Aquatic Geochemistry最新文献

In the face of rapidly compounding climate change impacts, including ocean acidification (OA), it is critical to understand present-day stress exposure and to anticipate the biogeochemical conditions experienced by vulnerable ecosystems like coral reefs. To meaningfully predict nearshore carbonate chemistry, we must account for the complexity of the local benthic community, as well as connectivity between habitats and relevant endmember carbonate chemistry. Here, we adopt a system-scale approach to predict site-scale effects of benthic metabolism on the carbonate system of the Florida Reef Tract (FRT). We utilize bimonthly carbonate chemistry data from ten cross-shelf transects spanning 250 km of the FRT to model changes in dissolved inorganic carbon (DIC) and total alkalinity (TA). Benthic habitat maps were used to broadly classify communities known to impact carbonate chemistry. A SLIM 2D hydrodynamic model with mesh resolution reaching 100 m over reefs and along the coastline was used to determine the relevant water mass histories and identify the upstream benthic communities shaping local carbonate chemistry. These historical metabolic footprints, or “flowsheds”, were used to build predictive models of the change in DIC and TA at each station. The best predictive models included the chemical impacts of benthic ecosystem metabolism, as defined by water mass trajectories, weighted endmember chemistry, volume, time, and other environmental parameters (light, temperature, salinity, chlorophyll-a, and nitrate). Considering water mass for 5 days prior to sample collection yielded the highest model skill.

The elemental records of the sediments from two IODP cores, U1501C (Oligocene and Late Miocene-Pliocene) and U1499A (Pliocene to Pleistocene) in the Northern South China Sea have been studied here to understand the variability in the sedimentary provenance and depositional environment, which are impacted by the tectonic and East Asian monsoon evolution through time. The major oxides and REE abundances indicate the sources of sediment influx to be significantly from the South China, North and North eastern parts of SCS since ~ 33 Ma, and prominent contributions from Pearl River, Hainan Island and Taiwanese rivers since ~8.3 Ma. The depositional redox is corroborated by the Ce anomaly and trace element proxies such as U/Th, V/Cr, V/(V + Ni), and Ni/Co. The chemical weathering intensity, evidenced by the Chemical Index of Alteration and major elements (Ca/Ti, Na/Ti, Al/K, Al/Ti, AL/Na), and La/Sm ratios, was observed to be low. Early Oligocene witnessed the deposition of littoral sediments, caused by the initial rifting and spreading in SCS. During the late Miocene (~ 8.3 Ma), sedimentation was influenced by the prevailing arid climate and intensification of East Asian Winter monsoon (EAWM). Since Pliocene–Pleistocene (~ 5.3 Ma−0.01 Ma), the sediment deposition remained unaffected by tectonism, but was majorly influenced by the intensification of EAWM and the glacial-interglacial cycles.

The Aral Sea is well known throughout the World as an inland lake disappearing due to unsustainable use of natural water resources for economic purposes. The degradation of the sea led to irreversible transformations of the ecosystem in the region and other destructive consequences. It has become a natural laboratory, allowing the study of the morphometric transformation of the properties of its waters under the influence of environmental conditions. This article is devoted to the study of temporal variability in the biogeochemical and physical characteristics with an emphasis on the metamorphosis of the ionic composition of the Aral waters and its individual water bodies (i.e., the Large and Small Aral Seas, Lakes Chernyshev and Tshchebas) in the period 1873 − 2022 based on newly obtained (2021 and 2022) and literature data. Periods of hydrochemical evolution are identified reflecting the order of salt deposition lasting for several years. The latest of these periods lasted from 2014 to 2022 waters in the salinity range of 126˗244 ‰. It was characterized by the ({text{SO}}_{4}^{2-})/Clˉ ratio of 0.31, while Mg²⁺/Na⁺ 0.34 and Ca²⁺/Na⁺ 0.02. Migration curves for the Aral Sea's water reflect the influence of a number of regional features on the formation of the ion-salt composition of waters was constructed. The biogeochemical features of the final stage of the Aral Sea are discussed using the example of the former bay and now lake Chernyshev. Its salinity of ~ 243 ‰ and the microbial community inhabiting it, along with the ionic composition, determines the properties of its waters.

This study investigates the biogeochemical and environmental characteristics of humic acids isolated from sediment samples of five lakes located in the European taiga zone. Sediment samples were analyzed using advanced techniques, including CHN analysis, solid-state 13C-NMR spectroscopy, and FTIR spectroscopy. The results show that the humic acids from the studied lake sediments exhibit lower degrees of aromaticity compared to those in terrestrial soils, indicating a lower degree of humification under aquatic reducing conditions. This suggests that aquatic environments favor the preservation of relatively labile organic compounds. The affinity of metals to form complexes with the humic acids varied among the lakes, with metals such as Co, Pb, V, and Sb forming stable chelate complexes, while Mn and Cd exhibited higher geochemical mobility. The findings provide insight into the role of humic substances in controlling the distribution and mobility of metals in aquatic ecosystems, contributing to our understanding of biogeochemical processes in taiga lake environments.

