Study On The Transfer Course Of The Nitrogen Element Of Lake WuLiangSuHai Through Hydrophytes Harvesting Project

Lake eutrophication is a serious problem all over the world. Taking the typical plant type lake— lake Wuliangsuhai as research object, the paper constructs a total nitrogen control model and studies the transfer course of nitrogen element of Lake Wuliangsuhai through hydrophytes harvesting project. The model will be used to study the circulation and transformation of nitrogen in water body of lakes, ensure the biological effect of aquatic ecosystem and know about the flow and transformation relationship between the substance and the energy in ecosystem. Meanwhile, it is the theoretical foundation to know about the evolution process of lake ecosystem and carry out the eutrophication moderate control plan.The model comprises 15 state variable equations and 17 assistant equations, which analyze the circulation of nitrogen element in nutrient levels that include the macro-hydrophytes, phytoplankton, zooplankton and fish. Meanwhile, the transformation of the different form nitrogen which includes organic detritus nitrogen, ammonia—N, nitrate—N, nitrate—N and the release of nitrogen element in sediment quality is described. The relationship between the quantity of remnant hydrophytes and the nitrogen quantity of release after hydrophytes dieing is analyzed. On condition that the other factors is invariable, if the harvesting quantity of hydrophytes is 50 thousand tons every year, continuously harvest hydrophytes for 5 years and 10 years, the concentration of nitrogen in sediment quality will decrease 20.11 percent and 32.73 percent respectively by the model calculation. Those analysis will provide theoretical foundation on eutrophication moderate control of plant type lakes by the mechanization way.