Basal Study On The Ecological Restoration And Reconstruction In Wulihu Lake

Aquatic-terrestrial ecotone (ATE) is an important functional interface zone between the ecosystems of freshwater and terrene, which can provide essential ecosystem services such as lakeshore stabilization, fisheries resources and habitant, food for migratory, aesthetic scenery and recreational opportunities for human populations. It also offers a protection on water body from harmful impacts of terrestrial matter such as nutritive materials and heavy metals. Due to the higher population and more activities from human population more and more ATEs have been deteriorated and the ecological function has been worse, which turns out to be an outstanding challenge for the human life environment. The ecological restoration and reconstruction has been paid more attention to. Since 2003, China has conducted a series of research and practice in Taihu Lake. This thesis focused on the research and assessment on the ecological reconstruction of Wulihu Lake, a part of Taihu Lake. Based on the completed reconstruction in west part of the lake, the influences from the multi-factors, such as the bank structure and biology as well as wetland, were researched. The plan of the ecological reconstruction on east part of Wulihu Lake was designed based on the results above. The research results are followed:1. With impact from the three type's lakeshore structure of ATE, the physical-chemical indexes, phytoplankton, nitrogen and phosphobacteria in the waters were influenced significantly. On the point of the ability to minimize the nutritive salt, it can be ordered as wetland lakeshore (WL), gravelly lakeshore (GL) and vertical lakeshore (VL). In summer and fall, the ability to minimize the NH4+-N,NO3--N,TN and TP by lakeshore is stronger, while in winter, with relatively high biomass of phosphobacteria, the concentration of TP was also reduced in GL and WL. The ecological lakeshore index which was proposed for the long term monitoring program of the lakeshore ecological condition,was 1.84 in the east Lake Wulihu.2. The results also indicated that, the hydrophytes in the lake can increase the distribution of nitrogen cycle bacteria, decreased the concentration of nutritive salt, such as TN, NH4+-N and NO3--N, improving the water quality and minimize the alga biomass. The ecology function of reed was very strong in growing seasons, while in spring and winter the planted floats and submerged plant have better ecology function. The variety of ecological indexes can be indicated by the biomass and diversity of periphyton.3. There were distribution rules of N, P in the soil percolate of the ATE. The concentration of DON,NO3--N,TN and TP was high in topsoil percolate and it decreased with depth. But the concentration of NH4+-N was the lowest in topsoil percolate and increased with depth. The vertical distribution of nutritive salt was dependant on the humidity and seasons. It was highly correlated with the distribution of TOC, ORP, root biomass and edaphon in soil.4. The study about the heavy metals in wetland and plants indicated that the concentrations of heavy metals decreased with increasing depth in the top 40 cm soil, and then increased slightly with increasing depth. investigation also indicated that the concentrations of Cd, Cr, Pb and Zn exceeded the geochemical background values in Taihu Lake area, and the concentrations of Cd at all depth soil exceeded the Environment quality Standard for Soils of China. Correlation analysis suggested the heavy metals had the same origin. The dominant plants of the wetland were reed and false loosestrife, and the root is the main organ where heavy metals were largely accumulated. The general order was root >rhizome >stem >leaf, whereas in the false loosestrife, leaf was the main organ for Cr accumulation. Both reed and false loosestrife had the highest concentration factor to the Cu.5. The landscape vegetation has the function of ecology as well as the scenic; the research on the simulative overland runoff indicated that the order of the purify ability of TN,NH4+-N was Festuca arundinacea>Trifolium repens > Zoysia japonica; with TP, the order was F.arundinacea>Z.japonica>T.repens, and regarding NO3--N, the order was T. repens>F.arundinacea>Z.japonica. Generally, the strength of purify function increases with higher depth and lower slope.6. Based on the environment status of the lake Wulihu and the basal research of the west lake Wulihu, this thesis made the primary plan for the ecological restoration and reconstruction of the east lake Wulihu. The whole lake zone was divided as ecological protection zone, plants restoration zone, eco-system reconstruction zone and else zone, then the four zones were programmed respectively. With implementation of this project, the water quality of the Lake Wulihu can be improved significantly and the ecological function can be recovered to meet the environment requirement from the Eleventh Five-Year Plan for Environmental Protection. Besides this, it also improves the ecological, economical and general social development harmoniously.