巢湖主要入湖河流表层沉积物镉的分布特征及污染评价

DISTRIBUTION AND RISK EVALUATION OF CADMIUM IN SURFACE SEDIMENTS FROM THE MAJOR INFLOW RIVERS OF CHAOHU LAKE

采集巢湖主要入湖河流表层沉积物样品33个,研究镉的空间分布特征,分析其主要来源及影响因素,揭示沉积物中镉的富集规律及其生态风险。研究表明:巢湖流域河流表层沉积物中的镉空间分异特征明显,镉的富集主要集中在流经合肥城区、郊区以及部分中小城镇的河段,南淝河、店埠河等城市河流沉积物中镉的平均含量是杭埠河、丰乐河等非城市流域的2倍以上。沉积物镉含量与钙呈显著正相关,显示二者在成因上的密切联系。粒度效应也在一定程度上影响沉积物中镉的含量。南淝河上的部分采样点镉的富集系数超过10.0,达到严重污染的程度。城区下游采样点人为污染贡献均超过50%,部分达85%以上。说明流经合肥市区的南淝河向巢湖输送的沉积物中,镉的生态风险大,是巢湖流域镉等重金属污染控制的重点。

After being discharged into aquatic environment, pollutants are partitioned between the sediments and overlying water columns. Therefore, stream sediments have been widely used as environmental indicators to evaluate current and historical water pollution and to trace sources of contamination. The Chaohu Lake, the fifth largest freshwater lake in China, is subject to versatile pollution sources, including heavy metals inputs from the inflow rivers of the lake. In this study, thirty-three surface sediment samples from the major inflow rivers of the Chaohu Lake were collected and analyzed for the contents of cadmium and other physical chemical properties. The major purposes of the study are to eharacterize the Cd distribution in river sediments, trace the sources of pollution and to evaluate its ecological risk in the watershed of the lake. Our results showed that the concentrations of cadmium in the river sediments varied from 67.4μg/kg to 1 659.0μg/kg. The mean value of Cd was 339.0 μg/kg, which was 3.5 times of that of soil background value in Anhui Province. The cadmium distribution had distinct spatial patterns. High concentrations of cadmium were found in the sediments of river sections flowing through the urban and suburban areas in the watershed. The Nanfei River, the Dianbu River and the Shiwuli River which flow through the urban and suburban areas of Hefei, the largest city in the watershed, had the highest Cd level in their river sediments. The Hangbu River, the Fengle River and other non-urban rivers were less enriched with Cd. The relationship between cadmium contents and other elements was analyzed by Pearson＇s correlation. Cd was positively correlated with TP, organic matter （OM） and calcium. These findings indicate that Cd and P, Ca in stream sediments might have same sources of emission. In addition, a significant negative correlation was observed between Cd and SiO2, suggesting that gain size effect also affected the distribution of cadmium in the sediments to a certain degree. In order to quantify possible anthropogenic inputs, the enrichment factors （EF） of cadmium in the river sediments were calculated. The EF values of Cd averaged 3.9, suggesting Cd enrichment in the sediments. Cadmium enrichment factors of the Nanfei River sediments could be as high as more than 10.0, revealing high ecological risk of polluted sediment to aquatic system in the study area. For urban and downstream urban sections of the rivers, anthropogenic Cd contribution accounted for more than 50% of their total concentrations in sediments, with the highest being about 85~//oo. More serious cadmium pollution had been found in the Nanfei River than that in other inflow rivers, as the Nanfei River receiving untreated domestic and industrial wastewater from Hefei City （the largest urban centre in the region） and other cities. Therefore, the urban section of the Nanfei River is the priority area of environmental restoration in terms of Cd pollution.