Applied Geochemistry (v.26, #8)
Relation between the dissolution rates of single minerals and reservoir rocks in acidified pore waters by Murray M. Allan; Alison Turner; Bruce W.D. Yardley (1289-1301).
► Mineral dissolution rates under conditions of CO2 storage are little affected by stirring rates. ► The dissolution of reservoir rocks can be predicted from that of the constituent minerals. ► Reservoir rocks rich in illite/smectite and feldspars have the best potential to stabilise CO2 in solution.A series of kinetic experiments has been carried out to investigate the rates of dissolution (release of Al and Si) of common sandstone minerals in response to acidification of pore waters (pH = 3), using an experimental procedure designed to maximise the proportion of solid to fluid, and to minimise possible damage from agitation. The results have then been compared with those from experiments using disaggregated sandstones from two North Sea reservoirs. Experiments were carried out at 25 °C and 80 °C and in 0.01, 0.1 and 1 M NaCl solutions, with a pH of 3. Hydrochloric acid was used as the source of acidity and rate constants were determined based on both release of Al and Si. Mineral dissolution rates were closely comparable to literature values, despite the different experimental technique, except in the case of smectite where particle aggregation appears to have inhibited reaction. The dissolution rates calculated for reservoir sandstones based on their modal mineralogy and surface areas agree within a factor of 2 with the measured vales. Based on the reaction rates measured here, reservoir rocks rich in feldspar, illite and/or smectite are likely to react most rapidly with acidified pore waters.
Occurrence of fossil organic matter in modern environments: Optical, geochemical and isotopic evidence by Y. Graz; C. Di-Giovanni; Y. Copard; M. Elie; P. Faure; F. Laggoun Defarge; J. Lévèque; R. Michels; J.E. Olivier (1302-1314).
► Fossil organic matter contribution is significant in some modern carbon pools (soils or riverine particles). ► Fossil organic matter fate appears to be controlled by the nature of the weathering processes. ► The physical and chemical properties of fossil organic matter lead to a variation of its sensitivity toward weathering.This study relates to the input and fate of fossil organic matter (FOM) in the modern environment, and focuses on two experimental watersheds overlying Jurassic marls: Le Laval and Le Brusquet (1 km2 in area), located near Digne, Alpes-de-Haute-Provence, France. Considering that FOM delivery is mainly a result of different processes affecting sedimentary rocks [(bio)chemical and mechanical weathering], samples from different pools were collected: bedrocks, weathering profiles, soils and riverine particles. The samples were examined using complementary techniques: optical (palynofacies methods), geochemical (Rock-Eval 6 pyrolysis, C/N ratio), molecular (gas chromatography/mass spectrometry) and isotopic (stable C isotopic composition). As a result, FOM markers were identified and tracked through the different pools. The results highlight the contribution of FOM, which can be found in all the studied pools. Transfer of FOM between bedrocks/weathering profiles (governed mainly by chemical weathering) and bedrocks/riverine particles (governed mainly by mechanical weathering) reveals any qualitative change. Weathering profiles/soils transition [governed by (bio)chemical weathering] is characterized by alteration of the FOM, which is difficult to describe because fossil material is mixed with recent organic matter (ROM). Despite this latter point, the study provides evidence for a relative resistance of FOM to weathering processes and points to its contribution to the modern geosystem and the C cycle.
The geochemical and isotopic record of evaporite recycling in spas and salterns of the Basque Cantabrian basin, Spain by V. Iribar; B. Ábalos (1315-1329).
Stable isotopes and hydrochemistry disclose two types of saline groundwater whose source is the dissolution of Triassic (Keuper) or Cretaceous (Wealden) evaporites, that are recycled from the older ones.Display Omitted► Saline springs compositions are used to delineate extent of subsurface evaporites. ► Origin of Wealden vs. Triassic evaporites constrained using δ 34SSO4, δ 18OSO4 and Cl/Br ratio. ► Geological structures and saline water circulation relation.Evaporite outcrops are rare in the Basque Cantabrian basin due to a rainy climate, but saline springs with total dissolved solids ranging from 0.8 to 260 g/L are common and have long been used to supply spas and salterns. New and existing hydrochemistry of saline springs are used to provide additional insight on the origin and underground extent of their poorly known source evaporites. Saline water hydrochemistry is related to dissolution of halite and gypsum from two evaporitic successions (Triassic “Keuper” and Lower Cretaceous “Wealden”), as supported by rock samples from outcrops and oil exploration drill cuttings. The δ 34S value of gypsum in the Keuper evaporites and sulfate in the springs is δ 34SSO4 = 14.06 ± 1.07‰ and δ 18OSO4 = 13.41 ± 1.44‰, and the relationship between Cl/Br ratio of halite and water shows that waters have dissolved halite with Br content between 124 and 288 ppm. The δ 34S value of gypsum in the Wealden evaporites and sulfate in the springs is δ 34SSO4 = 19.66 ± 1.76‰, δ 18OSO4 = 14.93 ± 2.35‰, and the relationship between Cl/Br ratio of halite and water shows that waters have dissolved halite with Br content between 15 and 160 ppm. Wealden evaporites formed in a continental setting after the dissolution of Keuper salt. Gypsum δ 34SSO4 and δ 18OSO4 modification from Keuper to Wealden evaporites was due mainly to bacterial SO4 reduction in an anoxic, organic matter-rich environment. Saline springs with Wealden δ 34SSO4 values are present in a 70 × 20 km wide area. Saline water temperatures, their δ 2HH2O and δ 18OH2O values, and the geological structure defines a hydrogeological model, where meteoric water recharges at heights up to 620 m above spring levels and circulates down to 720 m below them, thereby constraining the height range of evaporite dissolution. Groundwater flow towards saline springs is driven by gravity and buoyancy forces constrained by a thrust and fault network.
Sources and distribution of aliphatic and polycyclic aromatic hydrocarbons in Yellow River Delta Nature Reserve, China by Chuanyuan Wang; Wanchun Wang; Shijie He; Jianguo Du; Zhigao Sun (1330-1336).
► Sources and distribution of petroleum hydrocarbon in Yellow River Delta National Nature Reserve (YRDNNR) were analyzed. ► Petroleum pollution in sediments of YRDNNR was relatively low or moderate. ► Petroleum pollution in Core Area and Buffer Area was weaker than that of Experimental Area. ► Pyrolytic input may be a major source of PAHs in YRDNNR. ► Petrogenic inputs were more apparent at some sites due to oil exploration of Shengli Oilfield.Sediment samples collected from the Core Area, Experimental Area and Buffer Area of Yellow River Delta National Nature Reserve (YRDNNR), China, were analyzed by GC–MS in order to determine the degree of hydrocarbon contamination, and identify the sources of aliphatic hydrocarbons and PAHs. The total petroleum hydrocarbon contents of sediments were relatively low or moderate compared to world-wide locations reported to be chronically contaminated by oil. On the whole, the degree of petroleum contamination in the Core Area and Buffer Area in YRDNNR is weaker than that of the Experimental Area. The potential ecosystem risk assessment indicated that PAHs will not cause immediate adverse biological effects in the YRDNNR. Besides oil-related hydrocarbon inputs in this region, aliphatic hydrocarbon analysis showed the presence of hydrocarbons of terrestrial origin at some sampling sites, characterized by high CPI values. Based on PAH ratios and principal component analysis, pyrolytic input may be a major source of PAHs in YRDNNR sediment, while petrogenic inputs were more apparent at some sites in the Experimental Area due to oil exploration in the Shengli Oilfield.
