Applied Geochemistry (v.37, #C)

Microcosm assessment of the biogeochemical development of sulfur and oxygen in oil sands fluid fine tailings by Michael Chen; Gillian Walshe; Ernest Chi Fru; Jan J.H. Ciborowski; Christopher G. Weisener (1-11).
Bitumen recovery from Alberta oil sands generates fluid fine tailings, which are retained in tailings ponds where solids settle and release process water. The recovered water is recycled for bitumen extraction, while the resulting tailings are incorporated into various landforms for reclamation, with one option being conversion of tailings basins to viable end pit lakes. Tailings ponds commonly host diverse microbial communities, including SO4-reducing prokaryotes. The highly reducing nature of the hydrogen sulfide produced by these prokaryotes may impact the biogeochemical cycling of key nutrients. However, the behavioral dynamics of hydrogen sulfide production in ponds containing fluid fine tailings remain to be clearly explained. In this study, microcosms are used as analogues of the sediment–water interface of a tailings pond undergoing reclamation to determine sulfide generation patterns and the behavior of O2. In the microcosms, hydrogen sulfide fluxes correlated positively with biotic activity, reaching levels of over 2 × 103  nmol cm−2  s−1, leading to Fe sulfide formation. Depth-related hydrogen sulfide profiles in the microcosms were comparable to those encountered in situ, in Syncrude’s West In-Pit, an active tailing pond. Oxygen diffusion across the fluid fine tailing sediment–water interface was controlled to different degrees by both biotic and abiotic processes. The results have implications for quantitatively estimating the impact of hydrogen sulfide production, O2 availability, and biogeochemical cycling of key nutrients important for the success of life in fluid fine tailings-affected ecosystems. This paper shows that this production of hydrogen sulfide may be a self-limiting process, which will begin to decrease after a period of time.

Chemical analyses derived from petroleum exploration wells are notorious for their lack of key solute data and their potential to represent mixtures of reservoir and drilling fluids rather than pristine formation compositions. These drawbacks notwithstanding, they usually pose the only access to the reservoir geochemistry. Two literature protocols were applied to a dataset of incomplete major element analyses from 148 petroleum well samples from a database compilation of the Perth Basin whose deeper aquifers may serve as potential hot sedimentary aquifers for geothermal direct heat applications. The first protocol included a set of quality control criteria that reduced the number of relatively genuine formation well samples from the raw data pool by 71%. The remaining well analyses are invariably NaCl solutions of low to medium alkalinity and an ionic strength only occasionally reaching seawater salinity. The low amount of total dissolved solids indicates the absence of extended evaporites in the North Perth Basin and the prevalence of meteoric water infiltration and circulation at depths.The culled well samples underwent as a second protocol a forced equilibrium treatment to reconstruct in situ reservoir concentrations of missing elements (Si, Al, K), organic acid anions and non-carbonate alkalinity, and pH. The petroleum well samples were modelled to be in equilibrium with chalcedony (and kaolinite, albite, and paragonite) in the reservoir which yielded better convergence than using quartz instead. The derived formation temperatures correspond to geothermal gradients in the majority of cases between 25 and 35 °C, in accord with literature findings. Those wells drilled to depth <1600 m returned questionably high geothermal gradients, an indication of incomplete mineral–fluid equilibrium. The measured pH (at ambient temperature) deviated in >90% of the wells from the calculated pH, either due to degassed CO2 or unaccounted acetate alkalinity. The wells were further modelled to be undersaturated with respect to amorphous silica and anhydrite and not likely to experience scaling of any of these two phases during geothermal production at depth <3800 m. For calcite, scaling predictions depend in how far bubbling and phase segregation can be suppressed. For the six different stratigraphies investigated here, calculated bubble points were low, indicating that pressurisation of the entire production and re-injection line seems viable. Based on a calcite growth model from the literature it is shown that, if bubble formation and concomitant carbonate flash scaling cannot be averted, the production well should be as shallow as the temperature requirements of the geothermal production allow for.This study promotes the application of readily accessible protocols and a scaling model to deep well samples that may otherwise appear to have little geochemical value because of the way the samples were collected and handled. After data culling and treatment, insights into the geochemistry and scaling potential of deep clastic formations of the North Perth Basin that may hold the potential for geothermal exploitation as hot sedimentary aquifers can be gained.

