δ34S SO4 Research Articles

Occurrence and mobilization of radium in fresh to saline coastal groundwater inferred from geochemical and isotopic tracers (Sr, S, O, H, Ra, Rn)

Salinization in groundwater systems can induce water–rock interaction, including the release of naturally-occurring trace elements of health significance such as radium (Ra), with possible implications for the usability of water resources in addition to the increase of dissolved solids (TDS) concentrations. In general, radium mobility is limited by chemical removal mechanisms including adsorption onto clays and/or Mn and Fe oxides, exchange processes, and coprecipitation with secondary barite. In order to examine the effect of aquifer salinity gradients on the distribution of naturally-occurring Ra in fresh to saline groundwater and the relationship to water–rock interaction and Ra removal mechanisms, two contrasting systems were investigated: the shallow unconfined coastal aquifer in Agadir (southwestern Morocco) and the confined Cretaceous (Cape Fear) and Pliocene (Yorktown) aquifers of the Atlantic Coastal Plain (North Carolina, USA). Geochemical and isotopic indicators of salinity sources (e.g. cation ratios, δ18O, δ2H, Br−/Cl−, δ34S–SO42-,δ18O–SO42-) were used to identify the relative contributions of seawater and other saline waters and subsequent geochemical modification by water–rock interaction. Radium activities (224Ra, 226Ra, 228Ra), radon-222, alkaline earth metal (Mg, Ca, Sr, Ba) concentrations and ratios, and 87Sr/86Sr ratios were analyzed to identify water–rock interaction processes affecting alkaline earth metals including Ra. The Morocco coastal aquifer is generally oxic, exhibits a range of salinity and water types (Cl− 163–2120mg/L, median 932mg/L), and exhibits Ca/Na ratios above the seawater value, typical of monovalent–divalent cation exchange (base-exchange reactions) in coastal aquifers. In contrast, the Atlantic Coastal Plain aquifers are anoxic, sulfate-reducing, cover a wider salinity range (Cl− 5–9890mg/L, median 800mg/L) representing a transition between Na–HCO3- and Na–Cl− waters, and exhibit Ca/Na ratios below that of modern seawater typical of reverse base-exchange reactions. Possible salinity sources in the Morocco coastal aquifer include seawater intrusion, Mesozoic evaporites, other natural saline waters, and/or wastewater, whereas the Atlantic Coastal Plain is primarily affected by old seawater present in the aquifer system. Radium activities are generally low and vary significantly within each aquifer, for example 226Ra ranges from 1.8–27.7mBq/L in the Morocco coastal aquifer (median 8.1mBq/L) and 1.9–214mBq/L in the Atlantic Coastal Plain (median 18.9mBq/L). The highest Ra activities were observed in the most saline wells sampled in the Atlantic Coastal Plain. At total dissolved solids (TDS) concentrations above an apparent threshold of ∼5000mg/L, radium activities increase in a generally linear fashion with salinity in the Atlantic Coastal Plain, broadly comparable to previous studies indicating a threshold range of ∼3000–10,000mg/L. At lower TDS concentrations, water–rock interaction processes that vary with local aquifer conditions appear to control Ra distribution rather than merely salinity. In the Morocco coastal aquifer, adsorption of Ra and coprecipitation with secondary barite are apparently favorable to control Ra levels in groundwater. Radium removal in the anoxic Atlantic Coastal Plain aquifers appears to be associated with adsorption and/or exchange processes, with the additional possibility of barite precipitation in the Cape Fear aquifer indicated by barite saturation. Overall, the locally-variable factors that can control Ra sources and mobility in fresh to brackish groundwater at near-neutral pH include variation in solid-phase radioactivity, redox state affecting adsorption sites, availability of competing divalent cations, and barite saturation.

The Use of Stable Sulfur, Oxygen and Hydrogen Isotope Ratios as Geochemical Tracers of Sulfates in the Podwiśniówka Acid Drainage Area (South-Central Poland)

The paper presents the results of determinations of stable S and O isotopes of dissolved sulfates and O and H stable isotopes of waters from three ponds, that is, Marczakowe Doly acid pond, Marczakowe Doly fish pond and Podwiśniowka acid pit pond, located in the Holy Cross Mountains (south-central Poland). The δ34SV-CDT and δ18OV-SMOW of SO4 2− in waters of three ponds (n = 14) varied from −16.2 to −9.5 ‰ (mean of −13.6 ‰) and from −8.1 to −3.2 ‰ (mean of −4.8 ‰), respectively. The mean δ34S–SO4 2− values were closer to those of pyrite (mean of −25.4 ‰) and efflorescent sulfate salts (mean of −25.6 ‰), recorded previously in the Podwiśniowka quarry, than to sulfates derived from other anthropogenic or soil and bedrock sources. The SO4 2− ions formed by bacterially induced pyrite oxidation combined with bacterial (dissimilatory) dissolved sulfate reduction, and presumably with subordinate mineralization of carbon-bonded sulfur compounds, especially in both Marczakowe Doly ponds. In addition, the comparison of δ18O–SO4 2− and δ18O–H2O values indicated that 75–100 % of sulfate oxygen was derived from water. Due to the largest size, the Podwiśniowka acid pit pond revealed distinct seasonal variations in both δ18O–H2O (−9.2 to −1.6) and δD–H2O (−29.7 to −71.3) values. The strong correlation coefficient (r 2 = 0.99) was noted between δ18O–H2O and δD–H2O values, which points to atmospheric precipitation as the only source of water. The sediments of both acid ponds display different mineral inventory: the Marczakowe Doly acid pond sediment consists of schwertmannite and goethite, whereas Podwiśniowka acid pit pond sediment is composed of quartz, illite, chlorite and kaolinite with some admixture of jarosite reflecting a more acidic environment. Geochemical modeling of two acid ponds indicated that the saturation indices of schwertmannite and nanosized e-Fe2O3 (Fe3+ oxide polymorph) were closest to thermodynamic equilibrium state with water, varying from −1.44 to 3.05 and from −3.42 to 6.04, respectively. This evidence matches well with the obtained mineralogical results.

