Ecological geochemical risk assessment of cadmium in soil-sediment of Danjiangkou Reservoir

The multi-objective geochemical survey in Shiyan-Danjiangkou area of Hubei Province was organized by the Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences during 2013-2015. It aimed to determine the geochemical distribution characteristics of elements in the survey area, conduct land resource environmental assessment and basic geological research, and provide basic data for the sustainable development of national and local economic and social sciences. The investigation revealed the accumulation of cadmium in the bottom sediments of Danjiangkou Reservoir and soil along the Hanjiang River. In order to protect the water source area of Danjiangkou and the water quality and safety of the South-to-North Water Transfer Project, the characteristics of cadmium content in soil and bottom sediments in different ecological areas of Danjiangkou reservoir area were systematically studied, and the background value and enrichment coefficient of cadmium content were calculated, which provided information for reservoir cadmium pollution prevention and ecological restoration. The eco-geochemical risk assessment of cadmium show that 100% of the water-fluctuating zone soil, 100% Hanjiang bottom sediment, 99.45% deep soil and 92.14% top soil belong to the agricultural land with low risk of cadmium pollution. The proportions of low, medium, and high-potential ecological risks in reservoir sediment samples account for 15.52%, 20.69%, and 63.79%, respectively. Based on the analysis of the relationship between the content of cadmium in soil and bottom product and the content of pH, Corg, and major elements, it is recommended to cut off upstream pollution sources, prevent soil erosion, prevent soil acidification, and carry out ecological restoration measures to prevent cadmium pollution of bottom sediments in the reservoir area and reduce its ecological risks.