Understanding the impact of natural processes and anthropogenic activities on geochemical evolution is vital for groundwater protection and utilization. This research was devoted to identifying the water quality status and the main controlling factors of the hydrochemical evolution of karst groundwater by combining hydrogeochemical indicators with multi-isotope analysis techniques in the Heilongdong Spring Basin, North China. The results showed that the karst groundwater in the area was of meteoric origin, and the dissolution of carbonate minerals was dominant in water–rock interactions. Meanwhile, the positive and negative cation exchange occurred in the process. The main hydrochemical types of karst groundwater were HCO₃-Ca·Mg and HCO₃-Ca in the recharge area, while the predominant hydrochemical types were the HCO₃·SO₄-Ca·Mg and HCO₃·SO₄-Ca in the runoff and discharge area. Under the influence of coal mining and other factors, the average concentrations of major ions kept rising in the runoff area where coal mines were distributed, and the SO₄²⁻ concentrations of the karst groundwater changed the most in the study area. In addition, sewage from agricultural production and domestic sources had also negatively impacted the quality of regional groundwater in the runoff and discharge area, as evidenced by the increasing NO₃⁻ and Cl⁻ contents in the Quaternary sediment groundwater, Permian bedrock groundwater and a small portion of karst groundwater. These results were helpful to explain the mechanism of gradual hydrogeochemical changes and provided a scientific basis for the effective management and utilization of karst groundwater.

Heilongdong Spring Basin (HSB) is located in a semi-arid region in northern China. In the past few decades, it has been influenced by anthropogenic activities. Currently, there is a lack of information about the impact on the hydrogeochemistry and groundwater quality of different aquifers. To address this concern, the present study used conventional hydrochemical diagrams, stable isotope analysis and multivariate statistical techniques to analyze hydrochemical characteristics and controlling factors of shallow and deep groundwater in the study area. The results showed that all groundwater samples were weakly alkaline. The shallow groundwater (SGW) was mainly composed of SO₄-Ca and SO₄·HCO₃-Ca·Mg water types with high TDS values. However, the predominant water types of deep groundwater (DGW) were HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg types with relatively low TDS. The large majority of shallow groundwater had poor water quality, which was influenced by natural factors and anthropogenic activities, characterized by high concentrations of SO₄²⁻, NO₃⁻, and Cl⁻. In contrast, the overall water quality of deep groundwater was good, mainly controlled by the natural background. Nonetheless, a few karst groundwater samples of DGW in runoff areas exhibited close hydraulic connections with SGW samples and presented contamination to a certain degree. Our research results provide a scientific basis for the utilization and protection of groundwater in different aquifers in northern China.

The Sangu Spring Basin is located in an important economic area, and groundwater is the main source of water for local life and industry. Understanding the sources of chemical components in groundwater is important for the development and utilization of groundwater. In this paper, we analyzed the origin of the chemical components of groundwater and their evolution in the Sangu Spring Basin using statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and combined hydrochemistry–isotope analyses. The results show that the groundwater in the Sangu Spring Basin is mainly derived from atmospheric precipitation, that the groundwater in stagnant and confined environment zones was formed under colder climatic conditions, and that the surface water (SW) has a close hydraulic relation with the groundwater. Water–rock interaction is the main factor controlling the composition of groundwater. The compositions of groundwater are mainly derived from carbonate weathering, silicate weathering, and dissolution of gypsum. Na⁺ and K⁺ in groundwater mainly come from the dissolution of albite and potassium feldspar, rather than rock salt. Ion exchange occurs in karst groundwater (KGW) and fissure groundwater (FGW), and ion exchange is dominated by the exchange of Mg²⁺ and Ca²⁺ in the groundwater with Na⁺ and K⁺ in the rock or soil. Sulfate in groundwater is derived from dissolution of gypsum, infiltration of atmospheric precipitation, and leakage of SW. Groundwaters with the highest sulfate content are located in the vicinity of SW, as a result of receiving recharge from SW seepage. Groundwaters with higher sulfate contents are located in the stagnant and deeply buried zones, where sulfate is mainly derived from the dissolution of gypsum. SW seepage recharges groundwater, resulting in increased levels of Cl⁻, NO₃⁻ and SO₄²⁻ in groundwater. These insights can provide assistance in the protection and effective management of groundwater.

Groundwater in the alpine canyon regions of the Qinghai-Tibet Plateau is influenced by multiple recharge sources and geological structures, resulting in complex recharge processes and evolution mechanisms. This study focuses on the alpine canyon region of Zheduotang and integrates unsupervised machine learning with isotope tracers (δD, δ¹⁸O, and ³H) to systematically identify groundwater sources and their evolutionary processes. By integrating self-organizing maps (SOM) and K-means clustering, the water samples are classified into four groups, highlighting variations in hydrochemical facies, mineralization levels, and dominant ion sources among different water bodies. The results indicate that groundwater hydrochemical evolution is jointly governed by lithology and water-rock interaction intensity. Groundwater in the granite-dominated area is characterized by low-TDS Ca-HCO₃ and Ca-Mg-HCO₃, suggesting rapid shallow recharge, whereas groundwater in the metamorphic sandstone–slate area exhibits higher TDS with enriched Ca²⁺, Mg²⁺, and HCO₃⁻, indicative of longer flow paths and stronger water-rock interactions. Isotopic evidence indicates that groundwater and surface water are predominantly recharged by atmospheric precipitation and snow-ice meltwater, with recharge elevations ranging from 3594 to 5103 m, typically 400–800 m higher than their corresponding discharge elevations. Groundwater recharge in the study area occurs through three principal modes: direct recharge via high-elevation fractures, sustained input from alpine glacial lakes, and river leakage, and is strongly controlled by geological structures overall.