Geochemistry of some rare earth elements in groundwater,Vierlingsbeek, The Netherlands

Groundwater samples were taken from seven bore holes at depths ranging from 2 to 41m nearby drinking water pumping station Vierlingsbeek, The Netherlands and analysed for Y, La, Ce, Pr, Nd, Sm and Eu. Shale-normalized patterns were generally flat and showed that the observed rare earth elements (REE) were probably of natural origin. In the shallow groundwaters the REEs were light REE (LREE) enriched, probably caused by binding of LREEs to colloids. To improve understanding of the behaviour of the REE, two approaches were used: calculations of the speciation and a statistical approach.For the speciation calculations, complexation and precipitation reactions including inorganic and dissolved organic carbon (DOC) compounds, were taken into account. The REE speciation showed REE(3+), REE(SO(4))(+), REE(CO(3))(+) and REE(DOC) being the major species. Dissolution of pure REE precipitates and REE-enriched solid phases did not account for the observed REEs in groundwater. Regulation of REE concentrations by adsorption-desorption processes to Fe(III)(OH)(3) and Al(OH)(3) minerals, which were calculated to be present in nearly all groundwaters, is a probable explanation.The statistical approach (multiple linear regression) showed that pH is by far the most significant groundwater characteristic which contributes to the variation in REE concentrations. Also DOC, SO(4), Fe and Al contributed significantly, although to a much lesser extent, to the variation in REE concentrations. This is in line with the calculated REE-species in solution and REE-adsorption to iron and aluminium (hydr)oxides. Regression equations including only pH, were derived to predict REE concentrations in groundwater. External validation showed that these regression equations were reasonably successful to predict REE concentrations of groundwater of another drinking water pumping station in quite different region of The Netherlands.     

Rare earth elements in ichthyoliths: Variations with redox conditions and depositional environment

A study has been made of the rare earth element (REE) geochemistry of ichthyoliths from six oceanic regions (Peru/Chile Shelf, Tyrrhenian Sea, Namibian Shelf, Cook Islands, Pacific Ocean and the Cape Basin), including both oxic and anoxic sedimentary depositional environments. The REE contents of vertebrae and scales of modern fish are extremely low (e.g. 0.01–0.06 μg g⁻¹ Nd), but REE are significantly enriched in ichthyoliths recovered from sediments (e.g. 0.78–1460 μg g⁻¹ Nd) Ichthyoliths from anoxic shelf sediments have low REE contents and positive or weakly negative Ce anomalies. Ichthyoliths from oxic deep-sea sediments have high REE contents and strongly negative Ce anomalies. The REE patterns reflect the heavy REE enrichment of sea water, but do not record the inter-oceanic differences shown by sea water. The Ce anomalies of deep-sea ichthyoliths both resemble sea waters and generally reflect inter-oceanic differences (more negative Ce anomalies in the Pacific than in the Atlantic ocean). The REE uptake by ichthyoliths appears to occur during very early diagenesis. The REE patterns are useful indicators of the redox status of the sedimentary depositional environments, and, for deep-sea ichthyoliths, provide an approximate record of the redox condition of contemporaneous sea water.     

Mineralogical and geochemical controls of arsenic speciation and mobility under different redox conditions in soil, sediment and water at the Mokrsko-West gold deposit, Czech Republic

Naturally contaminated soil, sediment and water at the Mokrsko-West gold deposit, Central Bohemia, have been studied in order to determine the processes that lead to release of As into water and to control its speciation under various redox conditions. In soils, As is bonded mainly to secondary arseniosiderite, pharmacosiderite and Fe oxyhydroxides and, rarely, to scorodite; in sediments, As is bonded mainly to Fe oxyhydroxides and rarely to arsenate minerals.The highest concentrations of dissolved As were found in groundwater (up to 1141 μg L^− 1), which mostly represented a redox transition zone where neither sulphide minerals nor Fe oxyhydroxide are stable. The main processes releasing dissolved As in this zone are attributed to the reductive dissolution of Fe oxyhydroxides and arsenate minerals, resulting in a substantial decrease in their amounts below the groundwater level. Some shallow subsurface environments with high organic matter contents were characterized by reducing conditions that indicated a relatively high amount of S^− 2,0 in the solid phase and a lower dissolved As concentration (70-80 μg L^− 1) in the pore water. These findings are attributed to the formation of Fe(II) sulphides with the sorbed As. Under oxidizing conditions, surface waters were undersaturated with respect to arsenate minerals and this promoted the dissolution of secondary arsenates and increased the As concentrations in the water to characteristic values from 300 to 450 μg L^− 1 in the stream and fishpond waters. The levels of dissolved As(III) often predominate over As(V) levels, both in groundwaters and in surface waters. The As(III)/As(V) ratio is closely related to the DOC concentration and this could support the assumption of a key role of microbial processes in transformations of aqueous As species as well as in the mobility of As.     

