Aquatic Geochemistry最新文献

The aim of this research was to investigate the competition between methanogens and sulfate-reducing bacteria in hypersaline environments. Samples of photosynthetic microbial mats, both soft mats (salinities of 55–126?ppt) and gypsum-hosted endoevaporite mats (salinities of 77–320?ppt), were obtained from hypersaline environments in California, USA, Mexico and Chile. Methane production was determined from the increase in headspace methane concentration within incubation vials containing mat samples. At the end of the incubation period, the δ¹³C values of produced methane were measured. Soft microbial mat vials containing molybdate, a specific inhibitor of bacterial sulfate reduction, exhibited dramatically higher methane production rates and higher (enriched in ¹³C) methane δ¹³C values than the controls. This suggests that the inhibition of sulfate reduction allowed the methanogens at these sites to use the competitive substrates (H₂ and/or acetate) made available. Further, the higher δ¹³C values of the produced methane suggest that substrates (both competitive and non-competitive) were used to near completion. At the endoevaporite sites, which have much higher salinities than the soft mat sites, methane production was not significantly different and the methane δ¹³C values either remained the same or decreased (depleted in ¹³C) with added molybdate. We suggest that substrate availability increased enough to allow for somewhat greater isotopic fractionation resulting in the lower methane δ¹³C values that were observed, but not enough to significantly increase measured production rates. Where no changes in either methane production rates or δ¹³C values occurred, we hypothesize that salinity itself was inhibiting sulfate reduction and thus controlling microbe populations and rates of metabolism.

Reactions between cyanide and compounds, which contain S–S bonds, in aqueous media result in formation of thiocyanate. In this work, we studied the kinetics of reactions of thiosulfate with free cyanide and its complexes under environmental conditions. Rates of reactions between cyanide species and thiosulfate decrease in the following order: CN^??>?HCN?>?[Fe(CN)₆]^3??>?[Fe(CN)₆]^4?. However, at neutral and slightly acidic pH range, reaction of thiosulfate with iron-cyanide complexes outcompetes its reaction with free cyanide, which exists in equilibrium with complexed cyanide. At environmentally relevant conditions, the characteristic time of reaction between free cyanide and thiosulfate was found to be tens of thousands of years, while for iron-cyanide complexes it was found to be hundreds to millions of years. Examples of application of kinetic parameters for calculation of rates of cyanide consumption in industrial (coke oven wastewater) and non-polluted natural aquatic system (Delaware Great Marsh) are provided.

We have studied iron (Fe)-isotope signals in particles (>?0.22?μm) and the dissolved phase (<?0.22?μm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the R?ne and the Kalix, are enriched in Fe and organic carbon (up to 29?μmol/L and up to 730?μmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ⁵⁶Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH.

The nature of groundwater recharge along the mountain front (MF) and riparian zone (RZ) was discerned by multiple tools involving rain/water level relationship, geophysical of subsurface, seasonal hydrochemistry and environmental isotopic signatures. The proposed study has been carried out in Courtallam Hills, the north-western part of Tirunelveli District, South India. The study area is a hilly terrain with narrow valleys endowed with steep slopes. The relationship between water-level fluctuation and precipitation were evaluated by observing daily water level in 8-h interval at three piezometer zones and regular rainfall data.?It was inferred that the RZ played a role in storage zone and gets recharged from mountain block (MB) and lateral flow. The seasonal geochemistry of the groundwater was studied to determine the sources of recharge in MF and RZ. Geostatistical treatment of factor analysis revealed that weathering was the dominant recharge process along the foothill. The geophysical studies reveal good quality of groundwater observed in the northern part along with low conductance and high resistivity. The increased level of groundwater conductivity and lower resistivity was noted in southern part of the study area due to the irrigation activities. The isotopic tracers range from ??2.5 to ??12.6‰ for δ¹⁸O and from ??91.2 to ??15.5‰ for δ²H. Moreover, the groundwater recharge was evaluated by source of rainfall moisture. High-altitude recharge from MB along the MF was clearly indicated by depleted isotopic content of the water samples. It was also supported by hydrogeochemical and statistical evidences, showing that rainfall over both MB and MF zones provided the recharge to foothill aquifers, while the RZ zone was mainly recharged by local precipitation with less contribution from regional flows.

