Applied Geochemistry (v.25, #11)
Publisher’s note (iii).
Mobility of trace and potentially harmful elements in the environment from high sulfur Indian coal mines by B.P. Baruah; Puja Khare (1621-1631).
► Coal mine rejects have high acid producing potential and high concentration of toxic elements. ► The major processes that control release of trace and PHEs are acidic leaching, adsorption and precipitation. ► Critical loads of PHEs in mine waters exceeded regulatory levels. ► The trace and PHEs are associated with mineral matter and sulfides.Coal mine rejects and sulfide bearing coals are prone to acid mine drainage (AMD) formation due to aqueous weathering. These acidic effluents contain dissolved trace and potentially harmful elements (PHEs) that have considerable impact on the environment. The behavior of these elements in AMD is mainly controlled by pH. The focus of the present study is to investigate aqueous leaching of mine rejects for prediction of acid producing potential, rates of weathering, and release of PHEs in mine drainage. Mine reject (MR) and coal samples from the active mine sites of Meghalaya, India typically have high S contents (1.8–5.7% in MR and 1.7–4.7% in coals) with 75–90% of the S in organic form and enrichment of most of the PHEs in rejects. Aqueous kinetic leaching experiments on mine rejects showed high acid producing potential and release of trace and potentially harmful elements. The elements (Sb, As, Cd, Cr, Co, Cu, Pb, Mn, Ni, V and Zn) in mine sample leachates are compared with those in mine waters. The concentrations of Al, Si, P, K, Ti, Mn, Fe, Co, Ni, Cu, Zn and Pb are found to increase with leaching time and are negatively correlated with pH of the solution. The processes controlling the release of these elements are acid leaching, precipitation and adsorption. The critical loads of PHEs in water affected by AMD are calculated by comparing their concentrations with those of regulatory levels. The Enrichment Factors (EFs) and soil pollution indices (SPIs) for the elements have shown that PHEs from coal and mine reject samples are mobilized into the nearby environment and are enriched in the associated soil and sediment.
Multi-method characterization of DOM from the Turia river (Spain) by Sergio Navalon; Mercedes Alvaro; Isabel Alcaina; Hermenegildo Garcia (1632-1643).
► Analysis of the Turia river wáter. ► Fractioning of a fresh wáter with analysis of organic compounds. ► Determination of the composition of a natural fresh wáter.Water concentrates from Turia river (1.5 mg L−1 total organic C) obtained by nanofiltration (membrane mass cut-off 90 Da) were fractioned by non-ionic Amberlite resins (DAX8 and XAD4) to afford three samples termed as hydrophobic acid (50%), transphilic acid (24%) and hydrophobic neutral (12%). If a nanofiltration membrane 270 Da mass cut-off is used then about 50% of dissolved organic matter is not retained. These three fractions were characterized by analytical and spectroscopic techniques (1H NMR, MALDI–TOF-MS, ESI–API-MS, ESI–MS/MS). Overall, these data are compatible with the presence of oligosaccharides, oligopeptides and fatty acids as the main components of dissolved organic matter. Particularly revealing was the information from MALDI–TOF-MS and ESI–MS/MS where series of compounds differing in the number of hexose units were identified. The three fractions have many spectroscopic similarities and, particularly the hydrophobic and transphilic ones, are really almost identical. This similarity in the fraction composition shows that the conventional fractionation procedure is inefficient as a standard general method for separation of different compound types. The composition of dissolved organic matter was confirmed, and some individual organic compounds identified, by GC–MS analysis of the silylated derivatives obtained by reacting the fractions with a mixture of N,O-bis(trimethylsilyl)trifluoroacetamide with trimethylchlorosilane (10%). Thus, rather surprisingly, the dissolved organic matter of this natural raw water is predominantly composed of a relatively simple mixture of a few types of compounds with molecular weights well below 1100 Da (about six hexose units). These results, particularly the absence of detectable amounts of high molecular weight humic acids and low molecular weight phenolic compounds indicates that trihalomethanes formed in the water disinfection process by Cl2 really derive from oligosaccharides and oligopeptides. Also, the data suggests alternative strategies to effect a more efficient fractionation of the dissolved organic matter.
