δ34S SO4 Research Articles

Integrated analysis of ammonium origins in a Serbian anoxic alluvial aquifer: Insight from physicochemical, isotopic, microbiological data

The significance of examining groundwater quality is highlighted by the fact that 75% of the European Union population relies on groundwater for their water supply. In the Republic of Serbia, over 50% of the groundwater used for public water supply comes from alluvial aquifers, with 80–90% of this water originating from river water infiltration. This study investigates the origin of increased ammonium concentrations (up to 4.7 mgN/l) in the Danube alluvial aquifer near Kovin-Dubovac area, Serbia, a potential future regional water supply source surrounded by intensive agricultural production and an open coal mine. Comprehensive research involved statistical processing of physicochemical data (13 parameters from 33 sampling sites), isotopic analyses (δ15N–NH4 – 12 samples; δ34S–SO4, δ18O–SO4 in 5 samples), and microbiological tests (denitrifying, sulphate-reducing, iron-related, and heterotrophic aerobic bacteria in 15 samples). Factor analysis revealed significant positive loadings (>0.5) among indicators of autochthonous organic matter origin (Fe2+, Fetot, and TOC), geological matrix components (Na, H2S, Cl), and groundwater state parameters (pH, Eh, and NH4+). This multifaceted approach and the spatial concentration gradients of parameters associated within extracted principal components revealed the predominance of two NH4+ sources. The riparian zone is characterized by sediment organic matter mineralization, increased iron content, and natural ammonium origin (δ15N–NH4+ from +4.82‰ to +6.93‰) accompanied by conditions suitable for DNRA and sulphate reduction. Approaching to the hinterland lower iron and total organic matter content, accompanied by increased redox values revealed the signature of fertilizers application (δ15N–NH4+ −0.84‰ and −0.33‰), associated with denitrification influence. This multifaceted approach reduces ambiguity, providing a clearer interpretation of results when discerning the origin of nitrogen and aquifer potential for nitrogen loss or conservation in a reducing groundwater environment.

Weathering in landslide-prone areas: Evidences from hydrochemistry and sulfur isotopic compositions in the Bailong River, northeastern Qinghai-Tibet Plateau

Investigating weathering processes in landslide-prone areas is important for understanding the carbon budget due to weathering during mountain building. Here, we present the monthly hydrochemistry and sulfur isotopic compositions of SO42− (δ34S–SO42−) in the Bailong River which drained landslide-prone areas in the northeastern Qinghai-Tibet Plateau. Ca2+ and HCO3− were dominant in cations and anions respectively, and δ34S–SO42− values varied over a narrow range, from 5.1‰ to 6.7‰. We constrained the sources of major cations and SO42− through an inverse model and the mass balance model of δ34S–SO42−. The results showed that cations in the Bailong River were mainly from carbonate weathering, and sulfide oxidation was an important source of SO42−. Weathering in the Bailong River catchment showed an CO2 source over geologic timescales due to the reaction of H2SO4. The relationship between weathering fluxes and physical erosion rate indicated that high runoff facilitated physical erosion, and in turn accelerated chemical weathering. However, under the conditions of extreme discharge and physical erosion, SO42− fluxes from sulfide oxidation were not as high as expected, which was ascribed to the transport of old landslide deposits where most sulfides had been exhausted. Therefore, in tectonically active areas with massive landslides, the high erosion rate caused by landslides promoted chemical weathering, but sulfide oxidation did not respond sensitively to strong physical erosion under high runoff conditions. This study helped to understand the relationship among landslides, chemical weathering, and geologic carbon cycle.

The Ernesto Cave, northern Italy, as a candidate auxiliary reference section for the definition of the Anthropocene series

