Aquatic Geochemistry最新文献

Ultra-trace (<?1?ng?g^?1) rare earth elements and yttrium (REE?+?Y) and high field strength element (HFSE) geochemistry of freshwater can constrain element sources, aqueous processes in hydrologic catchments, and the signature of dissolved terrestrial fluxes to the oceans. This study details an adapted method capable of quantifying?≥?38 elements (including all REE?+?Y, Nb, Ta, Zr, Hf, Mo, W, Th, U) with minimal sample preparation in natural water aliquots as low as?≤?2?mL. The method precision and accuracy are demonstrated using measurement of the National Research Council – Conseil national de recherches Canada (NRC-CNRC) river water certified reference material (CRM) SLRS-6 sampled from the Ottawa River (OR). Data from SLRS CRM are compared to those of new, filtered (<?0.45?μm) stream water samples from the central Ottawa River basin (ORB), and discussed in terms of processes and geochemical signatures inherited from the highly evolved igneous/metamorphic Archean and Proterozoic bedrock in the catchment. The ORB waters have significantly LREE?>?HREE-enriched REE?+?Y patterns, small natural positive Y and Gd anomalies, and negative Eu and Ce anomalies. These REE?+?Y features are coherent downstream in the OR apart from amplification of Eu and Ce anomalies during REE removal/dilution. The OR samples capture a downstream decrease in sparingly soluble HFSE (Th, Nb, Ta, Zr, Hf), presumably related to their colloid-particulate removal from the dissolved load, accompanied by crustal Zr/Hf (32.5?±?5.1) and supercrustal Nb/Ta (25.1?±?7.7) ratios. Subcrustal Th/U (0.17–0.96) and supercrustal Mo/W (12.0–74.5) ratios in all ORB waters indicate preferential release and aqueous solubility of U?>?Th and Mo?>?W, with the latter attributed primarily to preferential W adsorption on soil or upstream aquatic (oxy)(hydr)oxide surfaces.

Chemical weathering in the Himalayan river basins is among the highest in the world and has received vast research attention related to past climate change. Many early estimates of chemical weathering are based on a small number of water property data that ignore those spatial and seasonal variations. Therefore, this study analyzed spatial and seasonal variations in chemical weathering in the Mekong Basin, where the geology, climate, and hydrologic cycle of the basin vary significantly from the lower to upper reaches and from dry to rainy seasons. We separately estimated the origins of dissolved elements and potential CO₂ consumption rates using the numerous chemical compositions of river water throughout the entire basin and in both seasons. The CO₂ consumption rate in the rainy season is three to five times that in the dry season that may be due to the high temperature and precipitation. Despite the low temperatures and dryness of the upper and middle basins, the CO₂ consumption rate is approximately twice that in the lower reaches; this can be attributed to active physical denudation in steep mountainous areas which increases the surface area for water–rock interactions. The total CO₂ consumption obtained by combining each season and basin was 48?70?×?10⁹?mol/a and 148?159?×?10⁹?mol/a for silicate and carbonate weathering, respectively, which are almost half the values of previous estimates. Our results suggest that seasonally and spatially separated evaluations are important for generating estimates of chemical weathering in large Himalayan rivers.

