Sulfur isotopic composition of H2S and SO4(2-) from mineral springs in the Polish Carpathians

A number of springs in Carpathian Mts. contain dissolved H2S and SO4(2-) in concentrations above 10 mg/dm3. In this study we have investigated the sulfur isotope composition (delta34S) of the dissolved sulfur species in the springs from the flysch area in the Carpathian Mts. along the tectonic dislocation. It is believed that some of these springs may carry a major fraction of dissolved sulfur species of extremely deep sulfur (of mantle origin), which is subjected to SO4(2-)-H2S isotope exchange at high temperatures. The original isotopic compositions may be modified by reduction/oxidation at low temperatures and by admixture of sulfur from other sources. In order to distinguish the sulfur of mantle origin we investigated delta34S of dissolved sulfide and sulfate and on the basis of known concentrations we calculated delta34S of total dissolved sulfur. The isotope fractionation between sulfate and sulfide helped to distinguish the sulfur origin. Evaluating the sulfur isotope exchange, we selected 4 springs which likely have only weakly disturbed sulfur of mantle origin.     

Stable Sulfur Isotope Effects Related to Local Intense Sulfate Reduction in a Tidal Sandflat (Southern North Sea): Results from Loading Experiments

Abstract

Anoxic sediment surfaces coloured black by iron monosulfides (“black spots”) evolve in tidal sandflats of the Wadden Sea (southern North Sea) as a result of the degradation of buried organic matter. To follow the short- and long-term effects of organic matter burial on pore water and sediment isotopic biogeochemistry, formation of artificial black spots was initiated on the Groninger Plate (site RP63) in the backbarrier tidal flats of Spiekeroog island. Changes in concentrations (DOC, TA, TOC, sulfate, sulfide, TRS, Fe) and isotopic compositions (sulfate, sulfide, TRS, pyrite, TOC) were followed for up to 12 months and compared to reference areas. 13°C ratios of TOC clearly mirror the early diagenetic degradation of organic matter. At least temporarily closed system sulfate reduction is inferred for the artificial black spot from the variation of sulfate concentrations and stable sulfur isotope partitioning, In the interstitial waters of the black spot, 34S/32S values of coexisting dissolved sulfate and sulfide yield fractionation degrees between ?5 and ?25%. On the reference area, 34S/32S are fractionated by ?32 to ?42% as calculated from the isotope composition of solid phase reduced sulfur and pore water sulfate. Sulfur isotope fractionation seems to increase with decreasing sulfate reduction rate. Limiting factor seems to be the availability of DOC. Between the pyrite pool and the dissolved sulfide in the black spot, no significant isotope exchange is observed within 12 months.     

Sulfur Isotopic Composition of H2S and SO4 2− from Mineral Springs in the Polish Carpathians

Abstract

A number of springs in Carpathian Mts. contain dissolved H₂S and SO₄ ^2- in concentrations above 10 mg/dm³. In this study we have investigated the sulfur isotope composition (δ³⁴S) of the dissolved sulfur species in the springs from the flysch area in the Carpathian Mts. along the tectonic dislocation. It is believed that some of these springs may carry a major fraction of dissolved sulfur species of extremely deep sulfur (of mantle origin), which is subjected to SO₄ ^2-—H₂S isotope exchange at high temperatures. The original isotopic compositions may be modified by reduction/oxidation at low temperatures and by admixture of sulfur from other sources.

In order to distinguish the sulfur of mantle origin we investigated δ³⁴S of dissolved sulfide and sulfate and on the basis of known concentrations we calculated δ³⁴S of total dissolved sulfur. The isotope fractionation between sulfate and sulfide helped to distinguish the sulfur origin. Evaluating the sulfur isotope exchange, we selected 4 springs which likely have only weakly disturbed sulfur of mantle origin.     

