Nitrogen And Phosphorus Purification Of Ecological Ditch And Nitrogen Removal Efficiency Of Myriophyllum Spicatum L.

Non-point pollution is one of the main problems of environmental pollutions.Releases of large amount of nitrogen (N) and phosphorous (P) from farmland into rivers and lakes are the main cause of eutrophication. Thus, more and more interests are being raised on the use of ecological ditch between rivers/lakes and farmland for the remediation of area source pollutions.To investigate the effectiveness of purification of drainage by ecological ditch, we continuously monitored plants, water quality indexes and sediments. By establishing houseplants experiments, we also investigated that the uptake of total N by Myriophyllum spicaturm L from the system of overlying water and sediments, the content of N in Myriophyllum spicaturm L and its contribution to the total N removal was thoroughly analysized. The following conclusions were drawn:1) Ecological ditch had good total N removal efficency of 1.71%-57.50% from inlet during the period from September to December in 2009 and January, May, July, August, December in 2010. No significant purification was observed during other months. This was ascribed to the big hydraulic loading or plants cutting.2) The assembly of Myriophyllum spicaturm L, Juncus effuses and Arundo donax L had better removal efficiency than other assemblies during monitoring period.3) The average concentration of N and Pin biomass (leaves and stems) of 15 kinds of aquatic plants were 1.15-2.02 and 1.09-2.10 times higher, respectively, in summer than in fall and winter. The concentrations of N and P decreased or increased at start and then declined in most of these plants. Typha, Oenanthe javanica, Arundo donax L and Lythrum salicariav had higher concentrations of N and P in the leaves and stems than other aquatic plants. In the first growing season (from Auguest to November in 2009), the accumulated dry biomass was the highest (0.09-13.85 kg/m2) in November, with the greater dry biomass of Canna indica and the lowest of Arundo donax L. The biomass was higher in the second growing season than the first one (June to August in 2010); Canna indica had the best uptake of N (90.60 g/m2) and P (6.44 g/m2) in the first growing season compared to biomass of 96.17 g/m2 and 12.26 g/m2 in the second season. Acorus calamus, Myriophyllum spicaturm L and Cyperus alternifolius all had the potential of N and P uptake.4) Ammonia nitrogen (NH4+-N) and nitrate (NO3--N) can be accumulated in the sediments of ecological ditch. But NO3-N would be released during rainy day or farmland drainage.5) In nitrogen treatments NO and N1, Myriophyllum spicaturm L can absorb NO3--N from the overlying water. In nitrogen treatment N2, Myriophyllum spicaturm L had no significant removal efficiency. In nitrogen treatment N3, much nutrient made nutritional stress on the growth of Myriophyllum spicaturm L, resulting in the increase of the concentration of NO3--N in overlying water.6) In nitrogen treatments NO and N3, Myriophyllum spicaturm L had no significant NH4+-N removal efficiency in the overlying water while there was significant removal efficiency in other treatments N1 and N2.7) In nitrogen treatments NO, N1 and N2, Myriophyllum spicaturm L had no significant NO3--N removal efficiency in the sediments while there was significant removal efficiency in other treatment N3.8) In nitrogen treatments NO and N1, Myriophyllum spicaturm L had no significant NH4+-N removal efficiency in the sediments; Significant NO3--N removal was observed in nitrogen treatment N2; The concentrations of NH4+-N became higher with the decay of plants.9) Accumulation of biomass and the uptake of N by Myriophyllum spicaturm L were more favored in the sediments N1 and N2 compared to NO and N3.10) In the sediments NO, N1, N2 and N3, total N in the system decreased by 0.68 g, 1.91 g,5.86 g and 3.48 g respectively. The contribution of Myriophyllum spicaturm L in reducing N 55.12%,69.76%,20.10% and 13.32% while denitrification accounted for 44.88%,30.24%,79.9% and 86.68% individually. In the sediments NO and N1, N uptake by Myriophyllum spicaturm L was the main path of N removal; in the sediments N2 and N3, N uptake was not beneficial for the growth of Myriophyllum spicaturm L and removal of N as redundant N had nutritional stress on the plants.