High-frequency variability of aggregate transport under water erosion of well-structured soils

The transport of soil aggregates from plots of 7.3 and 1.5 m² caused by the erosion of typical rendzina soil by a shallow supercritical laminar overland flow was studied using a high-speed digital video camera. The diameters of the removed aggregates had a lognormal distribution, and the time intervals between the passages of two successive aggregates had an exponential distribution. Therefore, transport of soil aggregates is a compound Poisson random process, which is formed by summing local independent random erosion processes.     

Adsorptionsisothermen als Regelgrößen beim Transport von Schwermetallen in Böden

Adsorption isotherms as regulators controlling heavy metal transport in soils The adsorption and desorption of Pb²⁺ and Cd²⁺ from equilibrium solutions with heavy metal contents up to 5000 μg/1 were determined in bulk experiments for soil samples from an acid Braunerde developed in loess loam, taken from the humic surface layer of the mineral soil (0–10 cm) and from the subsoil fairly free from organic matter (30–40 cm). Pb and Cd in solutions were determined by flameless atomic absorption spectroscopy. Pb was more strongly retained in the solid phase than Cd, and higher amounts of heavy metals were retained in the humic surface soil than in the subsoil free of organic matter. In the case of Pb adsorption/desorption showed slight hysteresis in the subsoil. The quantity/intensity (Q/I) relationships found in the experiments could be described by the Freundlich equation. The Q/I-relationships were substituted in the general transport equation. With a simulation model the transport of Pb and Cd through the soil with vertical water flow was calculated by the use of the Continuous Simulation Programming Language (CSMP). Two different cases were considered: a small, continuous increase in the heavy metal input of the soil surface, and a high, instantaneous peak input. Simulation of the transport and distribution mechanisms induced by the inputs over a period of 10 years showed strong retention of lead in the surface layer and consequently a strong damping of the concentration peak in the soil solution. In contrast, cadmium is distributed more quickly over the whole profile, yet the concentration peak in the solution phase is, too, damped considerably in the surface layer by temporary retention in the solid phase. The results of the simulation runs are in accordance with the situation in real soils where often strong accumulation of Pb is found in the top soil, while Cd is accumulated only slightly.     

Cr3+污染对稻田土壤的反硝化细菌种群数量及其活性影响的研究

在实验室条件下,对黄松稻田土壤、紫色稻田土壤和红壤稻田土的反硝化细菌(DenitrifyingBacteria,DNB)种群数量及其反硝化活性,以及Cr2(SO4)36H2O处理4周后Cr3+污染对DNB种群数量及其反硝化活性影响进行了研究。结果表明,紫色稻田土壤、黄松稻田土壤和红壤稻田土的DNB种群数量每克干土分别为(59.04～157.59)104cfu、(42.89～108.97)104cfu和(32.14～75.30)104cfu。在每千克干土中加入200mgCr3+时,对稻田土的DNB种群数量及其活性有明显的抑制作用,但稻田土壤还能通过自身的能力,在培养3周后完全恢复稻田土壤的DNB种群数量及其活性。随着Cr3+加入量的增加,Cr3+对DNB的毒性越来越大,稻田土壤通过自身来恢复DNB种群数量及其活性越来越困难,但可通过外界力量(如调节土壤pH)逐渐恢复稻田土壤的生物活性。     

添加生物质炭对旱地红壤中硝态氮水平运移的影响

[目的]探讨不同生物质炭施用量条件下旱地红壤中NO-3-N的含量及水平运移规律,为该地区的农田水分管理和环境保护提供科学依据。[方法]采用室内水平扩散率仪测定不同生物质炭施用量[C0(0t/hm~2,不施用生物质炭),C1(2.5t/hm~2),C2(5t/hm~2),C3(10t/hm~2),C4(20t/hm~2),C5(30t/hm~2)和C6(40t/hm~2)]条件下土壤中硝态氮水平运移速率和运移浓度。[结果]生物质炭施用对土壤中硝态氮的水平运移速率和水平运移浓度影响显著。随着生物质炭施用量的增加,硝态氮的水平运移速率和水平运移浓度呈先增加后降低的趋势,而土壤水扩散率呈逐渐降低趋势。C5(30t/hm~2)处理下硝态氮的水平运移速率和水平运移浓度均出现最大值,分别为0.67cm/min,165.52mg/kg。随着生物质炭施用量的继续增加,C6(40t/hm~2)处理的硝态氮的水平运移速率和水平运移浓度较C5(30t/hm~2)处理有所降低,硝态氮浓度最大值均出现在湿润峰峰面上。分析影响硝态氮水平运移规律的因素表明,生物质炭降低了土壤的容重、增加了土壤有机碳和孔隙度,从而导致了各处理硝态氮的水平运移规律发生了变化。[结论]生物质炭可以改善土壤的理化性状,促进硝态氮的水平运移,在利用生物质炭改良旱地红壤理化性状的同时,也要注意防止氮素流失对环境的影响,降低其对地表水的潜在污染风险。     