Identifying the Sources of Solutes in Karst Groundwater in Chongqing, China: a Combined Sulfate and Strontium Isotope Approach

Abstract:Groundwater from karst subterranean streams is among the world's most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes' sources is very important to ensure the normal function of life support systems. In this paper, thirty–five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca–HCO3 type or Ca (Mg)–HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca–SO4 type (G25 site) or Ca–HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The δ34S–SO42– fell into a range of –6.8‰–21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42– values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sulfide mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.

Sources of sulfur in Deccan Trap rivers: A reconnaissance isotope study

Abstract Sulfur isotopic composition (δ34S) of dissolved SO 4 2 - was measured in waters of rivers draining the Deccan Trap basalts in order to elucidate the source(s) of elevated SO 4 2 - content in some of these rivers, observed in an earlier study. The δ34S values range from 8.7‰ to 19.5‰, with an average of 14.5 ± 2.8‰, values generally enriched in 34S compared to data available from other Indian rivers. The Bhima River (a tributary of the Krishna) and most of its tributaries have δ34S within the 14 ± 2‰ range and high dissolved SO 4 2 - concentrations (256–1556 μM). Measured δ34S of 7 of the saline/alkaline soils suggest that the high dissolved SO 4 2 - in the Bhima river system is likely derived from this source and/or gypsum concretions in the soils. The δ34S–SO4 relationship for the Krishna River and its smaller tributaries follows a mixing pattern of two end-members, rainwater with low SO 4 2 - and low δ34S and an unknown, likely a pollution, source with intermediate SO 4 2 - content and heavy δ34S. The most important finding that this study brings out is the minimal role that the weathering of basalt-sulfides play in contributing to the dissolved SO 4 2 - in the rivers. This rules out the role of H2SO4-, and supports H2CO3-mediated weathering as the dominant process in the Deccan settings.

The sulphur isotope and hydrochemical characteristics of Skeiðarársandur, Iceland: identification of solute sources and implications for weathering processes

AbstractThe hydrochemistry of sulphur in the active outwash plain of Skeiðarársandur, SE Iceland shows considerable variety reflecting differences in sources and processes, and is investigated in this article using δ34S values of dissolved sulphate and igneous sulphide minerals, δ18OH2O, and ionic concentrations in waters. Seawater‐derived sulphate is a notable component only in the lower sandur (δ34SSO4 = +6·8‰ VCDT). δ34SSO4 in the Skeiðará glacial melt river range from +3·4 to +8·8‰δ34S. The higher values occur during a flood event and reflect geothermal sulphate contributions from the Grímsvötn caldera. ‘Kettle‐hole lakes’ formed since the November 1996 jökulhlaup form important ecological niches and show evidence of coupled sulphide oxidation and carbonate and possibly silicate dissolution and have the lowest δ34SSO4 values (average −0·8‰) attributed to higher proportions of sulphide oxidation‐derived SO42− and/or bacterially mediated sulphide oxidation. The hydrochemistry of eastern sandur groundwater is influenced by a hydrothermal source of reduced sulphur from the Grímsvötn caldera or a localized area of geothermal springs, and contrasts with the hydrochemistry of the majority of groundwaters and the Sulá and Gígjukvísl rivers in western and central Skeiðarársandur. These have lower [Ca2+ + Mg2+], [Na+ + K+] and SO42− concentrations and δ34S values consistent with sulphate derived from the oxidation of igneous sulphides. In comparison to catchments dominated by atmospherically transported sulphate, catchments such as this where the sulphur system is dominated by internal sources (rock‐derived and geothermal) will not be sensitive to the temporal decreasing trends in contributions from long‐range airborne sulphate resulting from reductions of sulphur emissions in North America and Europe. Copyright © 2009 John Wiley & Sons, Ltd.

The Application of Stable Isotopes for Assessing the Hydrological, Sulfur, and Iron Balances of Acidic Mining Lake ML 111 (Lusatia, Germany) as a Basis for Biotechnological Remediation

Stable isotope (δ18O–H2O, δ2H–H2O δ34S–SO42-) andhydrochemical data (SO42-, Fe-concentrations) have beenused to estimate the annual groundwater inflow and outflow of mining lake ML 111 and to calculate the total amount of dissolvedsulfate and iron that is carried into the lake by groundwater. The hydrological balance suggests an annual groundwater inflow of 23 700 m3 and an annual groundwater outflow of 15 700 m3. The calculation of the sulfur and iron balances yielded an annual sulfate input of 37 800 kg and an annual iron input of 7000 kg with the groundwater inflow. Furthermore it was shown that significant fluxes of these elements go into the lake sediments which results in continuous release of acidity in the lake water.