The Cambrian–Ordovician Knox Group, a thick sequence of dolostone and minor dolomitic sandstone, is a prospective CO2 sequestration target in the southern Illinois Basin, USA. Thorough evaluation of the Knox Group is critical because the main sequestration target elsewhere in the Illinois Basin, the Cambrian Mount Simon Sandstone, is thin or absent throughout most of Kentucky. A 2477-m-deep carbon storage test well in Hancock County, Kentucky, was drilled, and 626 metric tons of CO2 was injected into the Knox saline reservoirs. To understand the long-term fate of CO2 injected into the Knox reservoirs, geochemical reactions between CO2, brine and rock-forming minerals were modeled using TOUGHREACT. The modeling benefited from a robust data set collected from the test well, including core porosity and permeability, petrographic and X-ray powder diffraction mineralogy, brine chemistry, temperature and pressure measurements. Kinetic batch models and 2-D radial reactive transport models were used to evaluate the migration of the injected CO2, changes in brine chemistry, and mineral dissolution and precipitation. Results from the kinetic models suggest that sections of the Knox dominated by dolomite have very limited mineral-trapping capacity for CO2, whereas thin sections of dolomitic sandstone with aluminosilicate minerals such as K-feldspar facilitate mineral trapping. The 2-D model for the CO2 injection test suggests that, because of the presence of thick permeable intervals in the Knox and the small volume of injected CO2 in the test, the radius of influence is less than 11 m from the well. The hypothetical long-term injection model indicates, on the other hand, that commercial-scale injection would influence a much larger area and part of the injected CO2 remains in the supercritical/gas phase for a long time. Because of the buoyancy effect, most supercritical/gas-phase CO2 migrates upward and stays in the top of the reservoirs dominated by dolomite with small mineral-trapping capacity.

Regional spatial distribution of multiple elements in the surface sediments of the eastern Tsushima Strait (southwestern Sea of Japan) by Atsuyuki Ohta; Noboru Imai; Shigeru Terashima; Yoshiko Tachibana; Ken Ikehara (43-56).
A total of 402 coastal sea-sediment samples were collected from the continental shelf, slope, and basin off Tsushima Island in the western Sea of Japan, and were analyzed for 51 elements as part of a nationwide marine geochemical mapping project. The samples were compared to potentially related sample sets, and the results were considered from the viewpoint of the origin of marine surface sediments in the western Sea of Japan. The spatial distribution of elemental concentrations in the coastal sea sediments correspond to texture, grain size, the presence of shells and foraminifera, and the mud content of surface marine sediments. Most elemental concentrations increased with increasing mud content. Some samples located in littoral areas included sediment particles apparently supplied from nearby rivers, but their contribution was limited. Overall, the mean chemical compositions of clastic material in coastal sea sediments appear to differ from those of stream sediments in adjacent terrestrial areas. In addition, the geochemistry of the coastal sea sediments cannot be fully explained by the mixing of the material supplied from Korean and Chinese stream sediments, which are the most feasible sources. Coastal sea sediments in the study area are well mixed by transportation processes; therefore, elemental abundances in these marine sediments may be homogenized to such an extent that it is not possible to determine their origin. Alternatively, most of the clastics in the sediment may actually represent relict reworked material, originally formed in the Yellow Sea and Tsushima Strait during the last glacial stage and subsequent transgression.

Mining influenced water may contain high metal and sulfate loads, and have low pH (acid mine drainage). Removal of these metals prior to environmental discharge is critical to maintain ecosystem vitality. Limestone based passive treatment systems are commonly used for pH neutralization. The same conditions that lead to pH neutralization may also remove a substantial amount of metals from solution, but the connection between treatment conditions and metal removal are not well understood. In this study, zinc and nickel removals are quantified in batch reactor simulated limestone treatment of acid mine drainage. The resulting solid phase is characterized with a sequential extraction procedure, and the removals are interpreted using surface complexation and surface precipitation models. Zinc and nickel removals are closely linked to the initial iron concentration in the mine water, but are also affected by pH, alkalinity, calcium and sulfate concentrations. The surface complexation model was based on literature descriptions of hydrous ferric oxide. In order to obtain a sufficient fit to the data, the surface site density was increased to an unrealistically high value. Uptake data was also fit to an existing surface precipitation model. The values used are similar to those found in previous studies. Both models indicate that adsorption is not the dominant removal process in the treatment system. Using adsorption only models will generally underpredict metal removals within limestone based treatment systems.