Effects of strong ionic polarization in the soil electric field on soil particle transport during rainfall

Specific ion effects are now thought to be important in nature. We studied the specific ion effects on soil particle transport during rainfall simulation (150 mm hour^?1, 110 minutes) in sodium nitrate (NaNO₃), potassium nitrate (KNO₃) and caesium nitrate (CsNO₃) solutions. The results showed marked differences in the intensity of soil particle transport in Na⁺, K⁺ and Cs⁺ systems. The differences increased sharply with the decrease in electrolyte concentration, which indicated strong specific ion effects on soil transport and suggested that the differences could not be explained by ionic size, hydration effect or dispersion force. The cationic non‐classical polarization in a strong electric field increases the Coulomb attractive force between the cation and clay surface, and further adversely decreases the strength of the electric field. With the absolute effective charge coefficients, γ, of Na⁺ (1.110), K⁺ (1.699) and Cs⁺ (2.506), we recalculated the true surface potentials of soil particles in NaNO₃, KNO₃ and CsNO₃ solutions. The true surface potentials decrease sharply with the increase in ionic non‐classical polarization, and then the electrostatic repulsive pressure between particles in the soil should decrease sharply. Comparison of fitting the equation for transport intensity in NaNO₃ solution with that in KNO₃ and CsNO₃ solutions showed clearly that the soil electric field controlled the aggregate breakdown and particle transport. The results suggested that the stronger the non‐classical polarization for cations in the soil, the weaker is the electrostatic field that forms and the soil erosion at the same solution concentrations.     

Occurence and transport of mercury within a small catchment area

To contribute to the understanding of Hg flow to forest lakes the storage of Hg in the soil of a catchment was quantified, the transport of Hg from the recharge area to the discharge area was studied and a mass balance for different soil horizons was calculated. The transport of Hg in soil, ground and stream water was estimated using water flows from a hydrological model and by determining Hg in water sampled with a clean procedure. The estimate for the annual Hg flux out of the till overburden in the catchment was 3.4 g km⁻². The annual flux was reduced to 1.3 g km⁻² in the stream, indicating interception in a lake. The transport was predominantly taking place in the upper 50 cm of the soil. The storage of Hg in the soil was 8.8 kg km⁻², which is large compared to the flux. A net accumulation, amounting to 80% of the Hg deposition, is almost entirely located to the nor layer.     

农药污染对水稻田土壤硫酸盐还原菌种群数量及其活性影响的研究

在实验室条件下 ,施用杀虫剂 (呋喃丹 )、杀菌剂 (多菌灵 )和除草剂 (丁草胺 )后 ,对黄松稻田土壤、紫色稻田土壤和红壤稻田土的硫酸盐还原细菌 (Sulfate reducingbacteria ,SRB)种群数量和硫酸盐还原活性的影响。结果表明 ,紫色稻田土壤、黄松稻田土壤和红壤稻田土的SRB种群数量和硫酸盐还原活性的范围分别为 (66 83～ 12 7 81)× 10 4 cfug- 1干土、(45 87～ 10 5 0 7)× 10 4 cfug- 1干土和 (3 81～ 61 62 )× 10 4 cfug- 1干土和S- 2 (7 14～ 11 57) μgg- 1d- 1干土、S- 2 (6 84～ 9 0 7) μgg- 1d- 1干土、S- 2 (1 91～ 6 67) μgg- 1d- 1干土 ,且稻田土SRB种群数量和土壤硫酸盐还原活性之间具有正相关性。每kg干土中加入 1mg的丁草胺或呋喃丹 ,能促进SRB的生长及其硫酸盐还原活性。 1kg干土中加入 5mg的多菌灵、50mg的丁草胺或呋喃丹 ,对SRB的生长和硫酸盐还原活性有明显的抑制作用。施用丁草胺和呋喃丹 7d时 ,多菌灵 14d时 ,对水稻田土壤的SRB种群数量和硫酸盐还原活性的抑制影响最大 ,然后逐渐减轻 ,最后显示出某种程度的促进作用     