Large volumes of seawater were sampled in the Gulf of Trieste (northern Adriatic Sea) in order to study the interactions between colloidal organic matter (COM) and metal(loid)s (Me) in coastal waters. COM (>?5?kDa) was isolated by ultrafiltration and characterized using ¹H NMR spectroscopy and elemental C_org. and N_tot. analyses. COM in the gulf represents about one quarter of the dissolved organic carbon (DOC), and according to ¹H NMR analysis, it is composed of polysaccharides (30–45%), lipids (30–55%), proteins and carboxyl-rich alicyclic molecules (CRAM) (15–20%), and humics (<?1%). An accumulation of COM was observed in the late spring–early summer. The polysaccharide and lipid fractions increased up to twofold and the protein fraction decreased, reflected in a higher C_org./N_tot. (28, molar) ratio. Higher concentrations of humics were observed due to local freshwater discharges in spring. COM from the Isonzo/So?a River differed from the marine COM exhibiting higher protein/CRAM and higher humic contents. COM from the Isonzo/So?a mouth at salinities 16–33 was compositionally similar to marine COM. Analysis of Me, performed by ICP-MS and CVAFS (Hg), showed that Hg (nearly 100%), Cu (20%), Cr (10%), and Se (10%) have the highest Me affinity to colloids. Similar to COM, Hg and Cu rapidly increased till summer due to their sequestration in accumulated COM (transfer to particulate phase). The observed Me/C_org. ratios (Co, Cd, Hg?<?U, Cr, Ni, Mn?<?As, Zn, Cu, V?<?Se, Al, Fe) differ somewhat from those of the Irving–Williams series and can be explained by the composition of COM and variable background concentrations of studied Me in the northern Adriatic. Data from the salinity gradient in the metal-contaminated (especially Hg, Pb, Zn) Isonzo/So?a mouth showed flocculation of Al and Ba and desorption of V, Co, As, Se, Cs, U, and Hg, from the riverine particles with increasing ionic strength, while Fe, Mn, Cu, Cr, Ni, Zn, Cd, and Pb did not correlate with salinity.

Seagrass ecosystems have a potential role in climate change mitigation due to their ability to store high amount of carbon, particularly in the sediment. Studying the factors and mechanisms responsible for this storing capacity is essential to understand seagrass carbon sink function. Therefore, in this study, we identified the sources of organic carbon (C_org) in seagrass sediments and the implication to C_org stocks from four islands in the Spermonde Islands that located at different zones. We used the Bayesian stable isotope mixing model?to estimate the proportional contribution of different sources to sediment carbon. Seagrass meadows that located in adjacent to high anthropogenic activities (deforestation and aquacultures) with direct exposure to wave actions, such as on the Bauluang Island, accumulated organic carbon that derived from multiple sources, where phytoplankton contributed the highest, while on the other three islands that are relatively protected from wave actions, the highest contribution (~?75%) was from autochthonous production (seagrass-derived). Sediment C_org stocks vary spatially, ranging from 11.9 to 32.1?Mg C ha^?1 (based on the obtained depth of 20–55?cm), or 40.5 to 83.5?Mg C ha^?1 if extrapolated to 1?m depth. The variability of sediment properties and C_org stocks in this study is not solely determined by the geographical differences (inshore, nearshore and offshore islands), but also influenced by other local factors such as hydrodynamics that control the distribution of carbon sources, anthropogenic pressures and species composition. These factors should be taken into account when developing coastal management strategies, as efforts are being undertaken to include coastal ecosystems (including seagrass ecosystems) on the National Green House Gasses Reduction Strategy.

Sweet Springs Creek, located in the Valley and Ridge Province of the Appalachian Mountains in southeastern West Virginia and southwestern Virginia, USA, contains major fluvial tufa formations at the sites of localized fractures and faults. Sweet Springs Creek receives input from higher-temperature thermal springs of lower pH and higher sulfate concentration that differ significantly in chemical composition due to differences in the underlying geology. In this study, theoretical rates of tufa accumulation were compared with those measured on travertine tiles left in situ for 30?days during periods of high and low stream flow above and below the sites of major fluvial tufa formations. Consistent with the chemistry of the spring waters, observed and predicted tufa accumulation rates in the stream were low compared to others reported worldwide. Tufa formation rate estimates were consistently higher during seasonal conditions of low flow, warm temperatures, and higher pH that occurred in late summer, but net annual accumulation may still be zero or less due to formation erosion during periodic flooding events. Computer tomography analysis determined that the natural porosity of travertine tiles results in a total surface area 32% greater than that calculated based solely on tile dimensions, which may overestimate initial tufa accumulation rates in situ. Measured rates of carbonate deposition on travertine tiles were 1.6–82?× lower than rates predicted based on theoretical models, consistent with the hypothesis of rate reduction due to variable diffusional boundary layer limitations and variability in stream hydrology. The generation of loose, platy, and unconsolidated precipitate on tiles under geochemical conditions predicted to be the greatest for optimal tufa formation suggested that the precipitation of particulate calcite in the stream system may predominantly result in the formation of unconsolidated marl deposits.

