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.

In recent years, numerous ancient landslides initially triggered by historic earthquakes on the eastern Tibetan Plateau have been reactivated by fault activity and heavy rainfall, causing severe human and economic losses. Previous studies have indicated that short-term heavy rainfall plays a crucial role in the reactivation of ancient landslides. However, the deformation behavior and reactivation mechanisms of seasonal rainfall-induced ancient landslides remain poorly understood. In this paper, taking the Dandu ancient landslide as an example, field investigations, ring shear experiments, and interferometric synthetic aperture radar (InSAR) deformation monitoring were performed. The cracks in the landslide, formed by fault creeping and seismic activity, provide pathways for rainwater infiltration, ultimately reducing the shear resistance of the slip zone and causing reactivation and deformation of the Dandu landslide. The deformation behavior of landslides is very responsive to seasonal rainfall, with sliding movements beginning to accelerate sharply during the rainy season and decelerating during the dry season. However, this response generally lags by several weeks, indicating that rainfall takes time to infiltrate into the slip zone. These research results could help us better understand the reactivation mechanism of ancient landslides triggered by seasonal rainfall. Furthermore, these findings explain why many slope failures take place in the dry season, which typically occurs approximately a month after the rainy season, rather than in the rainy season itself.

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.