Methane-derived carbonates in a native sulfur deposit: stable isotope and trace element discriminations related to the transformation of aragonite to calcite

Abstract Stable isotope ((13)C, (18)O, (34)S) and trace element (Sr(2+), Mg(2+), Mn(2+), Ba(2+), Na(+)) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ(13)C = -41 to -47‰ vs. PDB) associated with native sulfur (δ(34)S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ(18)O = -3.9 to -5.9‰ vs. PDB) and a secondary SrSO(4) (δ(18)O = + 20‰ vs. SMOW; δ(34)S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ(34)S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.     

Evaluation of the sulfate dynamics in groundwater by means of environmental isotopes

Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as 834S, delta18O-H2O, deltaD, tritium, and 85K5r. delta34S values of the groundwater sulfate vary between -19...+ 37 per thousand CDT. No simple correlation exists between sulfate concentrations and delta34S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and 14C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable delta18O and 8D, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling.     

Sulfur Isotope Fractionation in the Biogeochemical Sulfur Cycle of Marine Sediments

Abstract

The sulfur isotopic record of sedimentary sulfides (mainly pyrite) and sulfates shows considerable variations in time and plays an important role in the biological and geochemical interpretation, e.g., of the evolution of life and the oxygen partial pressure of Earth's atmosphere (e.g. [1]). From a comparison of experimental results with Desulfovibrio spp. it can be inferred that the S isotope fractionation during reduction of sulfur compounds is controlled by the number of electrons transferred (Fig. 1). Sulfur isotope discrimination in the sulfur cycle of marine sediments is dominated by dissimilatory bacterial sulfate reduction (BSR), and [2] used laboratory experiments with mesophilic bacteria to postulate that high sulfate reduction rates with abundant sulfate at enhanced temperature dominated the Ocean water chemistry during early Archean time. Experiments with pure cultures of thermophilic sulfate reducers [3] and natural hydrothermally influenced communities [4], however, demonstrated that isotope discrimination is close to average fractionation by mesophiles and that temperature is not directly influencing isotope discrimination during BSR.     

Methane-Derived Carbonates in a Native Sulfur Deposit: Stable Isotope and Trace Element Discriminations Related to the Transformation of Aragonite to Calcite

Abstract

Stable isotope (¹³C, ¹⁸O, ³⁴S) and trace element (Sr²⁺, Mg²⁺, Mn²⁺, Ba²⁺, Na⁺) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ¹³C = ?41 to ?47‰ vs. PDB) associated with native sulfur (δ³⁴S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ¹⁸O = ?3.9 to ?5.9‰ vs. PDB) and a secondary SrSO₄ (δ¹⁸O = + 20‰ vs. SMOW; δ³⁴S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ³⁴S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.     

Isotope studies to the sorption behavior of atmospheric sulfate in humus layers of scots pine ecosystems

The sorption potential for SO4(2-) in humus layer samples from field sites along a deposition gradient was determined experimentally in batch experiments. The Freundlich equation was used to quantify the sorption of added SO4(2-) in humus layer samples and to determine site-dependent sorption parameters. SO4(2-) sorption in humus layers is a concentration-dependent process. The linearity of isotherms reveals that SO4(2-) is reversibly bound in the organic surface layer, as long as soil solution concentrations remain above 26 to 44 mg SO4(2-) L(-1). Natural isotope variations of sulfur in SO4(2-) were analysed to investigate the degree of sorption of dissolved atmospheric and added SO4(2-). Both sulfate species differed significantly in their isotope composition. The pattern of delta34S values for SO4(2-) in all equilibrium solutions confirm the findings from sorption isotherms, showing a close relationship between the sulfur isotope ratios of SO4(2-) in soil solutions and the amount of SO4(2-) sorbed at the humus layer matrix. Stored atmospheric SO4(2-) in humus layers is released at sites where sulfate concentration in throughfall drops below 26 mg SO4(2-) L(-1). Concentration of soluble Fe decreased with increasing sulfate sorption, thus supporting the assumption that active Fe for example is important. Iron probably stabilizes the reactive surface of humus complexes and therefore has a positive influence on the SO4(2-) sorption in humus layers.     

