Response of Chesapeake Bay to Nutrient Load Reductions

A eutrophication model package was employed to examine the response of mainstem Chesapeake Bay to nitrogen and phosphorus load reductions. In addition to sensitivity analyses, the bay was examined under limit-of-technology nutrient controls and all-forest conditions. Scenarios were run in a time-variable mode for a minimum of 10 years. Decade-long simulations were required to achieve a near-complete response to load reductions. Analyses indicated that the primary effect of phosphorus controls was the limitation of algal biomass during the spring bloom and in the upper bay during summer. Nitrogen controls limited algal biomass primarily in the lower bay. Nitrogen controls were more effective than phosphorus controls in limiting algal production and in reducing anoxic volume. Limit-of-technology load reductions, under average hydrologic conditions, improved minimum summer-dissolved oxygen by ≈0.5 gm m −3 and reduced anoxic volume by 40%. Anoxia was largely absent under all-forest, average hydrologic conditions but persisted during wet, highly stratified years.