Geochemical tracing and hydrogeochemical modelling of water–rock interactions during salinization of alluvial groundwater (Upper Rhine Valley, France) by Y. Lucas; A.D. Schmitt; F. Chabaux; A. Clément; B. Fritz; Ph. Elsass; S. Durand (1644-1663).
► Major and trace elements along with strontium and uranium isotopic ratios show that groundwater geochemical characteristics along the saline plumes cannot reflect a conservative mixing. ► A coupled hydrogeochemical model demonstrates that cationic exchange between alkalis from polluted waters and alkaline-earth elements from montmorillonite present in the host rock of the aquifer is the primary process. ► The model requires only a small amount of montmorillonite. ► It is necessary to consider the pollution history to explain the important chloride, sodium and calcium concentration modifications. ► The model shows that the rapidity of the cationic exchange reactions insures a reversibility of the cation fixation on clays in the aquifer.In the southern Upper Rhine Valley, groundwater has undergone intensive saline pollution caused by the infiltration of mining brines, a consequence of potash extraction carried out during the 20th century. Major and trace elements along with Sr and U isotopic ratios show that groundwater geochemical characteristics along the saline plumes cannot reflect conservative mixing between saline waters resulting from the dissolution of waste heaps and one or more unpolluted end-members. The results imply the occurrence of interactions between host rocks and polluted waters, and they suggest that cationic exchange mechanisms are the primary controlling process. A coupled hydrogeochemical model has been developed with the numerical code KIRMAT, which demonstrates that cationic exchange between alkalis from polluted waters and alkaline-earth elements from montmorillonite present in the host rock of the aquifer is the primary process controlling the geochemical evolution of the groundwater. The model requires only a small amount of montmorillonite (between 0.75% and 2.25%), which is in agreement with the observed mineralogical composition of the aquifer. The model also proves that a small contribution of calcite precipitation/dissolution takes places whereas other secondary mineral precipitation or host rock mineral dissolution do not play a significant role in the geochemical signature of the studied groundwater samples. Application of the model demonstrates that it is necessary to consider the pollution history to explain the important Cl, Na and Ca concentration modifications in groundwater samples taken over 2 km downstream of waste heaps. Additionally, the model shows that the rapidity of the cationic exchange reactions insures a reversibility of the cation fixation on clays in the aquifer.
The role of dissolved molecular oxygen in abiotic pyrite oxidation under acid pH conditions – Experiments with 18O-enriched molecular oxygen by Claudia Heidel; Marion Tichomirowa (1664-1675).
► A small amount of molecular oxygen is permanently incorporated into sulfate during pyrite oxidation. ► Molecular oxygen may be incorporated into sulfate by sulfite oxidation and tetrathionate oxidation. ► Molecular oxygen is incorporated into water molecules during its cathodic reduction. ► Molecular oxygen mainly accepts electrons from pyrite and minor from dissolved and adsorbed ferrous iron.Several O isotope studies have shown that SO 4 2 - produced from aqueous pyrite oxidation mainly contains water-derived O and minor atmospherically-derived O2. However, the incorporation of O2 into SO 4 2 - has been shown to decrease continuously during pyrite oxidation experiments. Hence, it remains uncertain if (and how) O2 is permanently incorporated into SO 4 2 - during pyrite oxidation.Abiotic aerobic batch pyrite oxidation experiments in aqueous solutions were performed under acid pH conditions. After 151 days, 18O-enriched O2 was injected into the headspace of the reaction vessels. Increasing δ 18 O SO 4 values with increasing injection volume of 18O-enriched O2 indicated the permanent incorporation of about 9% O2 into the produced SO 4 2 - during pyrite oxidation from 151 to 201 days. Molecular oxygen may be incorporated into SO 4 2 - by oxidation of the S intermediate species sulfite (and maybe tetrathionate) into SO 4 2 - . However, only 4% of the O2 consumed during the experiments was incorporated into SO 4 2 - . Slightly increased δ 18 O H 2 O values from experiments with the largest injection of 18O-enriched O2 indicated the incorporation of O2 into water molecules which may proceed during the cathodic reduction of O2. Thus, O2 was an important electron acceptor under aerobic acid conditions. The observed ε SO 4 - O 2 value indicated that the oxidation of dissolved Fe2+ by O2 did not play an important role. Furthermore, the lack of 32S enrichment in SO 4 2 - compared to pyrite indicated that the oxidation of adsorbed Fe2+ by O2 should not be a dominant mechanism, although it may be catalyzed onto the pyrite surface. Hence, O2 should accept electrons predominantly from pyrite.