Sulphur diagenesis in the sediments of the Kiel Bight, SW Baltic Sea, as reflected by multiple stable sulphur isotopes

In this work, the biogeochemistry of marine sediments from the Kiel Bight, coastal SW Baltic Sea, is studied based on the abundance and isotopic composition of organic carbon and different forms of sedimentary sulphur. Active bacterial sulphate reduction, partly under sulphate-limiting conditions, is evident from paired δ(34)S and δ(18)O values of pore water sulphate. The resulting pore water sulphide is partly precipitated as acid-volatile iron sulphide and subsequently forms sedimentary pyrite, partly serves in later diagenetic sulphurisation of organic matter, or remains dissolved in the pore water, all evident from the respective δ(34)S values. Microbial sulphate turnover is associated with an apparent isotopic fractionation between dissolved sulphate and dissolved sulphide (Δ(34)S) that varies between 46 and 66‰.     

Evaluation of the Sulfate Dynamics in Groundwater by Means of Environmental Isotopes

Abstract

Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as δ³⁴S, δ¹⁸O-H₂O, δD, tritium, and ⁸⁵Kr. δ³⁴S values of the groundwater sulfate vary between -19…+ 37‰ CDT. No simple correlation exists between sulfate concentrations and δ³⁴S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and ¹⁴C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable δ¹⁸O and δD, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling.     

Sulfur and oxygen isotope geochemistry of acid mine drainage--the polymetallic sulfide deposit "himmelfahrt fundgrube" in Freiberg (Germany)

We investigated physical, chemical and isotope (S, O) parameters of sulfate from acid mine drainage from the polymetallic sulfide ore deposit Freiberg (Gennany), which was mined for more than eight hundred years. Two main groups of water were distinguished: 1. Flowing mine water with sulfate concentrations of less than 9,000 mg/l and pH values higher than 3.2, 2. Pore water in weathered low grade ores and pools with sulfate concentrations higher than 9000mg/l and pH values below 3.2. The sulfur and oxygen isotope composition of sulfate from flowing mine waters reflects mixing of sulfate from two sulfur sources: a) atmospheric sulfur from precipitation and b) sulfate formed as a result of sulfide oxidation processes. Sulfur isotope values of mine water sulfate were used to estimate the contribution of sulfate derived through oxidation of sulfides. The sulfur isotope composition of pore water sulfate and precipitated sulfate (jarosite) from weathered low grade ore samples is identical to the sulfur isotope composition of primary sulfides. The oxygen isotope composition of pore water sulfate from low grade ore samples indicates that the oxidation process proceeds relatively slowly in 02-depleted waters, probably without significant microbial catalysis.     

Isotopic assessment of sources and processes affecting sulfate and nitrate in surface water and groundwater of Luxembourg

Surface water and deep and shallow groundwater samples were taken from selected parts of the Grand-Duchy of Luxembourg to determine the isotopic composition of nitrate and sulfate, in order to identify sources and/or processes affecting these solutes. Deep groundwater had sulfate concentrations between 20 and 40 mg/L, delta34S(sulfate) values between -3.0 and -20.0 per thousand, and delta18O(sulfate) values between +1.5 and +5.0 per thousand; nitrate was characterized by concentrations varying between < 0.5 and 10 mg/L, delta15N(nitrate) values of approximately -0.5 per thousand, and delta18O(nitrate) values approximately +3.0 per thousand. In the shallow groundwater, sulfate concentrations ranged from 25 to 30 mg/L, delta34S(sulfate) values from -20.0 to +4.5 per thousand, and delta18O(sulfate) values from approximately +0.5 to +4.5 per thousand; nitrate concentrations varied between approximately 10 and 75 mg/L, delta15N(nitrate) values between +2.5 and +10.0 per thousand, and delta18O(nitrate) values between +1.0 and +3.0 per thousand. In surface water, sulfate concentrations ranged from 10 to 210 mg/L, delta34S(sulfate) values varied between -9.3 and +10.9 per thousand, and delta18O(sulfate) values between +3.0 and +10.7 per thousand were observed. Nitrate concentrations ranged from 10 to 40 mg/L, delta15N(nitrate) values from +6.5 to +12.0 per thousand, and delta18O(nitrate) values from -0.4 to +4.0 per thousand. Based on these data, three sulfate sources were identified controlling the riverine sulfate load. These are soil sulfate, dissolution of evaporites, and oxidation of reduced S minerals in the bedrock. Both groundwater types were predominantly influenced by sulfate from the two latter lithogenic S sources. The deep groundwater and a couple shallow groundwater samples had nitrate derived mainly from soil nitrification. All other sampling sites were influenced by nitrate originating from sewage and/or manure. A decrease in nitrate concentration observed along one of the rivers was attributed to denitrification. It appears that sulfate within Luxembourg's aquatic ecosystem is mainly of lithogenic origin, whereas nitrate is often derived from anthropogenic activities.     

