Phosphorus Budget and Remediation Plan for Big Platte Lake, Michigan

This paper presents a phosphorus budget and modeling case study for Big Platte Lake Michigan and the Platte River watershed. These analyses are a necessary component of a credible total maximum daily load (TMDL) for Big Platte Lake and may be more broadly applicable to similar systems and other water quality management issues. A calibrated Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) model is used to simulate total phosphorus loads from the watershed. A nonsteady state lake model is developed to predict total phosphorus concentrations in both the water column and the sediments. Temperature and dissolved oxygen models are used to predict the anoxic periods in the lake hypolimnion to facilitate calculation of the internal phosphorus loading due to sediment release. Following calibration, the models were used to determine allowable total phosphorus loads for Big Platte Lake for typical hydraulic conditions. Current measured total phosphorus loads exceed model calculated allowable loads. Therefore various nonpoint remediation alternatives were evaluated as a means to reduce the excess loading. The credibility of the analyses was enhanced because of the availability of laboratory measurements of sediment phosphorus release rates and an extraordinarily comprehensive database of current and historical lake and tributary water quality measurements.