Assessing the natural recovery of a lake contaminated with Hg using estimated recovery rates determined by sediment chronologies by Matthew J. Parsons; David T. Long; Sharon S. Yohn (1676-1687).
► Identifying the cause of Hg contamination via correlations to iron ore production. ► Using Hg:Al ratio to show changes in pathway from a point to non-point source. ► Overcoming challenges to age determination using event-based dating. ► Using sediment cores to estimate recovery rates and identify arrested recovery.Deer Lake is an impoundment located near Ishpeming, Michigan, USA. Iron mining assay laboratories located in Ishpeming disposed of Hg salts to the city sewer whose outfall was located along an inlet to Deer Lake. An effort to remediate the system in the mid 1980s which consisted of drawing down water in the impoundment in order to volatize Hg from the sediments did not result in recovery of the system. Since the mid 1990s, the remediation strategy has been to allow the continual burial of the contaminated sediments, i.e., natural recovery. The goal of this study was to assess the effectiveness of this strategy. This was accomplished by investigating the state of the system in terms of its recovery and estimating the time frame for recovery. Sediment cores were collected in 2000 to determine historical trends in accumulation rates and concentrations of Hg and other metals. Sedimentation rates and sediment ages were estimated using 210Pb. Event-based dating (e.g., peak of 137Cs in 1963) was used to supplement 210Pb data due to non-monotonic features in the 210Pb profile and activities that were not at supported levels at the base of the core. Selected results are that: (1) drawdown significantly influenced sedimentation patterns causing slopes for 210Pb profiles that reflected the influx of older sediment, (2) periods of Fe production correlate to Hg loading indicating the point source for contamination, a relationship not previously identified, (3) Hg:Al ratios indicate a recent change to a watershed pathway for Hg loading and (4) Hg concentrations had decreased from their peak, remain elevated, and were increasing after 1997. The cause of the recent Hg concentrations may be related to influx of contaminated watershed soils or sediments. Estimating the time frame for recovery is challenging in this system because the process of natural recovery seems to have been arrested and deeper, uncontaminated sediments, were not recovered as a basis for reference. However, a recovery to background conditions is likely not achievable since rates of Hg loading to nearby lakes and the current rate of atmospheric deposition are greater than an estimate of background conditions for Deer Lake. Assuming recovery continued after 2000, estimates of the time required for recovery varied based on the system state used to define it (e.g., recent rates of wet Hg deposition or Hg surface concentrations/fluxes from similar systems), but were less than 12 a. However, the recent increasing values of recovery indicators (e.g., Hg concentrations) suggests that these estimates are conservative and will be longer if recovery remains arrested, which may in part be due to the legacy of Hg contamination on the landscape. This study shows that estimates of recovery of highly disturbed lake systems can be made in the absence of within lake reference conditions by using comparisons to reference systems and challenges of estimating ages from atypical 210Pb activity profiles can be overcome in part using event-based dating techniques.
Effects of desferrioxamine-B on the release of arsenic from volcanic rocks by Barbara Casentini; Maurizio Pettine (1688-1698).
