Applied Geochemistry (v.24, #3)

Black shale is often rich in sulfides and trace elements, and is thus a potential environmental threat in a manner similar to acid sulfate soils and active or abandoned sulfide mines. This study aims at characterising how exposed and processed (mined and burnt) black shale (alum shale) in Degerhamn, SE Sweden, affects the chemistry (Al, As, Ba, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Mo, Ni, K, Si, Na, Sr, S, U, V and Zn) of the groundwater. There were large variations in groundwater chemistry between nearby sampling points, while the temporal variations generally were small. Acidic groundwater (around pH 4), found in deposits of burnt and carbonate-poor shale where the conditions for sulfide oxidation were favourable, was strongly elevated in Al, U and several chalcophilic metals (Cd, Co, Cu, Ni and Zn). Cadmium and U were also, together with Mo, abundant in many of the near-neutral waters, both in the non-mined black shale bedrock and in the deposits of burnt shale. An extrapolation to a national level suggests that the dispersion of Ni from naturally occurring black shale is similar to that from anthropogenic point sources, while for Cd and As it is assessed to be approximately one tenth of that from point sources. The processed shale was, however, a much larger source of metals than the black shale bedrock itself, showing this material’s potential as a massive supplier of metals to the aquatic environment. A comparison of waters in contact with the processed Cambrian–Ordovician black shale in Degerhamn and acid sulfate soils of the region shows that these two sulfide-bearing materials, in many respects very different, delivers basically the same suite of trace elements to the aquatic environment. This has implications for environmental planning and protection in areas where these types of materials exist.

Since July 2002, tertiary treated waste water has been used to artificially recharge the phreatic aquifer of the dunes in the Belgian western coastal plain. The purpose of this project is to develop a sustainable water source, and thereby minimize lowering of the water table while maintaining production capacity. The recharged water is extracted via production wells located south and north of two ponds used for the recharge. The uniqueness of this system is that the total dissolved solids in this recharge water is low (50 mg/L) in comparison with natural dune water (550 mg/L). In this paper, water quality of recharge water, groundwater between ponds and extraction wells, extracted water and dune water is analysed. The extraction water quality is determined by mixing of recharged water and dune water. Mineralisation of the recharge water occurs mainly by carbonate dissolution. Further O2 consumption, NO 3 - reduction and oxidation of Fe sulfide minerals are distinguished. At the beginning of 2007 clogging of the ponds began to occur and it was observed that extraction rates and temperature of the recharge water influenced the amount of water which could be recharged. Using Cl data, it is confirmed that all the recharged water is recovered by the extraction wells. Finally, it is concluded that the quality of the extracted water does not change significantly as a function of time.

