 21 to 23% of the amounts applied, respectively, in both the flooded and upland soils. The microelement application enhanced the leaching of calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), and phosphorus (P). Replacement of exchangeable cations by the microelements was suggested in the successive extraction of elements from the soils after incubation. Under the upland conditions, 31–33% of the Cu and Fe increased in soil was extracted with diethylenetriaminepentaacetic acid?/?triethanolamine (bound to humus), whereas 26–31% of the Mn and Zn increased was exchangeable. Extractability was smaller under the flooded conditions for all the microelements, suggesting that fertilization in the dry season is more effective.     

Changes in Copper Speciation and Geochemical Fate in Freshwaters Following Sewage Discharges

The main factors determining the geochemical fate of copper in urban freshwaters affected by raw sewage discharges were investigated in this work. Water samples from the Iraí and Iguaçu rivers were collected monthly during a 1-year period at two points located upstream and downstream from the city of Curitiba, in Brazil. Results revealed that raw sewage discharges from the heavily urbanized area caused an enhancement of humic-coated suspended solids in the Iguaçu River. In these waters copper is predominantly associated with the humic-coated particles whereas in the Iraí River copper was found primarily in the aqueous phase. The transfer of copper from the aqueous to the solid phase changed its physical speciation along the watercourse. Thus, aspects related to the overall transport of trace metals in watercourses become an important issue to be considered in further studies concerning the effect of sewage discharges on the geochemical speciation and fate of trace metals in urban rivers.     

Modelling Soil Detachment of Different Management Practices in the Red Soil Region of China

Soil erosion from cropland is a primary cause of soil degradation in the hilly red soil region of China. Soil characteristics and the resistance of soil to erosion agents can be improved with appropriate management practices. In this study, hydraulic flume experiments were conducted to investigate the effects of five management practices [manure fertilizer (PM), straw mulch cover (PC), peanut–orange intercropping (PO), peanut–radish rotation (PR) and traditional farrow peanut (PF)] on soil detachment. Based on the results, three conservation management practices (PC, PM and PO) increased the resistance of soil to concentrated flow erosion. The rill erodibility of different treatments was ranked as follows: PC (0·001 s m⁻¹) < PM (0·004 s m⁻¹) < PO (0·007 s m⁻¹) < PF (0·01 s m⁻¹) < PR (0·027 s m⁻¹). The rill erodibility was affected by soil organic content, aggregate stability and bulk density. The soil detachment rate was closely correlated with the flow discharge and slope gradient, and power functions for these two factors were developed to evaluate soil detachment rates. Additionally, the shear stress, stream power and unit stream power were compared when estimating the soil detachment rate. The power functions of stream power and shear stress were equivalent, and both are recommended to predict detachment rates. Local soil conservation can benefit from the results of this study with improved predictions of erosion on croplands in the red soil region of China. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of Oxalate and Humic Acid on Arsenate Sorption by and Desorption from a Chinese Red Soil

Studies on arsenate (As(V)) sorption and desorption have been mainly limited to soil minerals and sorption and desorption reactions in whole soils are poorly understood. In this study the sorption of As(V) by and phosphate-induced desorption from a Chinese red soil were studied in the presence of oxalate and humic acid (HA). Arsenate was strongly sorbed mainly through ligand exchange reactions on the soil. Arsenate sorption decreased in the presence of oxalate or HA. Oxalate and HA influenced As(V) sorption mainly by competing for sorption sites and reducing sorption sites, and oxalate could also decrease sorption through dissolving clay minerals. Oxalate and HA could also facilitate As(V) desorption from the soil. Both sorption and desorption kinetics were two stage processes. Sorption kinetics conducted from 0.2–840 h showed that As(V) sorption increased with increasing residence time. Sorption equilibrium was retarded and the maximum sorption decreased in the presence of oxalate or HA. Phosphate-induced desorption kinetics conducted on the soil with 24 h and 840 h of sorption equilibrium time showed a significant effect of equilibrium time on As(V) desorption. The presence of oxalate or HA during the sorption process resulted in more As(V) desorption. Due to the degradation of oxalate, soil treated with oxalate and with a sorption equilibrium time of 840 h showed no significant difference in desorption kinetics from untreated soil.     

