GREAT-LAKES TOTAL PHOSPHORUS MODEL - POST AUDIT AND REGIONALIZED SENSITIVITY ANALYSIS

The multisegment mass balance model of Great Lakes total phosphorus presented by Chapra and Sonzogni (1979) was used with annual phosphorus loading estimates to simulate phosphorus concentrations in 11 Great Lakes basins for the period 1974 to 1987. Comparison of the model results with field data collected since 1980 shows fairly good agreement, in spite of some overprediction of concentration in Lakes Superior and Ontario. A Monte Carlo technique known as regionalized sensitivity analysis was used both to identify those model parameters (including initial conditions) that were most important for producing an acceptable simulation and to examine new values for some model parameters. The model results were most sensitive to the parameters representing within-lake removal processes. Despite its simplicity, the Great Lakes total phosphorus model performed well and could be useful for establishing data quality objectives for phosphorus load estimates and surveillance programs.