Compositional fractionation of polyaromatic hydrocarbons in the karst soils, South China

This study aims to explore the condensation and fractionation trends of persistent organic pollutants (POPs) in the karst soils. The tiankeng is a karst surface expression that can act as a focal point for introduction of contaminants to a karst aquifer, which may serve both as condenser for vapor phase POPs and as barrier/sink for particulate associated less volatile POPs. The fractionation of POPs in soils from the upper rim and floor of tiankeng is of interest in understanding the role of tiankeng in the long-distance transport of POPs. In the present study, polycyclic aromatic hydrocarbons (PAHs) in the surface soils from the upper rim and floor of Dashiwei tiankeng in Southern China were analyzed. The total PAH concentrations in soils were 23.40–190 ng g⁻¹, with phenanthrene being the most abundant. The distribution patterns of PAH compounds in the soil samples matched well with their properties. It indicated the heavy PAHs were susceptible to retention by the floor soils of tiankeng than light PAHs. A plot of Cfloor/Crim against PAH molecular weight gave a good positive relationship in the molecular weight range of 152–276. It is suggested that the floor soils can be focal points of more concentrated PAH and deserve attention. The concentrations of total PAHs in the floor soils (43.40–190 ng g⁻¹, mean 87.76 ng g⁻¹) were higher than those in the upper rim (23.40–88.94 ng g⁻¹, mean 57.74 ng g⁻¹). In addition, there was a shift in compound pattern with an increase in the proportion of light PAHs (2–3 rings), a decrease in heavy PAHs (5–6 rings) and a relatively stable content of 4-ring PAHs. A combination of particulate scavenging and cold condensation is proposed as the major mechanism for the compositional fractionation of PAHs in the soils from the upper rim and floor of tiankeng.     

Contamination and potential mobility assessment of heavy metals in urban soils of Hangzhou,China: relationship with different land uses

Concentration and distribution of heavy metals (Cd, Cu, Pb and Zn) in urban soils of Hangzhou, China, were measured based on different land uses. The contamination degree of heavy metals was assessed on the basis of pollution index (PI), integrated pollution index (IPI) and geoaccumulation index (I _geo). The 0.1 mol l⁻¹ HCl extraction procedure and gastric juice simulation test (GJST) were used to evaluate the potential mobility and environmental risk of heavy metals in urban soils. The average concentration of Cd, Cu, Pb and Zn in urban soils was measured at 1.2 (with a range of 0.7–4.6), 52.0 (7.4–177.3), 88.2 (15.0–492.1) and 206.9 (19.3–1,249.2) mg kg⁻¹, respectively. The degree of contamination increased in the order of industrial area (IA) > roadside (RS) > residential and commercial areas (RC) > public park and green areas (PG). The PIs for heavy metals indicated that there is a considerable Cd, Cu, Pb and Zn pollution, which originate from traffic and industrial activities. The IPI of these four metals ranged from 1.6 to 11.8 with a mean of 3.5, with the highest IPI in the industrial area. The assessment results of I _geo also supported that urban soil were moderately contaminated with Cd and to a lesser extent also with Cu, Pb and Zn. The IP and I _geo values reveal the pollution degree of heavy metal was the order of Cd > Pb > Zn ≈ Cu. It was shown that mobility and bioavailability of the heavy metals in urban soils increased in the order of Cd > Cu > Zn ≈ Pb. Owing to high mobility of Cd and Cu in the urban soils, further investigations are needed to understand their effect on the urban environment and human health. It is concluded that industrial activities and emissions from vehicles may be the major source of heavy metals in urban contamination. Results of this study present a rough guide about the distribution and potential environmental and health risk of heavy metals in the urban soils.     

