Aquatic Geochemistry最新文献

In the global carbon cycle, rivers are the main transport channel for terrestrial carbon sources into the ocean, and their CO₂ fluxes at the water–air interface affect the carbon budget. As an important component of the carbon cycle in the terrestrial ecosystem, karst regions exhibit carbon source and sink effects due to their special environmental conditions. To elaborate the spatial and temporal distribution of CO₂ fluxes at the water–air interface of karst rivers and the influencing factors, systematic monitoring of small karst rivers in southwest China was conducted between November and December 2019 and between June and July 2020, respectively. The results show that: (1) the water chemistry of Chiwuxi River belonged to the HCO₃–Ca–Mg type, and Ca²⁺ and HCO₃⁻ temporally showed a larger concentration in the dry season than in the wet season. (2) CO₂ partial pressure (pCO₂) and CO₂ fluxes showed a seasonal characteristic of higher values in the wet season than in the dry season. pCO₂ ranged from 323.59 to 1380.38 μatm and CO₂ fluxes ranged from −24.31 to 353.74 mmol (m² d)⁻¹. During the wet season, the Chiwuxi River showed a carbon source effect. During the dry season, the photosynthesis of aquatic plants reduced CO₂ outgassing. (3) Isotopic compositions of dissolved inorganic carbon (δ¹³C_DIC) showed a higher value in the dry season than in the wet season. The dissolved inorganic carbon mainly originated from soil CO₂ and carbonate weathering. To improve the understanding of riverine carbon cycling, it is necessary to study CO₂ fluxes at the water–air interface of small rivers in the karst region. Thus, this will help to reduce the uncertainty of CO₂ fluxes in global rivers.

This work focuses on the characterization of a typical coastal karst watershed by addressing its physico-chemical parameters. The concentrations of the main ions clearly indicate the dominance of Ca²⁺ and HCO₃⁻ with a carbonate weathering rate equivalent to 230t/Km²/year; that is a typical weathering of karst watersheds. The spatio-temporal variability of dissolved organic matter (DOM) is also assessed in the watershed. Many samples were collected under different hydrological conditions from three representative sites. The evolution of OM composition along an urbanization gradient from upstream to downstream Kadisha watershed reveals the very strong impact of urban discharges on the receiving waters. Substantial differences in DOC results are highlighted in relation to the urban or natural origin of the DOM. Upstream OM flux is quantified and compared to downstream OM flux showing that, during the low flow period, the downstream flux is 29 times higher than the upstream. Also, a large fraction of non-humic substances, including hydrophilic organic matter HPI, is detected in the downstream section impacted by urban discharges. The higher values of SUVA noticed for DOM at upstream compared to downstream, reflects the low aromaticity and non-humic character of DOM in downstream. These outcomes show the impact of the Tripoli urban discharges on the quality and quantity of OM in the receiving waters downstream of the Kadisha catchment. This is typical at low water period when the dilution factor of urban discharges in the receiving waters is the least.

As renewable energy, geothermal can contribute substantially to the energy transition. To generate electricity or to harvest heat, high-saline fluids are tapped by wells of a few kilometres and extracted from hydrothermal reservoirs. After the heat exchanger units have been passed by, these fluids are reinjected into the reservoir. Due to the pressure and temperature differences between the subsurface and the surface, as well as the cooling of the fluids in the power plant, unwanted chemical reactions can occur within the reservoir, in the borehole, and within the power plant itself. This can reduce the permeability of the reservoir as well as the output of the geothermal power plant. This study aims to simulate real subsurface reactions using batch and leaching experiments with sandstone or sandstone powder as solid phase, and deionised water or natural brine as liquid phase. It is demonstrated that fluid composition changes after only a few days. In particular, calcite, aragonite, clay minerals, and zinc phases precipitate from the natural brine. In contrast, in particular minerals containing potassium, arsenic, barium, and silica are dissolved. Due to the experimental set-up, these mineral reactions mainly took place on the surface of the samples, which is why no substantial changes in petrophysical properties could be observed. However, it is assumed that the observed reactions on the reservoir scale have a relevant influence on parameters such as permeability.