Annually laminated stalagmites ER77 and ER78 from Grotta di Ernesto provide an accurate annual record of environmental and anthropogenic signals for the last ~200 years. Two major transitions are recorded in the stalagmites. The first coincides with the year 1840 CE, when a change from porous and impurity-rich-laminae to clean, translucent laminae occurs. This is accompanied by a steady increase in the growth rate, a decrease in fluorescence and a sharp increase in δ13C values. These changes concur with the end of the Little Ice Age. The second transition takes place around the year 1960 CE and corresponds with an increase in both annual growth rate and sulfur concentration in stalagmite ER78 at 4.2 mm from the top, and with the deflection point in the 14C activity curve in stalagmite ER77 at 4.8 mm from the top. This latter is the stratigraphic signal proposed as the primary guide for the definition of the Anthropocene series. The following shift toward depleted δ34S–SO4 in stalagmite ER78 suggests that industrial pollution is a major source of sulfur. The interpretation of atmospheric signals (S, δ34S, 14C) in the stalagmites is affected by attenuation and time lags and the environmental signals are influenced by soil and ecosystem processes, while other anthropogenic signals (δ15N, 239Pu) are not recorded. For these reasons, the stalagmite record is here proposed as an auxiliary (reference) section rather than a global standard. In summary, Grotta di Ernesto contains one of the best stalagmite records documenting the Anthropocene, and one of only two stalagmite records where the S peak has been measured at high resolution.

Quantitative identification of groundwater contamination sources by combining isotope tracer technique with PMF model in an arid area of northwestern China

Nowadays, groundwater quality has deteriorated because of intensive human activities. It is important to accurately identify the pollution source for controlling the deterioration of groundwater quality. However, the accuracy of the current source analysis method needs to be improved. In this study, we combined hydrochemical method, isotope tracing technique and PMF model, for the first time, to trace the source of groundwater pollution in Beichuan River basin, Qinghai Province, China. According to the results, there were 35.8% of Fe, 34.1% of total hardness, 24.3% of SO42− and 8.09% of NO3− samples exceeded the Grade III standards for Groundwater quality in China, which indicated that the groundwater in the study area has been significantly affected by human activities. Hydrochemical method suggested that the chemical component originated from rock weathering, cation exchange and mineral dissolution. Based on isotope tracing technique (δ15N–NO3-, δ18O–NO3-, δ34S–SO42− and δ18O–SO42−), the primary sources of nitrate and sulfate in groundwater were soil nitrogen and oxidation of sulfide minerals in the forest area, domestic sewage and oxidation of sulfide minerals in the urban and industrial area, and mixed sources in the village and agricultural area. Finally, the pollution source of groundwater was distinguished by combining the PMF model, isotope tracing technique and hydrochemical method. Results showed that the main pollutant of groundwater is domestic sewage in the urban, village and industrial area. The contribution rates to groundwater pollution were 60.7%, 60.8% and 57.8%, respectively. However, in the forest and agricultural area, the main source changed to water-rock interaction and chemical fertilizer, and the contribution rates to groundwater quality were 53.5% and 61.0%, respectively. Our results suggested that the coupling tracing methodology can improve the accuracy of source resolution in the water environment and it can be applied to other areas of the world.

Isotope evidence for temporal and spatial variations of anthropogenic sulfate input in the Yihe River during the last decade

Pyrite oxidation and sedimentary sulfate dissolution are the primary components of riverine sulfate (SO42−) and are predominant in global SO42− flux into the ocean. However, the proportions of anthropogenic SO42− inputs have been unclear, and their tempo-spatial variations due to human activities have been unknown. Thus, field work was conducted in a spatially heterogeneous human-affected area of the Yihe River Basin (YRB) during a wet year (2010) and drought years (2017/2018). Dual sulfate isotopes (δ34S–SO42- and δ18O–SO42-) and Bayesian isotope mixing models were used to calculate the variable anthropogenic SO42− inputs and elucidate their temporal impacts on riverine SO42− flux. The results of the mixing models indicated acid mine drainage (AMD) contributions increased from 56.1% to 83.1% of upstream sulfate and slightly decreased from 46.3% to 44.0% of midstream sulfate in 2010 and 2017/2018, respectively, in the Yihe River Basin. The higher upstream contribution was due to extensive metal-sulfide-bearing mine drainage. Sewage-derived SO42− and fertilizer-derived SO42− inputs in the lower reaches had dramatically altered SO42− concentrations and δ34S–SO42- and δ18O–SO42- values. Due to climate change, the water flow discharge decreased by about 70% between 2010 and 2017/2018, but the riverine sulfate flux was reduced by only about 58%. The non-proportional increases in anthropogenic sulfate inputs led to decreases in the flow-weighted average values of δ34S–SO42- and δ18O–SO42- from 10.3‰ to 9.9‰ and from 6.1‰ to 4.4‰, respectively. These outcomes confirm that anthropogenic SO42− inputs from acid mine drainage (AMD) have increased, but sewage effluents SO42− inputs have decreased.