Polyphase metamorphism in the eastern Carnic Alps (N Italy–S Austria): clay minerals and conodont Colour Alteration Index evidence

Thermal evolution of the Palaeozoic–Triassic sequences of the Carnic Alps has been characterized by b cell dimension and Kübler Index (illite “crystallinity”) of K-white micas (KI), árkai Index (AI) of chlorites, clay mineral assemblages and conodont Colour Alteration Index (CAI). Data indicate at least two metamorphic events, Variscan and Alpine. In the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas. It was characterized by low-intermediate pressure facies. The thermal peak was mainly due to an extensional regime during the Bashkirian. A younger thermal overprint generated by Alpine orogeny was of lower grade, reaching high diagenetic–anchizonal conditions characterized by high-pressure facies. Inverted metamorphic patterns are associated with middle to late Miocene thrusting. Hydrothermal alteration in the northern part of the region can be linked with emplacement of Oligocene plutons and high heat flow along the Periadratic lineament. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Urbanization pressure increases potential for soils-related hazards,Denton County,Texas

The Dallas-Fort Worth region was the fastest growing metropolitan area in the US in the decade 1990–2000. Rapid urbanization accompanied this population growth. A GIS-based analysis of urban growth in Denton County revealed that 53% of new urban development was on soils rated of low suitability for urban uses by the Soil Conservation Service. This compares to only 15% of urban areas on low-suitability soils prior to 1990. These soils are considered poorly suited for urban uses because they are montmorillonitic expansive soils. Expansive soils are known to cause damage to structures, including slab foundations used extensively in new housing in the Dallas–Fort Worth region. Increased urban development on these soils has increased the potential for soils-related hazards.     

Behavior of expansive soils stabilized with fly ash

Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying. Disposal of fly ash, which is an industrial waste in both cost-effective and environment-friendly way receives high attention in China. In this study, the potential use and the effectiveness of expansive soils stabilization using fly ash and fly ash-lime as admixtures are evaluated. The test results show that the plasticity index, activity, free swell, swell potential, swelling pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of the curing time for the treated soil, the swell potential and swelling pressure decreased. Soils immediately treated with fly ash show no significant change in the unconfined compressive strength. However, after 7 days curing of the fly ash treated soils, the unconfined compressive strength increased significantly. The relationship between the plasticity index and swell-shrinkage properties for pre-treated and post-treated soils is discussed.     

Geochemical distribution of arsenic,cadmium, lead and zinc in river sediments affected by tailings in Zimapán,a historical polymetalic mining zone of México

High arsenic (As) groundwater is widely distributed in northwestern Hetao Plain, an arid region with sluggish groundwater flow. Observed As concentration in groundwater from wells ranges from 76 to 1,093 μg/l. Most water samples have high total dissolved solids, with Cl and HCO₃ as the dominant anions and Na as the dominant cation. The major hydrochemical types of most saline groundwaters are Na–Mg–Cl–HCO₃ and Na–Mg–Cl. By contrast, fresh groundwaters generally belong to the Na–Mg–HCO₃ type. High concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions, as evidenced by high concentrations of dissolved organic carbon, ammonium, as well as dissolved sulfide and Fe, dominance of arsenite, relatively low concentrations of nitrate and sulfate, and occasionally high content of dissolved methane (CH₄). High As groundwaters from different places at Hetao Plain experienced different redox processes. Fluoride is also present in high As groundwater, ranging between 0.40 and 3.36 mg/l. Although fluorosis poses an additional health problem in the region, it does not correlate well with As in spatial distribution. Geochemical analysis indicates that evapotranspiration is an important process controlling the enrichment of Na and Cl, as well as trace elements such as As, B, and Br in groundwater. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Assessment of heavy metal contamination in soils around Balanagar industrial area,Hyderabad, India

The concentration of heavy metals such as Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Y, Zn, Zr were studied in soils of Balanagar industrial area, Hyderabad to understand heavy metal contamination due to industrialization and urbanization. This area is affected by the industrial activities like steel, petrochemicals, automobiles, refineries, and battery manufacturing generating hazardous wastes. The assessment of the contamination of the soils was based on the geoaccumulation index, enrichment factor (EF), contamination factor, and degree of contamination. Soil samples were collected from Balanagar industrial area from top 10–50 cm layer of soil. The samples were analyzed using X-ray fluorescence spectrometer for heavy metals. The data revealed that the soils in the study area are significantly contaminated, showing high level of toxic elements than normal distribution. The ranges of concentration of Cr (82.2–2,264 mg/kg), Cu (31.3–1,040 mg/kg), Ni (34.3–289.4 mg/kg), Pb (57.5–1,274 mg/kg), Zn (67.5–5819.5 mg/kg), Co (8.6–54.8 mg/kg), and V (66.6–297 mg/kg). The concentration of above-mentioned other elements was similar to the levels in the earth’s crust pointed to metal depletion in the soil as the EF was <1. Some heavy metals showed high EF in the soil samples indicating that there is a considerable heavy metal pollution, which could be correlated with the industries in the area. A contamination site poses significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may results in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems.     

