Search Results (120)

Inland rivers in arid regions are important water resources that support ecosystem stability and human activities. This study comparatively investigated the hydrochemical characteristics, controlling factors, and irrigation suitability of six glacier-fed inland rivers along the southern margin of the Tarim Basin using hydrochemical analysis, Gibbs and Piper diagrams, ion-ratio analysis, principal component analysis (PCA), and PHREEQC inverse mass-balance modeling. The six rivers exhibited distinct hydrochemical characteristics despite their common origin in the Kunlun Mountains. Carbonate weathering dominated the Bostan and Nur rivers, while the Kaxi River exhibited relatively stable hydrochemical characteristics mainly associated with rock weathering. In contrast, evaporite dissolution and evaporative concentration exerted stronger influences on the Uruksayi and Buzang rivers, which also showed more pronounced longitudinal variations in major ion concentrations. The Keriya River showed an overall transition from silicate-weathering-dominated conditions in the upper reaches toward stronger evaporite dissolution and evaporative concentration downstream. PHREEQC inverse mass-balance modeling suggested that halite dissolution, gypsum dissolution, dolomite dissolution, calcite precipitation, and cation exchange contributed to the hydrochemical evolution of the Keriya River. Several abrupt variations in ion concentrations were observed along the river courses, suggesting that localized processes, including tributary mixing, groundwater inputs, or potential anthropogenic influences, may contribute to these hydrochemical changes. PCA extracted two principal components explaining 86.0% of the total variance. PC1 (70.5%) represented overall ion enrichment and mineralization, whereas PC2 (15.5%) reflected carbonate-related hydrochemical variations. Irrigation suitability assessment showed that all rivers exhibited low sodium hazards, while salinity was the main factor limiting irrigation suitability in the middle and lower reaches of the Keriya River and in the Uruksayi and Buzang rivers. This study improves the understanding of hydrochemical evolution and water quality assessment of arid inland rivers and provides scientific support for sustainable water resource management and oasis ecosystem protection in the southern Tarim Basin. Full article

This study investigated nitrate contamination, potential nitrate sources, and transformation processes in shallow and deep groundwater of a steep coastal agricultural catchment in western Japan. Hydrochemistry and Endmember Mixing Analysis (EMMA) were applied to shallow and deep groundwater samples collected along a groundwater flow path. A spring and a river sample were used for comparative purposes. The results suggested that the groundwater hydrochemistry comprised mixed, Ca-HCO₃, Ca-Cl, and Na-Cl water types. Nitrate concentrations exceeded 10 mg L⁻¹ in 51.1% (23 out of 45) of the groundwater samples, higher in upstream groundwater than downstream groundwater, especially in deep wells. EMMA suggested agricultural recharge water as potentially the main nitrate source contributor to groundwater. Sewage contributions were greater in shallow wells, and deep natural groundwater in deep wells. The transformation processes were associated with nitrate addition via fertilizers and nitrification, water mixing, and nitrate removal potential by denitrification in shallow downstream wells. Sewage contributions were associated with the shallow downstream groundwater in areas with a greater residential area. Groundwater mixing was suggested to influence hydrochemical variability, especially in DD groundwater, which showed stronger coastal influences. These findings improve understanding of nitrate contamination and support sustainable groundwater management in steep coastal agricultural areas. Full article