Sulfur and Oxygen Isotope Geochemistry of Acid Mine Drainage—The Polymetallic Sulfide Deposit “Himmelfahrt Fundgrube” in Freiberg (Germany)

Abstract

We investigated physical, chemical and isotope (S, O) parameters of sulfate from acid mine drainage from the polymetallic sulfide ore deposit Freiberg (Germany), which was mined for more than eight hundred years. Two main groups of water were distinguished:

1. Flowing mine water with sulfate concentrations of less than 9000 mg/1 and pH values higher than 3.2

2. Pore water in weathered low grade ores and pools with sulfate concentrations higher than 9000 mg/1 and pH values below 3.2.

The sulfur and oxygen isotope composition of sulfate from flowing mine waters reflects mixing of sulfate from two sulfur sources: a) atmospheric sulfur from precipitation and b) sulfate formed as a result of sulfide oxidation processes. Sulfur isotope values of mine water sulfate were used to estimate the contribution of sulfate derived through oxidation of sulfides. The sulfur isotope composition of pore water sulfate and precipitated sulfate (jarosite) from weathered low grade ore samples is identical to the sulfur isotope composition of primary sulfides. The oxygen isotope composition of pore water sulfate from low grade ore samples indicates that the oxidation process proceeds relatively slowly in O₂-depleted waters, probably without significant microbial catalysis.     

Origin and distribution of sulphate in surface waters of the Mansfeld mining district (Central Germany)--a sulphur isotope study.

In the Mansfeld region (Central Germany) copper mining contributed to an enormous pollution of the environment. Metal- and sulphate-bearing sediments and leachates emerge from the former copper smelters and mining waste heaps, spread along local rivers and finally reach the Saale river. A sulphur isotope study on water and stream sediments was performed along the River "B?se Sieben" and from its tributaries to determine the different sulphur sources. Four major sulphur sources exist in the area: metal sulphide mineralisations (Kupferschiefer), met alliferous sulphidic flue dust, slag, and anhydrite and gypsum of Permian and Triassic age. We obtained delta34S(SO4)-values in water samples varying from +4 per thousand to -18 per thousand CDT, clearly reflecting the input of sulphate from different sources. Sulphate from the oxidation of sulphidic mining residues is restricted to the mining area and cannot be traced for more than 5 km downstream. The major source for sulphate is the dissolution of gypsum and anhydrite. The sulphur isotope composition in dissolved and sedimentary adsorbed sulphate differs only slightly from each other. Microbial dissimilatory sulphate reduction can not be excluded in the shallow sediment layers.     

Isotope variations in white-tailed kites from various habitats in California: possible limitations in assessing prey utilization and population dynamics