Links between climate change, water-table depth, and water chemistry in a mineralized mountain watershed by Andrew H. Manning; Philip L. Verplanck; Jonathan Saul Caine; Andrew S. Todd (64-78).
Recent studies suggest that climate change is causing rising solute concentrations in mountain lakes and streams. These changes may be more pronounced in mineralized watersheds due to the sensitivity of sulfide weathering to changes in subsurface oxygen transport. Specific causal mechanisms linking climate change and accelerated weathering rates have been proposed, but in general remain entirely hypothetical. For mineralized watersheds, a favored hypothesis is that falling water tables caused by declining recharge rates allow an increasing volume of sulfide-bearing rock to become exposed to air, thus oxygen. Here, we test the hypothesis that falling water tables are the primary cause of an increase in metals and SO4 (100–400%) observed since 1980 in the Upper Snake River (USR), Colorado. The USR drains an alpine watershed geologically and climatologically representative of many others in mineralized areas of the western U.S. Hydrologic and chemical data collected from 2005 to 2011 in a deep monitoring well (WP1) at the top of the USR watershed are utilized. During this period, both water table depths and groundwater SO4 concentrations have generally increased in the well. A numerical model was constructed using TOUGHREACT that simulates pyrite oxidation near WP1, including groundwater flow and oxygen transport in both saturated and unsaturated zones. The modeling suggests that a falling water table could produce an increase in metals and SO4 of a magnitude similar to that observed in the USR (up to 300%). Future water table declines may produce limited increases in sulfide weathering high in the watershed because of the water table dropping below the depth of oxygen penetration, but may continue to enhance sulfide weathering lower in the watershed where water tables are shallower. Advective air (oxygen) transport in the unsaturated zone caused by seasonally variable recharge and associated water table fluctuations was found to have little influence on pyrite oxidation rates near WP1. However, this mechanism could be important in the case of a shallow dynamic water table and more abundant/reactive sulfides in the shallow subsurface. Data from WP1 and numerical modeling results are thus consistent with the falling water table hypothesis, and illustrate fundamental processes linking climate and sulfide weathering in mineralized watersheds.

Metal contents of Porites corals from Khang Khao Island, Gulf of Thailand: Anthropogenic input of river runoff into a coral reef from urbanized areas, Bangkok by Kentaro Tanaka; Shigeru Ohde; Michael D. Cohen; Anond Snidvongs; Monthon Ganmanee; Cameron W. McLeod (79-86).
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been used to assess the impact of metal pollution on Porites skeletons taken from the Gulf of Thailand since the 1980s. The collection period coincided with a series of laws enacted by the Thai government to curb environmental pollution. The extent of metal pollution by riverine input, including aerosol deposits, was assessed by comparing the metal/Ca (Me/Ca) ratios in the Thai corals to the ratios of another colony of corals sampled from Rukan-sho, a relatively unpolluted coral reef located in Okinawa, Japan. In this comparison, high riverine inputs of Ba, V, Cd and Pb were observed in the Thai coral samples. Higher V/Ca ratios found in the Thai corals compared to the Rukan-sho coral suggest anthropogenic V inputs due to fuel oil pollution in the Gulf since the late 1990s. The levels of Cd in the coral suggest a gradual decrease in the Gulf in the late 1990s, with a drastic drop in concentration from the 1980s. The historical variation in Pb/Ca ratios recorded in the coral skeletons suggests that exposure to anthropogenic Pb was a result of discharge from urbanized areas from 1984 to 1998, which has been gradually reduced since Thailand prohibited the use of leaded gasoline in the late 1990s.

Forms of phosphorus in sediments from the Goczałkowice Reservoir by N. Młynarczyk; M. Bartoszek; J. Polak; W.W. Sułkowski (87-93).
The occurrence of Total P (P-Tot) and the mineral forms of P (P-Min) in sediments from Goczałkowice Reservoir were investigated using inductively coupled plasma-optical emission spectrometer (ICP-OES). The method is based on sequential extractions of the sediment samples, each releasing four forms of inorganic P: loosely bound P, P bound to Al (P-Al), P bound to Fe (P-Fe) and P bound to Ca (P-Ca). Sediment samples for studies presented in this work were collected in April, August and November of 2009 from four sites of the Goczałkowice Reservoir. Significant variations in the P forms with sediment grain size were observed. The most abundant form of inorganic P in the bottom sediment was P-Fe. Other P forms were as follows: P-Ca > P-Al > loosely bound-P. Moreover, P compounds were studied using 31P NMR. It was found that the predominant form was inorganic orthophosphate.