►Origin of arsenic in volcanic aquifers. ►The ability of siderophore to complex iron can trigger arsenic mobilization from volcanic rocks. ►Levels above 250 μM Dfob siderophores noticeably enhance arsenic release in lava, tuff, peperino and unconsolidated fallout deposits within 30 days period. ►Arsenic released is correlated to iron release. As/Fe trend shape evidenced different release mechanisms in the studied volcanic rocks, related to the peculiarity of As distribution on the surface and the strength of Fe bonds present in the rocks. ►The mobilized amount of As significantly correlates with released Al, Si, Mn and Fe as major rock constituents and V, Ga, Sb as minor elements commonly found in geothermal fluids.Microorganisms play an important role in As mobilization into groundwater by directly influencing As speciation or indirectly inducing solubilisation from As-bearing phases, such as Fe, Mn and Al oxides. Iron oxide dissolution could also be induced by siderophores, small-molecule compounds produced by microorganisms to favour Fe uptake. Well waters exceeding the potable water limit of 10 μg As L−1 (0.133 μM) have been widely reported in geothermal areas. Mechanisms responsible for these high As concentrations have not yet been thoroughly elucidated and the complexity of As mobilization in volcanic aquifers is still open to multiple interpretations. The present study was based on batch release experiments aimed at verifying and quantifying the effect of siderophores on As mobilization from volcanic rocks (lava, tuff, peperino and fallout deposit) at different pH and ligand concentration. In the experiments the siderophore trihydroxamate desferroxamine B (Dfob) was used and its effect on As release from volcanic rocks was manifest after the first days. The most favourable pH for As release was pH 6 while concentrations above 250 μM Dfob considerably enhanced As and Fe concentrations in solution. The As release from rocks was between 2.0–10% at pH 6 and 2.4–8.8% at pH 8. The As/Fe ratio in solution changed with time suggesting different release mechanisms and higher mobility of As compared to Fe during the first phase of the experiment. The presence of siderophore increased Fe dissolution rates up to 10 orders of magnitude. The As release correlated with Al, Mn, Fe, Si, V, Ga and Sb and the release of all these elements increased with increasing Dfob concentration. In alkaline environments also Cu, Zn and Pb were mobilized. The presence of siderophores represents a possible trigger for As mobilization from iron binding minerals to the water phase, with interesting implications for groundwater quality, plant uptake and bacterial communities.
Temporal changes in tree-ring nitrogen of Pinus thunbergii trees exposed to Black-tailed Gull (Larus crassirostris) breeding colonies by Lopez C.M. Larry; Mizota Chitoshi; Yamanaka Toshiro; Nobori Yoshihiro (1699-1702).
► N concentration and isotope ratio on tree-rings can be an important tool to infer past N soil conditions where trees grow. ► Changes in avian population on established or new breeding grounds caused by natural or anthropogenic mechanism could be inferred from the analysis shown in this paper. ► The property of trees to retain N concentration and N isotope characteristics is found in Pinus thunbergii. The use of other trees for similar analysis have to be determined because other species (Pinus densiflora, for example) do not have this property.Natural abundances of 15N/14N ratios (commonly designated by δ 15N notation) of annual rings from Pinus thunbergii trees were determined after transplantation from a nursery to breeding colonies of Black-tailed Gull (Larus crassirostris) in Miyagi and Aomori and a control site in Yamagata, in northeastern Japan. Tree-rings were collected in July/August/September, 2009. Transplanting was conducted in the year 2000 in the Miyagi site, whereas there is no information about transplanting data in the Aomori and Yamagata sites. Soils associated with piscivorous (fish eating) avian colonies receive large seasonal input of organic N in the form of feces. The organic N is microbiologically transformed into inorganic N in soils, from which P. thunbergii derives its N. The resulting NH 4 - and NO 3 - N are characterized by distinctly heavy δ 15N ratios, due to coupled processes of mineralization, volatilization, nitrification and denitrification of feces. In general, total N concentration along with δ 15N values stored in the annual rings of P. thunbergii increased steadily after transplanting from the nursery to locations under continued avian N input. Tree-ring N content and isotopic ratios provided a reliable record of past annual available soil N caused by changes in the Black-tailed Gull population, and thus can serve as an environmental tool to estimate past avian population dynamics.
Effects of long-term irrigation with treated wastewater. Part I: Evolution of soil physico-chemical properties by Lobna Gharbi Tarchouna; Patricia Merdy; Michel Raynaud; Hans-Rudolf Pfeifer; Yves Lucas (1703-1710).