White-tailed kite (Elanus leucurus) populations in the 1930s were close to extirpation in the United States. But by the 1940s, an upward trend towards recovery was apparent and continued to their current stable population levels. These dramatic fluctuations in kite numbers may have been related to changes in rodent prey populations due to the conversion of native habitats to agriculture. To address this question, we evaluated the use of stable isotope analysis in determining if a shift in diet could be isotopically differentiated in current and historic kite populations. We first compared delta13C, delta15N, and delta34S values from present-day kite flight feathers and prey fur samples from four locations in California. The total ranges of isotope values for kite and their rodent prey were similar within each site. Carbon isotope values ranged from -27.1 to -22.2 per thousand in Arcata, -26.1 to -16.9 per thousand in Davis, -27.0 to -15.0 per thousand in Cosumnes, and -28.2 to -11.6 per thousand in Santa Barbara. Nitrogen isotope values ranged from 3.2 to 15.7 per thousand in Arcata, 2.8 to 12.7 per thousand in Davis, 4.0 to 15.7 per thousand in Cosumnes, and 1.7 to 20.0 per thousand in Santa Barbara. Sulfur isotope values ranged from -7.8 to 12.4 per thousand in Arcata, -1.1 to 9.2 per thousand in Davis, 0.7 to 10.9 per thousand in Cosumnes, and -8.6 to 15.6 per thousand in Santa Barbara. Carbon, nitrogen, and sulfur isotope values at each site reflect typical trophic enrichments due to physiological processes. At each site, delta13C and delta15N values reflected the influence of a predominantly C3 or a mixed C3/C4 plant community. Sulfur isotope values reflect the influence of predominant marine or terrestrial sulfur sources at each site. However, variability in isotope values may limit the usefulness of such analyses for addressing prey utilization and population dynamics.     

Chlorine isotope fractionation associated with volcanic activity at the Kusatsu-Bandaiko hot spring in Japan

Stable chlorine isotope compositions (delta(37)Cl, per-mil: per thousand, vs. a standard sample of sea water) of Kusatsu-bandaiko hot water samples, taken regularly in the years between 1974 and 1995 in the Kusatsu-Shirane volcanic region, Japan, were measured mass-spectrometrically. The results show that the delta(37)Cl values of the waters taken before 1984 were at around-0.12 per thousand, whereas those after 1984 were at around+0.18 per thousand. The delta(37)Cl values are thus distinct across 1984, which is consistent with the classification by the Cl to S molar ratio (Cl/S): the higher the Cl/S ratio, the larger the delta(37)Cl value. The delta(37)Cl value increased as much as 0.30 per thousand during 5 years between 1980 and 1984. This isotopic enrichment is likely correlated with increasing Cl/S ratios, suggesting that the heavier isotope ((37)Cl) may have preferentially increased in the original Cl source of the hot spring across 1984 when volcanic activity likely increased at Mt Kusatsu-Shirane.     

A robust and fast method of sampling and analysis of delta13C of dissolved inorganic carbon in ground waters

The stable carbon isotopic composition of dissolved inorganic carbon (delta13C(DIC)) is traditionally determined using either direct precipitation or gas evolution methods in conjunction with offline gas preparation and measurement in a dual-inlet isotope ratio mass spectrometer. A gas evolution method based on continuous-flow technology is described here, which is easy to use and robust. Water samples (100-1500 microl depending on the carbonate alkalinity) are injected into He-filled autosampler vials in the field and analysed on an automated continuous-flow gas preparation system interfaced to an isotope ratio mass spectrometer. Sample analysis time including online preparation is 10 min and overall precision is 0.1 per thousand. This method is thus fast and can easily be automated for handling large sample batches.     

Hekla cold springs (Iceland): groundwater mixing with magmatic gases

We have analysed the chemical and stable isotope compositions of four spring waters situated just northwest of the Hekla volcano, where cold water emerges from the base of the lava flows. The stable isotope ratios of water (H, O), dissolved inorganic carbon (C) and sulphate (S) were used to determine whether magmatic gases are mixing with the groundwater. The waters can be characterised as Na-HCO₃ type. The results show that deep-seated gases mix with groundwater, substantially affecting the concentration of solutes and the isotopic composition of dissolved carbon and sulphate.     