Trace element source terms for mineral dissolution by Madeline E. Schreiber; J. Donald Rimstidt (94-101).
We present an approach for determining source terms for modeling trace element release from minerals, using arsenic (As) as an example. The source term function uses laboratory-measured mineral dissolution rates to predict the time rate of change of As concentrations (mol/L s) released to water by the dissolving mineral. Application of this function to As-bearing minerals (realgar, orpiment, arsenopyrite, scorodite, pyrite, and jarosite) in air saturated water at 25 °C shows that mineralogy, grain size and pH are important factors affecting the As source term while DO concentration and temperature are relatively unimportant for conditions found in typical aquifers. The derived function shows that the source term decreases as a function of (1 −  t/tL )2, where tL is the grain lifetime, due to the shrinkage of the mineral grains as they dissolve. For some models, either a constant or an instantaneous term might be used, provided that certain time constraints are met. The methods outlined in this paper are intended to help bridge the gap between laboratory measurements and field-based models. Although this paper uses As as an example, the methods are general and can be used to predict source terms for other mineral-derived trace elements to groundwater.

A lake sediment core from Vermillion Lake, Sudbury, Ontario was tightly sampled and analyzed for a wide range of trace elements as well as for Pb isotopes. The data resolve multiple historical events in the 140-a history of logging and mining in the Sudbury area in unprecedented detail. Lead-210 data, 137Cs activity and historical information on the start of anthropogenic activities in the Sudbury area were combined to derive an age model for the sedimentary column. Using the age information, it is possible to identify sediment sections enriched and depleted in trace metal(loid)s, particularly Ni and Cu, the two most relevant metals in the Sudbury area. Maxima and minima in the chronology of Ni and Cu coincide well with local production values for both elements until environmental regulations in the 1990s resulted in a decrease in their emission and drainage into Vermillion Lake. Differences in the deposition rates of Ni and Cu, trace-metal distribution patterns throughout the sedimentary column, Pb-isotope data, and comparison with data for local rocks and ores in the Sudbury area were used to identify the sources of pollutants in the early and late periods of mining activities. In addition, the environmental impact on the sediment itself was also studied via the variation of water content and organic matter. Finally, a surficial Fe–Mn-enriched layer with elevated concentrations of the oxy-anions (PO4)3−, (AsO4)4−, and (MoO4)2− was identified. This can be distinguished from accumulation of Zn and an increase in the Y / Ho ratio in the upper core sections, which likely imply increasing drainage of fertilizers into the Vermillion River watershed. The chemistry, mineralogy, and isotope composition of the Vermillion Lake sediment column thus contain a very detailed >140-a account of initial severe anthropogenic disturbance, the efforts of remediation and the effects of changing land use towards agricultural and recreational activities.

Phytolith, the opal of amorphous silica formed in plant tissues, is present in most plants (mainly Poaceae, Cyperaceae and so on). The carbon bio-sequestration within the phytoliths of plants, one of the most promising approaches of long-term CO2 sequestration, is a significant mechanism of long-term biogeochemical carbon sequestration. This study analyzed the production and accumulation of phytolith-occluded-carbon (PhytOC) in Baiyangdian reed wetland of China. The plant phytolith extraction was undertaken with microwave digestion procedures and the soil phytolith extraction was based on the method of heavy liquid separation. The determination of the carbon content of phytoliths was based on phytolith-Si dissolution methods. The production flux of PhytOC for aboveground reed was 3.7–4.2 g CO2  m−2  a−1 and the accumulation flux of PhytOC for soil layer (0–15 cm) of soil deposition was 0.03 g CO2  m−2  a−1. The results imply that PhytOC content in reed dry biomass mainly depends on the content of the silicon taken up by the plant and the occluded carbon content of phytoliths during the plant growth. In Baiyangdian reed ecosystems, the rate of PhytOC for aboveground reed is about 6.77–7.69 × 108  g e CO2  a−1, and the accumulation rate of PhytOC for 0–15 cm soil layer is around 5.49 × 106  g CO2  a−1. Assuming the plant-area (5.7 × 108  ha) of global wetland with the similar maximum flux (0.054 t e CO2  ha−1  a−1) of reed PhytOC sequestration of atmospheric CO2, about 3.08 107 tone CO2 every year would be sequestrated by wetland ecosystem. The appropriate management of reed wetlands to maximize ANPP and select plant species with high-phytolith content or high-efficiency of phytolith occlusion of carbon has the potential to result in considerable production and accumulation quantities of PhytOC in reed wetland ecosystems.

