Applied Geochemistry (v.33, #C)
Mercury in European agricultural and grazing land soils by Rolf Tore Ottesen; Manfred Birke; Tor Erik Finne; Mateja Gosar; Juan Locutura; Clemens Reimann; Timo Tarvainen (1-12).
► Mercury concentrations in agricultural and grazing land soil of Europe are presented. ► The paper presents the Hg-background for two types of soil-use at the European scale. ► Geology and climate dominate the continental-scale Hg distribution. ► Anthropogenic Hg sources are visible on a local scale.Agricultural (Ap, Ap-horizon, 0–20 cm) and grazing land soil samples (Gr, 0–10 cm) were collected from a large part of Europe (33 countries, 5.6 million km2) at an average density of 1 sample site/2500 km2. The resulting more than 2 × 2000 soil samples were air dried, sieved to <2 mm and analysed for their Hg concentrations following an aqua regia extraction. Median concentrations for Hg are 0.030 mg/kg (range: <0.003–1.56 mg/kg) for the Ap samples and 0.035 mg/kg (range: <0.003–3.12 mg/kg) for the Gr samples. Only 5 Ap and 10 Gr samples returned Hg concentrations above 1 mg/kg. In the geochemical maps the continental-scale distribution of the element is clearly dominated by geology. Climate exerts an important influence. Mercury accumulates in those areas of northern Europe where a wet and cold climate favours the build-up of soil organic material. Typical anthropogenic sources like coal-fired power plants, waste incinerators, chlor-alkali plants, metal smelters and urban agglomerations are hardly visible at continental scales but can have a major impact at the local-scale.
Investigation of tectonically affected groundwater systems through a multidisciplinary approach by R. Gambillara; S. Terrana; B. Giussani; D. Monticelli; S. Roncoroni; S. Martin (13-24).
► Importance of a multidisciplinary approach for the study of the mountain aquifers. ► Role played by faults and the fracture systems in groundwater circulation. ► Integration of PCA, traditional geochemical methods and geo-structural analyses.This study uses a multidisciplinary approach to obtain a complete picture of the groundwater system of complex mountain aquifers. An Alpine region (the north-western area of Lake Como, Italy), characterized by two regional fault systems (The Breglia and Grona fault systems) containing different lithologies, was investigated using the multidisciplinary approach described here. The use of Principal Components Analysis (PCA), classical geochemical bivariate and trivariate diagrams of major and trace elements, and geostructural data, including remote sensing, permitted the identification of three principal groups of water. The first group, characterized by an enrichment of Ca2+ and HCO 3 - , flow in limestone. The second group is enriched in HCO 3 - , Ca2+ and Mg2+ and circulates through dolomite rocks. The third group, characterized by a decrease of Ca2+ and Mg2+, an increase of Na+ + K+ and a high Si/electrical conductivity (EC) ratio, flow in the basement rocks. Nevertheless, some peculiarities were evident. The matching of PCA, hydrochemical and geostructural information explains the role played by faults in water circulation. In particular, the Breglia fault permits the rise of deep water from crystalline basement and dolomite. Similarly, the Grona fault plays a role on drainage in proximity to the contact between the crystalline basement and the sedimentary cover. The springs located near the Grona fault rise into the crystalline basement but reflect a dolomite water chemistry. The multidisciplinary approach allowed understanding of the groundwater system and identification of fault systems not detectable with a geostructural survey.
Hydrothermal contamination of public supply wells in Napa and Sonoma Valleys, California by M.J. Forrest; J.T. Kulongoski; M.S. Edwards; C.D. Farrar; K. Belitz; R.D. Norris (25-40).
► We analyzed the geochemistry of 44 public supply wells in Napa and Sonoma Valleys. ► We investigated mixing of groundwater with hydrothermal fluids. ► We used multivariate statistical analyses and modeling to characterize wells. ► We found that nine public supply wells contained 14–30% hydrothermal fluids. ► Some contaminated wells contain potentially harmful concentrations of As, F and B.Groundwater chemistry and isotope data from 44 public supply wells in the Napa and Sonoma Valleys, California were determined to investigate mixing of relatively shallow groundwater with deeper hydrothermal fluids. Multivariate analyses including Cluster Analyses, Multidimensional Scaling (MDS), Principal Components Analyses (PCA), Analysis of Similarities (ANOSIM), and Similarity Percentage Analyses (SIMPER) were used to elucidate constituent distribution patterns, determine which constituents are significantly associated with these hydrothermal systems, and investigate hydrothermal contamination of local groundwater used for drinking water. Multivariate statistical analyses were essential to this study because traditional methods, such as mixing tests involving single species (e.g. Cl or SiO2) were incapable of quantifying component proportions due to mixing of multiple water types. Based on these analyses, water samples collected from the wells were broadly classified as fresh groundwater, saline waters, hydrothermal fluids, or mixed hydrothermal fluids/meteoric water wells. The Multivariate Mixing and Mass-balance (M3) model was applied in order to determine the proportion of hydrothermal fluids, saline water, and fresh groundwater in each sample. Major ions, isotopes, and physical parameters of the waters were used to characterize the hydrothermal fluids as Na–Cl type, with significant enrichment in the trace elements As, B, F and Li. Five of the wells from this study were classified as hydrothermal, 28 as fresh groundwater, two as saline water, and nine as mixed hydrothermal fluids/meteoric water wells. The M3 mixing-model results indicated that the nine mixed wells contained between 14% and 30% hydrothermal fluids. Further, the chemical analyses show that several of these mixed-water wells have concentrations of As, F and B that exceed drinking-water standards or notification levels due to contamination by hydrothermal fluids.
Measuring reactive pools of Cd, Pb and Zn in coal fly ash from the UK using isotopic dilution assays by M. Izquierdo; A.M. Tye; S.R. Chenery (41-49).
► Isotope dilution is a useful method to resolve the reactivity of Cd and Pb in ash. ► Only 0.3–3% of the total Pb and Zn and 4–13% of the total Cd in coal ash are labile. ► Fly ash weathering exerts little impact on the lability of Cd, Pb and Zn. ► A 0.05 M EDTA extraction can be used as a simple proxy for isotope dilution assays.Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO3 and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.
Hydrochemical and isotopic patterns in a calc-alkaline Cu- and Au-rich arid Andean basin: The Elqui River watershed, North Central Chile by Jorge Oyarzún; María José Carvajal; Hugo Maturana; Jorge Núñez; Nicole Kretschmer; Jaime M. Amezaga; Tobias S. Rötting; Gerhard Strauch; Geoffrey Thyne; Ricardo Oyarzún (50-63).
