Applied Geochemistry (v.27, #8)

The sources and budget for dissolved sulfate in a fractured carbonate aquifer, southern Sacramento Mountains, New Mexico, USA by Anna Szynkiewicz; B. Talon Newton; Stacy S. Timmons; David M. Borrok (1451-1462).
► Dedolomitization controls water chemistry in the studied carbonate aquifer. ► S isotope composition of sulfate is controlled by evaporite dissolution and sulfide oxidation. ► Sulfate derived from pyrite weathering accounts for 0–10% of the total SO4 budget. ► Sulfuric acid from sulfide oxidation is partly responsible for carbonate dissolution.Climate change in the SW USA is likely to involve drier conditions and higher surface temperatures. In order to better understand the evolution of water chemistry and the sources of aqueous SO4 in these semi-arid settings, chemical and S isotope compositions were determined of springs, groundwater, and bedrock associated with a Permian fractured carbonate aquifer located in the southern Sacramento Mountains, New Mexico, USA. The results suggest that the evolution of water chemistry in the semi-arid carbonate aquifer is mainly controlled by dedolomitization of bedrock, which was magnified by increasing temperature and increasing dissolution of gypsum/anhydrite along the groundwater flow path. The δ 34S of dissolved SO4 in spring and groundwater samples varied from +9.0‰ to +12.8‰, reflecting the mixing of SO4 from the dissolution of Permian gypsum/anhydrite (+12.3‰ to +13.4‰) and oxidation of sulfide minerals (−24.5‰ to −4.2‰). According to S isotope mass balance constraints, the contribution of sulfide-derived SO4 was considerable in the High Mountain recharge areas, accounting for up to ∼10% of the total SO4 load. However, sulfide weathering decreased in importance in the lower reaches of the watershed. A smaller SO4 input of ∼2–4% was contributed by atmospheric wet deposition. This study implies that the δ 34S variation of SO4 in semi-arid environments can be complex, but that S isotopes can be used to distinguish among the different sources of weathering. Here it was found that H2SO4 dissolution due to sulfide oxidation contributes up to 5% of the total carbonate weathering budget, while most of the SO4 is released from bedrock sources during dedolomitization.

► Origin of sulfate in the NURS was studied by the combined use of S isotopes and hydrochemistrical data. ► Highly enriched δ 34S was found in groundwater and surface water contaminated by sewage. ► Relatively low δ 34S values with low SO 4 2 - concentrations were derived from the oxidation of sulfide minerals and rainwater. ► While relatively low δ 34S values with high SO 4 2 - concentrations were derived from the chemical fertilizers.Sulfur isotopic compositions (δ 34S) and major ions were measured in groundwater and surface waters in order to elucidate the source(s) of elevated SO 4 2 - content in some of these waters in the Nandong Underground River System (NURS), located in an agricultural and urbanization-dominated area in SW China. The major chemical composition of analyzed groundwater and surface water from NURS was characterized by Ca–HCO3 or Ca (Mg)–HCO3 type in forested and grass land areas, and Ca–Cl (+NO3  + SO4) or Ca (Mg)–Cl (+NO3  + SO4) type in urban and agricultural areas, respectively. The anomalously high SO 4 2 - concentrations in waters collected from urban and agricultural areas indicated a likely anthropogenic origin for SO 4 2 - . The groundwater collected from forested and grass land areas was characterized by relatively low δ 34 S – SO 4 2 - , from −1.7‰ to +4.3‰, and low SO 4 2 - concentrations of less than 10 mg L−1, consistent with an origin for SO 4 2 - in these waters from a mixture of rainfall-derived SO 4 2 - and SO 4 2 - from oxidation of bedrock sulfide. High SO 4 2 - groundwater and surface water (>20 mg L−1) collected from urban areas was characterized by elevated δ 34 S – SO 4 2 - , from +8.3‰ to +12.1‰, compared to lower δ 34 S – SO 4 2 - in samples from cultivated land areas (−3.7‰ to +6.4‰), indicating that the SO 4 2 - in these two groups of waters resulted from different anthropogenic sources. The S isotopic composition of SO 4 2 - in urban areas is consistent with addition of SO 4 2 - from detergent/sewage, whilst in cultivated land areas isotope composition indicates that additional SO 4 2 - could be derived from fertilizers and/or increased oxidation of sulfide.

► We update knowledge on some Portugal’s most important mineral waters. ► Results highlight the complexity of CO2-rich groundwaters circulation. ► New hypothesis on flow paths and water–rock interaction are presented. ► Sr isotopes were a powerful toll to redefine the reservoir the waters come from. ► Conclusions are vital to ensure economic use of drinkable CO2-rich mineral waters.Strontium isotopes and other geochemical signatures are used to determine the relationships between CO2-rich thermal (Chaves: 76 °C) and mineral (Vilarelho da Raia, Vidago and Pedras Salgadas: 17 °C) waters discharging along one of the major NNE–SSW trending faults in the northern part of mainland Portugal. The regional geology consists of Hercynian granites (syn-tectonic-310 Ma and post-tectonic-290 Ma) intruding Silurian metasediments (quartzites, phyllites and carbonaceous slates). Thermal and mineral waters have 87Sr/86Sr isotopic ratios between 0.716713 and 0.728035. 87Sr/86Sr vs. 1/Sr define three end-members (Vilarelho da Raia/Chaves, Vidago and Pedras Salgadas thermal and mineral waters) trending from rainfall composition towards that of the CO2-rich thermal and mineral waters, indicating different underground flow paths. Local granitic rocks have 87Sr/86Sr ratios of 0.735697–0.789683. There is no indication that equilibrium was reached between the CO2-rich thermal and mineral waters and the granitic rocks. The mean 87Sr/86Sr ratio of the thermal and mineral waters (0.722419) is similar to the Sr isotopic ratios of the plagioclases of the granitic rocks (0.71261–0.72087). The spatial distribution of Sr isotope and geochemical signatures of waters and the host rocks suggests that the thermal and mineral waters circulate in similar but not the same hydrogeological system. Results from this study could be used to evaluate the applicability of this isotope approach in other hydrogeologic investigations.

