Numerical modeling of algae in the patuxent estuary

Abstract

The Patuxent Estuary, a tributary of the Chesapeake Bay, has suffered excessive algal productivity over the last several decades. Although the phosphorus and nitrogen loads from point sources have been dramatically reduced since the 1980s and 1990s with costly management practices, the algal bloom problem has not been improved significantly. A physical‐biological model using the CE‐QUAL‐W2 framework was developed to address the eutrophication processes in the Patuxent Estuary and serve as a linkage between watershed model and aquatic ecosystem and fishery model. The model was calibrated with 1997–1998 data and verified with 1998–1999 data. The impact of land use change in the Patuxent Watershed on algal productivity was examined by running scenarios representing land use changes and subsequent load reduction or load increase. Model results revealed that there is no simple positive or negative correlation between watershed nutrient loads and algae productivity. Under low freshwater inflow conditions, nutrients are the limiting factors, while physical transport plays a more important role than nutrients under high flow conditions. In addition to watershed nutrient loads, internal nutrient release from sediment may become important under low dissolved oxygen conditions.