► Major ions are provided by rock weathering and NaCl recycling. ► Aridity and cal-alkaline lithology effects abate acid drainage. ► Factors affecting hydrochemistry in mineral rich zone are addressed. ► Stable isotopes confirm the meteoric origin of groundwaters. ► High sulfate contents are explained by widespread sulfide minerals.The geochemistry of surface water and groundwater from the Elqui River basin, North-Central Chile, was studied in spring 2007 and fall 2008 to obtain a general understanding of the factors and mechanisms controlling the water chemistry of steep rivers located in mineral-rich, arid to semi arid zones. Besides its uniform intermediate igneous lithology, this basin is known for acid drainage and high As contents in the El Indio Au–Cu–As district, in its Andean head. Abundant tailings deposits are present in the middle part of the basin, where agricultural activities are important. According to the results, the chemical and isotopic composition of the Elqui basin surface water and groundwater is related to uniform calc-alkaline lithology and the major polluting system of the chemically reactive, but closed El Indio mining district. The resulting compositional imprints in surface and ground-water are, (a) high SO4 levels, reaching about 1000 mg/L in the Toro River water, directly draining the mining area; (b) a major depletion of Fe and pollutant metals in surface water after the confluence of the Toro and La Laguna rivers; (c) similar chemical composition of surface and ground-waters that differ in H and O isotopic composition, reflecting the effect of differential evaporation processes downstream of the Puclaro dam; and (d) seasonal variations of Fe, Mn, Cu and Zn in surface water. In contrast, the groundwater chemistry exhibits moderate seasonal changes, mainly in HCO 3 - content. In spite of the acid drainage pollution, water quality is adequate for human consumption and irrigation. This is a consequence of both the dominant calc-alkaline lithology and the existing arid climate, resulting in neutral to moderately alkaline pH values that are responsible for the precipitation of metal hydroxides and As sorption by Fe(OH)3.
Cement–fly ash stabilisation/solidification of contaminated soil: Performance properties and initiation of operating envelopes by Reginald B. Kogbara; Abir Al-Tabbaa; Yaolin Yi; Julia A. Stegemann (64-75).
► Cement and fly ash were used for treatment of a mixed contaminated soil. ► The stabilisation treatment was evaluated by mechanical and leaching tests. ► The binder effectively reduced the leachability of most metals. ► The binder has the potential to maintain acceptable leachability levels over time. ► Design charts were produced to assist in optimisation of treatment process design.This study was aimed at evaluating the mechanical and pH-dependent leaching performance of a mixed contaminated soil treated with a mixture of Portland cement (CEMI) and pulverised fuel ash (PFA). It also sought to develop operating envelopes, which define the range(s) of operating variables that result in acceptable performance. A real site soil with low contaminant concentrations, spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, was treated with one part CEMI and four parts PFA (CEMI:PFA = 1:4) using different binder and water contents. The performance was assessed over time using unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. With binder dosages ranging from 5% to 20% and water contents ranging from 14% to 21% dry weight, the 28-day UCS was up to 500 kPa and hydraulic conductivity was around 10−8 m/s. With leachant pH extremes of 7.2 and 0.85, leachability of the contaminants was in the range: 0.02–3500 mg/kg for Cd, 0.35–1550 mg/kg for Cu, 0.03–92 mg/kg for Pb, 0.01–3300 mg/kg for Ni, 0.02–4010 mg/kg for Zn, and 7–4884 mg/kg for total petroleum hydrocarbons (TPHs), over time. Design charts were produced from the results of the study, which show the water and/or binder proportions that could be used to achieve relevant performance criteria. The charts would be useful for the scale-up and design of stabilisation/solidification (S/S) treatment of similar soil types impacted with the same types of contaminants.
Influence of humic acid on the sorption of pentachlorophenol by aged sediment amended with rice-straw biochar by Liping Lou; Feixiang Liu; Qiankun Yue; Fang Chen; Qiang Yang; Baolan Hu; Yingxu Chen (76-83).
Display Omitted► HA altered rice-straw biochar’s (RBC) surface property and reduced its adsorptivity. ► The adsorptivity of sediment (S) + HA/RBC decreased less than the S + RBC and S + HA + RBC. ► Sorption curves of other treatments became closer to the S + HA/RBC system with aging. ► The faster reduction in adsorptivity with more fresh HA implied the key role of HA.Black carbon (BC), especially biochar, is a potential material for the remediation of hydrophobic organic compounds (HOCs) pollution in soils and sediments. Recent studies have reported that the adsorption capability of BC in sediment was reduced as time increased. It was hypothesised that this behaviour was caused by the presence of natural organic matter (NOM), but few systematic studies have examined the influence of NOM on the sorption ability of BC in sediment (S). The results of this study revealed that a humic acid (HA) coating changed the surface properties, blocked the micropores, and decreased the sorption capacity of rice-straw biochar (RBC) towards pentachlorophenol. With increasing aging time, the reductions in the sorption capacity of the S + RBC and S + HA + RBC systems occurred more rapidly than in the S + HA/RBC (HA-coated RBC) system, and the sorption curves became closer to that of the S + HA/RBC system, indicating that HA may play a primary role in reducing the sorption capacity of RBC in the sediment. With higher HA contents, the sorption capacity of the complex sediments was lower and decreased more rapidly.
Using hydrogeochemistry to understand inter-aquifer mixing in the on-shore part of the Gippsland Basin, southeast Australia by H. Hofmann; Ian Cartwright (84-103).
► First 14C data for the inter-mountainous Gippsland Basin. ► Hydrogeochemistry shows inter-aquifer mixing, which is not possible with head data. ► Groundwater flow occurs across aquifer boundaries horizontally and vertically. ► Isotope data indicate chemical processes such as methanogenesis in some aquifers. ► Although 14C age correction is difficult, we correct for geochemical processes.Groundwater in the Latrobe Valley in the Gippsland Basin of southeast Australia is important for domestic, agricultural and industrial uses. This sedimentary basin contains a number of aquifers that are used for water supply, dewatered for open pit coal mining, and which are potentially influenced by off-shore oil and gas production. Major ion chemistry together with stable and Sr isotope data imply that the main hydrogeochemical processes are evapotranspiration with minor silicate and carbonate weathering; methanogenesis and SO4 reduction in reduced groundwater associated with coal deposits have also occurred. Groundwater has estimated 14C ages of up to 36 ka and is largely 3H free. Carbon-14 ages are irregularly distributed and poorly correlated with depth and distance from the basin margins. The observations that the geochemistry of groundwater in aquifers with different mineralogies are similar and the distribution of 14C ages is irregular implies that the aquifers are hydraulically connected and horizontal as well as vertical inter-aquifer mixing occurs. The connection of shallow and deeper aquifers poses a risk for the groundwater resources in Gippsland as contaminants can migrate across aquifers and dewatering of shallow units may impact deeper parts of the groundwater system.