Runoff recharge increases during the wet season in arid inland river basins; however, solute inputs along river courses, evaporite salt dissolution, and leaching from saline sediments may still substantially modify the chemical composition of surface waters. To identify the sources of major ions, hydrochemical controlling processes, and salt-enriched river reaches during the wet season in the Cele River Basin, 107 surface water samples were collected from the mainstream of the Cele River and five major tributaries in August 2025. Field and laboratory analyses were conducted for pH, total dissolved solids (TDS), electrical conductivity (EC), dissolved oxygen (DO), and major ions, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, and HCO₃⁻. Piper diagrams, Gibbs diagrams, ionic ratios, Spearman correlation analysis, and principal component analysis (PCA) were used to characterize the major-ion composition, hydrochemical facies, and controlling factors. The results show that the surface waters were generally weakly alkaline, with pH values ranging from 7.42 to 8.46. TDS and EC exhibited pronounced spatial heterogeneity, with higher salinity levels in the Buzang River, the Cele River mainstream, and the Uluk Say River, and relatively lower mineralization in the Bostan River and Nur River. SO₄²⁻ and Cl⁻ dominated the anionic composition, together accounting for 80.3% of total anions, whereas Ca²⁺ + Mg²⁺ and Na⁺ + K⁺ jointly controlled the cationic composition, accounting for 57.3% and 42.7% of total cations, respectively. The Piper diagram indicated that the Cl·SO₄–Na·Ca type was the dominant hydrochemical facies, accounting for 67.3%, suggesting a pronounced sulfate–chloride salt-enrichment signature during the wet season. Evidence from Gibbs diagrams, ionic end-member ratios, and PCA further indicates that the hydrochemical composition is primarily constrained by rock weathering and jointly influenced by sulfate and chloride salt dissolution, evaporation–concentration processes, and leaching from saline sediments. These processes reflect the coexistence of runoff dilution and salt reloading during the wet season. The Buzang River, Cele River mainstream, and Uluk Say River should be prioritized for continuous water-quality monitoring and salinity-risk early warning, while TDS, EC, Na⁺, Cl⁻, and SO₄²⁻ can serve as core indicators for diagnosing wet-season water–salt processes and tracking water-quality baselines. This study identifies the key salt-enriched reaches, major ion sources, and hydrochemical control mechanisms of surface waters in the Cele River Basin during the wet season, providing a scientific basis for water-quality protection, oasis agricultural water regulation, and sustainable water–salt management in arid inland river basins. Full article

Groundwater is one of the basic requirements for life, economic and social developments in the Bazo River catchment, Rift Valley, Southern Ethiopia. In the study area, availability of water is faced with several problems, such as quality issues due to high levels of fluoride in some samples, spring scarcity in the lowlands, unprotected river water used for drinking, and high demand for good quality water. The aim of this study was to investigate the hydrogeochemical characteristics and to evaluate groundwater quality for domestic and irrigation uses. Thirty-four primary groundwater samples were collected from the field and analyzed in the water quality lab of Arba Minch University. Two water quality indices (WQI and EWQI), a variety of irrigation water quality indices, and GIS-based spatial analysis were utilized in this study. Cations were present in the descending order of Na > Ca > Mg > K > Fe, and anions were HCO₃⁻ > Cl > SO₄ > NO₃⁻ > F. Excepting two samples (BH8 and SP3), the water samples were acceptable for drinking. Sodium, TDS, and fluoride levels were over the limit of drinking water in BH8 and SP3. Rock–water interaction, cation exchange, and silicate mineral weathering were the main hydrogeochemical reactions that controlled groundwater composition in the area, based on Gibb’s diagram, chloro-alkaline indices, and major ions ratios. Groundwater facies were identified as Ca.HCO₃, Na.HCO₃ and mixed Ca-Na/Ca.Mg.Na.HCO₃ types using a Piper plot. The water quality index was computed, and its spatial variations were mapped using GIS. About 82.35% of groundwater samples were excellent for drinking use and 94.12% (SAR) of groundwater were acceptable for irrigation. These study results are useful to help develop inclusive strategies and interventions to address groundwater quality aspects in the study area, underlining the significance of managing and monitoring water resources. The findings underscore the need for effective management and monitoring strategies to ensure sustainable groundwater resources in the Bazo River catchment. Full article

The evolution of groundwater in the Puhe River Basin is closely related to the ecological security of the Beijing–Tianjin–Hebei water source conservation zone. Based on 122 groundwater samples, this study systematically investigated the hydrochemical characteristics, evolution mechanisms, and water quality of shallow groundwater using mathematical statistics, Piper diagrams, ionic ratio analysis, and a variable fuzzy pattern recognition model. The results showed that shallow groundwater in the middle and upper reaches is generally weakly alkaline, fresh to hard water, with HCO₃–Ca and HCO₃·SO₄–Ca as the dominant hydrochemical facies. Groundwater hydrochemistry is primarily controlled by rock weathering, and the dissolution of silicate and carbonate rocks is the main source of major ions. Calcite and dolomite are in dynamic equilibrium between dissolution and precipitation, whereas gypsum and halite remain undersaturated. Overall, groundwater quality is generally good; however, anthropogenic activities in cultivated and construction lands have altered local hydrochemical composition and caused water quality deterioration in some areas. These findings improved the understanding of groundwater hydrochemical evolution in typical small watersheds of the northern Hebei hilly region and provided a scientific basis for the sustainable management and protection of groundwater resources in the Beijing–Tianjin–Hebei water source conservation area. Full article