Role of carbon and sulfur biogeochemical cycles on the seasonal arsenic mobilization process in the shallow groundwater of the Bengal aquifer

The bacterial reduction process of As-coated Fe(III)–OOH and SO42− in the sediment plays an important yet complex role in contributing to groundwater arsenic (As) concentration. The process utilizes dissolved organic carbon in the aquifer, which varies seasonally. The present observation documented seasonal variability (between dry pre-monsoon and post-monsoon periods) in the potential methanogenesis and intensity of bacterial reduction activity in the shallow and a few deep groundwaters from the West Bengal region, India (Nadia district). The dataset from the present study includes physical parameters (i.e., pH, Eh, electrical conductivity), multiple redox-sensitive solutes (i.e., dissolved total As, Fe, SO42− concentration), dissolved inorganic carbon (DIC) or HCO3− concentration, major element ratio (HCO3−/Na, Ca/Na), and stable isotopes in the dissolved inorganic carbon (δ13C-DIC) and dissolved sulfate (δ34S–SO42-) phases in the groundwater samples. Multiple years of observations documented a seasonal pattern of microbially-mediated reduction of As-coated Fe(III)–OOH and potential methanogenesis with limited bacterial sulfate reduction (BSR), causing excess As mobilization in the groundwater registering low sulfate concentration. The process was documented predominantly during the dry pre-monsoon period compared to the post-monsoon period. However, a few seasonal shallow groundwater samples showed abundant sulfate concentration and a signature of potentially active BSR, with low dissolved As concentrations. We showed here that dissolved SO42− concentration and δ34S–SO42- isotope enrichment factor can be reliable indicators of the intensity of BSR using the Rayleigh fractionation model simulation.

Multiple stable isotopes and geochemical approaches to elucidate groundwater salinity and contamination in the critical coastal zone: A case from the Bou-areg and Gareb aquifers (North-Eastern Morocco)

Mediterranean areas are characterized by complex hydrogeological systems, where water resources are faced with several issues such as salinity and pollution. Fifty-one water samples were gathered from the Bou-areg coastal and the Gareb aquifers to evaluate the source of water salinity and to reveal the processes of the different sources of pollution using a variety of chemical and isotopic indicators (δ2H–H2O, δ18O–H2O, δ34S–SO4, and δ18O–SO4). The results of the hydrochemical analysis of water samples show that the order of dominated elements is Cl− > HCO3− > SO42- > NO3− and Na+ > Ca2+ > Mg2+ > K+ and evidenced extremely high salinity levels (EC up to 22000 μS/cm). All samples exceeded the WHO drinking water guidelines, making them unfit for human consumption. Ion ratio diagrams, isotopic results, and graphical comparing indicate that the mineralization of groundwater in the area, is controlled by carbonate dissolution, evaporite dissolution, ion exchange, and sewage invasion. The return of irrigation water plays a significant role as well in the groundwater recharge and its mineralization by fertilizers mainly. Evaporites (Gypsum), sewage, and fertilizers constitute the main sources of sulfates in the investigated water resources. These scientific results will be an added value for decision-makers to more improve the sustainable management of groundwater in water-stressed regions. The use of chemical and isotopic tracers once again shows their relevance in such zones where systematic monitoring is lacking.

Sulfur Isotope and Stoichiometry–Based Source Identification of Major Ions and Risk Assessment in Chishui River Basin, Southwest China