At a Cr(VI) contaminated site in Thun, Switzerland, a permeable reactive barrier (PRB) was installed in 2008. Downstream Cr(VI) concentrations did not indicate any sign of its successful operation more than 2 years after PRB installation. The cause for this potential PRB failure was investigated by performing Cr isotope measurements and a multi-tracer experiment. The combination of reactive (Cr isotopes) and non-reactive tracers allowed characterizing the groundwater flow regime in the vicinity of the PRB in detail. In particular, it could be confirmed that most of the Cr(VI) load is currently bypassing the barrier, whereas only a minor Cr(VI) load is flowing through the PRB. Fitting of observed breakthrough curves using a conventional advection dispersion model resulted in average linear flow velocities of 13–15 m/day for the bypassing Cr(VI) load and 4–5 m/day for the Cr(VI) flowing through the barrier. Using a Rayleigh fractionation model a Cr(VI) reduction efficiency of 77–98% was estimated for the Cr(VI) load that is flowing through the barrier. In contrast, a value of 0–23% was estimated for the current overall PRB reduction efficiency. It is concluded that the PRB bypass and the low overall Cr(VI) reduction efficiency are caused by a limited PRB permeability inherited from skin effects that occurred during PRB emplacement.

Release of mantle and crustal helium from a fault following an inland earthquake by Koji Umeda; Koichi Asamori; Tomohiro Kusano (134-141).
Static stress changes caused by megathrust slip of the 2011 Mw 9.0 Tohoku-Oki earthquake considerably affected the seismicity patterns in inland areas, resulting in the occurrence of numerous earthquakes along several active faults in Japan. On June 30, 2011, the Mj 5.4 central Nagano earthquake occurred at a shallow depth of 5 km, indicating the reactivation of the Gofukuji fault in Central Japan. This study was undertaken to elucidate spatial and temporal changes of 3He/4He ratios around a source region before and after an inland earthquake using both existing and new and helium isotope data from hot spring and drinking water wells. Gas samples near the Gofukuji fault and its surrounding active faults are characterized by an increase in postseismic 3He/4He ratios. In contrast, the postseismic ratios decreased by up to about 30% away from the mainshock epicenter. Episodic faulting could either release stored crustal (radiogenic) helium from host rocks, or enhance the transfer of mantle volatiles through permeable fault zones, such that subsequent fluid flow near to the source region could then explain the spatio-temporal variations in 3He/4He ratios.

Evidence for microbially mediated production of elemental mercury (Hg0) in subarctic lake sediments by Michelle L. Brazeau; Jules M. Blais; Andrew M. Paterson; Wendel (Bill) Keller; Alexandre J. Poulain (142-148).
The production and fate of Hg0 in lake sediments remains poorly characterized, although it can potentially influence Hg toxicity and mobility. Using slurry incubations, we assessed the effect of nutrients, pH, ionic strength, and tested the role of microbes, on Hg0 production from pristine lake sediments of the Hudson Bay Lowlands in Ontario, Canada. We showed that Hg0 production from oxygenated sediments was low (<1% of the Hg flux to sediments), biogenic, and did not appear to be dependent on the predicted HgII speciation in the slurry. The addition of biologically labile carbon sources and ionic strength, particularly [Na+], had the greatest impact on Hg0 production, increasing it by over 10-fold. These results suggest that under changing conditions, such as increasing temperature or alteration of water chemistry as observed in numerous locations throughout Arctic and subarctic environments, a fraction of sedimentary Hg may be remobilized and available for microbial reduction.

High cadmium concentration in soil in the Three Gorges region: Geogenic source and potential bioavailability by Yizhang Liu; Tangfu Xiao; Zengping Ning; Huajun Li; Jiang Tang; Guangzhu Zhou (149-156).
This study investigated the distribution and sources of Cd in soils from a Cd-rich area in the Three Gorges region, China. The results showed that in the study area arable soils contain 0.42–42 mg kg−1 Cd with 0.12–8.5 mg kg−1 in the natural soils, corresponding to high amounts of Cd (0.22–42 mg kg−1) in outcropping sedimentary rocks in the area. Both lognormal distribution and enrichment factor (EF) plots were applied in an attempt to distinguish between geogenic and anthropogenic origins of Cd in the local soils. The lognormal distribution plots illustrated that geogenic sources dominated in soils with low and moderate Cd concentrations (<8.5 mg kg−1), whereas anthropogenic sources (agricultural activities, coal mining) significantly elevated Cd contents in some arable soils (>8.5 mg kg−1). The enrichment factor plots illustrated that the majority of the soil samples had EF values of <5, pointing to a geogenic origin of Cd in the soils, whereas some arable soils had EF values >5, pointing to an additional anthropogenic input of Cd to the soils. Sequential extraction results showed that Cd soluble in water and weak acid (water-soluble, exchangeable and carbonate fraction of the soil) accounts for an average of 31% of the total soil Cd, which indicates high potential for Cd mobility and bioavailability. The findings point to a potential health risk from Cd in areas with high geogenic background concentrations of this metal.

