Large amounts of terrestrial dissolved organic matter (DOM) are delivered into estuaries following rainfall and runoff events. An unknown portion of this DOM is composed of dissolved organic nitrogen (DON), of which some part is bioavailable and represents a major nutrient source to biota in receiving waters. The consequences of this loading on the ecological and biogeochemical responses of estuarine systems has not been documented for the relatively short time periods (days) following major external loading events. In this study, we propose to quantify the labile and recalcitrant portions of DON that are altered and/or sequestered by the biota in North Inlet, a relatively pristine estuary in coastal SC. We will measure the concentration and isotopic composition (d   N) of bulk, labile, and recalcitrant DON in a tributary river and along a downstream transect in North Inlet. Samples will be collected every three months over the course of a year, and following high DOM loading events. We will also perform experimental bioassays to determine phytoplankton responses to additions of terrestrial DOM. Nitrogen stable isotopes will be used as tracers to differentiate the relative amounts of terrestrial and autochthonous DON in North Inlet estuary. 

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Funding: ASPIRE-I, USC Office of the Vice President for Research