Hydrochemistry and sulfur isotope (δ34S–SO42−) of Chishui River watershed in Southwest China were measured to identify the sources of riverine solutes, the potential impact of human activities, water quality, and health risk. The main findings indicated that the HCO3− (2.22 mmol/L) and Ca2+ (1.54 mmol/L) were the major ions, with the cation order of Ca2+ (71 ± 6%) > Mg2+ (21 ± 6%) > Na+ + K+ (8 ± 3%) and the anion sequence of HCO3− (55 ± 9%) > SO42− (41 ± 9%) > Cl− (4 ± 3%). The riverine δ34S–SO42− values fluctuated from −7.79‰ to +22.13‰ (average +4.68‰). Overall, the water samples from Chishui River presented a hydrochemical type of Calcium–Bicarbonate. The stoichiometry and PCA analysis extracted three PCs that explained 79.67% of the total variances. PC 1 with significantly positive loadings of K+, Mg2+, F−, HCO3− and relatively strong loading of Ca2+ revealed the natural sources of rock weathering inputs (mainly carbonate). PC 2 (Na+ and Cl−) was primarily explained as atmospheric contribution, while the human inputs were assuaged by landscape setting and river water mixing processes. The strongest loadings of SO42− and NO3− were found in PC 3, which could be defined as the anthropogenic inputs. The H2SO4–involved weathering processes significantly impacted (facilitated weathering) the concentrations of riverine total ions. Sulfur isotope compositions further indicated that riverine SO42− were mainly controlled by anthropogenic inputs SO42− compared to the sulfide oxidation derived SO42−, and the atmospheric contribution was very limited. The results of risk and water quality assessment demonstrated that Chishui River water was desirable for irrigation and drinking purposes due to low hazard quotient values (<1, ignorable risk), but long–term monitoring is still worthy under the circumstances of global environmental change.

Reactive transport modelling of porewater geochemistry and sulfur isotope fractionation in organic carbon amended mine tailings

Field experiments previously conducted to assess organic carbon (OC) amendments for in situ biological treatment of tailings porewater at the Greens Creek Mine (Alaska, USA) showed sulfate reduction, metal-sulfide precipitation, and decreased fluxes of sulfate and dissolved metals. Here, we develop two reactive transport models using the reactive transport code MIN3P to simulate hydrogeochemical processes and δ34S–SO4 isotope fractionation over four years in test cells containing unamended (control) and amended (5 vol % OC) tailings. These models successfully simulate observed data including pH, SO4, δ34S–SO4, Ca, Fe, K, Mg, Mn, Si, and Zn. The models also indicate that dissolution of carbonate and, to a lesser extent, aluminosilicate minerals neutralize acidic porewater generated from sulfide mineral oxidation and sulfate reduction reactions. Application of a constant kinetic fractionation factor of 0.9820 to simulate measured δ34S–SO4 trends confirms that sulfate removal principally results from microbially-mediated sulfate reduction in conjunction with OC oxidation and subsequent metal-sulfide precipitation. Gypsum precipitation/dissolution and thiosulfate disproportionation have negligible effects on modelled porewater δ34S–SO4 signatures. Our simulations are consistent with the previous findings that metal-sulfide precipitation controls Fe and Zn attenuation in amended tailings and that coprecipitation reactions contribute to metal removal. Overall, these simulations demonstrate that coupled reactive transport modelling incorporating stable isotope fractionation can improve the understanding of hydrogeochemical and biogeochemical controls within in situ treatment systems, further illustrating the benefits and limitations of this technique for improving water quality of mine drainage.

Differentiation of natural and anthropogenic contaminant sources using isotopic and microbial signatures in a heavily cultivated coastal area.

Hydrogeochemical and multiple isotope data for groundwater samples were obtained and interpreted to discriminate anthropogenic and natural contaminant sources in a coastal aquifer underlying a heavily cultivated watershed in Hwaseong, South Korea. The local aquifers are vulnerable to contamination, due to high anthropogenic N inputs and the location close to the ocean facilitating seawater intrusion. Thus, to effectively control the groundwater quality in the study area, it is necessary to differentiate between anthropogenic and natural contaminant sources. The concentrations of NO3-N in the groundwater ranged between 0.14 and 45.6mg/L in August 2015 and 0.2-39.6mg/L in March 2016. High concentrations of Cl- (388-1107mg/L) and a high electrical conductivity (1027-2715μS/cm) were observed in the study area, suggesting that the groundwater was affected by seawater intrusion. Furthermore, δ15N-NO3-, δ34S-SO42- values and 87Sr/86Sr of groundwater were determined to reveal the origins of the natural and anthropogenic contaminants and the groundwater mean residence times (MRT) and 87Sr/86Sr ratios were used to assess the hydrogeochemical processes along the flow path in the study area. Young groundwater was affected by an anthropogenic contamination source with contributions of 26-46% adding nitrate to the aquifer, whereas old groundwater was impacted by mixing with seawater with contributions of 10-20% with low concentrations of NO3-N, but elevated concentrations of chloride and sulfate. Recently recharged uncontaminated groundwater showed oxic conditions with a diverse microbial community structure, whereas young groundwater contaminated by anthropogenic sources showed a less diverse microbial community structure. The results of this study suggest that multiple isotopes combined with groundwater MRT and microbial data can be applied to distinguish natural and anthropogenic contaminant sources in a groundwater system.

