Soil pH is a fundamental geochemical parameter with direct implications for environmental quality, but its spatial drivers in geologically complex mountain regions remain poorly understood. This study investigated surface soil pH across 452 sites in Pingquan City, a semi-arid, lithologically heterogeneous mountainous area of Hebei Province, China. The results show that the soil in Pingquan City is predominantly alkaline, with higher pH in southwestern and northeastern areas and lower pH in the northwest. Soil pH ranged from 4.62 to 9.98, with strong positive spatial autocorrelation. Comprehensive quality assessment indicated that the overall soil quality is moderately low. GeoDetector analysis identified average annual temperature, soil texture, elevation, and bedrock lithology as dominant structural drivers, with bi-factor enhancement interactions. GeoSHAP further uncovered two local effects: precipitation exerts a positive influence on pH in carbonate-rock-dominated areas, reversing the leaching–acidification pattern; and temperature functions as a proxy variable integrating co-varying topography, parent material, and texture rather than a direct thermal driver. The combined application of spatial autocorrelation, GeoDetector, and GeoSHAP provides an effective framework for identifying spatial phenomena, discriminating dominant drivers, and explaining local variations. These findings support regional soil quality assessment and land management, and provide a geochemical baseline for safeguarding groundwater resources in mountainous regions.

The geochemical characteristics of major elements in lake sediments provide insights into aquatic environmental variations, the regional geological background, and the intensity of weathering processes. This study investigates Dongping Lake (DL) using 20 surface sediment samples, analyzing nine major elements. Spatial interpolation was used to characterize their distribution patterns, while principal component analysis, self-organizing maps, and absolute factor analysis–multiple linear regression methods were applied to identify element sources and interpret their geological significance using weathering indicators. Results show that surface sediments are dominated by SiO₂ (46.49%), Al₂O₃ (13.10%), and CaO (11.25%). Controlled by hydrodynamic conditions, major elements are mainly concentrated in the southern part of the lake near the inflows of the Dawen and Liuchang Rivers, with concentrations decreasing from south to north. Riverine transport is the primary source of major elements, with the Dawen River contributing the most followed by the Liuchang and Yellow rivers. Weathering indicators suggest that source rocks have experienced moderate chemical weathering, reflecting initial sedimentation in a tectonically active setting under warm and humid conditions and relatively short transport distances. These findings provide a geochemical basis for understanding sedimentary processes and environmental evolution in the Dongping Lake basin and offer valuable support for regional water resource management, ecological restoration, and sustainable watershed governance.