Growth Characteristics And Purifying Effect Of Trapa Bispinosa Roxb In Baiyangdian Lake

Lake eutrophication has become a worldwide problem of water pollution control. As an effective mean of pollution control, ecological restoration, can improve their water quality, restore and maintain the natural ecosystem function, by regulating of aquatic ecosystems and strengthing the management of aquatic plants. Baiyangdian wetland is the largest freshwater lake in North China, and plays an important role in protecting the ecological health and environmental safety. In recent years, due to declined water level, deteriorated water quality, Baiyangdian lake is becoming shrinken markedly, which not only affects the health of the local population and income, also the its biodiversity and ecosystem services. The lake is mainly made up of swamps, and has abundant species. As a typical cultivated macrophyte, water chestnut(Trapa bispinosa Roxb) takes an important role in the Baiyangdian wetland. In this paper, growth parameters of water chestnut and environmental factors including sediment and water quality were investigated in order to know its growing process and water-purifying function, contrast the environmental effects of water chestnut and lotus (Nelumbo nucifera Gaertn), estimate ecosystem service values, and explore rational harvest time.The results showed that the dry weight and the main rosettes of trullate of water chestnur increased over time, which depicted the growth pattern of the water chestnut in Baiyangdian lake. Affect by temperature, the palnt’s growth began between April and May and ended in late September or early October, fast growth period occurred from July to September. The biomass of plant reached the maximum in late September when the fruits became mature. Fresh weight per individual of water chestnut increased and N, P concentration in water decreased gradually over time. Nutrient balance between the sediment-water interface fluctuationed, due to N, P compensation from sediment into water. Nitrogen and phosphorus accumulation in parts and whole plant of water chestnut increased gradually, and reached the maximum in early August, then declined. In the same time, nutrient in root of the plant after the transfer of decay in the late maturity went up on a certain degree.Wate chestnut and lotus could keep higher water transparency and remain rich biodiversity in the water body of plant growing regions in Baiyangdian lake, especially in the water chestnut region in summer. The water chestnut and lotus assimilated and utilized the nutriment, decreased the nitrogen and phosphorus concentrations obvionsly comparing with the control areas. Growth stage in July, water chestnut uptook more nitrogen and phosphorus than lotus. But in mature peroid of September, water chestnut gradually slowed the absorption rate and began to release nutrients into water, which uptake rate was less than the lotus.The optimal harvest time of the water chestnut in Baiyangdian lake was on the end of the September each year, after the fruit’s maturity. Through the harvest frouts and whole plant, we could obtain 214,180 yuan as the comprehensive economic benefit per hectare. So suggestions were put forward that research and management of the water chestnut should be strengthen in Baiyangdian lake, in order to increase the comprehensive utilization, achieve incomee, improve the living standard of local people and promote various ecosystem services of the Baiyangdian lake.