Measured Sulfate Concentrations Research Articles

Sulphate reduction determines the long-term effect of iron amendments on phosphorus retention in lake sediments

PurposeThis field study aimed to guide the planning of iron amendments for phosphorus retention by investigating the long-term fate of iron added to two urban lakes (Plötzensee and Groß Glienicker See) in Berlin, Germany. The contributions of iron dosing to improve lake status as well as the relevance of competing processes for management success were evaluated.MethodsSediment stratigraphy, as well as occurrence of iron minerals, and fluxes between water and sediment were examined using geochemical analyses (i.e. element composition, sequential extraction, X-ray diffraction, and pore water analyses). A one-box lake model was used to relate these fluxes to monitoring data from the water column and to sediment inventories.ResultsIn both lakes, the added iron was preserved in the sediment. Whereas phosphorus retention increased following the addition of iron to Groß Glienicker See, sulphur was retained by the excess iron in Plötzensee. This contrasting effect is attributed to significantly different sulphate reduction rates in two lakes (Wilcoxon rank sum test: W = 25, p = 0.008). According to the one-box model, sulphate reduction explained both the decrease in measured sulphate concentrations after iron application as well as the observed increase in sulphur deposition in the sediments.ConclusionManagement interventions involving iron amendments to enhance phosphorus retention must consider the competing process of iron sulphide formation during the entire management plan period, and additional iron may need to be applied to account for this effect.

The sulfur cycle below the sulfate-methane transition of marine sediments

The study of sulfate reduction below the sulfate-methane transition (SMT) in marine sediments requires strict precautions to avoid sulfate contamination from seawater sulfate or from sulfide oxidation during handling. We experimented with different methods of sampling porewater sulfate and found that modifications to our sampling procedure reduced the measured sulfate concentrations from hundreds of micromolar to ten micromolar or less. We here recommend some key modifications to porewater sampling to avoid contamination or oxidation artifacts, for example when measuring very low sulfate concentrations below the SMT of marine sediments. At three sites in Aarhus Bay, the sulfate concentrations below the SMT remained around ten micromolar. The calculated free energy change, ΔGr, available for sulfate reduction by such low concentrations is between −17.9 and −11.9 kJ mol−1 sulfate. This is near or below the energy yields that have previously been calculated for microbial sulfate reduction in marine sediments. The three sites are characterized by measurable and very different sulfate reduction rates depending on the depth and sediment age of the SMT. Our data show that sulfate is being consumed below the SMT in spite of the low sulfate concentrations. As sulfate is not drawn down to even lower concentrations, it must be continually regenerated below the SMT, most likely by Fe(III)-driven sulfide oxidation concurrent with the sulfate reduction. We conclude that the low sub-SMT sulfate concentrations are in steady state between reduction and production and are thermodynamically controlled by the minimum ΔGr requirements by sulfate reducing bacteria while sulfate reduction rates are controlled by the rate of sulfide oxidation. This study deals with the general sampling of uncontaminated pore water and hints to a systemic problem with low levels of contamination in porewater induced by coring and pore water extraction. Below the SMT, this contamination could be detected but above the SMT it goes unnoticed. Low levels of contamination as observed in this study may affect other low concentration or redox-sensitive elements in pore water.

A comparison of results from a hydrologic transport model (HSPF) with distributions of sulfate and mercury in a mine-impacted watershed in northeastern Minnesota

The St. Louis River watershed in northeast Minnesota hosts a major iron mining district that has operated continuously since the 1890s. Concern exists that chemical reduction of sulfate that is released from mines enhances the methylation of mercury in the watershed, leading to increased mercury concentrations in St. Louis River fish. This study tests this idea by simulating the behavior of chemical tracers using a hydrologic flow model (Hydrologic Simulation Program FORTRAN; HSPF) and comparing the results with measured chemistry from several key sites located both upstream and downstream from the mining region. It was found that peaks in measured methylmercury (MeHg), total mercury (THg), dissolved organic carbon (DOC), and dissolved iron (Fe) concentrations correspond to periods in time when modeled recharge was dominated by active groundwater throughout the watershed. This helps explain why the timing and size of the MeHg peaks was nearly the same at sites located just upstream and downstream from the mining region. Both the modeled percentages of mine water and the measured sulfate concentrations were low and computed transit times were short for sites downstream from the mining region at times when measured MeHg reached its peak. Taken together, the data and flow model imply that MeHg is released into groundwater that recharges the river through riparian sediments following periods of elevated summer rainfall. The measured sulfate concentrations at the upstream site reached minimum concentrations of approximately 1 mg/L just as MeHg reached its peak, suggesting that reduction of sulfate from non-point sources exerts an important influence on MeHg concentrations at this site. While mines are the dominant source of sulfate to sites downstream from them, it appears that the background sulfate which is present at only 1–6 mg/L, has the largest influence on MeHg concentrations. This is because point sourced sulfate is transported generally under oxidized conditions and is not flushed through riparian sediments in a gaining stream watershed system.

