Search Results (41)

The Cochin Backwater region in Southern India is one of the most dynamic estuaries, strongly influenced by seasonal river runoff and seawater intrusion. This study explores the relationship between monsoonal rains, salinity, and stable isotopic composition (δ¹⁸O and δ¹³C) to estimate the contribution of freshwater fluxes at different seasonal intervals for the Cochin Backwater (CBW) estuary. Seasonal variations in oxygen isotopes and salinity revealed distinct trends indicative of freshwater–seawater mixing dynamics. The comparison of Local and Global Meteoric Water Lines highlighted the occurrence of enriched isotope values during the Premonsoon season, showing significant evaporation effects. Carbon (C) isotopic analysis in dissolved inorganic matter (δ¹³C_DIC) at 17 stations during the Premonsoon season revealed spatially distinct carbon dynamics zones, influenced by various sources. These characteristic zones were categorized as Zone 1, dominated by seawater, exhibiting heavier δ¹³C_DIC values; Zone 2, showing significant contributions of lighter terrestrial δ¹³C; and Zone 3, reflecting inputs from regional and local paddy fields with a distinct C₃ isotopic signature (−25‰), modified by estuarine productivity. In addition, different advanced machine learning techniques were tested to improve analysis and prediction of seasonal variations in isotopic composition and salinity. Although the data were sufficiently robust for demonstrating the feasibility and advantages of ML in isotopic hydrology, further expansion of the dataset would be essential for improving the accuracy of models, especially for δ¹³C. The combination of these advanced machine learning models not only improved the predictive accuracy of seasonal freshwater fluxes but also provided a robust framework for understanding the estuarine ecosystem and could pave the way for better management and conservation strategies of the CBW estuarine system. Full article

Water hardening and NO₃⁻ pollution have affected water quality globally. These environmental problems threaten social sustainability and human health, especially in piedmont agricultural areas. The aim of this study is to determine the biogeochemical mechanisms of HCO³–Ca water and NO₃⁻ pollution in a typical piedmont agricultural area (Qingshui River, Zhangjiakou, China). Here, an extensive biogeochemical investigation was conducted in a typical piedmont agricultural area (Qingshui River, China) using multiple hydrochemical, isotopic (δ²H-H₂O, δ¹⁸O-H₂O and δ¹³C-DIC) and molecular-biological proxies in combination with a forward model. In the region upstream of the Qingshui River, riverine hydrochemistry was dominated by HCO₃–Ca water, with only NO₃⁻ concentrations (3.08–52.8 mg/L) exceeding the acceptable limit (10 mg/L as N) for drinking water quality. The riverine hydrochemistry responsible for the formation of HCO₃–Ca water was mainly driven by carbonate dissolution, with a contribution rate of 49.8 ± 3.96%. Riverine NO₃⁻ was mainly derived from agricultural NH₄⁺ emissions rather than NO₃⁻ emissions, originating from sources such as manure, domestic sewage, soil nitrogen and NH₄⁺-synthetic fertilizer. Under the rapid hydrodynamic conditions and aerobic water environment of the piedmont area, NH₄⁺-containing pollutants were converted to HNO₃ by nitrifying bacteria (e.g., Flavobacterium and Fluviimonas). Carbonate (especially calcite) was preferentially and rapidly dissolved by the produced HNO₃, which was attributed to the strong acidity of HNO₃. Therefore, higher levels of Ca²⁺, Mg²⁺, HCO₃⁻ and NO₃⁻ were simultaneously released into river water, causing riverine HCO₃–Ca water and NO₃⁻ pollution in the A-RW. In contrast, these biogeochemical mechanisms did not occur significantly in the downstream region of the river due to the cement-hardened river channels and strict discharge management. These findings highlight the influence of agricultural HNO₃ on HCO₃–Ca water and NO₃⁻ pollution in the Qingshui River and further improve the understanding of riverine hydrochemical evolution and water pollution in piedmont agricultural areas. Full article