Understanding how the development of large-scale coal mining bases affects river hydrochemistry is a key scientific issue in the field of water environment research. In this study, the Qingyang–Binzhou section of the Jinghe River Basin was selected as the study area, and a total of 29 water samples were collected in April 2025 from the upper to lower reaches of the coal mining base. Hydrochemical analysis, ion ratio methods, and the positive matrix factorization (PMF) model were comprehensively applied to systematically characterize the hydrochemical features and identify the pollution sources in the river under the influence of large-scale coal mining activities. The results showed that the mean concentrations of Na⁺, SO₄²⁻, Cl⁻, and total dissolved solids (TDS) in the mainstream were as high as 414 mg/L, 728 mg/L, 226 mg/L, and 1636 mg/L, respectively, reflecting a significant impact of coal mining activities on river hydrochemistry. Four spatial variation patterns were observed along the river: the first pattern was characterized by “stable in the upper reaches, sharp increase in the middle reaches, and fluctuating increase in the lower reaches,” represented by Na⁺ and SO₄²⁻; the second pattern showed “stable in the upper reaches, slight decrease in the middle reaches, and fluctuating decrease in the lower reaches,” represented by pH; the third pattern exhibited “fluctuating in the upper reaches, sharp decrease in the middle reaches, and extremely low levels in the lower reaches,” represented by NO₃⁻; and the fourth pattern was dominated by irregular variations controlled by nitrogen transformation processes, represented by NH₄⁺ and NO₂⁻. Gibbs plots and ion ratio diagrams indicated that the hydrochemistry of sites unaffected by coal mine drainage was primarily controlled by rock weathering, whereas contaminated samples shifted toward the evaporation-concentration zone and extended beyond its typical range, reflecting an “anthropogenic salinization effect” induced by the input of mine water superimposed on the arid to semi-arid climatic background. The PMF model identified three main pollution sources: coal mining and mine water discharge (48.3%), domestic sewage (30.2%), and carbonate weathering (21.5%). This study reveals the significant modification mechanism of river hydrochemistry by large-scale coal mining base development, providing a scientific basis for targeted water pollution control in the Jinghe River Basin and for water environment management in similar mining areas. Full article

The Yangtze River, the largest river system in Asia, continues to receive substantial nitrogen loads despite the implementation of management measures. Within this vast and complex system, the spatial patterns and drivers of key nitrogen transformation processes, such as nitrification and denitrification, remain poorly constrained. In particular, systematic isotopic evidence from studies spanning the entire upstream–midstream–downstream continuum remains scarce. This study integrates multiple isotopes (δ¹⁵N-NO₃⁻, δ¹⁸O-NO₃⁻, δ¹⁵N-NH₄⁺) with hydrochemical techniques to elucidate the dominant controls on nitrogen transport and transformation and their spatial heterogeneity across the Yangtze River Basin. Results indicate that dissolved inorganic nitrogen (DIN) is the dominant form of nitrogen pollution in the basin. NO₃⁻ concentrations exhibited significant spatial variability, following the pattern downstream (2.86 mg/L) > upstream (1.83 mg/L) > midstream (1.75 mg/L). Isotopic signatures revealed that nitrification is the dominant process controlling the formation and transformation of NO₃⁻ throughout the basin. Most δ¹⁸O-NO₃⁻ values (−5.20‰ to +12.78‰) fell within or close to the theoretical range for nitrification, and a strong positive correlation was observed between δ¹⁵N-NO₃⁻ and δ¹⁵N-NH₄⁺ (R² = 0.72, p < 0.01), collectively confirming that the conversion of NH₄⁺ to NO₃⁻ is the primary pathway. Conversely, denitrification was significantly suppressed under the prevailing high dissolved oxygen conditions (mean 9.78 ± 2.46 mg/L), as further evidenced by the lack of a significant correlation between δ¹⁵N-NO₃⁻ and ln(NO₃⁻). Furthermore, preferential assimilation of NH₄⁺ by phytoplankton reduced the efficiency of nitrate removal via biological assimilation and influenced isotopic composition. These findings provide a scientific basis for identifying priority nitrogen sources and optimizing targeted nitrogen management strategies in the Yangtze River Basin. Full article

