Study On Retention And Purification Effect Of N And P In Pond Wetlands

There are plenty of pond wetlands distributed in the conjunction area of the farmland-lake system in Taihu lake area. These pond wetlands have retention and purification effect of N and P. The main work in the thesis included: study on the retention and purification effect of N and P in a selected pond wetland after rainfall runoff, study on the cumulant and purification effect of N and P by three sorts of plants abundantly growing in the pond in different time. The results were shown as follow:(1) The agricultural non-point source pollutants (N and P) from ambient fields after rainfall runoff were abundantly intercepted in the pond. The retention quantity and rate were closely related to fertilization level, plant sorts, rainfall, water level, area and so on.(2) Among three sorts of plants, the contents of N and P in Althernanthera philoxeroides were less than those in Wild rice (Zizania latifolia) and Reed (Phragmites communis). In growth periods. between Reed and wild rice, the absorption effect of N and P by haulm and leaves was better than that of roots The absorption effect of N and P by haulm and leaves of Wild rice was better than that by haulm and leaves of Reed. The absorption effect of N by roots of Wild rice was better than that by roots of Reed. But the absorption effect of P by roots of Wild rice was worse than that by roots of Reed. In fading and dying period, the release of N and P from haulm and leaves was earlier than that from roots. The release of N and P from haulm and leaves of Wild rice were more than that from haulm and leaves of Reed. The release of N from roots of Wild rice was more than that from roots of Reed. The release of P from roots was not evident. The purification rate by the absorption of grown plants took 25 percent and 53.9 percent in the total purification quantity.(3) The removal velocities of N and P by three plants changed slowly from April to June. From July to August, the removal velocities grew evidently, and came to peak value in July. In September the removal velocities declined evidently, and by October the removal velocities became negative. The removal velocities of N and P byAlthernanthera philoxeroides were the least from April to August. The removal velocities of N by Wild rice were larger than those by Reed. The removal velocities of P by Wild rice and Reed were similar in this period. The removal velocities of N and P by Althernanthera philoxeroides were the largest by September, while those by Wild rice were the least.