► The long-term impact of irrigation on a Mediterranean sandy soil irrigated with Treated wastewater (TWW) was beneficial with regard to water and nutrient supplying. ► The exchangeable cations was not fixed on the exchange complex but partly stored as labile salts or in concentrated soil solution. ► Both saturated and unsaturated hydraulic conductivity exhibited a significant diminution in the irrigated soil, but remained high enough to prevent soil salinization. ► Exchangeable Sodium Percentage (ESP) exhibited high values (20% on average) and the soil organic carbon was lowered due to irrigation. ► No significant effect was noticed on soil mineralogical composition due to irrigation.The long-term impact of irrigation on a Mediterranean sandy soil irrigated with Treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 years experiment. In this first part, the evolution of the physico-chemical soil properties was described. The irrigation with TWW was beneficial with regard to water and nutrient supplying. All the exchangeable cations other than K+ were higher in the irrigated soil than in the reference one. A part of the exchangeable cations was not fixed on the exchange complex but stored as labile salts or in concentrated soil solution. Despite the very sandy soil texture, both saturated and unsaturated hydraulic conductivity exhibited a significant diminution in the irrigated soil, but remained high enough to allow water percolation during rainy periods and subsequent leaching of accumulated salts, preventing soil salinization. In the irrigated soil, exchangeable sodium percentage (ESP) exhibited high values (20% on average) and the soil organic C was lower than in the reference. No significant effect was noticed on soil mineralogical composition due to irrigation.
Effects of long-term irrigation with treated wastewater. Part II: Role of organic carbon on Cu, Pb and Cr behaviour by Lobna Tarchouna Gharbi; Patricia Merdy; Yves Lucas (1711-1721).
► Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil, given that the domestic TWW has low Cu, Cr, and Pb concentrations. ► The nature of the soil organic carbon (SOC) is influencing the potential mobility of the studied metals: irrigation lowered the Humic Acids (HA) and Non-Humified Fractions of the SOC and made the Fulvic Acids (FA) fraction more mobile. ► Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. ► Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. ► Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.The long-term impact of irrigation on a Mediterranean sandy soil irrigated with treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 year experiment. In this second part, we focused on Cu, Cr and Pb behaviour in relation with soil organic carbon (SOC). Soil samples were collected every 3 months during 2 years at the depths 0–20, 20–40 and 40–60 cm and were analysed for exchangeable and total metals, organic carbon content, metal sequential extraction and humic substances – Humic Acids (HA), Fulvic Acids (FA) and Non-Humified Fraction (NHF). Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil. Irrigation lowered the HA and NHF fractions of SOC and made the FA fraction more mobile. Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.
Rhizosphere and flooding regime as key factors for the mobilisation of arsenic and potentially harmful metals in basic, mining-polluted salt marsh soils by Antonio María-Cervantes; Héctor M. Conesa; María Nazaret González-Alcaraz; José Álvarez-Rogel (1722-1733).
► The influence of rhizosphere in pH and Eh depends of the plant species. ► Changes in Eh and pH after flooding and rewetting mobilise metals into soil solution. ► The risk assessment of polluted salt marshes should take into account flood dynamics.The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536 mg kg−1 As, 37 mg kg−1 Cd, 6746 mg kg−1 Pb, 15,320 mg kg−1 Zn). The results show that the changes in redox conditions (from 300 mV to −100 mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100 μg L−1 Cd, 30 μg L−1 Pb, 7 mg L−1 Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120 μg L−1 Cd and 50 μg L−1 Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation.
The origins and behaviour of carbon in a major semi-arid river, the Murray River, Australia, as constrained by carbon isotopes and hydrochemistry by Ian Cartwright (1734-1745).
