[Spatial Variability and Contamination of Arsenic in Soils of Xijiang River Basin]

In this study, 2585 soil samples were collected in the Xijiang River Basin in Guangxi Zhuang Autonomous Region and the spatial variability and contamination of Arsenic in soils were evaluated using geostatistical and GIS tools. The results showed that the concentrations of As in surface soils (23.82 mg·kg^-1) were higher than the background values of the Guangxi and Xijiang Rivers in natural soils; the upstream values (Diaojiang River and Huanjiang River) (30.22 mg·kg^-1) were significantly higher than those in other regions. Concentrations of As in soil samples were in the order of soil in mining areas > soil in dryland > natural soil > paddy soil. As in mining areas were significantly higher than in other areas; high As concentrations were measured in the upstream of the Diaojiang River basin and the downstream of the Huanjiang River Basin. Low concentration clusters were in the six villages of Nandan, which are far from the mine, and in the upper reaches of the Dahuanjiang River and Xiaohuanjiang River Basin. Spatial autocorrelations of arsenic in the watershed soil were evident and the structural variability was dominant. The concentration of As in the upper reaches decreased from the northwest to the southeast. High As concentrations were distributed naturally along the river basin; concentrations in the middle and lower reaches of the basin were between 0.44 mg·kg^-1 and 40 mg·kg^-1. The concentration levels of As in total soil samples ranged from no-pollution to slight pollution, and the pollution was mainly distributed in the administrative areas of the city and the intensive areas of mining activities, among which the soil pollution in Jinchengjiang River and Nandan counties was more prominent. Effective measures should be taken to strengthen the safety level of tailings reservoirs during the rainy season, so as to maintain the production levels while protecting living standards of local residents.