Defining element associations and inferring geological processes from total element concentrations in Australian catchment outlet sediments: Multivariate analysis of continental-scale geochemical data by Patrice de Caritat; Eric C. Grunsky (104-126).
Display Omitted► Australia-wide geochemical dataset of catchment outlet sediments covers 6 M km2. ► Total element concentrations analysed by PCA after imputation and clr-transformation. ► Four first PCs account for 59% of variance. ► Element associations show lithology, weathering, etc. control regolith composition. ► Maps of PC distributions relate to ground, airborne and spaceborne datasets.In this paper, the geochemical composition of surficial regolith is statistically analysed and compared to independent geoscientific datasets to infer processes governing regolith composition. Surface (0–10 cm depth) and sub-surface (∼60–80 cm depth) transported sediment samples from the National Geochemical Survey of Australia were analysed for total element content in both coarse (<2 mm) and fine (<75 μm) grain-size fractions. Multi-element total content data was obtained from mainly XRF and total digestion ICP-MS analysis, of which the 50 elements satisfying data quality criteria, plus Loss on Ignition, are used herein.Censored data (<lower limit of detection) was imputed using a nearest neighbour-based analysis. The compositional data was transformed using centered log ratios (clr) to circumvent closure issues. A Principal Component Analysis (PCA) was then performed on the dataset. The first four PCs account for 59% of the variance in the dataset. Both negative and positive loadings of each of these PCs relate to geological processes consistent with the element associations they represent as well as the spatial distribution patterns they produce. The positive loadings of PC1 represent the accumulation of resistant minerals rich in Rare Earth Elements (REEs) that results from intense weathering, except in southeastern Australia where they reflect REE-enriched igneous and sedimentary rocks. Negative PC1 loadings represent secondary minerals formed during weathering (carbonates, sulfates, Fe-oxyhydroxides). Negative PC2 loadings are a mixture of elements (e.g., Co, Mn, Zn, V) characterising mafic and ultramafic minerals; conversely negative PC3 loadings (e.g., K, Rb, Na, Sr, Ca) represent more felsic minerals. Spatial distributions of the PCs are compared with independent spatial information from geological maps, airborne radiometric and spaceborne spectroscopic datasets. The differences between surface and sub-surface and between coarse and fine grain-size fractions are analysed. The implied processes (e.g., lithological control, weathering, transport, secondary mineral precipitation) overall match well with this new geochemical evidence. Future work directions with this dataset include lithological prediction and mineral prospectivity analysis.
Major and trace element compositions (including REE) of mineral, thermal, mine and surface waters in SW Germany and implications for water–rock interaction by Susanne Göb; Anselm Loges; Nils Nolde; Michael Bau; Dorrit E. Jacob; Gregor Markl (127-152).
► Mine, thermal and mineral waters in SW Germany were analyzed for major and trace elements. ► Rare earth elements provide information about interaction with host rocks. ► Rb/Cs ratios indicate interaction with clay minerals. ► Trace elements in calcite precipitates are controlled by incorporation of particles.The near-surface water cycle in a geologically complex area comprises very different sources including meteoric, metamorphic and magmatic ones. Fluids from these sources can react with sedimentary, magmatic and/or metamorphic rocks at various depths. The current study reports a large number of major, minor and trace element analyses of meteoric, mineral, thermal and mine waters from a geologically well-known and variable area of about 200 × 150 km in SW Germany. The geology of this area comprises a Variscan granitic and gneissic basement overlain in parts by Triassic and Jurassic shales, sandstones and limestones. In both the basement and the sedimentary rocks, hydrothermal mineralization occurs (including Pb, Cu, As, Zn, U, Co and many others) which were mined in former times. Mineral waters, thermal waters and meteoric waters flowing through abandoned mines (mine waters) are distributed throughout the area, although the mine waters concentrate in and around the Schwarzwald.The present analyses show, that the major element composition of a particular water is determined by the type of surrounding rock (e.g., crystalline or sedimentary rocks) and the depth from which the water originates. For waters from crystalline rocks it is the origin of the water that determines whether the sample is Na–Cl dominant (deeper origin) or Ca–HCO3 dominant (shallow origin). In contrast, compositions of waters from sedimentary rocks are determined by the availability of easily soluble minerals like calcite (Ca–HCO3 dominant), halite (Na–Cl dominant) or gypsum (Ca–SO4 dominant). Major element data alone cannot, therefore, be used to trace the origin of a water. However, the combination of major element composition with trace element data can provide further information with respect to flow paths and fluid–rock interaction processes. Accordingly, trace element analyses showed, that:The chemical compositions of carbonate precipitates from thermal waters indicate that rare earth elements (REEs), Rb and Cs concentrations in the minerals are controlled by the incorporation of clay particles that adsorb these elements.
Geochemical characterization of arsenic-rich coal-combustion ashes buried under agricultural soils and the release of arsenic by Veronika Veselská; Juraj Majzlan; Edgar Hiller; Katarína Peťková; Ľubomír Jurkovič; Ondrej Ďurža; Bronislava Voleková-Lalinská (153-164).
► Sources, mineralogy and mobility of As in coal-combustion ashes were investigated. ► After a dam failure in 1965, the spilled ashes were buried under agricultural soils. ► Primary carriers of As within coal-combustion ashes are aluminosilicate glasses. ► The most probable secondary carriers of labile As are oxyhydroxides of Si, Al, and Fe. ► Arsenic stored in ashes is a long-term contamination source for the environment.A combination of geochemical and mineralogical methods was used to determine the concentrations, mobility, and sources of As in coal-combustion ashes and soils in the vicinity of a thermal power plant at Nováky, central Slovakia. Fresh lagooned ash, ashes buried under agricultural soils for 45 a, and the overlying soils, contain high concentrations of As ranging from 61 to 1535 mg/kg. There is no differences in the water extractable percentages of As between the fresh lagooned ash and buried ashes, which range from 3.80% to 6.70% of the total As. This small amount of As may perhaps reside on the surfaces of the ash particles, as postulated in the earlier literature, but no evidence was found to support this claim. Electron microprobe analyses show that the dominant primary As carriers are the aluminosilicate glasses enriched in Ca and Fe. The acid NH 4 + -oxalate extraction hints that the oxyhydroxides of Si, Al, and Fe are the most probable secondary carriers of labile As. The X-ray absorption spectroscopy (XAS) analyses show that As in the lagooned and buried ashes occurs mostly as As(V). The long-term burial of the coal-combustion ash under agricultural soil did not cause any major change of its chemical composition or As lability compared to the fresh lagooned ash.
A comparison study of the C–A and S–A models with singularity analysis to identify geochemical anomalies in covered areas by Renguang Zuo; Qinglin Xia; Daojun Zhang (165-172).