Lake systems are essential for the environment, the biosphere, and humans but are highly impacted by anthropogenic activities accentuated by climate change. Understanding how lake ecosystems change due to human impacts and natural forces is crucial to managing their current state and possible future restoration. The high sensitivity of shallow closed lakes to natural and anthropogenic forcing makes these lacustrine ecosystems highly prone to variations in precipitation and sedimentation processes. These variation processes, occurring in the water column, produce geochemical markers or proxies recorded in lake sedimentary archives. This study investigated specific proxies on high-resolution sedimentary archives (2–3 years resolution) of the Trasimeno lake (Central Italy). The Trasimeno lake underwent three different hydrological phases during the twentieth century due to several fluctuations induced mainly by human activities and climate change. The Trasimeno lake, a large and shallow basin located in the Mediterranean area, is a good case study to assess the effects of intense anthropogenic activity related to agriculture, tourism, industry, and climate changes during the Anthropocene. The aim is to identify the main characteristics of the main sedimentary events in the lake during the last 150 years, determining the concentrations of major and trace elements, the amount of organic matter, and the mineralogical composition of the sediments. This type of work demonstrates that studying sediment archives at high resolution is a viable method for reconstructing the lake’s history through the evolution/trends of the geochemical proxies stored in the sediment records. This effort makes it possible to assess past anthropogenic impact and, under the objectives of the European Green Deal (zero-pollution ambition for a toxic-free environment), to monitor, prevent, and remedy pollution related to soil and water compartments.

Graphical abstract

We investigated the detrital influx, chemical weathering intensity, provenance and pedogenesis over the past 2,500 years in the catchment of Pookot Lake, southern India. The down-core variations of metal/Al ratios (Na/Al, K/Al, Mg/Al, Ca/Al, Fe/Al, Mn/Al, Zn/Al, Ba/Al) of the Pookot sediments indicate changes in the rainfall-induced terrigenous inflow to the lake. In contrast, fluctuations in the chemical index of alteration (CIA) and Rb/Sr values denote the variability in the strength of chemical weathering in the watershed of the lake. The results show that the detrital influx, and hence rainfall, remained steady except during 1500–600 cal. years B.P. (high) and 600–300 cal. year B.P. (low) in the Pookot lake catchment. However, the periods of high/low chemical weathering intensity in the catchment do not correspond to periods of high/low detrital influx to the lake basin. The similar shale-normalized rare earth elemental curves point to a uniform provenance. The past pedogenic activity is indicated by pedogenic χ_lf and pedogenic χ_fd derived from citrate-bicarbonate-dithionite (CBD) extraction. The data indicate that the fine-grained magnetite/maghemite formed during the pedogenesis mainly contributes to the magnetic signal of sediments. The degree of pedogenesis was strong during 2500–2000 cal. years B.P. and moderate throughout 1500–600 cal. years B.P. The pedogenic intensity became stronger again during ~ 600 cal. years B.P., which weakened between 600 and 300 cal. years B.P. and remained steady thereafter. The present study indicates that detrital influx proxies like metal/Al ratios are more suitable for reconstructing past climate in tropical climate rather than chemical weathering indices.

The resuspension of sediment leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget. Especially in the warmer months with a lower oxygen saturation and higher biological activity, the oxygen content can reach critical thresholds in estuaries like the upper Elbe estuary. Many studies have dealt with the nutrient fluxes that occur during a resuspension event. However, the sediment properties that influence the oxygen consumption potential (OCP) and the different biochemical processes have not been examined in detail. To fill this gap, we investigated the biogeochemical composition, texture, and OCP of sediments at 21 locations as well as the temporal variability within one location for a period of 2 years (monthly sampling) in the upper Elbe estuary. The OCP of sediments during a seven-day resuspension event can be described by the processes of sulphate formation, nitrification, and mineralisation. Chlorophyll, total nitrogen (N_total), and total organic carbon showed the highest correlations with the OCP. Based on these correlations, we developed a prognosis model to calculate the OCP for the upper Elbe estuary with a single sediment parameter (N_total). The model is well suited to calculate the oxygen consumption of resuspended sediments in the Hamburg port area during the relevant warmer months and shows a normalised root mean squared error of < 0.11 ± 0.13. Thus, the effect of maintenance measures such as water injection dredging and ship-induced wave on the oxygen budget of the water can be calculated.

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of seawater carbonate chemistry across different reefs is critical for elucidating future impacts on coral reefs. To date, most studies have focused on select habitats, whereas fewer studies have focused on reef scale variability. Here, we investigate the temporal and spatial seawater physicochemical variability across the entire Heron Island coral reef platform, Great Barrier Reef, Australia, for a limited duration of six days. Autonomous sensor measurements at three sites across the platform were complemented by reef-wide boat surveys and discrete sampling of seawater carbonate chemistry during the morning and evening. Variability in both temporal and spatial physicochemical properties were predominantly driven by solar irradiance (and its effect on biological activity) and the semidiurnal tidal cycles but were influenced by the local geomorphology resulting in isolation of the platform during low tide and rapid flooding during rising tides. As a result, seawater from previous tidal cycles was sometimes trapped in different parts of the reef leading to unexpected biogeochemical trends in space and time. This study illustrates the differences and limitations of data obtained from high-frequency measurements in a few locations compared to low-frequency measurements at high spatial resolution and coverage, showing the need for a combined approach to develop predictive capability of seawater physicochemical properties on coral reefs.

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.