Interactions between isolation and nutrient loading and their response of esturine phytoplankton

The response of natural estuarine phytoplankton communities to nutrient enrichment was investigated using large-volume outdoor continuous cultures. The five-year study in the Patuxent River, MD, revealed a strong enrichment potential for nitrogen (N) during summer/fall, often resulting in tenfold increases in biomass within 48 hr. Largely due to increased centric diatom growth rates, the resulting unstable blooms rapidly declined, leading to successional assemblages quite different in composition relative to unenriched controls. Phosphorus enrichment did not affect individual species growth rates or produce changes in assemblage composition, and produced only weak, delayed response during two winter experiments. Subsequent experiments to investigate the role of light intensity demonstrated a strong potential for light limitation in the river during fall and winter, whether or not a nutrient response was present.