Sorption of trace metals by standard and micro suction cups in the absence and presence of dissolved organic carbon

Both the bioavailability of a trace metal (TM) in a soil and the risk of leaching to the ground water are linked to the metals concentration in the soil solution. Sampling soil solution by tension lysimetry with suction cups is a simple and established technique that is increasingly used for monitoring dissolved TM in soils. Of major concern, however, is the sorption of TM by the walls of the samplers. Metal sorption by different materials used in suction cups can vary widely, depending also on the chemistry of the soil solution. We compared the sorption of Cu, Zn, Cd, and Pb by different standard-size and micro suction cups in the laboratory at two pH values (4.5 and 7.5 or 8.0) in absence and presence of dissolved organic carbon (DOC). In addition, we investigated the sorption of DOC from different origins by the cup materials. At both pH values, the weakest sorption of all four TMs was exhibited by standard-size suction cups based on nylon membranes and by hollow fibers made from polyvinyl alcohol (PVA). At alkaline pH, borosilicate glass, ceramic materials, and polytetrafluorethylene (PTFE) mixed with silicate were characterized by generally strong sorption of all investigated TMs. In addition, Cu and Pb were strongly sorbed at low pH by PTFE-silicate and a ceramic material used for the construction of standard-size suction cups. On the other hand, sorption of Cu, Zn, and Cd by ceramic capillaries produced from pure aluminum oxide was negligible at low pH. Micro suction cups made of an unknown polymerous tube sorbed Cu strongly, but were well suited to monitor Zn, Cd, and Pb at low pH, and, in the presence of DOC, also at high pH. Major cations (Na+, Mg2+, K+, Ca2+) and anions (Cl-, NO3-, SO4(2-)) were not or very weakly sorbed by all cup materials, except for Mg2+, K+, and Ca2+ by borosilicate glass at pH 7.5. Trace metal sorption by suction cups was generally greatly reduced in the presence of DOC, especially at alkaline pH. The sorption of DOC itself depended on its source. Dissolved organic carbon from leaf litter extracts with a probably large hydrophobic fraction was sorbed more strongly than mainly hydrophilic DOC from a mineral soil solution.     

Adsorption of cadmium, copper, nickel, and zinc to a poly(tetrafluorethene) porous soil solution sampler

Suction cups made of poly(tetrafluorethene) (PTFE) are widely used for sampling of soil solution. A brand (Prenart) of PTFE cups was tested for adsorption of Cd, Cu, Ni, and Zn at low concentrations under different conditions. In a laboratory experiment adsorption from a 10 microg L(-1) heavy metal solution with a 0.01 M NaCl background electrolyte was investigated at pH 3.6, 4.5, and 5.8 by pumping the solutions through the cups. The effect of three different ionic compositions was also investigated using 0.01 M CaCl2, 0.01 M NaCl, and no background electrolyte at pH 4.5. In 0.01 M NaCl electrolyte at pH 5.8 the cups acted as effective filters. At pH 3.6 after 300 mL of solution had passed through the cup, equivalence between the Cd and Ni concentrations in influent and effluent was found. No equivalence between effluent and influent concentrations was found for Zn and Cu at pH 4.5 and 5.8. With Ca as the electrolyte, no adsorption of Cd, Ni, or Zn was found. In Na electrolyte, equivalence between influent and effluent concentrations for Cd, Ni, and Zn was reached. The difference between effluent and influent concentrations of Zn, Ni, and Cd remained significant in the absence of electrolyte. For all pH values and electrolytes the difference between effluent and influent concentrations of Cu was significant. It is concluded that PTFE cups affect the concentrations of heavy metals sampled at low soil solution concentrations. Cadmium, Cu, Ni, and Zn adsorb to the cup at pH > 4.5 and low ionic strength.     