Tracking nitrate and sulfate sources in groundwater of an urbanized valley using a multi-tracer approach combined with a Bayesian isotope mixing model

Over the past decades, groundwater quality has deteriorated worldwide by nitrate pollution due to the intensive use of fertilizers in agriculture, release of untreated urban sewage and industrial wastewater, and atmospheric deposition. Likewise, groundwater is increasingly polluted by sulfate due to the release of domestic, municipal and industrial wastewaters, as well as through geothermal processes, seawater intrusion, atmospheric deposition, mineral dissolution, and acid rain. The urbanized and industrialized Monterrey valley has a long record of elevated nitrate and sulfate concentrations in groundwater with multiple potential pollution sources. This study aimed to track different sources and transformation processes of nitrate and sulfate pollution in Monterrey using a suite of chemical and isotopic tracers (δ2H–H2O, δ18O–H2O, δ15N–NO3, δ18O–NO3 δ34S–SO4, δ18O–SO4) combined with a probability isotope mixing model. Soil nitrogen and sewage were found to be the most important nitrate sources, while atmospheric deposition, marine evaporites and sewage were the most prominent sulfate sources. However, the concentrations of nitrate and sulfate were controlled by denitrification and sulfate reduction processes in the transition and discharge zones. The approach followed in this study is useful for establishing effective pollution management strategies in contaminated aquifers.

Using δ34S–SO4 and δ18O–SO4 to trace the sources of sulfate in different types of surface water from the Linhuan coal-mining subsidence area of Huaibei, China

Many studies have been carried out on the water environment in coal-mining subsidence area, which have mainly focused on the two aspects of nitrogen and phosphorus as well as heavy metal pollution in water. However, little attention has been paid to the problem of sulfate pollution. The surrounding conditions of subsidence area in Linhuan are complex, and there are a large number of coal gangue accumulation and coal mining activities. The sulfate pollution in water body is serious, while the specific sulfate source remains unclear. In the present study, the mining subsidence area in Linhuan, Huaibei was selected as the main study area, and 21 water samples were systematically collected from river water, subsidence area water and mine drainage. The conventional hydrochemical indexes were analyzed, and sulfur and oxygen isotopes were used to trace sources of sulfate in river water and subsidence area water. Our results showed that the total dissolved solid content was high in surface water, the hydrochemical type of Huihe River water was mainly Na+-Ca2+-HCO3-, and the hydrochemical type of subsidence area water was mainly Na+-Cl--SO42-. Before flowing through the mining area, sulfate in the main stream of Huihe River was mainly derived from two aspects: the dissolution of evaporative salt rocks in the upper reaches. The sulfate in the Baohe River tributaries was mainly derived from the combined effects of atmospheric precipitation. The two rivers converged and were discharged into the subsidence area, causing serious sulfate pollution and affecting the water quality in the subsidence area. The δ34SSO4 value and SO42− content showed a good correlation in river water, subsidence area water and mine drainage, indicating that the SO42− content in the subsidence area was mainly affected by double-ended sources. Besides the impact of the Huihe River, the discharge of local mining waste water was also an important sulfate source, reflecting the effect of coal-mining activities on the water environment.