Phosphorus sorption and recovery using mineral-based materials: Sorption mechanisms and potential phytoavailability by Laura A. Wendling; Peter Blomberg; Tuija Sarlin; Outi Priha; Mona Arnold (157-169).
Recovery and re-use of P within hitherto unexploited waste streams may serve to reduce pressure on limited phosphate rock reserves. Since the mid-20th century there has been a dramatic increase in the use of mined phosphate rock for food production. Although economically exploitable quantities of phosphate rock are found in several countries, food security in those areas without domestic phosphate rock reserves is potentially vulnerable. Development and utilisation of efficient, cost-effective techniques for P recovery from solid and liquid waste materials may also reduce energy and/or material requirements for P acquisition. Phosphorus may be removed from solution via selective sorption to a solid phase and direct use of the material as a fertilizer or soil conditioner, or the sorbed P may subsequently be stripped from the solid sorbent and chemically precipitated as a high-purity fertilizer. Ideal sorbents for P recovery from solution possess high phosphate sorption capacity and selectivity, are capable of kinetically rapid P sorption from solution, and are stable materials resistant to degradation during both P sorption and desorption. This review provides a critical assessment of P sorption to a range of mineral-based materials and the potential application of these materials to P recovery schemes.

Cobalt(II) sequestration on fungal biogenic manganese oxide enhanced by manganese(II) oxidase activity by Jianing Chang; Yukinori Tani; Hirotaka Naitou; Naoyuki Miyata; Haruhiko Seyama; Kazuya Tanaka (170-178).
Display OmittedWe examined the ability of biogenic manganese oxide (BMO) formed in the cultures of a Mn(II) oxidizing fungus, Acremonium strictum strain KR21-2, to sequester Co(II) and found that the newly formed BMO effectively sequestered Co(II) under aerobic conditions with virtually no release of Mn(II). Under anaerobic conditions, smaller amounts of Co(II) were sequestered and a significant amount of Mn(II) was released. Similar trends were observed when the BMOs were poisoned with 50 mM NaN3 or heated at 85 °C for 1 h. X-ray absorption near-edge structure spectroscopy and two-step extraction confirmed that oxidation of Co(II) to Co(III) occurs with BMOs with higher oxidation efficiency under aerobic conditions. These results demonstrate that BMOs can reoxidize Mn(II) through the Mn(II) oxidase associated with the BMO phase and can subsequently provide a new reaction site for Co sequestration. The ability of BMO to sequester Co(II) was also found to be long lasting in 20 mM 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES) buffer (pH 7.0) containing no nutrients to maintain fungal growth, because sequential treatment of BMOs with the Co(II) solution every 24 h for at least 8 days led to Co(II) sequestration. In addition, Co accumulation in the solid phase was eventually 2.48-fold relative to the accumulation of Mn oxide (molar ratio). X-ray diffraction results suggest that the continuing Co(II) oxidation by newly formed BMOs results in the formation of heterogenite (β-CoOOH) aggregates. Assays using the concentrated Mn(II) oxidase crude solution showed that the preformed Mn oxide phase was important for further Mn(II) oxidation in coexisting Co(II). The fact that the coexisting Co(II) was less inhibitory to Mn(II) oxidation if the preformed Mn oxide phase was present suggests a possible electron path from Co(II) to the final electron acceptor O2 through BMO and Mn(II) oxidase in BMO/enzyme aggregation. These results suggest that fungal BMOs supporting Mn(II) oxidase activity can serve as an effective Co(II) sequestering material, without the need for additional nutrients.

