Variations In Sulfate Concentrations Research Articles

Sulfate in streams and groundwater in a cold region (Yukon Territory, Canada): Evidence of weathering processes in a changing climate

Analyses of the sulfur (S) and oxygen (O) stable isotope ratios (δ34SSO4 and δ18OSO4) of dissolved sulfate in streams and groundwater in Yukon Territory (YT, Canada) indicates that the dominant source of this major ion is oxidation of sulfide minerals. In these streams, sulfate has a large range in δ34SSO4 values (−19 to +10‰), which is consistent with the lower portion of the documented range for δ34S of sulfides in bedrock in YT (∼ −35 to +55‰). Furthermore, the large majority of the δ18OSO4 data plot within the expected field for sulfide oxidation in cross-plots of δ18OSO4 versus the O isotope ratios of ambient water (δ18OH2O). δ18OSO4 values plotting above that field were likely affected by microbial sulfate reduction, a process that enriches residual sulfate in both 34S and 18O. The stable isotope data indicate that dissolution of marine-evaporite gypsum, which has higher δ34SSO4 and δ18OSO4 values compared to all stream and groundwater samples, is a minor to negligible source of sulfate in the YT streams. Association of sulfate with other solutes indicates release of various metals from sulfide minerals, and suggests dominance of silicate weathering in response to oxidation of the sulfides. Variations in sulfate concentrations in YT streams are largely related to geology, while terrain and climate, including extent of permafrost, are also important factors. Long-term monitoring of sulfate concentrations in YT streams indicates increasing concentrations over time, in both streams impacted by mining, and in streams that have not been affected much by historical in-catchment industrial activities. Increases were largest in streams in northern and central-south YT in the presence of thawing continuous to discontinuous permafrost.

Cyclic variations of sulfate and boron concentrations and isotopes in deep groundwaters in the Aquitaine Basin, France

Concentrations and isotope contents of major and trace elements are principal factors in determining the origin of the chemical composition of groundwater. This paper focuses specifically on the use of sulfur and boron isotopes to characterize the origin of cyclic variations in the deep Eocene aquifer in the Aquitaine sedimentary basin (southwest of France). It is part of a multi-layer system mainly composed of sands and sandstone deposits. Groundwater contained in this deep reservoir is known to present stable chemical compositions, allowing its use for various purposes like drinking water, geothermal energy, thermal activity and agricultural irrigation. However, among the dozens of wells exploiting this aquifer and despite the reservoir's substantial depth, variations in sulfate concentration have been identified in a limited area of the reservoir. These fluctuations are cyclic and they seem to be correlated with water level variations due to gas storage activities nearby in the same aquifer. Regular water samplings and analyses of major and trace elements and their isotopes have identified that bore concentration variations are correlated with sulfate variations. A geochemical modelling approach based on water mixes elucidates the causes of these variations in chemical composition, especially the boron and sulfate concentrations and their respective δ11B and δ34SSO4 values. From these numerical results, we identify that different sources explain the variations of boron concentration, one part coming from the silicates alteration (present in sub-layers of the exploited aquifer) and the other part coming from the evaporites alteration (present in the underlying molasse unit). These results also confirm the existence of mass and potentially water transfers between the different sub-layers of the reservoir and with the underlying molasse aquitard, implying new constraints for the future hydrogeologic modelling.

Halophilic Archaea Mediate the Formation of Proto-Dolomite in Solutions With Various Sulfate Concentrations and Salinities.

In the past several decades, sulfate concentration and salinity have been considered to be the two essential hydrochemical factors in the formation of dolomite, yet arguments against this hypothesis have existed simultaneously. To clarify the effects of sulfate concentration and salinity in the mineralization of dolomite, we conducted experiments on dolomite precipitation mediated by a halophilic archaeon, Natrinema sp. J7-1 with various sulfate concentrations and salinities. This strain was cultured in a series of modified growth media (MGM) with salinities of 140, 200, and 280‰. Cells in the post-log phase were harvested and used to mediate the formation of dolomite in solutions with various sulfate concentrations of 0, 3, 29.8, and 100 mM and salinities of 140, 200, and 280‰. X-ray diffraction (XRD) spectra showed that proto-dolomite, monohydrocalcite, and aragonite formed in samples with cells, yet only aragonite was detected in samples without cells. Proto-dolomite was found in all biotic samples, regardless of the variation in salinity and sulfate concentration. Moreover, the relative abundances of proto-dolomite in the precipitates were positively correlated with the salinities of the media but were uncorrelated with the sulfate concentrations of the solutions. Scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS) results showed that all the proto-dolomites were sphere or sphere aggregates with a mole ratio of Mg/Ca close to 1.0. No obvious variations in morphology and Mg/Ca were found among samples with various sulfate concentrations or salinities. This work reveals that a variation of sulfate concentration in solution (from 0 to 100 mM) does not affect the formation of dolomite mediated by halophilic archaea, but an increase of salinity (from 140 to 280‰) enhances this process. Our results indicate that under natural conditions, an increase in salinity may be more significant than the decrease of sulfates in microbe-mediated dolomite formation.