Origin of calcium sulfate-type water in the Triassic carbonate thermal water system in Chongqing, China: A chemical and isotopic reconnaissance

Chongqing, located in the southwestern China, was named as “A spa city of the world”. It's most geothermal reservoirs are developed in carbonate rock aquifers, and those thermal waters are characterized by high concentrations of sulfate and low HCO3−. However, little was known about the origin and genesis of those thermal waters, which is necessary for their protection and determination of regime of exploitation. Therefore, thermal and surface waters were sampled seasonally and analyzed for hydrogeochemical and isotopic compositions (δ18O/δ2H; δ34S–SO4; δ18O–SO4) to decipher the origin of the thermal waters in the Triassic carbonate aquifers in Chongqing area. Key questions include the relative significance of hydrothermal processes and solute supply. The results showed that: (1) the major chemical composition of analyzed the thermal waters from Chongqing area was characterized by Ca-SO4; (2) the δ2H and δ18O values of the thermal waters ranged from −48.6‰ to −63.1‰ with an average value of −54.2‰, and from −6.5‰ to −9.2‰ with an average value of −8.0‰, respectively, indicating that the thermal waters originated from the local rain water with an elevation of 415 m to 1453 m above mean sea level; (3) the estimated geothermal temperatures varied from 63.8 °C to 78.3 °C (Quartz), indicating that the depth of the geothermal reservoir varied from 411 m to 1728 m, which is located in the Lower Triassic Jialingjiang formation; (4) the δ34S-SO42- and δ18O-SO42- in the geothermal waters ranged from 29.7‰ to 34.1‰ with a mean value of 32.1‰, and from 12.5‰ to 16.5‰ with a mean value of 15.2‰, respectively, suggesting that the high SO42− concentrations resulted mainly from the dissolution of gypsum in the second part of the Lower Triassic Jialingjiang Formation; (5) three processes of water-rock interactions (gypsum dissolution, carbonate dissolution by carbonic acid and carbonate dissolution by sulfuric acid) in the thermal system were unveiled by the hydrogeochemical and isotopic models. Among these three processes, gypsum dissolution seems to be primarily responsible for solute composition of the thermal water. This study also indicates the integration of hydrogeochemical and isotopic data is very useful tool to decipher the origin and genesis of the carbonate thermal waters.

Identification of Sulfate Sources in the Groundwater System of Zaozhuang: Evidences from Isotopic and Hydrochemical Characteristics

Karst groundwater is an important source of water supply for the industrial and agricultural proposes and drinking water in Zaozhuang City. In recent years, with the development of industrialization and increasing of domestic water consumption, the sulfate pollution of karst groundwater has become a serious problem. 36 samples of surface and different depth of groundwater were collected in southern Zaozhuang City in August, 2014. Based on the analysis of the hydrochemical composition and the isotopic characteristics of δD, δ18O-H2O, and δ34 S-SO42-, this paper analyzed the influence of hydrogeochemical evolution of groundwater and human input in the area, in order to identify the scope and ways of sulfate pollution. The results showed that the basic hydrochemical type was HCO3·SO4-Ca, formation of geochemical components mainly included the dissolution of carbonate and sulfate minerals, oxidation of pyrite and the influence of human activities. Moreover, the main recharge of groundwater in study area was the atmospheric precipitation. The hydraulic connection was closely linked between the surface water and different depth of groundwater. The variation range of groundwater δ34 S-SO42- values was from 0.2‰ to 9.3‰, and the relationship between the δ34 S-SO42- value and SO42- value of groundwater showed different sources of sulfate. The sources of sulfate in groundwater included the dissolution of gypsum, the oxidation of pyrite, the leaching of fertilizer and infiltration of domestic sewage and industrial wastewater. In addition to the original geological factors, wastewater infiltration of industrial and mining enterprises was the main reason for the increase of sulfate content in the groundwater.

Stable isotopic evidence for anaerobic maintained sulphate discharge in a polythermal glacier

To understand the sources and sinks of sulphate and associated biogeochemical processes in a High Arctic environment, late winter snowpacks, the summer melt-waters and rock samples were collected and analysed for major ions and stable isotope tracers (δ18O, δ34S). The SO42¯/Cl¯ ratio reveal that more than 87% of sulphate (frequently > 95%) of total sulphate carried by the subglacial runoff and proglacial streams was derived from non-snowpack sources. The proximity of non-snowpack sulphate δ34S (∼8–19‰) to the δ34S of the major rocks in the vicinity (∼−6 to +18‰) suggest that the non-snowpack sulphate was principally derived from rock weathering. Furthermore, Ca2++Mg2+/SO42ˉ molar shows that sulphate acquisition in the meltwaters was controlled by two major processes: 1) coupled-sulphide carbonate weathering (molar ratio ∼ 2) and, 2) re-dissolution of secondary salts (molar ratio ∼ 1). The δ34S–SO4 = +19.4‰ > δ34S–S of rock, accompanied by increased sulphate concentration also indicates an input from re-dissolution of secondary salts. Overall, δ18O composition of these non-snowpack sulphate (−11.9 to −2.2‰) mostly stayed below the threshold δ18O value (−6.7 to −3.3‰) for minimum O2 condition, suggesting that certain proportion of sulphate was regularly supplied from anaerobic sulphide oxidation.

