Submitted to: Annual Conference on Ecosystems Restoration and Creation
Publication Type: Proceedings
Publication Acceptance Date: 10/27/2005
Publication Date: 10/27/2005
Citation: Sigua, G.C., Griffin, J.C., Coleman, S.W. 2005. Stormwater best management practice: Conversion of improved pastures to wetland systems. In: Cannizzaro, P.J., editor. Proceedings of the 32nd Annual Conference on Ecosystems Restoration and Creation, October 27-28, 2005, Tampa, Florida. p. 141-152.
Technical Abstract: Creation and restoration of wetlands of about 41 hectares (100 acres) located in northeastern Hillsborough County Florida is underway. The study site was largely drained and converted to beef cattle pasture in the early 1940’s. These improved pastures are being converted into an enhanced stormwater wetland to remove phosphorus and primary pollutants from stormwater originating from 2,400 hectares (5,800 acres) mixed land use catchments within the Hillsborough River watershed. The enhanced BMP or BMP in series will include an alum treatment facility in addition to wetland cells to treat stormwater runoff and baseflow. By combining treatment mechanisms (wetland + alum treatment) in series rather than using a single method of treatment for stormwater, the overall levels and reliability of pollutant removal can be improved. Treatment approach includes the use of a sediment sump, a shallow wetland with intermittent deep pools and a final treatment with aluminum sulfate (alum) injection and flocculent removal. The injection of alum, Al(SO4)2 .12H2O into a stormwater flow has been documented elsewhere for the control of phosphorus and, to a lesser extent, nitrogen. Alum also exhibits excellent treatment efficiencies for other pollutants (suspended solids, heavy metals, fecal coliforms, etc.) found in stormwater. The design of the wetland treatment includes treatment cells planted with a variety of emergent plants emphasizing persistent species such as iris, rush, and cordgrass. These species are known to enhance nutrient uptake. The overall design plan of the wetland cells will ensure that maintenance activities can be carried out efficiently within the cells to allow periodic removal of aged plants to further enhance the nutrient removal efficiency of the cells. Estimated pollutant removal efficiency of the combined system (wet/dry season) is about 97 percent for total phosphorus, 40 percent for total nitrogen and 83 percent for total suspended solids.