Evaluating Suwannee River Discharge Effects on Water Quality in Big Bend Region

Scientists are using satellite images and data collected on the ground to assess how water color and nutrients discharged from the Suwannee River affects water quality and, in turn, seagrass beds in the nearshore areas of Florida’s Big Bend region. This NASA-funded project is a collaborative effort between the Fish and Wildlife Research Institute, the University of South Florida College of Marine Science and the Florida Department of Environmental Protection.

The Suwannee River is the 10th largest river draining into the Gulf of Mexico and the third largest river in the state of Florida. River water is normally a dark color and river discharge contains increasing amounts of the nutrients nitrogen and phosphorus. These nutrients can degrade water quality in nearshore areas by fostering the growth of microscopic algae, which can reduce water clarity. These areas contain extensive seagrass beds that require light for survival. Low water clarity can prevent light penetration, which can cause seagrasses to be damaged and possibly die.

Satellite information – when linked to coastal water quality and measured changes in color, cloudiness and presence of microscopic algae – can provide important insights about water clarity and the amount of light available to seagrass ecosystems. Scientists are comparing images captured by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) with data collected on the ground to try to establish connections between nutrient loads, water quality and seagrass health. They conducted coastal water quality surveys near the mouth of the Suwannee River and offshore of the Steinhatchee River, a pristine region of Big Bend. Comparing conditions of the two areas will provide insights on how the Suwannee River discharge affects seagrass ecosystems in the Big Bend region. Findings from the study will support ongoing assessment of the Total Maximum Daily Load (TMDL) program for the Suwannee River estuary. This program helps protect 205,300 acres of seagrass beds in Big Bend nearshore waters that provide important habitat for fish, shellfish, turtles and manatees.

Scientists are also joining diverse sets of information – including seagrass distribution and abundance; water quality; remotely-sensed ocean color data; and riverine nutrient loads – to accomplish the following tasks:

• Continue to develop and test new formulas at the University of South Florida (USF) Institute for Marine Remote Sensing to estimate water clarity, turbidity, chlorophyll-a concentrations (microscopic algae) and colored dissolved organic matter in coastal waters using MODIS satellite imagery.
• Use water quality data collected in the Big Bend region in 2010 and 2011 to calibrate and evaluate MODIS remotely-sensed optical water quality information.
• After establishing the relationship between in-water measurements and satellite data, evaluate MODIS imagery collected during the last 10 years to provide a history of remotely-sensed water quality for the Suwannee River estuary and nearshore areas in the Gulf of Mexico.
• Attempt to establish measurable relationships between Suwannee River nutrient loads and the calibrated MODIS remotely-sensed optical water quality measurements.
• Relate annual changes in seagrass species composition, distribution and abundance since 2002 to satellite data.
• Continue to develop user-friendly tools allowing managers and stakeholders in the Suwannee River watershed to extract remotely-sensed optical water quality information from MODIS imagery. This information is provided at the USF College of Marine Science Optical Oceanography Laboratory’s Suwannee Estuary Project Web page.