Identifying the sources of nitrate contamination of groundwater in an agricultural area (Haean basin, Korea) using isotope and microbial community analyses

An integrated study based on hydrogeochemical, microbiological and dual isotopic approaches for nitrate and sulfate was conducted to elucidate sources and biogeochemical reactions governing groundwater contaminants in different seasons and under different land use in a basin of Korea. The land use in the study area is comprised of forests (58.0%), vegetable fields (27.6%), rice paddy fields (11.4%) and others (3.0%). The concentrations of NO3–N and SO42− in groundwater in vegetable fields were highest with 4.2–15.2mgL−1 and 1.6–19.7mgL−1 respectively, whereas under paddy fields NO3–N concentrations ranged from 0 to 10.7mgL−1 and sulfate concentrations were ~15mgL−1. Groundwater with high NO3–N concentrations of >10mgL−1 had δ15N–NO3− values ranging from 5.2 to 5.9‰ and δ18O values of nitrate between 2.7 and 4.6‰ suggesting that the nitrate was mineralized from soil organic matter that was amended by fertilizer additions. Elevated concentrations of SO42− with δ34S–SO42− values between 1 and 6‰ in aquifers in vegetable fields indicated that a mixture of sulfate from atmospheric deposition, mineralization of soil organic matter and from synthetic fertilizers is the source of groundwater sulfate. Elevated δ18O–NO3− and δ18O–SO42− values in samples collected from the paddy fields indicated that denitrification and bacterial sulfate reduction are actively occurring removing sulfate and nitrate from the groundwater. This was supported by high occurrences of denitrifying and sulfate reducing bacteria in groundwater of the paddy fields as evidenced by 16S rRNA pyrosequencing analysis. This study shows that dual isotope techniques combined with microbial data can be a powerful tool for identification of sources and microbial processes affecting NO3− and SO42− in groundwater in areas with intensive agricultural land use.

The origin of solutes within the groundwaters of a high Andean aquifer

This paper investigates the origin of solutes within the groundwaters of the Monturaqui–Negrillar–Tilopozo (MNT) aquifer system within the high Andes of the Atacama Desert that discharges into the Salar de Atacama. Key questions include the relative significance of volcanic hydrothermal processes and evaporitic brine recycling over solute supply as well as the pathways of solute ingress to the MNT aquifer system. Groundwaters were analysed for elemental (major, minor and trace) and isotopic (δ18O/δ2H; δ13C–DIC; δ34S–SO4; 87Sr/86Sr) constituents to which various hydrochemical and multivariate statistical methods have been applied. Groundwaters are all classified as thermal and show increasing temperatures (27–35°C) and concentrations of HCO3 (4.4–10.4mmolL−1 dissolved inorganic carbon [DIC]) with increasing proximity to Volcano Socompa resulting from an increasing mass flux of steam and magmatic CO2 (pCO2=0.016 to 0.10atm; δ13C–CO2=−9.3 to −3.6‰ (V-PDB)) boiled off a deep hydrothermal reservoir. Superimposed upon this gradational and relatively smooth spatial increase in heat and mass flow is a sharp, structurally controlled, increase in TDS (826–3632mgl−1) and a concomitant change in δ34S–SO4 (+0.79 to 4.9‰ (V-CDT)) and 87Sr/86Sr values (0.707375–0.706859) associated with the inflow of evaporitic solutes. Evaporitic inputs are chemically and isotopically distinct from localised secondary hydrothermally derived solutes with major, minor and trace element data suggesting an origin within a highly oxidising, alkaline, evaporitic lake receiving dilute inflows enriched in volcanic/fumarolic sulfur mineralisation probably from volcanoes Socompa, Salín or Pular that delimit the eastern topographic extent of the aquifer system. The conceptual model presented in this paper proposes that basal leakage of evaporitic brines from active salar(s), within the high altiplano/volcanic arc, are actively entrained by sub-regional groundwater flow and conveyed to the MNT aquifer system where they mix with solutes derived from localised secondary hydrothermal gas–water–rock interaction. This work provides detail on the origin and processes controlling the solute composition of groundwater inflows to the Salar de Atacama within the volcanically active and hyperarid Atacama Desert and may be of significance to conceptual models of evaporitic brine evolution, recycling of evaporitic brines and hydrothermalism in arid regions.

