Sulfur Pool Research Articles

Spatial distribution of organic and pyritic sulfur in surface sediments of eutrophic Jiaozhou Bay, China: Clues to anthropogenic impacts

Anthropogenic perturbations exert important impacts on sulfur geochemistry in marine sediments. In the study, chemical extraction was used to quantify four sulfur pools, i.e., pyrite, humic-acid sulfur (HA-S), fulvic-acid sulfur (FA-S), and residual organic sulfur (ROS), in surface sediments of eutrophic Jiaozhou Bay. Results show that riverine inputs are the main control on organic matter (OM) distribution in the sediments. OM enrichment in the eastern coast is mainly due to discharges of anthropogenic wastes. Spatial coupling of pyrite and FA-S vs. TOC points to the impacts of OM enrichment on formation and preservation of pyrite and FA-S. Poor spatial coupling of HA-S vs. TOC is due to low fractions of diagenetic OS in the pool. ROS is mainly from riverine inputs and anthropogenic OS has been superimposed on this pool. Spatial coupling among TOC, pyrite-S and FA-S is a sensitive indicator of anthropogenic impacts on benthic processes of the bay.

Carbon, Nitrogen and Sulphur Pools and Fluxes in Pyrite Containing Reclaimed Soils (Technosols) at Gabra Village, Bulgaria

The present paper deals with the characteristics of C, N and S pools and fluxes in pyrite containing Technosols located in the area of Chukurovo mine (Gabra village, Bulgaria) in a view of nutrient geochemical transformations in a specific technogenic environment. The role of vegetation and soil microbiota for stabilization of nutrient pools and fluxes has also been taken into consideration. Chemical and microbiological assays are used to analyze the contents and transformation rates of C, N and S. Determination of C:N and C:S ratios filling out the knowleadge of interactions between studied nutrients in pyrite containing environment. Cinnamon forest soils /Endogleyic Luvisols (Siltic, Chromic) are also included in the study in order to provide a basis for comparison. According to the results obtained carbon and nitrogen geochemical pools are interlinked by organic matter in Gleyic Technosols (Siltic). Soil microbiota predominantly manage nitrogen organic and inorganic fluxes and presumably are the main reason for low saturation of organic matter with nitrogen (C:N=11). In young Technosols /Stagnic Technosols (Clayic)/prevail the pools of coal carbon and the scarce fluxes of nitrogen. The average value of C:N is 38 but still the strong correlation between elements exists. Pyrite is the main source of sulfur providing predominance of inorganic pools and fluxes. It conceals the natural interlink beteewn carbon and sulphur organic pools resulting in very low values of C:S (average value of 7.5). Microorganisms responsible for the oxidative turnover of inorganic sulfur compounds prevail and further sustain the acidic pH in young soil solum.

Sulfate migration in a river affected by acid mine drainage from the Dabaoshan mining area, South China

Sulfate, a major component of acid mine drainage (AMD), its migration in an AMD-affected river which located at the Dabaoshan mine area of South China was investigated to pursue the remediation strategy. The existing factors of relatively low pH values of 2.8–3.9, high concentrations of SO42- (∼1940mgL−1) and Fe3+ (∼112mgL−1) facilitated the precipitation of schwertmannite (Fe8O8(OH)6SO4·nH2O) in the upstream river. Geochemical model calculations implied the river waters were supersaturated, creating the potential for precipitation of iron oxyhydroxides. These minerals evolved from schwertmannite to goethite with the increasing pH from 2.8 to 5.8 along the river. The concentration of heavy metals in river waters was great reduced as a result of precipitation effects. The large size of the exchangeable sulfate pool suggested that the sediments had a strong capacity to bind SO42-. The XRD results indicated that schwertmannite was the predominant form of sulfate-bearing mineral phases, which was likely to act as a major sulfate sink by incorporating water-borne sulfate into its internal structure and adsorbing it onto its surface. The small size of reduced sulfur pools and strong oxidative status in the surface sediments further showed that SO42- shifting from water to sediment in form of sulfate reduction was not activated. In short, precipitation of sulfate-rich iron oxyhydroxides and subsequent SO42- adsorption on these minerals as well as water dilution contributed to the attenuation of SO42- along the river waters.

Geochemical and microbiological responses to oxidant introduction into reduced subsurface sediment from the Hanford 300 Area, Washington.