Mapping of total nitrogen,available phosphorous and potassium in Amik Plain,Turkey

Soil nitrogen, phosphorous, and potassium concentrations accurately revealed spatial distribution maps and site-specific management-prone areas through inverse distance weighting (IDW) method in the Amik Plain, Turkey. Spatial mapping of soil nitrogen, phosphorous, and potassium is a very severe need to develop an economically and environmentally sound soil management plans. The objectives of this study were (a) to map spatial variability of total N, available P, and exchangeable-K content of Amik Plain’s soils and (b) to locate problematic areas requiring site specific management strategies for the nutrient elements. Spatial analyses of Kjeldhal-N, Olsen-P, and exchangeable-K concentrations of the soils were performed by the IDW method. Mean N content for surface soils (0–20 cm) was 1.38 g kg⁻¹, available P was 28.19 kg ha⁻¹ and exchangeable-K was 690 kg ha⁻¹ with the differences between maximum and minimum being 7.63 g N kg⁻¹, 242 kg P ha⁻¹, and 2,082 kg K ha⁻¹. For the surface soil, site-specific management-prone areas of Kjeldahl-N, Olsen-P, and exchangeable-K for “low and high + very high” classes were found to be 20.1–17.8%, 24.7–10.0%, and 4.1–39.6%, respectively. Consequently, lands with excessive nutrient elements require preventive-leaching practices, whereas nutrient-poor areas need fertilizer applications in favor of increasing plant production.     

Environmental contamination of Zn,Cd, Ni,Cu, and Pb from industrial areas in Hamadan Province,western Iran

Eleven surface soil samples from calcareous soils of industrial areas in Hamadan Province, western Iran were analyzed for total concentrations of Zn, Cd, Ni, Cu and Pb and were sequentially extracted into six fractions to determine the bioavailability of various heavy metal forms. Total Zn, Cd, Ni, Cu and Pb concentrations of the contaminated soils were 658 (57–5,803), 125.8 (1.18–1,361), 45.6 (30.7–64.4), 29.7 (11.7–83.5) and 2,419 (66–24,850) mg kg⁻¹, respectively. The soils were polluted with Zn, Pb, and Cu to some extent and heavily polluted with Cd. Nickel values were not above regulatory limits. Copper existed in soil mainly in residual (RES) and organic (OM) fractions (about 42 and 33%, respectively), whereas Zn occurred essentially as RES fraction (about 69%). The considerable presence of Cd (30.8%) and Pb (39%) in the CARB fraction suggests these elements have high potential biavailability and leachability in soils from contaminated soils. The mobile and bioavailable (EXCH and CARB) fractions of Zn, Cd, Ni, Cu, and Pb in contaminated soils averaged (7.3, 40.4, 16, 12.9 and 40.8%), respectively, which suggests that the mobility and bioavailability of the five metals probably decline in the following order: Cd = Pb > Ni > Cu > Zn.     

Cyclic Swell–Shrink Behaviour of a Compacted Expansive Soil

Laboratory cyclic swell–shrink tests were carried out on compacted expansive soil specimens to study in detail the effect of changes in shrinkage pattern on the swell–shrink behaviour of compacted expansive soils. Compacted soil specimens were allowed to swell and either shrank fully or partially shrank to several predetermined heights in each cycle. The tests were carried out at a surcharge pressure of 50 kPa. The test results revealed that shrinkage of compacted saturated soil specimens to predetermined height in each shrinkage cycle provides similar conditions as that of the controlled suction tests with an increasing number of swell–shrink cycles. The water content of soil specimens and hence soil suction was found to remain nearly constant for each pattern of shrinkage. For soil specimens equilibrated to a given swell–shrink pattern, suction at the end of shrinkage cycles was changed from a higher suction to a lower suction, and also from a lower to a higher suction. The experimental results showed that there may be an immediate equilibrium state attained by the soil in terms of swell–shrink potential if suction at the shrinkage cycles was less than the past suction; otherwise, the equilibrium state was accompanied by fatigue of swelling. The volumetric deformation of the soil specimen subjected greater shrinkage was found to be much larger than the corresponding vertical deformation. The compressibility index of microstructure, κ_m, was determined for several shrinkage patterns. It is shown that κ_m is heavily influenced by suction at the end of shrinkage cycles.     