不同压实水平下铁尾矿砂和土壤的水力学特征比较

由于尾矿砂的不良结构和严重压实,水土流失严重,水分已成为其生态恢复的重要限制因素。因此以水分运移为主线,通过室内土柱模拟,研究铁尾矿砂和土壤在自然状态到最大压实状态间5个压实水平(铁尾矿砂1.50~1.70 g/cm^3,土壤1.30~1.50 g/cm^3)的水力学特征差异,为尾矿砂的合理改良提供依据。结果表明:铁尾矿砂自然容重1.50 g/cm^3的水分入渗能力低于土壤自然容重1.30 g/cm^3的水分入渗能力。随容重的增大,尾矿砂和土壤的水分运移特征均呈幂函数减小的趋势,但分别在1.60,1.40 g/cm^3处入渗能力明显降低。从水分参数入渗率、湿润锋距离、累计入渗量、饱和导水率、剖面水分分布整体来看,在较低容重范围内,土壤水分运移能力高于铁尾矿砂,但由于容重对土壤水分运移的影响大于铁尾矿砂,在较高容重范围内,土壤的水分运移能力则不如铁尾矿砂。铁尾矿砂和土壤的水分特征曲线形状也完全不同,铁尾矿砂呈现"上凸"形,表现为高吸力段缓低吸力段陡,土壤水分特征曲线均为"下凹"形,表现为高吸力段陡低吸力段缓。因此,尾矿砂中可以添加土壤或者类似土壤结构的基质来增强其不良的持水性和导水性,促进生态恢复。     

Prediction of vertical soil organic carbon profiles using soil properties and environmental tracer data at an untilled site

Soil organic carbon (SOC) has considerable spatial and temporal variability both at the hillslope and catchment scale as well as down the soil profile. In recent years the distribution of SOC down the soil profile has become an area of interest in the understanding of the carbon sequestration potential of soils. Most studies however have concentrated on highly disturbed agricultural sites with little data available for untilled locations. In this study the vertical distribution of SOC is examined at a grassland site in the Young River area of Western Australia that has remained undisturbed by human activity for 50 years. Soil physical properties (texture, rock content) as well as the distribution of the environmental tracers ¹³⁷Cs and ²¹⁰Pb were assessed with the aim of better understanding the transport processes which produce the observed vertical distribution of SOC. While no consistent relationship was found between SOC and soil physical properties significant relationships were found between the distribution of SOC and the environmental tracers, ¹³⁷Cs and ²¹⁰Pb. Finite element simulations based on a diffusion/convection/decay model showed that the transport of ¹³⁷Cs and ²¹⁰Pb down the soil profile is likely to be driven by the same (primarily diffusive) processes. The same model used in conjunction with plant input and decay data generated from the RothC-26.3 soil carbon model revealed that transport of SOC down the soil profile, while also a diffusion process, was significantly slower indicating that different processes and/or pathways are involved in SOC transport at this site.     

Impact of microbial activity on the leaching of soluble N forms in soil

The hydrological transport of low-molecular weight organic nitrogen (LMWON) compounds has received little attention in the literature, particularly relative to inorganic nitrogen (N), with less attention given to the decoupling of the carbon (C) and N cycles following rainfall events. We determined the impacts of the soil biota on the transport of N compounds in a loam soil, using ¹⁵N and ¹³C to trace the vertical transport of ¹⁵N¹³C-urea, ¹⁵N¹³C-amino acids, ¹⁵NO₃, and ¹⁵NH₄ through the soil profile, following simulated rainfall events. This research has demonstrated that biotic assimilation leads to rapid decoupling of the C and N cycles during leaching, with C transport limited to the soil surface (<?2 cm), whereas N which was stored within the soil profile during a single rainfall event could be remobilised and leached (a further 2–6 cm) following an additional rainfall event.     

Short‐term transport of cadmium during a heavy‐rain event simulated by a dual‐continuum approach