► The C–A and S–A models are compared with singularity analysis. ► The grassland cover weakens the concentration values of geochemical elements. ► The C–A model has a limitation to identify weak anomalies in covered areas. ► The S–A model suffers the edge effects in an irregular study area. ► The value of singularity index is influenced by the selection of window size.Fractal/multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry. Identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data. In this study, three fractal models, consisting of the concentration–area (C–A), spectrum–area (S–A) and singularity index models were applied to identify geochemical anomalies in the covered area located in the Chaobuleng Fe polymetallic district, Inner Mongolia (China). The results show that (1) the grassland cover weakens the concentrations of geochemical elements; (2) the C–A model has a limitation to identify weak anomalies in covered areas; (3) the S–A model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area; and (4) the singularity index is a useful tool to identify weak geochemical anomalies.
Phosphorus distribution and fractionation during weathering of amphibolites and gneisses in different climatic setups of the Kaveri river catchment, India by Akanksha Mishra; Jayant K. Tripathi; Pankaj Mehta; V. Rajamani (173-181).
► Phosphorus fractionation in weathering profiles recapitulates that of the soil chronosequences. ► Phosphorus fractionation pattern is independent of bedrock lithology. ► Phosphorus fractionation is a function of climate through weathering.Phosphorus distribution and fractionation during weathering of rocks are seminal to its availability to the life system. Here, the P fractionation pattern is reported in weathering profiles of two different rock types i.e. amphibolites and granitic gneisses, subjected to semi-arid and humid climatic conditions in the catchment of the Kaveri river, southern India, known for its fertile flood plain and delta. Weathering profiles developed on the two rock types were analysed for evaluating the intensity of chemical weathering using major ion geochemistry and for accompanying P fractionation. The Chemical Index of Alteration (CIA) and the mineralogy of different zones of the weathering profiles show that profiles under humid climatic conditions are more weathered than those under semi-arid conditions. It was also found that P, present dominantly as the apatite inorganic P (AIP) fraction in the bedrocks was converted into non-apatite inorganic P (NAIP) and organic P (OP), both of which increase with progressive weathering. The two major rock types show a very similar pattern of P fractionation during weathering which is similar to those observed in soil chronosequences. However, the transfer of P from AIP to OP and NAIP is near total in both rock types under humid conditions of weathering. Under semi-arid conditions, a part of AIP was also available in the most weathered zone. Thus the lithology of the bedrock has little, and climate a dominant, control on P fractionation during rock weathering. It was also observed that there is a net loss of total P during the weathering associated fractionation that could be attributed to the incorporation into biologically available forms and their subsequent removal to the fertile floodplains and delta in an undisturbed riverscape.
Spatial distribution and methylation of mercury in a eutrophic reservoir heavily contaminated by mercury in Southwest China by Haiyu Yan; Qiuhua Li; Bo Meng; Cuiping Wang; Xinbin Feng; Tianrong He; Janusz Dominik (182-190).
► Total mercury is high in sediment, but low in water column. ► The ratios of MeHg/THg in sediment and water column are relatively low. ► The eutrophication does not lead to elevated net methylation rate of Hg in BHR.In Baihua Reservoir (BHR), a Hg-contaminated and eutrophic reservoir in SW China, water and sediment samples were collected in June 2010 for the determination of Hg species, metal, major ion and nutrient concentrations. Using a stable isotope tracer technique, 202HgCl2 and Me198HgCl were spiked into sediment cores to study methylation and demethylation processes. The inorganic Hg concentration range was 600–13,000 ng/g (dry weight, dw) in the top 10 cm of sediment; exceeding the local background concentration (260 ng/g, dw). Concentrations of Hg species in the water column and pore water were similar to non-Hg contaminated reservoirs in the same watershed. Dissolved total Hg(DHg)and dissolved methylmercury (DMeHg) (mean ± SD) in the pore water in BHR were 6.8 ± 3.1 and 0.27 ± 0.20 ng/L, respectively. Dissolved Hg, DMeHg and reactive Hg (RHg) in the water column were 2.3 ± 0.9, 0.23 ± 0.22, and 0.77 ± 0.17 ng/L, respectively. The vertical distributions of Hg species showed inorganic Hg and methylmercury (MeHg) concentrations peaked near the bottom of the water column, implying the impact of thermal stratification and eutrophic conditions on the production and distribution of Hg species in this reservoir. The methylation rate (<0.1%/day) in these sediments was lower and the demethylation rate (17.6%/day) was higher than those reported in other eutrophic reservoir studies.
Modeling of Cs+ diffusion and retention in the DI-A2 experiment (Mont Terri). Uncertainties in sorption and diffusion parameters by Josep M. Soler; Paul Wersin; Olivier X. Leupin (191-198).
► An in situ diffusion experiment at Mont Terri has been modeled. ► Cs+ migration can be explained using sorption parameters measured in the laboratory. ► Cs+ batch-sorption data can be applied to in situ experiments (no upscaling). ► Differences in the sorption model translate into different diffusion coefficients. ► Effect of poor mixing in the circulation system has been included.In the DI-A2 experiment several non-reactive and reactive tracers were injected as a pulse in a packed-off borehole in the Opalinus Clay. Unlike the previous DI-A1 test, the design of the Teflon filter in the injection borehole forced the water to flow through the filter and the open space between the filter and the borehole wall (the filter itself did not act as a diffusion barrier between the circulating solution and the rock). The decrease in tracer concentration in the liquid phase was monitored during a period of a year. Afterwards, the borehole section was overcored and the tracer profiles in the rock were analyzed. A main interest of this experiment was to understand the chemical behavior of sorbing tracers: Cs+ (stable), 85Sr2+, 60Co2+ and Eu3+ (stable). The complete dataset (except for Eu3+ because of strong sorption to experimental equipment) was analyzed in a previous study with a 2D diffusion–reaction model and the derived diffusion and sorption parameters were compared with laboratory data. As in DI-A1, a difference by a factor of about 2 for sorption (magnitude of the Freundlich isotherm) was obtained between in situ and laboratory batch sorption experiments.Recent experimental and modeling studies have shown equivalent Cs+ sorption on intact and disaggregated Opalinus Clay samples. In view of these developments, new modeling of Cs+ diffusion and retention in the DI-A2 experiment has been performed using CrunchFlow. The calculations include transport by diffusion and a multisite cation exchange model to account for the retention of Cs+. The new results show that upscaling of Cs+ sorption from laboratory to field is no longer required. However, a difference in sorption by a factor of about 2 is still explained by the use of different versions of the same cation exchange model (a small difference in the selectivity coefficient for one type of site). This uncertainty in sorption leads to an uncertainty in the effective diffusion coefficient (De ) for Cs+, also by a factor of 2 (2–4 × 10−10 m2/s). Clearly, the values of De obtained are correlated with the strength of sorption in the model, with stronger sorption leading to larger De values. Discrimination between the two versions of the exchange model is not possible when using only the results of the in situ test. Additionally, during early times (t < 10 days) the drop in Cs+ concentration in the circulation system is slower than expected. Due to the experimental setup, this slow decrease in concentration cannot be caused by the filter in the contact between borehole and rock. Poor mixing in the circulation system could explain this effect.
