A watershed scale assessment of phosphorus remediation strategies for achieving water quality restoration targets in the western Everglades

Abstract

Watershed scale models have become important tools to assess the effectiveness of regional and farm level remediation strategies for ecological restoration. The Everglades is an ecologically unique and complex system posing numerous challenges to water managers in South Florida. The Feeder Canal Basin (FCB) in Hendry County, Florida, drains 277 km2 of land into the central Everglades. During 2008–2017, the average annual total phosphorus (TP) concentration at the FCB outflow was approximately 89 μg/L, almost an order of magnitude higher than the restoration target for the Everglades marshes. This study aimed at evaluating remediation strategies - Best Management Practices (BMPs) and Stormwater Treatment Areas (STAs) to achieve TP targets for ecosystem restoration using an integrated modeling framework with a top-down approach. The baseline regime was modeled using the Watershed Assessment Model with multi-gage calibration (2000−2003) and validation (2004–2010). With the model performing satisfactory to very good for all gage locations, results indicated that row crops, groves & orchards, and improved pastures were largely responsible for TP concentrations and/or loads. BMP scenario results showed that TP loads could be reduced by 8% to 24% at the FCB outlet under minimal or very aggressive BMPs, respectively, indicating the need for additional water quality improvement projects to meet restoration targets. A preliminary design of two STAs, using the Dynamic Model for Stormwater Treatment Areas, estimated that a total of 52 km2 and 11.3 km2 of STAs will be required to achieve the TP concentration targets. The analysis framework employed in this study can be replicated in other watersheds to provide a holistic picture of remediation measures required to achieve water quality targets.