Groundwater geochemistry and its implications for arsenic mobilization in shallow aquifers of the Hetao Basin, Inner Mongolia

Arsenic concentrations in shallow groundwaters from the Hetao Basin of Inner Mongolia range between 0.6 and 572 microg/L. High As groundwaters generally occur in the shallow alluvial-lacustrine aquifers, which are mainly composed of black (or dark grey) fine sands in a reducing environment. They are characterized by high concentrations of dissolved Fe, Mn, HCO(3)(-), P and S(2-), and low concentrations of NO(3)(-) and SO(4)(2-). Low SO(4)(2-) coupled with high S(2-) suggests that SO(4)(2-) reduction has been an active process. In the reducing groundwaters, inorganic As(III) accounts for around 75% of total dissolved As. Total As contents in the sediments from three representative boreholes are observed to be 7.3-73.3 mg/kg (average of 18.9 mg/kg). The total As is mildly-strongly correlated with total Fe and total Mn, while a quite weak correlation exists between total As and total S, suggesting that the As is associated with Fe-Mn oxides, rather than sulfides in the sediments. It is found in the sequential extraction that chemically active As is mainly bound to Fe-Mn oxides, up to 3500 microg/kg. The mobilization of As under reducing conditions is believed to include reductive dissolution of Fe-Mn oxides and reduction of adsorbed As. Although exchangeable As is labile and very vulnerable to hydrogeochemical condition, the contribution is relatively limited due to the low concentrations. The competition between As and other anions (such as HPO(4)(2-)) for binding sites on Fe-Mn oxides may also give rise to the release of As into groundwater. Slow groundwater movement helps accumulation of the released As in the groundwaters.     

Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales

The importance of upland groundwater systems in providing a medium for nitrogen transformations and processes along flow paths is investigated within the Afon Gwy moorland catchment, Plynlimon, mid-Wales. Dissolved organic nitrogen (DON) was found to be the most abundant form of dissolved nitrogen (N) in most soils and groundwaters, accounting for between 47 and 72% of total dissolved nitrogen in shallow groundwater samples and up to 80% in deeper groundwaters. Groundwater DON may also be an important source of bio-available N in surface waters and marine systems fed by upland catchments. A conceptual model of N processes is proposed based on a detailed study along a transect of nested boreholes and soil suction samplers within the interfluve zone. Shallow groundwater N speciation reflects the soilwater N speciation implying a rapid transport mechanism and good connectivity between the soil and groundwater systems. Median nitrate concentrations were an order of magnitude lower within the soil zone (<5-31 microg/L) than in the shallow groundwaters (86-746 microg/L). Given the rapid hydrostatic response of the groundwater level within the soil zone, the shallow groundwater system is both a source and sink for dissolved N. Results from dissolved N(2)O, N(2)/Ar ratios and dissolved N chemistry suggests that microbial N transformations (denitrification and nitrification) may play an important role in controlling the spatial variation in soil and groundwater N speciation. Reducing conditions within the groundwater and saturated soils of the wet-flush zones on the lower hillslopes, a result of relatively impermeable drift deposits, are also important in controlling N speciation and transformation processes.     

