Using Fluorescence to Determine the Fate and Bio-reactivity of Dissolved and Particulate Organic Nitrogen in the Neuse River Estuary, North Carolina, USA

Alexandria Hounshell1, Benjamin L Peierls2, Hans W Paerl1, Chris L Osburn3 and Betsy Abare2, (1)University of North Carolina at Chapel Hill, Institute of Marine Sciences, Chapel Hill, NC, United States, (2)University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, NC, United States, (3)North Carolina State University, Marine, Earth, and Atmospheric Sciences, Raleigh, NC, United States
Abstract:
Both terrestrial and autochthonous organic matter in estuarine ecosystems have received increased attention as potential substrates for microbial metabolism and nutrient sources for supporting phytoplankton production, particularly as nitrogen (N) sources in these N-sensitive systems. The fate and bio-reactivity of organic matter within the Neuse River Estuary, North Carolina, USA was examined during nutrient addition bioassays in summer and fall 2014 and summer 2015. In addition to inorganic nutrient additions, the tested terrestrial organic matter sources included river dissolved organic matter, poultry litter extract, and wastewater treatment effluent. Using excitation emission matrices (EEMs) and parallel factor analysis (PARAFAC), identified fluorescent signatures for both dissolved and particulate organic matter were used as a proxy for organic nitrogen. Separate PARAFAC models based on particulate plus dissolved and dissolved organic matter only were generated using bioassay samples. Components identified in each model showed similarities to modeled components previously generated from in situ Neuse River Estuary samples, although some components were unique indicating potential differences in production and degradation pathways in the experimental system. By correlating the modeled fluorescent signatures with other biogeochemical parameters, including phytoplankton production and biomass, the role of organic matter, specifically organic N, in sustaining primary production and nutrient cycling was explored. Preliminary results indicate in situ autochthonous production of organic matter fluorescence due to both phytoplankton and bacterial production and potential biologic degradation of several fluorescent components identified by PARAFAC. The hypothesized results have important implications for managing organic matter (specifically organic N) loading to N-sensitive estuaries downstream from watersheds undergoing rapid agricultural and urban expansion.