Optical Analysis of Chromophoric Dissolved Organic Matter as a Tracer of Organic Material in the Neuse River Estuary, Eastern North Carolina

This study presents the first extensive examination of the optical properties of chromophoric dissolved organic matter (CDOM) including spectral slope ratios (SR) and fluorescence spectroscopy excitation emission matrices (EEM), in the Neuse River and Neuse River estuary. In situ samples, laboratory mixing experiments, and mathematical mixing models were performed to determine the conservative or non-conservative behavior of CDOM in the Neuse River and its estuary. SR values increased in surface waters progressing along the salinity gradient of the Neuse River, with lower values reflecting riverine or terrestrial source and higher values reflecting a marine source (Freshwater = 0.75; Estuarine water = 1.11). SR values for in situ samples, in lab mixing experiments and calculated mixing models revealed similar trends, with SR values exhibiting conservative behavior until higher salinities where increased variability is seen. Maximum fluorescence for in situ samples, in lab mixing experiments, and calculated mixing models showed conservative mixing within the Neuse River during the winter, but in the early spring in-situ samples were non-conservative. Further analysis on the compositional differences and peak ratios will also be examined to determine further trends seen in Neuse River. It is apparent that the composition and source of the CDOM is being altered; possibly by means of a hydrological, photochemical or microbial processes. EEM’s and SR values have proved useful in detecting different processing mechanisms of dissolved organic matter (DOM) occurring for estuarine systems like the Neuse River. SR values and EEM’s have revealed vital information on the chemistry and source of CDOM as it progresses down the river into the coastal ocean.