Revisiting the Great Lakes Water Quality Agreement phosphorus targets and predicting the trophic status of Lake Michigan

LM3-Eutro is a high-resolution eutrophication model with several improved features lacking in historical Great Lakes models. We calibrated LM3-Eutro using a 2-year (1994-1995) dataset and performed a hindcast simulation from 1976 to 1995 to evaluate the model's ability to make predictions over an extended period of time. Results show a reasonable agreement between model output and field data over this time period. The model predicted that an annual loading of 5600 metric tons (MT) would result in a lake-wide annual total phosphorus (TP) concentration of 7.5 mu g L(-1). Using best estimates of future TP loadings, LM3-Eutro forecasts suggest that lake Michigan will remain oligotrophic and will continue to meet the 7 mu g L(-1) spring TP concentration Great Lakes Water Quality Agreement objective. (C) 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.