Lake Process Models Applied to Reservoir Management

Two simplified models of lake processes are used to predict the trophic state of the proposed Tocks Island Lake to be constructed on the Delaware River, north of Trenton, N.J. Using independent estimates of phosphorus entering the lake area via the river, both models predicted the lake would be eutrophic with hypolimnetic dissolved oxygen demands exceeding 5 mg/l and midsummer Secchi Disk transparency depths as low as 0.6 m. Point source phosphorus loads to the basin were estimated from known wastewater discharges, and nonpoint loads from known land uses and area loading factors. Then, proposed measures to reduce the phosphorus load were tested for effectiveness by calculating the proportional decrease in load brought about by each measure and applying the proportion to the phosphorus load entering the lake area. The new load was then used with the models to predict the new trophic state. It was found that very stringent controls would be required to bring a significant change in the trophic state toward mesotrophy.