疏浚对巢湖双桥河水环境容量的影响

双桥河是巢湖受污染较为严重的入湖河流之一,其入湖口距巢湖市自来水厂取水口仅500 m,同时也是巢湖市的主要行洪河道,为了改善水质状况并提高河道行洪能力,于2010年3—5月对双桥河进行了疏浚。本文作者于2009年12月—2010年10月对双桥河监测断面及排污口进行了监测,在分析双桥河水质及现有污染源的基础上,选择CODMn、TP、NH3-N和TN作为水质敏感参数,对疏浚前后双桥河的不同河段污染物质的水环境容量进行了模拟计算,并调查了水生植被覆盖度及沉积物氮磷含量的变化。结果表明,疏浚后整个河道水生植被的覆盖度由40%降低到5%左右,各污染物的降解系数都有较大程度的降低,同时疏浚后短期内CODMn和TP的环境容量均有一定程度的降低,而NH3-N和TN的环境容量变化较小。分析认为,这一方面是由于疏浚后河道内水生植物覆盖度的降低导致水体的自净能力降低,另一方面是由于疏浚过程中的扰动引起大量沉积物的再悬浮及污染物的释放。所以在减少外来污染的前提下,对重富营养化水体底泥进行疏浚并开展水生植被恢复工程应是控制富营养化的有效途径。

Effect of dredging engineering on water environmental capacity of Shuangqiao River, Chaohu Lake

Shuangqiao River,one of the contaminated inflows of the Chaohu Lake,is the main flood channel in Chaohu City.Its estuary is 500 m away from the intake of water factory.To improve the water quality and increase the capacity of flood,the sediment dredging was conducted in March 2010.This study simulated the capacities of CODMn,TP,NH3-N and TN of different water sections before and after dredging from December of 2009 to July of 2010.Results indicated that the aquatic vegetation coverage was reduced from 40% to 5% after the dredging.The degradation coefficients of contaminants decreased greatly,capacity of CODMn and TP were reduced,those of NH3-N and TN were less impacted.The ability of water self-clarification was reduced because of the diminished coverage of aquatic vegetation,as well as the resuspension of sediment and some pollutants released from the sediment disturbanced during the dredging.It suggested that the effective way to control eutrophication might be reestablishment of aquatic macrophytes in the dredging area,meanwhile limit the external input.