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BACKGROUND Diethylenetriaminepentaacetic acid (DTPA) dissolution and reprecipitation (DDARP) method is used frequently to eliminate encapsulated nitrate during barite precipitation. However, the effect of DDARP on barite precipitated from different kinds of natural water is rarely reported, particularly it is not clear whether the DDARP method plays a role in eliminating the effect of organic matter on barite from organic-rich water samples. OBJECTIVES To obtain more accurate sulfate oxygen isotope values, using the modified DDARP method and identify the factors affecting the oxygen isotope values of barite from natural water samples. METHODS Element Analyzer (EA) coupled with Isotope Ratio Mass Spectrometry (IRMS) was used to determine the oxygen isotope values of original and purified barite. RESULTS After purification, oxygen isotope values of high grade barite reagent show little variations, indicating that purification of high grade barite reagent is not needed and it can be directly used as the laboratory standard. However, oxygen isotope values of barite from Yellow River water have large variations from 0.6 to 1.0 with an average of 0.8‰, indicating that it is necessary to purify natural water barite. The differences in oxygen isotope values between original and purified barite from natural water samples vary from -0.4‰ to +1.9‰, and the average differences of oxygen isotope values are 0.7‰, 0.2‰, 0.3‰, -0.3‰, 0.1‰ and 1.4‰ for dissolved detergent, groundwater, river water, sewage, dissolved fertilizer, and rainwater, respectively. The large positive differences of oxygen isotope values (from +0.5‰ to +1.9‰) between original and purified barite is found in rainwater samples due to nitrate encapsulated in barite, which is related to the high molar ratio of nitrate to sulfate in rainwater (from 0.2 to 1.9 with an average of 0.7). The negative differences of oxygen isotope values (from -0.2‰ to 0.4‰) are observed in sewage with respect to the organic matter encapsulated in barite from organic-rich sewage, suggesting that the purification method can remove organic interference. CONCLUSIONS The modified DDARP method works well in eliminating nitrate and organic matter encapsulated in barite. It can be used to purify barite to obtain more accurate oxygen isotope values of sulfate in natural water samples. The proposed method can be used as a standard purification method for water body sulfate oxygen isotope determination.

This study incorporated stable isotope analyses with chemical analyses to determine the origin and migration of sulfur sources in East Asia, and these findings were compared with our decadal research from 2000 to 2001 and 2002 to 2003. The multiple sulfur isotope composition ( 32 S, 33 S and 34 S) of the dissolved sulfate in precipitation was first measured from 2011 to 2013 in Seoul, South Korea. The δ 34 S nss values were −1.1‰ to 7.9‰ (avg. 3.6‰), strongly suggesting that sulfur derived from the combustion of Chinese coal is the predominant source of sulfate in the Seoul region. Low NO 3 /SO 4 2− ratios in the precipitation samples indicated an insignificant effect of sulfur from vehicle exhaust. The seasonal variation of δ 34 S nss values appears to be caused by increasing biogenic sulfur activity during the spring and summer seasons. The some Δ 33 S values (0.13‰–0.16‰) measured in the three samples were sufficiently small; thus, whether these values can be attributed to mass-independent fractionation remains unclear. Measuring the Δ 33 S anomalies in dissolved sulfate provides valuable insights for identifying the sources of sulfur transferred from the stratosphere to the troposphere and upper troposphere. [ABSTRACT FROM AUTHOR]

Oxygen ( 16 O, 17 O and 18 O) and sulfur ( 32 S, 33 S, 34 S and 36 S) isotope ratios of and major ion (Na + , Ca 2 + , Cl − , NO 3 − and SO 4 2 − ) concentrations in lakes, ponds and creeks from Deception Island, Antarctic Peninsula were analyzed to study the sources of sulfate, its oxidation, and the surficial processes of the dissolved sulfate. The positive relationship between the δ 34 S sulfate (8.1‰ to 17.3‰) and the Cl − /SO 4 2 − molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals. The average sea salt fraction (28%) and δ 34 S nss values (from 5.6‰ to 15.9‰) indicate that a combination of sea salt and marine biogenic sulfide provide the high δ 34 S end-member of the dissolved sulfates. The relatively low δ 18 O sulfate (from − 4.6‰ to 0.7‰) of Deception Island water suggests a role of local water in the formation of sulfate. Slightly negative but mass-dependent Δ 17 O sulfate values imply that atmospheric oxidation by O 3 and H 2 O 2 are negligible, while these values might suggest a significant role of oxidation by molecular oxygen and OH. The distinctly low δ 34 S sulfate value of two samples (DCW-2 and DCW-3) suggests the input of sulfate from sulfide oxidation. Slight elevation of δ 34 S sulfate values up to 17.3‰ compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of Deception Island water and sediments. Both Δ 33 S sulfate and Δ 36 S sulfate values are homogeneous and near zero, implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to Deception Island water. [ABSTRACT FROM AUTHOR]

