Restoration Of Aquatic Vegetation And Its Ecological Effects In Eutrophic Lake

Eutrophication induces aquatic vegetation declines,"Cyanobacterial bloom", deterioration of water quality and regime shifts in shallow lakes.Restoration of aquatic vegetation is considered as an important approach to improve water quality and enhance ecosystem stability. In this study, we transplanted aquatic macrophytes in large enclosures with temporal aids of water treatments and selecting aquatic macrophytes species according to their habitat preferences. Ecological effects of the transplantation were examined by comparing water chemicals and biological indices in the enclosures with and without aquatic macrophytes and the open water in the lake out of the enclosures. During the experimental period (April2011to June2012), all of macrophytes in the enclosure survived and built relatively stable communities. The water quality was better in the enclosure with aquatic vegetation than in the one without vegetation, concentrations of TN, NH4+-N, TP and light extinction in water (Kd) in the vegetated enclosure decreased by30.55%,44.09%,36.04%and42.13%as compared to the open water, respectively, and decreased by5.96%,13.40%,6.70%and7.60%as compared to the enclosure without aquatic vegetation, Secchi depth (SD) increased by74.59%and8.70%as compared to the open water and the enclosure without aquatic vegetation, respectively, phytoplankton biomass was lower and zooplankton biomass was higher in the vegetated enclosure than in the one without aquatic vegetation and in the open water. In addition, aquatic vegetation tended to decrease contents of total nitrogen and phosphorus in sediment and sediment pore water and NH4+-N concentrations in sediment pore water, but did not affected PO43--P and NO3--N in sediment pore water. The study implied that selection of eutrophication tolerant aquatic macrophytes species facilitated restoration of aquatic vegetation and thus improve water quality in eutrophic water.Vallisneria natans, a submerged plant with a wide geographical range in our country. Has important ecological functions, and is one of the pioneer species of aquatic vegetation reconsruction in lake.In this study, by setting sandy, argillaceous and sandy and argillaceous intervals type of substrate, to determine the biomass accumulation, ramets and allocation of Vallisneria natans in different substrate, meanwhile, measured the SC, starch, FAA, carbon, nitrogen and phosphorus in root, stolon and leaf of Vallisneria natans in different substrate. The result showed, the biomass and remets of Vallisneria natans grown in the infertile sandy substrate were both significantly lower than the plants grown in the nutritious argillaceous substrate, but the proportion of the root and stolon biomass to total biomass of Vallisneria natans grown in sandy substrate were significantly higher than the plants grown in argillaceous substrate, and in the sandy and argillaceous intervals treatments, the ramets of Vallisneria natans more distributed in sandy substrate; The physiological indicators, the SC and FAA in root and leaf of Vallisneria natans grown in sandy substrate are significantly higher than the plants grown in the argillaceous substrate, the SC in stolon of Vallisneria natans grown in sandy substrate was significantly lower than its grown in the argillaceous substrate, and FAA in stolon of Vallisneria natans no significantly difference between the two types of substrate, the starch in root of Vallisneria natans grown in sandy substrate was significantly lower than that in argillaceous substrate, but the starch in stolon and leaf were significantly higher than the latter, the carbon in root, stolon and leaf of Vallisneria natans were also found significantly difference between different substrate, the nitrogen in different tissues of Vallisneria natans not change along with the nitrogen in substrate, but the phosphorus rised along with it rised in substrate. In conclusion, the type of substrate played an important role in growth and physiological feature of Vallisneria natans, nutritious and macroporous substrate in favour of biomass accumulation and emerged more ramets of Vallisneria natans, but the interaction mechanism between the type of substrate and the physiological metabolism of Vallisneria natans needs further research.