Organic alkalinity is a poorly understood component of total titration alkalinity in aquatic environments. Using a numerical method, the effects of organic acid (HOA) and its conjugate base (OA^?) on seawater carbonate chemistry and buffer behaviors, as well as those in a hypothetical estuarine mixing zone, are explored under both closed- and open-system conditions. The simulation results show that HOA addition leads to pCO₂ increase and pH decrease in a closed system when total dissolved inorganic carbon (DIC) remains the same. If opened to the atmosphere (pCO₂?=?400?μatm), CO₂ degassing and re-equilibration would cause depressed pH compared to the unperturbed seawater, but the seawater buffer to pH change ?(left( {beta _{{{text{DIC}}}} , = left( {frac{{partial ln left( {left[ {{text{H}}^{ + } } right]} right)}}{{partial {text{DIC}}}}} right)^{{ - 1}} } right)) indicates that weaker organic acid (i.e., higher pK_a) results in higher buffer capacity (greater β_DIC) than the unperturbed seawater. In comparison, OA^? (with accompanying cations) in the form of net alkalinity addition leads to pCO₂ decrease in a closed system. After re-equilibrating with the atmosphere, the resulting perturbed seawater has higher pH and β_DIC than the unperturbed seawater. If river water has organic alkalinity, pH in the estuarine mixing zone is always lower than those caused by a mixing between organic alkalinity-free river (at constant total alkalinity) and ocean waters, regardless of the pK_a values. On the other hand, organic alkalinity with higher pK_a provides slightly greater β_DIC in the mixing zone, and that with lower pK_a either results in large CO₂ oversaturation (closed system) or reduced β_DIC (in mid to high salinity in the closed system or the entire mixing zone in the open system). Finally, despite the various effects on seawater buffer through either HOA or OA^? addition, destruction of organic molecules including organic alkalinity via biogeochemical reactions should result in a net CO₂ loss from seawater. Nevertheless, the significance of this organic alkalinity, especially that comes from organic acids that are not accounted for under the currently recognized “zero proton level” (Dickson in Deep Sea Res 28:609–623, 1981), remains unknown thus a potentially interesting and relevant research topic in studying oceanic alkalinity cycle.

Methane production usually increases from the acidic sphagnum-dominated ombrotrophic peatlands to minerotrophic ones with more neutral pH and higher coverage of vascular plants. Along this ombrotrophic–minerotrophic gradient, pH, microbial communities, and properties of dissolved organic matter in porewater all vary greatly. The hydrographic change resulted from permafrost thaw and projected global warming can potentially connect the minerotrophic and ombrotrophic sites via porewater and turn acidic bogs to minerotrophic fens. It is thus very important to investigate how the anaerobic carbon degradation processes respond to changes in fundamental factors like pH, temperature, properties of dissolved organic matter, and microbial communities resulted from such hydrographic change. In this study, one ombrotrophic (pH?=?3.9) and one minerotrophic peatland site were sampled in Fairbanks, Alaska in Sep 2017 and a 42-day-period anaerobic laboratory incubation was conducted to study the changes in anaerobic carbon degradation processes including primary and secondary fermentation, methanogenesis, and acetogenesis when pH, temperature, and porewater were manipulated individually and a combination of two or three of these factors. The results suggested lowering pH would inhibit many anaerobic carbon degradation processes in the minerotrophic peatland except primary fermentation. Elevating pH in the ombrotrophic site did not stimulate its methanogen community, but primary fermentation responded better with increasing pH than with increasing temperature alone. Replacing the porewater in the minerotrophic site with that from the ombrotrophic site with high aromaticity did not inhibit methanogenesis but potentially brought in highly efficient primary fermenters. Acetoclastic methanogenesis, acetogenesis, and syntrophy only exist in the minerotrophic site but not at the ombrotrophic one. Porewater from the minerotrophic site could potentially introduce acetoclastic methanogens and syntrophs to the ombrotrophic site but would not make them active unless both pH and temperature were increased. When ground water connects ombrotrophic and minerotrophic peatlands due to thawing of permafrost, secondary fermenters and acetoclastic methanogens could be introduced to acidic bogs and cooperate efficiently to degrade the stored carbon in ombrotrophic peatlands especially under elevated temperature conditions.

