Distribution of soil heavy metals and ecological risk assessment of agricultural land in Nianchu River basin, Tibet

Taking the cultivated soil in Bailang County and Jiangzi County of Nianchu River basin in Tibet as the research objects, the contents of 9 kinds of heavy metals, Hg, As, Pb, Cd, Cr, Cu, Mn, Zn and Ni, were investigated and analyzed. The single factor index method, Nemerow comprehensive pollution index method and other methods, combined with the spatial interpolation method were used to evaluate the heavy metal pollution of agricultural land in Nianchu River basin. Meanwhile, correlation analysis and principal component analysis were used to explore the sources of soil heavy metals. The results showed that: 1) The content of Hg, Cu, Mn and Ni in the soil of agricultural land showed different degrees of accumulation, compared with the background values of the soil environment in Tibet. Compared with Soil Environmental Quality: Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018), As had the highest rate exceeding the standard. From Jiangzi County to Bailang County, the comprehensive ecological risk index of soil heavy metals in agricultural land gradually increased. 2) The regional pollution load index of the study area was 1.45, which was a low pollution level. Severe pollution was concentrated in Bailang County. 3) Principal component analysis showed that the sources of 9 kinds of heavy metals could be divided into natural and anthropogenic complex factors, mining factors, agricultural factors, soil parent material factors and atmospheric transmission factors.