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ADDITIONAL BACKGROUND INFORMATION Contribution of Fertilizer in Stormwater Runoff Soil infiltration(Kelling and Peterson 1975),fertilizer application rate(Barth 1995),and irrigation practices/storm event timing(Linde and Watschke 1997; Shuman 2004)all affect the resulting percentage of fertilizer composed in runoff from urbanized areas where nutrient fertilization through landscape management practices takes place.Most urbanized areas tend to have highly compacted soils and/or a higher degree of impervious surfaces than more natural lands.As a result,the fraction of rainfall which becomes surface water runoff and therefore the total nutrient loading from these areas tends to be high.Added to this is the degree of saturation of the underlying soils both in terms of its nutrient and hydrologic adsorption.If soils are saturated during fertilizer application,then the propensity for nutrient fertilizer and decomposing lawn material to contribute towards runoff concentrations is greater upon subsequent rain events(Linde and Watschke 1997).The combination of these factors tends to"mean that lawn runoff is probably a major source,if not the major source,of nutrients in watersheds with high percentages of residential land"(Table 1;Baker 2007). Table 1: Comparison of nutrient concentrations of lawn runoff to treated and untreated sewage and lower concentration limits causing lake eutrophication(Adapted from Baker 2007). Total Total Nitrogen Phosphorus (mgfL) (mg/L) Lawn runoff 3-5 0.5-2.0 Raw sewage 38 6.5 Effluent from a typical US metropolitan treatment plant 4.2 0.4 Tampa Bay Estuary direct discharges 3 max - Effluent from secondary treatment plant 3-5 2-7 Concentrations typical of eutrophic lakes 1 <0.1 In the Tampa Bay watershed,few studies have investigated the underlying contribution of fertilizer to total nutrient loads to the bay or to surface water runoff from various land uses.One study of the Lake Tarpon watershed found that an estimated 79%of the groundwater nitrogen load to the lake was derived from fertilizer sources(LBG 2004).The land uses within the Lake Tarpon watershed are fairly urbanized(>48%)compared to other areas of the bay and were historically converted from citrus agriculture,so this estimate of fertilizer contribution to groundwater nitrogen loadings is likely at the higher range of estimates. In other areas of the country,typical ranges of fertilizer contribution within stormwater runoff are between 10—25%depending on soil conditions and 4 ri 96,- C;k