铜在土壤中的淋溶迁移特征研究

以棕壤为供试土壤,采用室内土柱淋溶模拟试验方法,研究了相当于泰安平均年降水量条件下铜在土壤垂直方向上的迁移转化特征.结果表明:各处理土壤中的铜在0～10 cm土层中均有不同程度的迁移转化.土壤铜含量越高,年降水量条件下表层土壤中铜的淋失量越大,沉淀态铜和矿物残留态铜所占的比例增加了28.57%～33.49%.高铜土壤中,钙含量的增加使交换态铜比例降低幅度为9.97%～10.48%,使铜的迁移量最大可减少15.54%;随褐煤施入量的增加,表层交换态铜含量减少,铜向5～10 cm土层中的淋溶量减少显著,有机结合态铜的含量增加22.76%～36.07%.     

Soil microbial properties under N and P additions in a semi-arid, sandy grassland

Surface (0–15 cm) soil samples were collected from a semi-arid, sandy grassland in Keerqin Sandy Lands, Northeast China to study changes in soil microbial and chemical properties after five consecutive years of nitrogen (N) and phosphorus (P) additions. Nitrogen and P additions and their interactions negligibly affected soil organic carbon and total N contents, while P addition significantly increased soil total P content. Soil pH was significantly decreased by N addition, which significantly increased net nitrification rate, whereas it did not affect net N mineralization rate. No significant effects of N and P additions and their interactions on basal respiration were detected. In addition, N addition significantly decreased microbial biomass C (MBC) and N, and thus microbial quotient, but increased dissolved organic C and microbial metabolic quotient due to the significant decrease of MBC. Our results suggest that in the mid-term the addition of N, but not P, can change soil microbial properties, with a possible decline in soil quality of semi-arid, sandy grasslands.     

Effects of Grasses on the Fate of VOCs in Contaminated Soil and Air

Plant toxicity and chemical removal tests were conducted to investigate the remediation ability of grasses with respect to volatile organic contaminants (VOCs) in contaminated soil and air. Eastern gamagrass (Tripsacum dactyloides) and annual ryegrass (Lolium rigidum) were exposed to artificially contaminated soil or air containing a mixture of 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) under controlled laboratory conditions. The results showed that the grasses are more severely affected in hydroponics than potted soil contaminated with a mixture of these contaminants. It was observed from the results that more contaminants were detected in the shoot and root of plants grown in a closed system with contaminated air than in an open system with contaminated soil. It is suggested from the results that grasses can be used for purification of VOCs from contaminated air especially in a closed system, but the purification effects are likely to be low. The results also suggested that the concentration level of VOCs in shoot, root, and soil could be used as contamination indicator at contaminated sites.     

Modelling moisture‐induced soil reflectance changes in cultivated sandy soils: a case study in citrus orchards

The value of hyperspectral imagery in agricultural management has been amply demonstrated. Despite this, image interpretation is often drastically impeded by changes in soil moisture content (SMC). Soil moisture variations dominate the spectral reflectance in the 350–2500‐nm wavelength domain and affect the effectiveness of spectral indices used to monitor variations in soil and vegetation properties. Consequently, removing soil moisture effects in spectral images is critical and would provide a significant breakthrough for agricultural remote sensing. Yet, current available soil moisture reflectance models fail to properly address the moisture‐induced reflectance changes occurring within soils of the same texture class. This very much limits the operational implementation of these models, particularly in agricultural fields where within‐field variations in soil characteristics such as organic matter and clay content prevail. In this study, the effect of SMC on the reflectance in the 400–2500‐nm spectral domain was studied for six sandy soils located in citrus orchards in the Western Cape Province, South Africa. In a series of experiments, novel insights into soil moisture reflectance modelling of sandy cultivated soils are provided. The wavelength and soil‐specific variations in model parameters are mechanistically modelled and a general model for moist reflectance of cultivated sand soils is presented and successfully tested. Model comparison and validation demonstrate that the model fit of soil‐type‐specific models can be approximated (R² = 0.82; RRMSE = 0.14) while a significant increase in model fit compared with the traditional general models (R² = 0.59; RRMSE = 0.28) was achieved.     

