Spatial differentiation and influencing factors analysis of Pb in soils in the small watershed of typical area in the Southern Taihang Mountains

Heavy metal pollution has been one of the most significant concerns on the soil environmental quality for the Taicang agricultural sustainability and human health. It is of paramount importance to analyze the spatial variations and influencing factors of regional distribution in the soil heavy metal. Among them, the Manghai River watershed is nestled within a typical ecological zone in the southern Taihang region. Rapid socioeconomic development has also been experienced by the convergence of industries, such as non-ferrous metal smelting, coal coking, and mining. Soil environmental pollution is also coupled with the unique terrain and topographical features, especially heavy metal pollution, notably lead (Pb) and cadmium (Cd). Much attention has been gained to prevent and control the soil heavy metal pollution in this region. This study aims to unveil the spatial variation patterns and influencing mechanisms of soil Pb content at the scale of the Manghai River watershed. The sampling points were employed as a 1 km×1 km grid using high-resolution remote sensing imagery and land use data. A total of 121 topsoil samples (0-20 cm) and 15 environmental auxiliary samples were collected, including 5 surface water samples, 5 dust samples, and 5 sediment samples. The classic statistical methods, geostatistics, and geographic detectors were utilized to probe the spatial variation characteristics of soil Pb content and their influencing factors. Results were as follows: 1) Soil Pb content was relatively high with an average of 110.40 mg/kg, particularly over the regional background values. Notably, the soil Pb content exceeded the threshold to identify the soil pollution risk at some locations in the agricultural land, indicating the sever contamination risks; 2) There was an outstanding variation in the soil Pb content across the study area, with the marked variances in various directions. The spatial patterns were dominated in the variability along the south-north (0°) and northeast-southwest (45°) axes, indicating the influence of structural factors, such as the parent material and terrain; 3) Empirical Bayesian kriging spatial interpolation showed that there was a gradual, belt-like increase in the soil Pb content from the southwest to the northeast, indicating the distinct local features. The northeastern foothill plain and central plain areas emerged as the focal points to monitor and control the soil Pb pollution risks; 4) Geological type and land use were the primary determinants of spatial distribution differences in the soil Pb content. The combined influence significantly heightened the impact of factors, like proximity to the mines and industries. Therefore, a comprehensive investigation can be preferred on the regional heavy metal pollution within the complex environments, including the geological and topographical factors, natural elements, such as atmospheric conditions, and complex interactions with industrial and agricultural activities. There was also the spatial heterogeneity of distribution patterns in the soil heavy metal pollution using watershed units. The spatial distribution and influencing factors of soil Pb pollution can provide precise support to the prevention, control, and remediation of soil heavy metal pollution under the complex environment of the southern Taihang region.