Sulfur and oxygen isotopes were employed to identify SO sources in surface water and groundwater in the Babu subterranean river basin (BSRB). Our study revealed SO enrichment in the BSRB waters compared with adjacent areas. The SO in some samples originated mainly from precipitation; in others, it was derived mainly from sulfide dissolution in coal seams or from gypsum dissolution. In the water at the subterranean river exit, 13% of SO originated from precipitation, 40% from sulfide oxidation in coal seams, and 47% from gypsum dissolution. [ABSTRACT FROM AUTHOR]

Summary: The North China Plain (NCP) is a typical Cenozoic sedimentary basin and one of the largest alluvial plains in eastern Asia. It consists of piedmont alluvial plain, central alluvial-lacustrine plain, and littoral alluvial plain from west to east, where Quaternary aquifer systems developed in different depths. Groundwater from these aquifers is the most important water resource and supports a population of 200 million in the NCP. Currently the Quaternary groundwater is depleting fast due to both human and natural factors. Characterizing biogeochemical processes in groundwater is central to understanding groundwater chemistry. To identify the sources of dissolved sulfate () and address subsequent biogeochemical processes in groundwater, we conducted a study of spatial distributions of δ34SSO4 and δ18OSO4 in the Quaternary aquifers in the northern part of the NCP. The [], δ34SSO4, and δ18OSO4 along the west–east groundwater flowpaths in the three alluvial plains are analyzed and examined. The Quaternary groundwater (∼20°C) has a [] of 37.25–177.41mg/L with []/[Cl−] ratios ranging from 0.12 to 2.79. The δ34SSO4 and δ18OSO4 range from 4.9‰ to 30.9‰ and from 4.7‰ to 14.0‰, respectively. Supported by other geochemical and isotopic parameters such as total dissolved solids (TDS) concentrations, δD and δ18O of groundwater (δD and δ18OH2O), and 14C contents in groundwater, our study concludes that: (1) The shallow groundwater in the piedmont area is characterized by higher concentration of 153.22mg/L with δ34SSO4 of 10.0–14.5‰ and δ18OSO4 of 4.7–9.0‰, whereas the groundwater in the piedmont area is characterized by lower concentration of 37.25mg/L with δ34SSO4 of 4.9–7.3‰ and δ18OSO4 of 5.8–7.5‰. Therefore, the in the shallow groundwater is dominated by weathered sulfate minerals from the Taihang mountains and sulfate derived from oxidation of sulfides in infiltration paths, whereas the in the deep groundwater is dominated by atmospheric sulfate from precipitation and sulfate derived from decomposition of organic matter during its recharge processes; (2) Dissimilatory microbial sulfate reduction (DMSR) occurred in the deep confined aquifers in both central and littoral plains, where δ34SSO4 and δ18OSO4 increase along the groundwater flowpaths and present specific patterns for each aquifer which imply variable contributions from DMSR processes; (3) The deep confined aquifer in the littoral plain has a lower DMSR rate than the other aquifers, probably due to the effect of its lower permeability on physical exclusion of bacteria from the aquifer matrix. This study can provide a biogeochemical background for assessing groundwater evolution and its quality in the NCP. [Copyright &y& Elsevier]

