Aquatic Geochemistry最新文献

Estuarine total alkalinity (TA), which buffers against acidification, is temporally and spatially variable and regulated by complex, interacting hydrologic and biogeochemical processes. During periods of net evaporation (drought), the Mission-Aransas Estuary (MAE) of the northwestern Gulf of Mexico experienced TA losses beyond what can be attributed to calcification. The contribution of sedimentary oxidation of reduced sulfur to the TA loss was examined in this study. Water column samples were collected from five stations within MAE and analyzed for salinity, TA, and calcium ion concentrations. Sediment samples from four of these monitoring stations and one additional station within MAE were collected and incubated between 2018 and 2021. TA, calcium, magnesium, and sulfate ion concentrations were analyzed for these incubations. Production of sulfate along with TA consumption (or production) beyond what can be attributed to calcification (or carbonate dissolution) was observed. These results suggest that oxidation of reduced sulfur consumed TA in MAE during droughts. We estimate that the upper limit of TA consumption due to reduced sulfur oxidation can be as much as 4.60 × 10⁸ mol day⁻¹ in MAE. This biogeochemical TA sink may be present in other similar subtropical, freshwater-starved estuaries around the world.

The High Oum-Er-Rbia basin, located in the Moroccan Middle Atlas, is a karstic region with significant water sources that have essential functions regarding agriculture, hydropower production, industrial and drinking water. The region contains abundant wetlands, especially springs, rivers and natural lakes. These systems are highly sensitive to the effects of climate change, experiencing considerable lake level, water chemistry, and biological fluctuations in response to regional hydrological balances. This study focuses on the hydrogeochemical processes and mechanisms that control the chemical composition and variability of Azigza Lake, a typical tectono-karstic lake system of the region. Water monitoring was implemented from July 2013 to October 2014 with a monthly water sampling for physicochemical measurements and major ion concentration analyses of lake water and the surrounding groundwater. Both waters show a relatively low salinity due to the fresh input from the Lower Jurassic karst formation. Lake waters are slightly alkaline and of the calcium-magnesium-bicarbonate type. The geochemistry of the lake waters is mainly controlled by carbonate weathering through water–rock interaction and, to a lesser extent, by cation exchange and precipitation of carbonate minerals. The hydrochemistry of the lake showed clear responses to seasonal changes in precipitation and evaporation, with higher conductivity during the wet period. During the beginning of the wet season, groundwater evolution could be explained by a simple first flush stormwater. The rapid response of lake water to subsurface and underground waters confirms the dominance of an underground conduct flow regime. These changes and behaviors highlight the sensitivity of Azigza system to regional hydrological and climatic changes.

The aggregation and dispersion of metals and organic matter are an important morphological alteration process for their transportation and bioavailability in coastal areas. However, variable mixing behaviours can be observed for some substances (e.g. Mn and Cu) due to the variable interaction systems in natural systems. In this study, riverine freshwater in the Shira and Midori rivers, Kumamoto, Japan, was mixed with artificial seawater to investigate the aggregation and dispersion behaviours of trace metals (i.e. Fe, Al, Mn, Zn, Cu, V, and Ni) and organic matter. In particular, their interactions were examined with differentiating the fast and slow transformations and considering the effects of suspended substances. Comparisons of sequential processes, including seawater mixing, decantation, centrifugation, and multiple filtrations, illustrated the aggregation and dispersion characteristics of the metals and organic matter as follows. A strong aggregating nature was evident for Fe in estuarine systems. In addition, the slow aggregation of Fe was accelerated by river-borne suspended substances. Small Fe (oxy)hydroxide particles were the major forms of dissolved Fe in both freshwater and estuarine systems and were partly associated with the other metals. In contrast, Zn and Ni were characterised by strong dispersion properties, although it can resorb onto suspended substances in estuarine systems. Synchronous behaviours with Zn and Ni were observed for V, Cu, and organic matter in the Midori River. The adsorption of Mn onto suspended substances was evident in the freshwater systems instead of the estuarine systems. Meanwhile, the behaviour of Mn is known to be dependent on its abundance in suspended forms, its redox state, and the influence of Fe. V and Cu, which are non-conservative in nature, were affected by other metals such as Fe, Zn, and Ni. Al, whose behaviour is largely dependent on the target estuary, which was also affected by other metals. Slow aggregation of organic matter was induced by suspended substances which were produced by fast transformation. In addition, evident interactions between suspended and dissolved substances were observed with the behaviours of Fe, Zn, Ni, and organic matter, indicating that the deposition and dispersion at the early stage of estuarine mixing can influence the subsequent slow transformation in real environments.

Two basaltic rocks were reacted in acid sulfate and non-acid sulfate solutions with an initial pH value of 2 in the presence and absence of A. ferrooxidans to determine if basalt dissolution can support the metabolically active growth of A. ferrooxidans. Similar elemental release rates (R_Si, R_Ca, R_Mg) calculated for both biotic and abiotic experiments suggest rather a negligible microbial impact on the dissolution of basaltic rocks within the acid sulfate solution. Nevertheless, in contrast with the abiotic experiments, measurements of remarkably high concentration of Fe(III)_aq in microbial experiments confirmed the bacterial metabolism. Moreover, detected cell division and increasing total cell numbers with the extent of the experiments provide further evidence for the growth of metabolically active A. ferrooxidans during the dissolution of the rocks. Formation of jarosite ((K, Na, H₃O)Fe₃(SO₄)₂(OH)₆) only in the biotic experiments is attributed to the microbially catalyzed Fe(II)_aq oxidation. Overall, our results showed that acidic solutions that reacted with basaltic rocks can sustain the growth of Fe(II)_aq oxidizing bacteria. Furthermore, identification of jarosite only in the biotic experiments emphasizes the enzymatic Fe(II) oxidation as the key step for its formation during basalt weathering at acid conditions, highlighting its biosignature potential on Earth and Earth-like planets (e.g., Mars).

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.