Researchers are quantifying how shallow groundwater discharge impacts the quality of major rivers and estuaries in Southwest Florida to help managers in the region mitigate nutrient pollution and protect ecosystem resilience.
Why We Care
The Estero Bay Watershed is a vital ecological and economic resource, home to over 226,000 residents and diverse wildlife, including the West Indian manatee. However, the region has faced significant ecological disturbances, such as harmful algal blooms and fish kills.
In this low-lying landscape, the water table is high, and the Surficial Aquifer System is intricately connected to surface water bodies. Groundwater serves as a major conduit for transporting dissolved nutrients and pollutants — including nitrogen and phosphorus — from urban development and agricultural runoff into the watershed’s rivers and the Estero Bay estuary. Understanding the volume and chemistry of this groundwater “baseflow” is essential for effective environmental management and the preservation of coastal water quality.
What We Are Doing
This community-supported project, led by Florida Gulf Coast University (FGCU), employs a three-pronged approach to quantify groundwater–surface water interactions across the Estero Bay Watershed:
- Hydrograph Separation: Researchers are using multi-year streamflow and precipitation data from the US Geological Survey and Lee County monitoring stations to differentiate between direct runoff and groundwater-fed baseflow in the Estero River, Imperial River, and other key tributaries.
- Tracer Mixing Models: By analyzing Dissolved Organic Matter (DOM) and temperature profiles from monthly sampling events, the team is developing End-Member Mixing Analysis (EMMA) models to calculate the specific contributions of groundwater to surface water bodies.
- Numerical Modeling: Using MODFLOW and SEAWAT software, the team is building 3D finite-difference models to simulate variable-density groundwater flow and measure the flux between the Surficial Aquifer System and the watershed’s major rivers.
The project team includes principal investigator Dr. Rachel Rotz, co–principal investigator Dr. Ahmed Elshall, and consultant Dr. Tom Missimer, supported by a team of postdoctoral associates and students from FGCU’s Water School.
Benefits of Our Work
This research will provide watershed managers and decision-makers with a calibrated numerical tool to calculate nutrient loading from groundwater to surface water. By identifying key pathways and sources of contaminants, local and state agencies — such as the South Florida Water Management District and the Florida Department of Environmental Protection — can implement targeted regulatory standards and conservation initiatives to reduce nutrient infiltration.
Further, the project fosters community engagement through partnerships with the Bonita Bay Community Association and Engage Estero, ensuring that scientific findings directly inform local policy and public understanding of water resource sustainability.