Acid mine drainage represents a major source of water pollution in the Lousal area. The concentrations of trace metals and the rare earth elements (REE) in the host rocks, stream sediment, surface waters and acid mine drainage (AMD) associated with abandoned mine adits and tailings impoundments were determined, in order to fingerprint their sources and to understand their mobility and water–rock interaction. The results show that the Fe–SO4-rich acid waters vary substantially in composition both spatially and seasonally. These waters include very low pH (mostly in the range 1.9–3.0), extreme SO4 concentrations (4635–20,070 mg L−1 SO 4 2 - ), high metal contents (Fe, Al, Cu, Zn and Mn) and very high REE contents. The trace metal concentrations decrease downstream from the discharge points either due to precipitation of neoformed phases or to dilution. The North-American shale composite (NASC)-normalized patterns corresponding to sediment from one stream (Corona stream) show a flat tendency or are slightly enriched in light-REE (LREE). The NASC-normalized patterns corresponding to acidic mine waters show enrichment in the middle REE (MREE) with respect to the LREE and heavy REE (HREE). Moreover, the REE concentrations in acidic mine waters are 2 or 3 orders of magnitude higher than those of the surface waters. Changes of REE concentrations and variation of Eu anomaly show two spatially distinct patterns: (a) pond and spring waters with higher REE concentrations (ranging from 375 to 2870 μg L−1), that records conspicuous negative Eu anomaly, and (b) seeps from tailings impoundments corresponding to lower REE concentrations than the first pattern (ranging from 350 to 1139 μg L−1) with typically negative Eu anomaly. The stream water samples collected from the impacted stream during the spring show a low pH (2.8–3.1) and contain high concentrations of Fe and trace elements (up to 61 mg L−1). Also, temporal variations of the REE concentrations were observed in the Corona waters. The results obtained show that the REE concentrations increase during the winter–spring transition. Stream waters draining the Lousal mine area show high REE concentrations, reaching a maximum value of about 2846 μg L−1 (spring). The MREE concentrations are usually enriched with respect to both the LREE and HREE. A decrease in REE concentrations and a pH increase from 3 to 6 was observed downstream of the confluence of a tributary stream.The geochemistry of the waters strongly influenced the mineralogy and geochemistry of efflorescent sulfates precipitated on the banks of the streams polluted by AMD. The mineralogy is dominated by hexahydrite, rozenite, szomolnokite, alunite, gypsum, halotrychite, coquimbite, copiapite and schwertmannite. The REE concentrations determined in the efflorescent sulfates suggest a selective partitioning of the HREE onto Mg–Al-oxyhydroxides.

A hot spring in granite of the Western Tianshan, China by Kurt Bucher; Lifei Zhang; Ingrid Stober (402-410).
The western Tianshan range is a major Cenozoic orogenic belt in central Asia exposing predominantly Paleozoic rocks including granite. Ongoing deformation is reflected by very rugged topography with peaks over 7000 m high. Active tectonic deformation is tied to an E–W trending fracture and fault system that sections the mountain chain into geologically diverse blocks that extend parallel to the orogen. In the Muzhaerte valley upwelling hot water follows such a fault system in the Muza granite. About 20 L min−1 Na–SO4–Cl water with a temperature of 55 °C having a total mineralization of about 1 g L−1 discharge from the hot spring. The water is used in a local spa that is frequented by the people of the upper Ili river area. Its waters are used for balneological purposes and the spa serves as a therapeutic institution. The major element composition of the hot water is dominated by Na and by SO4 and Cl, Ca is a minor component. Dissolved silica (1.04 mmol L−1) corresponds to a quartz-saturation temperature of 116 °C and a corresponding depth of the source of the water of about 4600 m. This temperature is consistent with Na/K and Na/Li geothermometry. The water is saturated with respect to fluorite and contains 7.5 mg L−1  F as a consequence of the low Ca-concentration. The water is undersaturated with respect to the primary minerals of the reservoir granite at reservoir temperature causing continued irreversible dissolution of granite. The waters are oversaturated with respect to Ca–zeolite minerals (such as stilbite and mesolite), and it is expected that zeolites precipitate in the fracture pore space and in alteration zones replacing primary granite.The stable isotope composition of O and H supports a meteoric origin of the water. The Cl/Br mass ratio of 1500 suggests that the salinity results from halite dissolution. Salts leached from powders of Muza granite show the same Cl/Br signature as the hot spring water. Sodium chloride is stored in fluid and solid inclusions in the granite, which have been introduced to quartz by ductile shearing and faulting related to ongoing orogenesis. The hot water remobilizes the salt that is continuously liberated by the tectonic deformation. Water–granite interaction contributes a thenardite-component (Na2SO4) to the major element composition by albite dissolution in H2SO4. The water–rock interaction along faults and fractures transforms and alters Muza granite to a low-temperature epigranite.

