Nitrogen (N) is present in several forms in terrestrial and aquatic systems. In water bodies, N is present in inorganic (NH₄, NO₃) and organic (both dissolved and particulate) forms. Nitrogen carried via stormwater runoff or leaching from fertilized urban landscapes to water bodies can have detrimental effects on water quality because the inorganic N forms are readily available to phytoplankton. There is growing evidence that a part of the dissolved organic N (DON) may also be bioavailable to phytoplankton. DON in urban stormwater runoff, for example, has been shown to be highly bioavailable. The objective of this research is to characterize the sources and chemical fractionation of organic N in stormwater runoff from an urban residential neighborhood and in streamwater along an urban to rural gradient. We hypothesize that urban stormwater DON will be highly fractionated into labile low-molecular weight fractions and that streamwater DON will become increasingly bioavailable with increased urbanization because of shifts in vegetation patterns and hydrologic flowpaths. To test this hypothesis, we are collecting stormwater runoff from an urban neighborhood near Tampa, Florida and streamwater from both urban and rural sub-basins of the adjacent Alafia River.