Geochemistry and biogeochemistry of rare earth elements in a surface environment (soil and plant) in South China

Plants and soils derived from different kinds of parent materials in South China were collected for analyses of rare earth elements (REEs) by inductively coupled plasma-mass spectrometry (ICP-MS). The distribution patterns and transportation characteristics of REEs in the soil–plant system were studied. The results show that geochemical characteristics of REEs depend on the types of soils, soils derived from granite being the highest in REE concentration. In a soil profile, REE concentrations are higher in B and C horizons than those in A horizon, with Eu negative anomaly and Ce positive anomaly. Plants of different genera growing in the same sampling site have quite similar REE distribution pattern, but plants of the same genera growing in different soils show considerable variation in characteristics of REEs. The patterns of the different parts of plant resemble each other, but the slope of the patterns becomes different. REEs have fractionated when they were transported and migrated from soil to plant root, stem and leaf, revealing that heavy REEs are relatively less available. REEs distributions in plants are influenced by the soil they grow in and also characterized by their individual biogeochemical characteristics. Biological absorption coefficients indicate difference of REE absorption capacity of plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spatial distribution, source identification and affecting factors of heavy metals contamination in urban–suburban soils of Lishui city, China

An investigation on spatial distribution, possible pollution sources, and affecting factors of heavy metals in the urban–suburban soils of Lishui city (China) was conducted using geographic information system (GIS) technique and multivariate statistics. The results indicated that the topsoils in urban and suburban areas were enriched with metals, such as Cd, Cu, Pb, and Zn. Spatial distribution maps of heavy metal contents, based on geostatistical analysis and GIS mapping, indicated that Cd, Cr, Cu, Mn, Ni, Pb, and Zn had similar patterns of spatial distribution. Their hot-spot areas were mainly concentrated in the densely populated old urban area of the city. Multivariate statistical analysis (correlation analysis, principal component analysis, and clustering analysis) showed distinctly different associations among the studied metals, suggesting that Cr, Cu, Ni, Pb, Cd, and Zn had anthropogenic sources, whereas Co and V were associated with parent materials and therefore had natural sources. The Cd, Cr, Ni, Pb, and Zn contents were positively correlated with soil organic matter, pH, and sand content (p < 0.01). It is concluded that GIS and multivariate statistical methods can be used to identify hot-spot areas and potential sources of heavy metals, and assess soil environment quality in urban–suburban areas.     

High cadmium concentrations in Jurassic limestone as the cause for elevated cadmium levels in deriving soils: a case study in Lower Burgundy,France

Cadmium (Cd) is a highly toxic element and its presence in the environment needs to be closely monitored. Recent systematic surveys in French soils have revealed the existence of areas in eastern and central France, which show systematically high cadmium concentrations. It has been suggested that at least part of these anomalous levels are of natural origin. For the Lower Burgundy area in particular, a direct heritage from the Jurassic limestone bedrock is highly suspected. This potential relationship has been studied in several localities around Avallon and this study reports new evidence for a direct link between anomalously elevated cadmium contents of Bajocian and Oxfordian limestone and high cadmium concentrations in deriving soils. Soils in this area show cadmium concentrations generally above the average national population values, with contents frequently higher than the ‘upper whisker’ value of 0.8 μg g⁻¹ determined by statistical evaluation. In parallel, limestone rocks studied in the same area exhibit cadmium concentrations frequently exceeding the mean value of 0.030–0.065 μg g⁻¹ previously given for similar rocks by one order of magnitude, with a maximum of 2.6 μg g⁻¹. Mean ratios between the cadmium concentrations of limestone bedrock and deriving soils (Cd_soil/Cd_rock), calculated for different areas, range from 4.6 to 5.7. Calculations based on the analyses of both soils from a restricted area and fragments of bedrock sampled in the immediate vicinity of high-concentration soils are around 5.5–5.7. Cd_soil/Cd_rock is useful in determining the potential of soils in Lower Burgundy to reflect and exacerbate the high concentrations of cadmium present in parent bedrocks.     