Experimental investigation of sulphur isotope partitioning during outgassing of hydrogen sulphide from diluted aqueous solutions and seawater

The diffusion of hydrogen sulphide across the sediment-water interface and subsequent liberation to the atmosphere may occur in iron-deficient coastal marine environments with enhanced microbial activity in surface sediments and corresponding accumulation of dissolved H2S in near-surface pore waters. The involvement of analogue processes in periods of global mass extinctions during Earth's history (e.g. at the Permian-Triassic boundary) is currently in discussion [L.R. Kump, A. Pavlov, and M. Arthur,Massive Release of Hydrogen Sulfide to the Surface Ocean and Atmosphere During Intervals of Oceanic Anoxia, Geology 33, 397 (2005)]. The outgassing of H?S is associated with a fractionation of the stable sulphur isotopes, which has so far only been investigated experimentally at selected acidic and neutral pH values, and no experiments with seawater had been carried out. In this communication, we report on sulphur isotope fractionation that takes place during the experimental degassing of H?S from aqueous solution by an inert gas (N?) at 21 °C. Experiments were conducted in the pH range between 2.6 and 10.8, corresponding to the dominance fields of dissolved hydrogen sulphide (H?S(aq)), bisulphide (HS-(aq)), and mixtures of both sulphide species. Overall isotope enrichment factors between -1.6 and +3.0‰ were observed, with the residual dissolved sulphide being enriched or depleted in 3?S compared to the liberated H?S at low and high pH values, respectively. The difference in the low and high pH isotope fractionation effects can be explained by isotope exchange between H?S(aq) and HS-(aq) [B. Fry, H. Gest, and J.M. Hayes, Sulfur Isotope Effects Associated with Protonation of HS- and Volatilization of H?S, Chem. Geol. (Isot. Geosci. Sec.) 58, 253 (1986); R. Ge?ler and K. von Gehlen, Investigation of Sulfur Isotope Fractionation Between H2S Gas and Aqueous Solutions, Fresenius J. Anal. Chem. 324, 130 (1986)] followed by the subsequent transfer of H?S(aq) to the gaseous phase. The assumption of pure physical outgassing of H?S(aq) at low pH values leads to an isotope enrichment factor of -0.9 ± 0.4‰ (n = 14) which is caused by the combined differences in dehydration and diffusion coefficients of H?32S(aq) and H?3?S(aq). In the pH range of natural surface and shallow pore waters, 3?S will be equal to or enriched in the gaseous phase compared to the aqueous solution, therefore creating no or a slight enrichment of 32S in the aqueous solution. Experiments in seawater solution showed no significant influence of increased ionic strength and changed corresponding aqueous speciation on sulphur isotope effects.     

Identifying sources and processes controlling the sulphur cycle in the Canyon Creek watershed, Alberta, Canada

Sources and processes affecting the sulphur cycle in the Canyon Creek watershed in Alberta (Canada) were investigated. The catchment is important for water supply and recreational activities and is also a source of oil and natural gas. Water was collected from 10 locations along an 8?km stretch of Canyon Creek including three so-called sulphur pools, followed by the chemical and isotopic analyses on water and its major dissolved species. The δ(2)H and δ(18)O values of the water plotted near the regional meteoric water line, indicating a meteoric origin of the water and no contribution from deeper formation waters. Calcium, magnesium and bicarbonate were the dominant ions in the upstream portion of the watershed, whereas sulphate was the dominant anion in the water from the three sulphur pools. The isotopic composition of sulphate (δ(34)S and δ(18)O) revealed three major sulphate sources with distinct isotopic compositions throughout the catchment: (1) a combination of sulphate from soils and sulphide oxidation in the bedrock in the upper reaches of Canyon Creek; (2) sulphide oxidation in pyrite-rich shales in the lower reaches of Canyon Creek and (3) dissolution of Devonian anhydrite constituting the major sulphate source for the three sulphur pools in the central portion of the watershed. The presence of H(2)S in the sulphur pools with δ(34)S values ～30?‰ lower than those of sulphate further indicated the occurrence of bacterial (dissimilatory) sulphate reduction. This case study reveals that δ(34)S values of surface water systems can vary by more than 20?‰ over short geographic distances and that isotope analyses are an effective tool to identify sources and processes that govern the sulphur cycle in watersheds.