CONTEMPORARY-ISSUES IN WATERSHED AND WATER-QUALITY MODELING FOR EUTROPHICATION CONTROL

Three issues are discussed: controllability of nonpoint nutrient loadi ngs using watershed models; the sometimes counter intuitive results fr om eutrophication models from nutrient controls for coastal waters; an d the potential significant interaction of improvement in habitat for suspension feeding bivalves. For the Chesapeake Bay watershed model, a nd for Limit of Technology (LOT) controls, a 16% and 45% reduction in nitrogen and phosphorus, respectively, is calculated. For the Bay, it is concluded that removal of phosphorus only is less effective than ni trogen in improving bottom water DO because of differential transport of nitrogen downstream. For the Delaware estuary, a significant declin e in phytoplankton chlorophyll has been observed in the absence of any nutrient controls but in the presence of improved DO. A simple model is offered that hypothesized an increase iii benthic bivalve filtratio n of overlying water as a result of improvement in DO. (C) 1998 IAWQ. Published by Elsevier Science Ltd.