Understanding the hydrochemical characteristics and formation mechanisms of rivers in the Huxi Catchment is essential for water resource conservation, as these rivers serve as the primary water source for Taihu Lake. A total of 14 surface water samples were collected from the rivers in Huxi catchment, and the concentrations of seven major ions—namely, ${\mathrm{N}\mathrm{a}}^{+}$, ${\mathrm{K}}^{+}$, ${\mathrm{C}\mathrm{a}}^{2+}$, ${\mathrm{M}\mathrm{g}}^{2+}$, ${\mathrm{C}\mathrm{l}}^{-}$, ${\mathrm{S}\mathrm{O}}_4^{2-}$, and ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$—were determined. Positive Matrix Factorization (PMF), Absolute Principal Component Score–Multiple Linear Regression (APCS-MLR), and the Principal Component Analysis-based Endmember Mixing Model (PCA-EMM) were employed to quantify the contributions of anthropogenic activities. While APCS-MLR can only identify the impacts of human activities, PMF and PCA-EMM can further distinguish between agricultural activities and wastewater discharge. Significant positive correlations were observed between the PMF and PCA-EMM results, but PMF overestimated the contribution of anthropogenic impacts. PCA-EMM showed that the natural background accounted for 63%, while human activities contributed 37% (domestic sewage 23%, agricultural activities 14%). By integrating ion composition data from representative sources, PCA-EMM overcomes the limitations of traditional methods that lack source verification and provides robust methodological support for the source apportionment of water chemistry. Full article

Surface water–groundwater interactions within oasis–desert ecotones of arid regions play a pivotal role in sustaining regional water security and ecological stability. Taking the Niya River Basin in Xinjiang, Northwest China, as a representative inland watershed, this study systematically elucidates the mechanisms and seasonal dynamics of surface water–groundwater coupling under the combined influences of natural processes and anthropogenic activities. A total of 68 surface water and groundwater samples were collected during the dry, normal, and wet hydrological periods. Integrated hydrochemical characterization, mineral saturation index analysis, and stable isotope (δ²H and δ¹⁸O) mass balance modeling were employed to quantify recharge contributions and unravel hydrogeochemical evolution pathways. Results indicate that the waters in the study area are predominantly brackish to saline, with consistent dominant ionic assemblages (SO₄²⁻ and Na⁺) across all hydrological periods, highlighting evaporite dissolution as the primary control on solute composition. Hydrochemical evolution is jointly regulated by evaporation concentration, water–rock interactions, and cation exchange processes. Surface water chemistry reflects the combined effects of silicate weathering and evaporite dissolution, whereas groundwater chemistry is mainly governed by evaporite dissolution coupled with pronounced cation exchange. Stable isotope signatures reveal substantial secondary evaporation of regional precipitation prior to recharge. Frequent bidirectional recharge between surface water and groundwater was observed, exhibiting distinct seasonal transitions. During the dry period, groundwater provides significant baseflow support to surface water (48.6% in the oasis zone and 54.3% in the desert zone). In the normal period, recharge direction reverses, with surface water becoming the dominant source of groundwater recharge (99.0% in the oasis zone and 76.6% in the desert zone). In the wet period, spatial heterogeneity becomes evident: surface water continues to dominate groundwater recharge in the oasis zone (92.7%), whereas groundwater recharge to surface water prevails in the desert zone (50.5%). This study identifies a seasonally dynamic “discharge–infiltration–zonal regulation” bidirectional recharge pattern in arid inland river systems. The findings advance the mechanistic understanding of hydrological connectivity reconstruction within oasis–desert ecotones and provide a scientific basis for optimized regional water resource allocation and groundwater salinization risk mitigation. Full article

