Aquatic Geochemistry最新文献

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.

Speciation diagrams in pH-Eh space at some pressure, temperature, and composition are highly useful in indicating the thermodynamic behavior expected in a system. While these diagrams are found frequently throughout geochemical literature, they often overlook the geometric behavior of stability fields and fail to address the specific impacts of ionic strength and fluid composition. Modeling results from the Salton Sea and Krafla geothermal sites suggest a positive correlation between ionic strength and the H₂O_(l) stability field area or reactivity domain. In addition, the Si-bearing species (selected due to the propensity of adverse scale occurrence) within the Salton Sea brine are shifted farther apart than the centroids of the same Si species in the comparatively dilute Krafla. These modeling observations imply that geothermal brines at equilibrium accommodate a larger H₂O reactive field in pH-Eh space, allowing for the possibility that water–rock interactions could occur at pH-Eh conditions that would conventionally be unexpected if ionic strength is not considered.

Dissolved organic matter (DOM) is the most active organic component in terrestrial ecosystems. In this study, 165 soil samples which were dominated by moss were collected from grasslands with similar vegetation in urban residential areas from 55 cities across different climatic zones of China. The water extractable organic matter (WEOM) of samples was analyzed. The results showed that WEOM content ranged from 23.5 to 517.6 mg kg⁻¹ in the soil samples. Four fluorescent components including two tryptophan-like components (C1 and C4) and two humic-like components (C2 and C3) were identified by excitation–emission matrices combined with parallel factor analysis (EEM-PARAFAC). Proportions of humic-like components (C2 + C3) were 54–66%, which is 1.2–2.0 times of the tryptophan-like component proportion (C1 + C4) for all samples. The proportions of C2 and C3 were highest in the tropical monsoon climate (TroM) zone compared to that in the other climatic zones. Structural equation model and decomposition of variation showed that soil nutrient content was the main contributing factor of soil WEOM. Content Total nitrogen content and mean annual temperature (MAT) were the main factors influencing soil HIX but they had the opposite effects. Our results suggested that increasing soil nutrient content contributed the increase in soil WEOM content, but increasing MAT reduced the humification degree of WEOM.

Daejeon is well-known in South Korea for having the highest concentrations of uranium in the Jurassic granite aquifer. This study reports the texture and chemistry of uraninite and discusses the potential of uraninite as an effective source mineral of U in granite aquifers based on uraninite dissolution and U-migration. Its texture and mineral chemistry were examined using FE-SEM and EPMA, respectively, to investigate the occurrence of uraninite. The Pb isotope ratios of the minerals in granite were tested to verify their potential as geochemical tracers for elemental migration. The Pb isotope ratios were obtained using a SHRIMP IIe/MC ion microprobe. Uraninite occurred with muscovite and pyrite as large grains of up to 500 μm in length in the altered granite. Coffinite, a secondary U-mineral, occurs in the cracks within uraninite. The uraninite U content ranged from 79.12 to 89.05 wt. % and uraninites have major impurities of Th, and Pb ranged from 1.82 to 3.49 and 2.13 to 2.42 wt. %, respectively. The breakdown of uraninite may result in the redistribution of U and Pb and facilitate U-migration during surface weathering. The Eh–pH conditions of groundwater are suitable for the dissolution of uraninite, and the uranyl carbonate complex ion (UO₂(CO₃)₂²⁻) is the dominant U-species in the study area. The Pb isotope ratios indicated that uraninite contained radiogenic Pb, feldspar contained common Pb, and pyrite contained a mixture of both components. These Pb isotopic signatures indicate that the radiogenic Pb in uraninite has migrated from uraninite to pyrite. Considering the relatively high mobility of U compared to Pb, the migration of radiogenic Pb from uraninite to pyrite suggests that U can also migrate from uraninite to its surroundings when a reaction with groundwater occurs. Based on hydrological conditions and the Pb isotope signature, uraninite is considered a substantial and compelling host mineral for interpreting a source of uranium in the granite aquifer of the study area.