Release of trace elements in wetlands: role of seasonal variability

Dissolved concentrations were determined for Fe, Mn, Al, Cu, Zn, La, U, Th, Cd and As in a wetland and its recipient stream to reveal the effect of seasonal changes in environmental conditions on the cycling and transfer of trace elements at the transition between terrestrial and aquatic ecosystems. These preliminary results from the wetland show marked seasonal changes in dissolved concentration for all elements except Zn and Cu. Concentrations are found to be low until about mid-February and then increase abruptly. The onset of trace element release appears to coincide with a marked decline in redox potential and increase of organic carbon content. Because this decline is itself correlated with a pronounced increase in temperature and dissolved Fe. Mn and organic carbon content, we suggest that the microorganisms which use soil iron and manganese oxy-hydroxides as electron acceptors catalyzed the change in redox conditions and induced an increase of DOC. Temporal changes were also observed in the recipient stream which showed marked positive concentration peaks during stormflow events (except Zn). The seasonal processes occurring in the wetland appear to play a major role in determining the amount of trace elements which are transferred from the wetland to the river.     

Manganese concentrations in Scottish groundwater

Groundwater is increasingly being used for public and private water supplies in Scotland, but there is growing evidence that manganese (Mn) concentrations in many groundwater supplies exceed the national drinking water limit of 0.05 mg l^− 1. This study examines the extent and magnitude of high Mn concentrations in groundwater in Scotland and investigates the factors controlling Mn concentrations. A dataset containing 475 high quality groundwater samples was compiled using new data from Baseline Scotland supplemented with additional high quality data where available. Concentrations ranged up to 1.9 mg l^− 1; median Mn concentration was 0.013 mg l^− 1 with 25th and 75th percentiles 0.0014 and 0.072 mg l^− 1 respectively. The Scottish drinking water limit (0.05 mg l^− 1) was exceeded for 30% of samples and the WHO health guideline (0.4 mg l^− 1) by 9%; concentrations were highest in the Carboniferous sedimentary aquifer in central Scotland, the Devonian sedimentary aquifer of Morayshire, and superficial aquifers. Further analysis using 137 samples from the Devonian aquifers indicated strong redox and pH controls (pH, Eh and dissolved oxygen accounted for 58% of variance in Mn concentrations). In addition, an independent relationship between Fe and Mn was observed, suggesting that Fe behaviour in groundwater may affect Mn solubility. Given the redox status and pH of Scottish groundwaters the most likely explanation is sorption of Mn to Fe oxides, which are released into solution when Fe is reduced.Since the occurrence of elevated Mn concentrations is widespread in groundwaters from all aquifer types, consideration should be given to monitoring Mn more widely in both public and private groundwater supplies in Scotland and by implication elsewhere.     

Biological reduction of uranium in groundwater and subsurface soil

Biological reduction of uranium is one of the techniques currently studied for in situ remediation of groundwater and subsurface soil. We investigated U(VI) reduction in groundwaters and soils of different origin to verify the presence of bacteria capable of U(VI) reduction. The groundwaters originated from mill tailings sites with U concentrations as high as 50 mg/l, and from other sites where uranium is not a contaminant, but was added in the laboratory to reach concentrations up to 11 mg/l. All waters contained nitrate and sulfate. After oxygen and nitrate reduction, U(VI) was reduced by sulfate-reducing bacteria, whose growth was stimulated by ethanol and trimetaphosphate. Uranium precipitated as hydrated uraninite (UO2 x xH2O). In the course of reduction of U(VI), Mn(IV) and Fe(III) from the soil were reduced as well. During uraninite precipitation a comparatively large mass of iron sulfides formed and served as a redox buffer. If the excess of iron sulfide is large enough, uraninite will not be oxidized by oxygenated groundwater. We show that bacteria capable of reducing U(VI) to U(IV) are ubiquitous in nature. The uranium reducers are primarily sulfate reducers and are stimulated by adding nutrients to the groundwater.     

Co-regulation of redox processes in freshwater wetlands as a function of organic matter availability?

