Study On Biomanipulation Method Of Eutrophicated Lianhua Lake

Eutrophication has become a hotspot for the research of worldwide environment. It's urgent for remediation. However, prevention and cure of it is not only intractable but also expensive during the remediation of water pollution. In the water ecosystem,the growth of phytoplankton are not only influenced by environment factors, but also controlled by biotic factors. This shows a kind of possibility that the standing crop of phytoplankton can be decreased by changing biotic community structure. this way avoids the danger of eutrophication, and reaches the aim of improving the quality of water. It can be named as biomanipulation. On the base of classical biomanipulation principle, this experiment studied by changing quantity and density of benthos i.e. Hyriopsis cumingii to control the quantity and community structure of phytoplankton. It decreased the concentration of nutrient content, increased transparence, and improved water quality. This research subjected to National Plan 863-"The demonstration of restoration project to the eutrophicated water of Wuhan city". Because of biotic tests usually need a long period, this results are partly phasic achievement of the research. Following are the main results: 1)Taking sample water from Lianhua lake, putting some Hyriopsis cumingiis into the water.The experiment shows that purifying eutrophiced water by Hyriopsis cumingii is feasible and effective. 2)In order to prove that Hyriopsis cumingii have remediation effects on the eutrophiced Lianhua lake, a medial-scale experiment was carried out on the surface of the lake. The results show that the removal rates of TP and chorophyll-a were high. 3)The medial-scale experiment showed that the species composition,the dominant genus,biomass and other parameters of phytoplankton have been greatly influenced upon the input of Hyriopsis cumingiis. Phytoplanktons in the treated enclosure are more than that in blank enclosure regarding to the species and genus. .the dominant genus changed from Microcystis to the others,such as Selenastrum Reinsch,Scenedesmus Mey,Tetraedron minimum(A.Br.)Hansg. evidently, the percentage of species in treated enclosure in class 150μm and 50-150μm is lower than that in blank enclosure, furthermore, it happens species small than class 10μm. phytoplankton in treated enclosure by using Hyriopsis cumingii seem to have miniaturization development trend. the experiment showed that the biomanipulation is applicable and effective with adequate density .the result of experiment offer a important reference data for controlling the phytoplankton.