Did shifting seawater sulfate concentrations drive the evolution of deep-sea methane-seep ecosystems?

The origin and evolution of the faunas inhabiting deep-sea hydrothermal vents and methane seeps have been debated for decades. These faunas rely on a local source of sulfide and other reduced chemicals for nutrition, which spawned the hypothesis that their evolutionary history is independent from that of photosynthesis-based food chains and instead driven by extinction events caused by deep-sea anoxia. Here I use the fossil record of seep molluscs to show that trends in body size, relative abundance and epifaunal/infaunal ratios track current estimates of seawater sulfate concentrations through the last 150 Myr. Furthermore, the two main faunal turnovers during this time interval coincide with major changes in seawater sulfate concentrations. Because sulfide at seeps originates mostly from seawater sulfate, variations in sulfate concentrations should directly affect the base of the food chain of this ecosystem and are thus the likely driver of the observed macroecologic and evolutionary patterns. The results imply that the methane-seep fauna evolved largely independently from developments and mass extinctions affecting the photosynthesis-based biosphere and add to the growing body of evidence that the chemical evolution of the oceans had a major impact on the evolution of marine life.

Hydrogen production from sulfate- and ferrous-enriched wastewater

The quantitative relationship between sulfate reducing bacteria (SRB) and hydrogen (H 2) production from sulfate (SO 4 2−) and ferrous [Fe(II)] enriched wastewater was investigated. Both Fe(II) (0–11,600 mg/L) and SO 4 2− (0–20,000 mg/L) improved the H 2 production efficiency from wastewater. The H 2 yields were increased up to 1.9 mol H 2/mol glucose in 580–1750 mg Fe(II)/L and 1000–3000 mg SO 4 2−/L enriched wastewater at pH 5.8–6.2. Quantitative Fluorescence In Situ Hybridization (FISH) analyses revealed that the specific sulfate reducing activities (SSRA) were increased from 0.08 and 0.06 to 0.16 and 0.21 g TS/g SRB h in response to variations in sulfate concentration from 300–20,000 mg/L at pH 5.8 and 6.2, respectively. H 2 production was not influenced by low SSRA (≤0.1 g TS/g SRB h), which was independent of pH variation. The results demonstrated that the SSRA and Fe(II) concentration can significantly influence on the biological H 2 production from SO 4 2− and Fe(II) containing wastewater.

Hydrogen ‘leakage’ during methanogenesis from methanol and methylamine: implications for anaerobic carbon degradation pathways in aquatic sediments

The effect of variations in H2 concentrations on methanogenesis from the non-competitive substrates methanol and methylamine (used by methanogens but not by sulfate reducers) was investigated in methanogenic marine sediments. Imposed variations in sulfate concentration and temperature were used to drive systematic variations in pore water H2 concentrations. Specifically, increasing sulfate concentrations and decreasing temperatures both resulted in decreasing H2 concentrations. The ratio of CO2 and CH4 produced from 14C-labelled methylamine and methanol showed a direct correlation with the H2 concentration, independent of the treatment, with lower H2 concentrations resulting in a shift towards CO2. We conclude that this correlation is driven by production of H2 by methylotrophic methanogens, followed by loss to the environment with a magnitude dependent on the extracellular H2 concentrations maintained by hydrogenotrophic methanogens (in the case of the temperature experiment) or sulfate reducers (in the case of the sulfate experiment). Under sulfate-free conditions, the loss of reducing power as H2 flux out of the cell represents a loss of energy for the methylotrophic methanogens while, in the presence of sulfate, it results in a favourable free energy yield. Thus, hydrogen leakage might conceivably be beneficial for methanogens in marine sediments dominated by sulfate reduction. In low-sulfate systems such as methanogenic marine or freshwater sediments it is clearly detrimental--an adverse consequence of possessing a hydrogenase that is subject to externally imposed control by pore water H2 concentrations. H2 leakage in methanogens may explain the apparent exclusion of acetoclastic methanogenesis in sediments dominated by sulfate reduction.