This entry examines Lorenz’s error growth models with quadratic and cubic hypotheses, highlighting their mathematical connections to the non-dissipative Lorenz 1963 model. The quadratic error growth model is the logistic ordinary differential equation (ODE) with a quadratic nonlinear term, while the cubic model is derived by replacing the quadratic term with a cubic one. A variable transformation shows that the cubic model can be converted to the same form as the logistic ODE. The relationship between the continuous logistic ODE and its discrete version, the logistic map, illustrates chaotic behaviors, demonstrating computational chaos with large time steps. A variant of the logistic ODE is proposed to show how finite predictability horizons can be determined, emphasizing the continuous dependence on initial conditions (CDIC) related to stable and unstable asymptotic values. This review also presents the mathematical relationship between the logistic ODE and the non-dissipative Lorenz 1963 model. Full article

Reclaimed landfill areas are excluded from various development options including construction, while contaminated zones around such places have no such restrictions. The successful reclamation of landfills means that the old landfill visually fits in well with its surroundings, but soil and water contamination problems remain valid. Former landfills were built without properly preparing the land, which resulted in the migration of contaminants in groundwater for a long period after these landfills were closed, further resulting in the limited use of such areas, at least for some purposes. Due to the development of cities, landfills formerly located in suburbs are becoming a part of these cities. In order to optimally and safely use these spaces, knowledge regarding the quality of the soil and water environment is necessary. This article presents methodological considerations regarding the use of carbon and sulfur isotope methods to assess groundwater contamination around former municipal waste landfills, especially reclaimed municipal landfills. It has been shown that natural groundwater is characterized by low values of both δ¹³C_DIC and δ³⁴S (δ¹³C_DIC from −20 to −10‰ and δ³⁴S at approximately −5‰), whereas leachate-contaminated groundwater is characterized by high values of both parameters (δ¹³C_DIC from −10 to + 5‰ and δ³⁴S from +5 to +20‰). The aim of this article is to demonstrate that carbon and sulfur isotope methods extended via SWOT analysis are universal and reliable methods for assessing the migration of pollutants, thus facilitating decisions regarding management. Full article

Lake carbon cycle in lake ecosystems is critical for regional carbon management. The application of carbon isotope techniques to terrestrial and aquatic ecosystems can accurately elucidate carbon flow and carbon cycling. Lake ecosystems on the Qinghai–Tibetan Plateau are fragile and sensitive to climate and environment changes, and the carbon cycle impact on the carbon isotopic composition (δ¹³C) of dissolved inorganic carbon (DIC) in these systems has not been well studied, limiting the ability to devise effective management strategies. This study explored the relationship among the δ¹³C position of the DIC (δ¹³C_DIC) in Genggahai Lake, the lake environment, and the climate of the watershed based on the observed physicochemical parameters of water in areas with different types of submerged macrophyte communities, combined with concomitant temperature and precipitation changes. Overall, the Genggahai Basin δ¹³C_DIC exhibited a large value range; the average δ¹³C_DIC for inflowing spring water was the most negative, followed by the Shazhuyu River, and then lake water. Variations in the photosynthetic intensity of different aquatic plants yielded significantly changing δ¹³C_DIC-L values in areas with varied aquatic plant communities. Hydrochemical observations revealed that δ¹³C_DIC-I and aquatic plant photosynthesis primarily affected the differences in the δ¹³C_DIC-L values of Genggahai Lake, thereby identifying them as the key carbon cycle components in the lake. This improves the understanding of the carbon cycle mechanism of the Qinghai–Tibetan Plateau Lake ecosystem, which is beneficial to improving sustainable lake development strategies. Full article

Carbonic acid and sulfuric acid speleogenesis describe a dichotomy between epigenetic and hypogenetic caves and carbon and sulfur cycling in karst, but do not acknowledge the global spectrum of cave formation. This paper, part one of a two-part investigation, tests and revises speleogenetic models from a classic karst landscape using dissolved ion concentrations δ¹³C_DIC, and δ³⁴S in water samples collected at four sites across the Bluespring and Lost River karst basins in the Mitchell Plateau, Indiana, USA. Analyses revealed elevated sulfur in both karst basins but differently sourced; H₂S (δ³⁴S = −14.2‰) evolved from petroleum seeps in Bluespring Caverns accounted for up to 61% of sulfur in the cave stream, while evaporite beds (δ³⁴S = [+14.50‰, +17.91‰]) of the St. Louis Limestone contributed up to 100% of sulfur at Orangeville Rise, a terminal spring of the Lost River karst basin. These results have implications for carbon–sulfur cycle linkages, particularly the potential acceleration of carbon flux from sulfuric acid dissolution in otherwise epigenetic settings. We suggest a new paradigm for speleogenesis in the North American midcontinent—speleogenesis in the Mitchell Plateau and similar settings is not epigenetic or hypogenetic, but instead polygenetic with competing chemical processes varying across space and time. Full article

