Non-point Source Pollution Treatment By Phragmites Communis Wetlands In The Lake Taihu Basin

Non-point source pollution has been the main factor of surface water eutrophication. Many studies show that wetlands can control the non-point source pollution effectively. The Lake Taihu basin is abundant in phragmites communis wetlands, which play an important role in NPS management. More rescerches emphasize on purify machanism of wetlands and the remainder studies on effect ignore the whole decontamination process include rainfall.Associated with the sub-project of "863" program, initiated by Ministry of Science and Technology, and by the way of pint-sized experiment in laboratory combining with pilot experiment in field, this paper discussed these contents:1. Static study on the ability of phragmites communis wetlands in removing nitrogen and phosphorusThe results show that: The removal of TN and TP with retention time by phragmites communis are accorded with linear relation. The deep level soil of phragmites communis wetlands cumulate more TN and TP than cropland. TP has excellent transfer ability and distributes equably in different level soil. The content of TN obviously increased for the death of phragmites communis.2. Study on the removal effect of TN by phragmites communis wetlandsThis paper educed the equation to calculate the rainfall and TN catch rate of wetlands by hydrological means. By the way of experiment, the range of TN removal coefficient Kat in phragmites communis wetlands was comfirmed, which changes from 0.00214 m/d to 0.01114 m/d. Then we got the calculate model of TN removal rate.3. Study on the removal effect of TP by phragmites communis wetlandsBy the way of experiment, this paper determined the different removal coefficients K of TP in three typical rainfall intensities, 50mm, 25mm and 10mm, are 0.474m/d, 0.106 m/d and 0.046 m/d. Then we got the calculate model of TP removal rate. This paper also calculated the TP removal quantity in each sq.m. wetlands absorbed by phragmites communis annually.4. Application and discussionFor example, this paper calculated the removal effect of TN and TP caused bythe rainfall in phragmites communis wetlands in 16 March, 2005. The removal rates of TN and TP are 6.76%and 42.64%. This paper also discussed some factors which influence the efficiency and ability of phragmites communis wetlands in treating Non-point source pollution.