Long-term trends of black carbon and sulphate aerosol in the Arctic: changes in atmospheric transport and source region emissions

Abstract. As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport) and building on previous work (Hirdman et al., 2010), this paper studies the long-term trends of both atmospheric transport as well as equivalent black carbon (EBC) and sulphate for the three Arctic stations Alert, Barrow and Zeppelin. We find a general downward trend in the measured EBC concentrations at all three stations, with a decrease of −2.1±0.4 ng m−3 yr−1 (for the years 1989–2008) and −1.4±0.8 ng m−3 yr−1 (2002–2009) at Alert and Zeppelin respectively. The decrease at Barrow is, however, not statistically significant. The measured sulphate concentrations show a decreasing trend at Alert and Zeppelin of −15±3 ng m−3 yr−1 (1985–2006) and −1.3±1.2 ng m−3 yr−1 (1990–2008) respectively, while there is no trend detectable at Barrow. To reveal the contribution of different source regions on these trends, we used a cluster analysis of the output of the Lagrangian particle dispersion model FLEXPART run backward in time from the measurement stations. We have investigated to what extent variations in the atmospheric circulation, expressed as variations in the frequencies of the transport from four source regions with different emission rates, can explain the long-term trends in EBC and sulphate measured at these stations. We find that the long-term trend in the atmospheric circulation can only explain a minor fraction of the overall downward trend seen in the measurements of EBC (0.3–7.2%) and sulphate (0.3–5.3%) at the Arctic stations. The changes in emissions are dominant in explaining the trends. We find that the highest EBC and sulphate concentrations are associated with transport from Northern Eurasia and decreasing emissions in this region drive the downward trends. Northern Eurasia (cluster: NE, WNE and ENE) is the dominant emission source at all Arctic stations for both EBC and sulphate during most seasons. In wintertime, there are indications that the EBC emissions from the eastern parts of Northern Eurasia (ENE cluster) have increased over the last decade.

Two modelling approaches to water-quality simulation in a flooded iron-ore mine (Saizerais, Lorraine, France): A semi-distributed chemical reactor model and a physically based distributed reactive transport pipe network model

The flooding of abandoned mines in the Lorraine Iron Basin (LIB) over the past 25 years has degraded the quality of the groundwater tapped for drinking water. High concentrations of dissolved sulphate have made the water unsuitable for human consumption. This problematic issue has led to the development of numerical tools to support water-resource management in mining contexts. Here we examine two modelling approaches using different numerical tools that we tested on the Saizerais flooded iron-ore mine (Lorraine, France). A first approach considers the Saizerais Mine as a network of two chemical reactors (NCR). The second approach is based on a physically distributed pipe network model (PNM) built with EPANET 2 software. This approach considers the mine as a network of pipes defined by their geometric and chemical parameters. Each reactor in the NCR model includes a detailed chemical model built to simulate quality evolution in the flooded mine water. However, in order to obtain a robust PNM, we simplified the detailed chemical model into a specific sulphate dissolution–precipitation model that is included as sulphate source/sink in both a NCR model and a pipe network model. Both the NCR model and the PNM, based on different numerical techniques, give good post-calibration agreement between the simulated and measured sulphate concentrations in the drinking-water well and overflow drift. The NCR model incorporating the detailed chemical model is useful when a detailed chemical behaviour at the overflow is needed. The PNM incorporating the simplified sulphate dissolution–precipitation model provides better information of the physics controlling the effect of flow and low flow zones, and the time of solid sulphate removal whereas the NCR model will underestimate clean-up time due to the complete mixing assumption. In conclusion, the detailed NCR model will give a first assessment of chemical processes at overflow, and in a second time, the PNM model will provide more detailed information on flow and chemical behaviour (dissolved sulphate concentrations, remaining mass of solid sulphate) in the network. Nevertheless, both modelling methods require hydrological and chemical parameters (recharge flow rate, outflows, volume of mine voids, mass of solids, kinetic constants of the dissolution–precipitation reactions), which are commonly not available for a mine and therefore call for calibration data.

Attribution of sulfate aerosols in Federal Class I areas of the western United States based on trajectory regression analysis

Atmospheric aerosols can significantly reduce visibility and result in regional haze. The Clean Air Act amendments established a national visibility goal to remedy existing impairment and prevent future impairment in Federal Class I areas (national parks and wilderness areas designated by Congress), most of which are in the western United States. In order to identify the major source regions of the atmospheric aerosols in the Class I areas of the western United States, air mass backtrajectories were calculated for 84 western Class I areas every 3 h at a starting height of 500 m over the years 2000–2002 using the NOAA HYSPLIT v4.6 model. For each Class I area, multiple-linear regression between the Interagency Monitoring of Protected Visual Environments (IMPROVE) measured sulfate concentrations and the air mass residence times in the pre-defined potential source regions was conducted. Results suggest that shipping and other port emissions from along the Pacific Coast contributed significantly to atmospheric aerosol concentrations over large areas of the western United States.