Pliocene-aged reduced lacustrine sediment from below a subsurface redox transition zone at the 300 Area of the Hanford site (southeastern Washington) was used in a study of the geochemical response to introduction of oxygen or nitrate in the presence or absence of microbial activity. The sediments contained large quantities of reduced Fe in the form of Fe(II)-bearing phyllosilicates, together with smaller quantities of siderite and pyrite. A loss of ca. 50% of 0.5 M HCl-extractable Fe(II) [5-10 mmol Fe(II) L(-1)] and detectable generation of sulfate (ca. 0.2 mM, equivalent to 10% of the reduced inorganic sulfur pool) occurred in sterile aerobic reactors. In contrast, no systematic loss of Fe(II) or production of sulfate was observed in any of the other oxidant-amended sediment suspensions. Detectable Fe(II) accumulation and sulfate consumption occurred in non-sterile oxidant-free reactors. Together, these results indicate the potential for heterotrophic carbon metabolism in the reduced sediments, consistent with the proliferation of known heterotrophic taxa (e.g., Pseudomonadaceae, Burkholderiaceae, and Clostridiaceae) inferred from 16S rRNA gene pyrosequencing. Microbial carbon oxidation by heterotrophic communities is likely to play an important role in maintaining the redox boundary in situ, i.e., by modulating the impact of downward oxidant transport on Fe/S redox speciation. Diffusion-reaction simulations of oxygen and nitrate consumption coupled to solid-phase organic carbon oxidation indicate that heterotrophic consumption of oxidants could maintain the redox boundary at its current position over millennial time scales.

Understanding hydrogen sulfide storage: probing conditions for sulfide release from hydrodisulfides.

Hydrogen sulfide (H2S) is an important biological signaling agent that exerts action on numerous (patho)physiological processes. Once generated, H2S can be oxidized to generate reductant-labile sulfane sulfur pools, which include hydrodisulfides/persulfides. Despite the importance of hydrodisulfides in H2S storage and signaling, little is known about the physical properties or chemical reactivity of these compounds. We report here the synthesis, isolation, and characterization (NMR, IR, Raman, HRMS, X-ray) of a small-molecule hydrodisulfide and highlight its reactivity with reductants, nucleophiles, electrophiles, acids, and bases. Our experimental results establish that hydrodisulfides release H2S upon reduction and that deprotonation results in disproportionation to the parent thiol and S0, thus providing a mechanism for transsulfuration in the sulfane sulfur pool.

Ratiometric measurement of hydrogen sulfide and cysteine/homocysteine ratios using a dual-fluorophore fragmentation strategy.

Hydrogen sulfide (H2S) is an integral signaling molecule in biology with complex generation, translocation, and metabolism processes that are intertwined with cellular thiols. Differentiating the complex interplay between H2S and biological thiols, however, remains challenging due to the difficulty of monitoring H2S and thiol levels simultaneously in complex redox environments. As a step toward unraveling the complexities of H2S and thiols in sulfur redox homeostasis, we present a dual-fluorophore fragmentation strategy that allows for the ratiometric determination of relative H2S and cysteine (Cys) or homocysteine (Hcy) concentrations, two important metabolites in H2S biosynthesis. The key design principle is based on a nitrobenzofurazan-coumarin (NBD-Coum) construct, which fragments into spectroscopically differentiable products upon nucleophilic aromatic substitution with either H2S or Cys/Hcy. Measurement of the ratio of fluorescence intensities from coumarin and the NBD-Cys or NBD-Hcy adducts generates a sigmoidal response with a dynamic range of 3 orders of magnitude. The developed scaffold displays a rapid response (<1 min) and is selective for sulfhydryl-containing nucleophiles over other reactive sulfur, oxygen, and nitrogen species, including alcohol- and amine-functionalized amino acids, polyatomic anionic sulfur species, NO, and HNO. Additionally, NBD-Coum is demonstrated to differentiate and report on different oxidative stress stimuli in simulated sulfur pools containing H2S, Cys, and cystine.