Effect of groundwater pH and ionic strength on strontium sorption in aquifer sediments: Implications for 90Sr mobility at contaminated nuclear sites by Sarah H. Wallace; Samuel Shaw; Katherine Morris; Joe S. Small; Adam J. Fuller; Ian T. Burke (1482-1491).
► The sorption of 90Sr to sediments representative of the UK Sellafield site is investigated. ► In artificial groundwater based solutions the degree of 90Sr sorption is controlled by pH. ► In a simulant tank liquor solution, sorption is limited by cation competition due to elevated Na+. ► Sr is adsorbed to sediments as weakly bound surface complexes even in experiments aged for 1 year. ► After 1 year most Sr can be extracted with MgCl2, a finding useful to remediation strategies.Strontium-90 is a beta emitting radionuclide produced during nuclear fission, and is a problem contaminant at many nuclear facilities. Transport of 90Sr in groundwaters is primarily controlled by sorption reactions with aquifer sediments. The extent of sorption is controlled by the geochemistry of the groundwater and sediment mineralogy. Here, batch sorption experiments were used to examine the sorption behaviour of 90Sr in sediment–water systems representative of the UK Sellafield nuclear site based on groundwater and contaminant fluid compositions. In experiments with low ionic strength groundwaters (<0.01 mol L−1), pH variation is the main control on sorption. The sorption edge for 90Sr was observed between pH 4 and 6 with maximum sorption occurring (K d  ∼ 103  L kg−1) at pH 6–8. At ionic strengths above 10 mmol L−1, and at pH values between 6 and 8, cation exchange processes reduced 90Sr uptake to the sediment. This exchange process explains the lower 90Sr sorption (K d  ∼ 40 L kg−1) in the presence of artificial Magnox tank liquor (IS = 29 mmol L−1). Strontium K-edge EXAFS spectra collected from sediments incubated with Sr2+ in either HCO3-buffered groundwater or artificial Magnox tank liquor, revealed a coordination environment of ∼9 O atoms at 2.58–2.61 Å after 10 days. This is equivalent to the Sr2+ hydration sphere for the aqueous ion and indicates that Sr occurs primarily in outer sphere sorption complexes. No change was observed in the Sr sorption environment with EXAFS analysis after 365 days incubation. Sequential extractions performed on sediments after 365 days also found that ∼80% of solid associated 90Sr was exchangeable with 1 M MgCl2 in all experiments. These results suggest that over long periods, 90Sr in contaminated sediments will remain primarily in weakly bound surface complexes. Therefore, if groundwater ionic strength increases (e.g. by saline intrusion related to sea level rise or by design during site remediation) then substantial remobilisation of 90Sr is to be expected.

Temperature-dependent leaching of chemical elements from mineral water bottle materials by Clemens Reimann; Manfred Birke; Peter Filzmoser (1492-1498).
► Total concentrations of 40 elements in glass bottles are reported. ► Leaching of elements from bottles to water at different temperatures is tested. ► Thirty-one of 60 measured elements in water show an effect of temperature on leaching. ► Antimony leaching from PET bottles increases dramatically at temperatures >40 °C. ► Many more elements leach from glass than from PET bottles.It is well established that minute amounts of chemical elements will leach from bottle materials (glass or PET – polyethylene terephthalate) to water stored in such bottles. This study investigated whether leaching increases with storage temperature. For glass bottles this is clearly the case for a long list of elements: Ag, Al, As, B, Ba, Ca, Co, Cr, Cs, Cu, Fe, Ga, Ge, K, La, Li, Mg, Mo, Na, Ni, Pb, Rb, Sb, Se, Sn, Sr, Ti, U, V, W and Zr. However, for glass bottles drinking water maximum admissible concentration values as defined by European authorities are not exceeded even after 1 week of leaching at 80 °C. The critical temperature limit where leaching substantially increases for many elements appears to be 45 °C. For PET bottles, Sb is the only element where leaching is observed at all temperatures and again leaching strongly increases at 45 °C. For PET bottles Sb concentrations observed in water after 1 week storage at 80 °C reach almost four times the maximum admissible concentration values for drinking water but do not exceed the relevant higher limit for food (including water) packaged in PET.

