Aquatic Geochemistry最新文献

To deepen the comprehension of the geochemical behaviour of salt-forming elements (K, Li, B, Ca, Mg, Sr) and distribution patterns in the primary lithium-rich salt lake region of Qaidam Basin, 31 river and lake surface sediments from various hydrogeological settings spanning high mountain to terminal salt lake regions were gathered from the Nalenggele River, the primary feeder river of the lithium-rich salt lakes. Through sequential extraction procedure, we identified notable variances in the chemical speciation of elements across various hydrological environments. Excluding elements bound to the residual fraction, all other chemical speciation content of salt-forming elements show distinct regional variations, suggesting a predominant influence of evaporation and hydrodynamic and the inherent chemical properties of elements are also very important in determining their chemical speciation distribution characteristics. Meanwhile, we have found that in addition to being absorbed and fixed by secondary clay minerals, Li bound to Fe–Mn oxides may also play a crucial role in Li isotope fractionation from the river to the terminal salt lake brine and the precipitation of evaporation salt minerals could influence the B isotope fractionation to a certain extent. Furthermore, The Li and B lost to sediments during the migration process have potential utility and there is scope for enhanced exploitation in the future. Therefore, the results obtained from the sequential extraction procedure of sediments evidently serve as a valuable method for understanding the geochemical behaviour of salt-forming elements in the epigenetic environment.

Bromine (Br) is a vital chemical raw material primarily obtained from marine brine. The bromine/chlorine (Br/Cl) ratio serves as a crucial indicator for predicting marine potash mineralization in evaporites. As salinity increases, bromine gradually accumulates through evaporation in residual brine. During the process of brine evaporation to the potassium salt stage, the bromine content in the brine can exceed 1000 ppm. The marine brine sourced from the weathering crust reservoir at the top of the Ordovician Majiagou Formation in the Jingbian gas field, Ordos Basin, in northwestern China, displays an exceptionally high bromine content (averaging 1590 ppm), surpassing levels found in contemporary seawater. Based on analysis of major compositions, only brine evaporates to the gypsum stage. Despite extensive exploration in the region, large-scale potassium salt deposits have not been identified. This heightened concentration of bromine in low salinity brine suggests supplementation from additional organic bromine sources. The strata adjacent to the high-bromine oil field water in the Jingbian gas field, Ordos Basin, consist of the Ordovician marine evaporite strata of the Majiagou Formation and the overlying Carboniferous and Permian marine and continental deposits rich in fossil algae. Interactions between hydrocarbons and oilfield water contribute to the notable bromine anomaly observed in the Jingbian gas field in the Ordos Basin. Elevated bromine levels have also been noted in brine from various oil fields worldwide. Through an analysis of the major compositions of brines and bromine, this study will elucidate the reasons behind the presence of high bromine brines.

Mahai Basin (MH), located in the northern Qaidam Basin (QB), possesses abundant K-rich brine resources. The investigation on the origin of deep K-rich confined brine and the variations in K–Mg elements corresponding to the evolution in MH shed light on the significance of assessment and utilization of brine deposits. This study presents multiple isotopes (δ¹⁸O–δD, ⁸⁷Sr/⁸⁶Sr) and hydrochemical characteristics for various waters (including river water, surface brine, intercrystalline brine, confined brine and anticlinal brine) in the MH. Our findings corroborate that: (1) confined brine exhibits relatively high K⁺ (average value of 6.88 g/L) and low Ca²⁺–Sr²⁺ concentrations, compared to anticlinal brine, and its chemical composition resembles the evolution of Yuqia River in Ca–SO₄–HCO₃ diagram, suggesting that contemporary river water is the primary source of confined brine. (2) The δ¹⁸O–δD values of confined brine in MH ranged from − 17.80 to − 27.40‰ and 1.50 to 2.40‰, respectively, and fall on the right field of the local evaporation line, indicating successive evaporation and concentration processes. (3) The ⁸⁷Sr/⁸⁶Sr ratios (0.71142–0.71145) of confined brine fall between river water (0.71150–0.71183) and anticlinal brine (0.71135), combining with river water and confined brine which exhibit low Sr content, and further confirming the origin of confined brine is a mixture by river and anticlinal brine and much river recharge budget. (4) Considering the evolution of sedimentary facies (Dezongmahai Lake area as an example) and the gradual increase in K and Mg contents in MH, the enrichment of K and Mg exhibits a certain correlation with the evolution of MH. Notably, the brine in the northeast of the basin displays the highest levels of K and Mg, indicating that this region serves as the ultimate depositional center.

Brine groundwater in Quaternary salt lakes is widely exploited to extract potassium, lithium, and boron; the complex hydrogeological parameters of brine aquifers could cause significant difficulties in brine resource assessment and exploitation. However, the origin and porosity of brine aquifers remain unclear. This study presents an approach that utilizes geochemical indicator analysis with paleogeographic reconstruction to better assess porosity in salt lake aquifers. We identified 15 representative boreholes in Mahai Salt Lake, and the lithology, porosity, and chloride contents of their respective sediments, the pore porosity of each borehole in the study area ranges from 38.17 to 0.51%, the average chloride content of each borehole ranges from 26.63 to 38.74%, found that the vertical porosity fluctuations of halite deposits were significantly larger than those of detrital deposits, the sediments in the boreholes consisted predominantly of halite-containing debris or fine-debris-containing halite, reflecting the paleoenvironmental signatures of the salt lake. According to lithology and sedimentary environment, four brine aquifers were classified and the chloride and porosity distribution characteristics in the I–IV brine aquifers were further illustrated. Based on information of paleolake evolution in Qaidam Basin, we established a conceptual model to identify the impact factors for the porosity distribution pattern in the I–IV brine aquifers.