Soil microbial activity and a free-living nematode community in the playa and in the sandy biological crust of the Negev Desert

The effect of environmental factors and soil properties on microbial and soil free-living nematode communities was investigated in two desert soil formations, a playa and sandy biological crust. Soil samples were collected from October 2007 to September 2008 from the upper (0–10 cm) soil layers in the Negev Desert area. Unlike microorganisms, soil free-living nematodes were found to be negatively dependent on monthly rain and positively dependent on water evaporation. We suggest that water evaporation from pore caves in both soil formations increases the predation success of soil free-living nematodes, while daily rain increases the survival potential of soil microorganisms since the predators require more time to find their prey. Soil properties were found to have a different influence on microbial and soil free-living nematode communities in the two soil formations. Microbial respiration and biomass were negatively correlated with calcium and potassium in the playa area and with sodium in the sandy biological crust area. The free-living nematode community exhibited a negative correlation with electrical conductivity and sodium and a positive correlation with potassium in the playa samples, while no dependence on soil properties was found in the sandy biological crust samples. It can, therefore, be concluded that soil properties affect predation rate in the playa samples through changes in porosity. Generally accepted ecological indices such as trophic diversity (T), Simpson’s dominance (λ), Shannon–Weaver (H′), maturity (MI), and basal (BI) indices pointed to specific ecological conditions at the two observed soil formations.     

Soil Test to Predict the Copper Availability in Pasture Soils

Abstract

The proportion of copper (Cu) that can be extracted by soil test extractants varied with the soil matrix. The plant‐available forms of Cu and the efficiency of various soil test extractants [(0.01 M Ca(NO₃)₂, 0.1 M NaNO₃, 0.01 M CaCl₂, 1.0 M NH₄NO₃, 0.1 M HCl, 0.02 M SrCl₂, Mehlich‐1 (M1), Mehlich‐3 (M3), and TEA‐DTPA.)] to predict the availability of Cu for two contrasting pasture soils were treated with two sources of Cu fertilizers (CuSO₄ and CuO). The efficiency of various chemical reagents in extracting the Cu from the soil followed this order: TEA‐DTPA>Mehlich‐3>Mehlich‐1>0.02 M SrCl₂>0.1 M HCl>1.0 M NH₄NO₃>0.01 M CaCl₂>0.1 M NaNO₃>0.01 M Ca(NO₃)₂. The ratios of exchangeable: organic: oxide bound: residual forms of Cu in M1, M3, and TEA‐DTPA for the Manawatu soil are 1:20:25:4, 1:14:8:2, and 1:56:35:8, respectively, and for the Ngamoka soil are 1:14:6:4, 1:9:5:2, and 1:55:26:17, respectively. The ratios of different forms of Cu suggest that the Cu is residing mainly in the organic form, and it decreases in the order: organic>oxide>residual>exchangeable. There was a highly significant relationship between the concentrations of Cu extracted by the three soil test extractants. The determination of the coefficients obtained from the regression relationship between the amounts of Cu extracted by M1, M3, and TEA‐DTPA reagents suggests that the behavior of extractants was similar. But M3 demonstrated a greater increase of Cu from the exchangeable form and organic complexes due to the dual activity of EDTA and acids for the different fractions and is best suited for predicting the available Cu in pasture soils.     

Modelling long-term phosphorus leaching and changes in phosphorus fertility in excessively fertilized acid sandy soils

The sound management of agricultural soils that are heavily loaded with phosphorus (P) involves minimizing the losses of P responsible for eutrophication of surface waters, while ensuring enough P for crops. This paper describes a simple model to examine the compatibility of these two objectives in acid sandy soils in a temperate humid climate. The model is based on several assumptions regarding reversible and irreversible P sorption by P-reactive soil compounds (mainly poorly crystalline Fe and Al oxides) and release of P to water (water-P test). Model inputs are amount of P leached, P uptake by crops, and contents of poorly crystalline Fe and Al oxides in soil. The model predicts that reducing the amount of leached P to what is environmentally acceptable (e.g. 0.44 kg P ha^–1 year^–1, equivalent to 1 kg P₂O₅ ha^–1 year^–1) results in the long run in available soil P test values below target concentrations for optimum crop growth. When the amount of leached P is set to a fixed value the model predicts that soils with large contents of Fe and Al oxides can maintain the initial soil P test values for longer periods than other soils. The content in available P decreases if fertilizer P is applied to the soil at a rate equal to P uptake by crops. These results stress the difficulties involved in trying to make agricultural and environmental needs compatible in acid sandy soils.