Sediment and nutrient management solutions to improve the water quality of Lake Okeechobee

Two separate models, the Internal Loading Phosphorus Model (ILPM) and the Lake Okeechobee Water Quality Model (LOWQM) were used to predict outcomes of 3 alternatives to reduce internal sediment loads: (1) the baseline simulation, which reduced external phosphorus (P) loads over time to meet the total maximum daily load of 140 metric tons to the lake by 2015; (2) the baseline plus a large-scale chemical treatment, which used alum to bind sediment P; and (3) the baseline plus a large dredging project, which removed P-laden sediments. The ILPM and LOWQM differed greatly in their approach to simulate water quality, but their predictions for each scenario were similar. The baseline showed progressive improvements of water quality that approached the in-lake restoration goal of 40 g P/L within 40 years; chemical treatment predicted this goal would be reached in 15 years; and dredging would potentially meet the goal within 30 years. Increasing or reducing the effectiveness of each treatment resulted in higher or lower predicted total phosphorus concentrations, respectively, but little change in the overall time line. An economic analysis found that in 2002 USD, chemical treatment would cost $500 million and dredging would cost $3 billion. Based on the model results, the economic analysis and other comprehensive technical evaluations of the scenarios, the baseline simulation was recommended as the preferred plan, and the management focus will remain on reduction of external P loads.