Aquatic Geochemistry最新文献

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.

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.

To accurately predict the impacts of ocean acidification on shallow-water ecosystems, we must account for the biogeochemical impact of local benthic communities, as well as the connectivity between offshore and onshore water masses. Estimation of residence time can help quantify this connectivity and determine the degree to which the benthos can influence the chemistry of the overlying water column. We present estimates of nearshore residence time for Guam and utilize these estimates to model the effects of benthic ecosystem metabolism on the coral reef carbonate system. Control volume and particle tracking approaches were used to estimate nearshore residence time. These estimates were paired with observed patterns in the reef carbonate system around Guam using water samples collected by NOAA’s National Coral Reef Monitoring Program. Model performance results suggest that when considering the effects of benthic metabolism on the carbonate system, it is paramount to represent the contact time of the water volume with the benthos. Even coarse estimates of residence time significantly increase model skill. We observed the highest predictive skill in models including control volume derived estimates of residence time, but only when those estimates were included as an interaction with benthic composition. This work shows that not only is residence time critically important to better predict biogeochemical variability in coral reef environments, but that even coarse hydrodynamic models can provide useful residence time estimates at management relevant, whole-ecosystem scales.

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).