Simulation of Long-Term Trends in Chesapeake Bay Eutrophication

Abstract

A predictive mathematical model was employed to examine trends in Chesapeake Bay eutrophication from 1959 to 1988. The model provided details of processes and substances for which no record existed. The simulation indicated the volume of anoxic water was largest in the decade 1969–78. Since then, anoxic volume has declined. The decline was largely due to hydrodynamic effects. In 1969–78, high runoff caused the Bay to be highly stratified and inhibited oxygen transport to bottom waters. Less runoff in the years 1979–88 diminished stratification and allowed enhanced oxygen transport to bottom waters. When only years of similar stratification were compared, an increase in anoxic volume was noted from the 1959–68 decade to the 1979–88 decade. The increase was associated with increasing nitrogen concentration in runoff from two major tributaries and with increasing chlorophyll concentration in the mainstem Bay.