Le Zhou

To clarify the recharge sources, water cycle evolution mechanisms, and water-rock interaction patterns of typical karst spring basins in the northern Taihang Mountains, this study investigated the Shuimocao karst spring group through a 1:50,000 hydrogeological survey and continuous dynamic monitoring of spring and river discharge. A total of 38 hydrochemical samples and 26 hydrogen and oxygen isotope samples were collected and tested. Integrating high-density resistivity profiling, hydrochemical identification, isotope tracing, and hydrological dynamic analysis, this study systematically explored the basin tectonic evolution, karst development features, hydrochemical signatures, and groundwater water cycle mechanisms, while elucidating the driving factors responsible for spring drying up. The results indicate that Meso-Cenozoic tectonic movements established the fundamental tectonic framework of the study basin. Highly soluble limestone of the Ordovician Majiagou Formation provides essential material conditions for karst development, whereas concealed faults and epikarst zones constitute dominant migration pathways for surface water and groundwater. Major hydrochemical ions are primarily derived from carbonate and silicate rock weathering, accompanied by staged cation exchange, while anthropogenic activities significantly disturb water quality in the spring discharge zone. Quantitative end-member mixing analysis (EMMA) identifies three groundwater recharge pathways: leakage from the Tongtian River (51.93%) serves as the primary recharge source, followed by Sanhui River leakage (28.79%) and lateral groundwater runoff from the Yebei area (19.29%). Precipitation only acts as an indirect, time-lagged driving factor rather than a direct water source. Overall, the spring system is predominantly recharged by river infiltration and secondarily by lateral groundwater inflow, forming a tectonically controlled water cycle pattern: "surface water infiltration - karst conduit migration - flow regulation by faults and aquicludes - concentrated spring discharge". The extreme spring drying event in 2020 resulted from the superposition of extreme drought and persistent groundwater overexploitation, and groundwater flow field alteration induced by water level decline was the direct cause of well water turbidity. This study reveals the surface water-groundwater coupling mechanism of typical northern karst basins, providing a representative case and scientific reference for karst groundwater exploitation, spring ecological conservation, and analogous hydrogeological studies in the Taihang Mountains.

To elucidate the solute sources, migration and enrichment mechanisms of water bodies in the endorheic lake region of the Qiangtang Plateau on the Tibetan Plateau and clarify the hydrogeochemical cycling patterns in alpine arid environments, this study focuses on two core scientific objectives: quantitative identification of the multi-source contributions of aquatic solutes, and revelation of the key processes governing the enrichment of strategic elements including lithium (Li) and boron (B). To achieve these goals, we conducted systematic hydrogeological field investigations and collected 28 multi-type water samples, covering springs, rivers, thermal springs, freshwater lakes, salt lake brines, atmospheric precipitation, and glacial meltwater. The physicochemical properties, major ions, and trace elements of all samples were comprehensively analyzed. On this basis, the hydrogeochemical characteristics, evolutionary processes, and solute origins of regional waters were systematically explored. Combined with PHREEQC numerical simulation, principal component analysis (PCA), and Pearson correlation analysis, the dominant controlling factors of water geochemistry were quantified, and a conceptual hydrogeochemical evolution model was established. The results reveal a clear hydrogeochemical evolutionary gradient across the study area: water bodies evolve from low-salinity HCO₃-Ca recharge end-members and transitional HCO₃·SO₄-Ca(Mg) type water to highly mineralized Cl-Na (SO₄·Cl-Na) salt lake brines, accompanied by synchronous enrichment of Li, B, arsenic (As), and other characteristic elements. Solute accumulation in regional waters is governed by the ternary coupling effects of evaporative concentration, rock weathering and leaching, and deep geothermal fluid input, while cation exchange and mineral dissolution–precipitation reactions further modulate ionic composition and ratios. Elements including As, Li, B, and chloride (Cl⁻) exhibit conservative migration behaviors in non-hydrothermal waters, whereas thermal springs possess unique geochemical signatures driven by deep fluid recharge. PCA results indicate that evaporative concentration serves as the primary controlling factor with a contribution rate of 55.39%; rock weathering provides the basic solute load (17.09%); and the coupled processes of deep fluid mixing and carbonate precipitation regulate elemental fractionation (14.21%). These findings systematically clarify the hydrogeochemical evolution laws and multi-source coupling mechanisms of inland lake waters in the Qiangtang Plateau. Furthermore, this study establishes a conceptual framework of “multi-source recharge–water–rock interaction–evaporative concentration”, advances the understanding of alpine hydrological cycling under climate change, and provides a solid scientific foundation for hydrological cycle research and green exploration of strategic mineral resources in endorheic salt lake regions.

To reveal the solute sources, migration and enrichment mechanisms of water bodies in the endorheic lake region of the Qiangtang Plateau, Tibetan Plateau, and to clarify the hydrogeochemical cycling patterns in alpine arid zones, this study took typical en-dorheic lake areas in the region as the research object, conducted a systematic hydro-geological survey, collected 28 groups of water samples of various types (including springs, rivers, thermal springs, freshwater lakes, salt lake brines, atmospheric precip-itation and glacial meltwater), tested their major ions, trace elements and physical properties, and comprehensively investigated the hydrogeochemical characteristics, evolution laws and solute sources of water bodies, quantified the dominant control-ling factors and established a conceptual hydrogeochemical model by combining methods such as PHREEQC modeling, principal component analysis (PCA) and Pear-son correlation analysis; the results show that water bodies in the study area exhibit a distinct evolutionary gradient, from the low-salinity HCO₃-Ca recharge end-member, through transitional HCO₃·SO₄-Ca(Mg) water, to highly mineralized Cl-Na(SO₄·Cl-Na) salt lake brine, with synchronous enrichment of Li, B, As and other elements; solute sources are controlled by a ternary coupling mechanism of evaporative concentration, rock weathering and leaching, and deep geothermal fluid input, while cation ex-change and mineral dissolution-precipitation further regulate ionic ratios; As, Li, B and Cl⁻ display conservative migration in non-hydrothermal waters, whereas thermal springs show unique geochemical signatures due to the input of deep-seated fluids; PCA reveals that evaporative concentration (contribution rate 55.39%) is the dominant controlling factor, rock weathering (17.09%) provides the basic solute load, and the coupled process of deep fluid mixing and carbonate precipitation (14.21%) regulates elemental fractionation, and this study constructs a conceptual model of "multi-source recharge–water–rock interaction–evaporative concentration", which clarifies the evo-lutionary laws of regional water bodies and provides a scientific basis for water cycle research and green exploration of strategic mineral resources in salt lakes of the en-dorheic regions on the plateau.