ABSTRACT
The Stormwater Treatment Areas (STAs) are large wetlands constructed for phosphorus (P) retention for Everglades restoration in south Florida (USA), and include areas of submerged aquatic vegetation (SAV) at a globally unprecedented scale (~12,000 ha). The goal of this study was to elucidate the fate of P retained in large-scale SAV wetlands, and the associated temporal trends in P removal and retention. In a well-performing, 929-ha SAV-dominated STA surface water flow-through treatment wetland, measurements of accrued soil depth and soil P storage performed every ~4-6 years revealed a steady-state longitudinal soil P enrichment profile established within the first ~4 years of flow-through operation. Subsequently, the SAV soils accrued P at a relatively steady rate (1.13 g P m-2 yr-1 for the entire 17-year period) without indication of temporal P enrichment, spatial expansion of soil P enrichment in the inflow region, or impairment of water column P removal efficiency. Phosphorus sequestration occurred via accumulation of new sedimentary material (0.9-1.5 cm yr-1), rather than enrichment of existing soil. These soil surveys were accompanied by measurements of porewater SRP concentrations, soil P release under anoxia, and soil P fractions, which demonstrated that soil P release potential and concentrations of highly labile soil P generally decreased over time. These findings demonstrate that the P retention mechanisms operating within this large SAV wetland can be sustainable under managed steady-state conditions. Susceptibility of SAV to extreme environmental perturbations in this and other wetlands, however, remains a research priority.