The Marano and Grado Lagoon (northern Adriatic Sea, Italy) is contaminated mainly by mercury (Hg) of mining and industrial origin. This work aims to investigate the sedimentary records of Hg of a tidal flat–saltmarsh (TF–S) system and to understand the role played by tidal fluxes in terms of the transport, accumulation and release of Hg due to the periodic flow of the tide. The complex history of the sources of Hg in the area of the TF–S system has resulted in several fluctuations of Hg in sediments over time; due to its higher sedimentation rate (1.3?cm year^?1) than the subtidal areas of the Grado lagoon, the outer area of the TF–S system is more active in terms of accumulation (from 56 to 81?mg?m^?2 year^?1) than the inner area. Fluxes were estimated at the mouth of a principal tidal creek by combining discrete hourly tidal flow measurements with weighed measurements of dissolved (DHg) and particulate (PHg) mercury obtained via water sample collection. Mercury, mainly in particulate form, is drained by the tidal creek from the marsh during a tidal semi-cycle. The highest flux of PHg was recorded during ebb tide in July (1071?mg). The calculation of the quantitative flows of PHg and DHg highlighted a tendency for Hg to be exported from the TF–S to the lagoon channel during a tidal semi-cycle. However, the results obtained here for the Hg fluxes do not allow for the depiction of a constant positive or negative budget as that found in the literature for macro-scale budget calculations at lagoon tidal inlets. A possible explanation for there being no constant trend in the PHg and DHg budget is that our TF–S system is located in a lagoon area where previous findings reported accretion or a balance situation between erosion and sedimentation processes.

This study reports analyses of Ra isotopes in a Mediterranean stream, the Vidourle river, whose upper course drains the granitic and metamorphic basement of the SE part of the French Massif Central (Cévennes) and then flows through the karstified carbonates of Jurassic and Cretaceous ages. In these low-Ra waters (²²⁶Ra activities range from 1.5 to 4.9?mBq/L), all four Ra isotopes were successfully analyzed through gamma spectrometry during a single analysis. ²²⁶Ra activities and (²²⁸Ra/²²⁶Ra) ratios are distinctly higher in waters draining the Variscan basement than in waters affected by dissolution of Mesozoic carbonates, in agreement with U contents and Th/U ratios of both rock types. This results in a general N-S decrease, which parallels the evolution of the ⁸⁷Sr/⁸⁶Sr ratios. (²²⁸Ra/²²⁶Ra) ratios reported vs 1/(²²⁶Ra) display linear relationships suggesting mixing of several water components related to the lithology. Ra might thus have a more conservative behavior than usually assumed, possibly because of the high water/rock ratio and flow rate in karst environment. Short-lived Ra isotopes (²²⁴Ra and ²²³Ra) are often in excess compared to their equilibrium values, due to their supply through alpha-recoil processes. ²²³Ra activities in a Vidourle tributary can be explained by mixing of two water components, with a negligible radioactive decay of ²²³Ra during underground water flow. The calculated minimum flow rates (40–60?m/h) are in agreement with those deduced from artificial tracer experiments.

The Florida Everglades has one of the most severe methylmercury (MeHg) contamination issues in the USA, resulting from factors including high rates of atmospheric mercury (Hg) deposition and sulfate inputs from agricultural lands. Sulfate loading stimulates microbial sulfate reduction and production of toxic and bioaccumulative MeHg. Controls on regional Hg emissions have been successful in reducing Hg deposition and MeHg production in wetlands in other areas, but this has not been the case for the Everglades as the Hg deposited here appears to come from unknown global sources of emissions. We posit that reductions in sulfate loading to the Florida Everglades can be an effective alternative approach used to reduce MeHg production. This study tested this hypothesis (1) by evaluating temporal trends in MeHg concentrations in response to a reduction in sulfate loading at a site in central Water Conservation Area (WCA) 3 and (2) using ecosystem-scale models to predict the effects of reductions in sulfate loading on sulfate concentrations in surface water and MeHg Risk. At the WCA site, we report a decline in sulfate concentrations (from about 9?mg/L in the late 1990s to levels of <?1?mg/L by 2001) due to changes in water delivery as part of Everglades restoration. Concurrent with the decline in sulfate, declines in MeHg concentrations in surface water and fish and wading bird tissues were observed at this site. These results suggest the efficacy of reducing MeHg production and bioaccumulation in the ecosystem through a reduction in sulfate loading. A previously developed model was used to predict the effects of reductions in sulfate loading (97%, 33%, and 10% reduction scenarios) on sulfate concentrations in surface water and MeHg Risk in the Everglades. The model identified areas of the ecosystem where MeHg Risk is most sensitive to the reductions in sulfate loading. Results show that reductions of >?33% in sulfate loading will significantly benefit the Everglades by reducing MeHg Risk.

