Evaluating light attenuation and low salinity in the lower estuary with RECON (River, Estuary, and Coastal Observing Network)

The southern portion of the Charlotte Harbor region, which includes Pine Island Sound, San Carlos Bay, and the lower Caloosahatchee Estuary, has over 11,700 ha of submerged aquatic vegetation (SAV). The SAV species in the region have been used as environmental indicators because they are affected by nutrient loading, algae blooms, and freshwater discharges. Management approaches to reduce nutrient loading, phytoplankton concentrations, and high freshwater discharges in the region have also been applied to meet water clarity targets (light attenuation). In an effort to understand the duration and effect of low salinity periods in the lower estuary on water clarity, salinity data at several River, Estuary, and Coastal Observing Network (RECON) sites were analyzed. Optical parameters associated with increased light attenuation (fluorescent dissolved organic matter, chlorophyll, turbidity) were significantly higher during lower salinity periods (less than 25). In addition, discrete light attenuation coefficients, collected as part of RECON monthly maintenance, were analyzed. A synthesis and evaluation of the conditions in the lower Caloosahatchee during the study period (2008-2014) suggest that flow and load reductions would result in increased water clarity.