δ34S and Δ33S records of Paleozoic seawater sulfate based on the analysis of carbonate associated sulfate

This study updates the δ34S and Δ33S temporal records of Paleozoic and early Mesozoic seawater sulfate using analysis of carbonate associated sulfate of biogenic and whole rock carbonate. The time resolution of carbonate samples studied here is on the order of millions of years which is longer than the timescale for homogenization of seawater sulfate–sulfur (one tenth of a million years), but is comparable to the timescale for isotope evolution of sulfate in the oceans. This δ34S record confirms the long-term decreasing trend that is discernible over the 250 million year timescale of sampling, and the Δ33S record of seawater sulfate for the Paleozoic is consistent with an average value of −0.002±0.004‰ (2σ, 540–251 Ma) that is distinct from the positive Δ33S observed today and inferred for the rest of the Cenozoic. Both δ34S and Δ33S records of seawater sulfate suggest the presence of shorter-timescale variations that occur on timescales of tens of millions of years, arguably driven by changes in intensity of sulfide oxidation in cycling of sulfur and/or by rapid changes in sulfur influx to the oceans and its associated sulfur isotopes. The Permian–Triassic boundary marks a transition in co-trajectories of δ34S and Δ33S from in-phase to anti-phase. The biogeochemical forcing that causes this is unclear.This newly calibrated record remains consistent with an earlier assertion (Wu et al., 2010) that the sulfur isotope fractionation (Δ34SSW-PY) between oceanic sulfate (δ34SSW) and coeval sedimentary pyrite (δ34SPY) was smaller during the Paleozoic than in the Cenozoic, and reached lowest values during the Carboniferous. The δ34SIN and Δ33SIN estimates of influx sulfur to the oceans afforded by the isotope mass balance model for each geologic period throughout the Paleozoic reveal a change from higher positive values of δ34SIN (more negative values of Δ33SIN, approximately −0.030‰) to lower positive values of δ34SIN (slightly negative values of Δ33SIN, approximately −0.003‰). This change is interpreted to reflect the evolution of the Earth surface sulfur pool and the rapid recycling of newly formed evaporite sulfate minerals, as arguably supported by our estimates of integrated erosion rates over geologic time for pyrite and evaporite ((6.1–6.4)×10−9 a−1, and (7.7–7.8)×10−9 a−1, respectively).

S9-1 Sulfurtransferases and their role in hydrogen sulfide generation

The rhodanese superfamily (EC 2.8.1.x) includes tandem-domain thiosulfate:cyanide sulfurtransferase (TST, EC 2.8.1.1) and the strictly related 3-mercaptopyruvate:cyanide sulfurtransferase (MPST, EC 2.8.1.2). TST is the key enzyme, in the active center of which the persulfide group is created. The highly reactive sulfane sulfur atom of this group can be transferred to a substrate, e.g., cyanide detoxification, or can be passed to another protein acceptor participating in different cellular processes, e.g., biosynthesis of cofactors or thionucleosides. MPST transfers the sulfur atom from mercaptopyruvate, a product of cysteine transamination, to acceptors, such as cyanide (forming thiocyanate) or sulfite (forming thiosulfate – a sulfane sulfur-containing compound). Several metabolic reactions are known to generate sulfane sulfur in vitro , but their relative importance in vivo is not yet known. Current knowledge about sulfur donors assumes that the primary source of sulfane sulfur in eukaryotic cells relies on l -cysteine desulfuration pathway. Gamma-cystathionase (CTH, EC 4.4.1.1), an enzyme on the pathway, participates in endogenous production of H 2 S from l -cysteine. A product of CTH reaction, thiocystine, has been suggested to serve as the sulfane sulfur donor substrate for rhodanese. The potential role of the sulfane sulfur pool as an H 2 S reservoir and factors influencing the activity of sulfane sulfur-generating enzymes are under debate. The current study demonstrates that the MPST-dependent mitochondrial H 2 S-producing pathway is affected by oxidative stress, what may attenuate the production of H 2 S, and leads to various pathophysiological conditions. The intriguing problem is to identify possible sulfane sulfur donor(s) and/or acceptor(s), and to determine the regulatory role of sulfur in cellular metabolism.

SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle.

