The responses of plankton (bacteria, phytoplankton, and zooplankton) in a series of estuarine segments, characterized by various rates of flushing, to nutrient loading are being studied. At least two segments with each range of flushing rate are being studied presently. Earlier studies in which three segments were studied intensively but not frequently were completed. Such active parameters as species composition, primary production, and phosphorus uptake rates were measured. The present study is utilizing a numerical box model for mixing rates between the studied segments.