1. In last fiscal year, we have collected the literatures about the utilization of food-web manipulation for lowering the eutrophication in the water reservoirs and have completed the analyses of water quality and biotic community in the Sinsan Water Reservoir (SWR) in three seasons. During this year, we have continued such works to complete the data of winter season. 2. Bioindication using algae and zooplankton indicate that the water quality in SWR was in slightly eutrophic state and between β- and α-mesosaprobic level, with slight to moderate level of organic pollution. The aquatic ecosystem was stable over the studied time. The occurrence of spring Microsystis-bloom is related to the key nutrient, phosphate, which was brought from hypo- to epilimnion during overturn in late winter. The dominant phytoplankton are green algae and cyanobacteria, mostly of small size (<30 μm). Basing on the characteristics of the aquatic community structure, we suggest the suitable model for food-web manipulation in SWR is: phytoplankton-zooplankton-bivalve. 3. Experiments done in the laboratory show that freshwater clam and pearl bivalve can consume a large quantity of planktonic algae, making the aquatic chlorophyll a down to as low as 0-2μg/L. The filtering rate is so efficient that suspended culture of bivalve gain more encourage and attention. clams are effective in feeding Chlorella cells with a rate of 3.10~5.50×107 cells.g-1.h-1, while pearl bivalve of 2.46-3.94×107 cells.g-1.h-1. The reasonable and ideal number of freshwater clams being cultured was estimated to be between 1-3 clams per square meter. 4. In SWR, 160 pearl bivalves have been incubated and observed for a period of 7 months. The survival rate has been as high as 85-90% at the early stage. No death of test organisms was observed after 2-3 months, suggesting a high adaptation of pearl bivalves to the environment of SWR. Over the incubation period, a decline in Microcystis density was obtained. The size of pearl formed is related to bivalve body size. However, the produced pearl was limited, possibly due to low nutrient concentrations, when compared with the conventional culture ponds. 5. A device for mixing epilimnion water was tested in SWR. A mixing depth down to 10 m was found to be effective in breaking the thermal stratification and in lowering the growth of Microcystis, but enhance the growth of certain algae. As a result, changes in phytoplankton assemblage occurred. 6. An experiment with artificial wetland grown with water plants has been proven to be effective in removal phosphorus, ammonium, suspended solid, and bacteria from inflow water. In addition, floating islands planted with certain water plants were effective in reducing nitrogen and phosphorus contaminations in the water reservoir. 7. A simulation of the dynamic water quality and the ecosystem of reservoir are represented by WASP and Ecopath models. The water quality simulated results show a good agreement to the field data with WASP model in 2004-2006. With the field study of bivalves this year, biological parameters of bivalves in Ecopath were confirmed. The outcome by Ecopath model indicates that the aquatic ecosystem in this reservoir is in mature status. Basing on the combined model of WASP and Ecopath, an incubation of ca. 2300 bivalves is needed in order to increase the water quality to mesotrophic state. Basing on the results of the present study, several conclusions and suggestions are provided.

Eco-engineering, food web manipulation,Reservoir water quality