Total Phosphorus Model for the Great Lakes

A model based on conservation of mass is developed to simulate total phosphorus budgets for the Great Lakes. Phosphorus loadings are generated from variables indicative of human development, such as population and land use. The loadings are input to a budget model that can be solved for total phosphorus concentration as a function of time. A historical simulation is generated from census information for the period 1800 to 1970 and compares favorably with present measurements. The historical profiles indicate a dramatic increase in human impact on Lakes Erie, Ontario, and Michigan from 1950 to 1970 due to point sources. Projections indicate that, if point source effluents are reduced to 1 mg/l of total P by 1980, all the lakes will show some improvement in trophic condition. However, the analysis also indicates that control of diffuse sources, particularly in Lake Erie, will be necessary if oligotrophy is the ultimate goal.