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H₂SO₄ is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H₂SO₄ on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ¹³C_DIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ¹³C_DIC values (−17.0% to −14.7‰) and the [Ca²⁺ + Mg²⁺]/[HCO₃⁻] (0.98 to 1.25) and [Ca²⁺ + Mg²⁺]/[HCO₃⁻ + SO₄²⁻] (approximately 1) equivalent ratios of samples prove that H₂CO₃ and H₂SO₄ simultaneously participate in carbonate weathering. The contribution rates of H₂SO₄ to [Ca²⁺ + Mg²⁺] and [HCO₃⁻] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H₂SO₄ on different lithological carbonate weathering is different. H₂SO₄ precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies. Full article

The significance of CO₂ emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO₂ emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO₂ emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO₂ degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO₂ degassing flux. Affected by the pCO₂ concentration gradient between the water and ambient air, the spring water showed a high CO₂ degassing flux (166.19 ± 91.91 mmol/(m² d)). After the spring outlet, the CO₂ degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m² d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 10⁴/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ¹³C_DIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO₂ concentration, thus limiting the amount of CO₂ off-gassing (90.56 ± 55.03 mmol/(m² d)). Full article

In deep karst reservoirs, the internal environment is complex, and thermal stratification isnot the only factor controlling the vertical distribution of the DIC concentration. Previous studies have not fully understood the migration and transformation of DIC in a deep-water reservoir. In this study, a deep-water reservoir in southwest China was chosen, and the spatial and temporal characteristics of the DIC concentration, pCO₂, δ¹³C_DIC value, and SIc were investigated. It was found that the Pingzhai Reservoir is a double temperature leapfrog reservoir. The DIC concentration, pCO₂, Sic, and δ¹³C_DICvalues showed annual cycle variation. During the thermal stratification phase, the DIC concentration, pCO₂, Sic, and δ¹³C_DICvalues were significantly different between the surface layer and the lower layer. However, during the mixing and mixed phases, the differences were not significant. The vertical divergence of the DIC in the Pingzhai Reservoir was influenced by the subtemperate layer, human activities, and sources. The formation of the subtemperate layer was due to the submerged flow formed when river water enteredthe reservoir, which provides a channel for DIC from the river to enter the lower layer of the reservoir. Human activities increased the solubility of carbonate rocks in the reservoir, and the source of DIC was one of the factors contributing to the concentration stratification of DIC in the reservoir. Full article

This article presents the new data on the chemical and gas composition, the content of stable isotopes of oxygen, hydrogen, carbon, and sulfur in natural mineral waters of the Essentuki field. A detailed study of the geological and hydrogeological features of the water circulation area, its major chemical composition, the content of organic matter in water, temperature conditions and δ¹⁸O_SMOW, δD_SMOW, δ¹³C_DIC, δ¹⁸O_DIC, δ³⁴S_VCDT, δ¹³C_CO2, δ¹³C_CH4, δ¹⁵N values made it possible to specify the genesis of water, gas, and solute components of the Essentuki CO₂-rich mineral water field. The stable isotopes values (δ¹⁸O_SMOW and δD_SMOW) in the water phase ranges from −13.75 to −9.69‰ and from −101.08 to −74.34‰, respectively. They correspond to GMWL, which indicates their predominantly infiltration genesis. The values of δ¹³C_DIC in mineral waters of the Essentuki field vary widely from −14.43 to +8.59‰ and indicate their mixed genesis. δ¹⁵N gas values in mineral waters of the Essentuki field vary quite widely from −2.31 to 2.50‰ indicating a different source of this gas. Obtained data prove that all mineral waters in the Essentuki field are infiltration waters, and the heterogeneous component composition of waters circulating in different aquifers reflects the lithological composition of water-bearing strata, the rate of openness/closure of faults and the intensity of reactions in the «water-rock-gas-organic matter» system. Full article