Isotopic and geochemical evolution of ground and river waters in a karst dominated geological setting: A case study from Lijiang basin, South-Asia monsoon region by Tao Pu; Yuanqing He; Tao Zhang; Jinkui Wu; Guofeng Zhu; Li Chang (199-212).
► The river and ground water were of Ca2+–Mg2+– HCO 3 - type with similar ion compositions. ► Limestone and dolomite were the main end-members to water geochemistry. ► The δ 18O similarity of surface and ground water suggested their common source. ► Melt water and precipitation were the main recharge of river and ground water. ► Frequent transformation of surface and ground water occurred in the karst region.Analysis of O isotopes and major ions in river and spring waters in Lijiang basin–Yulong Mountain region, SW China was carried out to identify the geochemical evolution affecting water quality and recharge sources of ground water. Both the river and ground water in the area were of the Ca2+–Mg2+– HCO 3 - type with similar ion compositions and showed small seasonal variations, normally high in the dry season and low in the wet season. From the upper basin downward there was a general increasing trend for the total ion concentrations in the river and ground water. Water–Rock interaction is the significant contributor to water geochemistry while there is little anthropogenic influence as a whole in the region. The co-relationship of Mg2+/Ca2+ versus Na+/Ca2+ indicated that limestone and dolomite were the main end-members controlling the variations in chemical composition of river and spring waters. The groundwater showed relatively depleted stable isotopic composition compared to modern rainfall, meltwater and river water. The similarity of δ 18O for both surface and groundwater samples was due to their frequent transformation in karst regions and suggested rapid recharge of the groundwater aquifers by surface water coming from precipitation and ice–snow melt water from Yulong Mountain. The predominant recharge area of the Lijiang water resource is located at the high elevation with groundwater discharge southwards to the lowlands of the basin, providing water for Lijiang city.
Organic phosphorus fractionation in wetland soil profiles by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy by Min Li; Jing Zhang; Guangqian Wang; Haijun Yang; Michael J. Whelan; Sue M. White (213-221).
► Chemical sequential extraction and 31P NMR spectroscopy were used for organic P analysis. ► Organic P includes orthophosphate, monoester and diester phosphate and pyrophosphate. ► Highly resistant organic P and monoester phosphate were the dominant organic P. ► HCl pretreatment can remove most inorganic P and increase organic P recovery rate. ► A comprehensive organic P chemical sequential fractionation approach was proposed.Organic P (OP) plays an important role in soil P cycling and is a potential P source for wetland plants. In this study, a modified chemical sequential fractionation method and 31P nuclear magnetic resonance spectroscopy (31P NMR) of NaOH–EDTA extracts were used to examine the distribution of organic P fractions and compounds in soil profiles of the Beijing Yeyahu Wetland, China. The influence of acid treatment prior to NaOH–EDTA extraction on 31P NMR spectra was also investigated. Results show that highly resistant OP was the major class of organic P. The rank order of organic P fractions was highly resistant OP (on average accounting for 68.5% of total OP) > moderately resistant OP (15.8%m of total OP) > moderately labile OP (11.4% of total OP) > labile OP (4.3% of total OP). Most of the organic P fractions decreased with soil depth due to the accumulation of plant residues in surface soils and the deposition and diagenesis of soils. Moderately (r = 0.586, p < 0.01) and highly (r = 0.741, p < 0.01) resistant OP fractions were positively correlated with soil organic matter. Phosphorus compounds including orthophosphate (23–74.6% of total P in spectra), monoester phosphate (18.6–76%), diester phosphate (nil-7.8%) and pyrophosphate (nil-6.7%) were characterized using 31P NMR. Monoester-P was the dominant soil organic P compound identified. The proportion of monoester-P increased significantly in NaOH–EDTA extracts with HCl pretreatment and it was confirmed by chemical analysis. Therefore, it can be concluded that HCl pretreatment can remove more than half of the inorganic P and increase the overall recovery rate of organic P during subsequent NaOH–EDTA extraction, which might be a new approach for organic P detection. Furthermore, the OP chemical sequential fractionation method presented in this study is an integrated and comprehensive approach which can be used for further verification.
The sources and fluxes of dissolved chemistry in a semi-confined, sandy coastal aquifer: The Pingtung Plain, Taiwan by Caroline E.A. Martin; Albert Galy; Niels Hovius; Mike Bickle; In-Tian Lin; Ming-Jame Horng; Damien Calmels; Hongey Chen (222-236).
► We analysed groundwater chemistry from 43 wells in the Pingtung Plain, Taiwan. ► Sources of dissolved chemistry were assessed using ternary mixing relationships. ► Groundwater chemical fluxes were computed using hydraulic head and conductivities. ► Rain, hot springs, seawater and weathering contribute to groundwater chemistry. ► Subsurface chemical fluxes range from 1% to 12% of total flow (surface and subsurface).Groundwater chemical fluxes from the Pingtung Plain in SW Taiwan to the ocean were determined by analysing waters from 43 wells at varying depths through a 237 m deep window across the Pingtung Plain, for major dissolved cations, anions, dissolved SiO2, and stable isotopic composition of O and H, and computing their subsurface water fluxes from measurements of hydraulic heads and formation permeabilities. The results show that between 1.5% ( SO 4 2 - ) and 12.3% (Ba2+) of the total chemical weathering flux discharged to the ocean (Kaoping River combined with groundwater) can be attributed to the groundwater. Estimated propagated errors at 1σ on subsurface fluxes are ±20%. Multi-year daily hydraulic head data give the direction of groundwater flow through the plain, and indicate that pumping has led to episodic reversals of flow, facilitating seawater intrusion in the near-coast aquifer. Tracing end-member proportions using mixing relationships shows that, in addition to seawater and meteoric water, hot-spring activity contributes to the dissolved chemistry of the groundwater. In addition to these three end-members, the weathering of carbonate and silicate minerals in the plain accounts for the remainder of the chemical budget. Hydrological connectivity exists throughout the drilled depth of the basin, but chemical gradients show that flow is stratified, with up to a twofold increase in silicate-derived Na+ seen in deeper horizons as compared to the near surface. For all ions except SO 4 2 - , the average concentrations of dissolved species in the coastal groundwaters exceed those of the river, ranging from a factor of 1.33 in the case of Li+ to 27.29 in the case of Cl−. The results suggest that submarine groundwater chemical fluxes through the drilled depth of the Pingtung Plain into the Taiwan Strait are modest in comparison to those related to surface runoff.
