Don Scavia

Professor Emeritus, University of Michigan

Chesapeake Bay Hypoxia Forecasts and Scenarios

Since 2007, we have been providing annual forecasts of the extent of the hypoxic volume in the main stem of the Chesapeake Bay.  The model predicts mean July hypoxic volumes using January to May total nitrogen (TN) loads from the Susquehanna River, and is based on an adaptation of the Streeter-Phelps oxygen sag model, adapted from a similar model we built for the Gulf of Mexico. It simulates organic matter decay, oxygen flux through the pycnocline, and sub-pycnocline up-estuary advection in simple first-order processes. TN loading from the Susquehanna River is used as a surrogate for biological oxygen demand from decay of phytoplankton biomass, consistent with studies that have shown the middle reaches of Chesapeake Bay are nitrogen-limited and that phytoplankton biomass in the mid-Bay accounts for as much as 90% of the annual organic matter budget of the estuary.  Using the Susquehanna River loads, and initial oxygen deficit estimated from oxygen measurements, the hypoxic volume forecasts, error bounds, and model coefficients were  estimated using Bayesian inference for  22 years of data.

Applications of this work have been published in the following papers, and a special website dedicated to the annual forecasts can be found here.