Wetlands have important filter functions in landscapes but are considered to be the biggest unknowns regarding their element dynamics under global climate change. Information on sink and source function of sulphur, nitrogen, organic matter and acidity in wetlands is crucial for freshwater regeneration. Recent results indicate that redox processes are not completely controlled by the sequential reduction chain (that is electron acceptor availability) but that electron donor availability may be an important regulator. Our hypothesis was that only sites which are limited in their electron donor availability (low concentrations of dissolved organic carbon (DOC)) follow the concept of the sequential reduction chain. We compared the results of two freshwater wetland systems: 1) three forested fens within a boreal spruce catchment in a low mountain range in southern Germany (high DOC regime) and 2) three floodplain soils within a groundwater enrichment area in the Rhein valley in northwest Switzerland (low DOC regime). Micro scale investigations (a few cm(3)) with dialyse chambers as well as soil solution and groundwater concentrations at the forested fens (high DOC regime) indicated simultaneous consumption of nitrate and sulphate with release of iron, manganese and methane (CH(4)) as well as an enrichment in stable sulphur isotopes indicating a co-existence of processes attributed to different redox gradients. Soil and aquifer gas measurements down to 4.6 m at the groundwater enrichment site (low DOC regime and carbon limitation) showed extreme high rates of metabolism with carbon dioxide (CO(2))(,) dinitrous oxide (N(2)O) and CH(4) concentrations reaching fifty, thirty and three times atmospheric concentrations, respectively. Simultaneously, groundwater oxygen (O(2)) saturation was between 50 and 95%. We concluded that independent of DOC regime the sequential reduction chain was not a suitable concept in our systems. Instead of electron acceptor or donor availability micro site variability might explain the co-existence of redox processes within our sites.     

Movement of heavy metals into a shallow aquifer by leakage from sewage oxidation ponds

The concentrations of Mn, Ni, Cu, Cd and Cr were measured in a shallow perched groundwater aquifer which underlies the Dan Region Sewage Reclamation Project (Israel). The contribution of effluents to the groundwaters has been evaluated on the basis of chloride concentration. Groundwater which are estimated to contain more than 60% effluents showed a hundred-fold decrease in Cu and Mn at a distance of 650 m away from the ponds, as compared with the near ponds samples. Ni and Cd showed only a small decrease in concentration over a distance of 150 m, and then stayed constant. The concentrations of Cu and particularly of Mn in the groundwaters near the oxidation ponds is equivalent to or greater than in the ponds themselves. It is suggested that Cu and Mn are mobilized from the precipitated sludge into the interstitial waters. They percolate into the groundwater near the ponds and then are precipitated by increasing aeration during the movement of the water away from the pond area. Cd and Ni form stable soluble organic chelates which are only slightly removed by interaction with the sandy soil of the aquifer.     

Temperature-induced impacts on groundwater quality and arsenic mobility in anoxic aquifer sediments used for both drinking water and shallow geothermal energy production

Aquifers used for the production of drinking water are increasingly being used for the generation of shallow geothermal energy. This causes temperature perturbations far beyond the natural variations in aquifers and the effects of these temperature variations on groundwater quality, in particular trace elements, have not been investigated. Here, we report the results of column experiments to assess the impacts of temperature variations (5°C, 11°C, 25°C and 60°C) on groundwater quality in anoxic reactive unconsolidated sandy sediments derived from an aquifer system widely used for drinking water production in the Netherlands. Our results showed that at 5 °C no effects on water quality were observed compared to the reference of 11°C (in situ temperature). At 25°C, As concentrations were significantly increased and at 60 °C, significant increases were observed pH and DOC, P, K, Si, As, Mo, V, B, and F concentrations. These elements should therefore be considered for water quality monitoring programs of shallow geothermal energy projects. No consistent temperature effects were observed on Na, Ca, Mg, Sr, Fe, Mn, Al, Ba, Co, Cu, Ni, Pb, Zn, Eu, Ho, Sb, Sc, Yb, Ga, La, and Th concentrations, all of which were present in the sediment. The temperature-induced chemical effects were probably caused by (incongruent) dissolution of silicate minerals (K and Si), desorption from, and potentially reductive dissolution of, iron oxides (As, B, Mo, V, and possibly P and DOC), and mineralisation of sedimentary organic matter (DOC and P).     