Quantitative back-trajectory apportionment of sources of particulate sulfate at Big Bend National Park, TX

As part of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study, a quantitative back-trajectory-based receptor model, Trajectory Mass Balance (TrMB) was used to estimate source apportionment of particulate sulfur measured at Big Bend National Park, Texas, during July–October 1999. The model was exercised using a number of sets of trajectories generated by three different trajectory models, with three different sets of input gridded meteorology, and tracked for 5, 7, and 10 days back in time. The performance of the TrMB model with the different trajectory inputs was first evaluated against perfluorocarbon tracers and synthetically generated sulfate concentrations from a regional air quality model, both of which had known attributions. These tests were used to determine which trajectories were adequate for the TrMB modeling of measured sulfate concentrations, illustrated the magnitude of the daily uncertainties as compared to the uncertainties in the mean attributions, and demonstrated the value of a robust evaluation process. Depending on trajectories, mean sulfate source apportionment results were 39–50% from Mexico, 7–26% from the eastern US, 12–45% from Texas, and 3–25% from the western US. These ranges were inclusive of the best BRAVO attribution estimates for Mexico, Texas, and the western US, but TrMB underestimated the eastern US contribution as compared to the BRAVO best estimates.

Anaerobic biodegradability of cellulose and hemicellulose in excavated refuse samples using a biochemical methane potential assay

Improved techniques are needed to predict potential methane generation from refuse buried in landfills. The Biochemical Methane Potential (BMP) test was used to measure the methane potential of ten refuse samples excavated from a Berkeley, CA, landfill. The test was conducted in 125-ml serum bottles containing phosphate-buffered medium and inoculated with anaerobically digested sewage sludge. Comparison of the measured BMP to the theoretical BMP calculated from measured cellulose and hemicellulose concentrations indicated that cellulose plus hemicellulose is not well correlated with the measured BMP. The average of the measured to theoretical BMP was 19.1% (range 0-53%, s.d. = 16.9%). Measured sulfate concentrations showed that sulfate was an insignificant electron sink in the samples tested. Once methane production from the refuse was complete, 0.072 g of Whatman no. 1 filter paper was added to two of the four serum bottles incubated for each sample. An average of 84.9% (s.d. = 2.5%) of the added filter paper was recovered as methane, suggesting that some cellulose and hemicellulose present in refuse is recalcitrant or otherwise not bioavailable.

Plasma concentrations of inorganic sulfate in Alzheimer's disease.

Recent reports have suggested that plasma concentrations of inorganic sulfate may be lower in patients with Alzheimer's disease (AD). We measured sulfate concentrations in 10 patients with AD and found an average concentration of 0.28 mM, which was not significantly different from the mean concentration in age-matched controls (0.32 mM) or young healthy controls (0.27 mM). These results indicate that plasma sulfate concentrations are not altered in AD and that previous reports suggesting altered metabolism of sulfur-containing xenobiotics in neurodegenerative diseases should be reevaluated.

The Occurrence and Effect of Sulfate Reduction and Sulfide Oxidation on Coastal Limestone Dissolution in Yucatan Cenotes

AbstractDissolution of carbonate minerals in the coastal halocline is taking place in the karst terrain along the northeastern coast of the Yucatan Peninsula. The dissolution is being accelerated in cenotes (sinkholes) where sulfate reduction and oxidation of the produced sulfide is occurring.Hydrogen‐sulfide concentrations ranged from 0.06 to 4 mmolal within the halocline in two sinkholes. Relative to concentrations expected by conservative mixing, fluids with high hydrogen‐sulfide concentrations were correlated with low sulfate concentrations, high alkalinities, low pH values, and heavy sulfur isotope values for sulfate. Hydrogen‐sulfide concentrations were less than those predicted from sulfate reduction, calculated from deficiencies in measured sulfate concentrations, indicating mobility and loss of aqueous sulfide.Fluids with low hydrogen‐sulfide concentrations were correlated with very high calcium concentrations, high strontium and sulfate concentrations, slightly elevated alkalinities, low pH values, and sea‐water sulfur isotope values for sulfate. Gypsum dissolution is supported by the sulfur isotopes as the major process producing high sulfate concentrations. However, oxidation of aqueous sulfide to sulfuric acid, resulting in carbonate‐mineral dissolution is needed to explain the calcium concentrations, low pH values, and only slightly elevated alkalinities.The halocline may trap hydrogen sulfide that has been stripped from the underlying anoxic salt water. The halocline can act as a stable, physical boundary, holding some of the hydrogen sulfide until it is oxidized back to sulfuric acid through interaction with the overlying, oxygenated fresh water or through the activity of sulfide‐oxidizing bacteria.

