The relationships among phytoplankton biomass, nutrient loading and hydrodynamics in an inner-shelf estuary

Complex interactions among biological, physical and chemical parameters within coastal ecosystems often make it difficult to define the impacts of nutrient loading on the abundance and distribution of phytoplank-ton biomass. In an effort to address the consequences of nutrient loading, the objective of this study was to define the relationships between changes in nutrient loading and phytoplankton biomass response. The nutrient source to this estuary is the Suwannee River, Florida, U.S.A., which is enhanced in discharge and nitrates by numerous groundwater springs. A network of 18 sites within the river and adjoining coastal environment was sampled monthly from April 1998 to April 2001. The highest phytoplankton biomass in the estuary was observed during periods of elevated riverine discharge and subsequent elevated nutrient loading into the coastal region. In addition, regional variation in phytoplankton biomass was dependent upon residence time within the estuary. The highest standing crops were observed in regions of the estuary subject to the slower flushing rates. Periods of exceptionally high phytoplankton biomass (> 30 μg chl a L-1) were associated with on-shore wind events that increased residence time within the estuary.