The response of coastal systems to global acidification depends strongly on river inputs, which can alter the total alkalinity (A_T) and dissolved inorganic carbon (DIC) in seawater. The northern Adriatic Sea (NAd) is a shallow continental shelf region that currently receives about 15% of the total freshwater input in the Mediterranean Sea, where the role of riverine discharges on the carbonate system has been poorly studied. In particular, river discharges can alter the carbonate system in the sea, affecting both the equilibrium chemistry and biological processes. For the main rivers flowing into the NAd (the Po, Adige, Brenta, Piave, Livenza, Tagliamento, Isonzo, Timavo and Rižana), data were collected for the pH, concentrations of the total alkalinity (A_T), Ca²⁺ and Mg²⁺ and the isotopic ratio of stable carbon in the dissolved inorganic carbon (δ¹³C_DIC). The DIC fluxes were estimated using the THINCARB (THermodynamic modeling of INOrganic CARBon) model for the compilation of the A_T and pH data. The results show that the total transport of the A_T in the rivers was 205 Gmol yr⁻¹ while the transport of the DIC was 213 Gmol yr⁻¹, of which about 70% was from the Po River. About 97% of the DIC in the river waters was in the form of bicarbonates. The high Mg²⁺/Ca²⁺ ratios indicate that dolomite weathering is predominant in the Adige, Piave, and Livenza river basins, while lower ratios in the Timavo and Rižana rivers indicate a greater proportion of calcite. The mean δ¹³C-DIC value was estimated to be −10.0 ± 1.7 ‰, a value nowadays considered typical for the DIC flux inputs in oceanic carbon cycle modeling. The DIC flux depends on the mineral weathering and biological activity in each river basin. However, these natural processes can be modified by anthropogenic disturbances that should be better quantified. Full article

To study the distribution features of microorganisms in distinct hydrological areas of the southern Qinshui Basin, C-N-S microorganisms were studied using 16S RNA sequencing, metagenome sequencing and geochemical technologies, showing the high sensitivity of microorganisms to the hydrodynamic dynamics of coal. The hydrodynamic intensity of the #3 coal gradually decreased from the runoff areas to the stagnant areas. The stagnant zones have higher reservoir pressure, methane content, δ¹³C_DIC and TDS and lower SO₄²⁻, Fe³⁺ and NO₃⁻ concentrations than the runoff areas. C-N-S-cycling microorganisms, including those engaged in methanogenesis, nitrate respiration, fermentation, nitrate reduction, dark oxidation of sulfur compounds, sulfate respiration, iron respiration, chlorate reduction, aromatic compound degradation, denitrification, ammonification and nitrogen fixation, were more abundant in the stagnant areas. The relative abundance of C-N-S functional genes, including genes related to C metabolism (e.g., mcr, mer, mtr, fwd and mtd), N metabolism (e.g., nifDKH, nirK, narGHI, nosZ, amoB, norC and napAB) and sulfur metabolism (e.g., dsrAB and PAPSS), increased in the stagnant zones, indicating that there was active microbiological C-N-S cycling in the stagnant areas. The degradation and fermentation of terrestrial plant organic carbon and coal seam organic matter could provide substrates for methanogens, while nitrogen fixation and nitrification can provide nitrogen for methanogens, which are all favorable factors for stronger methanogenesis in stagnant areas. The coal in the study area is currently in the secondary biogenic gas generation stage because of the rising of the strata, which recharges atmospheric precipitation. The random forest model shows that the abundance of C-N-S microorganisms and genes could be used to distinguish different hydrological zones in coal reservoirs. Since stagnant zones are usually high-gas-bearing zones and high-production areas of CBM exploration, these microbiological indicators can be used as effective parameters to identify high-production-potential zones. In addition, nitrate respiration and sulfate respiration microorganisms consumed NO₃⁻ and SO₄²⁻, causing a decrease in the content of these two ions in the stagnant areas. Full article