Cloud chemistry research at Whiteface Mountain

Cloud collection principles are briefly reviewed; the performance of two collectors in common use is compared. Two cloud event studies (one during winter, the other during summer) are presented to contrast typical time-dependent histories of chemical concentrations for the two seasons. During winter, the oxidation rate of SO 2 is low, resulting in measured sulfate concentrations independent of SO 2 concentrations. During summer, SO 2 is rapidly oxidized by H 2 O 2 with a residue of H 2 O 2 persisting in cloud water after SO 2 has been converted. Changes in the gas phase concentrations of SO 2 and H 2 O 2 are shown during a cloud event. Both gases drop to very low concentrations in cloud with H 2 O 2 tending to recover after available SO 2 has been oxidized. The meteorology for each event is presented to illustrate the role of atmospheric structure in the transporting of emitted material and in determining cloud water compositions. Finally, a cloud chemistry climatology for winter and summer is presented, based upon 6 years of observations at Whiteface Mountain. DOI: 10.1111/j.1600-0889.1989.tb00127.x

Modeling the Effects of Acid Deposition: Uncertainty and Spatial Variability in Estimation of Long‐Term Sulfate Dynamics in a Region

The choice of appropriate parameter values for mathematical models that are meant to describe long‐term (decades or longer) changes in hydrochemical catchment response to atmospheric deposition is difficult because long time series of observations are generally unavailable. Some information about the range (or distribution) of stream chemistry variables across a given region is often available, however, and this should provide useful guidance in selecting allowable values for parameters for regional application of the model. We develop a method for using data that describe the present‐day distribution of stream water chemistry in a region to constrain allowable ranges of parameters in a mathematical model and to infer particular parameter combinations that are inconsistent with observations. We apply the method to a simple model of catchment sulfate dynamics using measured sulfate concentrations from several streams in Shenandoah National Park, Virginia. Acceptable parameter combinations for this case are well defined by a single linear axis. Extrapolation of the distribution of sulfate concentrations into the future using these acceptable parameter combinations suggests that a shift in mean sulfate concentration in the southwest section of the park would be detectable with 90% certainty 8 to 10 years hence, assuming that atmospheric deposition remains constant.

Global and local influences on the chemical composition of snowfall at Dye 3, Greenland: the record between 10 ka B.P. and 40 ka B.P.

Wisconsin Age ice from Dye 3, Greenland, shows a number of δ 18O level changes which indicate the occurrence of rapid climate transitions. In order to study the effect of climate change on geochemical fluxes we have selected several of these transitions for chemical analysis. At each transition we have measured chloride, nitrate and sulfate concentrations with 5 cm depth resolution. All three anionic species show significant variations which correlate with the measured δ 18O shifts. In general, periods of high δ 18O (warm periods) have lower anion concentrations than adjacent periods of low δ 18O (cold periods). However, the relative concentration shifts are not the same for all species, indicating that the concentration variations cannot be caused only by changes in snow accumulation rate acting on a constant anion flux. In addition to these rapid concentration changes, over the last 40 ka slower, secular variations in baseline concentrations also occurred. Baseline chloride and sulfate concentrations reached maxima near time of maximum ice volume. Baseline nitrate, on the other hand, remained relatively constant until near the end of the glaciation when its concentration rose. If a constant sulfate flux is assumed, the measured sulfate concentrations imply a dependence of snow accumulation rate on δ 18O for the Wisconsin which is similar to that presently observed in Greenland. The sulfate concentrations would then suggest that Wisconsin snowfall rates were, at times, as much as eight times lower than today.

Diffusion-coupled oxidation of atmospheric sulphur dioxide

INCREASING evidence of the toxicity of atmospheric sulphates, together with the upward trend in fossil fuel combustion, have made the rate of formation of atmospheric sulphates one of the most important topics in current air pollution research. Many investigators1 have measured sulphate concentrations in plumes and air sheds, and have usually fitted their data to a linear SO2 oxidation rate expression. The reported values thus obtained for the rate constant vary by up to two orders of magnitude1. Moreover, the linear rate expression is inconsistent with the findings of numerous field investigators2–5, whose data suggest that the oxidation occurs almost exclusively near the SO2 source, rather than uniformly throughout a dispersing atmosphere. The analysis given here deduces that the oxidation may occur almost wholly near the source, and describes the circumstances in which this will happen. It is also shown that in these conditions the oxidation proceeds not to completion but to a fractional asymptotic limit, and that half the final sulphate yield will be obtained in an amount of time whose limits are predictable, constant for any given dispersion pattern, and independent of the magnitude of the rate constants and other chemical parameters.