Summer deposition of sulfate and reactive nitrogen to two alpine valleys in the Canadian Rocky Mountains

Summer deposition of sulfate and reactive nitrogen (mainly nitrate, and ammonium) to two alpine valleys in the Southern Canadian Rocky Mountains was investigated to constrain their major sources and evaluate physiographic influences on deposition. The effects of elevation, aspect, and air mass trajectory were evaluated using stable isotope composition (δ15N–NO3−, δ18O–NO3−, and δ34S–SO42−) and major ion concentrations for bulk precipitation. Deposition in the two valleys was related to synoptic scale weather conditions and the route the air mass followed, the location of major emission sources relative to the study site, and atmospheric residence time. Distinct differences in deposition at a relatively small scale between two opposing alpine valleys was mainly related to the orientation of the two valleys relative to the physiography of the Western Canadian Cordillera and the dominant pathways of air mass transport. Sulfate was found to be dominantly from distant sources, while NO3− was strongly enhanced by emissions from local to regional combustion. Local to regional pollutants were preferentially transported to the NNW facing Robertson Valley during NW-upslope synoptic conditions while precipitation in the SE facing Haig Valley was from relatively clean air with minimal influence from local and regional pollutants particularly at the highest elevation site.

Sulfur isotopic signatures of water-soluble sulfate in needles of Pinus Massoniana Lamb in two Chinese areas

This study analyzed the water-soluble sulfate (SSO4) and total sulfur (ST) concentrations and their isotopic signatures (δ34SSO4 and δ34ST) in needles of Pinus massoniana Lamb collected from Guiyang (seriously affected by acid rain) and Yunnan areas (acid rain did not occur), China SW. The results indicated that the SSO4 concentrations in needles of Pinus massoniana Lamb collected from several Chinese areas were found to be significantly correlated to ambient sulfur dioxide (R2 = 0.9176, p = 0.01), showing that SSO4 concentrations in needles were more reliable to indicate atmospheric sulfur. The average δ34SSO4 (−7.2 ‰) and δ34STS (−5.1 ‰) in needles in Guiyang areas were significantly lower than those in Yunnan areas (+3.9 and +5.7 ‰, respectively), which were in accordance with the lower δ34S of coals in Guiyang areas than in Yunnan areas. The δ34SSO4 and δ34STS in needles became less positive with a distance from a plant combusted 34S-enriched coals while for another plant combusted 34S-depleted coals, more positive was observed. These results indicated that δ34SSO4 in needles was also a good indicator of atmospheric sulfur sources. A very small difference between δ34 ST and δ34 SSO4 for most needle samples suggested that little isotopic fractionation accompanies sulfur assimilation processes.

Hydrochemical indications of human impact on karst groundwater in a subtropical karst area, Chongqing, China

The application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of solutes from the natural background of those due to human activities. Multiple isotopes (δ13C–DIC, δ34S–SO42−) and chemical parameters were measured in rainwater, groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the Laolongdong karst catchment in Chongqing Municipality, SW China. Overall, the dissolution of carbonate rock controls Ca2+, Mg2+ and HCO3− content in rainwater and karst groundwater. SO42− originated mainly from gypsum dissolution in karst groundwater. Carbonate rocks in the studied site could be dissolved jointly by H2CO3 from the natural CO2–H2O reaction and other acids (organic acids and HNO3) from sewage and soils. Sewage discharge from urban areas and agriculture activities lead to the increase of NO3−, PO43− and Cl− in karst groundwater. To protect and sustainably utilize the karst aquifer, sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited.