Aquatic Geochemistry最新文献

In a warming climate, land-to-water carbon mobilization is increasing in glacier and permafrost area. To identify the connection between exported river carbon content and the permafrost or glacier condition in the high-altitude mountain area, we studied the dissolved organic carbon and dissolved inorganic carbon concentration in three streams of Qinghai–Tibet Plateau (QTP), which were located in the continuous permafrost, seasonal permafrost and glacial basin, respectively. It was found that the DIC and DOC concentrations were lower in the glacial rivers compared with the permafrost derived rivers; but more DOC would be exported from glacier due to the large amount of melted glacier water in the high mountainous area. DIC/DOC ratio in rivers reflected the watershed landscape types. In the permafrost area, the river recharged by seasonal permafrost had higher DIC concentration than the river in the continuous permafrost region, suggesting that increased DIC concentration could be a precursor of permafrost degradation. Research is meaningful to estimate the DOC and DIC export from high mountain area.

Spring waters with high-pCO₂ content are widely distributed in the Sikhote-Alin region in Russia. Mukhen spa is one such spring located in the northern Sikhote-Alin region. This spa has two types of upwelling spring waters and exhibits distinct chemical signatures. One of the springs originates from a shallow aquifer and features hydrogen and oxygen isotopic ratios of meteoric water with a high ³He/⁴He ratio, whereas the other originates from a deeper aquifer and features a distinctly negative δ¹⁸O with a lower ³He/⁴He ratio. To understand this apparent discrepancy and the water circulation dynamics beneath Mukhen springs, we utilized all published data concerning the major solute elements and isotopic ratios of Mukhen spring waters and compared them with the He isotopic compositions on several springs in the far eastern region, which are newly analyzed in this study. The results show that the shallow aquifer comprises meteoric water that interacts with the crust enhanced by the gas component welling up from deep underground, while the fluid in deep aquifer fingerprinted the hydration reaction of silicate and involves a mantle component possibly delivered by a deep-seated fluid and/or gas upwelling along the tectonic fault through the western margin of the Sikhote-Alin region.

Triclosan (TCS) is an antimicrobial compound found in many household products used across the world. TCS is not completely removed in wastewater systems, resulting in trace-level concentrations present ubiquitously in surface waters. The direct photodegradation of TCS has been widely studied, with results indicating that TCS breaks down to chlorophenols and dioxins. To date, no studies have specifically investigated the effects of alkalinity on the photolysis of the acidic form of TCS. This study assessed the effect of carbonate/bicarbonate alkalinity, which is ubiquitous in natural waters, on the photolysis rate of TCS. Results indicate that bicarbonate enhances the photodegradation of TCS at pH values well below the pK_a of TCS (7.9), with direct photolysis reaction kinetics that are very slow in the absence of buffers, but significant in the presence of bicarbonate (0.711 h⁻¹ at pH 6.55). At pH values well above its pK_a, both unbuffered- and buffered-mediated photolysis increased dramatically (1.92 h⁻¹ for direct photolysis and 2.86 h⁻¹ in buffered water) and is attributable to the increased photoreactivity of TCS by its conjugate base. Photolysis of methyl triclosan (MeTCS), a non-acidic analog of TCS, demonstrated the importance of TCS’s acidic functionality as MeTCS did not degrade at any pH. The observed influence of alkalinity on the acidic form of TCS photolysis was attributed to both a decrease in its excited state pK_a, coupled with TCS deprotonation through an excited state proton transfer to a base (bicarbonate and to a lesser degree hydrogen phosphate) resulting in the more photo-labile conjugate base form of TCS.

Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in the cycling of these elements. Indeed, recent studies have begun shedding light on the possible role of soluble, ligand-bound Mn(III) in promoting abiotic transformations under environmentally relevant conditions. Here, using the kinetic data of Karolewski et al. (Geochim Cosmochim Acta 293:365–378, 2021), we provide the chemical mechanism for the abiotic oxidation of nitrite (NO₂⁻) by Mn(III)-pyrophosphate, Mn^IIIPP, to form nitrate (NO₃⁻). Nitrous acid (HNO₂), not NO₂⁻, is the reductant in the reaction, based on thermodynamic and kinetic considerations. As soluble Mn(III) complexes react in a one-electron transfer reaction, two one-electron transfer steps must occur. In step one, HNO₂ is first oxidized to nitrogen dioxide, ·NO₂, a free radical via a hydrogen atom transfer (HAT) reaction. We show that this inner sphere reaction process is the rate-limiting step in the reaction sequence. In step two, ·NO₂ reacts with a second Mn^IIIPP complex to form the nitronium ion (NO₂⁺), which is isoelectronic with CO₂. Unlike the poor electron-accepting capability of CO₂, NO₂⁺ is an excellent electron acceptor for both OH⁻ and H₂O, so NO₂⁺ reacts quickly with water to form the end-product NO₃⁻ (step 3 in the reaction sequence). Thus, water provides the O atom in this nitrification reaction in accordance with the O-isotope data. This work provides mechanistic perspective on a potentially important interaction between Mn and nitrogen species, thereby offering a framework in which to interpret kinetic and isotopic data and to further investigate the relevance of this reaction under environmental conditions.