Dolomite effect on borosilicate glass alteration by Mathieu Debure; Pierre Frugier; Laurent De Windt; Stéphane Gin (237-251).
► Dolomite is a common mineral of clayey formations considered for radioactive waste disposals. ► Borosilicate glass/dolomite interaction have been studied by batch tests and solid analysis. ► Mg provided by dolomite combines with Si from glass to yield secondary Mg–silicates. ► This precipitation increases glass alteration, though in a moderate manner. ► Geochemical modeling allows to quantify the alteration mechanisms involved.Dolomite (CaMg(CO3)2) is one of the common rock-forming minerals in many geological media, in particular in clayey layers that are currently considered as potential host formations for a deep radioactive waste disposal facility. Magnesium in solution is one of the elements known to potentially enhance the alteration of nuclear glasses. The alteration of borosilicate glasses with dolomite as a Mg-bearing mineral source was investigated for 8 months in batch tests at 90 °C. Glass composition effects were investigated through two compositions (SiBNaAlCaZrO and SiBNaAlZrO) differing in their Ca content. The Ca-rich glass alteration is slightly enhanced in the presence of dolomite compared to the alteration observed in pure water. This greater alteration is explained by the precipitation of Mg silicate phases on the dolomite and glass surfaces. In contrast, the Ca-free glass alteration decreases in the presence of dolomite compared to the alteration observed in pure water. This behavior is explained by Ca incorporation in the amorphous layer (formed during glass alteration) coming from dolomite dissolution. Calcium acts as a layer reorganizer and limits glass alteration by reducing the diffusion of reactive species through the altered layer. Modeling was performed using the GRAAL model implemented within the CHESS/HYTEC geochemical code to discriminate and interpret the mechanisms involved in glass/dolomite interactions. Magnesium released by dolomite dissolution reacts with silica provided by glass alteration to form Mg silicates. This reaction leads to a pH decrease. The main mechanism controlling glass alteration is the ability of dolomite to dissolve. During the experiment the quantities of secondary phases formed were very small, but for longer time scales, this mechanism could supply sufficient Mg in solution to form large amounts of Mg silicates and sustain glass alteration. The ability of the GRAAL model to reproduce the concentrations of elements in solution and solid phases regardless of the amount of dolomite and the glass composition strongly supports the basic modeling hypothesis.
Sourcing sedimentary cherts with archaeological use through the combination of chromatographic and spectroscopic techniques by M. Olivares; M. Irazola; X. Murelaga; J.I. Baceta; A. Tarriño; K. Castro; N. Etxebarria (252-259).
► Cherts from prehistoric quarries of the Basque Country and Ebro Basins were analysed. ► Bitumen and kerogen fractions of cherts were analysed to study their provenance. ► Distribution of biomarkers allowed distinguishing between marine and lacustrine cherts. ► The analyses were conducted by Chromatographic and Spectroscopic techniques. ► Raman spectra provided information about the maturity of some extracts.The nature and distribution of organic matter in geological cherts of archaeological use can serve to estimate the sources and origins of some remains of lithic industry. For example, organic and biomarker analysis can provide information to allow a deeper insight into source catchment areas, artefact displacement or the way in which the artefacts were employed. In this work, soluble (bitumen) and insoluble (kerogen) organic matter were isolated from several chert samples with different depositional history and analysed by means of gas chromatography–mass spectrometry (GC–MS) and spectroscopic techniques such as infrared and Raman spectroscopy. Chemometric treatment of the results allowed observation of differences between organic matter content on the basis of the depositional setting of the cherts. Samples with a continental deposition seemed to preserve more organic matter with little alteration. The hydrocarbon profiles of these samples were dominated by high molecular weight n-alkanes, alkylcyclohexanes and isoprenoid groups which allowed distinguishing them from the rest of the analysed samples.
Tracing groundwater with low-level detections of halogenated VOCs in a fractured carbonate-rock aquifer, Leetown Science Center, West Virginia, USA by L. Niel Plummer; Philip L. Sibrell; Gerolamo C. Casile; Eurybiades Busenberg; Andrew G. Hunt; Peter Schlosser (260-280).
► Low-level GC–ECD analyses of halogenated VOCs are applied to groundwater tracing. ► Most groundwater samples at the LSC are affected by non-atmospheric anthropogenic sources. ► Low-level detections of halogenated VOCs traced old landfill leakage and chlorinated water. ► Groundwater ages typically range from 4 to 7 years in the fractured, karstic carbonate rocks. ► Groundwater ages are related to climatic and geologic factors.Measurements of low-level concentrations of halogenated volatile organic compounds (VOCs) and estimates of groundwater age interpreted from 3H/3He and SF6 data have led to an improved understanding of groundwater flow, water sources, and transit times in a karstic, fractured, carbonate-rock aquifer at the Leetown Science Center (LSC), West Virginia. The sum of the concentrations of a set of 16 predominant halogenated VOCs (TDVOC) determined by gas chromatography with electron-capture detector (GC–ECD) exceeded that possible for air–water equilibrium in 34 of the 47 samples (median TDVOC of 24,800 pg kg−1), indicating that nearly all the water sampled in the vicinity of the LSC has been affected by addition of halogenated VOCs from non-atmospheric source(s). Leakage from a landfill that was closed and sealed nearly 20 a prior to sampling was recognized and traced to areas east of the LSC using low-level detection of tetrachloroethene (PCE), methyl chloride (MeCl), methyl chloroform (MC), dichlorodifluoromethane (CFC-12), and cis-1,2-dichloroethene (cis-1,2-DCE). Chloroform (CHLF) was the predominant VOC in water from domestic wells surrounding the LSC, and was elevated in groundwater in and near the Fish Health Laboratory at the LSC, where a leak of chlorinated water occurred prior to 2006. The low-level concentrations of halogenated VOCs did not exceed human or aquatic-life health criteria, and were useful in providing an awareness of the intrinsic susceptibility of the fractured karstic groundwater system at the LSC to non-atmospheric anthropogenic inputs. The 3H/3He groundwater ages of spring discharge from the carbonate rocks showed transient behavior, with ages averaging about 2 a in 2004 following a wet climatic period (2003–2004), and ages in the range of 4–7 a in periods of more average precipitation (2008–2009). The SF6 and CFC-12 data indicate older water (model ages of 10s of years or more) in the low-permeability shale of the Martinsburg Formation located to the west of the LSC. A two-a record of specific conductance, water temperature, and discharge recorded at 30-min intervals demonstrated an approximately 3-month lag in discharge at Gray Spring. The low groundwater ages of waters from the carbonate rocks support rapid advective transport of contaminants from the LSC vicinity, yet the nearly ubiquitous occurrence of low-level concentrations of halogenated VOCs at the LSC suggests the presence of long-term persistent sources, such as seepage from the closed and sealed landfill, infiltration of VOCs that may persist locally in the epikarst, exchange with low-permeability zones in fractured rock, and upward leakage of older water that may contain elevated concentrations of halogenated VOCs from earlier land use activities.
