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Land Use-Specific Runoff Coefficients&Stormwater Quality Concentrations Land use-specific runoff coefficients were obtained from published literature, including references for the west-central and south Florida geographic area.A range of runoff coefficient values for each land use was developed to account for seasonal changes in rainfall/runoff relationships,and for local soils conditions,as described in Zarbock et al.(1994)and used for previously modeled current and future load conditions for the Tampa Bay estuary(Zarbock et al. 1996a;Janicki et al.2001).These coefficients are presented in Appendix A. An extensive list of regional water quality concentration data for nonpoint source total nitrogen has been compiled for the modeling effort,and is described in Zarbock et al.(1994;1996b),Pribble et al.(2001),Poe et al.(2005)and Janicki Environmental(2008).The values are from a number of stormwater sampling programs and represent averaged values from multiple samples from each program(Appendix B). Modeling Approach All nonpoint source loads for baseline conditions were estimated using a model- based approach for urbanized areas in the Tampa Bay watershed(Table 1; Figure 1),as follows: TNi_=ILU;•EMC;-(RFj-RU;j),where: ij TNS= total annual nitrogen load across urbanized land use category i and seasonal category j(tons), LUi= area of urbanized land use category i(acres), EMCi=land use specific event mean total nitrogen concentration(mg/L), RFj= USGS basin-specific rainfall in dry and wet season category j(in.), RUij= land use and soil-type specific runoff coefficient for land use category i and seasonal category j. Reductions associated with fertilizer ordinance implementation for a rainy season prohibition of fertilizer application were applied to wet season load estimates across all urbanized land uses according to the following adjustments to the loading model employed above.Reduction estimates encompassed the estimated contribution of fertilizer to urbanized runoff,as follows prorating the expected fertilizer contribution to the difference between an urbanized land use and a natural land use: EMC(adjusted)i=EMCi—[(EMCi—EMCforest)•X],where: EMC(adjusted)i= adjusted land use specific event mean concentration based upon a scaled contribution of fertilizer to the runoff concentration, 9 595-&3