This study investigated weathering and hydrobiogeochemical processes in a silicate dominated watershed (Svratka river) in the Czech Republic in comparison with nearby carbonate dominated catchments. Elemental and isotopic analysis of river waters, particulates and sediments provided a more holistic view of weathering contributions, anthropogenic contamination, biological activity and evasion or sinks of CO₂ to the atmosphere. In water samples, we determined total alkalinity after Gran 1974, and cations and anions were determined with inductively coupled plasma–optical emission spectrometer and ion chromatograph. δ¹³C_DIC in water samples was determined with isotope ratio mass spectrometer. pCO₂ and saturation indexes of calcite and dolomite were calculated with PHREEQC speciation program. Evasion fluxes were calculated after Broecker, 1974. Isotopic composition of carbon and nitrogen in particulate matter and sediments were determined with isotope ratio mass spectrometer. Mineral composition of sediments was determined with XRD method and elements with XRF method. Further enrichment factors of elements were calculated. The Svratka river, which is the major tributary of the Dyje river, is dominated by Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ (as total alkalinity). Partial pressure (pCO₂) concentrations range from close to 0–572-fold of atmospheric pressure. Isotopic composition of carbon in dissolved inorganic carbon (δ¹³C_DIC) value ranged from − 13.3 to − 8.0‰ reflecting degradation of organic matter and exchange with the atmosphere. Bicarbonate weathering intensity for the Svratka river at its mouth is 11.8 mol/(l⋅km²⋅s), more on par with silicate terrains and lower than nearby carbonate watersheds. Isotopic composition of carbon (δ¹³C) and isotopic composition of nitrogen (δ¹⁵N) values of river sediment reflect soil and temperate plant (C3 plant) values, while higher δ¹⁵N values could be attributed to application of organic fertilizers in lower reaches. The river sediments, which came from weathering of crystalline rocks, are dominated by silt size, geochemically less mature quartz, feldspar and muscovite particles. All the stream sediments examined revealed slightly increased amounts of Zn, Cu and Pb. However, using Al as the normalization element to calculate enrichment factors, Zn, Cu and Pb are only elevated downstream, related to industrial contamination. This study is important for local and global level since it deals with contribution of weathering rates and contribution of CO₂ to the atmosphere in silicate watershed.

The geochemistry of limestone from Nkapa and Logbajeck formations, Douala sub-basin, has been studied using major, trace elements and stable isotopes in order to decipher paleo-redox condition, depositional and post-depositional imprints and paleotemperature. Collectively, U/Th Ni/Co, V (V + N), V/Cr and Ce/Ce* ratios clearly indicate an oxic depositional condition for the samples. The ratios of Mn/Sr suggest less significant diagenetic alteration on limestone composition. The carbon isotopic signals δ¹³C ranged from − 0.26 to 0.86‰ PDB while oxygen isotope δ¹⁸O is from − 2.24 to − 7.94‰.‰ PDB. The isotopic composition of δ¹³C (− 1.9 to 0.79‰) shows a discrepancy from modern carbonate sediments. The poor correlation and scattered distribution of δ¹³C versus δ¹⁸O plot in calcareous sediments reflect different degrees of burial diagenesis and/or the potential impact of meteoric water. The average estimated temperature of formation for the limestone is 44.08 °C revealing a warm period during its deposition. The paleosalinity values (Z) for the studied area vary from 111.45 to 127.11‰ indicating a marine to fresh water depositional environment. The δ¹³O versus δ¹⁸O bivariate diagram indicates that the limestone is predominantly marine limestone, freshwater limestone, late cement and Pleistocene limestone.

In this study, we present a new ⁸⁷Sr/⁸⁶Sr isoscape map of Central and NE Germany. This area is characterized by an alternation of sedimentary basins and mountainous regions with a very variable lithology. Since lithology and rock age have a major impact on the isotopic composition of biologically available strontium, Central and NE Germany should reveal highly variable ⁸⁷Sr/⁸⁶Sr ratios. From lithological characteristics, particularly high ratios are expected in the mountainous regions of the Erzgebirge/Fichtelgebirge and the Harz Mountains. In contrast to these predictions, published ⁸⁷Sr/⁸⁶Sr isoscape maps of Central and NE Germany record rather uniform and low ⁸⁷Sr/⁸⁶Sr ratios. From this observation, we suspected that existing isoscape maps might be computed from an insufficient database, with mountainous regions being underrepresented. Our goal was to gather ⁸⁷Sr/⁸⁶Sr baselines for each major lithology of Central and NE Germany and to produce an accurate isoscape map of Central and NE Germany. In the first step, we evaluated the suitability of stream water and groundwater as a proxy for biologically available strontium. In a selected watershed, we present mixing relationships and a stream network model. We show that groundwater is prone to very local geologic and anthropogenic influences and should thus be avoided. Instead, we focussed our further sampling on stream water. Altogether, we used 119 new measurements of groundwater and stream water and a set of 23 auxiliary variables as a database for our new isoscape map of Central and NE Germany. Due to a sampling strategy that focussed on covering each major lithology, our measurements and the final isoscape map show a clear contrast between sedimentary basins and mountainous regions. For regions that have been sufficiently sampled, a direct comparison of the isoscape map with published and new data shows good agreement. Although Central and NE Germany were part of published isoscape maps, our new map is the first that predicts ⁸⁷Sr/⁸⁶Sr ratios in mountainous regions with high accuracy.