Spatial differentiation characteristics and environmental risk assessment of heavy metals in wetland sediment in an agricultural runoff area in the Qilu Lake basin

To understand the spatial differentiation characteristics and potential hazards of heavy metals in lakeside wetlands caused by low-pollution water in the agricultural runoff area of Qilu Lake, the surface sediments of 32 different types of wetlands(river wetlands n=13, constructed wetlands n=10, and lake wetlands n=9) in the lakeside agricultural runoff area were collected to detect the contents of the heavy metals Cu, Zn, Pb, Cr, Cd, Ni, and Hg. The spatial distribution characteristics of the seven heavy metals were analyzed by inverse distance weighted interpolation in ArcGIS, and the Hakanson potential ecological risk index method was used to evaluate the risks of heavy metal pollution in the Qilu Lake agricultural runoff area. The results showed that the degree of pollution of the seven heavy metals in different types of wetlands was different, and the average content was in the order of river wetlands > constructed wetlands > lake wetlands. The average content of heavy metals was in the order of Zn > Cr > Cu > Ni > Pb > Cd > Hg. Except for Pb, the heavy metals exceeded the background value of Yunnan soil, and the proportion of Cd samples exceeding backgroung value was as high as 100%. The risk index of the agricultural runoff area ranged from 112 to 1 241, with an average of 264, which indicated a moderate risk level. There were clear differences in the distribution of heavy metals, which was higher in the north than in the south and higher in the west than in the east. The areas with a high distribution were consistent with the results of the potential ecological risk assessment. The correlation analysis showed that the sources of Cu, Ni, Cr, and Zn pollution were mainly agricultural activities; the sources of Pb pollution were mainly related to road traffic, but were also affected by industrial activities; and the sources of Cd pollution were mainly agricultural activities and industrial activities. There were spatial differences in heavy metal pollution among the different types of wetlands in the Qilu Lake agricultural runoff area, among which Cd and Hg pollution were serious. High ecological risk areas appeared in the northwest and southwest, which should be given more attention