Geochemical, mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer by K.M. Campbell; R.K. Kukkadapu; N.P. Qafoku; A.D. Peacock; E. Lesher; K.H. Williams; J.R. Bargar; M.J. Wilkins; L. Figueroa; J. Ranville; J.A. Davis; P.E. Long (1499-1511).
► U, sulfate, and Fe reduction has occurred in a zone of naturally reduced sediment. ► Reduced U has accumulated in the naturally reduced sediment. ► Reduction is likely stimulated by increased organic matter and lower permeability. ► U(IV) persists in the naturally reduced lenses even under oxidizing conditions. ► Zones of natural reduction may seasonally act as a U source or sink to the aquifer.Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO4 reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.

Abiotic reduction of uranium by Fe(II) in soil by Drew E. Latta; Maxim I. Boyanov; Kenneth M. Kemner; Edward J. O’Loughlin; Michelle M. Scherer (1512-1524).
► Abiotic reduction and immobilization of U(VI) occurs in a reduced Iowa soil. ► The U is immobilized as U(IV) and non-uranyl U(V) or U(VI) phases. ► Soil characterization indicates the presence of structural Fe(II) in clay minerals or a green-rust like phase. ► U(VI) reduction is coupled with Fe(II) oxidation in the soil. ► Abiotic reduction of U(VI) may be an important process in reduced, Fe-rich environments.Structural Fe(II) has been shown to reduce several oxidized environmental contaminants, including NO3, chlorinated solvents, Cr(VI), and U(VI). Studies investigating reduction of U(VI) by soils and sediments, however, suggest that abiotic reduction of U(VI) by Fe(II) is not significant, and that direct enzymatic reduction of U(VI) by metal-reducing bacteria is required for U(VI) immobilization as U(IV). Here evidence is presented for abiotic reduction and immobilization of U(VI) by structural Fe(II) in a redoximorphic soil collected from a hillside spring in Iowa. Oxidation of Fe(II) in the soil after reaction with U(VI) was demonstrated by Mössbauer spectroscopy and reduction of U(VI) by the pasteurized soil using U LIII-edge X-ray absorption spectroscopy (XAS). XAS indicates that both reduced U(IV) and oxidized U(VI) or U(V) are present after U(VI) interaction with the Fe(II) containing soil. The EXAFS data show the presence of a non-uraninite U(IV) phase and evidence of the oxidized U(V) or U(VI) fraction being present as a non-uranyl species. Little U(VI) reduction is observed by soil that has been exposed to air and oxidation of Fe(II) to goethite has occurred. Soil characterization based on chemical extractions, Mössbauer spectroscopy, and Fe K-edge XAS indicate that the majority of Fe(II) in the soil is structural in nature, existing in clay minerals and possibly a green rust-like phase. These data provide compelling evidence for abiotic reduction of U(VI) by structural Fe(II) from soil near Fe-rich oxic–anoxic boundaries in natural environments. The work highlights the potential for abiotic reduction of U(VI) by Fe(II) in reduced, Fe-rich environments.

Investigating high zircon concentrations in the fine fraction of stream sediments draining the Pan-African Dahomeyan Terrane in Nigeria by Roger M. Key; Christopher C. Johnson; Matthew S.A. Horstwood; Dan J. Lapworth; Katherine V. Knights; Simon J. Kemp; Michael Watts; Martin Gillespie; Michael Adekanmi; Tunde Arisekola (1525-1539).
► Zr values in Nigeria’s stream sediments are exceptionally high (on a global scale). ► Underlying bedrock Zr values are not unusual. ► Continuous chemical/physical weathering processes concentrate Zr (in zircon) in streams.Sixteen hundred stream sediments (<150 μm fraction) collected during regional geochemical surveys in central and SW Nigeria have high median and maximum concentrations of Zr that exceed corresponding Zr concentrations found in stream sediments collected from elsewhere in the World with similar bedrock geology. X-ray diffraction studies on a sub-set of the analysed stream sediments showed that Zr is predominantly found in detrital zircon grains. However, the main proximal source rocks (Pan-African ‘Older Granites’ of Nigeria and their Proterozoic migmatitic gneiss country rocks) are not enriched in zircon (or Zr). Nevertheless, U–Pb LA-ICP-MS dating with cathodoluminescence imaging on detrital zircons, both from stream sediment samples and underlying Pan-African ‘Older Granites’ confirms a local bedrock source for the stream sediment zircons. A combination of tropical/chemical weathering and continuous physical weathering, both by ‘wet season’ flash flooding and ‘dry season’ unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases, thereby increasing the Zr contents in stream sediments. The strong correlation between winnowing index (Th/Al) and Zr concentration across the study area support this interpretation. Therefore, ‘anomalous’ high values of Zr, as well as other elements concentrated in resistant ‘heavy’ minerals in Nigeria’s streams may not reflect proximal bedrock concentrations of these elements. This conclusion has important implications for using stream sediment chemistry as an exploration tool in Nigeria for primary metal deposits associated with heavy minerals.