Groundwater is a strategic resource for maintaining ecological balance and supporting human development in arid inland basins. However, under the dual pressures of climate change and human activities, it faces threats in both quantity and quality. This study selects the Chahan Usu River watershed in the eastern Qaidam Basin, a typical arid inland basin on the Tibetan Plateau, to assess the current quality of groundwater resources and reveal the formation mechanisms and material sources of its hydrochemistry. The results show that the groundwater in the watershed is generally weakly alkaline, with some areas exhibiting high salinity. The dominant cations and anions are Na⁺ and Cl⁻, respectively. The hydrochemical type is mainly Cl-Na, with a minority being mixed Cl-Mg·Ca. Overall, the groundwater in the watershed is suitable for domestic use. However, in the middle and lower reaches of the Chahan Usu River, nitrate and ammonia nitrogen contamination reduce its suitability. Meanwhile, although long-term use of this groundwater would not lead to soil degradation, its widespread high salinity and high sodium content make it unsuitable for irrigation. Water–rock interactions with evaporites and silicate rocks are the main mechanisms controlling groundwater chemistry in the watershed. Among them, halite minerals contribute most of the Na⁺ and Cl⁻, while sulfate minerals provide Ca²⁺ and SO₄²⁻. In addition, cation exchange is widespread. This study provides a reference for ensuring the security and sustainable development of groundwater resources on the plateau. Full article

The Aksu River Basin, the main headwater of the Tarim River, contributes more than 70% of the main stream’s runoff and is therefore critical in maintaining hydrological stability in this arid river system. In recent decades, rapid oasis expansion and growing agricultural water withdrawals have intensified competition for surface and groundwater, posing increasing ecological risks to the downstream Tarim River Basin. To quantitatively characterize river–groundwater hydrological responses under intensive water use, we combined statistical analysis, field observations, and distributed hydrological modeling within a basin-scale conceptual framework. Multiple lines of evidence—water level monitoring, hydrochemical tracers, stable isotopes, and the integrated surface–groundwater model MIKE SHE—were used to identify river–groundwater interaction mechanisms in the Aksu alluvial plain. Results reveal a typical three-stage spatial exchange pattern: river recharge to groundwater in the upstream reach, groundwater discharge to the river in the midstream, and renewed river infiltration to groundwater downstream. The patterns inferred from water levels, hydrochemistry, and isotopes are broadly consistent, while water-level data better resolve left–right bank asymmetry. The MIKE SHE model supports the seasonal bidirectional exchange dynamics and reproduces runoff behavior with acceptable performance (RMSE and residual standard deviation within 20% of observed means and R² > 0.7 during both calibration (2010–2017) and validation (2018–2021)). The proposed multi-evidence framework captures the spatio-temporal variability of river–groundwater interactions in arid regions and provides spatially differentiated guidance for conjunctive surface–groundwater regulation and integrated water resources management in the Tarim River Basin. Full article

Groundwater is a critical resource in the arid Chili River sub-basin (3246 km²) in Arequipa, southern Peru, yet the aquifer systems, their recharge mechanisms, and chemical evolution remain poorly characterized. This study integrates hydrogeological mapping, major-ion hydrochemistry (31 samples from springs and wells), and stable-isotope tracing (δ¹⁸O and δ²H, 11 sources) to delineate aquifer types, groundwater flow systems, and recharge dynamics across an elevation gradient of 2000–4000 m a.s.l. Three principal aquifer groups were identified: unconsolidated porous aquifers beneath the Arequipa urban area, fracture-controlled volcanic aquifers associated with the Chachani, Misti, and Pichupichu volcanic complexes, and sedimentary fractured aquifers of the Yura Group. Piper and Stiff diagrams reveal a chemical evolution from calcium-bicarbonate waters at high elevations to sodium-chloride waters in the lowlands, while scatter-plot analysis distinguishes local, intermediate, and regional flow systems. Elevated boron concentrations linked to borate deposits on Pichupichu volcano pose a potential health risk in supply springs such as La Bedoya. Isotopic signatures confirm that wells are recharged predominantly by high-altitude rainfall (>4000 m a.s.l.), whereas springs integrate water from multiple elevations through fractured volcanic formations. These findings provide a scientific basis for recharge-zone protection, abstraction planning, and water-quality monitoring to sustain groundwater supply under increasing urbanization and climatic variability. Full article