The transport of solutes in soils, and its intensification due to preferential flow, plays crucial role when problems related to the groundwater pollution are dealt with. The objective of this study was to examine transport of cadmium (Cd) in response to an extreme rainfall event for three different soils using numerical modeling. The ^115mCd²⁺ concentration profile had been measured in the Bodiky reference site (Danubian Lowland, Slovakia) by the radioactive‐tracer technique and used for the calibration of the dual‐continuum model S1D. The Cd transport during a single rain event was predicted with the S1D model for light, medium‐heavy, and heavy soil in the same region. The Cd transport through the soil profile was simulated by the one‐dimensional dual‐permeability model, which assumes the existence of two pore domains: the soil‐matrix domain and the preferential‐flow domain. The model is based on Richards' equation for water flow and advection‐dispersion equation for solute transport. A modified batch technique enables to distinguish process of adsorption in the matrix domain and the preferential pathways. Modeling with classical single‐permeability approach and dual‐continuum approach without considering the particle‐facilitated transport led to negligible Cd penetration. The rainfall event with extremely high rainfall intensity induced deep penetration of Cd in the medium‐heavy and heavy soil, which may indicate increased vulnerability to shallow groundwater pollution for the respective sites in Danubian Lowland region. The highest Cd leaching was predicted for heavy clay soil, where the preferential particle‐facilitated transport of Cd through the soil profile was significant due to the contrasting properties of the soil‐matrix domain and the preferential‐flow domain. The results of the sensitivity analysis suggested only slight effect of the transfer rate coefficients on simulated Cd leaching.     

Simulation des Anionen-Transports in ungestörten Bodensäulen unter stationären Fließbedingungen

Simulation of anion transport in undisturbed soil cores under steady-state flow conditions Miscible displacement experiments with undisturbed soil columns were carried out in the laboratory. Objective of the experiments was to collect information about the transport of Cl^? and NO₃^? through field soils. The experiments were carried out with a forest soil and an agricultural soil. The flow velocity of the chloride and the nitrate solution was either 1 cm/day or 0,3 cm/day. Of each soil there were 5 replicates. The effluent of each of the columns was analyzed and the collected data were used for model calculations. It was found that the breakthrough curves of Cl^? and NO₃^? were similar in shape. For the well-aggregated forest soil the apparent diffusion coefficient was much larger than for the agricultural soil. For both soils practically all of the chloride could be recovered in the effluent, but for nitrate considerable losses within the soil column were noted. It was also found that the chloride breakthrough could be described with a simple convection-dispersion equation. However a reduction of the total pore space, accounting for anion exclusion, was needed. Furthermore it was observed that for nitrate an additional sink term in the convection-dispersion equation was needed to account for the observed nitrate losses. It appears that the transport of nitrate and chloride through the soils that were studied can be described mathematically, provided the anion exclusion space and the rate of nitrate losses are known. The nature of the anion exclusion and the nitrate transformation needs further study.     

重金属污染对水稻田土壤硫酸盐还原菌种群数量及其活性的影响

在实验室条件下,采用重金属Cd2+、As5+、Cu2+、Pb2+和Cr3+处理黄松稻田土壤、紫色稻田土壤和红壤稻田土,28d后分析重金属污染对水稻田土壤的硫酸盐还原菌(SRB)种群数量和硫酸盐还原活性(SRA)的影响。结果表明,在每千克干土中加入200mgPb2+时,对稻田土壤的SRB种群数量和SRA有促进作用;当加入的Cd2+、As5+、Cu2+、Pb2+和Cr3+每千克干土分别超过1.0、30、500、400和200mg时,对稻田土壤SRB种群数量和SRA有明显抑制作用。随着加入量的增加,重金属对水稻田土壤的SRB种群数量和SRA的抑制作用越来越强,水稻田土壤通过自身来恢复SRB种群数量和SRA所需的时间也越长。同一种重金属元素对不同土壤的SRB种群数量和SRA抑制的污染临界值也有差异。     

Characterizing the impact of diffusive and advective soil gas transport on the measurement and interpretation of the isotopic signal of soil respiration

By measuring the isotopic signature of soil respiration, we seek to learn the isotopic composition of the carbon respired in the soil (δ¹³C_R-s) so that we may draw inferences about ecosystem processes. Requisite to this goal is the need to understand how δ¹³C_R-s is affected by both contributions of multiple carbon sources to respiration and fractionation due to soil gas transport. In this study, we measured potential isotopic sources to determine their contributions to δ¹³C_R-s and we performed a series of experiments to investigate the impact of soil gas transport on δ¹³C_R-s estimates. The objectives of these experiments were to: i) compare estimates of δ¹³C_R-s derived from aboveground and belowground techniques, ii) evaluate the roles of diffusion and advection in a forest soil on the estimates of δ¹³C_R-s, and iii) determine the contribution of new and old carbon sources to δ¹³C_R-s for a Douglas-fir stand in the Pacific Northwest during our measurement period. We found a maximum difference of −2.36‰ between estimates of δ¹³C_R-s based on aboveground vs. belowground measurements; the aboveground estimate was enriched relative to the belowground estimate. Soil gas transport during the experiment was primarily by diffusion and the average belowground estimate of δ¹³C_R-s was enriched by 3.8-4.0‰ with respect to the source estimates from steady-state transport models. The affect of natural fluctuations in advective soil gas transport was little to non-existent; however, an advection-diffusion model was more accurate than a model based solely on diffusion in predicting the isotopic samples near the soil surface. Thus, estimates made from belowground gas samples will improve with an increase in samples near the soil surface. We measured a −1‰ difference in δ¹³C_R-s as a result of an experiment where advection was induced, a value which may represent an upper limit in fractionation due to advective gas transport in forest ecosystems. We found that aboveground measurements of δ¹³C_R-s may be particularly susceptible to atmospheric incursion, which may produce estimates that are enriched in ¹³C. The partitioning results attributed 69-98% of soil respiration to a source with a highly depleted isotopic signature similar to that of water-soluble carbon from foliage measured at our site.     