Bulk geochemical parameters and organic matter biomarkers in a short, high resolution gravity core (Lake Valencia, Venezuela) were examined to reconstruct anthropogenic impacts on the lake’s conditions. During the period of ca. 1840–1990, sedimentary organic matter was characterized by high contents of total organic C (TOC) and total N (TN), low TOC/TN values as well as relatively enriched δ 13C and δ 15N signals, suggesting a primary autochthonous (algae and macrophytes) organic matter origin. The occurrence of large amounts of C23 and C25 relative to C29 and C31 n-alkanes indicated substantial inputs from submerged/floating macrophytes. The variations of C32 15-keto-ol, tetrahymanol, diploptene, C32 bishomohopanol, 2-methylhopane, dinosterol and isoarborinol concentrations over the investigated period record changes in the planktonic community structure, including Botryococcus braunii, bacteriavore ciliates, cyanobacteria, Eustigmatophytes and dinoflagellates. A principal shift occurred in the 1910s when cyanobacteria and dinoflagellates became more abundant at the expense and decline of B. braunii and Eustigmatophytes, likely related to increasing anthropogenic activity around the lake. A second shift (less obvious) occurred in the 1960s when cyanobacteria became the sole predominant planktonic class, coinciding with further deterioration of lake conditions.

Almost invariably the compositions of porewaters given for highly compacted bentonite are calculated values because reliable water samples from compacted material are virtually impossible to obtain, even by squeezing under very high pressures. Assumptions and simplifications are made in the geochemical models used to perform such calculations and the predictions are seldom if ever tested. One of the main hypotheses in a recently proposed model for calculating the porewater in compacted bentonite was that the initial pH is determined by the state of the amphoteric surface hydroxyl groups, SOH type sites, on the montmorillonite component. The calculations indicated that the initial pH of the porewater is a value close to 8. The aims of the work reported here are to check the predictions of the model in terms of the pH, which is one of the most important parameters for any porewater, and the strong buffering effect of the SOH type sites. The concept behind the tests was to take a powdered bentonite and a background electrolyte (0.2 M CaCl2) containing known quantities of acid or base (pH values between 1.5 and 12), mix them together at a high solid to liquid ratio (312 g L−1) and then allow them to react in the absence of air in a closed system. If the model concepts and parameter values are valid, then the model should be able to predict the pH measured in such experiments. The model calculations agreed well with the measured pH values and confirmed that it is highly likely that the SOH type sites determine the initial pH of the porewater in compacted bentonite systems. Further, these amphoteric surface hydroxyl groups at the edges of montmorillonite provide an extremely high buffer capacity in the compacted system for maintaining the bentonite porewater pH at a value of ∼8.

Influence of upwelling saline groundwater on iron and manganese cycling in the Rio Grande floodplain aquifer by Matthew F. Kirk; Laura J. Crossey; Cristina Takacs-Vesbach; Dennis L. Newell; Robert S. Bowman (426-437).
Salinity contributions from upwelling groundwater significantly degrade water quality in the Rio Grande, a major source of water for the southwestern USA. This study considers the influence of this upwelling water on the geochemistry and microbiology of the Rio Grande floodplain alluvial aquifer. The composition of surface water, groundwater, and floodplain sediment samples collected from three transects in the Socorro Basin was examined. Terminal-restriction fragment length polymorphism (T-RFLP) was also used to examine microbial biomass samples. The distribution of salinity in the floodplain groundwater largely reflects the configuration of local groundwater flow and mixing of two major water sources, deeply-sourced saline groundwater and river water. Microbial populations in the shallow aquifer consume O2 and NO 3 - and serve to redistribute metal oxides from the saturated zone to locations of groundwater discharge at the surface and possibly near the water table. The upwelling saline groundwater affects floodplain microbial processes by transporting reduced metals and organic electron donors to the alluvial aquifer system. This enhances metal reduction in the saturated zone and ultimately metal oxidation at or near the surface. Geochemical modeling suggests that mixing of the saline groundwater with more dilute water in the floodplain creates conditions more favorable for metal oxidation to occur and thereby influences the distribution of metal oxides.