Multivariate analysis of sediment data from the upper and middle Odra River (Poland) by Agnieszka Gielar; Edeltrauda Helios-Rybicka; Stefan Möller; Jürgen W. Einax (1540-1545).
► We examined multivariate data analysis in the field of the river sediment pollution. ► The cluster analysis allowed us to distinguish three groups of sediments localizations. ► The chemometrics approach used to the river dataset reveals a new level (latent) of information.River pollution data are characterized by high variability. Multivariate statistical methods help to determine a complex set of these multidimensional data and to extract latent information (e.g. differently polluted areas, discharges). The chemometric methods can handle interactions between different pollutants and relationships among various sampling locations. This study presents an application of multivariate data analysis in the field of environmental pollution. The dataset consists of As, Cd, Cr, Cu, Fe, Ni, Mn, Pb and Zn contents of sediment samples collected in the upper and middle Odra River (Poland) in three sampling campaigns (November 1998, June 1999, and May 2000). As chemometric tools cluster analysis (CA), multivariate analysis of variance and discriminant analysis (MVDA) and factor analysis (FA) were used to investigate the matrix of 60 sampling points.The cluster analysis shows that pollution can be divided into three groups which were strongly dependent on the level of the contamination (high for Cu, Cr, Fe, Pb and Zn) and the localization of the samples (upper and middle Odra River). Multivariate analysis of variance and discriminant analysis helps to confirm the results from the CA. This method was used also to apply real reduction in the tested matrix dimension by use of forward strategy. In the fourth step of that strategy the variables Cu, Cr, Pb, and Fe are sufficient to describe the variability in the river sediments and to separate the classes. Two factors extracted by the factor analysis explained approximately 54% of the total variance of the system and allow identification of the dominant anthropogenic sources in the river system. Factor 1 describes 39.06% of the common variance and is highly loaded by Cr, Cu and Zn. Factor 2 includes pollution with Fe and Pb and explains 14.97% of the common variance. The interpretation of factor analysis was confirmed by the representation of factor scores as a function of the river distance in kilometers. Thereby, the pollution sources from the Głogów–Legnica Cu-mining activities could be determined. For Fe and Pb contents a slight decrease can be detected from 1999 and 2000. Furthermore, it can be shown that the contents of Cr, Cu and Zn increased in the sediments along the Odra River course but the basic contamination structure remained unchanged for the investigated years.

► Field observation further supports significant contribution of dust to semi-arid lake. ► First qualification of 13 elements of dust to Lake Qinghai sediment at four seasons. ► Further highlight the dominant atmospheric input of potential harmful metals. ► Behavior and source determine various elemental contributions of dust to sediment.Located at the midpoint of the Asian “airborne dust corridor”, Lake Qinghai receives substantial dust annually, which may impact the biogeochemical cycles of the system. In order to determine quantitatively the flux and chemical contributions of dust to Lake Qinghai sediment, dust samples were collected monthly at two sites surrounding the lake from June 2009 to May 2011. The results demonstrate similar chemical compositions of dust samples to the local loess, implying strong representativeness of regional dust. The average dust deposition flux is 265.7 ± 55.0 g/m2/a, constituting 56.6 ± 11.7% of the modern sediment, approximating to previous estimates (∼65%). Contributions of dust-derived elements in the sediment differ substantially, with a minimum of 16.7% for Sr and a maximum of 83.9% for Cu. Among these elements, the contribution of lithophile elements (Na, Al, K, Ti, Mn, Fe and Rb) is close to that of the bulk dust; the contributions of mobile elements (Mg, Ca and Sr) are low, only 16.7% (Sr)–26.1% (Mg), whereas potentially harmful metals (Cu, Zn and Pb) have high contributions (70.3–83.9%). Seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment, in agreement with the high dust flux in spring. These observations not only quantify the contribution of dust to the sediment of Lake Qinghai, but also highlight the important role of dust in the accumulation of various elements in the sediment, especially for potentially harmful metals.

► Biogenic elements in two 210Pb dated cores in the East China Sea were analyzed. ► P species in coastal sediment reflected the Changjiang runoff variation. ► Biogenic proxies in offshore sediment indicated the variations in winter monsoon. ► Eutrophication in the ECS in recent decades was recorded in coastal sediment. ► P species with distinct biogeochemistry were promising proxies of paleoenvironment.Increasing eutrophication and seasonal anoxia in bottom water in the Changjiang Estuary and its adjacent waters has progressed in recent decades, caused by elevated anthropogenic N and P input. Sedimentary biogenic elements were investigated to determine whether the biogenic proxies could be used in paleoenvironmental studies in an energetic estuary, as well as to reconstruct the histories of environmental changes in the East China Sea (ECS). Two 210Pb-dated cores from the coastal and offshore waters were analyzed for organic C (TOC) and its stable isotope (δ13C), total N (TN), biogenic Si (BSi), total P (TP) and P species. In coastal sediment, the variations of P species, especially Fe-P, Al-P and detrital apatite P (Det-P), reflected the dry–wet oscillations in the Changjiang River for the past century, which has influenced the sediment grain size and terrestrial material input. Much lower BSi content (0.756%) at 16–22 cm likely recorded the pronounced decrease in silicate flux in the Changjiang River and its lower flow in the late 1980s. In offshore sediment, higher concentrations of TOC, TN, BSi, Ex-P, Fe-P and Lea-OP indicated higher primary productivity in response to the strong winter monsoons during the 1960s–1980s, and their 20-a fluctuations were in agreement with the decadal variations of the winter monsoon. Low contents and little variations of Al-P and Det-P indicated the slight influence of the terrestrial sediment input in offshore waters. The influence of human activities on the environment in recent decades has also been recorded in coastal sediment. Grain-size normalized concentrations of TOC, TN, TP, Ex-P, Fe-P and Lea-OP increased by 24%, 23%, 15%, 13% and 51% in the upper 16 cm of coastal sediment, indicating elevated P and N load and primary productivity since the 1990s. Elevated TN/TP ratios and decreased BSi/TOC recorded the changed nutrient structure and the decrease in the proportion of the diatom to phytoplankton community. However, the sediment record indicated that the eutrophication might actually have started from the end of the 20th century rather than the reported middle of 20th century. In contrast, biogenic elements in offshore sediment did not reflect disturbance by human activities. This study revealed that multi-nutrient proxies in sediment in the ECS could indicate natural environmental changes including runoff and the winter monsoon over the past century, as well as the influence of human activities in recent decades. Phosphorus species with distinct origins and biogeochemical behaviors could effectively reflect different aspects of past environmental conditions.