Validation of procedures to quantify nonextractable polycyclic aromatic hydrocarbon residues in soil

This study was conducted to optimize butanol solvent shake extraction, dichloromethane soxtec extraction, and methanolic saponification extraction for the selective extraction of aged polycyclic aromatic hydrocarbons from soil. Extraction kinetics for these methods was established to determine the optimal time necessary to achieve exhaustive compound extraction. This resulted in times of 12, 6, and 5 h, respectively, for butanol, dichloromethane, and saponification, to extract polycyclic aromatic hydrocarbons from previously spiked, then aged soil. Increasing the soil mass to butanol volume ratio reduced the proportion of polycyclic aromatic hydrocarbon extracted by butanol, highlighting the importance of determining and maintaining a constant soil to solvent ratio for comparative purposes. Drying soil samples before dichloromethane soxtec extraction reduced by 30 to 76% the amount of polycyclic aromatic hydrocarbons extracted. The effect of sample drying is discussed with relevance to enhancing the formation of nonextractable compounds in soil and compound losses previously assumed by volatilization. The optimized extraction procedures provided low variability with relative standard deviations < or = 5.2% for analysis of multiple replicates. The results obtained by the optimized procedures provided equivalent or improved reproducibility to those obtained by other methods reported in the literature.     

Effect of soil properties on saturated and unsaturated virus transport through columns

Viruses from contaminant sources can be transported through porous media to drinking water wells. The objective of this study was to investigate inactivation and sorption of viruses during saturated and unsaturated transport in different soils. Bacteriophages phiX174 and MS-2, and Br- tracer in a phosphate-buffered saline solution were introduced into saturated and unsaturated soil columns as a step function under constant flow rate and hydraulic conditions. Results showed that significantly greater virus removal occurred in the unsaturated columns than in the saturated columns in the two soils containing high metal oxides content. However, the increase in virus retention under unsaturated conditions was not significant in two other soils having high phosphorus and calcium contents and high pH, and in another soil with high organic matter content. The results imply that the extent of water content effect on inactivation and sorption of viruses can range from significant to minimal depending on the properties of the transport medium. We found that the presence of in situ metal oxides was a significant factor responsible for virus sorption and inactivation. Therefore, soils with high metal oxides content may have the potential to be used as hydrological barriers in preventing microbial contamination in the subsurface environments. We also found that the water content effect on virus removal and inactivation strongly depended on solid properties of the testing medium.     

Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible.     

Copper and calcium transport through an unsaturated soil column

To determine the relative importance of the physical and chemical factors that influence the movement of heavy metals through soils, leaching experiments were carried out under conditions of constant molarity during unsaturated steady-state water flow through a Manawatu fine sandy loam (a Dystric Fluventic Eutochrept). The movement and exchange of copper was studied in a binary Cu-Ca system. The movement of the associated anions, namely chloride and sulfate, was also monitored. The measurements were compared with predictions from the convection-dispersion equation (CDE), linked with cation exchange theory. The agreement between the measured and predicted breakthrough of sulfate and copper was good. This indicates that copper retardation in the Manawatu soil is closely related to the cation exchange capacity, and that exchange between Ca and Cu is the main process of Cu retardation in the Manawatu soil. However, copper appeared slightly later in the effluent than predicted, indicating that non-exchange processes are also involved in copper transport. Measurements of suction cups could also be used to obtain the parameters for the CDE to describe sulfate movement through the soil. Time domain reflectometry (TDR) measurements of the bulk-soil electrical conductivity could be used to monitor the movement of both sulfate and copper. This indicates that TDR can also be used to monitor cation transport and exchange through the soil, provided the percolating solution causes a sufficient change in the electrical conductivity.     

Influence of organic waste type and soil structure on the bacterial filtration rates in unsaturated intact soil columns

