A framework for estimating ecological risks posed by nutrients and trace elements in the Patuxent River

The continued urbanization of coastal watersheds can influence the quality of water that enters rivers and estuaries. Intelligent management of aquatic resources will require the capability to quantitatively assess and evaluate the impacts of alterations in surface waters that result from changes in patterns of land use. An aquatic ecosystem model was developed and linked to an empirical landscape model to estimate ecological risks posed by nutrients and potentially toxic trace elements (copper [Cu], cadmium [Cd], arsenic [As]) in the Patuxent River, Maryland. The empirical landscape model translated reductions in croplands within the Patuxent River watershed into corresponding changes in nitrate estimated to enter the river. Trace element concentrations were increased in relation to urbanization associated with the loss of agricultural lands in the watershed. The aquatic ecosystem model used the altered inputs of nutrients and trace elements to estimate changes in the annual production dynamics of selected producer and consumer populations within the Patuxent River. The models were implemented for four mainstem locations that defined a transect from the upper freshwater portion of the river to downstream estuarine locations. Ecological impacts were estimated for 4 hypothetical changes in land use that consisted of 10%, 7.5%, 5%, and 2.5% watershed coverage by cropland. Impacts were estimated as the probability (risk) of different magnitudes of increases or decreases in total annual production of populations representative of freshwater and estuarine food webs in the Patuxent River.