The Manuguru geothermal area, located in the Khammam district of Telangana state, India, is one of the least explored medium-enthalpy geothermal systems in India. In this study, subsurface reservoir temperature was estimated by applying various methodologies such as chemical geothermometry, multicomponent geothermometry and mixing models. Chemical geothermometers provided wide range in temperature estimation, and most of them (Na–K, Na–K–Ca, Mg-corrected Na–K–Ca) were found to be unsuitable for predicting reservoir temperature due to the absence of attainment of equilibrium between suitable mineral pairs. The temperature range estimated from the quartz geothermometers varied from 72 to 120?°C which matched closely with values obtained from K–Mg geothermometers. To overcome this problem and to better constrain the reservoir temperature, multicomponent solute geothermometry modelling was carried out by applying the GeoT computer code. Fluid reconstruction was done after taking into account both the degassing and mixing phenomena. GeoT modelling of the reconstructed fluid provided excellent clustering of the minerals. From the GeoT modelling study, it was found that minerals like quartz, chalcedony, calcite, etc., attained simultaneous equilibrium with thermal waters in the temperature range of 130?±?10?°C, which can be taken as the most probable reservoir temperature. The subsurface temperature (137?°C) obtained from the mixing model further validated the results obtained from multicomponent geothermometry. This integrated multicomponent method and the simulation program used in this study take into account various processes (i.e. mixing, degassing, non-attainment of equilibrium, etc.) which affect the composition of the thermal fluids during its ascent to the surface. The statistical approach of ‘best clustering minerals’ used in this model helps to overcome the problems encountered in applying cation or single-component geothermometers in the medium-enthalpy geothermal systems.

The reduced sulfur species, sulfide, elemental and thiosulfate were considered in the thermal waters of Jiangxi Province for the first time. It is shown that the sulfur speciation content significantly varies and depends on the pH values. The major part of reduced sulfur refers to sulfide species in the nitric thermal waters, to elemental—in the carbon dioxide thermal waters. The presence of both reduced and oxidized sulfur speciation indicates the possibility of sulfide minerals hydrolysis and disproportionation of the product of this reaction (SO₂) with the participation of hot water with the formation of elemental and sulfate sulfur. The isotopic composition of dissolved sulfate and sulfide sulfur speciation has shown that the process of bacterial reduction proceeds in the thermal waters, accompanied by accumulation of relatively heavy sulfur isotope in sulfates. Simultaneously with reduction, the oxidation of both sulfide minerals and newly formed hydrosulfide proceeds with formation of elemental, thiosulfates and also sulfates in the discharge zone was proceeded. It is shown that the process of sulfide oxidation mostly occurs in carbon dioxide thermal waters. Therefore, the elemental sulfur is predominant in carbon dioxide waters. The oxidation process is less significant in the nitric thermal waters, whereby the concentrations of sulfide ion are higher than sulfates. The ambiguous effect of sulfate reduction on the hydrogeochemical environment of the thermal waters is confirmed by the differing value of the carbon isotope ratio of HCO₃^? in the considered waters. The obtained isotopic composition data ³⁴δS(SO₄^2?) indicate host rocks as a source of sulfates in the thermal waters of Jiangxi Province.

The Manuguru geothermal area, situated in the Telangana state, is one of the least explored geothermal fields in India. In this study, the chemical characteristics of the groundwater (thermal and non-thermal waters) are investigated to elucidate the source of the solutes dissolved in the water and to determine the approximate residence time of the thermal waters. The major hydrogeochemical processes controlling the groundwater geochemistry have been deciphered using multivariate statistical analysis, conventional graphical plots and geochemical modelling (PHREEQC). Geochemically different groundwater clusters (bicarbonate type, bicarbonate–chloride type and chloride type) can clearly be identified from the chemometric analysis, i.e. PCA and HCA. Thermal waters are mostly Na–HCO₃ type having low EC and TDS compared to non-thermal groundwaters. Silicate weathering and ion exchange mainly contribute to the dissolved ion budget in the groundwater of the study area. The carbon isotopic composition of DIC (δ¹³C) points to silicate weathering with soil CO₂ coming from C₃ type of plants. Stable isotopes (δ¹⁸O, δ²H) data confirm the meteoric origin of the thermal waters with no oxygen-18 shift. The low tritium values of the thermal water samples reveal the long circulation time (>?50?years) of the recharging waters. Radiocarbon dating (¹⁴C) shows that the approximate residence time of the thermal waters ranges from 9952 to 18,663?year BP (before present).