Groundwater nitrate (NO₃⁻) pollution, caused by anthropogenic activities, poses a global threat to water security. The mixing of multiple nitrate pollution sources and the associated biogeochemical reactions may create a complex chemical background, which renders traditional hydrochemical methods and single δ¹⁵N isotope analysis approaches limited in accurately identifying pollution sources and quantifying their contribution ratios. Accordingly, we adopted an integrated framework incorporating hydrochemistry, isotopes, and the MixSIAR model. Within this framework, results from different components mutually validate each other, helping to achieve more accurate source identification and contribution quantification. Results revealed severe nitrate contamination with striking spatial heterogeneity: concentrations were significantly higher in the eastern region (9.3–1890.7 mg·L⁻¹, Mean: 472.8 mg·L⁻¹) than in the western region (8.5–204.1 mg·L⁻¹, Mean: 52.0 mg·L⁻¹). Hydrochemical and δ¹⁸O-NO₃⁻ evidence identified nitrification as the dominant nitrogen transformation process. Critically, the MixSIAR model quantified drastically different source contributions between the two regions. In the eastern industrial zone, industrial wastewater was the predominant source (61.3%), followed by manure and sewage (18.5%). In contrast, in the western agricultural area, natural and agricultural sources dominated, with soil nitrogen contributing 43.9% and chemical fertilizer 31.7%. The findings pinpoint specific pollution drivers for each region, offering a robust scientific basis for formulating differentiated and effective nitrate pollution control strategies. Full article

Integrating an end member catchment offers a mechanistic foundation for interpreting large basin hydrology. This critical aspect is rarely evident in Malawi’s river basin studies. This study characterizes the hydrochemistry of surface and groundwater and stable isotopes of water to gain a regional picture of how the Ruo River Transboundary Catchment (RRC) influences the Shire–Zambezi River Basin. Hydrochemistry (2013 to 2024) and stable isotope (2020 to 2022) data are used. Both Gibbs and Piper diagrams were used to interpret surface and groundwater facies and hydrogeochemical processes controlling mineralization of water. SI biplots were used to trace water sources, mixing signals, and evaporation trends. Low to moderate mineralization is noted in surface and groundwater sources, and electrical conductivity varied between 19 and 622 µS/cm and 31 and 1930 µS/cm for surface (12 sites) and groundwater (151 boreholes), respectively. Piper diagram analysis reveals a Ca-Mg-HCO₃ water type dominance. Gibbs plots suggested dissolution of silicate minerals and interaction of surface and groundwater. Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotope ratios in precipitation, surface, and groundwater exhibit a similar pattern, indicating a common meteoric input, variability in moisture source, and significant interaction of surface water and groundwater. SI plots indicate mixing of precipitation, surface, and groundwater of RRC. Finally, the Ruo River at flood stage reverses the flow of the Shire River sub catchments, impacting the water quality and quantity of the Zambezi, and, therefore, should be considered an important mixing end member in the Lower Shire Basin. Full article

Establishing reliable hydrochemical reference conditions is essential for water quality assessment and for the implementation of the European Union Water Framework Directive, particularly in regions where biological and hydromorphological data remain limited. This study aims to evaluate hydrochemical reference conditions in selected river headwaters of Western Ukraine and to examine the consistency between international and national water quality assessment approaches. Water samples were collected from four headwater and confluence sites and analysed for key physicochemical parameters, including nutrients, organic matter indicators, and major ions. Water quality was assessed using the Water Quality Index (WQI) and the Ukrainian Ecological Quality Index (IE), supported by correlation analysis and principal component analysis to identify dominant drivers of spatial variability. Most parameters complied with international and national standards, although elevated concentrations of ammonium, phosphates, biochemical oxygen demand, and nitrites were observed at specific sites. WQI differentiated headwaters with good and moderate water quality, whereas IE classified all sites as good, indicating methodological differences in sensitivity. Multivariate analysis showed that water quality variability was primarily controlled by biogenic and organic loading, while mineralization parameters reflected background geochemical conditions. The results demonstrate that hydrochemical indices can support the preliminary identification of reference conditions but also highlight systematic differences between assessment frameworks. These findings provide a methodological basis for harmonizing national water quality assessments with international standards and for improving reference site selection in data-limited regions. Full article