Polycyclic aromatic hydrocarbon concentrations in urban soils representing different land use categories in Shanghai

An extensive soil survey was carried out in Shanghai to investigate the spatial distribution and possible sources of polycyclic aromatic hydrocarbons (PAHs) in urban soils. Soil samples were collected from highways, iron-smelting plants, steel-smelting plants, shipbuilding yards, coking plants, power plants, chemical plants, urban parks, university campuses and residential areas and were analyzed for 16 PAHs by gas chromatography with mass detection. High PAH concentrations were found in all locations investigated, with mean values of soil total PAH concentrations in the range 3,279–38,868 μg/kg DM, and the PAH concentrations were significantly influenced by soil organic matter content. Soil PAH profiles in all districts were dominated by PAHs with 4–6 rings. Principal components analysis and diagnostic ratios of PAHs indicate that they were mainly derived from coal combustion and petroleum but in soils from highways the PAHs were derived largely from vehicle exhaust emissions. The high concentrations of PAHs found indicate that many urban soils in Shanghai represent a potential hazard to public health.     

Study on the swelling behaviour of blended clay–sand soils

Soils containing expansive clays undergo swelling that can be both detrimental and beneficial in various applications. In the Arabian Gulf coastal region, natural heterogeneous soils containing clay and sand (tills, shales, and clayey sands) support most of the civil infrastructure systems. Likewise, mixes of clay and sand are used for local earthwork construction such as roads and landfills. A clear understanding of the swelling behaviour of such soils is pivotal at the outset of all construction projects. The main objective of this paper was to understand the evolution of swelling with increasing clay content in local soils. A theoretical framework for clay–sand soils was developed using phase relationships. Laboratory investigations comprised of mineralogical composition and geotechnical index properties of the clay and sand and consistency limits, swelling potential, and morphology of clay–sand mixes. Results indicated that soil consistency of mixes of a local expansive clay and an engineered sand depends on the weighted average of the constituents. Mixes with 10% clay through 40% clay capture the transition from a sand-like behaviour to a clay-like behaviour. Influenced by the initial conditions and soil matrix, the swelling potential of the investigated mixes correlated well with soil plasticity (SP(%) = 0.16 (I _p)^1.188). The parameters sand void ratio and clay–water ratio were found to better explain the behaviour of blended clay–sand soils.     

Mechanism of cultivation soil degradation in rocky desertification areas under dry/wet cycles

Karst rocky desertification is a process of land degradation involving serious soil erosion, extensive exposure of basement rocks. It leads to drastic decrease in soil productivity and formation of a desert-like landscape. In this regard, changes in climatic conditions are the main origin of the soils degradation. Indeed, soils subjected to successive dry/wet cycling processes caused by climate change develop swelling and shrinkage deformations which can modify their water retention properties, thus inducing the degradation of soil–water capacity. The ecological characteristics of cultivation soils in karst areas, Southwest of China, are extremely easy to be affected by external environmental factors due to its shallow bedding and low vegetation coverage. Based on the analysis of the climate (precipitation) of this region during the past decades, an experimental study has been conducted on a cultivated soil obtained from the typical karst area in southwestern China. Firstly, the soil–water properties have been investigated. The measured soil–water retention curve shows that the air-entry value of the soil is between 50 and 60 kPa, while the residual saturation is about 12%. Based on the experimental results, three identifiable stages of de-saturation have been defined. Secondly, a special apparatus was developed to investigate the volume change behavior of the soil with controlled suction cycles. The vapor equilibrium technique was used for the suction control. The obtained results show that under the effect of dry/wet cycles, (1) the void ratio of the cultivated soil is continuously decreasing, leading to a gradual soil compaction. (2) The permeability decreases, giving rise to a deterioration of water transfer ability as well as a deterioration of soil–water retention capacity. It is then obvious that the long-term dry/wet cycling process caused by the climate change induce a continuously compaction and degradation of the cultivated soil in karst rocky desertification areas.     

