Geochemical Characteristics and Potential Ecological Risk Assessment of Soil Heavy Metals in the Lower Tarim River Reclamation Area

To identify the geochemical characteristics and potential ecological risk of heavy metals in soils of the lower Tarim River reclamation area, 125 surface soil samples were collected and their As, Hg、Ni、Cr、Cu、Zn、Cd and Pb concentrations and pH values were determined. The potential ecological risk of soil heavy metals was evaluated based on geostatistics, Nemerow comprehensive pollution index（Pn）and Potential ecological risk index（RI）, and the sources of heavy metals were analysed using Positive matrix factorization （PMF）. The results show that:①The average values of all heavy (class) metal elements in the study area did not exceed the national screening values for soil pollution risk control on agricultural land, and the levels were generally at normal levels. ②The range of variation of the index in the study area was 50.75 to 179.07, with 29.37%, 63.63% and 7% of the sample points with slight, medium and strong ecological risk respectively, indicating that the study area as a whole was in the medium ecological risk class. ③The results of the PMF model show that the heavy (class) metals in the study area come mainly from natural factors (48.88%) and their content is closely related to the geological background; followed by agricultural production (31.63%), the use of large amounts of chemical fertilisers and pesticides leads to a high content of heavy (class) metals in the cultivated area; coal combustion (12.20%) and transportation (7.29%) also contribute to the accumulation of heavy (class) metal elements. Coal combustion (12.20%) and transportation (7.29%) also contribute to the accumulation of heavy (class) metals.