巢湖柘皋河沉积物重金属分布特征与风险评价

Distribution characteristics and risk assessment of sedimentary heavy metals in Zhegao River of Chaohu Lake

选取柘皋河为对象,研究了巢湖东半湖入湖河流沉积物中重金属的污染状况。自流域上游至下游共布设13个监测点(编号S1~S13),调查分析表层沉积物中V、Cr、Ni、Cu、Zn、Cd和Pb等7种重金属的含量和分布特征。结果表明,柘皋河表层沉积物中重金属的污染程度为Cd>Cu>Ni>Pb>V>Zn>Cr,其中Cu和Cd在部分河段污染较重,最高含量分别达到173.78 mg·kg^(-1)和1.11 mg·kg^(-1)。自流域上游至下游,各重金属含量总体呈升高趋势。柘皋河上游河段的重金属污染最轻,其内梅罗综合指数为0.33,处于安全范围;下游污染加重,内梅罗综合指数达到1.67,处于轻度污染水平。应用潜在生态危害指数进行风险评估后发现:所调查的7种重金属中Cd和Cu存在较高的环境风险,特别是在流域下游风险值提高;流域下游的重金属综合生态危害指数RI大于300,具有强生态危害等级,下游段应是重金属污染治理的重点区域。聚类分析结果显示靠近柘皋河入巢湖河口的S12点是重金属累积的"汇"和"拐点",再往下游的河口地段因受到河湖水文-水质交换的影响其重金属含量反而极速下降。分析认为,流域农业面源和下游的水产养殖活动是柘皋河重金属污染的主要来源。沉积物粒径分级结果显示,重金属在河道中自上而下的迁移和累积与水中粘粒的随波逐流和在靠近河口地段发生较明显的沉降密切相关。对柘皋河沉积物中重金属的潜在释放风险进行了评价,并提出巢湖柘皋河重金属污染的治理与控制策略。

Zhegao River at the north bank of eastern Chaohu Lake was selected to investigate the sedimentary heavy metal contamination. Thirteen sampling sites （S 1-S 13） were set from upstream to downstream of the river and the contents of V, Cr, Ni, Cu, Zn, Cd and Pb in the surface sediment were analyzed. Results showed that the heavy metal contents in the surface sediment followed a descending order as： Cd 〉 Cu 〉 Ni 〉Pb〉 V 〉 Zn 〉 Cr. The level of Cd and Cu was high in some sites with the maximum values of 173.78 and 1.11 mg·kg-1, respectively. The content of sedimentary heavy metals showed an increasing trend from the upstream to the downstream, which was low in the upstream with a Nemerow composite index of 0.33 within a safe range and high in the downstream with a Nemerow index of 1.67, indicating slightly polluted. The potential ecological risk index of heavy metals indicated that Cu and Cd had a higher environmental risk among the seven investigated heavy metals, especially in the downstream. Comprehensive potential ecological risk index （RI） of heavy metals in the lower Zhegao River was over 300, indicating a strong ecological risk, so the downstream is the critical area for controlling heavy metal pollution. Clustering analysis results showed that S 12 near the confluence area of Zhegao River was the ＂sink＂ and ＂reflection point＂ of the heavy metal accumulation. On the contrary, the confluence area had dramatically decreased the heavy metal content under a strong interaction in water flow and water quality between the river and the lake. Analysis results suggested that the agricultural non-point source pollution in the watershed and the downstream aquaculture practice were the main al- lochthonous sources for the heavy metal contamination in Zhegao River. Sedimentary particulate size analysis results revealed that the transport and deposition of heavy metals from the upstream to the downstream were closely related to the clay fraction of suspended particulates that were drifted randomly with the water current accompanying the recurrent settling and re-suspension, and finally deposit in the lower section approaching the confluence area. We also evaluated the potential release risk of sedimentary heavy metals and put forward a heavy metal pollution control strategy in Zhegao River of Chaohu Lake.