Seston and dissolved organic carbon dynamics duringMicrocystis bloom with special reference to the effects of three Chinese domestic fishes in experimental enclosures

TheMicrocystis bloom that once disappeared from Donghu Lake, a shallow, eutrophic Chinese lake, was successfully resumed with the use of the enclosure method. Seston and dissolved organic carbon (DOC) dynamics during theMicrocystis bloom were investigated with particular emphasis on the effect of three Chinese domestic fishes (silver carp, bighead carp and grass carp). The results showed that the change of chlorophyll a obviously related to the fish species and its stocking density. Due to the release of extracellular ogranic carbon and increased bacterial activity, DOC increased apparently after silver and bighead carps were introduced. POC/DOC dropped considerably in the enclosures containing silver and bighead carps and in the surrounding lake water, which implied that the bacterial activity was more pronounced in such ecosystems. Statistical analysis indicated that the linear relationship between POC and chlorophyll a could reflect the state of algal growth and nutrient metabolism. It was expected that this study would provide some information on biomanipulation in the shallow, eutrophic lakes. This work was supported in part by a Grant-In-Aid from the Chinese Academy of Sciences, State Key Laboratory of Freshwater Ecology and Biotechnology (FEBL) affiliated to the Institute of Hydrobiology for the project “Control Ecosystem: An Approach to Lake Restoration”.