The Saga Plain is near Beppu–Shimabara graben, a region of potential active volcanism. In the graben, mantle He, which has a high 3He/4He ratio of 1.1 × 10−5, escapes easily from the underlying subduction zone. In groundwater of the Saga Plain, except in the Shiroishi district, this ratio gradually increased as the dissolved He content increased, to a maximum of 5 × 10−6. In central Shiroishi, however, the ratio reached a minimum of 8.7 × 10−7 with increasing dissolved He content, suggesting that groundwater in central Shiroishi has selectively accumulated radiogenic He, which has a very low ratio of 1 × 10−8, rather than reflecting the regional He, which is rich in mantle He. This can be explained if groundwater in Shiroishi has become mixed with fossil pore water drawn from impermeable marine clay aquitard layers. The withdrawal of pore water has also caused severe land subsidence in central Shiroishi.

The distribution and content of rare-earth elements (REEs) were determined in two radish species, the cultivated Raphanus sativus and the wild Raphanus raphanistrum, that were grown under laboratory-controlled conditions, in three substrates consisting of illite for one and two smectite substrates for the others, with the two smectite substrates being characterised by different porosities. The plants were split into leaves and stems + roots for analysis. The results indicate that both species take up systematically higher amounts of REEs when grown in the illite substrate, even considering that the smectite equivalent contains about three times more REEs. The REE uptake is also more plant species than mineral composition dependent: R. raphanistrum takes up 3.5–6.7 times more REEs than R. sativus, depending on the substrate, its porosity and the considered plant segments. Increased substrate porosity favours the take up of the REEs, but no specific uptake is observed in leaves relative to that in the combined stems and roots. The transfer of the REEs from minerals to plant organs does not appear to induce systematically identical patterns: (1) in the case of R. sativus, a positive Eu anomaly is visible in all patterns from both segment groups grown in both substrates. When grown in illite, the heavy REEs are also enriched in the stems and roots, which has not been observed in any other organ or in the other substrate and (2) in the case of R. raphanistrum, a very significant positive Gd anomaly, which is not expected to fractionate relative to the other REEs as do Ce and Eu, is observed in all segments of the plants grown in both substrates. A slight negative Ce anomaly is also visible in some of the REE patterns, suggesting some changes in the oxidation–reduction conditions in the substrates near the roots during plant growth. The comparison of the REE patterns from leaves relative to those of the roots + stems shows that those of R. raphanistrum grown in illite provide a spectrum that is very specific with significant deficits in La, Ce, Gd, Tm, Yb and Lu in the leaves. In the other cases, the patterns do not outline significant differences except for R. sativus grown in illite, in which the leaves are enriched in light and medium REEs from La to Gd relative to the stems + roots.

Towards a consistent geochemical model for prediction of uranium(VI) removal from groundwater by ferrihydrite by Jon Petter Gustafsson; Ellinor Dässman; Mattias Bäckström (454-462).
Uranium(VI), which is often elevated in granitoidic groundwaters, is known to adsorb strongly to Fe (hydr)oxides under certain conditions. This process can be used in water treatment to remove U(VI). To develop a consistent geochemical model for U(VI) adsorption to ferrihydrite, batch experiments were performed and previous data sets reviewed to optimize a set of surface complexation constants using the 3-plane CD-MUSIC model. To consider the effect of dissolved organic matter (DOM) on U(VI) speciation, new parameters for the Stockholm Humic Model (SHM) were optimized using previously published data. The model, which was constrained from available X-ray absorption fine structure (EXAFS) spectroscopy evidence, fitted the data well when the surface sites were divided into low- and high-affinity binding sites. Application of the model concept to other published data sets revealed differences in the reactivity of different ferrihydrites towards U(VI). Use of the optimized SHM parameters for U(VI)-DOM complexation showed that this process is important for U(VI) speciation at low pH. However in neutral to alkaline waters with substantial carbonate present, Ca–U–CO3 complexes predominate. The calibrated geochemical model was used to simulate U(VI) adsorption to ferrihydrite for a hypothetical groundwater in the presence of several competitive ions. The results showed that U(VI) adsorption was strong between pH 5 and 8. Also near the calcite saturation limit, where U(VI) adsorption was weakest according to the model, the adsorption percentage was predicted to be >80%. Hence U(VI) adsorption to ferrihydrite-containing sorbents may be used as a method to bring down U(VI) concentrations to acceptable levels in groundwater.