Organic wastes are considered to be a source for the potentially pathogenic microorganisms found in surface and sub-surface water resources. Following their release from the organic waste matrix, bacteria often infiltrate into soil and may be transported to significant depths contaminating aquifers. We investigated the influence of soil texture and structure and most importantly the organic waste properties on the transport and filtration coefficients of Escherichia coli and total bacteria in undisturbed soil columns. Intact soil columns (diameter 16 cm and height 25 cm) were collected from two soils: sandy clay loam (SCL) and loamy sand (LS) in Hamadan, western Iran. The cores were amended with cow manure, poultry manure and sewage sludge at a rate of 10 Mg ha(-1) (dry basis). The amended soil cores were leached at a steady-state flux of 4.8 cm h(-1) (i.e. 0.12 of saturated hydraulic conductivity of the SCL) to a total volume of up to 4 times the pore volume of the columns. The influent (C(0)) and effluent (C) were sampled at similar time intervals during the experiments and bacterial concentrations were measured by the plate count method. Cumulative numbers of the leached bacteria, filtration coefficient (lambda(f)), and relative adsorption index (S(R)) were calculated. The preferential pathways and stable structure of the SCL facilitated the rapid transport and early appearance of the bacteria in the effluent. The LS filtered more bacteria when compared with the SCL. The effluent contamination of poultry manure-treated columns was greater than the cow manure- and sewage sludge-treated ones. The difference between cow manure and sewage sludge was negligible. The lambda(f) and S(R) values for E. coli and total bacteria were greater in the LS than in the SCL. This indicates a predominant role for the physical pore-obstruction filtration mechanisms as present in the poorly structured LS vs. the retention at adsorptive sites (chemical filtration) more likely in the better structured SCL. While the results confirmed the significant role of soil structure and preferential (macroporous) pathways, manure type was proven to have a major role in determining the maximum penetration risk of bacteria by governing filtration of bacteria. Thus while the numbers of bacteria in waste may be of significance for shallow aquifers, the type of waste may determine the risk for microbial contamination of deep aquifers.     

Using phosphorus concentration in the soil solution to predict phosphorus desorption to water

The growing concerns about water eutrophication have made it urgent to restrict losses of phosphorus (P) from agricultural soils and to develop methods for predicting such losses. In this work, we used the paradigm of P sorption-desorption curves to confirm the hypothesis that the amount of dissolved reactive phosphorus (DRP) released to a dilute electrolyte tends to be proportional to the concentration of DRP in the soil solution raised to a power that decreases with increasing solution to soil ratio (W). The hypothesis was tested for a group of 12 widely ranging European agricultural soils fertilized with P in excess of crop needs. Phosphorus desorption was studied under near-static and turbulent conditions in laboratory experiments. The concentration of DRP in the 1:1 soil to water extract (P1:1) was used as a proxy for the DRP concentration in the soil solution. The amount of desorbed P was found to be correlated with P1:1 raised to a power that decreased from 0.7 to 0.9 at W=100 to 0.2 to 0.4 at W=10 000. Correlation was not improved by introducing additional variables related to P sorption-desorption properties. Olsen P was found to be of lower predictive value than P1:1. Also, the index of degree of soil saturation with phosphorus (DSSP) based on oxalate extraction failed to predict P desorption. The fact that P1:1 seemingly predicts P desorption accurately for a wide range of soils makes it potentially useful in areas of high soil diversity.     

SOIL MOISTURE VARIATION PATTERNS OBSERVED IN HAND COUNTY,SOUTH DAKOTA1

ABSTRACT: Sail moisture data were taken during nine sampling events (1976-1978) at a test site in South Dakota as part of the ground truth used in NASA's aircraft experiments studying the microwave sensing of soil moisture. This portion of the study dealt only with the spatial variability observed with regard to the ground data. Samples were taken over three surface depths at each point, and the data reported as the mean field moisture content within each of three surface horizons. The results shed additional light on the relationship between ground sampling and remote sensing of soil moisture. First, it was found that it is best to partition data of well drained sites from poorly drained areas when attempting to characterize the surface moisture content throughout an area of varying soil and cover conditions. It was also found that the moisture coefficient of variation within a field decreased as the mean field soil moisture increased, and that the standard deviation was at a maximum in the mid-range of observed moisture conditions (15-25 percent). Within field sample variation also decreases as the sample is integrated over a greater surface depth. It was determined that a sampling intensity of 10 samples per kilometer was adequate to characterize the mean field soil moisture at all three depths along a transect in the areas of moderate to good drainage-.     