Modelling the effects of bioturbation on the re-distribution of 137Cs in an undisturbed grassland soil

Under favourable conditions, soil ingestion by earthworm populations can be equivalent to approximately 5–10% of the topsoil mass per year. This suggests that for contaminants that are strongly bound to soil, earthworm ‘bioturbation’ may be a more important transport mechanism than water‐borne advection dispersion. It is therefore quite surprising that few modelling studies to date have explicitly considered the effects of biological processes on contaminant transport in soil. In this study, we present a general model that incorporates the effects of both ‘local’ and ‘non‐local’ biological mixing into the framework of the standard physical (advective‐dispersive) transport model. The model is tested against measurements of the redistribution of caesium‐137 (¹³⁷Cs) derived from the Chernobyl accident, in a grassland soil during 21 years after fallout. Three model parameters related to biological transport were calibrated within ranges defined by measured data and literature information on earthworm biomasses and feeding rates. Other parameters such as decay half‐life and sorption constant were set to known or measured values. A physical advective‐dispersive transport model based on measured sorption strongly underestimated the downward displacement of ¹³⁷Cs. A dye‐tracing experiment suggested the occurrence of physical non‐equilibrium transport in soil macropores, but this was inadequate to explain the extent of the deep penetration of ¹³⁷Cs observed at the site. A simple bio‐diffusion model representing ‘local’ mixing worked reasonably well, but failed to reproduce the deep penetration of Cs as well as a dilution observed close to the soil surface. A comprehensive model including physical advective‐dispersive transport, and both ‘local’ and ‘non‐local’ mixing caused by the activities of both endogeic and anecic earthworms, gave an excellent match to the measured depth profiles of ¹³⁷Cs, with predictions mostly lying within confidence intervals for the means of measured data and model efficiencies exceeding 0.9 on all sampling occasions but the first.     

基于HYDRUS模型的华北平原小麦种植区水盐运移模拟

土壤中水分和盐分是影响作物生长的两个关键因素,揭示水盐运移机制对阐明作物利用土壤水过程具有重要意义。本研究以华北平原典型农田——中国科学院禹城综合试验站为试验地,基于试验站内冬小麦种植地的长期土壤水分观测数据及室内土柱试验,应用HYDRUS-1D模型分别阐明土壤水分及盐分变化规律及分布特征,探究影响水盐运移的驱动因素,并评价HYDRUS-1D模型对研究区水盐运移模拟的适用性。水分运移模拟结果表明:浅层土壤水分运移模拟因受外界因素的剧烈影响而较深层土壤产生更大的误差,10cm、20 cm、30 cm、40 cm和60 cm处水分运移模拟结果的均方根误差分别为0.0348 cm~3·cm~(-3)、0.0179 cm~3·cm~(-3)、0.0179cm~3·cm~(-3)、0.0122cm~3·cm~(-3)和0.0053cm~3·cm~(-3);水分运移模拟的纳什效率系数平均值为0.826,变异系数为0.0560,表明模拟结果与实测土壤水分变化过程一致性较好。土柱试验结果显示:灌水8 L,入渗12 h、24 h、40 h、45 h和48 h后,各时刻土壤盐分含量在垂向上整体呈现先增大后减少的分布规律,均方根误差分别为0.181 g·kg~(-1)、0.131 g·kg~(-1)、0.120 g·kg~(-1)、0.034 g·kg~(-1)和0.027 g·kg~(-1),平均误差的平均值为0.174 g·kg~(-1)。受蒸发、耕作、根系等影响,理化性质变异性较大导致浅层土壤盐分运移模拟值与实测值偏差增大,纳什效率系数的变异系数达9.71。灌水8 L、16 L、24 L,入渗48 h后分别在土壤23 cm、26 cm、29 cm处出现盐分含量峰值,表明增加灌水量可加强盐分淋洗效果。此研究可为深入探究华北平原冬小麦土壤水盐运移规律、优化农田水资源管理、提高水资源利用效率提供一定理论基础。     