► Lab rates of Mn removal correlated (R 2  = 0.87) to field performance for seven beds. ► Fast rates of Mn removal were due to biological oxidation. ► Lab rates of Mn removal correlated (R 2  = 0.62) to bacterial biomass concentration.Oxic limestone beds are commonly used for the passive removal of Mn(II) from coal mine drainage (CMD). Aqueous Mn(II) is removed via oxidative precipitation of Mn(III/IV) oxides catalyzed by Mn(II)-oxidizing microbes and Mn oxide (MnO x ) surfaces. The relative importance of these two processes for Mn removal was examined in laboratory experiments conducted with sediments and CMD collected from eight Mn(II)-removal beds in Pennsylvania and Tennessee, USA. Sterile and non-sterile sediments were incubated in the presence/absence of air and presence/absence of fungicides to operationally define the relative contributions of Mn removal processes. Relatively fast rates of Mn removal were measured in four of the eight sediments where 63–99% of Mn removal was due to biological oxidation. In contrast, in the four sediments with slow rates of Mn(II) removal, 25–63% was due to biological oxidation. Laboratory rates of Mn(II) removal were correlated (R 2  = 0.62) to bacterial biomass concentration (measured by phospholipid fatty acids (PLFA)). Furthermore, laboratory rates of Mn(II) removal were correlated (R 2  = 0.87) to field-scale performance of the Mn(II)-removal beds. A practical recommendation from this study is to include MnO x -coated limestone (and associated biomass) from an operating bed as “seed” material when constructing new Mn(II)-removal beds.

► The Montastraea annularis Ba/Ca record was used as a proxy of precipitation. ► Correlation between annual precipitation and Ba/Ca time-series was significant. ► Total Ba/CaTC was ∼20% higher than Ba/Ca in the Ca-substitutive fraction. ► Coralline Ba/CaTC can be used for the reconstruction of historical precipitation. ► Coralline Ba/CaCaF can be used for the reconstruction of dissolved seawater Ba.The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/CaTC) and the Ca-substitutive fraction (Ba/CaCaF), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/CaTC (5.90 ± 0.56 μmol/mol) was ∼20% higher than Ba/CaCaF (4.85 ± 0.33 μmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/CaTC time-series is significant (r  = 0.77, p  < 0.05), allowing the use of the Ba/CaTC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/CaCaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater.

Zinc mineral weathering as affected by plant roots by David Houben; Philippe Sonnet (1587-1592).
► We assessed the effect of ryegrass root activity on the weathering of smithsonite. ► The root activity promoted the Zn release from smithsonite to leachates. ► Organic root exudates were closely involved in the smithsonite weathering. ► The total Zn amount liberated by smithsonite was doubled in the presence of plants. ► Revegetation strategies should consider the weathering of metal phases by plants.The re-vegetation of soils contaminated by potentially harmful metals is generally considered a suitable option to reduce the metal dispersion in surrounding environments. A continuous flow experiment was conducted to quantitatively assess the effect of Italian ryegrass (Lolium multiflorum Lam.) root activity on the weathering of smithsonite (ZnCO3), a common Zn mineral. At the end of the experiment (10 days), the total amount of Zn released by smithsonite was increased by a factor of 2.25 in the presence of plants. This increase was due not only to plant uptake but also to the enhancement of the Zn release into leachates. The rate of Zn release from smithsonite to leachates was 2.9 × 10−4  μg g−1  s−1 and 1.5 × 10−4  μg g−1  s−1 in the presence and the absence of plants, respectively. The strong correlation (r  = 0.95; p  < 0.001) between concentrations of Zn and dissolved organic C (DOC) produced by the rhizosphere activity in leachates indicated that organic root exudates and secretions were closely involved in smithsonite weathering. Although the results are derived from laboratory study, and further in situ investigations over the long term are needed, they clearly highlighted that plants can enhance metal release into the environment by accelerating mineral weathering. Therefore, it is suggested that the ability of plants to alter metal phases in soils should be further taken into account when re-vegetation strategies are proposed for the rehabilitation of metal-polluted soils.