Many aspects of Earth's early sulfur cycle, from the origin of mass-anomalous fractionations to the degree of biological participation, remain poorly understood--in part due to complications from postdepositional diagenetic and metamorphic processes. Using a combination of scanning high-resolution magnetic superconducting quantum interference device (SQUID) microscopy and secondary ion mass spectrometry (SIMS) of sulfur isotopes ((32)S, (33)S, and (34)S), we examined drill core samples from slope and basinal environments adjacent to a major Late Archean (∼2.6-2.5 Ga) marine carbonate platform from South Africa. Coupled with petrography, these techniques can untangle the complex history of mineralization in samples containing diverse sulfur-bearing phases. We focused on pyrite nodules, precipitated in shallow sediments. These textures record systematic spatial differences in both mass-dependent and mass-anomalous sulfur-isotopic composition over length scales of even a few hundred microns. Petrography and magnetic imaging demonstrate that mass-anomalous fractionations were acquired before burial and compaction, but also show evidence of postdepositional alteration 500 million y after deposition. Using magnetic imaging to screen for primary phases, we observed large spatial gradients in Δ(33)S (>4‰) in nodules, pointing to substantial environmental heterogeneity and dynamic mixing of sulfur pools on geologically rapid timescales. In other nodules, large systematic radial δ(34)S gradients (>20‰) were observed, from low values near their centers increasing to high values near their rims. These fractionations support hypotheses that microbial sulfate reduction was an important metabolism in organic-rich Archean environments--even in an Archean ocean basin dominated by iron chemistry.

Humic sulfur in eutrophic bay sediments: Characterization by sulfur stable isotopes and K-edge XANES spectroscopy

Organic sulfur (OS) is an important sedimentary sulfur pool in marine sediments and chemical extractions are often used for quantification of various OS pools, however, OS sources and mechanisms of OS formation are not well understood. In this study, sulfur stable isotope and sulfur X-ray absorption near edge structure (XANES) spectroscopy were combined to investigate the sources and speciation of humic-acid sulfur (HA-S) and fulvic-acid sulfur (FA-S) in sediments of eutrophic Jiaozhou Bay. Whilst there may be some indication that eutrophication has enhanced FA-S burial in the sediment, this has not substantially modified the characteristically low humic sulfur (i.e., HA-S + FA-S) contents of the sediments. Sulfur isotopic compositions indicate that both HA-S and FA-S are mixtures of diagenetic and biosynthetic OS in origin; HA-S is dominated by biosynthetic sulfur and FA-S by diagenetic source. Sulfur isotopic compositions and contents of pyrite and diagenetic OS indicate that inhibition of sulfurization by pyrite formation, if any, appears insignificant. XANES analysis suggests that the contents of high oxidized OS (i.e., sulfones and ester-sulfates) and strongly reduced OS species are comparable in the HA-S, whereas the FA-S is dominated by strongly reduced OS as a result of enhanced sulfurization.

Polysulfides as intermediates in the oxidation of sulfide to sulfate by Beggiatoa spp.

Zero-valent sulfur is a key intermediate in the microbial oxidation of sulfide to sulfate. Many sulfide-oxidizing bacteria produce and store large amounts of sulfur intra- or extracellularly. It is still not understood how the stored sulfur is metabolized, as the most stable form of S(0) under standard biological conditions, orthorhombic α-sulfur, is most likely inaccessible to bacterial enzymes. Here we analyzed the speciation of sulfur in single cells of living sulfide-oxidizing bacteria via Raman spectroscopy. Our results showed that under various ecological and physiological conditions, all three investigated Beggiatoa strains stored sulfur as a combination of cyclooctasulfur (S8) and inorganic polysulfides (Sn(2-)). Linear sulfur chains were detected during both the oxidation and reduction of stored sulfur, suggesting that Sn(2-) species represent a universal pool of bioavailable sulfur. Formation of polysulfides due to the cleavage of sulfur rings could occur biologically by thiol-containing enzymes or chemically by the strong nucleophile HS(-) as Beggiatoa migrates vertically between oxic and sulfidic zones in the environment. Most Beggiatoa spp. thus far studied can oxidize sulfur further to sulfate. Our results suggest that the ratio of produced sulfur and sulfate varies depending on the sulfide flux. Almost all of the sulfide was oxidized directly to sulfate under low-sulfide-flux conditions, whereas only 50% was oxidized to sulfate under high-sulfide-flux conditions leading to S(0) deposition. With Raman spectroscopy we could show that sulfate accumulated in Beggiatoa filaments, reaching intracellular concentrations of 0.72 to 1.73 M.

