Effects of Dry Down and Re-Hydration on Sediment P Storage in Stormwater Treatment Areas.

The Florida Everglades ecosystem is negatively impacted by phosphorus runoff, which leaches down into the soil, and subsequently alters its biotic and abiotic components. Consequently, Stormwater Treatment Areas (STAs) are constructed to reduce phosphorus-rich surface water from the Everglades Agricultural Area (EAA), before they are discharged into the Everglades Protection Area (EPA). STAs maintain a continuous sheet flow of water, operating as flow-through systems, and therefore causing flooded conditions. However, periodic dry-down and re-hydration of STAs may consolidate accumulated flocculent sediments, as well as improve inorganic P-retention capacity. The objective of this study was to determine the effects of hydrological fluctuations on sediment P storage/release by the STA soil, and on surface water quality. A nutrient analysis of STA2 from 2016 showed a decrease in soil total phosphates (TP) from inflow to the outflow of the cell. However, TP concentrations and percent ash content were higher in the recently accreted soil layer, but decreased with increasing depth, reaching their lowest values at the basal muck layer; indicative of the influence of mineral matter (CaCO3) in P adsorption. Data from 2016 was compared with soil core samples recently collected from similar locations as previous data, but subjected to three hydrological treatment phases: flooded, drained, and re-flooded. At the end of each phase samples were processed and analyzed for total carbon (TC), total phosphorus (TP), field bulk density (FBD), percent ash content (Ash%), carbon dioxide (CO2), and enzyme activity (EA) per standard protocols.