Spatial Distribution Characteristics and Source Apportionment of Soil Heavy Metals in Chinese Wolfberry Land Based on GIS and the Receptor Model

Abstract

A total of 119 surface soil samples (depth of 0-20 cm) were collected from a Chinese wolfberry demonstration garden in Zhongning of Ningxia, and samples were analyzed for seven heavy metals (Pb, Ni, Zn, Mn, Cu, Cr, and Cd). The single factor index, comprehensive index, and potential ecological risk were used to assess the soil heavy metal contamination with the soil background values of Ningxia as the evaluation standards. The absolute principal component scores and multivariate linear regression (APCS-MLR) model as well as geostatistic analysis were combined to identify and apportion the pollution sources of soil heavy metals. The results showed that the average concentrations of Pb, Ni, Zn, Mn, Cu, Cr, and Cd in soils were 34.78, 52.376, 83.692, 641.114, 38.130, 87.257, and 0.149 mg·kg-1, respectively. The mean concentrations of heavy metals were higher than the local soil background values but lower than the risk screening values for soil contamination of agricultural land. The comprehensive index results showed that the pollution degree of soil heavy metals was at the slightly polluted level in 81.51% of the samples, at the moderately polluted level in 16.81% of the samples, and at the unpolluted level in 1.68% of the samples. The comprehensive index values for potential ecological hazards were less than 60 in 13.45% of the samples, and these values were associated with a slight potential for ecological risks. The comprehensive index values for potential ecological hazards were less than 120 and more than 60 in 86.55% of the samples, and these values were associated with a moderate potential for ecological risks. The four main pollution sources of soil heavy metals in the study area included natural sources, industrial activity, traffic, and agricultural activity. Natural sources were the main source of Ni and Cr with average contribution rates of 55.49% and 64.66%, respectively. Industrial activity was the main source of Pb and Mn with average contribution rates of 46.93% and 42.53%, respectively. Traffic was the main source of Zn and Cu with average contribution rates of 43.51% and 53.71%, respectively. Agricultural activity was the main source of Cd with an average contribution rate of 76.79%. The study results indicated that soil heavy metals have tended to concentrate in the Chinese wolfberry demonstration garden, and the sources of heavy metals were complex and obviously influenced by human activities. Controls should be strengthened for sources that contribute to soil heavy metals to ensure the sustainable utilization of soil resources in the Chinese wolfberry land.