Roles of sulfate adsorption and base cation supply in controlling the chemical response of streams of western Virginia to reduced acid deposition

Decreased acid deposition over recent decades has led to reductions in streamwater acidity on a widespread basis throughout the U.S. and Europe. A notable exception has been the southern Appala- chian Mountains of the southeastern U.S., where declines in acid deposition have not translated into similar trends in stream chemistry in these watersheds with highly-weathered soils. To better characterize this observed behavior, streamwater samples collected at 64 sites in western Virginia on a quarterly basis from 1987 to 2011 were analyzed for chemical properties. Individual watershed response was strongly influ- enced by the dominant underlying bedrock, which affected sulfate (SO 2 ) adsorption and base cation supply. Overall, pH increased at a majority of sites across all bedrock types. However, acid neutralizing capacity (ANC) decreased at most sites underlain by base-poor bedrock, suggesting the susceptibility to episodic acidification remains a serious threat to these streams. The declines in ANC were more closely related the depletion of base cations (Ca 2? ,M g 2? ,K ? , and Na ? ) rather than increased SO 2 concentration. Sites with higher relative SO 2 adsorption exhibited little change in ANC. A mass balance analysis of sulfur at a base-poor watershed revealed that exports have recently surpassed inputs for the first time within the several-decade period of record. This pattern appears likely to continue, and if sustained, the depletion of the stored pool of sulfur signifies an important precursor for further improvements in streamwater acidity in the region.

Eelgrass fairy rings: sulfide as inhibiting agent

Distinct ‘fairy rings’ consisting of narrow fringes of eelgrass (Zostera marina L.) expand radially over a bottom of chalk plates outside the calcium carbonate cliffs of the island of Mon, Denmark. We conducted a survey to evaluate possible explanations for the formation of the rings and, more specifically, for the apparent die-off of eelgrass shoots on the inner side of the rings. The fairy rings were up to 15 m in diameter consisting of 0.3- to 1-m-wide zones of sea grass shoots at densities of up to 1,200 shoots m−2 and rooted in an up to 10-cm-thick sediment layer. On the outer side, shoots expanded over the bare chalk plates. On the inner side, shoots were smaller, had lower absolute and specific leaf growth, shoot density was lower and the sediment eroded leaving the bare chalk with scattered boulders behind. Sediment organic matter and nutrients and tissue nutrient contents were not different among positions. Sediment pools of acid volatile sulfides and chromium-reducible sulfur increased from outer to the middle positions of the rings, and so did total sulfur content of eelgrass tissues, while tissue δ34S isotope ratios, regardless of position in the fringes, were low reflecting substantial invasion of sulfide from the sediment. Neither the clonal growth pattern of eelgrass, sediment burial of shoots, hydrodynamic forcing nor nutrient limitation could explain the ring-shaped pattern. We conclude that the most likely explanation must be found in invasion of eelgrass shoots by toxic sulfide accumulating in the sediment due to low iron availability in the carbonate-rich environment.

Speciation and stable isotopic compositions of humic sulfur in mud sediment of the East China Sea: Constraints on origins and pathways of organic sulfur formation

Humic sulfur is commonly the most important pool of organic sulfur (OS) in marine sediments and also important for the budget of total sedimentary sulfur. In this study, contents and stable sulfur isotopic compositions of hydrolyzable organic sulfur (HYOS), humic acid sulfur (HA-S) and fulvic acid sulfur (FA-S) in one core collected from the East China Sea (ECS) inner shelf were determined to investigate the sources and pathways of OS formation and to compare diagenetic geochemistry of HA-S and FA-S. HYOS in the core is essentially biological in origin and diagenetically refractory, with a fairly low fraction of labile sulfur bearing biomolecules. HA-S in the core is largely terrigenous residual bio-OS, while FA-S is a mixture of marine bio- and diagenetic OS (diag-OS), with the diag-OS fractions between 44% and 71%. Both HA-S and FA-S contents in the core are at the lower ends of the corresponding values reported in the literature. The HA in the sediments is diagenetically inert, subject to neither significant diagenetic sulfurization nor bio-OS mineralization loss, while the FA is reactive, prone to both sulfurization and decomposition loss of diagenetically bound OS. Low contents of humic S [i.e., ∑(HA-S+FA-S)] in the core may suggest that OS burial has only minor contribution to the burial of total sulfur in the sediments due to generally low OM sulfurization.