Abstract: The sulfur isotopic composition of dissolved seawater sulfate is a basic parameter in quantification of fluxes in the global sulfur cycle. It has changed during Earth history but is generally assumed to be constant at a given time due to the long residence time of sulfate in the ocean. Past measurements in the modern ocean, however, have shown an unexpected variability. Since the known marine sedimentary record essentially reflects continental margin processes, we have investigated for the first time the isotopic composition of dissolved sulfate of a marginal sea, the North Sea by means of stable-isotope-ratio-monitoring mass spectrometry. Sampling took place in the water column at 30 stations during two seasons (early spring 1996 and summer 1997). Stable isotope results are compared to measurements of salinity, temperature, and phytoplankton biomass. Except for one profile, the isotopic composition was found to be essentially constant at both the spring (δ 34S=+20.9±0.13‰; n =131; versus V-CDT) and the summer campaign (δ 34S=+21.1±0.13‰; n =59). The mean composition of North Sea water sulfate of δ 34S=+21‰ is within 0.2‰ of δ 34S values found for essentially unpolluted coastal waters collected at different stations worldwide (Atlantic and Pacific Ocean) and the water column of the modern open ocean. [Copyright &y& Elsevier]

Interstitial water samples from seven ODP sites (Leg 181, Sites 1119–1125) of the southwestern Pacific Ocean have been analyzed for the stable sulfur isotopic composition of dissolved sulfate along with major and minor ions. Sulfate from the interstitial fluids (δ34S values between +20.7 and +60‰ vs. the SO2-based Vienna–Canyon Diablo troilite standard) was enriched in 34S with respect to modern sea water (δ34S≈+20.6‰) indicating that microbial sulfate reduction takes place to different extents at all investigated sites. Microbial sulfate reduction (MSR) was found at all sites, the intensity depending on the availability of organic matter which is controlled by paleo-sedimentation conditions (sedimentation rate, presence of turbidites) and productivity. Microbial net sulfate reduction was additionally confirmed by modeling interstitial water sulfate profiles. Areal net sulfate reduction rates up to 14 mmol m−2 yr−1 have been calculated which were positively related to sedimentation rates. Total reduced inorganic sulfur (TRIS; essentially pyrite) as a product of microbial sulfate reduction was isotopically characterized in squeeze cake samples and gave δ34S values between −51 and +9‰ indicating pyrite formation both close to the sediment–water interface and later diagenetic contributions. [Copyright &y& Elsevier]

In recent decades, surface water and groundwater in the Jinan spring catchment have become increasingly contaminated by sulfate due to the expansion of urbanization and the increasing intensity of anthropogenic activities. In this study, ten surface water samples and forty-three groundwater samples were collected in the catchment from June to September 2019, and their hydrochemistry and stable isotopes (δ34S SO4 , δ18O SO4 , δD H2O and δ18O H2O) combined with a Bayesian isotope mixing model were used to identify sources and transformations and to quantitatively evaluate the contribution of sulfate from multiple potential sources of pollution. The dual isotopes of sulfate and the isotope mixing model showed that sulfate in the surface water was mainly derived from evaporite dissolution (32.6%), sewage (18.8%), soil sulfate (15.4%) and sulfide oxidation (10.2%), while that in the groundwater was mainly derived from soil sulfate (32.4%) and sewage (30.6%). In groundwater, the proportions of sewage and evaporite dissolution increased from the indirect recharge area to the discharge area, while the contribution of soil sulfate and sulfide oxidation decreased. In regard to surface waters, the contribution proportion of evaporite dissolution to SO 4 2− in June was 40.9%, which was significantly higher than 24.2% in September, but the proportion of sewage, soil sulfate and sulfide oxidation was lower in June (13.7, 12.9 and 9.5%, respectively) than in September (23.8, 17.8 and 10.8%, respectively). There was no significant correlation between the ratio of SO 4 2−/Cl− and δ34S SO4 and δ18O SO4 in surface water and groundwater, indicating that bacterial sulfate reduction did not play a major role. This study can provide a reference for the development of effective pollution management strategies for water resources in karst areas of northern China. • The accuracy of sulfate tracing can be improved by combining multiple isotopes with land use and water chemistry. • A Bayesian isotope mixing model (Simmr) was employed to quantity SO 4 2− source. • Major sulfate sources of surface water were evaporite dissolution, sewage, soil-derived sulfate and sulfide oxidation; while for groundwater were soil sulfate and sewage. • Sulfate pollution in karst groundwater and surface water might be the coupling result of natural input and anthropogenic activities. [ABSTRACT FROM AUTHOR]