MODELING PERCOLATION LOSSES FROM A PONDED FIELD UNDER VARIABLE WATER-TABLE CONDITIONS1

ABSTRACT: A numerical simulation model was developed to predict the vertical and lateral percolation losses from a ponded agricultural field. The two-dimensional steady-state unsaturated/ saturated flow equation was solved using the finite-difference technique. A constant ponding depth was maintained at the soil surface with different water table conditions in an application of the model for rice fields bordered by bunds. Field experiments were conducted for two different water table depths to collect data on the spatial distribution of volumetric soil-moisture content for model verification. The measured soil-moisture content values were found to be in close agreement with those predicted by the model. The sensitivity analysis of the model with selected hydrologic conditions shows that the model is most sensitive to the values of saturated hydraulic conductivity, but relatively less sensitive to water table depth, ponding depth, and evaporation rate from the soil surface. It implies that, in a ponded rice field condition, the lateral and vertical percolation losses are mostly governed by the hydraulic conductivity of the soil. The vertical percolation losses were almost equal to the saturated hydraulic conductivity values and, in most cases, these losses increased with deeper water table depths. The lateral percolation losses also increased with deeper water table depths; however, these losses were relatively small in comparison to the vertical percolation losses. The vertical and lateral percolation losses increased with the increase in ponding depths. The lateral percolation losses through the bund decreased when the evaporation losses increased from the soil surface. The results of this study indicate that the percolation losses from a ponded field may be predicted accurately for a wide range of soil and hydrological conditions when the values of hydraulic conductivity, evaporation rate, depth of ponding, and water table depth are accurately known.     

Detailed characterization of solute transport in a heterogeneous field soil

There is a necessity for improved physical understanding of solute transport processes in heterogeneous soil systems. In situ nondestructive techniques like time domain reflectometry (TDR) and fiber optic miniprobes (FOMPs) permit the collection of unique measurements of solute transport processes in soils for the purposes of model development and validation. This study examined the application of TDR and FOMPs to measure solute transport at various points laterally and at two depths in a heterogeneous clay-loam soil. A miscible displacement experiment was performed at a constant irrigation flux to examine the applicability of these probes to field soils. In their first application to a field soil, the FOMPs were successfully calibrated and performed well in measuring solute breakthrough curves. Two flow regimes were identified in the soil profile, the first where lateral spreading of the solute occurred in the surface horizon, followed by convergence into preferential flow pathways in the second transport zone. The measured transport response was heterogeneous with at least two identifiable vertical flow phases. It was demonstrated using transfer function modeling and data from a corresponding laboratory study that the FOMPs were measuring the slower phase, while the TDR probes captured a composite of the fast and slow phases. The combination of these two techniques may be a means to separate solute transport phases in heterogeneous media and relate laboratory column results to field studies.     

Biosolids affect soil barium in a dryland wheat agroecosystem

In December 2003, the USEPA released an amended list of 15 "candidate pollutants for exposure and hazard screening" with regard to biosolids land application, including Ba. Therefore, we decided to monitor soil Ba concentrations from a dryland wheat (Triticum aestivum L.)-fallow agroecosystem experiment. This experiment received 10 biennial biosolids applications (1982-2003) at rates from 0 to 26.8 dry Mg ha(-1) per application year. The study was conducted on a Platner loam (Aridic Paleustoll), approximately 30 km east of Brighton, CO. Total soil Ba, as measured by 4 M HNO(3), increased with increasing biosolids application rate. In the soil-extraction data from 1988 to 2003, however, we observed significant (P < 0.10) linear or exponential declines in ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable Ba concentrations as a function of increasing biosolids application rates. This was observed in 6 of 7 and 3 of 7 yr for the 0- to 20- and 20- to 60-cm soil depths, respectively. Results suggest that while total soil Ba increased as a result of biosolids application with time, the mineral form of Ba was present in forms not extractable with AB-DTPA. Scanning electron microscopy using energy dispersive spectroscopy verified soil Ba-S compounds in the soil surface, probably BaSO(4). Wet chemistry sequential extraction suggested BaCO(3) precipitation was increasing in the soil subsurface. Our research showed that biosolids application may increase total soil Ba, but soil Ba precipitates are insoluble and should not be an environmental concern in similar soils under similar climatic and management conditions.     

