110 - Hydraulic Effect on Entrainment and Transport Mechanisms of Particulate Phosphorus in Stormwater Treatment Areas Dominated by Submerged Aquatic Vegetation

The implementation of Green Stormwater Infrastructure to reduce nutrient loading from stormwater runoff, and therefore mitigate the impact of anthropogenic activities on downstream nutrients and particulates has been highly documented. In southern Florida, Everglades Stormwater Treatment Areas (STAs) are constructed wetlands that reduce loading of agricultural and legacy phosphorus, largely originating in the Everglades Agricultural Area, and transported into sensitive downstream environments through canals. Although phosphorus (P) sequestration from STAs via physicochemical and biological mechanisms have been highly effective, it has been documented that these systems can continue to export some P in the form of the particulate phosphorus (PP) fraction. These particulates and their contained P can then be discharged into the Everglades system. Therefore, this investigation focused on studying the hydraulic drivers on entrainment and transport mechanisms of PP from STAs. First, particles dynamics in the STA were characterized using a digital floc camera: particle settling velocity was 1.5 mm s-1 overall site, particle densities resembled the density of freshwater for larger aggregates, and a median fractal dimension of 1.24 suggested a loosely packed floc. Second, critical shear bed stress was determined using a gust mesocosm chamber, resulting in a median value of 0.15 Pa. Then, turbulent kinetic energy and suspended sediment concentrations in STAs were determined using an acoustic doppler velocimeter. Finally, the larger critical shear stress noted at the bed in relation to in-situ observations suggested that submerged aquatic vegetation plays a greater role than erosion of sedimented materials on entrainment and transport mechanisms of PP in STAs.