Wolong Town, Pingquan City, is located in a typical low-mountainous area of northern China, where groundwater is a crucial drinking water resource, thus, investigating groundwater’s hydrochemical characteristics and assessing nitrate-related health risks are vital for protecting, developing, and utilizing water resources. In this study, 66 groundwater samples were collected and analyzed for physicochemical parameters and major ion concentrations. Results showed that the groundwater in Wolong Town was weakly alkaline (average pH = 7.6), and classified as fresh water with TDS ranging from 90.0 to 900 mg/L. The dominant hydrochemical type was identified as HCO₃⁻-Ca²⁺. Hydrochemical evolution was jointly regulated by natural water-rock interaction, anthropogenic nitrogen input, and environmental redox differentiation. Among these, water-rock interaction was the primary driver, where the hydrochemical composition was mainly shaped by the dissolution of halite, calcite, dolomite, and gypsum, coupled with cation exchange. Nitrate was the primary groundwater pollutant, with concentrations varying from 0.94 to 259 mg/L; elevation, soil type, and population density were key drivers influencing nitrate distribution. Health risk assessment indicated that nitrate posed significantly higher non-carcinogenic risks to infants and children than to adults, and long-term consumption of groundwater with excessive nitrate might induce adverse health effects. This study enhances understanding of shallow groundwater’s hydrochemical evolution and nitrate contamination-related health risks, thereby providing theoretical support for the sustainable development, utilization, and quality protection of groundwater resources in semi-arid low-mountainous areas.

Wetland lakes are crucial ecosystems that serve as vital ecosystems that harbor rich biodiversity and provide essential ecological services, particularly in regulating regional water resources, purifying water quality, and maintaining ecological equilibrium. This study aims to conduct an in-depth investigation into the hydrochemical characteristics and their controlling factors during the dry season of the Hengshui Lake wetland system. By collecting water samples from the lake and shallow groundwater, and using water chemistry diagrams, ion ratios, mineral saturation indices, and multivariate statistical methods, the study systematically analyzes the hydrochemical characteristics of Hengshui Lake Wetland and its controlling factors. The results show: there is significant stratified differentiation in the water chemical composition: the lake water is weakly alkaline and fresh, while the shallow groundwater is highly mineralized and saline. Both are dominated by Na⁺, Mg²⁺, SO₄²⁻, and Cl⁻. Significant differences exist in water chemistry types between the lake and shallow groundwater. The lake water exhibits homogenized characteristics with a dominant SO₄·Cl·HCO₃-Na·Mg type, whereas shallow groundwater displays five distinct hydrochemical facies indicative of multi-source recharge processes. Evaporation–rock interaction mechanisms dominate the system, as evidenced by a Gibbs diagram analysis showing evaporation crystallization as the primary control. Ion ratio calculations demonstrate synergistic effects between silicate weathering and evaporite dissolution, while mineral saturation indices confirm cooperative processes involving calcite/dolomite oversaturation and ongoing gypsum dissolution. Cation exchange indexes combined with chloro-alkaline indices reveal unidirectional recharge from lake water to shallow groundwater accompanied by active cationic exchange adsorption. Although the wetland predominantly maintains natural hydrological conditions, elevated γ(NO₃⁻)/γ(Na⁺) ratios in nearshore zones suggest initial agricultural contamination infiltration. This study shows that, as a typical example of a closed wetland, the hydrochemistry evolution of Hengshui Lake during the dry season is primarily dominated by the coupled effects of evaporation and rock–water interaction, with silicate weathering and evaporation rock dissolution as secondary factors, and human activity having a weak influence. The findings provide new insights into the understanding of the hydrochemical evolution process and its controlling factors in closed lakes, offering valuable data support and theoretical basis for the ecological restoration and sustainable management of closed lakes.

As a strategically important groundwater source in Shanxi Province, the Xinzhou Basin contends with localized fluoride and nitrate exceedances whose hydrogeochemical controls remain insufficiently characterized. This work compares the unconfined and confined aquifers of the basin on the basis of 40 samples collected in July 2025, combining hydrogeochemical diagramming, multivariate statistics and the USEPA non-carcinogenic risk model. Both systems are mildly alkaline, with pH means of 7.96 and 7.95. Ca²⁺ and Mg²⁺ dominate the cations and HCO₃⁻ the anions, and the two groups share the same facies spectrum: 27 of the 40 samples are HCO₃-Ca type and seven are Na-HCO₃ type, while no sample reaches the Cl-Na corner. Water–rock interaction is the overarching control. Combined carbonate and silicate weathering supplies most of the solute, and evaporite dissolution is restricted to three samples in which sulphate exceeds bicarbonate. Calcite and dolomite are at or above saturation in 39 and 38 samples, whereas gypsum and fluorite remain undersaturated throughout (SI −4.17 to −0.32 and −2.64 to −0.12) and continue to dissolve. The seven Na-HCO₃ samples carry the lowest Ca²⁺ fractions and the most negative chloro-alkaline indices, which identifies forward cation exchange as the process that removes Ca²⁺ and sustains fluorite dissolution. Nitrate has a mixed provenance, combining synthetic fertilizer, manure and domestic effluent, and soil organic nitrogen, and its imprint is stronger in the unconfined aquifer. Nitrate carries the larger hazard burden (HI up to 4.34, against 2.35 for fluoride), and unconfined groundwater records higher HI values than its confined counterpart, with ingestion as the dominant pathway. The two contaminants peak in different places: fluoride risk in the southern Xinfu–Dingxiang sector, and nitrate risk in Yuanping in the central basin. These results provide an evidence base for groundwater quality management, fluorosis mitigation and drinking-water security planning in the Xinzhou Basin.