Chemical evolution of the Mt. Hekla, Iceland, groundwaters: A natural analogue for CO2 sequestration in basaltic rocks by Therese K. Flaathen; Sigurður R. Gislason; Eric H. Oelkers; Árný E. Sveinbjörnsdóttir (463-474).
A detailed study of the chemical composition of the groundwater surrounding the Mt. Hekla volcano in south Iceland was performed to assess fluid evolution and toxic metal mobility during CO2-rich fluid basalt interaction. These fluids provide a natural analogue for evaluating the consequences of CO2 sequestration in basalt. The concentration of dissolved inorganic C in these groundwaters decreases from 3.88 to 0.746 mmol/kg with increasing basalt dissolution while the pH increases from 6.9 to 9.2. This observation provides direct evidence of the potential for basalt dissolution to sequester CO2. Reaction path calculations suggest that dolomite and calcite precipitation is largely responsible for this drop in groundwater dissolved C concentration. The concentrations of toxic metal(loid)s in the waters are low, for example the maximum measured concentrations of Cd, As and Pb were 0.09, 22.8 and 0.06 nmol/kg, respectively. Reaction path modelling indicates that although many toxic metals may be initially liberated by the dissolution of basalt by acidic CO2-rich solutions, these metals are reincorporated into solid phases as the groundwaters are neutralized by continued basalt dissolution. The identity of the secondary toxic metal bearing phases depends on the metal. For example, calculations suggest that Sr and Ba are incorporated into carbonates, while Pb, Zn and Cd are incorporated into Fe (oxy)hydroxide phases.

Effects of sewage sludge on solution chemistry and plant uptake of Cu in sulphide mine tailings at different weathering stages by Lovisa Stjernman Forsberg; Dan Berggren Kleja; Maria Greger; Stig Ledin (475-482).
This climate chamber experiment examines the effects of sewage sludge (SS) on sulphide mine tailings from the Aitik Cu mine in northern Sweden. The effects of SS were determined from Cu in solution and Cu uptake and growth of plants on tailings showing 3 different degrees of weathering. Possible relationships between Cu content in plants and Cu in solution measured in tailings (total dissolved Cu and free Cu) were also evaluated. Red fescue (Festuca rubra) was grown for 6 weeks in pots of the different tailings treated with SS or NPK fertiliser. Soil solution was sampled with Rhizon tension lysimeters and analysed for pH, dissolved organic C (DOC), free Cu, total dissolved Cu and SO 4 2 - . The effects of SS on Cu in solution and plants depended on the degree of weathering. In tailings with a low degree of sulphide oxidation, SS application resulted in increased solubility and shoot accumulation of Cu compared with NPK-treated tailings, probably due to DOC forming soluble complexes with Cu. Sewage sludge also seemed to promote translocation of Cu to shoots in those tailings. In highly weathered tailings, lower contents of total dissolved Cu and free Cu in solution and lower Cu levels in shoots were found in SS-treated samples than in NPK-treated. In the moderately weathered tailings, Cu concentrations in solutions were generally similar between treatments, but lower contents of Cu were found in shoots and roots of the fescue grown in the SS-treatment. Irrespective of degree of weathering and treatment, both free Cu and total dissolved Cu concentration in tailings correlated strongly with Cu levels found in fescue shoots.

Reply to the comment on “Arsenic release from biotite into a Holocene groundwater aquifer in Bangladesh” by Hossain M. Anawar and Martin Mihaljevič by Ashraf Ali Seddique; Harue Masuda; Muneki Mitamura; Keiji Shinoda; Takamoto Okudaira; Toshiro Yamanaka; Takaaki Itai; Teruyuki Maruoka; Kenji Uesugi; Kazi Matin Ahmed (486-490).