Metolachlor dechlorination by zerovalent iron during unsaturated transport

Permeable zerovalent iron (Fe0) barriers have become an established technology for remediating contaminated ground water. This same technology may be applicable for treating pesticides amenable to dehalogenation as they move downward in the vadose zone. By conducting miscible displacement experiments in the laboratory with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; a chloroacetanilide herbicide] under unsaturated flow, we provide proof-of-concept for such an approach. Transport experiments were conducted in repacked, unsaturated soil columns attached to vacuum chambers and run under constant matrix potential (-30 kPa) and Darcy flux (approximately 2 cm d(-1)). Treatments included soil columns equipped with and without a permeable reactive barrier (PRB) consisting of a Fe0-sand (50:50) mixture supplemented with Al2(SO4)3. A continuous pulse of 14C-labeled metolachlor (1.45 mM) and tritiated water (3H2O) was applied to top of the columns for 10 d. Results indicated complete (100%) metolachlor destruction, with the dehalogenated product observed as the primary degradate in the leachate. Similar results were obtained with a 25:75 Fe0-sand barrier but metolachlor destruction was not as efficient when unannealed iron was used or Al2(SO4)3 was omitted from the barrier. A second set of transport experiments used metolachlor-contaminated soil in lieu of a 14C-metolachlor pulse. Under these conditions, the iron barrier decreased metolachlor concentration in the leachate by approximately 50%. These results provide initial evidence that permeable iron barriers can effectively reduce metolachlor leaching under unsaturated flow.     

Free-air CO2 enrichment of sorghum: soil carbon and nitrogen dynamics

The positive impact of elevated atmospheric CO(2) concentration on crop biomass production suggests more carbon inputs to soil. Further study on the effect of elevated CO(2) on soil carbon and nitrogen dynamics is key to understanding the potential for long-term carbon storage in soil. Soil samples (0- to 5-, 5- to 10-, and 10- to 20-cm depths) were collected after 2 yr of grain sorghum [Sorghum bicolor (L.) Moench.] production under two atmospheric CO(2) levels: (370 [ambient] and 550 muL L(-1) [free-air CO(2) enrichment; FACE]) and two water treatments (ample water and limited water) on a Trix clay loam (fine, loamy, mixed [calcareous], hyperthermic Typic Torrifluvents) at Maricopa, AZ. In addition to assessing treatment effects on soil organic C and total N, potential C and N mineralization and C turnover were determined in a 60-d laboratory incubation study. After 2 yr of FACE, soil C and N were significantly increased at all soil depths. Water regime had no effect on these measures. Increased total N in the soil was associated with reduced N mineralization under FACE. Results indicated that potential C turnover was reduced under water deficit conditions at the top soil depth. Carbon turnover was not affected under FACE, implying that the observed increase in soil C with elevated CO(2) may be stable relative to ambient CO(2) conditions. Results suggest that, over the short-term, a small increase in soil C storage could occur under elevated atmospheric CO(2) conditions in sorghum production systems with differing water regimes.     

Bioremediation of residual fertilizer nitrate: I. Laboratory demonstration of an on-farm in situ pollution control system

This exploratory laboratory study was undertaken to develop and test an in situ bioremediation system intended to point the way toward a possible field application. The proposed method uses a water table management (WTM) system to deliver nutrients or other amendments to subsoil microorganisms for biostimulation and subsequent biodegradation of pollutants in the saturated and unsaturated zones of the soil. The study was carried out on packed soil columns and bioremediation of residual fertilizer nitrate was attempted. Different levels of organic carbon supplement (glucose C) were introduced into these columns via subirrigation in order to supplement the readily available organic carbon levels in the soil. The study was carried out in two experimental setups. The first setup investigated (i) the effect of addition of a high (970 mg L(-1)) and a low (120 mg L(-1)) glucose C level and (ii) the efficacy of using the subirrigation system as a method for nutrient delivery in bioremediation of leached nitrate. This setup was monitored with time, depth, and with reference to the nitrate residue in the soil solution. Leached nitrate was denitrified to less than 10 mg L(-1) nitrate N at both glucose levels. The second setup investigated the effect of a range of low levels of glucose C on nitrate decontamination, soil pH, and total microbial count in order to find out an optimal glucose C level that reduced the most nitrate and maintained the pH homeostasis of soil.     