The reported partition coefficients of REE with calcite are reviewed and critically discussed. In some of the reported experimental sets, REE concentrations are found to be supersaturated with respect to individual REE₂(CO₃)₃ but never to REE(OH)₃. Although the solutions are unsaturated with respect to individual REY carbonates, REY including Y are incorporated in calcite surfaces, where they are overgrown by calcite. Charge balances may be obtained by building {REY–Na-(CO₃)₂}_n or by exchange of 2Ca²⁺ against REY³⁺?+?blank space calcite lattice. These surface compounds may either be homogeneously distributed or clustered. Both the size and frequency of clusters increase with [REY]/[Ca] or [ΣREY³⁺]/[Ca²⁺] in solution. If these surface precipitates are removed into solutions saturated with respect to ΣREE₂(CO₃)₃, they start growing in the aqueous phase. In this case, the apparent D_REY and k_REY values decrease with increasing REY concentrations in solution. In previous studies, only the individual distribution coefficients are reported not considering that the entirety of REY determines their behavior in partitioning. Given enough time, these surface clusters equilibrate with the aqueous phase before being overgrown by calcite. In the double logarithmic plots of {REY}/{Ca} versus [REY]/[Ca] or [REY³⁺]/[Ca²⁺], two relationships evolve characterizing the REY distribution in marine calcite and experimental calcites grown in Mg²⁺-free solutions. The double logarithmic plots of partition coefficients of REY³⁺_i in calcite grown from seawater show a slope exceeding unity, whereas those from fluids without Mg²⁺ depict slopes less than unity being both in contrast to the Henderson–Kracek rule.

Dissolved organic matter (DOM) strongly participates in a variety of critical environmental and ecological processes and has a large impact on environmental quality. In this study, ultraviolet–visible absorbance spectroscopy and excitation–emission matrices of fluorescence spectroscopy in combination with parallel factor analysis (EEMs–PARAFAC) were applied to characterize a total of 92 DOM samples extracted from four typical soil types under three different land-use regimes across China. DOC concentrations ranged from 6.52?±?1.09 to 25.62?±?4.83?mg?L^?1 and were generally higher in red soil from Guangdong and Guangxi, especially in paddy soil. Three fluorescence components were identified in soil DOM by EEMs–PARAFAC, including high molecular weight UVA humic-like substances (C1), low molecular weight autochthonous humic-like substances (C2), and protein-like substances (C3). DOM from black soil in Heilongjiang, purple soil from Sichuan, and red soil from Zhejiang had more humic-like substances, whereas DOM from yellow soil in Guizhou and red soil from Guangdong and Guangxi had lower degree of aromaticity and higher proportion of microbial-derived protein-like components (C3). Moreover, DOM from paddy soil tended to be more of protein-like components (C3) than that from other land uses and DOM from dryland soil generally had more autochthonous humic-like substances (C2). Our results demonstrated that soil DOM characteristics both varied significantly by soil type and land use, and EEMs–PARAFAC could be a useful approach to characterize the components and sources of heterogeneous DOM in soils.

This study presents major element geochemistry, mineral magnetism and textural analysis of lake-bottom sediments collected from the Wular Lake located in the Kashmir Valley (northwest Himalaya). Connected to the Jhelum River, Wular Lake basin occupies?~?75% watershed area of the valley, covering?~?10,196?km², and makes it the major depo-centre for Kashmir Valley. The sediments represent dominant silt fraction with TiO₂, MgO, Fe₂O₃ and MnO enrichment; and depletion of Na₂O and P₂O₅ with reference to upper continental crust. The average CIA (64.17%) reflects moderate chemical weathering of the catchment source rocks. The mineral magnetic mapping identified distinct domains of restricted/reducing and?well-ventilated/oxic conditions, illustrating spatial environmental variability within the lake-bottom environments. The geochemical and mineral magnetic mapping therefore provides a baseline reference for emerging climate and anthropogenic changes being experienced in the Kashmir Valley.