Soil carbon stock of the Central-East Asia in the climate warming

Water samples from the Wujiang River, a typical karst river system, were analyzed for major ion concentrations and ~34S values of dissolved sulfate in order to identify the sources of sulfate, quantify the sulfate export flux and understand the role of sulfur cycling in chemical weathering rate of carbonate. Spatial variations in sulfate concentration and sulfur isotopic composition of tributaries over the catchment area are obvious, allowing to decipher S sources between rocks and atmosphere. According to the variations in sulfate concentration and isotopic composition, it is inferred that sulfate ions in the upper-reach river waters may have three sources, rain water, sulfate resultant from oxidation of pyrite in coal, and sulfate from sulfide deposits. In the lower reaches, the S isotopic composition of the samples lies mainly on a mixing trend between evaporite sulfate and rainwater sulfate, the contribution of sulfate from oxidation of pyrite being lesser. A pronounced seasonal variation in both content and isotopic composition of sulfate characterizes the Wujiang River. The average sulfate concentration of the waters is 0.65 mmol/L in winter, 0.17 mmol/L higher than that in summer. River water ~348 values range from -15.7%0 to 18.9%0 in winter, while the 634S values of river waters in summer vary to a lesser extent than in winter, from -11.5%o to 8.3%0. The 834S values of the main stream range from -6.7%0 to -3.9%0 in summer, averaging 3%0 lower than in winter. This indicates that in summer, when the discharge increases, the contribution of a source enriched in light isotopes to the atmosphere or the oxidation of pyrite in coal is more important. The sulfate export flux of the Wujiang River is calculated to be about 172 x 101~ g/a, the export flux in the high-flow period accounting for 80% of the total. Sulfide oxidation (sulfuric acid production) and subsequent weathering of carbonate are important processes in the study area. We determined that in summer about 75% of the riverine sulfate in the Wujiang River could be produced by sulfide oxidation. The relative contributions from rainwater and evaporite sulfate are only 20% and 5%, respectively. As a result, the erosion rate of carbonate by sulfuric acid is on the order of 35.1 t/km2/a (17.5 mm/ka) and the CO2 consumption rate is reduced approximately by 3.66• 105 mol/krn2/a.

Fast ground-water mixing and basal recharge in an unconfined, alluvial aquifer, Konza LTER Site, Northeastern Kansas

Ground-water chemistry and water levels at three levels in a well nest were monitored biweekly for two and a half years in a shallow unconfined floodplain aquifer in order to study the dynamics of such shallow aquifers. The aquifer, in northeastern Kansas, consists of high porosity, low hydraulic conductivity fine-grained sediments dominated by silt and bounded by fractured limestone and shale bedrock. Results show that the aquifer underwent chemical stratification followed by homogenization three times during the study period. The length of time between maximum stratification and complete homogenization was 3–5 months. The chemical parameters most useful for demonstrating the mixing trends were dissolved nitrate and sulfate. Higher nitrate concentrations were typical of unsaturated zone water and were sourced from fertilizer applied to the cultivated fields on the floodplain. Variations in sulfate concentrations are attributed to dissolution of rare gypsum in limestone bedrock and variable evapoconcentration in the unsaturated zone. The mixing of three chemically different waters (entrained, unsaturated-zone water; water entering the base of the floodplain aquifer; and water in residence before each mixing event) was simulated. The resident water component for each mixing event was a fixed composition based on measured water chemistry in the intermediate part of the aquifer. The entrained water composition was calculated using a measured composition of the shallow part of the aquifer and measurements of soil-water content in the unsaturated zone. The incoming basal water composition and the fractions of each mixing component were fitted to match the measured chemistry at the three levels in the aquifer. A conceptual model for this site explains: (1) rapid water-level rises, (2) water-chemistry changes at all levels in the aquifer coincident with the water-level rises, (3) low measured hydraulic conductivity of the valley fill and apparent lack of preferential flow pathways, (4) minuscule amounts of unsaturated-zone recharge, and (5) dissolved oxygen peaks in the saturated zone lagging water-level peaks. We postulate that rainfall enters fractures in bedrock adjacent to the floodplain. This recharge water moves rapidly through the fractured bedrock into the base of the floodplain aquifer. The recharge event through the bedrock causes a rapid rise in water level in the floodplain aquifer, and the chemistry of the deepest water in the floodplain aquifer changes at that time. The rising water also entrains slow-moving, nitrate-rich, unsaturated-zone water, altering the chemistry of water in the shallow part of the aquifer. Vertical chemical stratification in the aquifer is thus created by the change in water chemistry in the upper and lower parts of the saturated zone. As the water level begins to decline, the aquifer undergoes mixing that eventually results in homogeneous water chemistry. The rise in water level from the recharge event also displaces gas from the unsaturated zone that is then replaced as the water level declines following the recharge event. This new, oxygen-rich vadose-zone air equilibrates rapidly with saturated-zone water, resulting in a dissolved oxygen pulse in the ground water that peaks one-half to 2 months after the water-level peak. This oxygen pulse subsequently declines over a period of 2–6 months.

