Study On The Effect Of Aquatic Plant Community On Nitrogen And Phosphorus Purification In Water

In order to study the spatial and temporal variations of nitrogen and phosphorous in artificial wetlands after exogenous nutrient input, mosaic communities of different plant species were set up in a cement channel in greenhouse. Addition of N and P nutritional was in two manners:single exogenous nutrient input and continue exogenous nutrient input. After the addition of N and P nutritional solutions, the concentrations of dissolved total nitrogen (DTN), dissolved total phosphorous (DTP), NH4+-N、NO3-N and NO2--N in the surface, middle, and bottom layers of the bulk water were determined regularly. The results show that:(1) The DTN, NH4+-N, TP were remove significantly by the communities of Phragmites australis+Acorus calamus community, Lemna minor community, Cladophora glomerata community, Trapa quadrispinosa community, Trapa quadrispinosa+Hydrilla verticillata community, and Hydrilla verticillata+Myriophyllum spicatum community, and that of NO3--N was less obvious.(2) Under the conditions of high N and P nutrient loads (DTN>7.0mg-L"1; NH4+-N>4.28mg-L-1; TP>0.42mg-L-1), the order of DTN removal efficiency was Phragmites australis+Acorus calamus community> Lemna minor community> Cladophora glomerata community> Trapa quadrispinosa community> Trapa quadrispinosa+Hydrilla verticillata community> Hydrilla verticillata+Myriophyllum spicatum community; the order of NH4+-N removal efficiency was Lemna minor community> Cladophora glomerata community> Phragmites australis+Acorus calamus community> Trapa quadrispinosa+Hydrilla verticillata community> Hydrilla verticillata+Myriophyllum spicatum community> Trapa quadrispinosa community; the order of DTP removal efficiency was Trapa quadrispinosa+Hydrilla verticillata community> Lemna minor community> Phragmites australis+Acorus calamus community> Trapa quadrispinosa community> Cladophora glomerata community> Hydrilla verticillata+Myriophyllum spicatum community. The removal efficiency of N and P nutrients was higher in the community of Trapa quadrispinosa+Hydrilla verticillata than in the Trapa quadrispinosa community and Hydrilla verticillata community. The results showed that the removal efficiency of N and P nutrients in mosaic communities of different plant species was superior to that of one plant species. (3) The diffusion of nutrients from surface to the middle water layers was relatively slow, which took6days under the current experimental condition., The nutrient concentrations had insignificant changes except NO2-N in the bottom water layers, thus the exogenous nutrient input mainly affected the nutrient concentrations of surface and middle water layers. It was taken22d for DTP and NH4+-N concentrations to decrease to the initial concentrations. The DTN and NO3--N concentrations decreased more slowly. However, the NO2--N concentrations rose in the three water layers.(4) The aquatic communities could remove N and P nutrients obviously when adding exogenous continuously. The removal efficiency of NH4+-N was significant in all aquatic communities, and the order was Phragmites australis community> Trapa quadrispinosa+Hydrilla verticillata community> Hydrilla verticillata community> Trapa quadrispinosa community> Lemna minor community. The order of removal efficiency of DTP was Phragmites australis+Acorus calamus+Hydrilla verticillata community> Trapa quadrispinosa+Hydrilla verticillata community> Lemna minor> Trapa quadrispinosa> Hydrilla verticillata community. However, the removal efficiency of NO3--N and NO2-N was invisible with rising slightly.