The hydrochemical analysis method was used to reveal the sources and spatiotemporal variations of carbon and nitrogen elements in the Pingzhai Reservoir, and the C–N coupling cycle and its influence on the karst carbon sink are discussed. The results show the following: (1) The hydrochemical type of the study area is HCO₃-Ca. (2) From the river to the reservoir and then to the reservoir outlet, the values of HCO₃⁻ and δ¹³C_DIC showed an opposite trend. The values of NO₃⁻, δ¹⁵N-NO₃⁻, and δ¹⁸O-NO₃⁻ were different in each stage of the river. (3) HCO₃⁻ mainly comes from the weathering of carbonate rocks and the oxidative decomposition of organic matter. Nitrate mainly comes from chemical fertilizers, soil organic nitrogen, sewage, and livestock manure. (4) The average proportion of HCO₃⁻ produced by HNO₃ dissolving carbonate rock is 8.38%, but this part does not constitute a carbon sink. Compared with rivers, the proportion of HCO₃⁻ and (Ca²⁺ + Mg²⁺) produced by HNO₃ dissolving carbonate rock in reservoir water is relatively large. The input of nitrate not only pollutes the water body with NO₃⁻ but also changes the carbon source/sink pattern of the water–rock interaction. Full article

Cyclodextrins (CDs) are macrocyclic oligosaccharides, containing between six and eight alpha(1 → 4)-linked glucopyranoses. CDs have a hydrophobic cone-shaped internal cavity and a hydrophilic exterior surface. They form non-covalent inclusion complexes (ICs) with various drugs by trapping the full or partial inclusions in their cavity. Supramolecular ICs have gained attention in engineering entrapped drug performance field due to their potential to protect and modify the physicochemical properties of entrapped lipophilic and volatile drugs. However, the poor structural and mechanical properties of pure CD-ICs could restrict their application and the need for a suitable carrier system. Electrospun nanofibers have been the center of attention for biomedical applications due to their tunable physicochemical properties. Recent studies have highlighted that the entrapment of drug/CD-based ICs into nanofibers is an active research area since it facilitates high encapsulation, it modulates the release profile of the guest, integrates multi-type drugs, and leads to a synergistic effect. This mini-review first summarizes the potential benefits and shortcomings of drug/CD-ICs and nanofibers, and then, we discuss the advancements in the fabrication and characteristics of CD-ICs embedded nanofibers, along with some practical suggestions for potential biomedical applications. Full article

Groundwater is a valuable source of water for human consumption, and its quality is a current issue worldwide. Understanding carbon and water cycling presents the basis of biogeochemical reactions occurring in the aquifer; therefore, understanding their interaction is imperative for sustainable water management. In the paper, this interaction was investigated within the complex surface water (SW)–groundwater (GW) system in the Varaždin region (Croatia) by using a multi-parameter approach: δ¹³C_DIC values, carbon species (DIC, DOC), δ¹⁸O and δ²H values, geochemical indicators (T, pH, DO, EC), and δ¹³C measurements in solids. Both δ¹⁸O/δ²H and δ¹³C_DIC were recognized as good indicators to differentiate shallow and deep GW. Transit time of water (TT) was evaluated as an important parameter in controlling carbon cycling within the SW–GW system. Shallow GW is characterized by shorter TT, seasonal changes in carbon species and δ¹³C_DIC, and lower possibility of carbon capture in the system. Deep GW has longer TT without pronounced seasonal changes in carbon species and δ¹³C_DIC. The conceptual model of the carbon cycle revealed major sources and sinks of CO₂ in the study area. Our results suggest that GW acts as both source and sink for CO₂, depending on the prevailing geochemical process. Surface waters are primarily a source of CO₂, excluding the gravel pit, which acts primarily as a sink for CO₂. Our study shows that the current SW–GW dynamics regulate carbon balance without having negative impacts on groundwater quality but also demonstrates that implementing carbon cycle in water management studies is of vital importance for sustainable use of groundwater. Full article