Sorption of lead by phlogopite-rich mine tailings by Salla H. Venäläinen (1593-1599).
► The use of mine tailings from apatite ore beneficiation as a remediation agent. ► Precipitation and surface complexation of Pb. ► Tailings remove Pb efficiently from an aqueous solution. ► Tailings increase the Pb sorption capacity of mineral soil.The Pb sorption capacity of apatite ore mine tailings and its potential to act as a remediation agent in a Pb polluted areas were investigated. The tailings, originating from the Siilinjärvi carbonatite complex in Finland, consist mainly of phlogopite and calcite accompanied by apatite residues. The ability of the tailings to retain Pb from an aqueous solution was investigated using an isotherm technique. Furthermore, in a 3-month incubation experiment, uncontaminated mineral soil was amended with untreated tailings and with tailings artificially weathered with acid to increase the quantity of Al and Fe (hydr)oxides. Tailings of two particle-sizes (∅ > 0.2 mm and ∅ < 0.2 mm) somewhat differing in their mineralogical composition were investigated as separate amendments. All tailings materials were added to the soil in two dosages (5 g and 10 g of tailings per 125 g of soil). Following incubation, tailings-induced changes in the Pb sorption capacity of the soil were investigated with the isotherm technique. Finally, to investigate the distribution of sorbed Pb among various chemical pools, the soil samples amended with tailings were contaminated with Pb and then subjected to sequential fractionation analysis. The results revealed efficient removal of Pb from an aqueous solution by the tailings, presumably through precipitation and surface complexation mechanisms. Amending the soil with the tailings increased the mass-based maximum Pb sorption capacity from 10.8 mg kg−1 of the control soil to 14–20.5 mg kg−1 for the untreated tailings and to 32.1–72.1 mg kg−1 for the acid-treated material. The tailings transferred Pb from the exchangeable pool to the non-extracted one and thereby substantially decreased its bioavailability. The material with a particle diameter of less than 0.2 mm had a higher mass-based Pb sorption capacity than the large-sized material. The results suggest that the tailings may potentially serve as an immobilizing agent in polluted areas.

Attribution of uranium ore concentrates using elemental and anionic data by Elizabeth Keegan; Maria Wallenius; Klaus Mayer; Zsolt Varga; Gert Rasmussen (1600-1609).
► Trace metals and anion impurities analysed in uranium ore concentrate (UOC) samples. ► UOC samples from certain uranium deposit types had distinct impurity composition. ► Key impurities that differentiate groups of UOC samples identified.The capability to correctly identify the geological or geographical source of unknown uranium ore concentrates (UOCs) has obvious nuclear security benefits. This paper reports on a scoping study where the trace elemental and anionic compositions of 24 UOC samples, sourced mainly from mines in Australia and Canada, were examined for their ability to allow attribution of the sample to a particular geological U deposit type or to a particular geographical source. Results of statistical analysis using canonical analysis of principal coordinates (CAP) showed that samples originating from certain U ore deposit types, especially phosphorite and quartz-pebble conglomerate, contained a distinct impurity composition. Samples grouped according to their geographical region of origin appeared to contain distinctive impurities in certain cases (Elliot Lake and Bancroft, Ontario). The key impurities responsible for differentiating groups of samples from a particular geological deposit type were identified and the use of certain impurities as signatures of processing history is discussed. The methodology described in this scoping study provides a promising approach for more comprehensive databases.

Solubility of carbon dioxide in aqueous fluids and mineral suspensions at 294 K and subcritical pressures by Jörgen Rosenqvist; Andrew D. Kilpatrick; Bruce W.D. Yardley (1610-1614).
► CO2 solubility at subcritical P may be lower than predicted by modelling codes. ► Standalone models predict CO2 solubility better than fluid–rock interaction codes. ► Modelled CO2 solubilities depend strongly on the fugacity coefficient used. ► CO2-charged fluids reacted with clays may be less acidic than models suggest. ► CO2-charged fluids may thus mobilise less metal from grain surfaces than thought.An experimental investigation has been carried on the solubility of CO2 in water and 1 M NaCl between 0.3 and 4 MPa, in order to test the validity of the results given by various modelling codes. In addition to experiments with pure fluids, the effect of a range of likely reservoir minerals on CO2–water interactions, including K-feldspar, kaolinite, calcite, Ca-montmorillonite and Na-montmorillonite were also investigated. In addition to measurements of CO2 solubility, the pH of the CO2-saturated suspensions was also measured directly at pressures of up to 1 MPa. The results demonstrate that predictions of CO2 solubility made with PHREEQC and Geochemist’s Workbench agree to within 20% with the experimental value, provided corrections are first made off-line for the fugacity coefficient of CO2, while predictions from standalone models are slightly more accurate. In the presence of mineral suspensions, PHREEQC and Geochemist’s Workbench give good results for calcite and kaolinite but underestimate the pH of montmorillonite-bearing assemblages while slightly overestimating the pH of K-feldspar suspensions. These results are significant because they indicate that CO2-charged fluids reacted with clays may be less acidic than indicated by the models, which will impact predictions of the potential for dissolution of reservoir and cap rock minerals, as well as the potential for leaching of toxic metals.

