漫湾大坝上下游沉积物重金属与营养元素分布特征及环境风险评价

研究了漫湾水电站大坝上下游11个采样断面的沉积物中的有机质(OM)、总氮(TN)、总磷(TP)和金属元素Al、As、Cd、Cr、Cu、Mn、Ni、Pb、Zn的含量及空间分布特征,利用地积累指数法、潜在生态风险指数法对沉积物重金属的环境风险进行了评价.结果表明,As、Cd、Cr、Cu、Mn、Ni、Pb、Zn的平均年含量分别为31.88、0.80、63.26、32.55、607.81、32.11、36.54、132.29 mg·kg-1,与云南省土壤背景值相比,重金属元素均出现一定程度的富集.其中,Cd和As比其他金属元素污染重,处于中-强度污染状态.在大坝上游干流中靠近大坝的断面环境风险最高,支流断面风险水平普遍低于附近的干流断面,大坝下游断面的风险值明显低于大坝上游断面.干流沉积物重金属蓄积明显受大坝建设影响,支流则受其上游区域人类活动和大坝建设的共同影响.营养元素在村庄聚集区和坝前地区含量较高,干流断面含量高于临近的支流断面,表明大坝建设和库区居民生产生活共同影响沉积物营养元素的分布.相关性分析与聚类分析表明,毒性较高的重金属元素Cd、As、Pb可以聚为一类,而且相互间呈显著正相关关系,并与OM呈正相关关系.虽然沉积物的有机污染在大部分地区呈现清洁或较清洁的水平,但是有机质可以吸附Cd和As,对沉积物的重金属污染具有增强效应.

Distribution and environmental risk assessment of heavy metals and nutrients in sediments of upstream and downstream of Manwan Dam

Spatial distribution of organic matter (OM), total nitrogen (TN), total phosphorus (TP) and metals (Al, As, Cd, Cr, Cu, Mn, Ni, Pb, Zn) contents in sediments of upstream and downstream of Manwan Dam were measured. The risk assessment was conducted with geoaccumulation index and potential ecological risk index. The results indicated that the average contents of As, Cd, Cr, Cu, Mn, Ni, Pb, Zn were 31.88, 0.80, 63.26, 32.55, 607.81, 32.11, 36.54, 132.29 mg·kg^-1, respectively. Compared with the background value in soils of Yunnan Province, all elements were enriched to some extent. The pollutions of Cd and As were more serious in sediments. The samples collected from the section near to dam in mainstream showed a higher risk. The samples collected from the section in tributary showed a lower risk than the samples collected from the section in mainstream. The samples collected from the sections in downstream of dam were significantly lower than those in upstream. The contents of heavy metals in the sediment of mainstream were influenced by dam construction, and the sediment of tributary was affected by both dam construction and human activity. The samples collected from the section near the village or dam were high in contents of nutrients. The contents of nutrient in the samples collected from the mainstream were higher than those in tributary. The distributions of nutrients in the sediment were affected by human activities. Correlation analysis and cluster analysis demonstrated that the high toxic heavy metals including Cd, As, Pb can be clustered into one group and they were significantly positively correlated with each other and positively correlated with OM. Although the risk of nutrients was low in the study area, nutrients enhanced the effect on Cd and As absorption in the sediments, leading to higher risk level of heavy metals.