Distribution, Sources And Risk Assessment Of Heavy Metals In Surface Sediments Of The Lijiang River, A Typical Karst River Of Southwestern China

The subtropical karst in Guilin City is popular with fenglin karst, and it is regarded as "the capital of worldwide karst". Large amounts of scientists have made research on the karst in Guilin City. Guilin City is located in the karst basin, which results in low inversion layer and small wind, limiting the spreading of pollutants in the atmosphere. Due to the pollution of heavy metals has been more serious in Guilin City, it is essential to survey the heavy metals pollution in the Lijiang River (the main source of drinking water in Guilin City). Therefore,21surface sediments samples were collected from the Lijiang River (including mainstream and tributaries). Heavy metals were analyzed by using the ICP-MS, as well as the cold vapor atomic absorption spectrophotometry, and the occurrence, distribution, sources and risk assessment in surface sediments of the Lijiang River were studied.The pollution of Cd was the most serious in sediments of the Lijiang River. The contamination of the tributaries was more serious than those measured in the mainstream. The levels of heavy metals in sediments in present study were compared to those measured in sediments from other rivers, showing that sediments in the Lijiang River were moderately polluted by heavy metals. Heavy metals contamination was affected by human activities and tributary inputs. The highest variation coefficient of heavy metals in the Lijiang River (including mainstream and tributaries) were Cd (68%), Mn (64%), Hg (57%), Pb (40%) and Al (55%), indicating the spatial distribution of these five heavy metals in sediments of the Lijiang River is uneven.The correlation analysis, principal component analysis (PCA) and the cluster analysis methods were used for evaluating the sources of heavy metal contamination in sediments of the Lijiang River. The result of PCA showed that the first three principal components accounted for90%of the total variance. Factor one, including Mn, Cd, As, Hg and Cr, accounted for36%of the total variance. Factor two, including Cu, Zn and Pb, accounted for29%of the total variance. Factor three, including Fe and Al, accounted for25%of the total variance. The correlation analysis showed that these heavy metal elements have a significant positive correlation. These results suggested these heavy metal elements have the similar sources of natural and/or anthropogenic origins. The cluster analysis showed the same results as well.The geoaccumulation index (Igeo) and pollution load index methods were used for evaluating ecological risks of heavy metals in sediments of the Lijang River. The mean Er of Cd reach151(highest:320), suggesting a severe pollution of Cd in the study area. The heavy metal contamination in sediments of the Gantang River and the Xiangsi River is more serious. Igeo suggested that Cd in sediments of the Lijiang River may cause adverse ecological risks, particularly at the Gantang River and the Xiangsi River. This highlights that Lijiang River sediments may pose a serious threat to aquatic life, and urgent restoration and management is warranted to safeguard the aquatic system of karst area.