Solute response to changing nutrient loads in soil and walled ceramic cup samplers under continuous extraction

This report evaluates a vacuum-assisted walled percolation sampler preconditioned in soil, and examines the dynamic response of leachate solutes. The 20-cm walled percolation sampler extracted soil water under continuous tension via a ceramic cup collector embedded in a silica flour layer, whose upper surface interfaced with field soil. In the laboratory, alternating solutions with high and low NO3-N (232 or 3.6 mg L(-1)), molybdate-reactive P (MRP) (1.75 or 0.0 mg L(-1)), K+ (568 or 3.6 mg L(-1)), and Br- (9.6 or 0.0 mg L(-1)) concentrations were delivered directly to the (i) sampler ceramic cup; (ii) silica flour bed surface, or (iii) 12-mm soil layer placed over the silica flour bed. For alternating input solutions delivered to the silica-flour bed surface, (i) solute breakthrough (95% equivalency) occurred in 4 pore volumes and was the same for both the high and low concentration input phases of the application, and (ii) concentrations of NO3-N, Br-, and MRP in cumulative extracted water volumes were within 5% of those in corresponding input volumes. Alternating nutrient loads from high to low levels in the fixed flow rate input waters caused excess MRP (1.6 times that in the high concentration MRP solution) to leach from the calcareous soil. The dynamic character of P transport in K-fertilized soils deserves further study and may have important environmental implications.     

Solute movement through an allophanic soil

Allophanic soils are widespread around the world, but little research has been done on their transport properties. This study reveals the effect of two soil water potential heads and two water-flow regimes of continuous and intermittent flow on solute transport through undisturbed soil columns of Horotiu silt loam (Typic Hapludand), an allophanic soil. Two different methods--breakthrough curves (BTCs) and time domain reflectometry (TDR)--were employed to determine the extent of preferential solute transport in the topsoil. The TDR data were also used to look at the depth dependence of the transport properties. The convection-dispersion equation (CDE) with the appropriate boundary conditions adequately described the movement of both Br and Cl under the various flow conditions. Although no preferential flow was found under the imposed unsaturated flow conditions, the flow of water and transport of solute became more uniform with depth. The results show that both Br and Cl are retarded in this allophanic soil. Retardation values range from 1.5 to 1.9, and, as the TDR data showed, increase from the depth of 5.0 to 10.0 cm. Intermittent leaching results showed that there was no effect on solute concentrations in the leachate following no-flow periods. This suggests that water and solute transport in this soil were either relatively uniform or that transverse mixing during flow was already fast enough to eliminate concentration gradients between regions of different "mobility."     

Evaluation of rainfall erosivity in Bheta Gad catchment, Kumaun Hills of Uttar Pradesh, central Himalayas

The importance of the size of raindrop in causing soil detachment and splash has long been recognized, although the total energy expended on erosion by splash may be small. The aggressiveness of rainfall or its capacity to cause detachment can be expressed in terms of drop size, rainfall intensity and kinetic energy or momentum. An attempt has been made to determine the rainfall erosivity (EI) of two gauged stations where continuous rainfall recorders were installed, on the basis of rainfall characteristics. Thus, the relationship between average storm EI₃₀ (rainfall erosivity for 30 minutes interval) values and average depths of rainfall could be developed for the Bheta Gad basin of the Gomati River in the Hindu-Kush Himalayas. The analysis has revealed that if factors other than rainfall remain constant, soil splash erosion from cultivated fields is directly proportional to the rainstorm parameter identified as EI.     

Relationship between metal speciation in soil solution and metal adsorption at the root surface of ryegrass

The total metal content of the soil or total metal concentration in the soil solution is not always a good indicator for metal availability to plants. Therefore, several speciation techniques have been developed that measure a defined fraction of the total metal concentration in the soil solution. In this study the Donnan Membrane Technique (DMT) was used to measure free metal ion concentrations in CaCl(2) extractions (to mimic the soil solution, and to work under standardized conditions) of 10 different soils, whereas diffusive gradients in thin-films (DGT) and scanning chronopotentiometry (SCP) were used to measure the sum of free and labile metal concentrations in the CaCl(2) extracts. The DGT device was also exposed directly to the (wetted) soil (soil-DGT). The metal concentrations measured with the speciation techniques are related to the metal adsorption at the root surface of ryegrass (Lolium perenne L.), to be able to subsequently predict metal uptake. In most cases the metal adsorption related pH-dependently to the metal concentrations measured by DMT, SCP, and DGT in the CaCl(2) extract. However, the relationship between metal adsorption at the root surface and the metal concentrations measured by the soil-DGT was not-or only slightly-pH dependent. The correlations between metal adsorption at the root surface and metal speciation detected by different speciation techniques allow discussion about rate limiting steps in biouptake and the contribution of metal complexes to metal bioavailability.