Mobilization of arsenic from acid deposition – The Elbe River catchment, Czech Republic by F. Buzek; B. Cejkova; B. Dousova; I. Jackova; R. Kadlecova; Z. Lnenickova (281-293).
Temporal changes of As concentration in surface waters were observed in some areas of the Czech Republic. Mobilized As originates from past atmospheric deposition. To understand the factors influencing As aqueous concentration and mobility the chemistry and runoff generation of a number of brooks, springs and rivers in the central part of the Elbe River catchment, Czech Republic, were monitored. Seasonal variations of As (from 0.5 to 10.5 μg L−1), Fe (from 0.05 to 3.9 mg L−1) and DOC (dissolved organic C – from 1.2 to 17.5 mg L−1) were observed in monitored stream waters with maximum values of As and Fe in the summer months at pH values 7.6–7.8. The concentration of As in particles with a diameter < 60 μm correlates with the Fe concentration. There is no correlation between Fe and As in filtered samples (<0.45 μm). The As concentration in stream water colloids depends on an increase in DOC concentration and a decrease in ionic strength. The DOC stabilizes As in solution and reduces its re-adsorption on Fe colloids and consequently As concentration in the stream increases.
Arsenic volatilization in model anaerobic biogas digesters by Adrien Mestrot; Wan-Ying Xie; Ximei Xue; Yong-Guan Zhu (294-297).
Arsenic is a class 1 non-threshold carcinogen which is highly ubiquitous. Arsenic undergoes many different transformations (biotic or abiotic) between and within environmental compartments, leading to a number of different chemical species possessing different properties and toxicities. One specific transformation is As biotic volatilization which is coupled with As biomethylation and has been scarcely studied due to inherent sampling issues. Arsenic methylation/volatilization is also linked with methanogenesis and occurs in anaerobic environments.In China, rice straw and animal manure are very often used to produce biogas and both can contain high amounts of As, especially if the rice is grown in areas with heavy mining or smelting industries and if Roxarsone is fed to the animals. Roxarsone is an As-containing drug which is widely used in China to control coccidian intestinal parasites, to improve feed efficiency and to promote rapid growth. Previous work has shown that this compound degrades to inorganic As under anaerobic conditions. In this study the focus is on biotic transformations of As in small microcosms designed as biogas digester models (BDMs) using recently validated As traps, thus, enabling direct quantification and identification of volatile As species. It is shown that although there was a loss of soluble As in the BDMs, their conditions favored biomethylation. All reactors produced volatile As, especially the monomethylarsonic acid spiked ones with 413 ± 148 ng As (mean ± SD, n = 3) which suggest that the first methylation step, from inorganic As, is a limiting factor. The most abundant species was trimethylarsine, but the toxic arsine was present in the headspace of most of the BDMs. The results suggest that volatile As species should be monitored in biogas digesters in order to assess risks to humans working in biogas plants and those utilizing the biogas.
Mercury distribution in coals influenced by magmatic intrusions, and surface waters from the Huaibei Coal Mining District, Anhui, China by Zhicao Yan; Guijian Liu; Ruoyu Sun; Dun Wu; Bin Wu; Chuncai Zhou (298-305).
The Hg concentrations in 108 samples, comprising 81 coal samples, 1 igneous rock, 2 parting rock samples and 24 water samples from the Huaibei Coal Mining District, China, were determined by cold-vapor atomic fluorescence spectrometry. The abundance and distribution of Hg in different coal mines and coal seams were studied. The weighted average Hg concentration for all coal samples in the Huaibei Coalfield is 0.42 mg/kg, which is about twice that of average Chinese coals. From southwestern to northeastern coalfield, Hg concentration shows a decreasing trend, which is presumably related to magmatic activity and fault structures. The relatively high Hg levels are observed in coal seams Nos. 6, 7 and 10 in the southwestern coal mines. Correlation analysis indicates that Hg in the southwestern and southernmost coals with high Hg concentrations is associated with pyrite. The Hg concentrations in surface waters in the Huaibei Coal Mining District range from 10 to 60 ng/L, and display a decreasing trend with distance from a coal waste pile but are lower than the regulated levels for Hg in drinking water.
Uncertainty in geochemical modelling of CO2 and calcite dissolution in NaCl solutions due to different modelling codes and thermodynamic databases by Christoph Haase; Frank Dethlefsen; Markus Ebert; Andreas Dahmke (306-317).
A prognosis of the geochemical effects of CO2 storage induced by the injection of CO2 into geologic reservoirs or by CO2 leakage into the overlaying formations can be performed by numerical modelling (non-invasive) and field experiments. Until now the research has been focused on the geochemical processes of the CO2 reacting with the minerals of the storage formation, which mostly consists of quartzitic sandstones. Regarding the safety assessment the reactions between the CO2 and the overlaying formations in the case of a CO2 leakage are of equal importance as the reactions in the storage formation. In particular, limestone formations can react very sensitively to CO2 intrusion. The thermodynamic parameters necessary to model these reactions are not determined explicitly through experiments at the total range of temperature and pressure conditions and are thus extrapolated by the simulation code. The differences in the calculated results lead to different calcite and CO2 solubilities and can influence the safety issues.This uncertainty study is performed by comparing the computed results, applying the geochemical modelling software codes The Geochemist’s Workbench, EQ3/6, PHREEQC and FactSage/ChemApp and their thermodynamic databases. The input parameters (1) total concentration of the solution, (2) temperature and (3) fugacity are varied within typical values for CO2 reservoirs, overlaying formations and close-to-surface aquifers. The most sensitive input parameter in the system H2O–CO2–NaCl–CaCO3 for the calculated range of dissolved calcite and CO2 is the fugacity of CO2. Hence, the largest range of dissolved calcite is calculated at high fugacities and is 210 mmol/kgw. The average deviation of the results using the databases phreeqc.dat and wateq4f.dat in combination with the code PHREEQC is lowest in comparison to the results of the specific model of Duan and Li, which represents the experimental values at best. Still, the solubility of CO2 is overestimated in the formation water using these two databases. Therefore, the model results calculate a larger retention capacity, defined as the quantity of CO2 dissolved in the formation water, than the Duan and Li model would do.
Factors controlling terrigenic SF6 in young groundwater of the Odenwald region (Germany) by R. Friedrich; G. Vero; C. von Rohden; B. Lessmann; R. Kipfer; W. Aeschbach-Hertig (318-329).
