Studying On Plankton And Major Eutrophication Controling Factor Of Miyun Reservoir

Miyun Reservoir, the source of the surface water and the only source of drinking water in Beijing, is being confronted with the menace of the eutrophication. We discussed several problems, based on the research from 1980 to 2003.The community and cell density of phytoplankton determined the elementary productivity of Miyun Reservoir. One hundred and twenty -five species were inspected,which belong to 58 genera 8 phylum. And the community of phytoplankton changed with the season,the blue green algae type during growing season and diatom-green algae type beyond growing season. From 1980 to 2003, the cell density of phytoplankton increased by 3 times with the increasing of nutrient and now eutrophicational phytoplankton are common in the lake.Five water sampling collected from Miyun Reservoir were observed quantitatively. Thirty-six species of zooplankton including 11 protozoan, 15 rotifers,6 cladocero and 4 copepoda were found. The results showed the eutrophicational feature, such as lower biodiversity ,miniaturization and more amount.Benthic macroinvertebrates were studied in 5 sampling sites. The results indicated the species were becoming little and little. We only inspected 2 species Tubifex sp and Tokunagayasyrida akamus, which are all eutrophicational designate species.Compared with the research in 1980, TP, TN, CODMn, and BOD5 increased, reversely SD failed. The TSIM value of many guideline exceed 53,which showed eutrophication of water body. The level of nutrient changed with the season and sites. The water quality in Baihe Dam and Henghe were the best, secondly Chaohe Dam, Kuxi and Taoli, the worst Kudong and Jingou Cofferdam. Average value from the whole year indicated there was the tendency to eutrophication. However, the month value differed. During growth season the water body was in the state of eutrophication, beyond growth season in transition period.The relationship among different nutrients and the relationship between the nutrients and algae growth in Miyun Reservoir were comprehensively analysed. Combined with the experiment of algae growth potential, the influence of various environmental factors on eutrophication in Miyun Reservoir were investigated and the main controlling factors of eutrophication in the lake identified. It shows that the main controlling factor of eutrophication in Miyun Reservoir are light, temperature, nutrient , water capacity and velocity of flow, while the control of phosphorus is the key to control eutrophication in Miyun Reservoir.