On the interaction of pure and impure supercritical CO2 with rock forming minerals in saline aquifers: An experimental geochemical approach by Franziska D.H. Wilke; Mónica Vásquez; Thomas Wiersberg; Rudolf Naumann; Jörg Erzinger (1615-1622).
► Experiments to examine interaction between minerals, brine and impure/pure scCO2. ► Resulting formation of sulfuric and nitric acids is reflected in low pH. ► A larger amount of cations dissolved from the mineral phases when impure scCO2 used. ► Dissolution of carbonates; silicates do not exhibit significant alterations. ► Anhydrite partly transformed to gypsum during experiments with scCO2  + NO2.The aim of this experimental study was to evaluate and compare the geochemical impact of pure and impure CO2 on rock forming minerals of possible CO2 storage reservoirs. This geochemical approach takes into account the incomplete purification of industrial captured CO2 and the related effects during injection, and provides relevant data for long-term storage simulations of this specific greenhouse gas. Batch experiments were conducted to investigate the interactions of supercritical CO2, brine and rock-forming mineral concentrates (albite, microcline, kaolinite, biotite, muscovite, calcite, dolomite and anhydrite) using a newly developed experimental setup. After up to 42 day (1000 h) experiments using pure and impure supercritical CO2 the dissolution and solution characteristics were examined by XRD, XRF, SEM and EDS for the solid, and ICP–MS and IC for the fluid reactants, respectively. Experiments with mixtures of supercritical CO2 (99.5 vol.%) and SO2 or NO2 impurities (0.5 vol.%) suggest the formation of H2SO4 and HNO3, reflected in pH values between 1 and 4 for experiments with silicates and anhydrite and between 5 and 6 for experiments with carbonates. These acids should be responsible for the general larger amount of cations dissolved from the mineral phases compared to experiments using pure CO2. For pure CO2 a pH of around 4 was obtained using silicates and anhydrite, and 7–8 for carbonates. Dissolution of carbonates was observed after both pure and impure CO2 experiments. Anhydrite was corroded by approximately 50 wt.% and gypsum precipitated during experiments with supercritical CO2  + NO2. Silicates do not exhibit visible alterations during all experiments but released an increasing amount of cations in the reaction fluid during experiments with impure CO2. Nonetheless, precipitated secondary carbonates could not be identified.

► In this study, we examine regional formation water and gas geochemistry of the Sverdrup Basin. ► The High Arctic basin holds significant petroleum reserves and will be the likely focus of future exploration and development. ► Formation waters on average are consistent with a seawater origin but local brines develop in association with salt diapirs. ► Freshwater intrusion on the basin margin has associated microbial gas generation.The Sverdrup Basin holds significant reserves of discovered and undiscovered petroleum that have not been produced to date given its remote arctic setting. Loss of perennial sea ice increases the prospects for producing reserves from this region. Potential renewed drilling and production requires knowledge of formation water geochemistry to aid both exploration as well as regulatory development. Historic data shows formation waters typically have a seawater origin, although there is high variability in formation water geochemistry. Salt diapirs lead to localized brine generation with salinities over an order of magnitude higher than average for the basin. Evidence also shows fresh water influx occurred along the basin margins that initiated biogenic gas generation.

► There is prevalent of Type III kerogen with subordinate Type II or Type II/III. ► Biomarker parameters suggest deposition under suboxic to oxic conditions. ► The rocks are at the beginning of the oil window with some more mature samples.Organic geochemical evaluation of thirty-two Aptian to Campanian shale samples from seven wells drilled on the shelf of the Orange Basin (southwestern Atlantic margin) was carried out in order to determine their origin, depositional environment, thermal maturity and hydrocarbon potential. The shale samples, selected to represent highstand, lowstand and transgressive systems tracts, were analysed by Rock–Eval pyrolysis for total organic C characteristics and by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) for n-alkanes, aliphatic isoprenoid hydrocarbons and biomarkers (steranes, hopanes and tricylic terpanes). For most of the shale samples Rock–Eval data, hydrogen (HI) and oxygen index (OI) point to mainly Type III terrigenous organic matter. Only a few samples of Turonian age reveal a higher proportion of marine organic matter being classified as Type II/III or Type II. Biomarker parameters suggest that the samples are deposited under suboxic to oxic environmental conditions. Rock–Eval data and biomarker maturity parameters assign for most of the samples a maturity level at the beginning of the oil window with some more mature samples of Aptian, Albian and Cenomanian age. The hydrocarbon generation potential is low for most of the shelf shales as indicated by the S2/S3 ratio and HI values. Exceptions are some samples of Turonian and Aptian age.

