Role of hydrology in development of a vernal clear water phase in an urban impoundmen

摘要

1. Grazer control of phytoplankton and water transparency was responsive to interannual variations in river discharge and corresponding water retention time in Ford Lake, Michigan, U.S.A.2. A simple mathematical model was developed to separate the effects of washout from in situ zooplankton population dynamics. The threshold reservoir flushing time for development of a large Daphnia population and corresponding clear water phase during May was about 20 days. Predation by Leptodora was insufficient to cause the subsequent decline of the Daphnia population.3. Recruitment success by the zebra mussel Dreissena polymorpha appeared responsive to flushing time indirectly, through hydrological effects on the magnitude of the spring diatom crop.