► δ 13C and concentrations of DIC in Murray River controlled by mineralisation of organic carbon and evasion. ► Murray River is source of atmospheric CO2. ► In-river processing of carbon results in difficulties in determining carbon sources. δ 13C values of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate organic C (POC) together with δ 18O and δ 2H values of water, δ 34S values of dissolved SO4, and major ion concentrations were measured in the Murray River and its tributaries between November 2005 and April 2007 to constrain the origins and behaviour of riverine C. δ 13CDIC values in the Murray River vary between −9.5 and −4.7‰ with a range of <3‰ within any sampling round. δ 13CDIC values of the tributaries are −11.0‰ to −5.1‰. DIC concentrations of the Murray River increase from ∼25 mg/L in the middle and upper reaches of the river to 45–55 mg/L in the lower reaches. However, the mass ratio of DIC as a proportion of the total dissolved solids (TDS) decreases from ∼0.6–0.7 in the headwaters to ∼0.2–0.3 in the lower reaches of the river, with similar downstream changes in DIC/Cl ratios. This precludes simple evaporative concentration of DIC and is interpreted as the river evading CO2; this interpretation is consistent with pCO2 values that are in the range 550–11,200 ppm volume (ppmv), which are far higher than those in equilibrium with the atmosphere (∼360 ppmv). The δ 13CDIC values are similar to those that would be produced by the weathering of marine limestone (δ 13C ∼ 0‰). However, the lack of marine limestones cropping out in the Murray–Darling Basin and the relatively uniform δ 13CDIC values of the Murray River (even in upland reaches where the dominant rock types are metamorphosed silicates and granites) make this unlikely. Rather the high pCO2 values and δ 13CDIC values are best explained by a combination of mineralisation of low δ 13C organic C and evasion to the atmosphere. The rate of these two processes may attain near steady state and control both DIC concentrations and δ 13C values.
Mobility of metals in nickel mine spoil materials by Sophie Raous; Thierry Becquer; Jérémie Garnier; Éder de Souza Martins; Guillaume Echevarria; Thibault Sterckeman (1746-1755).
► This work allowed us to check characteristics of chromium and nickel speciation in leachates. ► Garnieritic spoil is a source of nickel through small size colloids or precipitate dissolution. ► Chromium could be released from garnierite and reached 1.5 mg L−1 after 40 days of leaching. ► N fertilisation led to an increase in Ni and Mg and a slight decrease in Cr released into the leachate. ► KH2PO4 extraction demonstrates the existence of large amounts of exchangeable CrVI in limonite.An understanding of the biogeochemical behaviour of metals in mine spoil materials is a prerequisite to rehabilitate Ni mining sites. The objective of this study was to characterize the fate of metals in different Ni ore spoil materials as influenced by hydrological conditions and fertilisation practices. In tropical ultramafic complexes, the different stages of lateritic weathering lead to two types of ores, and therefore, to two spoil types. They are mainly either a clay-rich saprolite, so-called “garnierite”, enriched in phyllosilicates, or a limonitic material, enriched in Fe oxides. Lysimeter columns were designed to monitor leaching waters through both spoil materials. The garnieritic spoil released higher concentrations of Mg (mean = 2.25 mg L−1), Ni (0.39 mg L−1) and Cr (1.19 mg L−1) than the limonitic spoil (Mg = 0.5 mg L−1; Ni = 0.03 mg L−1 and Cr = 0.25 mg L−1). Chromium was mainly in an anionic form in leaching solutions. As exchangeable pools of Cr(VI) in limonite (980 mg kg−1 of KH2PO4-extractable Cr) are considerable its release in water may still occur in the case of a pH increase. In mixed spoil, metal concentrations were almost as low as in the limonitic one. The effect of mineral-N fertilisation was a strong release of cations (Ni, Mg) into the leachate. Phosphate amendment did not affect the soil solution composition under experimental conditions.
Distribution, behavior, and transport of inorganic and methylmercury in a high gradient stream by J.R. Flanders; R.R. Turner; T. Morrison; R. Jensen; J. Pizzuto; K. Skalak; R. Stahl (1756-1769).
► Sources of inorganic mercury widespread in high-gradient fluvial system decades after mercury use ceased in watershed. ► Soils release more inorganic mercury than sediment, primarily complexed by colloids. ► Methylmercury is produced in wide range of habitats despite the high gradient and coarse-grained nature of river. ► Methylmercury under complex physical and chemical controls, including temperature, bioavailable mercury, and substrates (carbon and electron acceptors).Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14 km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1 N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg.
Hydrochemical characteristics and brine evolution paths of Lop Nor Basin, Xinjiang Province, Western China by Lichun Ma; Tim K. Lowenstein; Baoguo Li; Pingan Jiang; Chenglin Liu; Junpin Zhong; Jiandong Sheng; Honglie Qiu; Hongqi Wu (1770-1782).