Processes releasing arsenic to groundwater in the Caldes de Malavella geothermal area, NE Spain

Arsenic concentrations exceeding the World Health Organization drinking water guideline (10 μg/L) have been measured in thermal and non-thermal groundwaters from the Caldes de Malavella geothermal area (La Selva graben, NE Spain). The CO₂-rich Na-HCO₃ thermal waters (up to 60 °C at the spring) have elevated arsenic concentrations ([As_T] from 50 to 80 μg/L). The non-thermal waters are of Ca-Na-HCO₃-Cl type and have [As_T] between <1 and 200 μg/L, defining a hot-spot distribution. The present-day contribution of As from CO₂-rich thermal waters to non-thermal aquifers is very limited, as shown by the concentration of geothermal tracers such as Li and B. Redox-controlling processes appear to govern the mobility of As in the non-thermal waters. Arsenate is clearly predominant in most oxidizing groundwaters (>85% of As(V) over total As), whereas reducing, high-As groundwater reaches up to 100% in arsenite. The reductive dissolution of Fe(III) oxyhydroxides and the coupled release and reduction of adsorbed As explain the elevated dissolved arsenite (up to 190 μg/L) and Fe (up to 14 mg/L) content in the more reducing non-thermal groundwater. Conversely, the high levels of nitrate (up to 136 mg/L) ensure an oxidizing environment in most non-thermal groundwaters ([As_T] between <1 and 60 μg/L). Under these conditions, Fe(III) oxyhydroxides are stable and As release to groundwater is not related to their dissolution. Instead, dissolved arsenate concentrations up to 60 μg/L are explained by a competition for sorption sites with other species, mainly bicarbonate and silicic acid, while arsenate desorption due to pH increase is not considered a major process.     

Recovery from groundwater extraction in a small catchment area with crystalline bedrock and thin soil cover in Sweden

An experiment has been in progress since 1997 in a small catchment area (28,000 m(2)) with crystalline bedrock and thin soil cover to study the conceivable impact on groundwater conditions of tunneling and the use of groundwater. The impact on hydrology and hydrochemistry from intensive extraction of groundwater at a depth of 50 m in the bedrock has been studied at Lake G?rdsj?n in Sweden. The catchment area was first monitored under pristine conditions, followed by four and a half years of extraction and then a recovery phase. The geological conditions result in a low buffer capacity and high sensitivity to acidification. During the period of extraction, the surface runoff decreased by approximately 50% compared to a nearby reference area. The groundwater extraction caused increased fluctuation in groundwater levels in a wetland, which in turn caused oxidation of reduced sulfur to sulfate. The sulfate concentrations increased almost 100-fold in some instances, causing a lowering of the pH by one unit in shallow groundwater. Since extraction of the groundwater was discontinued, the pH has gradually risen and the sulfate concentrations have decreased. However, the concentration of sulfate in groundwater in the wetland has remained stable at approximately double the pre-experiment levels. Magnesium concentrations were lower after the experiment, caused by exhaustion of the magnesium pool in the wetland through acidification. The extraction of water from the bedrock shortened the retention times and increased the recharge of groundwater in the bedrock. After extraction was terminated, the groundwater levels in the boreholes recovered within a month to levels similar to those before extraction. The hydrochemistry of the bedrock groundwater, which was strongly affected by the hydrochemistry of shallow groundwater during the experiment, has also gradually begun to regain its pre-extraction signature. However, the surface runoff has remained low during the first 2 years of recovery, at about 60% of the volume compared to the unaffected catchment area. This could be explained by delayed recovery in resaturation of the shallow rock that was unsaturated during the experiment.     

The influence of the abandoned Kalecik Hg mine on water and stream sediments (Karaburun,Izmir, Turkey)

