Study On Reasonable Biomass Simulation Of Aquatic Plants And Plant Disposition In Yanming Lake Of Xi'an

Urban waterfront landscape become more popular among the city dwellers with the development of material life. As the most common waterscape, urban lakes can not only be the place for people to play and rest, but also improve the eco-environment and micro-climate. Yanming Lake No.2 is a shallow artificial lake located in Chan-Ba Ecological District of Xi'an. Excessive reproduction and growth of submerged plants (Myriophyllum spicatum) caused by water pollution and the lacking of management seriously influenced the landscape. Relative management decided to control the biomass of Myriophyllum by artificial harvesting. However, from a ecologycal point of view, aquatic plants have the function of water purification and inhibition to algae reproduction. Extensive cutting of water plant may lead to the increase of nitrogen and phosphorus and Algal Eutrophication at worse. Considering the ecological and landscape efficiency of aquatic plants, we take Yanming Lake No.2 as the main object of study in this paper. Ecological model of Lake No.2 has been established based on the Lotka-Volterra model and the Vollenweider model. The interaction relationship among aquatic plants, algae and nutrients (nitrogen and phosphorus) could be described in the model. In order to study the feasibility of Plants Harvest Plan and the reasonable biomass of aquatic plant in Lake No.2, we predicted the impact on Chla, TP and TN when Hydrophyte's biomass have been decreased using the ecological model. At the same time, plant configuration program has been designed to improve the lake landscape.The data measured through out the year of 2008 were used in model validation. The validation results showed that, calculated value fitted well with the measured values and the ecological model of Lake No.2 possessed a certain practical value. Ecological model was used to predict the concentration of Chla, TP and TN from November of this year to October of the following year, when the harvest rates of plants in October was 20%,40%,60% and 80%. Predicted results showed that the concentrations of Chla, TP and TN went higher with the increasing harvest rate. If the harvest rate was 60%, the prediction results of three indicators would be more than the eutrophication standard in May of the following year. In order to prevent the occurrence of algae-type eutrophication in the lake, the plants harvest rate was suggested to remain at 40%, that was maintain the biomass of plants at least of 2.35 kg/m2 in October. In addition, some kinds of Emerged plants and floating-leaved plants were adviced to planted in Lake No.2, such as Lotus, Water Lilies, Iris, Arrowhead, Purple Lythrum, Monochoria, Softstem bulrush, Giant reed, etc., while the submerged plants were harvesting. Because the natural landscape of the southern lake was beautiful, so the research about plant configuration was focused on the north shore of the lake and the zone around the island.