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average total seasonal precipitation(in.)for discrete subbasins of the watershed (Table 2).These estimates were used as the basis for hydrologic inputs to modeled estimates of total nitrogen loads from urbanized areas in the watershed. Table 2: Average total seasonal precipitation(in.)in USGS defined subbasins of the Tampa Bay watershed(SWFWMD 2008). Period of USGS Subbasin Record Little Seasonal Tampa Hillsborough Manatee Average Bay/Coastal River Alalia River Manatee River (1915-2008) Areas River Dry Season 20.99 22.62 21.73 21.36 20.93 Wet Season 30.66 31.00 30.96 31.95 32.91 Land Use/Land Cover Data Land use/land cover GIS data for 2006 were obtained from the SWFWMD and incorporated into the load estimate model(SWFWMD 2006).The land use data were recorded following the Florida Land Use Cover Classification System (FLUCCS)level 3 developed by the Florida Department of Transportation Thematic Mapping Section(FDOT 1985). For the purpose of assigning land use-specific runoff and pollutant loading factors,the 7 urbanized FLUCCS land uses were aggregated into 5 Coastal Land Use Code(CLUC)classes(Table 1;Appendices A&B),as presented in the most recent load estimate report prepared for Tampa Bay(2004-2007)(Janicki Environmental 2008).The aggregated land use classification system was developed by examining the source literature for the FLUCCS land uses,and combining hydrologically-similar land uses based on stormwater runoff coefficients and land use specific pollutant loading factors.Land use-specific stormwater runoff coefficients and pollutant concentrations were determined from a review of field investigations from central and south Florida,as described below. Soil Data The soils coverage includes discrete polygons of individual soil series(types)as identified and delineated by the USDA Natural Resources Conservation Service (NRCS)in the Hillsborough,Pinellas,Manatee,Polk,Pasco,and Sarasota county soil surveys.The GIS coverage of these data was obtained from the SWFWMD(2002).The discrete soils polygons represented a soil series,and were aggregated by hydrologic soil groups(A—D).The NRCS has assigned a hydrologic group identification to each soil series to indicate runoff generating characteristics."A"soils,in general,generate the least,and"D"soils the most amount of runoff for a given rainfall.The soils coverage was intersected with the land use coverage to provide the GIS layer used to estimate runoff coefficients. Each unique combination of land use type,soil series,and season has been assigned an associated runoff coefficient value(Appendix A). 8 rgC.l'