Display OmittedThe efficiency of As removal by Fe oxyhydroxide-based adsorbents was studied. Water containing micro-molar concentrations of As was cleaned using columns containing ferrihydrite-coated grains of sand or the commercial material granular ferric hydroxide, GFH®. Adsorption of considerable amounts of arsenate and arsenite were achieved on a sub-minute time scale with both adsorbents. Furthermore, efficient adsorption on GFH® can be achieved in seconds of empty bed contact time. Arsenate adsorption was affected by moderate changes in pH, while such an effect was negligible for arsenite. At slightly acidic pH substantially higher amounts of arsenate could be adsorbed. The Fe content of the coated sand was varied and it was found that more As was adsorbed on grains with a higher Fe content, however, the relationship was far from proportional. This is supported by scanning electron microscopy and energy dispersive spectroscopy, which showed that in addition to the occurrence of Fe in compounds coating the flakes, it also occurred adsorbed to the surface. The Fe oxyhydroxide coating was confirmed to be ferrihydrite using EXAFS spectroscopy. Batch experiments with ferrihydrite support the view that almost all can be adsorbed with a sufficient surplus of Fe oxide/hydroxide mineral suspension.

Biogeochemical indicators of buried mineralization under cover, Talbot VMS Cu–Zn prospect, Manitoba by Karla Leslie; Pim W.G. van Geffen; Bill MacFarlane; Christopher J. Oates; T. Kurt Kyser; David A. Fowle (190-202).
Results are presented of a surficial geomicrobiological investigation of glacial cover overlying buried mineralization at the Talbot prospect, Manitoba, Canada, where previous surficial geochemistry surveys indicated anomalous concentrations of elements above the buried mineralization. The Cu–Zn volcanogenic massive sulfide (VMS) occurrence is overlain by 100 m of Paleozoic dolomites and Quaternary glacial cover. The geomicrobiological investigation demonstrates that there is a distinct microbial ecology at the anomalous sampling locations, especially directly overlying buried mineralization. The combined geochemical and geomicrobiological analyses reveal the presence of an anomaly directly over mineralization due to oxidation of the buried ore. Specifically, geomicrobiological analyses yield an inverse correlation between Zn in the clay-size (<2 μm) fraction and total microbial biomass and a direct correlation between Cu in the clay-size (<2 μm) fraction and abundance of methanotrophic bacteria. These results demonstrate that microbiological analyses can be a useful addition to geochemical exploration by revealing metal transport and sequestration processes and enhancing surficial anomalies.

Natural and depleted uranium in the topsoil of Qatar: Is it something to worry about? by Basem Shomar; Mohamed Amr; Khalid Al-Saad; Yasir Mohieldeen (203-211).
This study examines uranium in soils of Qatar to investigate whether there is any detectable traces of depleted uranium (DU). 409 soil samples were collected using a 10 km grid system throughout the State of Qatar. The U concentrations and isotopic compositions (235U/238U) were determined using an ICP-MS. The U concentrations range from 0.05 to 4.7 mg/kg and the 235U/238U isotopic signatures are in the range 0.007–0.008, i.e. comparable to the isotopic ratio in natural uranium (NU). The distribution of these concentrations in the topsoil were used to see correlations with locations of pollution point sources and environmentally hot areas associated with human activity: industrial estates, solid waste dumping sites, wastewater treatment plants, sea harbors, airports, and public transport network. New thematic maps were built using Geographic Information System (GIS) software. The results showed that there is no linkage between the occurrence, distribution, concentrations and isotopic ratios of U and these hotspots. More importantly, due to the low concentration of organic matter (OM) in soils of Qatar, very limited P-fertilization, the alkaline nature of soil (pH 8) and low Fe/Mn contents make soil uranium concentrations very low. The residential areas, including the capital Doha, had the lowest total concentrations of uranium and isotopic ratios of the country while the northern and western parts showed the highest values.

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France) by Mahmoud Khaska; Corinne Le Gal La Salle; Joël Lancelot; ASTER team; Amad Mohamad; Patrick Verdoux; Aurélie Noret; Roland Simler (212-227).
In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl concentrations. Average and maximum Cl concentrations in the recharge waters were calculated (ClRef. and ClRef.Max) to be 0.51 and 2.85 mmol/L, respectively). Group A includes spring waters with Cl concentrations that are within the same order of magnitude as the ClRef concentration. Group B includes groundwater with Cl concentrations that range between the ClRef and ClRef.Max concentrations. Group C includes brackish groundwater with Cl concentrations that are significantly greater than the ClRef.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO3 to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Clmolar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display 87Sr/86Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The 36Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The 87Sr/86Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.

