武汉乌金港底泥重金属和磷污染特征及清淤深度的确定

  目的  武汉经济开发区(汉南区)26个重点湖泊中水质劣于Ⅳ类标准的湖泊有16个。研究武汉乌金港底泥中重金属和磷的污染特性，分析确定合适的清淤深度，对该区域类似的小微水体污染防治及环保清淤具有重要意义。  方法  以乌金港为例，通过2组实验分析乌金港底泥重金属和磷的污染特性:①对乌金港3个点位0~60 cm深度的底泥进行分层采样，分析6种重金属(铜、汞、砷、铅、镉、镍)的分布规律，采用地累积指数和潜在生态风险指数法对底泥重金属污染特征及风险进行分析评价。②采用综合污染指数法对3个点位污染层(0~15 cm)、过渡层(15~30 cm)和正常层(30~50 cm)底泥中磷质量分数进行分析评价，并通过解析实验分析底泥中可溶性活性磷与总磷的释放规律。  结果  乌金港底泥重金属污染特性:重金属质量分数随着深度的增加呈下降趋势，40~50 cm重金属质量分数趋于稳定，50 cm深度以下重金属质量分数接近土壤背景值或土壤环境质量二级标准；地累积指数(I_geo)分析可知:重金属污染程度大多处于轻度-中度污染，潜在生态风险指数值均小于40，风险较低。乌金港底泥中磷的污染特性:污染层、过渡层、正常层总磷质量分数呈现显著的递减规律；污染层和过渡层释放的可溶性活性磷质量浓度与总磷质量分数高于原上覆水，正常层不论是短期还是长期释放的可溶性活性磷与总磷均最低。  结论  乌金港底泥中的污染主要集中在污染层和过渡层，铜和铅是主要的生态风险因子，但处于低生态风险。为了更好地清除内源污染，综合分析底泥重金属和磷的污染特性，确定小微水体乌金港最优清淤深度为40 cm。图3表6参14

Heavy metal and phosphorus pollution characteristics and dredging depth in sediment of Wujin Port,Wuhan

  Objective  16 out of 26 key lakes in Wuhan Economic Development Zone (Hannan District) have water quality worse than Class Ⅳ standard. The purpose is to study the pollution characteristics of 6 heavy metals and phosphorus in the sediment, analyze and determine the appropriate dredging depth, which is of great significance to the prevention and control of similar small and micro water pollution and environmental dredging in this area.   Method  Taking Wujin Port as an example through 2 sets of experiments, the pollution characteristics of heavy metals and phosphorus in the sediment of Wujin Port were analyzed: (1) Stratified samples were taken from the sediment in the depths of 0?60 cm at 3 points, and the contents and the distribution pattern of 6 heavy metals( Cu, Hg, As, Pb, Cd and Ni ) were analyzed. Geo-accumulation index and potential ecological risk index method were used to analyze and evaluate the pollution characteristics and risks of heavy metals in the sediment. (2) Comprehensive pollution index method was used to analyze and evaluate the phosphorus content in the sediment of polluted layer (0?15 cm), transition layer (15?30 cm) and normal layer (30?50 cm) at 3 points, and the soluble active phosphorus (SRP) and total phosphorus (TP) in the sediment were analyzed through analytical experiments.   Result  With regard to the heavy metal pollution characteristics in the sediment, the contents of heavy metals decreased with the increase of depth, those in 40?50 cm tended to be stable, and those below 50 cm were close to the soil background value or the soil environmental quality Level Ⅱ standard. Geoaccumulation index (I_geo) showed that the degree of heavy metal pollution was mostly mild to moderate, and the potential ecological risk index value was less than 40, so the risk was low. The pollution characteristics of phosphorus in the sediment showed that TP content in polluted layer, transition layer and normal layer displayed an obvious decreasing law. The concentration of SRP and TP released from polluted layer and transition layer was higher than that from the original overlying water. SRP and TP released from the normal layer in both short term and long term were the lowest.  Conclusion  The pollution in the sediment of Wujin Port is mainly concentrated in polluted layer and transition layer. Cu and Pb are the main ecological risk factors, but they are at low ecological risk. In order to better remove endogenous pollution, it is determined that the optimal dredging depth of the small and micro water body in Wujin Port is 40 cm, based on the comprehensive analysis of the pollution characteristics of heavy metals and phosphorus in the sediment. Ch, 3 fig. 6 tab. 14 ref.]