Compaction characteristics of granular soils in United Arab Emirates

Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution, liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil samples were collected and their compaction results were used to test the validity of predictive model. The range of variables for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26; Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8. Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of HCH and DDT in soils following Wenchuan 5.12 Violent Earthquake in China

A large number of disinfectants and insecticides were used on a large scale after the Wenchuan 5.12 Violent Earthquake. The disinfectants and insecticides, including HCH (hexachlorocyclohexane) and DDT (dichlorodiphenyltrichoroethane) as representative OCPs, could lead to serious environmental problems. In order to disclose the residues of HCH and DDT in soils following the Wenchuan 5.12 Violent Earthquake, surface soils in Dujiangyan City and Beichuan County were sampled in 2009. The samples were analyzed by GC/MS after pre- treatment by ultrasonic solvent extraction. It has been found that the concentra-tions of γ-HCH, β-HCH and 4,4’-DDT in soils of Beichuan County were 94–102.4, 14.1–36.1 and 2.9–4.3 times high their concentrations in those of the Wolong Nature Reserve, and the concentrations in soils of Dujiangyan City were 52.4–61.6, 8.8 –45.3 and 5.4–6.2 times high their concentrations in soils of the Wolong Nature Reserve, respectively. According to the isomers of HCHs and metabolites of DDTs, it could be concluded that these areas may have additional inputs of lindane and 4,4’-DDT.     

Atmospheric stability index using radio occultation refractivity profiles

A new stability index based on atmospheric refractivity at ~500 hPa level and surface measurements of temperature, pressure and humidity is formulated. The new index named here as refractivity based lifted index (RLI) is designed to give similar results as traditionally used lifted index derived from radiosonde profiles of temperature, pressure and humidity. The formulation of the stability index and its comparison with the traditional temperature profile based lifted index (LI) is discussed. The index is tested on COSMIC radio occultation derived refractivity profiles over Indian region. The forecast potential of the new index for rainfall on 2°×2° latitude–longitude spatial scale with lead time of 3–24 hours indicate that the refractivity based lifted index works better than the traditional temperature based lifted index for the Indian monsoon region. Decreasing values of RLI tend to give increasing rainfall probabilities.     

Geochemical processes controlling the spatial distribution of selenium in soil and water,west central South Dakota,USA

Selenium (Se) is essential in the human diet, but has a low threshold for toxic concentration. It is recommended that nutrients such as Se should be consumed through foods as part of a normal diet. Se concentrations in crops and meat depend on the amount of labile Se in the soil where crops and forage are grown. Therefore, managing agriculture for optimal Se in grain crops and forage requires an understanding of the distribution and mobility of Se. Elevated concentrations of Se occur in waters, soils, and forage 120 km west of Pierre in west central South Dakota, USA. The research site lies in an elevated, dissected plain where soils developed on gently dipping Pierre Shale. Soils were sampled along catena transects and waters collected from soil, ponds, and shallow borings in areas of known elevated forage and crop Se. Soil extracts from saturated-paste extraction and acid (aqua regia and hydrofluoric acid) extraction were analyzed. Selenate was the dominant Se species in both acid and saturated-paste extracts; selenite and organic Se were below detection (<0.2 ppb) in the same soil extracts. On average, 98% of soil Se was not water-soluble. The distribution of total Se shows much less spatial variation than water-soluble Se in the areas sampled. Se shows correlation with organic carbon in soils and waters, suggesting its association with organic carbon. Ca shows some correlation to Se in acid extracts, but not in saturated-paste extracts or in waters. Total Se shows no significant correlation to Na, Mg, and total S in the soils. Se in saturated-paste extracts and water samples shows good correlations with Na, Mg, and SO₄, suggesting that evaporitic Na–Mg–sulfate minerals may temporarily concentrate water-soluble Se in shallow soils. The dissolution and precipitation of these Na–Mg–sulfate salts together with pH and oxidation–reduction conditions apparently control water-soluble Se distribution and mobilization in shallow subsurface environments.