► Ten source rocks and 42 oils from Tarim Basin are analyzed for steroids investigation. ► Cambrian rocks and oils have abnormally high contents of dinosteranes, norcholestanes. ► Two oil systems can be distinguished on the basis of less common steroids in Tarim. ► Oils with Cambrian origin were further discovered and may have promising prospect. ► Dinoflagellates might have flourished in Tarim Basin during the Cambrian.Two oil families in Ordovician reservoirs from the cratonic region of the Tarim Basin are distinguished by the distribution of regular steranes, triaromatic steroids, norcholestanes and dinosteroids. Oils with relatively lower contents of C28 regular steranes, C26 20S, C26 20R + C27 20S and C27 20R regular triaromatic steroids, dinosteranes, 24-norcholestanes and triaromatic dinosteroids originated from Middle–Upper Ordovician source rocks. In contrast, oils with abnormally high abundances of the above compounds are derived from Cambrian and Lower Ordovician source rocks. Only a few oils have previously been reported to be of Cambrian and Lower Ordovician origin, especially in the east region of the Tarim Basin. This study further reports the discovery of oil accumulations of Cambrian and Lower Ordovician origin in the Tabei and Tazhong Uplifts, which indicates a potential for further discoveries involving Cambrian and Lower Ordovician sourced oils in the Tarim Basin. Dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24-norcholestanes for dinoflagellates and diatoms. Therefore, the abnormally high abundance of these compounds in extracts from the organic-rich sediments in the Cambrian and Lower Ordovician and related oils in the cratonic region of the Tarim Basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the Tarim Basin during the Cambrian Period. Steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms, as well as define petroleum systems.

Display Omitted► Potwar Basin Pakistan contains marine to terrigenous crude oils. ► Aromatic biomarkers reveal oil classification and type of source organic matter. ► Abundance of heterocyclics depends on depositional environments of organic matter. ► Triaromatic/methyl triaromatic steroids show interesting source related distribution. ► Alkyl isomers of naphthalene, phenanthrene, dibenzothiphene, dibenzofuran, fluorene.In a previous study, oils in the Potwar Basin (Upper Indus) of Pakistan were correlated based on the dissimilarity of source and depositional environment of organic matter (OM) using biomarkers and bulk stable isotopes. This study is aimed at supporting the classification of Potwar Basin oils into three groups (A, B and C) using the distribution of alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, alkyldibenzofurans, alkylfluorenes, alkylbiphenyls, triaromatic steroids, methyl triaromatic steroids, retene, methyl retenes and cadalene. The higher relative abundance of specific methyl isomers of naphthalene and phenanthrene and the presence of diagnostic aromatic biomarkers clearly indicate the terrigenous and oxic depositional environment of OM for group A oil. Group B and C oils are of marine origin and the aforementioned heterocyclic and polycyclic aromatic hydrocarbons (HCs) differentiate them clearly into two different groups. The relative percentages of heterocyclic aromatic HCs reveal that the distribution of these compounds is controlled by the depositional environment of the OM. Sulfur-containing heterocyclic aromatic HCs are higher in crude oils generated from source rocks deposited in suboxic depositional environments, while oxygen-containing heterocyclic aromatic HCs in combination with alkylfluorenes are higher in marine oxic and deltaic oils. Biomarker and aromatic HC parameters do not indicate significant differences in the thermal maturity of Potwar Basin oils. Triaromatic and methyl triaromatic steroids support the division of Potwar Basin oils into the three groups and their relative abundances are related to source OM rather than thermal maturity. Significantly higher amounts of C20 and C21 triaromtic steroids and the presence or absence of long chain triaromatic steroids (C25, C26, C27, and C28) indicates that these compounds are probably formed from different biological precursors in each group. Different isomers of methyl substituted triaromatic steroids are present only for short chain compounds (C20–C22) and the origin of these compounds may be short chain methyl steranes from unknown biological precursors.

Potential of microbial methane formation in a high-temperature hydrocarbon seep by Yu-Chen Ling; Yun-Ju Chen; Chih-Hsien Sun; Ting-Wen Cheng; Pei-Ling Wang; Li-Hung Lin (1666-1678).
► Muddy sediments from a high-temperature seep of Taiwan were incubated. ► Methane production was stimulated by precursor addition at RT to 80 °C. ► Methanogenesis from CO2 and formate was more active at ⩾40 °C. ► Acetoclastic and methylotrophic methanogenesis was more active at 40–50 °C. ► Microbial methane contributes significantly to the overall methane inventory.Hydrocarbon seepage is a surface expression where fluids mixed with sediments and hydrocarbons are expelled through fracture systems that potentially tap into gas–petroleum reservoirs. Hydrocarbons released from most seeps appear to be thermogenic on the basis of their relative abundance and isotopic composition. The potential for subsurface microbial processes modifying these geochemical fingerprints remains poorly constrained. In this study, microcosm incubations were conducted on mud slurries supplied with/without various methanogenic precursors at temperatures ranging from ambient conditions to 90 °C, in order to assess microbial CH4 formation in the subsurface beneath hydrocarbon seeps. The analyses indicated that CH4 production was positive at ⩽80 °C, regardless of whether or not or which precursors were added. However, the pattern of CH4 production rates varied with the precursor and temperature. In general, the optimum CH4 production from H2/CO2 and formate occurred over a wide range of temperatures (⩾40 °C), whereas that from acetate, methanol and methylamine was restricted to relatively lower temperatures (40–50 °C). The CH4 recoveries, together with the C isotopic compositions of CH4, further indicated that the quantities of CH4 produced could not completely account for the quantities of precursor consumed, suggesting that a complex metabolic network was involved in the transformation of the added precursor and organic C inherited from inoculated sediments. Microbial CH4 was estimated to constitute 7–61% of the CH4 observed using experimentally-derived apparent isotope fractionations as the end member compositions. This illustrates the possibility that microbial CH4 produced at shallower depths could quantitatively and isotopically alter deeply-sourced thermogenic CH4 in hydrocarbon seep environments.