Diel patterns of oceanic dimethylsulfide (DMS) cycling: Microbial and physical drivers

AbstractDimethylsulfide (DMS) is a biogenic gas with potential climatic effects, and its marine emission depends on the interplay between microbial activity and physical forcing in the oceanic upper mixed layer. We investigated the diel cycling patterns of DMS and its precursor dimethylsulfoniopropionate (DMSP) in four experiments (28 to 48 h long) performed in mesotrophic to ultraoligotrophic Mediterranean and Sargasso Sea waters. Samples taken every 4 or 6 h were analyzed for dimethylated sulfur pools and incubated to measure DMS and DMSP cycling rates, as well as primary and bacterial production. In all four experiments, DMS budgets showed pronounced day versus night variability. In the three summer experiments, gross community DMS production (GPDMS) increased by twofold to threefold from nighttime to daytime, peaking 0–4 h after solar noon. This excess GPDMS was balanced by higher photochemical and microbial sinks during the day, effectively buffering DMS concentrations. In the only winter experiment, GPDMS exhibited opposed temporal dynamics and peaked at nighttime in parallel to total DMSP consumption. Community DMSP to DMS conversion yields were generally &lt;10% throughout the winter experiment and at night in summer, and increased to &gt;15% (even &gt;50%) during the day in summer, presumably due to phytoplankton radiative stress. Our data suggest that (1) diel variability should be taken into account in process studies, diagnostic, and prognostic models of DMS cycling and (2) the community DMS yield is a key variable that defines characteristic DMS cycling regimes.

Production, preservation, and biological processing of mass-independent sulfur isotope fractionation in the Archean surface environment

Mass-independent fractionation of sulfur isotopes (S MIF) in Archean and Paleoproterozoic rocks provides strong evidence for an anoxic atmosphere before ~2,400 Ma. However, the origin of this isotopic anomaly remains unclear, as does the identity of the molecules that carried it from the atmosphere to Earth's surface. Irrespective of the origin of S MIF, processes in the biogeochemical sulfur cycle modify the primary signal and strongly influence the S MIF preserved and observed in the geological record. Here, a detailed model of the marine sulfur cycle is used to propagate and distribute atmospherically derived S MIF from its delivery to the ocean to its preservation in the sediment. Bulk pyrite in most sediments carries weak S MIF because of microbial reduction of most sulfur compounds to form isotopically homogeneous sulfide. Locally, differential incorporation of sulfur compounds into pyrite leads to preservation of S MIF, which is predicted to be most highly variable in nonmarine and shallow-water settings. The Archean ocean is efficient in diluting primary atmospheric S MIF in the marine pools of sulfate and elemental sulfur with inputs from SO2 and H2S, respectively. Preservation of S MIF with the observed range of magnitudes requires the S MIF production mechanism to be moderately fractionating ( 20-40‰). Constraints from the marine sulfur cycle allow that either elemental sulfur or organosulfur compounds (or both) carried S MIF to the surface, with opposite sign to S MIF in SO2 and H2SO4. Optimal progress requires observations from nonmarine and shallow-water environments and experimental constraints on the reaction of photoexcited SO2 with atmospheric hydrocarbons.

Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes.

It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four sulfur isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.

Analytical measurement of discrete hydrogen sulfide pools in biological specimens

Hydrogen sulfide (H2S) is a ubiquitous gaseous signaling molecule that plays a vital role in numerous cellular functions and has become the focus of many research endeavors, including pharmacotherapeutic manipulation. Among the challenges facing the field is the accurate measurement of biologically active H2S. We have recently reported that the typically used methylene blue method and its associated results are invalid and do not measure bona fide H2S. The complexity of analytical H2S measurement reflects the fact that hydrogen sulfide is a volatile gas and exists in the body in various forms, including a free form, an acid-labile pool, and bound as sulfane sulfur. Here we describe a new protocol to discretely measure specific H2S pools using the monobromobimane method coupled with RP-HPLC. This new protocol involves selective liberation, trapping, and derivatization of H2S. Acid-labile H2S is released by incubating the sample in an acidic solution (pH 2.6) of 100mM phosphate buffer with 0.1mM diethylenetriaminepentaacetic acid (DTPA), in an enclosed system to contain volatilized H2S. Volatilized H2S is then trapped in 100mM Tris–HCl (pH 9.5, 0.1mM DTPA) and then reacted with excess monobromobimane. In a separate aliquot, the contribution of the bound sulfane sulfur pool was measured by incubating the sample with 1mM TCEP (tris(2-carboxyethyl)phosphine hydrochloride), a reducing agent, to reduce disulfide bonds, in 100mM phosphate buffer (pH 2.6, 0.1mM DTPA), and H2S measurement was performed in a manner analogous to the one described above. The acid-labile pool was determined by subtracting the free hydrogen sulfide value from the value obtained by the acid-liberation protocol. The bound sulfane sulfur pool was determined by subtracting the H2S measurement from the acid-liberation protocol alone compared to that of TCEP plus acidic conditions. In summary, our new method allows very sensitive and accurate measurement of the three primary biological pools of H2S, including free, acid-labile, and bound sulfane sulfur, in various biological specimens.

