Source identification of soil elements and risk assessment of trace elements under different land uses on the Loess Plateau, China

To investigate the source identification of soil elements and risk assessment of trace elements under different land-use types, 32 pairs of topsoil samples (0-20 cm) were collected from two subcatchments in the Liudaogou watershed. The areas of the two subcatchments were 0.343 and 0.045 km(2), respectively, and the two subcatchments were divided into four land-use types, including bare land, forestland (FL), grassland (GL) and check-dam land (CDL). The results showed that the coefficients of variations of all soil elements indicated moderate spatial variation. The mean concentrations of Cu, K, Mn, Na and Zn under different land-use types exceeded the soil background values. The results of correlation analysis and principal component analysis illustrated that high homology existed between Cu and Mn in subcatchment 1, and the main source was from coal mines and smelters. Consistent sources of Zn and K in subcatchment 1 were mainly fertilizers and sewage sludge. Cu, K, Mg, Mn, Na and Zn in subcatchment 2 had similar sources, mainly mining and smelting plants, fertilizers and sewage. In addition, Ca had high homology with Fe in two subcatchments, mainly from natural weathering. The enrichment factor values indicated that there was a certain degree of trace element pollution. The values of the pollution index and Nemerow integrated pollution index revealed that moderate pollution was mainly concentrated in FL, GL and CDL. The trace element pollution of GL and CDL may induce contamination of the food chain and threaten human health safety.