Abstract: Sediments collected from a number of ponds in Liuchahe watershed in Yangtze-Huaihe region of China were analyzed with chronological method to set up chronosequence of the undisturbed sediments for the purpose of studying historical process of Cd accumulation and its environmental impact.Results show that the rapid development of intensive agriculture in the past 30 years in the region led to application of large volumes of phosphate fertilizers,which resulted in Cd accumulation in the pond sediments in large volumes.The tempo-spatial distribution characteristics of Cd reversed by using pond sediments may divide Cd input history into two phases: the first phase refers to the decades before the 1980s,when the watershed was not or just slightly polluted with Cd;and the second phase,the decades after the 1980s,when the rapid intensification of farming activities has led to rapid accumulation of Cd in pond sediments and Cd input through human activities is on an increasing trend.The Cd risk assessment of the sediments indicates that about 10%-30% of total Cd is exchangeable Cd or carbonate-bonded Cd.The Cd in the sediments of these ponds is subject to a moderate level of exposure risk.

Key words: sediment, Cadmium, risk, Chaohu Lake