Assessing the effects of natural and anthropogenic stressors in the Potomac Estuary: Implications for long-term monitoring

Ecological conditions in the Potomac Estuary are affected by a variety of n atural and anthropogenic stressors. Natural climatic factors combined with anthropogenic activities affect fluxes of material through Potomac River wa tersheds and cause changes in ecological conditions in the Potomac Estuary. A basic premise of this ongoing study is that effects of anthropogenic and natural stressors can be distinguished. The investigation involves: 1) ana lysis of existing data using time series methods, 2) retrospective modeling to link the response of estuarine water quality to changes in stressors, a nd 3) new measurements on sediment cores from the Potomac Estuary. Estuarin e effects being considered include changes in the distribution and abundanc e of chlorophyll a, diatoms, dinoflagellates, ostracods, submerged aquatic vegetation, benthic fauna, dissolved oxygen, and foraminifera. Since curren t conditions may be due to the accumulation of effects over many years, our research considers variability and changes during the past century in the context of long-term changes during the past 500 years. The availability of large data sets from the past century, long-term information on variabilit y in precipitation from tree ring data from the past 300 years, and paleoec ological studies by other investigators in the Potomac Estuary and main ste m of Chesapeake Bay make the Potomac Estuary an ideal place to develop meth ods to distinguish between effects of natural and anthropogenic stressors i n estuaries, in the context of a varying, and perhaps changing, climate.