This study covers the geochemical investigations on water and stream sediments to evaluate the influence from the abandoned Kalecik Hg mine. The groundwater samples (S5, S8, S9, WW10) are neutral, slightly alkaline waters which have pH values varying between 7.3 and 7.5. Electrical conductivity (EC) values of groundwaters for spring samples are low (250-300 microS/cm). However, groundwater obtained from a deep well has a higher EC value of 950 microS/cm. Hg concentrations of groundwater samples vary between 0.01 and 0.13 microg/l. Hg concentrations of other water samples taken from mining area from surface waters and adits are between 0.10 and 0.99 microg/l. Adit water (A4) collected at the mine has the highest Hg content of 0.99 microg/l and a pH of 4.4. Trace element concentrations of mine water samples show variable values. As is observed only in MW1 (310 microg/l). A4 was enriched in Cd, Co and Cr and exceed the Turkish drinking water standards (Türk Standartlari Enstitüsü, 1997). Cu concentrations vary between 6.0 and 150 microg/l and are below the Turkish water standards. Mn concentrations in mine waters are between 0.02 and 4.9 mg/l. Only for sample A4 Mn value (4.9 mg/l) exceeds the standard level. Ni was enriched for all of the mine water samples and exceeds the safe standard level (20 microg/l) for drinking water. Of the major ions SO(4) shows a notable increase in this group reaching 650 mg/l that exceeds the drinking water standards. Stream sediment samples have abnormally high values for especially Hg and As, Sb, Ni, Cr metals. With the exception of sample Ss6 of which Hg concentration is 92 mg/kg, all the other samples have Hg contents of higher than 100 mg/kg. Pollution index values are significantly high and vary between 69 and 82 for stream sediment samples.     

Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China

High arsenic groundwater in the Quaternary aquifers of Datong Basin, northern China contain As up to 1820 µg/L and the high concentration plume is located in the slow flowing central parts of the basin. In this study we used hydrochemical data and sulfur isotope ratios of sulfate to better understand the conditions that are likely to control arsenic mobilization. Groundwater and spring samples were collected along two flow paths from the west and east margins of the basin and a third set along the basin flow path. Arsenic concentrations range from 68 to 670 µg/L in the basin and from 3.1 to 44 µg/L in the western and eastern margins. The margins have relatively oxidized waters with low contents of arsenic, relatively high proportions of As(V) among As species, and high contents of sulfate and uranium. By contrast, the central parts of the basin are reducing with high contents of arsenic in groundwater, commonly with high proportions of As(III) among As species, and low contents of sulfate and uranium. No statistical correlations were observed between arsenic and Eh, sulfate, Fe, Mn, Mo and U. While the mobility of sulfate, uranium and molybdenum is possibly controlled by the change in redox conditions as the groundwater flows towards central parts of the basin, the reducing conditions alone cannot account for the occurrence of high arsenic groundwater in the basin but it does explain the characteristics of arsenic speciation. With one exception, all the groundwaters with As(III) as the major As species have low Eh and those with As(V) have high Eh. Reductive dissolution of Fe-oxyhydroxides or reduction of As(V) are consistent with the observations, however no increase in dissolved Fe concentration was noted. Furthermore, water from the well with the highest arsenic was relatively oxidizing and contained mostly As(V). From previous work Fe-oxyhydroxides are speculated to exist as coatings rather than primary minerals.The wide range of δ³⁴S_[SO4] values (from − 2.5 to + 36.1‰) in the basin relative to the margins (from + 8‰ to + 15‰) indicate that sulfur is undergoing redox cycling. The highly enriched values point to sulfate reduction that was probably mediated by bacteria. The presence of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is also evidence of microbial reactions. The depleted signatures indicate that some oxidation of depleted sulfide occurred in the basin. It must be noted that the samples with depleted sulfur isotope values have very low sulfate concentrations and therefore even a small amount of sulfide oxidation will bias the ratio. No significant correlation was observed between δ³⁴S_[SO4] values and total arsenic contents when all the samples were considered. However, the wells in the central basin do appear to become enriched in δ³⁴S_[SO4] as arsenic concentration increases. Although there is evidence for sulfate reduction, it is clear that sulfate reduction does not co-precipitate or sequester arsenic. The one sample with high arsenic that is oxidizing cannot be explained by oxidation of pyrite and is likely an indication that there are multiple redox zones that control arsenic speciation but not necessarily its mobilization and contradict the possibility that Fe-oxyhydroxides sorb appreciable amounts of arsenic in this study area. It is evident that this basin like other two young sedimentary basins (Huhhot and Hetao in Inner Mongolia) of northern China with high arsenic groundwater is transporting arsenic at a very slow rate. The data are consistent with the possibility that the traditional models of arsenic mobilization, namely reductive dissolution of Fe-oxyhydroxides, reduction of As(V) to more mobile As(III), and bacteria mediated reactions, are active to varying degrees. It is also likely that different processes control arsenic mobilization at different locations of the basin and more detailed studies along major flow paths upgradient of the high arsenic aquifers will shed more light on the mechanisms.     

