Ecological Remedialion Technology In Eutrophic Lakes

Understanding the mechanisms of eutrophicalion of water body and developing feasible remediation technology is the frontier and hot research field in environment and ecology. As a new, cheap and ecological sound technology, ecological remediation technology in eutrophic lakes attracts many scientists all over the world.The objective of this study was to summarize the technology of phytoremediation of eutrophicated water system, through experiments in the field. First, floating plants should be introduced to reduce concentration of suspended substance and phytoplankton to improve water transparency; then the cold season macrophyte and the warm season macrophyte should be introduced to build the enchasing community on time and space, to make the water body clear stabilized. The major research and summary made were: technology on control the floating macrophyte and its feasible coverage; impact of submersed macrophyte to the amount and structure of phytoplankton.The main results obtained are summarized as follows:(1). Introduction of pioneer species and its ecological effect. At the beginning of phytoremediation, some r-strategy floating plants, as pioneering species, should be introduced to improve water transparency and to reduce concentration of nutrition for a suitable situation for introduction of submersed plants. The higher coverage of floating Plants(Eichhoria crassipes) is, the faster improvement of water transparency is. But it is a contradiction that water DO is gradually reduced with the increasing coverage, and the living beings in water will die. For the best effect, the appropriate coverage degree of floating plants which are first vegetated is about 20%; and the coverage degree should be controlled below 50%.(2). Floating plants can strongly restrain the amount of phytoplankton, but the impact to the population structure of phytoplankton is small.(3). During the upgrowth of submersed macrophyte, the concentration of nutrition such as N, P in water can be controlled at lower, the water body is clear.(4). Submersed macrophyte can control the amount of phytoplankton efficiently, and can change the population structure of phytoplankton through reducing the number of eutrophication phytoplankton such as Cyanophyta, Chlorophyta.(5). But in the alternate period of cold season plants and warm season plants, the concentration of nutrition is increased, the water transparency is decreased. Those changes are hard to the succession of cold season plants and warm season plants. How to make this succession be smooth is a question worth to be studied.