Studies done on small tropical west-flowing river catchments located in the Western Ghats in southwestern India have suggested very intense chemical weathering rates and associated CO₂ consumption. Very less studies are reported from these catchments notwithstanding their importance as potential sinks of atmospheric CO₂ at the global scale. A total of 156 samples were collected from a small river catchment in the southwestern India, the Payaswini–Chandragiri river Basin, during pre-monsoon, monsoon and post-monsoon seasons in 2016 and 2017, respectively. This river system comprises two small rivers originating at an elevation of 1350 m in the Western Ghats in peninsular India. The catchment area is dominated by biotite sillimanite gneiss. Sodium is the dominant cation, contributing ~ 50% of the total cations, whereas HCO₃⁻ contributes ~ 75% of total anions. The average anion concentration in the samples varied in the range HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ > F⁻, whereas major cation concentration varied in the range Na⁺  > Ca²⁺  > Mg²⁺  > K⁺. The average silicate weathering rate (SWR) was 42 t km⁻² y⁻¹ in the year 2016 and 36 t km⁻² y⁻¹ in 2017. The average annual carbon dioxide consumption rate (CCR) due to silicate rock weathering was 9.6 × 10⁵ mol km⁻²y⁻¹ and 8.3 × 10⁵ mol km⁻² y⁻¹ for 2016 and 2017, respectively. The CCR in the study area is higher than other large tropical river catchments like Amazon, Congo-Zaire, Orinoco, Parana and Indus because of its unique topography, hot and humid climate and intense rainfall.

Over the world, the available lithium (Li) resources are reserved mainly in closed-basin brines, with high Li concentration (> 150 mg/L) and low Mg/Li ratio (< 10) being critical for Li extraction using precipitation-based methods. In order to investigate the enrichment of Li over Mg during the formation of Li brine deposits, batch water–rock interacting experiments between igneous rocks and aqueous solutions were carried out under low (25, 50 and 75 °C) and high (200, 300 and 400 °C) temperature conditions. Our results show that for the experiments using water and accomplished under 25 °C, the Mg and Li concentrations vary from 0.470 and 0.782 mg/L in the solution interacted with Li-rich granite, to 5.626 and < 0.002 mg/L in that interacted with basalt, with Mg/Li ratio being slightly higher than those of the igneous rocks. By contrast, while a NaCl or Na₂SO₄ solution was used, the Mg and Li concentrations can be improved by up to tens of times, and the Mg/Li ratio also increased slightly. Lastly and above all, with increase in the water–rock interacting temperature from 25 to 400 °C, the Mg and Li concentrations in all solutions vary conversely and the Mg/Li ratio decreases by orders of magnitude, leading to the formation of Li-rich brines with very low Mg/Li ratios at temperatures above 200 °C. By comparing the results from our experiment to those from Li-rich springs, rivers and closed-basin brines, we conclude that water evaporation over time is fundamental for the concentration of Li in brines, meanwhile high-temperature hydrothermal processes are key to the formation of Li brine deposits with low Mg/Li ratios.

Equilibrium-kinetic modeling allows investigating metal behavior in the water–rock-organic matter system with time to evaluate anthropogenic effects on the environment. In the article, the interactions of stagnant mine drainage water of the flooded mine “Arsenic” with ore and gangue minerals were simulated using different organic matter incorporation approaches. If the model is closed to humic substances (no additional organic matter input), most fulvic acids are bound in the Fe fulvate complex. While under the removal of Fe fulvate from the model, the Cu fulvate becomes prevalent, the contribution of the fulvate complexes with Zn, Mg, and Ca also increases. This scenario simulates the organo-mineral complexes behavior well and allows identifying the sequence of metal binding to organic ligands as follows Fe > Cu > Zn > Mg > Ca. The second scenario imitates the constant input of organic matter to the model (open system regarding humic substances). The dissolved metal concentrations in the model solution are extremely high in comparison to the mine drainage water. This scenario demonstrates that excessive input of organic matter leads to the accumulation of the metals in a dissolved form and blocks the secondary mineral formation despite the faster dissolution of the primary minerals under a more acidic pH than in the first scenario. However, despite the differences between the model solution and the mine drainage water, this scenario is useful to address specific issues associated with changes in natural and anthropogenic conditions. Both scenarios show the importance of organic matter incorporation to the equilibrium-kinetic models.

The aim of this study was to develop an analytical method to determine free concentrations of Europium (Eu(III)) in natural waters. Europium(III) in solution was detected using cathodic stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). Optimization of analytical parameters allowed us to detect nanomolar levels of Eu(III) in solution. Free Eu(III) in solution was measured using the Donnan membrane technique in which a natural solution (the “donor”, containing various ligands) is separated from a ligand-free solution (the “acceptor”) by a cation-exchange membrane. This membrane allows only non-colloidal cationic species to pass through it, and after an adequate time equilibrium is reached between both compartments. Total Eu(III) concentration can then be quantified in the acceptor solution and related to free Eu(III) in the natural sample. Due to its high valency, free Eu(III) tends to adsorb strongly to the cation-exchange membrane. In order to determine the physicochemical conditions minimizing this adsorption, we analyzed solutions of different Eu(III) and Ca(II) (as background ion) concentrations. Results showed that 100 mM of Ca(II) were necessary to make adsorption of Eu(III) onto the membrane negligible. The optimized setup was then used to quantify Eu(III) complexation in a Eu(III)-dissolved organic matter solution.