Lithologically inherited variation in Pb isotope ratios in sedimentary soils in The Netherlands by N. Walraven; P.F.M. van Gaans; G. van der Veer; B.J.H. van Os; G.Th. Klaver; S.P. Vriend; J.J. Middelburg; G.R. Davies (228-241).
Knowledge on the lithologically inherited variation in present day Pb isotope ratios in soils is remarkably limited. Such information is essential to determine the anthropogenic Pb fraction and anthropogenic Pb sources in Pb-polluted soils. This study presents results of a survey of subsoil samples from approximately 350 rural locations covering the entire Netherlands, for which the bulk geochemical and Pb isotope composition was determined. The sample density was approximately 1 site per 70 km2. The aim was to establish a geochemical reference for the lithologically inherited variation in Pb isotope ratios in Dutch soils based on the subsoil samples, with which to compare the topsoils (companion paper in this journal issue).The lithologically inherited variation in Pb isotope ratios of the subsoils in The Netherlands is established at 1.175–1.221, 2.441–2.494 and 0.478–0.492 for 206Pb/207Pb, 207Pb/208Pb and 206Pb/208Pb respectively. The four main lithologies distinguished, sand, clay, peat and loess, have distinct Pb isotope signatures. No significant difference in isotope signature was found between marine and fluviatile clays. Multiple regression analysis established that the observed variation can be primarily explained by the textural and mineralogical variation within Dutch subsoils, with Al and Zr content representing useful predictors for the observed Pb isotope variability. Clay soils are characterised by a radiogenic Pb isotope signature that is notably low in 207Pb. Soils with a high Zr content are especially high in 206Pb. Although the vast majority (∼90%) of the Pb isotope variation in the subsoils appears to be controlled by lithological inheritance, some subsoils (mainly peats) are suspected of containing a component of non-lithologically derived Pb.

Tracing diffuse anthropogenic Pb sources in rural soils by means of Pb isotope analysis by N. Walraven; P.F.M. van Gaans; G. van der Veer; B.J.H. van Os; G.Th. Klaver; S.P. Vriend; J.J. Middelburg; G.R. Davies (242-257).
Knowledge of the cause and source of Pb pollution is important to abate environmental Pb pollution by taking source-related actions. Lead isotope analysis is a potentially powerful tool to identify anthropogenic Pb and its sources in the environment. Spatial information on the variation of anthropogenic Pb content and anthropogenic Pb sources in rural topsoils is remarkably limited. This study presents results of a survey of approximately 350 topsoil samples from rural locations covering the entire Netherlands, for which the bulk geochemical and Pb isotope compositions were determined. The specific aim of this study is to determine the anthropogenic Pb sources in the topsoils from rural areas in The Netherlands. The spatial distribution of anthropogenic Pb in soils in The Netherlands will be explained in terms of land use and pollution sources.Nearly all studied topsoils display Pb contents that exceed the amount expected based on the soil lithology. The range in Pb isotope ratios of the additional Pb fraction in rural Dutch topsoils is established at 1.056–1.199, 2.336–2.486 and 0.452–0.490 for 206Pb/207Pb, 207Pb/208Pb and 206Pb/208Pb, respectively. Five land use types are distinguished (forest, open nature, moor, arable land and grassland) with distinct isotopic compositions for added Pb. Additional Pb in soils of natural areas (forest, open nature and moor) has on average lower 206Pb/207Pb, 208Pb/207Pb and 206Pb/208Pb ratios than the agricultural soils (arable land and grassland). Additional Pb in both natural area soils and agricultural soils is interpreted to be of anthropogenic origin: most likely a mixture of coal/galena, incinerator ashes and gasoline Pb. The dominant sources of additional Pb in the topsoil of open nature areas are most likely incinerator ash and gasoline Pb. In contrast, the on average higher 206Pb/207Pb, 208Pb/207Pb and 206Pb/208Pb ratios of additional Pb in agricultural soils are most likely caused by the presence of animal manure and N–P fertilizers.Several areas are observed with notably high additional Pb contents (26–211 mg/kg on an organic matter-free basis) in the topsoil. The largest area is the Randstad area, which has the highest population and traffic density, and hosts a considerable fraction of the Dutch chemical industry. Two other areas with high additional Pb contents in the topsoil are located near the Dutch borders and are most likely influenced by German and Belgian chemical industries. The topsoils in the coastal dunes and southern, central and northern forests are characterized by relatively low additional Pb contents (<10 mg/kg on an organic matter-free basis). The population, traffic and chemical industry density is low in these areas and no fertilizers are applied.