Mobilization of cesium in organic rich soils: Correlation with production of dissolved organic carbon

A study of the downward movement of ¹³⁷Cs in an undisturbed forest soil is presented. Seasonal variations and depth profiles of ¹³⁷Cs activities were measured in seepage water, which is the transport medium for the downward movement of anthropogenic substances in soils. Furthermore the correlation of ¹³⁷Cs mobilization and production of dissolved organic carbon (DOC) was investigated. Seasonal variations of both ¹³⁷Cs and DOC fluxes in the seepage water in a depth of 5 cm depth were observed, where the maximum fluxes in the summer months were about one order of magnitude higher than the minimum fluxes in the winter months. ¹³⁷Cs fluxes are found to be correlated with DOC fluxes with a correlation coefficient of r = 0.63, and both are highly correlated with soil temperature. This indicates that cesium is bound to soil organic material. The production of DOC is controlled by microbial decomposition of soil organic matter and we assume that this holds true for the ¹³⁷Cs release as well. The actual transport velocity (0.2 ± 0.14 mm/a) of ¹³⁷Cs (calculated by the weighed mean of ¹³⁷Cs concentration in the seepage water and the total ¹³⁷Cs content of the soil) is about one order of magnitude less than the mean transport velocity (1.2 ± 0.3 mm/a) over the past 25 years (calculated from the ¹³⁷Cs depth profile). It is possible that the transport velocity of ¹³⁷Cs in undisturbed soils decreases with time as it binds to aged organic material which is less easily decomposable than fresh organic material.     

Soil and Sediment Geochemistry of the Iron Quadrangle, Brazil

Soils and sediments around gold ore deposit and mining sites in the Iron Quadrangle present positive As anomalies (median concentrations > 100 mg kg^-1) and wide ranges (< 20 to > 2000 mg kg^-1) even in densely populated areas. These anomalies can be related to geological structures, to hydrothermal ore deposits and to their continuous exploitation over the past three centuries. The paper presents new data on both As geochemistry and soil and sediment geochemistry in general, and discusses consequences of the encountered anomalies, their reasons and potential effects and how they compare with current screening and threshold values. While surface soil As-val-ues are reproducible at a given site, sediment anomalies show a strong seasonal variation that can be explained by tropical hydrologicai variances. Suggestions are presented on how to minimize the As-load in densely populated areas that might otherwise pose a potential health risk.     

Soil and sediment geochemistry of the iron quadrangle,Brazil the case of arsenic

Soils and sediments around gold ore deposit and mining sites in the Iron Quadrangle present positive As anomalies (median concentrations > 100 mg kg^-1) and wide ranges (< 20 to > 2000 mg kg^-1) even in densely populated areas. These anomalies can be related to geological structures, to hydrothermal ore deposits and to their continuous exploitation over the past three centuries. The paper presents new data on both As geochemistry and soil and sediment geochemistry in general, and discusses consequences of the encountered anomalies, their reasons and potential effects and how they compare with current screening and threshold values. While surface soil As-values are reproducible at a given site, sediment anomalies show a strong seasonal variation that can be explained by tropical hydrological variances. Suggestions are presented on how to minimize the As-load in densely populated areas that might otherwise pose a potential health risk.     

Soil and Sediment Geochemistry of the Iron Quadrangle, Brazil The Case of Arsenic

Soils and sediments around gold ore deposit and mining sites in the Iron Quadrangle present positive As anomalies (median concentrations > 100 mg kg^-1) and wide ranges (< 20 to > 2000 mg kg^-1) even in densely populated areas. These anomalies can be related to geological structures, to hydrothermal ore deposits and to their continuous exploitation over the past three centuries. The paper presents new data on both As geochemistry and soil and sediment geochemistry in general, and discusses consequences of the encountered anomalies, their reasons and potential effects and how they compare with current screening and threshold values. While surface soil As-val-ues are reproducible at a given site, sediment anomalies show a strong seasonal variation that can be explained by tropical hydrologicai variances. Suggestions are presented on how to minimize the As-load in densely populated areas that might otherwise pose a potential health risk.