Monday, November 5, 2007 - 1:30 PM
117-4
Effect of a Prescribed Burn on Phosphorus and N itrogen Removal in a Municipal Treatment Wetland.
John R. White1, Mark Sees2, Ronald Corstanje3, and Lisa M. Gardner1. (1) Wetland Biogeochemistry Institute, Louisiana State University, 3239 Energy, Coast & Environment Bld, Dept. of Oceanography & Coastal Sciences, Baton Rouge, LA 70803, (2) Orlando Easterly Wetlands, 25155 Wheeler Road, Christmas, FL 32709, (3) Rothamsted Research, Hertfordshire, England
Constructed wetlands dominated by emergent vegetation can build up significant amounts of detrital material. This buildup can result in short-circuiting of surface flow, release nutrients back into the water column and affect vigorous regrowth in the following season. This will have an impact on the treatment efficiency of constructed wetlands. We investigated the effect of a fire, as a mechanism to remove this detritus, on the water quality in a 480 ha. constructed wetland in central Florida . This wetland provides the final treatment for wastewater from the City of Orlando ’s wastewater reclamation facility. A paired cell design was implemented, with a burn in one cell, while the adjacent cell received no burn. Soluble reactive P (SRP), total P, and TKN were measured regularly at the inflow and outflow surface water culverts for a period of one month before and 4 months after the fire. Data were analyzed using an “intervention analysis”, a statistical approach which quantifies the extent of nutrient release and length of time for which the fire effect was predominant. Higher outflow SRP was observed for an estimated 3 weeks after the fire. The fire effect was estimated to generate an average outflow concentration of 0.397 mg P/L compared to the 0.121 mg P/L for the control. Similarly for total P, the estimated mean outflow was 0.477 mg P/L for the burn and 0.156 mg P/L for the control. Effect of the fire was very short-lived for TKN, with elevated values only within the first 5 days after the fire. These results indicate that a fire in an herbaceous wetland can lead to mobilization of both soluble and total P. From a management perspective, constructed wetlands which undergo prescribed burns should not release surface water for up to 3 weeks afterwards, to avoid exceeding permitted nutrient discharge limits.