The Biological Chain Study Of Algae Control In The Baiyangdian Lake

The eutrophication has been a global environmental problem in freshwater lakes, so it becomes more and more exigent to control eutrophication of water bodies. The situation is not optimistic in the Baiyangdian Lake. The survey results showed that the lake had existed severe eutrophication in 2005 and 2006. In this paper, we designed the biological chain of algae control, which constituted mainly by zooplankton, studied the food relationship between different trophic levels under the laboratory conditions, and put forward program to solve the problem of eutrophication by biomanipulation technology.This paper studied zooplankton and phytoplankton in Baiyangdian lake, as well as physical and chemical indicators of water quality. Based on this result, we know the extent of eutrophication of water bodies and the dominant of algae and zooplankton (Cladocera and Copepoda) which lead to eutrophication. The study further developed the biological chain in which zooplankton play a major role:the main algae leading to eutrophication(Chlorella pyrenoidosa, Cryptomonas ovata, Merismopedia sp.)→large size Cladocera→Copepoda which affected Cladocera population. We investigated the feeding of Daphnia pulex to algae and Cyclops vicinus to Cladocera under the laboratory conditions, and fix every trophic level interactions of biological chain.In this paper, the grazing rates of Cladocera on algae under the laboratory conditions were studied. The results showed that the biomass of algae influenced the grazing rate of Simocephalus vetulus and Daphnia pulex. The grazing rate dropped when the biomass exceeded the saturation quantity. When the biomass of Chlorella pyrenoidosa more than 14.75 mg/L,and Scenedesmus quadricanda more than 35 mg/L, the grazing rate of D. pulex slowed down. When the biomass of S. quadricanda more than 35 35 mg/L, the grazing rate of S. vetulus slowed down, on the contrary the grazing rate for C. pyrenoidosa increased always. Moreover determined the filter rate and Clearance rate of the Cladocera, and selectivity of algae.Our also research proceeding in feeding ecology of Cyclops vicinus demonstrates that in he feeding range of C. vicinus, they prefer feeding on smaller Cladocera individual. In late spring and early summer the breed of Cladocera begins, there will be a large number of Cladocera larvae, thus the predatory invertebrates such as C. vicinus begin feeding on the Cladocera larvae and its eggs, which is the major cause of Cladocera population decline in late spring and early summer. Moreover, with the increasing of the temperature, feeding rate of C. vicinus also increases, which further intensify the influence on the population of large-size Cladocera to some degree.In conclusion, the biological chain is identified on the basis of investigating the ingestion of plankton, which can Significant control the quantity of algae.