EVENT-SCALE RESPONSE OF PHYTOPLANKTON TO WATERSHED INPUTS IN A SUBESTUARY - TIMING, MAGNITUDE, AND LOCATION OF BLOOMS

Subestuaries receive direct runoff from a local watershed and exchange water at their mouth with a mainstem estuary. For subestuaries close to the headwaters of the mainstem estuary, the potential exists for a single rainfall event to supply nutrients to the subestuary on two time scales corresponding to arrival of flow from the two sources. We present a model of phytoplankton blooms based on the Rhode River-Muddy Creek subestuary of Chesapeake Bay which indicates that nutrient inputs from local sources should be capable of producing blooms of small scale and short duration, whereas influx from the mainstem estuary causes blooms of greater extent. Phytoplankton dynamics were simulated with a modification of models for nutrient-saturated standing crop, in which external nutrient inputs were assumed to favor growth of components of the community that have lower loss rates. Field data for two events during late spring and early summer 1989 demonstrated the initiation of blooms by the arrival of freshwater from local and remote sources. As predicted by the model, blooms initiated by the arrival of remote inputs were of larger spatial extent than those triggered by lor-al inputs.