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

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.

Applications of a simple regression model to acid rain data

AbstractThis paper addresses two vital and seemingly simple questions concerning wet deposition of sulfates, a major contributor to acid rain. The first is to estimate the annual wet deposition of sulfate at a monitoring site under emissions that existed during the 1980s. This problem is complicated by missing data. The second is to estimate accurately the effect of a change in pollution emissions on concentrations of sulfate in precipitation. This problem is made difficult by the substantial natural variations in sulfate concentrations due to weather variations between years. As a tool for addressing both of these problems, we develop a regression model for the sulfate concentration of precipitation on a particular day as a function of amount of precipitation and time of the year. The model is used as a basis for imputing missing sulfate concentrations to handle the missing‐data problem. It is also used to explain some of the variability in annual sulfate concentrations due to meteorology and hence provide more accurate estimates of the effect of changes in emissions.

Variations in aqueous sulfate concentrations at Panola Mountain, Georgia

Aqueous sulfate concentrations were measured in incident precipitation, canopy throughfall, stemflow, soil water, groundwater, and streamwater at three locations in a 41 ha forested watershed at Panola Mountain State Park in the Georgia Piedmont. To evaluate the variations in sulfate concentrations, sampling intensity was increased during storms by automated collection of surface water and by incremental subsampling of rainfall, throughfall, and soil solution. Canopy throughfall, stemflow, and runoff from a bedrock outcrop in the watershed headwaters were enriched in sulfate relative to incident precipitation due to washoff of dry deposition that accumulated between storms. Soil waters collected from zero-tension lysimeters at 15 cm and 50 cm below land surface also were enriched in sulfate relative to precipitation, groundwater and streamwater. Sulfate concentrations in groundwater and in streamwater at base flow varied in an annual sinusoidal pattern with winter maxima and summer minima. Stream discharge and groundwater levels varied in a similar annual pattern in phase with the sulfate concentrations. The temporal variability of sulfate concentrations at most groundwater sites was small relative to the spatial variability among groundwater sites. Streamwater sulfate concentrations during base flow were controlled by low-sulfate groundwater discharge. As flow increased, an increasing proportion of shallow, high-sulfate groundwater and soil water contributed to streamflow. The dominant control on stream sulfate concentration shifted from sulfate retention by adsorption in the mineral soil at base flow to mobilization of sulfate from the upper, organic-rich horizons of the soil at high flow.

Acid Deposition, Smelter Emissions, and the Linearity Issue in the Western United States

The variation in sulfur dioxide emissions from nonferrous metal smelters in the western United States over a 4-year period is compared with the variation in sulfate concentrations in precipitation in the Rocky Mountain states. The data support a linear relation between emissions and sulfate concentration. The geographic separation of emissions sources and precipitation monitors indicates a sulfur transport scale exceeding 1000 kilometers.

Effect of moisture variation on sulfate concentration in a buck solonetz soil

Abstract Sulfate concentration in the equilibrium solutions of a black solonetz soil was different at each moisture content. In the sub‐surface horizons a decrease in soil moisture up to about 35 percent resulted in a gradual increase of sulfate concentration. However, with further decrease in moisture the sulfate concentration increased abruptly. Variation of sulfate concentration appears to alter significantly certain cation ratios in the equilibrium solutions.