Iron-hydroxide, iron-sulfate and hydrous-silica coatings in acid-mine tailings facilities: A comparative study of their trace-element composition by J.L. Durocher; M. Schindler (1337-1352).
► Distribution and concentration of trace elements in rock coatings in Acid-Mine-Drainage systems. ► Coatings occur along ponds and lakes of different pH and composition and are composed of Fe-hydroxides, Fe-sulfates and hydrous silica. ► Silica-rich coatings have higher or similar trace-elements concentrations to Fe-rich coatings. ► High trace-metal concentrations in Si-rich coatings are the result of the formation of jarosite-type phases in a silica-rich matrix. ► Jarosite-type phases nucleate in silica-rich coatings via mixing of Fe-sulfate-rich solutions with trace-elements of underlying rock.Surface alteration-layers often coat minerals in acid-mine drainage systems and the characterization of their chemical composition is required to understand the uptake or release of potentially toxic elements. Samples with micrometer-thick rock coatings were collected from bedrock in contact with three acidic tailings ponds and a small lake, all located within the Copper Cliff mine tailings disposal area in Sudbury, Ontario, Canada. Distribution and concentration of trace-metals in the rock coatings were characterized with Laser-Ablation Inductively-Coupled Plasma Mass Spectroscopy and Micro X-ray Fluorescence Spectroscopy. The rock coatings are composed of goethite, ferrihydrite, schwertmannite, jarosite and amorphous silica. The latter phase is a product of the non-stoichiometric weathering of the underlying siliceous rock. Layers within the coatings are distinguished on the basis of their atomic Fe:Si ratios: FeO x coatings have Fe:Si > 4:1, Si–FeO x coatings have Fe:Si = 4:1 to 1:1 and SiO x coatings have Si > Fe. Iron-rich coatings (FeO x ) in contact with acidic tailings ponds (pH < 3.5) have lower trace-metal concentrations than their Si-rich counterparts, whereas FeO x in contact with lake water at near neutral pH have similar trace-metal concentrations than Si–FeO x and SiO x , most likely the result of higher adsorption rates of metals at near neutral pH conditions. High trace-metal concentrations in Si–FeO x and SiO x are explained by the presence of jarosite-group minerals, which formed within Si-rich alteration layers through mixing of leached alkaline cations and trace elements from the underlying rock and Fe3+-sulfate solutions from the pond. Calculated enrichment factors for trace metals and metalloids in the coatings (relative to the pond) indicate that the mobility for Pb, As, Cr and Cu in the upper part of tailings ponds is commonly lower than the mobility for Zn, Mn, Co and Ni. The environmental significance of these findings is discussed in terms of the attenuation of trace metals in the coatings and the widespread occurrences of silica gels and jarosite-group minerals.
Geochemistry of natural chromium occurrence in a sandstone aquifer in Bauru Basin, São Paulo State, Brazil by Reginaldo Bertolo; Christine Bourotte; Ricardo Hirata; Leonardo Marcolan; Ondra Sracek (1353-1363).
► Geochemical anomaly of chromium in quartzose sandstones (221 ppm). ► Groundwater with concentrations of Cr(VI) of up to 0.13 mg L–1, associated with aquifer levels with high pH values. ► Chromium diopsides and iron hydroxides may be the sources of Cr(III). ► Manganese oxides may oxidize Cr(III) to Cr(VI). ► A small amount of adsorbed Cr(VI) may be released to groundwater due to pH conditions.Anomalous concentrations of Cr(VI) occur in groundwaters of the Adamantina Aquifer, in a large region in the western state of São Paulo, sometimes exceeding the potability limit (0.05 mg L−1). To identify the possible geochemical reactions responsible for the occurrence of Cr in groundwater in Urânia, borehole rock samples were collected in order to carry out mineralogical and chemical analyses. In addition, multilevel monitoring wells were installed and groundwater samples were analyzed. Analyses of the borehole rock samples show the occurrence of a geochemical anomaly of Cr in the quartzose sandstones (average concentrations of 221 ppm). Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm. Sequential extraction experiments indicated weakly adsorbed Cr in the order of 0.54 ppm, and this quantity is enough to provide the Cr concentrations observed in groundwater. Groundwaters from the monitoring wells proved to be stratified, with the highest concentrations of Cr(VI) (0.13 mg L−1) being associated with high redox and pH values (over 10) and high concentrations of Na. Geochemical reactions that may explain the release of Cr from the solid phase to groundwater involve the release of Cr(III) from minerals (like chrome-diopside and Cr–Fe hydroxide), followed by oxidation of Cr(III) to Cr(VI), probably related to the reduction of Mn oxides present in the aquifer. Then cation exchange occurs and dissolution of carbonates which increases the pH of groundwater, resulting in the desorption and mobilization of Cr(VI) into groundwater.
Arsenic and other oxyanion-forming trace elements in an alluvial basin aquifer: Evaluating sources and mobilization by isotopic tracers (Sr, B, S, O, H, Ra) by David S. Vinson; Jennifer C. McIntosh; Gary S. Dwyer; Avner Vengosh (1364-1376).
► Elevated natural As and F occur in the Willcox Basin aquifer of Arizona. ► Oxyanion-forming elements are derived from volcanic-source aquifer sediments. ► Sr isotopes trace sediment sources linked to oxyanion-forming trace elements. ► 87Sr/86Sr > 0.720 indicates Proterozoic crystalline-source sediment contributing low As. ► Both sediment source and hydrogeochemical evolution (Ca/Na) affect As levels.The Willcox Basin is a hydrologically closed basin in semi-arid southeastern Arizona (USA) and, like many other alluvial basins in the southwestern USA, is characterized by oxic, near-neutral to slightly basic groundwater containing naturally elevated levels of oxyanion-forming trace elements such as As. This study evaluates the sources and mobilization of these oxyanionic trace elements of health significance by using several isotopic tracers of water–rock interaction and groundwater sources (87Sr/86Sr, δ34SSO4, δ11B, δ2H, δ18O, 3H). Values of δ2H (−85‰ to −64‰) and δ18O (−11.8‰ to −8.6‰) are consistent with precipitation and groundwater in adjacent alluvial basins, and low to non-detectable 3H activities further imply that modern recharge is slow in this semi-arid environment. Large variations in 87Sr/86Sr ratios imply that groundwater has interacted with multiple sediment sources that constitute the basin-fill aquifer, including Tertiary felsic volcanic rocks, Paleozoic sedimentary rocks, and Proterozoic crystalline rocks. In general, low concentrations of oxyanion-forming trace elements and F− are associated with a group of waters exhibiting highly radiogenic values of 87Sr/86Sr (0.72064–0.73336) consistent with waters in Proterozoic crystalline rocks in the mountain blocks (0.73247–0.75010). Generally higher As concentrations (2–29 μg L−1), other oxyanion-forming trace element concentrations (B, V, Cr, Se, Mo, Sb), and F− concentrations are associated with a group of waters exhibiting lower 87Sr/86Sr ratios (0.71012–0.71503), suggesting that sediments derived from Tertiary felsic volcanic rocks are a significant source of these trace elements in groundwater. δ34SSO4 (2.0–13.4‰) and δ11B (−6.7‰ to 18.2‰) variations suggest that rain-derived B and SO 4 2 - plus marine gypsum derived from Paleozoic sedimentary rocks and B derived from felsic volcanic rocks explain the observed values. In addition to the sources of these elemental and isotopic signatures, down-gradient hydrogeochemical modification associated with silicate weathering and perhaps cation exchange are recorded by the decreasing Ca/Na ratio. Very low levels of 226Ra in groundwater relative to U throughout the basin-fill aquifer are consistent with the oxic, neutral to high-pH conditions in which mobility of U is strongly favored relative to Ra. Used in combination, multiple isotopic and geochemical tracers can provide valuable information for understanding the relative importance of sediment source and hydrogeochemical processes for observed levels of As and other naturally-occurring trace elements. These tracers, in particular 87Sr/86Sr with its sensitivity to aquifer sediment source, can be applied to other alluvial basin-fill aquifers in the southwestern USA where multiple sediment types contribute varying amounts of As and other oxyanion-forming trace elements to groundwater.
Relation between the deposition and petrology of Shanxi coals and the composition of their extracts by Huaying Huai; Alec Gaines; Roger E. Tye (1377-1385).
► Describes the three different depositions of the important Shanxi coals. ► Reveals n-alkanes as biomarkers of the original vegetation in the depositions. ► Demonstrates branched alkane distributions to be determined by catagenesis. ► Identifies industrially important extractable aromatic compounds within the vitrinite. ► Shows benzene–methanol extracts to be resolvable by HPLC.The soluble organic material present in a set of 12 coal samples representing three major episodes of coal deposition in Shanxi Province, North China, has been examined. Shanxi coals, like those from Gondwanaland, contain little liptinite and accordingly the material extracted by pyridine yields only small quantities of n-hexane soluble n-alkanes, steranes and hopanes identifiable by gas-chromatography/mass spectrometry. The distribution of the n-alkanes is characteristic of the environment from which each of the Shanxi coals was formed but the distribution of the branched alkanes is generally determined by the dia- and catagenesis each coal experienced. Aromatic compounds identified in the extracts typify the small molecules present within the vitrinite lattice. Technologically significant benzene–methanol extracts deriving from vitrinite–inertinite have been characterised by proton NMR spectroscopy and partially separated by HPLC.
Investigation by multivariate analysis of groundwater composition in a multilayer aquifer system from North Africa: A multi-tracer approach by Lassaad Dassi (1386-1398).
► We investigate the hydrodynamics and hydrochemistry of a multilayer aquifer system. ► We examine the geochemical evolution, the origins and the circulation patterns of groundwater. ► The mineralization is controlled by water-rock interaction and return flow process. ► Groundwater derives from palaeoclimatic and modern end-members. ► Mixing by upward and downward leakage occurs between these two end-members.A multi-tracer approach has been carried out in the Sbeïtla multilayer aquifer system, central Tunisia, to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. It involves statistical data analysis coupled with the definition of the hydrochemical and isotopic features of the different groundwaters. Principal Components Analysis (PCA) of geochemical data used in conjunction with bivariate diagrams of major and trace elements indicate that groundwater mineralization is mainly controlled by water–rock interaction and anthropogenic processes in relation to return flow of irrigation waters. The PCA of isotopic data and bivariate conventional diagrams of stable and radiogenic isotopes i.e. δ18O vs. δ2H and δ18O vs. 14C provide valuable information about the origin and the circulation patterns of the different groundwater groups. They permit classifying groundwaters into three groups. The first group is characterized by low 3H concentrations, low 14C activities and depleted stable isotope contents. It corresponds to an old end-member in relation with palaeoclimatic recharge which occurred during the Late Pleistocene and the Early Holocene humid periods. The second group is distinguished by high to moderate 3H concentrations, high 14C activities and enriched heavy isotope signatures. It corresponds to a modern end-member originating from a mixture of post-nuclear and present-day recharge in relation to return flow of irrigation waters. The third group is characterized by an average composition of stable and radiogenic isotope signatures. It provides evidence for the mixing between the upward moving palaeoclimatic end-member and the downward moving present-day end-member.
Hydro-geochemical processes in an area with saline groundwater in lower Shire River valley, Malawi: An integrated application of hierarchical cluster and principal component analyses by Maurice Monjerezi; Rolf D. Vogt; Per Aagaard; John D.K. Saka (1399-1413).
► HCA and PCA were applied in an integrated manner to a major ion dataset of groundwater with localized high salinity. ► PCA was performed in R using FactoMineR package, with quantitative as well as supplementary variables. ► Clusters and PCs were interpreted in corroboration with geochemical relations. ► As a result, we defined hydro-geochemical processes affecting the spatial variation in groundwater chemistry and salinity.Our ability to adapt to changes in groundwater quality, arising from a changing climate and/or local pressures, is dependent on comprehension of the governing controls of spatial variation in groundwater chemistry. This paper presents results of an assessment of dominant hydro-geochemical processes controlling groundwater chemical composition, using an integrated application of hierarchical cluster analysis (HCA) and principal component analysis (PCA) of a major ion dataset of groundwater from lower Shire River valley, Malawi. The area is in the southernmost part of the western section of the East African Rift System (EARS) and has localised occurrence of saline groundwater. HCA classified samples into three main clusters (C1–C3) according to their dominant chemical composition: C1 (dominant composition: Na–Cl; median TDS: 3436 mg L−1), C2 (dominant composition: Na–HCO3; median TDS: 966 mg L−1) and C3 (dominant composition: alkali earths–HCO3; median TDS: 528 mg L−1). These clusters were in turn described by the principal components PC1, PC3 and PC2, respectively, resulting from the PCA. The results of the PCA and geochemical interpretation suggest that the spatial variation of groundwater quality in the area is influenced by the following processes: C3 samples result mainly from H2CO3 weathering of aluminosilicate minerals by percolating water supersaturated with CO2. In addition to aluminosilicate weathering, C2 samples are influenced by the processes of cation exchange of Ca2+ and Mg2+ in the water for Na+ on clay minerals, and carbonate precipitation. The increase in ionic strength of C2 samples is attributed to mixing with high TDS groundwater in proximity with C2 samples. The saline/brackish C1 groundwater results from the processes of evaporation (for samples with high water table close to the Shire marshes) and dissolution of Cl− and SO4-evaporative salts followed by mineralised seep from sedimentary Karoo and Cretaceous Lupata sandstones.
The influence of Fe(II) competition on the sorption and migration of Ni(II) in MX-80 bentonite by Wilfried Pfingsten; Mike Bradbury; Bart Baeyens (1414-1422).
► We model the diffusion of Ni(II) through bentonite using different sorption models. ► We examine sorption competition of Fe(II) and Ni(II) at different concentrations. ► Ni(II) breakthrough is 15 times earlier with Fe(II) sorption competition. ► Ni(II) sorption is non-linear and depends on the Fe(II) concentration levels. ► Sorption competition is important and has to be modelled by reactive transport codes.The results from batch sorption experiments on montmorillonite systems have demonstrated that bivalent transition metals compete with one another for sorption sites. For safety analysis studies of high level radioactive waste repositories with compacted bentonite near fields, the importance of competitive sorption on the migration of radionuclides needs to be evaluated. Under reducing conditions, the bentonite porewater chosen has a Fe(II) concentration of ∼5.3 × 10−5 M through saturation with siderite. The purpose of this paper is to assess the influence of such high Fe(II) concentrations on the transport of Ni(II) through compacted bentonite, Ni(II) was chosen as an example of a bivalent transition metal. The one-dimensional calculations were carried out at different Ni(II) equilibrium concentrations at the boundary (Ni(II)EQBM) with the reactive transport code MCOTAC incorporating the two site protolysis non electrostatic surface complexation/cation exchange sorption model, MCOTAC-sorb. At a Ni(II)EQBM level of 10−7 M without Fe(II) competition, the reactive transport calculations using a constant Kd approach and the MCOTAC-sorb calculation yielded the same breakthrough curves. At higher Ni(II)EQBM (10−5 M), the model calculations with MCOTAC-sorb indicated a breakthrough which was shifted to later times by a factor of ∼5 compared with the use of the constant Kd approach.When sorption competition was included in the calculations, the magnitude of the influence depended on the sorption characteristics of the two competing sorbates and their respective concentrations. At background Fe(II) concentrations of 5.3 × 10−5 M, and a Ni(II)EQBM level of 10−7 M, the Ni(II) breakthrough time was ∼15 times earlier than in the absence of competition. At such Fe(II) concentrations the Ni(II) breakthrough curves at all source concentrations less than 3.5 × 10−5 M (fixed by the NiCO3,S solubility limit) are the same i.e. Ni(II) exhibits linear (low) sorption.Competitive sorption effects can have significant influences on the transport of radionuclides through compacted bentonite i.e. reduce the migration rates. Since, for the case considered here, the Fe(II) concentration in the near field of a high-level radioactive waste repository may change in time and space, the transport of bivalent transition metal radionuclides can only be properly modelled using a multi-species reactive transport code which includes a sorption model.
Application of carbon isotopes to detect seepage out of coalbed natural gas produced water impoundments by Shikha Sharma; Joshua K. Baggett (1423-1432).
► Coalbed natural gas extraction results in large amount of produced water. ► Risk of deterioration of ambient water quality. ► Carbon isotope natural tracer for detecting seepage from produced water impoundments.Coalbed natural gas (CBNG) production from coal bed aquifers requires large volumes of produced water to be pumped from the subsurface. The produced water ranges from high quality that meets state and federal drinking water standards to low quality due to increased salinity and/or sodicity. The Powder River Basin of northeastern Wyoming is a major coalbed natural gas producing region, where water quality generally decreases moving from the southeastern portion of the basin towards the center. Most produced water in Wyoming is disposed into impoundments and other surface drainages, where it may infiltrate into shallow groundwater. Groundwater degradation caused by infiltration of CBNG produced water holding impoundments into arid, soluble salt-rich soils is an issue of immense importance because groundwater is a major source for stock water, irrigation, and drinking water for many small communities in these areas. This study examines the potential of using stable C isotope signatures of dissolved inorganic C (δ13CDIC) to track the fate of CBNG produced water after it is discharged into the impoundments. Other geochemical proxies like the major cations and major anions were used in conjunction with field water quality measurements to understand the geochemical differences between CBNG produced waters and ambient waters in the study area. Samples were collected from the CBNG discharge outfalls, produced water holding impoundments, and monitoring wells from different parts of the Powder River Basin and analyzed for δ13CDIC. The CBNG produced waters from outfalls and impoundments have positive δ13CDIC values that fall within the range of +12‰ to +22‰, distinct from the ambient regional surface and groundwaters with δ13CDIC values ranging from −10‰ to −14‰. The results from the study demonstrate that these contrasting δ13CDIC signatures can be used to trace seepage out of CBNG produced water impoundments into shallow groundwaters.
The geochemistry of aliphatic and polar organic tracers in sediments from Lake Bera, Malaysia by Noorhazlina Abu Bakar; Kheng Soo Tay; Nasr Yousef M.J. Omar; M. Radzi Bin Abas; Bernd R.T. Simoneit (1433-1445).
► Organic geochemistry of sediments from tropical freshwater lake. ► n-Alkan-2-ols were present in plant waxes. ► Pentacyclic triterpenoids found are diagenetic derivatives of lupeol and β-amyrin. ► 3,4-Seco-friedelan-3-oic acid is the photochemical alteration product of friedelin. ► Novel polyfunctional triterpenoids are primarily friedelane derivatives.The molecular distributions of homologous aliphatic lipid compounds (n-alkanes, n-alkanoic acids, n-alkanols, n-alkanals and n-alkan-2-ones) were investigated in sediments of Lake Bera, Malaysia as well as in plant waxes from the vicinity using gas chromatography–mass spectrometry. In addition, triterpenoids of the oleanane, ursane, lupane and friedelane series, and their diagenetic products were also identified. Using the aquatic proxy P aq, it was found that the n-alkanes present in surface sediments S1, S5 and S6 correspond to an input from emergent macrophytes, whereas in sediments collected from open water (S2, S3 and S4) they correspond to input from submerged/floating macrophytes. The presence of n-alkan-2-ols, a commonly found homologous series in the sediments as well as in the plant wax, is novel here. In addition, the presence of 24-methylcycloart-22-enol and 24-ethylcycloart-22-enol in sediments as well as the plant wax of Pandanus helicopus, a dominant reed around the lake, also supports the input of plant biomarkers to the sediments. The occurrence of 5-membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified (e.g. friedelan-2,3-dione) shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions. Also, the presence of ring-A degraded triterpenoids (dihydroputranjivic acid, 3-nor-2,4-seco-friedelane, 4α- and 4β-3-norfriedelanes, A-norfriedel-10-one, and A-norfriedel-8-en-10-one) and the aromatized triterpenoid hydrocarbons (mono- and triaromatic derivatives) as minor diagenetic products indicates photochemical and microorganism-mediated alteration reactions of natural products in the sediments. Additional novel polyfunctional friedelane derivatives, namely friedelane-2,3-dione, friedelane-1,3-diol-2-one and friedel-1(10)-ene-1,3-diol-2-one were identified for the first time in this study. These novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment. For future reference purposes, the mass spectra of the identified polar triterpenoids are also presented here. This study provides important data on the biogeochemistry of organic matter in a tropical lake of SE Asia.
Sources of elevated salinity in the Mississippi River Alluvial Aquifer, south-central Louisiana, USA by Stephanie E. Welch; Jeffrey S. Hanor (1446-1451).
► Salinization is impacting groundwater quality in southern Louisiana, USA. ► This includes the Mississippi River Alluvial Aquifer. ► Geochemical evidence indicates salt dome dissolution is responsible. ► Thus, salinization here is a natural, on-going process. ► The potential for remediation is slight, if not non-existent.Salinization is a process impacting groundwater quality and availability across much of southern Louisiana, USA. However, a broad divergence of opinion exists regarding the causes of this elevated salinity: updip-migrating marine waters from the Gulf of Mexico, saline fluids migrating up fault planes, movement of water from salt domes, and/or remnant seawater from the last major marine transgression. The Mississippi River Alluvial Aquifer (MRAA) in south-central Louisiana is recharged by the Mississippi River, and there are discharge zones to the west and east. Recharge waters from the Mississippi River are fresh, but Cl− levels in the western portions of the aquifer are as high as 1000 mg/L. The aquifer is an important source of water for several municipalities and industries, but prior to this study the source(s) of the elevated salinity or whether the salinization can be remediated had not been determined.The low Br/Cl ratios in the groundwaters are consistent with a saline endmember produced by subsurface dissolution of salt domes, not a marine source. The H and O isotopic systematics of the aquifer waters indicate meteoric sources for the H2O, not marine waters or diagenetically-altered deep brines. The westward salinization of aquifer water represents a broad regional process, instead of contamination by point sources. Mapping of spatial variations in salinity has permitted the identification of specific salt domes whose subsurface dissolution is producing waters of elevated salinity in the aquifer. These include the Bayou Choctaw and St. Gabriel domes, and possibly the Bayou Blue dome. Salinization is a natural, on-going process, and the potential for remediation or control is slight, if not non-existent.
Kinetics of iron (II) oxidation determined in the field by Jennifer N. Geroni; Devin J. Sapsford (1452-1457).
► Iron (II) oxidation rates were studied in the field. ► Values for the homogeneous oxidation rate constant k 1 were calculated. ► Values for k 1 were 1–3 orders of magnitude higher than those observed in laboratory studies. ► Apparent elevation in k 1 values may be a result of autocatalytic heterogeneous iron oxidation.This paper presents the results of extensive field trials measuring rates of Fe(II) oxidation at a number of Fe-bearing mine drainage discharges in the UK. Batch experiments were carried out with samples taken at regular intervals and Fe(II) concentration determined spectrophotometrically using 2′2-bipyridyl as the complexing agent. Initial concentrations for Fe(II) were 5.65–76.5 mg/L. Temperature, pH and dissolved O2 (DO) were logged every 10 s, with pH at the start of the experiments in the range 5.64–6.95 and alkalinity ranging from 73 to 741 mg/L CaCO3 equivalent. A numerical model based on a fourth order Runge–Kutta method was developed to calculate values for k 1, the rate constant for homogeneous oxidation, from the experimental data. The measured values of pH, temperature, [Fe(II)] and DO were input into the model with resulting values for k 1 found to be in the range 2.7 × 1014–2.7 × 1016 M−2 atm−1 min−1. These values for k 1 are 1–3 orders of magnitude higher than previously reported for laboratory studies at a similar pH. Comparison of the observed Fe(II) oxidation rates to data published by other authors show a good correlation with heterogenous oxidation rates and may indicate the importance of autocatalysis in these systems. These higher than expected rates of Fe oxidation could have a significant impact on the design of treatment schemes for the remediation of mine drainage and other Fe-bearing ground waters in the future.
Organic matter compositions and DOM release from the sediments of the shallow lakes in the middle and lower reaches of Yangtze River region, China by Shengrui Wang; Lixin Jiao; Suwen Yang; Xiangcan Jin; Haiqing Liang; Fengchang Wu (1458-1463).
► We confirm the contents of OC, DOC, AOC, HFOC and LFOC in studied sediments. ► The correlations between TN, TP, OC, DOC, AOC, LFOC, HFOC and the DOM release kinetic parameters of the sediments were significant. ► With the increasing of OC content the ratios of DOC to OC and AOC to OC decreased. ► The DOM release was related to the OC content. ► The DOM release was also related the organic matter composition characteristics.The contents of different organic matter components and dissolved organic matter (DOM) release kinetics of the sediments from the middle and lower reaches of the Yangtze River region were investigated, and their relationships discussed. The results show that organic C (OC) ranged from 8.14 to 43.65 g kg−1, dissolved organic C (DOC) from 0.38 to 1.38 g kg−1, active organic C (AOC) from 1.12 to 4.45 g kg−1, heavy fraction organic C (HFOC) from 6.86 to 39.08 g kg−1, accounting for 2.42–9.34%, 8.66–29.72% and 84.29–93.18% of OC, respectively. With increasing of OC content the ratios of DOC to OC and AOC to OC decreased. The contents of AOC, DOC, light fraction organic C (LFOC) and their contribution ratios to OC in studied sediments were higher than those reported in soils. The DOM release process of the studied sediments includes rapid and slow stages, and the rapid release occurred within 30 min, mainly in 5 min. The DOM release kinetic data in this investigation can be best fitted by the Power Function model. The correlations between total N (TN), total P (TP), OC, DOC, AOC, LFOC, HFOC and the DOM release kinetic parameters (k, c, a, b, rate 30) of the sediments were significant. There were also significant correlations between TN, TP, OC, DOC, LFOC and HFOC in sediments. So the DOM release from sediment was not only related to the OC content, but also related to the organic matter composition characteristics, especially the contents of DOC, AOC and LFOC.
Interpretation of undisturbed hydrogeochemical conditions in Neogene sediments of the Horonobe area, Hokkaido, Japan by Hiroshi Sasamoto; Randolph C. Arthur; Katsuhiro Hama (1464-1477).
► Representativeness of groundwater was evaluated by using distinctive techniques. ► Degassing could adversely affect representativeness of groundwater samples. ► Gas–water–rock interactions by degassing could alter groundwater compositions.Empirical, geostatistical and geochemical modeling techniques were used to determine whether chemical, isotopic and mineralogical data collected in surface-based borehole investigations at the Horonobe Underground Research Laboratory (URL) site in Hokkaido, Japan were representative of the natural environment before it was disturbed by borehole drilling, hydraulic testing and sampling. Water samples collected either by pumping groundwaters to the surface from borehole sections that had been isolated by inflatable packers or by squeezing porewaters from drillcores sampled from the same borehole and sampling depth were found to be similar in certain respects (m Na+, m Cl−, δ18O and δD) but not others (m SO42−, m Ca2+, m Mg2+ and m K+). The inconsistencies suggest that a majority of the porewater samples were contaminated as a result of pyrite oxidation and dissolution of carbonate minerals during sampling, storage and/or squeezing of the drillcores. Multivariate geostatistical analyses support this hypothesis, and further suggest that uncontaminated porewaters and groundwaters can be divided into three representative groups: a low salinity, low δ18O and low δD group; a moderate salinity, low Ca–Mg group; and a high salinity, high K and moderate Ca–Mg group. The groundwaters also contain high concentrations of dissolved gases, including CH4(g), CO2(g), H2S(g) and various hydrocarbons, which exsolve from the groundwaters as they are pumped to the surface for sampling. The effects of such degassing on the chemistry of groundwater samples was evaluated by using a reaction-path model to simulate the titration of gases collected at the surface back into the samples. Results suggest that undisturbed groundwaters are slightly more acidic than their sampled counterparts, and contain roughly equivalent activities of dissolved CH4(aq) and carbonate species. Redox potentials calculated using the corrected groundwater compositions and assuming equilibrium for the CH4(aq)/CO2(aq) redox couple are significantly more negative than those determined in situ in one borehole using a downhole chemical probe, and those that can be inferred from the ubiquitous presence of small amounts of framboidal pyrite and siderite in siliceous biogenic sediments of the Horonobe area. The empirical, geostatistical and geochemical modeling techniques considered in this study can be adapted for use in characterizing the hydrogeochemical environment of a site that will eventually be selected to host a geologic repository for high-level nuclear waste in Japan.
A δ34S isoscape of total sulphur in soils across Northern Ireland by Philip Stack; Luc Rock (1478-1487).
► We determined δ34S values of total soil S across Northern Ireland (NI). ► We examined spatial differences in δ34S to establish a ‘novel’ S isoscape for NI. ► A spatially coherent pattern of δ34S values was observed. ► δ34S values were higher in W and N compared to SE. ► Atmospheric S deposition is a controlling factor on regional variation of δ34S.A map of the spatial variation in isotopic composition of a substrate, or isoscape, provides a tool to address a range of research questions, such as the use of isotope fingerprinting to identify the origin of compounds. The focus of this study was to establish a soil S isotope map for Northern Ireland in order to investigate spatial variability within the isotopic composition of total soil sulphur (S). The sample resolution was about one sample every 141 km2. δ34S values were grouped based on soil type and soil parent material. Total soil S δ34S data were grouped according to soil type, to evaluate whether a soil’s characteristics affect its isotopic composition. Gleyed soils had a mean δ34S value of +6.3 ± 6.1‰, lower than the means for other soil types. A trend towards higher δ34S values (mean δ34S of +13.8 ± 6.0‰) was observed in soils with a high organic matter content. No trends in δ34S value were observed for other soil types. There were no discernible correlations between total soil S δ34S and soil parent material, with the exception of shale and mudstones. The majority of soils derived from shale and mudstones had δ34S values at or close to the mean of +4.9‰. A spatially coherent pattern of relatively high soil total S δ34S values in the west and north, and low in the SE, is discernible in Northern Ireland. Based on the observed spatial distribution, it has been concluded that the quantity and source (anthropogenic or marine) of wet atmospheric S deposition is a controlling factor on regional variation of soil δ34S in Northern Ireland. This S isoscape will assist studies of S cycling in Northern Ireland and may assist in the creation of an ‘isotopic fingerprint’ for a potential ‘input’ source needed to interpret data in traceability studies.
Chromium(VI) generation in vadose zone soils and alluvial sediments of the southwestern Sacramento Valley, California: A potential source of geogenic Cr(VI) to groundwater by Christopher T. Mills; Jean M. Morrison; Martin B. Goldhaber; Karl J. Ellefsen (1488-1501).
► Southern Sacramento Valley soil and sediment has abundant naturally-occurring Cr(III). ► Cr(III) resides mainly in chromite but some is associated with clays and Fe oxides. ► Cr(VI) is mostly absent in surface soil but ubiquitous in deeper soil and sediment. ► Cr(VI) increased linearly with time during lab soil incubations with no additions. ► Cation exchange processes resulted in greater Cr(VI) generation rates.Concentrations of geogenic Cr(VI) in groundwater that exceed the World Health Organization’s maximum contaminant level for drinking water (50 μg L−1) occur in several locations globally. The major mechanism for mobilization of this Cr(VI) at these sites is the weathering of Cr(III) from ultramafic rocks and its subsequent oxidation on Mn oxides. This process may be occurring in the southern Sacramento Valley of California where Cr(VI) concentrations in groundwater can approach or exceed 50 μg L−1. To characterize Cr geochemistry in the area, samples from several soil auger cores (approximately 4 m deep) and drill cores (approximately 25 m deep) were analyzed for total concentrations of 44 major, minor and trace elements, Cr associated with labile Mn and Fe oxides, and Cr(VI). Total concentrations of Cr in these samples ranged from 140 to 2220 mg per kg soil. Between 9 and 70 mg per kg soil was released by selective extractions that target Fe oxides, but essentially no Cr was associated with the abundant reactive Mn oxides (up to ∼1000 mg hydroxylamine-reducible Mn per kg soil was present). Both borehole magnetic susceptibility surveys performed at some of the drill core sites and relative differences between Cr released in a 4-acid digestion versus total Cr (lithium metaborate fusion digestion) suggest that the majority of total Cr in the samples is present in refractory chromite minerals transported from ultramafic exposures in the Coast Range Mountains. Chromium(VI) in the samples studied ranged from 0 to 42 μg kg−1, representing a minute fraction of total Cr. Chromium(VI) content was typically below detection in surface soils (top 10 cm) where soil organic matter was high, and increased with increasing depth in the soil auger cores as organic matter decreased. Maximum concentrations of Cr(VI) were up to 3 times greater in the deeper drill core samples than the shallow auger cores. Although Cr(VI) in these vadose zone soils and sediments was only a very small fraction of the total solid phase Cr, they are a potentially important source for Cr(VI) to groundwater. Enhanced groundwater recharge through the vadose zone due to irrigation could carry Cr(VI) from the vadose zone to the groundwater and may be the mechanism responsible for the correlation observed between elevated Cr(VI) and NO 3 - concentrations in previously published data for valley groundwaters. Incubation of a valley subsoil showed a Cr(VI) production rate of 24 μg kg−1 a−1 suggesting that field Cr(VI) concentrations could be regenerated annually. Increased Cr(VI) production rates in H+-amended soil incubations indicate that soil acidification processes such as nitrification of ammonium in fertilizers could potentially increase the occurrence of geogenic Cr(VI) in groundwater. Thus, despite the natural origin of the Cr, Cr(VI) generation in the Sacramento Valley soils and sediments has the potential to be influenced by human activities.
Carbonation of lignite fly ash at ambient T and P in a semi-dry reaction system for CO2 sequestration by Markus Bauer; Niklas Gassen; Helge Stanjek; Stefan Peiffer (1502-1512).
► The carbonation of lignite fly ash was achieved under semi dry conditions at low temperature and pressure conditions. ► Highest CO2-uptake was reached for intermediate liquid-to-solid ratios of 0.12–0.18 L kg−1. ► Increasing mixing intensity or pCO2 caused higher carbonation rates, suggesting limitation by CO2 supply. ► Up to 4.8 mmol CO2 g−1 were absorbed, corresponding to 53% of the theoretical CO2 binding capacity of the material. ► Both Ca and Mg containing phases were converted into carbonate minerals.The global rise in atmospheric greenhouse gas concentrations calls for practicable solutions to capture CO2. In this study, a mineral carbonation process was applied in which CO2 reacts with alkaline lignite ash and forms stable carbonate solids. In comparison to previous studies, the assays were conducted at low temperatures and pressures and under semi-dry reaction conditions in an 8 L laboratory mixing device. In order to find optimum process conditions the pCO2 (10–20%), stirring rate (500–3000 rpm) and the liquid to solid ratio (L/S = 0.03–0.36 L kg−1) were varied. In all experiments a considerable CO2 uptake from the gas phase was observed. Concurrently the solid phase contents of Ca and Mg (hydr)oxides decreased and CaCO3 and MgCO3 fractions increased throughout the experiments, showing that CO2 was stabilized as a solid carbonate. The carbonation reaction depends on three factors: Dissolution of CO2 in the liquid phase, mobilization of Ca and Mg from the mineral surface and precipitation of the carbonate solids. Those limitations were found to depend strongly on the variation of the process parameters. Optimum reaction conditions could be found for L/S ratios between 0.12 and 0.18, medium stirring velocities and pCO2 between 10% and 20%.Maximum CO2 uptake by the solid phase was 4.8 mmol g−1 after 120 min, corresponding to a carbonation efficiency for the alkaline material of 53% of the theoretical CO2 binding capacity. In comparison to previous studies both CO2 uptake and carbonation efficiencies were in a similar range, but the reaction times in the semi-dry process were considerably shorter. The proposed method additionally allows for a more simple carbonation setup due to low T and P, and produces an easier to handle product with low water content.
Reactive transport modelling of Cr(VI) treatment by cast iron under fast flow conditions by Christoph Wanner; Urs Eggenberger; Urs Mäder (1513-1523).
► Full characterization of cast iron shavings, used for Cr(VI) treatment by a PRB. ► Evaluation of long-term performance of planned PRB performing column experiments. ► Description of reaction network used for reactive transport modelling of planned PRB. ► Results of 1D calibration of reaction network by modelling column experiments.The Cr(VI) reduction behaviour of five different types of grey cast iron shavings meant for construction of a permeable reactive barrier (PRB) in Thun, Switzerland, was investigated by performing batch and column experiments. Closed system batch experiments clearly demonstrated that the largest shavings also containing the largest spherical C inclusions, were best qualified for the PRB due to their fast Cr(VI) reduction rate. However, the column experiment performed with this type of material revealed that a complete and long term Cr(VI) treatment by the planned PRB was questionable due to the site-specific high groundwater flow velocities and the almost O2 and CaCO3 saturated aquifer conditions. The experimentally observed Cr(VI) breakthrough is explained as a result of a decline of reactivity provoked by a strong passivation by observed Fe hydroxides (FeOOH-polymorphs) and carbonates (calcite and aragonite).The column experiment was simulated using the reactive transport modelling code CrunchFlow. Iron cycling and intra-aqueous reactions were incorporated into a previously described reaction network in order to model the strong decline in reactivity of grey cast iron. All key parameters like aqueous species concentrations and mineralogical evolution of the column were successfully modelled. The modelling results confirmed that the observed Cr(VI) breakthrough was caused by surface passivation of the Fe shavings. Complete oxidation of the initially present mass of shavings is not predicted to occur during the expected PRB lifetime of several decades. The model seems to be robust, and it is expected that an application of the calibrated model in 2D to field sites will allow a quantitative evaluation for the performance of planned PRB’s in such environments.
Solute distribution in porous rhyolite as evaluated by sequential centrifugation by Tadashi Yokoyama; Satoru Nakashima; Takashi Murakami; Lionel Mercury; Yusuke Kirino (1524-1534).
Extraction process of pore water with stepwise increase of centrifugal speed and solute concentrations as a function of pore radius (extraction ratio).Display Omitted► Pore water of a rock was centrifugally extracted with increasing centrifugal speed. ► As centrifugal speed increases, water is extracted in order of large to small pores. ► Solute concentrations in pore water change depending on pore size. ► Changes in solute concentrations reflect reaction and transport occurring in pores.Pore water in a porous rhyolite, having a porosity of 27% and pore radii ranging from >25 μm to 0.008 μm, was centrifugally extracted stepwise with increasing centrifugal speed to examine the potential variations of the compositions of pore water and their relationships to reaction and transport occurring in the rock. The rock was soaked for from 1 h to 7 days in an aqueous solution prior to centrifugation. To evaluate the effect of adsorption under minimum effect of dissolution, Li+ and Br− were added to the solution as tracer ions. As centrifugal speed increased, water was extracted in order of large to small pores and the thickness of residual water film became thinner. The concentrations of ions dissolving from the rock (Na+, K+, Ca2+, etc.) after 7 days of immersion were relatively constant in pores of 1–10 μm radii and exponentially increased by 3–100 fold with decreasing pore radius to 0.1 μm. These ions are dissolved from the rock and transported toward the exterior of the rock by diffusion. The calculation using a reactive-transport equation showed that the observed concentration changes reflect the change in solute distribution profile with pore size. The concentration of Si after 7 days of immersion was approximately constant or slightly decreased with increasing centrifugal speed, which appears to be controlled by the solubility. The concentration of Li+ decreased with increasing centrifugal speed after 1 h of immersion but the trend changed after 7 days of reaction. Initial behavior of Li+ is explained by adsorption on pore walls, and the change of trend is explained by desorption of that previously adsorbed, slight amounts of dissolution, and inflow from the outside of the rock. The change in concentration of Br− with increasing centrifugal speed was small, probably because Br− was not adsorbed on the surfaces. The sequential centrifugation thus provides information on the solute distribution associated with reaction and transport occurring in rock pores.
Hydrogeochemistry of three watersheds (the Erlqis, Zhungarer and Yili) in northern Xinjiang, NW China by Bingqi Zhu; Xiaoping Yang; Patrick Rioual; Xiaoguang Qin; Ziting Liu; Heigang Xiong; Jingjie Yu (1535-1548).
► Natural waters are neutral to alkaline and are soft-fresh waters. ► The mean TDS of 580 mg/L is 4.6 times that of the world spatial median. ► Waters chemistry controlled by carbonate dissolution processes. ► Cation exchanges reaction, soil–salt leaching and evaporation play an important role. ► The effects of local pollution are significant on the oases of the drainage basins.In the arid region of northern Xinjiang, one of the least-studied areas in China, three watersheds, namely those of the Yili, Zhungarer and Erlqis, have become the focus of attention due to rapidly increasing human population and water demands. The hydrogeochemistry of natural water from the three watersheds was investigated. The ionic chemistry of natural waters from these watersheds changes considerably on a regional scale. The waters are neutral to alkaline in nature and most of them are soft-fresh waters. The total dissolved solid (TDS) varies over two orders of magnitude with a mean value of 580 mg/L, about 1.2 times and 4.6 times those of the Huanghe (Yellow River) and the world spatial median, respectively, but only 40% and 0.8% of those of the Tarim and the western Alashan watersheds, respectively. Much of the solutes and physicochemical parameters in these waters are under the highest desirable limits of the World Health Organization (WHO) for drinking purpose and a plot of sodium adsorption ratio versus EC shows that most waters are of good water quality for irrigation. Water–rock interaction and saturation index (SI) for selected minerals are evaluated. The SI of these natural waters is out of equilibrium (undersaturated) with respect to major carbonates (calcite and dolomite) and evaporites (gypsum and halite). The high concentrations of alkali earth metals, alkalinity and the high (Ca + Mg)/(Na + K) and Na/Cl ratios indicate that the release of major solutes in these waters is controlled largely by dissolution processes of carbonate and partly by silicate weathering, while, cation exchange reactions, soil–salt leaching and evaporation processes also play an important role. The effects of local pollution are minimal in the montane and piedmont areas of these watersheds but are significant in the oases and central areas of the drainage basins.
Geochemical mapping in Shikoku, southwest Japan by Masumi U. Mikoshiba; Noboru Imai; Yoshiko Tachibana (1549-1568).
► Geochemical mapping in a fore-arc area was conducted using stream sediments. ► Areas with higher values of mafic elements are distributed along the axis of Shikoku. ► High values reflect mafic–ultramafic components in metamorphic rocks and accretionary complexes. ► These mafic–ultramafic components had possibly originated as oceanic rocks. ► Positive anomalies of chalcophile elements near mineral deposits and fault zones are detected.Geochemical mapping of Shikoku in the SW Japan Arc was conducted using stream sediments (<0.18 mm fraction) with sample densities of 1 site per 106 km2. Concentrations of 51 elements in 173 stream sediments were determined. Areas with especially high Cr, Ni, Mg and Co concentrations run intermittently and linearly through Shikoku, and coincide with exposures of the Mikabu greenstone complex composed of oceanic basaltic and gabbroic rocks with minor ultramafic bodies. Areas with higher concentrations of Fe, V, Sc, Ti, Mn, Cr, Ni, Mg, Co and Eu are distributed widely along the Shikoku Island axis; they mainly overlap with the zones of the high-pressure type metamorphic rocks (Sanbagawa Belt) and of the Jurassic accretionary complexes with sedimentary rocks (Chichibu Belt): in contrast, areas with lower concentrations spread over the northern coastal zone of Cretaceous granitoids (Ryoke Belt) and in the southern coastal zone of Cretaceous–Paleogene accretionary complexes (Shimanto Belt). Distribution patterns of these elements reflect that various amounts of mafic and ultramafic materials, possibly of oceanic origin, are associated with the rocks in the Sanbagawa and Chichibu Belts, although such components occur sparsely in the Shimanto and Ryoke Belts. Calcium, Sr, Na, Nb, Sm and Gd contents are lower along the southern coastal zone. High values of Th, U, La, Ce and Ba are associated with granitic rocks. The positive anomalies of Cu and Cd coincide with the distribution of stratabound Cu deposits in the Sanbagawa Belt. Positive anomalies of Sb in the northern area are associated with Sb deposits near the large Median Tectonic Line fault zone. A high-Hg zone is present in the southern fore-arc area. The median concentrations for stream sediments in Shikoku are higher in Hg, Cu, Ni, Cr, Rb, Li, Cs, K, slightly higher in Nb, Ta, La, Ce, Sn and lower in Ca than those for average Japanese stream sediments. The median concentrations for the four geologic zones show systematic wide variations of mafic associated elements, and narrow variations of lithophile elements generally more abundant in felsic rocks. The chemical compositions of the stream sediments in Shikoku largely reflect the concentrations in the pre-Neogene accretionary complexes and in the high-P metamorphic rocks mainly formed from clastic materials derived from continental margins, and ratios of mafic and ultramafic materials within surface rocks; they are partly influenced by sulfide mineralization and fluid migration.
Dissolution and carbonation of a serpentinite: Inferences from acid attack and high P–T experiments performed in aqueous solutions at variable salinity by Andrea Orlando; Daniele Borrini; Luigi Marini (1569-1583).
► In order to perform geological sequestration of CO2, serpentinite should be dissolved by acids or by aqueous solutions. ► At atmospheric pressure serpentinite is efficaciously dissolved at 70 °C using acid attacks. ► At higher P–T conditions, significant carbonation occurs at 30 MPa and 300 °C using CO2 saturated aqueous solutions.Dissolution experiments on a serpentinite were performed at 70 °C, 0.1 MPa, in H2SO4 solution, in open and closed systems, in order to evaluate the overall dissolution rate of mineral components over different times (4, 9 and 24 h). In addition, the serpentinite powder was reacted with a NaCl-bearing aqueous solution and supercritical CO2 for 24 h at higher pressures (9–30 MPa) and temperatures (250–300 °C) either in a stirred reactor or in an externally-heated pressure vessel to assess both the dissolution rate of serpentinite minerals and the progress of the carbonation reaction. Results show that, at 0.1 MPa, MgO extraction from serpentinite ranges from 82% to 98% and dissolution rate varies from 8.5 × 10−10 mole m−2 s−1 to 4.2 × 10−9 mole m−2 s−1. Attempts to obtain carbonates from the Mg-rich solutions by increasing their pH failed since Mg- and NH4- bearing sulfates promptly precipitated. On the other hand, at higher pressures, significant crystallization (5.0–10.4 wt%) of Ca- and Fe-bearing magnesite was accomplished at 30 MPa and 300 °C using 100 g L−1 NaCl aqueous solutions. The corresponding amount of CO2 sequestered by crystallization of carbonates is 9.4–15.9 mole%. Dissolution rate (from 6.3 × 10−11 mole m−2 s−1 to 1.3 × 10−10 mole m−2 s−1) is lower than that obtained at 0.1 MPa and 70 °C but it is related to pH values much higher (3.3–4.4) than that (−0.65) calculated for the H2SO4 solution.Through a thorough review of previous experimental investigations on the dissolution kinetics of serpentine minerals the authors propose adopting: (i) the log rate [mole m−2 s−1] value of −12.08 ± 0.16 (1σ), as representative of the neutral dissolution mechanism at 25 °C and (ii) the following relationship for the acidic dissolution mechanism at 25 °C: log rate = - 0.45 ( ± 0.09 ) × pH - 10.01 ( ± 0.30 ) . The initial dissolution rate (for 25 °C) by acid attack obtained in this work is consistent with this relationship. In contrast, the average dissolution rate (for 25 °C) determined in this study through the pressure-vessel experiments is ∼4.5 orders of magnitude lower than that computed through this equation, suggesting that silica armoring of serpentinite grains played a significant role in these experiments. Overall, the obtained data may improve both the planning of ex-situ mineral carbonation using the CO2 separated from biogas and the modeling of in-situ mineral carbonation.
Distributions and origins of lipid biomarkers in surface sediments from the southern Yellow Sea by Lei Xing; Shuqin Tao; Hailong Zhang; Yanguang Liu; Zhigang Yu; Meixun Zhao (1584-1593).
► Distributions of terrestrial and marine biomarker in Yellow Sea sediments are unlike. ► Productivity and sedimentation rate control the distribution of marine biomarkers. ► Biomarkers are reliable proxies for reconstruction of carbon cycle and ecosystem changes in the YS.This paper reports on the spatial distribution patterns and investigates the controlling mechanisms of phytoplankton biomarkers (brassicasterol for diatoms, alkenones for haptophytes, dinosterol for dinoflagellates) and terrestrial biomarkers (odd C number long-chain (C27 + C29 + C31) n-alkanes) in surface sediments from the southern Yellow Sea (SYS). The contents of the phytoplankton biomarkers in the SYS surface sediments reveals a clear spatial pattern, with low values near the coasts and increased values seaward, caused by higher phytoplankton primary productivity and low sedimentation rates in the basin. The contents of terrestrial biomarkers show high values in the northern part of the study areas off the Shandong Peninsula and Jiangsu coast, caused by inputs of materials from the modern Huanghe River and the old Huanghe delta, respectively. The results also indicate that biomarker ratios offer the best approach for reconstructing marginal sea C cycles, as these proxies can be used to estimate the contributions of both terrestrial and marine organic matter and to reconstruct paleoproductivity and paleoecological changes in the SYS.
Microdenticles on naturally weathered hornblende by Michael A. Velbel (1594-1596).
► Microdenticles are micron-scale denticles on weathered chain-silicates. ► In this example, microdenticles occur on larger denticles as arrays of imbricated pointed or rounded scales. ► They are late-stage features on already-corroded surfaces that show larger-scale evidence of typical hornblende weathering. ► These arrays of microdenticles formed by low-temperature aqueous alteration during natural weathering. ► Association with dilute weathering solutions suggests control by solutions highly undersaturated w.r.t. hornblende.Microdenticles (with lengths in the micron-submicron range rather than tens of microns) are developed on the lateral surfaces of larger “classic” denticles on naturally weathered hornblende from weathered amphibolite of the Carroll Knob Complex in western North Carolina. Microdenticles share the shape and orientation of the larger more typical denticles, producing arrays of microdenticles that give the larger host denticle the appearance of a surface covered with imbricate pointed or rounded scales. The arrays of imbricate microdenticles are formed by low-temperature aqueous alteration during weathering of the Carroll Knob Complex hornblende; they are later-stage corrosion forms on already-corroded surfaces of hornblende that show larger-scale evidence of typical weathering. In the Carroll Knob occurrence, hornblende microdenticles are associated with dilute weathering solutions, suggesting possible control by extreme undersaturation of solutions with respect to hornblende.
Corrigendum for an article of Special Issue – Ninth International Symposium on the Geochemistry of the Earth’s Surface (GES-9) – “Biochar application in a tropical, agricultural region: A plot scale study in Tamil Nadu, India” [Applied Geochemistry 26S (2011) S218–S221] by Utra Mankasingh; Poon-Chung Choi; Vala Ragnarsdottir (1597).
In this Corrigendum, the authors have noticed that they have made an error in two tables in their long abstract (AG 2505) for Applied Geochemistry.