Arsenic (As) contamination in soil and groundwater poses significant environmental and human health concerns. While chemical mechanisms like solubility equilibria, oxidation–reduction, and ionic exchange reactions have been studied to understand As retention in soil, the influence of capillarity on As transport remains poorly understood, particularly in semiarid soils with broader capillary fringes. This research aims to shed light on the capillary contribution to As attenuation and mobilization in the groundwater, focusing on degraded soil in the northeast of San Luis Potosí, Mexico. Groundwater surveys revealed a remarkable depletion of As concentrations from 91.50 to 11.27 mg L⁻¹, indicating potential As sorption by the underlying shallow aquifer. We examined soil samples collected from the topsoil to the saturated zone using advanced analytical techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and wet chemical analyses. Our findings unveiled the presence of three distinct zones in the soil column: (1) the A horizon with heavy metals, (2) dispersed calcium sulfate dihydrate crystals and stratified gypsum, and (3) a higher concentration of arsenic in the capillary fringe. Notably, the capillary fringe exhibited a significant accumulation of As, constituting 40% (169.22 mg kg⁻¹) of the total arsenic proportion accumulated (359.27 mg kg⁻¹). The arsenic behavior in the capillary fringe solid phase correlated with total iron behavior, but they were distributed among different mineral fractions. The labile fraction, rich in arsenic, contrasted with the more recalcitrant fractions, which exhibited higher iron content. Further, thermodynamic stability assessments using the geochemical code PHREEQC revealed the critical role of Ca₅H₂(AsO₄)₄:9H₂O in controlling HAsO₄²⁻ and the formation of HAsO₄:2H₂O and CaHAsO₄:H₂O. During experimentation, we observed arsenate dissolution, indicating the potential mobilization of As in aqueous species. This mobilization was found to vary depending on redox conditions and may become labile during flooding events or water table variations, especially when As concentrations are low compared to metal cations, as demonstrated in our experiments. Our research underscores the significance of developing accurate geochemical conceptual models that incorporate capillarity to predict As leaching and remobilization accurately. This study presents novel insights into the understanding of As transport mechanisms and suggests the necessity of considering capillarity in geochemical models. By comprehending the capillary contribution to As attenuation, we can develop effective strategies to mitigate As contamination in semiarid soils and safeguard groundwater quality, thereby addressing crucial environmental and public health

There are typical salt lake-type borate deposits in the northern Qaidam Basin, which are mainly distributed in Da Qaidam Lake (DQL), Xiao Qaidam Lake, and Mahai Basin (MHB). DQL has deposited famous solid borates and enriched a large number of brine boron deposits. It is the earliest industrial production base in China. Nanbaxian (NBX) to the west of DQL is a unique area where solid borates are deposited in MHB. Although there are three salt lakes in the MHB, borate deposits were only deposited in the salt pits of NBX, and the formation process of these borate deposits remains to be clarified. In this study, the major elements, boron contents, and d¹¹B values in the water and sediments of NBX were investigated in conjunction with the B-Na-Mg equivalence diagrams and relevant data from other salt lakes to elucidate the source of boron in MHB and the depositional conditions of borate minerals in NBX. The results are as follows: (1) The source of boron in NBX differs from that in three salt lakes in MHB. The source in NBX is mainly constrained by the weathering and fluid-rock (Boron-bearing ultra-high pressure metamorphic belt) interaction, while that in Dezongmahai and Niulangzhinv–Balunmahai lakes are primarily controlled by river water and anticlinal brine, respectively. (2) The high boron content (0.28 to 41.38 mg/L) and low d¹¹B values (- 34.71‰ to - 6.14‰) of the water-soluble phase of sediments in NBX are consistent with geochemical characteristics (d¹¹B: - 23.67‰ to - 3.0‰) of borates in DQL, demonstrating that the re-dissolution of borate deposits in NBX. (3) Deposition of borate minerals in the MHB requires ionic equivalents of Mg, Na, and B to 0.02 to 0.4, 0.25 to 0.75, and 0.2 to 0.7, respectively. Additionally, the brine hydrochemistry in which the borate are deposited must be of the carbonate or sulfate type, and the brine water should be greater than 8 in pH and 400 mg/L in boron content. This study provides a theoretical basis for exploring and exploiting salt lake-type borate deposits.

Soil-derived dissolved organic matter (DOM) has a significant impact on aquatic ecosystems. Identifying the fluorescence signatures of DOM from different soils in river and sea waters can provide valuable insights into its migration patterns. This makes crucial assessing the contributions of pH, salinity, and other milieu parameters to the variability of DOM optical properties. Present study investigates the changes in DOM of Chernozems under varying salinity using UV–visible absorbance spectroscopy and 3D-fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC). Water-extractable organic matter (WEOM) extracted from soils of two field experiments of contrasting land use: long-term bare fallow (LTBF) and annually mown steppe (Steppe), was used as a proxy for DOM. Diluted extracts were incubated with varying NaCl concentrations in the dark and then examined. Steppe WEOM exhibited fair constancy of optical parameters under increasing salinity, while significant changes of the optical indices and of PARAFAC components’s loadings were observed for LTBF WEOM. The remarkable stability of the Steppe WEOM can be attributed to its chemical diversity. Two distinct and sufficiently stable humic-like PARAFAC components have the potential to serve as markers of Chernozem DOM. The findings clearly demonstrate that salinity itself slightly reduces absorption and fluorescence and changes some optical indices of WEOM of Chernozems.