► The paper describes the principal hydrochemical features of the Lop Nor basin, the terminal point of China’s largest endorheic basin (Tarim basin), with emphasis on the chemical composition of inflow waters and groundwater brines. ► The paper applies principles of brine evolution and chemical divides to calculate brine evolution pathways and mineral sequences, using the computer program EQL/EVP. ► The results are compared with the mineral assemblages found in a 225 m-long core from the Lop Nor basin, to interpret the primary inflow water sources to the Lop Nor basin and the history of inflow water response to regional climatic changes.This study was carried out in the Lop Nor basin, a large arid closed drainage basin in Western China. The objective was to contribute to the understanding of the hydrological and hydrochemical processes of the Lop Nor basin by analysis of the chemical composition of different water sources and associated mineralogical characteristics of the playa sediments. The dominant river inflow waters to the Lop Nor basin are of the Na–Mg–Ca–SO4–Cl–HCO3 type. Spring inflow is dominated by Na+ and Cl−. Present-day concentrated groundwater brines vary little in the study area and are consistently rich in Na+ and Cl− and poor in Ca2+ and HCO 3 - + CO 3 2 - , but also contain a considerable amount of Mg2+ and SO 4 2 - . EQL/EVP (equilibrium/evaporation), a brine equilibrium model, simulated evaporation of inflow water and groundwater brines in an open system and showed good agreement between theoretically predicted and observed minerals in the Lop Nor basin. Brine chemical modeling cannot however explain the massive amounts of glauberite (Na2SO4·CaSO4) and polyhalite (K2SO4·MgSO4·2CaSO4·2H2O) deposits found in a 230 m deep core ZK1200B from the Lop Nor basin. EQL/EVP simulations under a closed system allowed brine reactions with previously formed minerals and indicate that glauberite forms by back reaction between brine, gypsum and anhydrite and polyhalite forms by reaction between brine and glauberite. Diagenetic textures related to recrystallization and secondary replacement were commonly observed in core ZK1200B, indicating significant mineral–brine interaction during crystallization of glauberite and polyhalite. Mineral assemblages predicted from the evaporation of Tarim river water match closely with natural assemblages and abundances, which can explain the unusual glauberite deposits in the Lop Nor basin. It is suggested that the Tarim river inflow is the dominant source over the lake’s history. The distribution of minerals in the cored sediments documents the history of inflow water response to wet and dry periods in the Lop Nor basin.
The use of O, H, B, Sr and S isotopes for tracing the origin of dissolved boron in groundwater in Central Macedonia, Greece by E. Dotsika; D. Poutoukis; W. Kloppmann; C. Guerrot; D. Voutsa; T.H. Kouimtzis (1783-1796).
► Multi-isotopic approach for the investigation of pollution in groundwater aquifers in Central Macedonia, Greece. ► Origin of Boron using isotope of B. ► Combination of geochemical parameters with multi-isotopic tools.The groundwater B concentration in Mesozoic karst, Neogene and alluvial aquifers in the West part of Chalkidiki province in Central Macedonia, Greece reaches 6.45 mg L−1, which exceeds the limit of 1 mg L−1, set by the European Union for drinking water. The high B contents have been detected in this area, not only near the shoreline, where seawater intrusion occurs, but also in the inland part of the basin. Multi isotope (2H, 18O, 34S, 18O(SO4), 11B, 87Sr/86Sr) data from borehole and thermal water springs allow identification of the possible B sources. The B dissolved in groundwater in the Chalkidiki area is mainly geogenic. The low δ 11B values, 0–1‰, similar to those of thermal fluids from continental geothermal fields, and the low Cl/B ratio compared to seawater both indicate a geothermal origin for B and reflect deep circulation and interaction with igneous rocks. The 87Sr/86Sr ratio also indicates that the deep-aquifer granodiorite is the predominant rock source of Sr, while the shallow limestone unit has negligible effects on the dissolved Sr budget in these thermal karst waters which O and H isotopes show to be of meteoric origin. The main source of high B in borehole water is mainly mixing with B-rich geothermal water. The mixing between geothermal water and water from the Neogene aquifer is also reflected by isotopic contents of SO4.