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), anions (Cl⁻, NO₃⁻, SO₄²⁻), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54-195 (mean 105 ± 48, n = 10), and 27-243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20-50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4-73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6-215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m⁻¹ mg⁻¹ L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5-3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5-2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3-4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC (R² = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.     

Seltenerdelement-, Yttrium-Gehalte und Bleiisotope in Thermal- und Mineralwässern des Schwarzwaldes

In the Black Forest, mineral waters from five wells in crystalline basement (granite and gneisses), their probable source rocks and the experimental leachates were evaluated for rare earth elements (REE), yttrium contents, and lead isotope ratios. The distribution of REE and Y, and the Pb-isotope ratios are powerful tools to identify the most likely type of rock that controls cation contents of the mineral water. Granites and gneisses lead to REE patterns with varying negative europium anomalies in waters; i. e., gneisses have a tendency for positive or only slightly negative europium anomalies in fluids, whereas granites exhibit negative anomalies. The comparison of REE and Y in the leachates and waters shows that these elements are characteristically redistributed during water-rock inter-action between rock-forming and accessory minerals, surface layers and adsorption films. REE and Y are leachable in the aquifer rocks, in which light REE are partially impoverished. REE and Y in samples from surface outcrops show enhanced leachable fractions. In alterated rocks, large fractions of ²⁰⁶ Pb are definitely leached from other solid phases than ²⁰⁷ Pb and ²⁰⁸ Pb.     

Migration forms of trace elements in natural fresh waters and the effect of the water storage

The concentration and physico-chemical state of 18 trace and major elements in river and lake waters were studied as a function of time (2h-35 days), for which the samples of water were stored in polyethylene bottles. The methods of investigation were dialysis, centrifugation, ion exchange filtration and electrophoresis, combined with instrumental neutron activation analysis. It was shown that considerable amounts of Mn, Co, Al, Sc, La, Ce, Fe, Cr and Th may be lost by the adsorption to the walls of polyethylene containers and that the ratio of forms of existence of Co, Mn, La, Ce, Sm, Fe, and Cr in the solution may be substantially changed during the storage for one week or more. Probable interpretations of these changes are given. Conclusions are also drawn about the state of individual trace and major elements in the waters studied.     

Hydrogeochemistry: an investigation tool to evaluate infiltration into large moving rock masses (case study of La Clapière and Séchilienne alpine landslides)

Isotopic and hydrogeochemical methods have been used to investigate groundwater movement inside the La Clapière and Séchilienne alpine landslides in southern France. The δ¹⁸O data were used to determine the infiltration altitudes of the two areas. The infiltration results indicate that the landslides are recharged from beyond the landslides' perimeters. Hydrogeochemical data on major ions were collected from springs. Numerical simulations of water–rock interactions were then undertaken. The major petrographic contrast between the limited sedimentary rocks and the more common micagneiss/micaschist results in a marked change between the measured and calculated groundwater contents. This contrast of 800 mg/l of SO₄ in the Triassic rocks but only 100 mg/l for the waters from the metamorphic strata at La Clapière is significant. Two different groundwaters have been identified in both landslides: (1) a perched shallow saturated zone near the slope summit; and (2) a deep saturated zone located at the foot of the slope. Chemical monitoring of spring waters in the two zones has allowed an assessment of the infiltration within the slope over time. There is a good correlation between the sulphate content of the perched waters and rate of slope movement, with a sulphate dilution peak corresponding to an acceleration in the movement of the landslip. However, there is no correlation between the chemistry of the deep aquifer and the speed of movement. It would appear therefore that the hydromechanical behaviour of the landslide depends on the vertical leakage from the perched aquifer down to the basal aquifer and the near-surface effects of the water movement. Electronic Publication