Recovery of sulfate saturated soils in the Plynlimon catchments, mid-Wales following reductions in atmospheric S inputs from the 1980s to 2011

Sulfate adsorption capacity of B-horizons of base-poor, predominantly stagnopodzol, soils from the Plynlimon catchments, mid-Wales was determined by combination of laboratory adsorption and desorption isotherms. Results show that sulfate adsorption capacity of a range of stagnopodzol (Histic-stagno-podzol (Leptic), WRB), brown podzolic soil (Histic-umbrisol (Leptic), WRB) and stagnohumic gley (Histic-stagno-gleysol, WRB) B-horizons was positively related to the amounts of extractable (pyrophosphate and oxalate) Fe + Al, with the stagnopodzol and brown podzolic soil Bs horizon having the largest adsorption capacity and stagnohumic gley Bg horizon the smallest adsorption capacity. Results show that dissolved organic carbon (DOC) has a negative but limited effect on sulfate adsorption in these soils. Results obtained from a set of historical soil samples revealed that the grassland brown podzolic soil Bs horizon and afforested stagnopodzol Bs horizon were highly saturated with sulfate in the 1980s, at 63% and 89% respectively, whereas data from some recently sampled soil from two sites revisited in 2010-11 indicates that percentage sulfate adsorption saturation has since fallen substantially, to 41% and 50% respectively. Between 1984 and 2009 the annual rainfall-weighted mean excess SO(4)-S concentration in bulk precipitation declined linearly from 0.37 mg S l(-1) to 0.17 mg S l(-1). Over the same period, flow weighted annual mean stream water SO(4)-S concentrations decreased approximately linearly from 1.47 mg S l(-1) to 0.97 mg S l(-1) in the plantation afforested Hafren catchment compared to a drop from 1.25 to 0.69 mg S l(-1) in the adjacent moorland catchment of the Afon Gwy. In flux terms, the mean decrease in annual stream water SO(4)-S flux has been approximately 0.4 kg S ha(-1) yr(-1), whilst the recovery in stream water quality in the Afon Cyff grassland catchment has been partly offset by loss of SO(4)-S by desorption from the soil sulfur pool of approximately 0.2 kg S ha(-1) yr(-1).

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

Sources and processes affecting the sulphur cycle in the Canyon Creek watershed in Alberta (Canada) were investigated. The catchment is important for water supply and recreational activities and is also a source of oil and natural gas. Water was collected from 10 locations along an 8 km stretch of Canyon Creek including three so-called sulphur pools, followed by the chemical and isotopic analyses on water and its major dissolved species. The δ2H and δ18O values of the water plotted near the regional meteoric water line, indicating a meteoric origin of the water and no contribution from deeper formation waters. Calcium, magnesium and bicarbonate were the dominant ions in the upstream portion of the watershed, whereas sulphate was the dominant anion in the water from the three sulphur pools. The isotopic composition of sulphate (δ34S and δ18O) revealed three major sulphate sources with distinct isotopic compositions throughout the catchment: (1) a combination of sulphate from soils and sulphide oxidation in the bedrock in the upper reaches of Canyon Creek; (2) sulphide oxidation in pyrite-rich shales in the lower reaches of Canyon Creek and (3) dissolution of Devonian anhydrite constituting the major sulphate source for the three sulphur pools in the central portion of the watershed. The presence of H2S in the sulphur pools with δ34S values ∼30 ‰ lower than those of sulphate further indicated the occurrence of bacterial (dissimilatory) sulphate reduction. This case study reveals that δ34S values of surface water systems can vary by more than 20 ‰ over short geographic distances and that isotope analyses are an effective tool to identify sources and processes that govern the sulphur cycle in watersheds.