Variation of light attenuation and the relative contribution of water quality constituents in the Caloosahatchee River Estuary

Submerged aquatic vegetation (SAV) is an important ecosystem resource in the Caloosahatchee River Estuary (CRE). Light attenuation is a primary factor controlling SAV distribution and abundance. Multiple data sets collected over decades throughout the CRE were compiled to develop a multiple regression model and quantify the relationship between water quality constituents (color, turbidity, and chlorophyll a (Chl a)) and light attenuation. The model was then used to assess the relative contribution of each constituent as a function of location in the estuary and magnitude of freshwater discharge at the Franklin Lock and Dam (S79). On average, both color and turbidity accounted for about 40% of variation of light attenuation, while Chl a accounted for 10%. Relative contributions varied with freshwater inflow and location. Color dominated in the upper estuary and/or during higher flow conditions. Turbidity was a major factor in the lower estuary and during lower flow conditions. Chl a dominated in the upper estuary, only rarely, during very low flow discharge. The observed relative contributions of color, turbidity, and Chl a suggest that while nutrient load reduction might improve water clarity, the assessment of the extent of improvement must account for the contributions of color and turbidity.