The mountainous Odenwald region in the federal state of Hesse/Germany is one of the main recharge areas for groundwater of the surrounding depressions, where substantial extraction for public water supply takes place. We investigated the groundwater to study residence times and mixing ratios of groundwater of different ages, define regions of groundwater recharge and understand the groundwater inflow from the Odenwald to the surrounding areas. This multi-tracer study included stable and radioactive gas and isotope tracers such as 2H, 18O, 3H, noble gases (He, Ne, Ar, Kr, Xe), 222Rn and SF6. Noble gases were used to calculate recharge temperatures of the groundwater and to correct all gas tracers for so called “excess air”. Comparing the results of the two independent dating methods – SF6 and 3H–3He – reveals that dating with SF6 is not possible in the crystalline region of the Odenwald, while the 3H–3He method gives robust groundwater ages. The results indicate that SF6 is influenced by a terrigenic source in the subsurface that varies with lithology. 222Rn data from part of the wells seem to be related to the terrigenic SF6, consistent with the idea of radiochemical SF6 production in rocks and release from the aquifer matrix.
The hyporheic zone composition of a mining-impacted stream: Evidence by multilevel sampling and DGT measurements by Barbara Palumbo-Roe; Rachel Dearden (330-345).
The importance of the hyporheic zone in influencing stream solute loads and stream ecosystems has been increasingly recognised. The hyporheic zone physicochemical composition of a stream stretch of the Rookhope Burn, a tributary of the River Wear in the North Pennines, UK, affected by historical mining of Pb ore, was characterised at two contrasting flow and temperature regimes. Vertical element concentration gradients were obtained using multilevel samplers down to a depth of 40 cm below the water–sediment boundary. Additional in situ Diffuse Gradients in Thin films (DGT) measurements of surface water and pore water were obtained.Circumneutral pH and oxidising conditions characterised the hyporheic zone of the study reach, composed of coarse-textured bed sediments. The surface hyporheic zone (top 15–20 cm) was dominated by the chemistry of the overlying water, while interactions with the solid phase were important for some elements in the deeper section of the hyporheic zone.Manganese was attenuated in the hyporheic zone as shown by SEM analysis of Mn-rich grain coatings from the bed sediment. Fine resolution data obtained through the use of the DGT probe deployed in the sediment at one sampling location, showed localised loss in Mn and Zn concentrations at 1.5–4.5 cm below the water–sediment interface. There was clear evidence for hyporheic pore water enrichment in Pb, which was unaffected seasonally, while Zn was greater in the summer sampling. These temporal variations of the hyporheic zone composition warrant consideration when accounting for the contribution of disperse inputs to mining impacted catchments, highlighting the need for hyporheic zone studies taking into account differences in seasons.The significance of the observed sediment-scale hyporheic processes on the reach-scale geochemical mass balance was estimated by using surface water geochemical loading calculations. Water metal mass balance from four previous sampling events indicated a constant loss of Mn load, a continuous gain of Pb load and a more temporally variable loss of Zn load for a 700 m stream stretch which included the study site. These results closely agreed with the present observations at the stream bed sediment scale, supporting the importance of hyporheic dynamic solute exchanges in affecting surface water quality for the study stream.
Numerical modeling of contaminated neutral drainage from a waste-rock field test cell by I. Demers; J. Molson; B. Bussière; D. Laflamme (346-356).
Contaminated drainage related to the leaching of soluble metals under near-neutral conditions, known as contaminated neutral drainage (CND), may arise when metal species are soluble at neutral pH. Such a phenomenon has been sporadically observed in effluent from the Tio mine waste-rock pile in Quebec, Canada, particularly from older sections of the pile, where Ni concentrations are increasing with time. It has been postulated that Ni is retained within the fresh waste rock as sorbed species, but as the rock ages, sorption sites become saturated and more Ni is released to the effluent. A field test program was initiated to evaluate the geochemical behavior of the waste rock. This paper presents a numerical analysis of CND generation from waste-rock field test cells including water flow and multi-component transport with geochemical reactions (e.g. sulfide oxidation, pH neutralization, and Ni sorption), using the code MIN3P. The model was able to represent the delay before Ni is seen in the effluent, as caused by sorption of Ni onto Fe-oxide particles. Once the sorption sites are saturated, the model allows Ni release into the effluent by millerite dissolution, expressed by the shrinking core model. A sensitivity analysis indicated that sorption parameters significantly affected the simulated results, so their selection should be based on sound independent field or experimental data.
Low head hyperfiltration through intact Burlington Limestone and Jefferson City Dolomite discs by Megan L. Hart (357-365).
Hyperfiltration is the ability of a membrane to retard the passage of a solute under a hydraulic head in excess of osmotic pressure. Disaggregated and recompacted shales, mudstones, clays and tuff have been shown to exhibit hyperfiltration-induced membrane effects in past experiments. However, limestone and dolomite have not previously been tested. Therefore, eight hyperfiltration experiments were performed on intact Burlington Limestone and Jefferson City Dolomite to assess the membrane properties of these lithologies. Four experiments were conducted on each lithology using 0.0050 and 0.0100 M Cl− solutions at heads of 0.50 and 1.00 m. Reflection coefficients, a measure of osmotic efficiency, ranged from 0.34 to 0.39 for the Burlington Limestone and 0.32 to 0.40 for the Jefferson City Dolomite. At the end of the hyperfiltration experiments, Cl− was concentrated within the cell above input concentrations by 85–95% for the Burlington Limestone and 79–105% for the Jefferson City Dolomite. An additional experiment passed 0.0020 M dissolved silica solution through the Burlington Limestone at a head of 0.965 bar (14 psi). The final concentration of silica within the cell was 0.0043 M dissolved silica at steady-state; a concentration 114% higher than the original input solution concentration. The reflection coefficient for this experiment was calculated to be 0.33. The results of these experiments suggest that membrane properties in these lithologies may be worthy of consideration in some geologic scenarios, including: (1) shallow or perched aquifers bounded by thin limestone or dolomite strata, (2) overpressured aquifers bounded by limestone or dolomite, (3) limestone or dolomite bounded aquifers with significant vertical components of flow, and (4) facies changes with significant lateral component of flow bounded by either lithology. Furthermore, the results suggest that silica cementation may be possible even under relatively low head conditions. Cementation due to hyperfiltration, even at shallow depths and low pressures should be further investigated. Similarly, other low permeability lithologies lacking a charged surface could potentially function as geologic membranes.
Erratum to “Biomarkers in surface sediments from the Cross River and estuary system, SE Nigeria: Assessment of organic matter sources of natural and anthropogenic origins” [Appl. Geochem. 31 (2013) 239–250] by Oliva Pisani; Daniel R. Oros; Orok E. Oyo-Ita; Bassey O. Ekpo; Rudolf Jaffé; Bernd R.T. Simoneit (366).