Saturday, 15 July 2006
153-33

Ten Years of Phosphorus Best Management Practices in the Everglades Agricultural Area.

Samira Daroub, Timothy Lang, Orlando Diaz, and Ming Chen. Univ of Florida, Everglades Res. and Educ. Center, Belle Glade, FL 33430-8003

The Everglades Agricultural Area (EAA), located south and downstream of Lake Okeechobee in south Florida, comprises 280 000 ha of productive organic soils (Histosols). Around 80% of the land is planted to sugarcane, and the rest to vegetables, sod and rice. Flat topography, shallow organic soils and impermeable marl/limestone bedrock limit water storage options throughout the region. These organic soils are drained by pumping water through a system of farm and basin canals. Concerns regarding the quality of agricultural drainage water from the EAA to the Everglades Protection Area led to a regulatory program in the Everglades Forever Act that requires EAA farmers to adopt Best Management Practices (BMPs) to reduce phosphorus (P) loads leaving the EAA basin by 25 percent compared to pre-BMP levels. A BMP permit issued by the South Florida Water Management District is required to be able to farm in the EAA. Stormwater Treatment Areas encompassing more than 16 000 ha have been constructed to further reduce P concentrations in the EAA drainage water before being delivered to the Everglades Protection Area. There are mainly three different categories of BMPs: nutrient control practices, water management practices and particulate and sediment controls. Each individual BMP has an assigned point value and growers are required to adopt a suite of BMPs totaling 25 points or greater. Research and monitoring were conducted at multiple farms in the EAA to evaluate success of BMPs at the farm level, and to test new BMPs to reduce P loads further. Monitoring is also done at the basin level by the South Florida Water Management District. It was shown that a considerable fraction of the P in the water is in a particulate form and that high particulate P loads are common with certain farming operations. The particulate P was found to mainly be from two sources: organic sediments from the canal bottoms and floating macrophytes. Concentrations and exports of P have decreased due to BMP implementation. In water year 2004, 147 metric tons P reduction was observed with the average corresponding P concentration in EAA basin drainage water decreasing from 173 ppb (pre-BMP) to 69 ppb. New management practices that may reduce P loads further include particulate matter controls: controlling floating aquatic plants in canals, clearing canals of high P content organic sediments, and reducing the transport of sediments due to high water velocity in the canals during drainage. Implementation of BMPs in the EAA is mandatory and is now considered part of the production system by most farmers. During the ten years since BMP program initiation in 1995, the EAA basin's annual P load reduction has averaged more than 50 percent compared to the pre-BMP base period and has exceeded the level mandated by law every year

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