Aquatic Geochemistry最新文献

The Tataleng River (TTR), as an important tributary of the Da Qaidam Salt Lake (DQSL) and Xiao Qaidam Salt Lake (XQSL) in the Qaidam Basin (QB), has an exceptionally high B content. However, the solute sources and the provenance of B in the TTR are still unclear, which significantly hinders a deeper understanding of the source–sink processes of the boron deposits in the QB. In this study, water samples were collected from tributaries, mainstreams, mud volcanoes, hot springs, and rainwater in the TTR area. Through hydrochemical analysis, forward modeling, and B isotope geochemistry methods, combined with the previous research results, some findings were obtained. The hydrochemical type of TTR is Ca–Mg–Cl, and the major mechanism of controlling chemical composition is rock weathering. The solute sources in the TTR are mainly from dissolution of evaporites (75.9%), atmospheric precipitation (20.8%), and a minor contribution from carbonates (3.1%) and silicates weathering (0.6%). The higher B content (0.89–4.30 mg/L, mean = 2.13 mg/L) and lower δ¹¹B value (0.79‰–4.71‰, mean = 4.17‰) of the TTR indicate that the B sources are mainly from mixture of mud volcanic waters (56.19–199.98 mg/L, mean = 113.51 mg/L, − 1.26‰–2.22‰, mean = 0.85‰) in the upper reaches, and the deep groundwater near the Indosinian granite in the lower reaches. The significant difference in boron resources between the two lakes may be due to the enrichment of B in the late Pleistocene in the DQSL, which received exceptionally rich soluble B carried by the ancient TTR during an active tectonic period, while the weakening of tectonic activity and the diversion of the ancient TTR resulted in the supply of B with significantly reduced content to the XQSL. These results are helpful for a deeper understanding of the ore-forming mechanisms of the boron deposits in salt lake.

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.

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.

The solid-liquid phase equilibria of aqueous system containing the sulfates of lithium and potassium (Li₂SO₄ + K₂SO₄ + H₂O) at T = 303.2 and 318.2 K were done by isothermal dissolution method. The phase equilibria data (solubility, density, and refractive index) of the system were determined experimentally. The corresponding solid-liquid phase diagram, density/refractive index versus composition diagrams, were plotted. There are two ternary invariant points and three crystallization regions corresponding to Li₂SO₄·H₂O, LiKSO₄, and K₂SO₄ in the phase diagram of system Li₂SO₄ + K₂SO₄ + H₂O at 303.2 and 318.2 K. A comparision of system Li₂SO₄ + K₂SO₄ + H₂O at different temperature (T = 288.2, 303.2, 318.2 and 348.2 K) shown that the double salt LiKSO₄ was formed in the above mentioned temperatures, and the crystallization region of the LiKSO₄ increases gradually with the increase of temperature.

There is growing concern about the effects of ocean acidification (OA) on coral reefs, with many studies indicating decreasing calcium carbonate production and reef growth. However, to accurately predict how coral reefs will respond to OA, it is necessary to characterize natural carbonate chemistry conditions, including the spatiotemporal mean and variability and the physical and biogeochemical drivers across different environments. In this study, spatial and temporal physiochemical variability was characterized at two contrasting reef locations in Bocas del Toro, Panama, that differed in their benthic community composition, reef morphology, and exposure to open ocean conditions, using a combination of approaches including autonomous sensors and spatial surveys during November 2015. Mean and diurnal temporal variability in both physical and chemical seawater parameters were similar between sites and sampling depths, but with occasional differences in extreme values. The magnitude of spatial variability was different between the two sites, which reflected the cumulative effect from terrestrial runoff and benthic metabolism. Based on graphical vector analysis of TA–DIC data, reef metabolism was dominated by organic over inorganic carbon cycling at both sites, with net heterotrophy and net calcium carbonate dissolution dominating the majority of observations. The results also highlight the potentially strong influence of terrestrial freshwater runoff on surface seawater conditions, and the challenges associated with evaluating and characterizing this influence on benthic habitats. The Bocas del Toro reef is a unique system that deserves attention to better understand the mechanisms that allow corals and coral reefs to persist under increasingly challenging environmental conditions.

There is limited research on the variations in brine element changes and the factors that influence them during large-scale exploitation. The Xitaijnar Salt Lake in the Qaidam Basin is a large brine lithium deposit. In this study, we investigated the variations in chemical composition and the factors that influence intercrystalline brine at different time periods. Hydrochemistry, mineralogy, and hydrogeochemical simulation methods were employed to understand the brine evolution. Our results indicate that after nearly 20 years of exploitation, the intercrystalline brine still belongs to the magnesium sulfate subtype, with only slight variations in salinity. The concentrations of Na, K, and SO₄ showed a slight increase, while the content of Mg and Cl decreased slightly. The concentrations of B and Li exhibited minor fluctuations. The provenance, water level, and hydraulic connection had minimal influence on the chemical composition of the intercrystalline brine. By contrast, the dynamic dissolution and precipitation of sulfate minerals and halite, as well as drastic changes in hydrological conditions (such as floods), were identified as the main factors affecting the chemical composition of brine. With the large-scale extraction of intercrystalline brine, the content of elements in the salt lake showed a decreasing trend. This can be attributed to the fact that intercrystalline brine is formed through long-term evaporation and concentration. Therefore, during the exploitation process, it is crucial to monitor the hydrochemical variations of intercrystalline brine and understand the controlling factors. The results of this study may prove useful for the sustainable development and utilization of salt lake resources worldwide.

Phosphate is a common component in natural growth solutions of ikaite. Although phosphate often occurs as a minor constituent, its presence may promote the formation of ikaite as it significantly inhibits the precipitation of calcite. The interactions of phosphate with ikaite and the role of a potential uptake of phosphate by ikaite, however, are poorly understood. In this study, the influence of phosphate on ikaite growth at 1 °C was investigated. Ikaite- and calcite-seeded growth experiments were conducted in cryo-mixed-flow reactors at saturation ratios 1.5 ≤ Ω_ikaite ≤ 2.9 (Ω = ionic activity product/solubility product). From these growth experiments, the rate constant k = 0.10 ± 0.03 µmol/m²/s and the reaction order n = 0.8 ± 0.3 were derived for ikaite. The reaction order implies a transport- or adsorption-controlled growth mechanism which supports a low energy pathway of ikaite growth via an attachment of hydrous CaCO₃⁰ complexes without any extensive dehydration of aqueous species as, for instance, required for calcite growth. A potential depletion of aqueous phosphate due to an uptake by ikaite growth was not detectable. Furthermore, growth retardation by phosphate, as known for calcite growth, was not evident. Thus, a significant incorporation of phosphate into growing ikaite could be precluded for the conditions applied in this study. The observed lack of incorporation of phosphate agrees with the previously suggested growth mechanism via the attachment of hydrous CaCO₃⁰ complexes which likely does not facilitate substantial substitution of carbonate by phosphate ions.