Research on the carbon-cycling process in high-altitude streams is crucial for understanding whether carbon acts as a source or sink for the atmosphere during present times of global climate change. In this study, we have quantified the post-monsoon CO₂ flux (FCO₂) from the Bhagirathi and Alaknanda rivers, which are two pristine watersheds in the Upper Ganga Basin in India with the help of analytical hydrochemistry and PHREEQC v.3.7.3 software. Our results show FCO₂ values of 88 gCO₂m⁻²d⁻¹ and 175 gCO₂m⁻²d⁻¹ from the upstream reaches of Bhagirathi and Alaknanda Rivers, respectively, which is significantly greater than the fluxes observed in the downstream reaches (18 gCO₂m⁻²d⁻¹ and 4.1 gCO₂m⁻²d⁻¹, respectively). This difference in FCO₂ is attributed to the major variation in gas transfer velocity (kCO₂) along elevation, with the upstream section exhibiting approximately eight times higher kCO₂ than the downstream section. The steeper bed slope leads to increased turbulence and energy dissipation at higher altitudes, enhancing the kCO₂ values. The partial pressure of CO₂ in the rivers was found to be approximately 2.5 times greater than the atmosphere. Our findings suggest that form-drag turbulence instead of bed friction, prevalent in the high-gradient reaches of the rivers, is the main driver of CO₂ degassing into the atmosphere. This study shows that Ganga headwater streams are sources of CO₂ to the atmosphere and underscores the need for monitoring other Himalayan streams for CO₂ flux.

The northeastern Sichuan Basin hosts deep brines with unusually high concentrations of potassium (K) and lithium (Li). This study examines deep brines abundant in K and Li in northeastern Sichuan Basin. Brine samples from Well ZK601 underwent comprehensive analysis for major elements, trace elements, and Sr isotopes. Lithium content in core samples correlated with regional brine reservoir features. Brine samples showed a salinity range of 354.6–363 g/L, with varying contents of Na⁺ (101–106 g/L), K⁺ (28.92–34.84 g/L), Cl⁻ (202.1–206 g/L), Br⁻ (2110–2980 mg/L), and Li⁺ (169.5–204.5 mg/L). The ⁸⁷Sr/⁸⁶Sr ratio in brine was 0.708324. Li notably increased post-green bean rock deposition in 71 core samples. The ratios are as follows: Br × 10³/Cl is 10.24, K × 10³/Cl is 169.13, nNa/nCl is 0.74, and SO₄ × 10³/Cl is 0.49. These brines likely originated from ancient seawater, evolving via rock interactions during burial, notably enriching K and Li through gypsum dehydration. Geochemical traits and Sr isotopes affirm ancient seawater origin, stressing continual water–rock interactions. The volcanic activity contributed significantly to lithium enrichment, consolidated during later burial stages. Brine reservoirs, mostly in formations like dolomite within the Jialingjiang Formation, associate closely with fractured zones. Structural traps define distribution, while fault systems govern enrichment. Accumulation mainly occurs in fractured zones, reflecting a mineralization model of seawater origins, metamorphism, filtration, and structural enrichment. In summary, our model outlines a transformation from seawater origins to structural controls enriching K and Li in deep brines in northeastern Sichuan Basin.

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.

Advancing underground hydrogen storage (UHS) is essential for a sustainable, emission-free future, with its success highly contingent on the unique properties of each subsurface reservoir. To ensure optimal storage, detailed site assessments are required. One of the critical gaps in knowledge necessary for ensuring safe storage is geochemical redox reactions, especially those involving iron. These redox reactions are crucial as they influence hydrogen retention or loss in the subsurface environments. In this study, we have theoretically addressed hydrogen consumption via abiotic reduction of a Fe³⁺ oxide under different Fe²⁺ activities. Simulations indicate that in scenarios, where the initial hydrogen partial pressure is extremely low (around 10⁻⁵ bars), decreasing the activity of Fe²⁺ by a factor of 10 can lead to a marked decrease in the initial hydrogen pressure by a maximum factor of 1000 within a few years. Variations in Fe²⁺ activity can significantly influence abiotic hydrogen consumption only under very low hydrogen partial pressures. This is primarily due to enhanced dissolution of Fe³⁺ oxides. In comparison, in conditions where hydrogen partial pressure is higher (> 10⁻² bars), reduction of Fe³⁺ oxide can yield magnetite, resulting in a muted loss of hydrogen over time. The transition in the reduction behavior of Fe³⁺ oxide from a ‘dissolution-driven’ process to ‘magnetite crystallization,’ which also determines the fate of stored hydrogen, depends on initial hydrogen partial pressure. Our results demonstrate that low quantities of hydrogen can be maintained within typical storage cycles spanning less than a year, depending upon aqueous Fe content.