南京城区黑臭河道底泥污染特征及生态风险评价

POLLUTION CHARACTERISTICS AND ECOLOGICAL RISK ASSESSMENT OF SEDIMENT FROM MALODOROUS RIVERS IN NANJING CITY

河道黑臭是目前我国许多城市面临的环境问题,研究其底泥中的污染物如有机质、氮磷和重金属的污染特征并据此进行生态风险评价,对城市黑臭河道的污染控制与生态修复具有十分重要的意义。选取南京城区内8条典型黑臭河道,采集其表层底泥样品进行分析,测得其中有机质、总氮、总磷的含量分别为0.75%~10.86%、0.05%~0.68%、0.04%~0.23%,三者之间呈显著正相关关系,表明了它们较好的同源性,应用沉积物质量标准评价发现,这3种污染物污染程度总体介于严重级与最低级之间,但氮磷的污染比有机质更为严重。底泥中6种重金属的平均含量均超过背景值,相关性分析结果表明Cu、Cr、Ni、Zn之间均呈极显著正相关关系,而重金属与营养物之间未发现较好的相关性,潜在生态风险评价结果表明底泥中重金属污染严重,84.2%的河道具有高潜在生态风险,各元素的潜在生态风险顺序依次为Cd〉Cu〉Pb〉Cr〉Ni〉Zn,Cd为主要污染物,具有很高潜在生态风险。与国内其他典型受污染水体相比,南京城区黑臭河道底泥中总氮、总磷与重金属Cd的污染更为严重。

Malodorous status of urban rivers is an environmental problem that occurs in many cities of our country.Study on the pollution characteristics of pollutants in sediment,such as organic matter,nitrogen,phosphorus and heavy metals,together with the ecological risk assessment,is of great significance to the pollution control and ecological restoration of malodorous rivers.Eight typical malodorous rivers were chosen in Nanjing City.Their surface sediment samples were collected and analyzed.The result showed that the contents of organic matter,total nitrogen and total phosphorus ranged from 0.75% to 10.86%,0.05%to 0.68% and 0.04% to 0.23%,respectively.Significant positive correlations were found among these three pollutants,indicating that they were from the same pollution source.Assessed by the sediment quality standard,it can be known that the contents of these three pollutants were all between the severe level and the lowest level in general.While the pollution of nitrogen and phosphorus was more serious than that of organic matter.The mean contents of the six heavy metals in sediment were all higher than their background value.Extremely significant positive correlations were shown between Cu,Cr,Ni and Zn,while no good correlations were found among different heavy metals and nutrients.The result of potential ecological risk assessment indicates that the pollution of heavy metals in the sediment of malodorous rivers was serious and the potential ecological risk of 84.2% of the samples was high.The potential ecological risk of these elements was Cd〉Cu〉Pb〉Cr〉Ni〉Zn in sequence.Cadmium was the key pollutant and had very strong ecological risk.Compared with other typical polluted water bodies in our country,the pollution of total nitrogen,total phosphorus and cadmium in the sediment of malodorous rivers in Nanjing City was more serious.