Hydrologic and Vegetation Effects on Water Column Phosphorus in Wetland Mesocosms

Abstract

Historic phosphorus (P) loading from agricultural areas has been identified as one of the major causes for ecological changes occurring in the Florida Everglades. The restoration plan for the Everglades includes construction of large stormwater treatment areas (STAs) to intercept and treat this relatively high nutrient water down to very low total P (TP) concentrations. One such STA has been in operation for approximately 10 yr and contains both emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) communities. The surface water TP concentrations in areas near the outflow range from 0.02 to 0.05 mg TP L−1 To simulate these areas, we investigated the interaction of vegetation type; EAV or SAV; and hydrology; continuously flooded or periodic drawdown; on the P removal capacity in mesocosms packed with peat soil obtained from STA‐1W. The surface water had low TP concentrations with an annual mean = 0.023 mg L−1 For SRP and TP, hydrologic fluctuations alone had no discernable impact on P treatment while vegetation type showed a significant impact. Influent soluble reactive P (SRP) decreased by 49% for the SAV treatments compared with 41% for the EAV treatments, irrespective of hydrology treatment. The reduction of dissolved organic P (DOP) was also higher for the SAV treatment averaging 33% while showing a reduction of 11% for the EAV treatments. There was no significant difference in the treatment efficiency of particulate P (PP) across the treatments. For TP, SAV treatments removed 45% of TP while EAV removed significantly less at 34%. By mass calculations, the EAV required 85% more P for plant growth than was removed from the water column in 1 yr compared with only 47% for the SAV. Therefore, the EAV “mined” substantially more P from the relatively stable peat soil, translocating it into the detrital pool.