Spatial variability of cropland lead and its influencing factors: A case study in Shuangliu county, Sichuan province, China

Spatial distribution of soil lead (Pb) in cropland is an important reference for regional planning and eco-environmental protection, but related information was not available in an individual county with potential contamination in the high-speed developing Chengdu Plain. In this investigation, 623 topsoil samples, randomly taken from the Shuangliu county, Sichuan province, China, were analyzed for the spatial variability of soil Pb and associated influencing factors by using multiple methods. The results showed that soil Pb presented a low spatial correlation in the isotropic scope, whereas relatively strong spatial correlation was observed in the directions of N65°E and N80°E. High risk areas with great probability of the soil Pb concentrations exceeding the baseline values (50 mg/kg and 80 mg/kg) were estimated to dispersely distribute across the study area. Shortest significant range (SSR) tests indicated that the soil Pb concentrations in plain regions and hilly regions were significantly higher than those in the mountainous regions. Furthermore, soils developed from the gray alluvium and old alluvium demonstrated significantly higher Pb concentrations than those from the purplish rock saprolith. Soil Pb concentrations in the buffer zones (0–800 m) of the four main highways firstly increased and then decreased with the increase in distance from these highways. The application rate of fertilizers, pesticides, and animal husbandry income was found to be responsible for the spatial variation of soil Pb. These results will be of reference values in environmental management and decision making in the agricultural sector.

Research Highlights
► The soil Pb concentrations increased in Shuangliu county during the recent decades.
► Spatial variability of the soil Pb concentrations in isotropic scope were much greater than those in the directions of N45°W, N0°E, N65°E, N80°E and N90°E.
► Soil Pb were dispersedly distributed across the study area., the cropland in the present study area was suitable and safe for crop and fruit plantation but unsafe for vegetable cultivation with regard to soil Pb concentrations.
► The effects of terrain condition on soil Pb distribution were mainly observed in relatively low altitude regions and mountainous region, and the Pb in soils developed from alluvium were significantly higher than those from purplish rock saprolith. The soil Pb in the buffer zones (0-800m) of the four main highways firstly increased and then decreased with the increase in the distance from these highways. Application rate of fertilizers, pesticides, and animal husbandry income were manifested to be the main factors influencing soil Pb variation.