外秦淮河底泥污染及疏浚效果

Sediment Pollution and Dredging Effect of Waiqinhuai River

外秦淮河是南京市一条重要的城市景观行洪河道,多年来受工业及生活污水影响,内源污染严重.为充分了解外秦淮河底泥污染特征,为疏浚提供决策依据,对河道上、中和下游典型断面底泥界面微环境以及营养物含量进行调查,采用有机指数法和污染指数法对底泥污染状况进行评估,同时根据污染物垂向分布特征模拟清淤对底泥内源释放削减的影响.结果表明,上中下游底泥界面以上DO均值分别为4.62、3.25和3.41mg·L^(-1),且分别在4.4、3.5和5.5 mm处消耗殆尽,是典型的城市河道污染特征体现.调查河段表层底泥的ω(TN)、ω(TP)和ω(OM)均值分别为1734mg·kg^(-1)、1337 mg·kg^(-1)和4.82%,底泥TN和OM的有机污染指数均值为0.48,处于尚清洁水平,TP的单项污染指数均值为3.18,处于重度污染水平.模拟30 cm清淤深度结果表明,底泥SRP和Fe^(2+)的释放速率较清淤前分别削减42%~82%和88%~96%,而NH_(4)^(+)-N的释放速率却较清淤前有所增加.DGT测定技术与底泥磷形态分析结果表明,清淤后表层底泥磷活性均明显下降,DGT-P和Mobile-P较对照处理削减比例分别为9%~11%和1%~35%.以上研究结果表明,外秦淮河底泥内源污染严重,清淤可在一定程度削减内源磷释放,可能是外秦淮河水质改善的重要措施.

The Waiqinhuai River is an important urban landscape flood channel in Nanjing,which has been seriously polluted by industrial and domestic sewage for many years.To fully understand the characteristics of Waiqinhuai river sediment pollution and provide a decision-making basis for dredging,the sediment interface microenvironment and nutrient content of river sediment collected from method-typical sections in the upper,middle,and lower reaches were determined,and the organic index and pollution index methods were used to evaluate the sediment pollution condition.We also simulated the effect of desilting on the reduction of endogenous release in sediment according to pollutant characteristics of vertical distribution.The results showed that the average dissolved oxygen concentrations at the upper,middle,and lower sediment interfaces were 4.62,3.25,and 3.41 mg·L^(-1),respectively;the concentrations were exhausted at 4.4,3.5,and 5.5 mm,respectively,which were typical characteristics of urban river pollution.The average contents of TN,TP,and OM in the surface sediment of the investigated reach were 1734 mg·kg^(-1),1337 mg·kg^(-1),and 4.82%,respectively.The organic pollution index of TN and OM in the sediment was 0.48 on average,which was at the clean level,whereas the individual pollution index of TP was 3.18 on average,which was at the severe pollution level.The results of simulating the dredging depth of 30 cm showed that the release rates of SRP and iron divalent were reduced by 42%-82% and 88%-96%,respectively,whereas the release rate of ammonia nitrogen was increased.The results of DGT determination and phosphorus speciation analysis showed that the phosphorus activity of surface sediment decreased significantly after desilting,and DGT-P and Mobile-P decreased by 9%-11% and 1%-35%,respectively,compared with those in the control treatment.These results indicated that the sediment of Waiqinhuai River was seriously polluted by endogenous phosphorus,and desilting could reduce the release of endogenous phosphorus to a certain extent,which may be an important method for improving the water quality of the Waiqinhuai River.