Characterization of CDOM in an organic-rich river and surrounding coastal ocean in the South Atlantic Bight

Abstract

Variability in chromophoric dissolved organic carbon (CDOM) was characterized in and around the Cape Fear River and Onslow Bay, North Carolina USA. The river end member of the study is extremely rich in CDOM, thus the Cape Fear River serves as a point source of CDOM-rich water into the southeastern Atlantic bight. The river plume is easily traceable and generally extends in a southwesterly direction along the coastline into Long Bay. Depending on physical processes and river flow, the plume can meander somewhat and may even turn northward for short periods of time. The oceanic end member of this study was the Gulf Stream. Samples from the Gulf Stream were obtained up to 97 km off shore. The experimental approach focused on the qualitative and quantitative description of CDOM from fresh-to-oceanic waters. CDOM was characterized by excitation emission matrix (EEM) fluorescence and UV/VIS spectroscopy. Variability of CDOM absorption in the relatively small area of the Cape Fear River estuary and surrounding coastal ocean was very high. The observed range of variability of CDOM absorption coeffi- Aquat. Sci. 65 (2003) 384-401 cient, a CDOM (350), extended over nearly the entire range of CDOM absorption in the literature: 0.046 = a CDOM (350) = 29.9 m -1 . Changes in CDOM absorption spectrum slope coefficient S, were small in the Cape Fear River plume area, but relatively large in Onslow Bay. CDOM EEM spectra indicated that a radical change in composition of CDOM occurs along the river-to-oceanic salinity gradient. CDOM in the coastal ocean was characterized by strong reduction of the three principal intensity peaks: A, C, and M, and a prominent contribution of the T peak to the fluorescence spectrum. The fluorescence intensity is linearly related with absorption. There is a strong inverse relationship between salinity and CDOM absorption. The distribution of the slope coefficient and the percent contribution of respective peak intensities to the total EEM intensity showed that CDOM undergoes conservative mixing until it approached oceanic salinity. Thus, CDOM is so concentrated in the river that mixing and other physical processes mask photochemical or biological alteration of its composition.

Spatial, geomorphological, and seasonal variability of CDOM in estuaries of the Florida Coastal Everglades

“…7;Jaffe´et al, 2004). The inflection point appears when the concentration of terrestrial-derived DOM becomes c 147 comparable to marine-derived DOM (e.g., de Souza Sierra et al, 1997;Kowalczuk et al, 2003). In this study such 'blue shifts' were mostly observed for the water samples collected during the dry season when the loading of terrestrial DOM was lower.…”

“…The inflection point depends on the DOC concentration of freshwater and marine water, and in open coastal systems, blue shift of k max is usually observed at salinity higher than 30 ( Fig. 7; also see de Souza Sierra et al, 1997;Kowalczuk et al, 2003;Jaffe´et al 2004). The blue shift in lower salinity indicates FB contains a high concentration of DOC with marine origin.…”

“…They have been applied to investigate the fate of DOM in numerous estuaries including the Everglades (e.g., Parlanti et al, 2000;Kowalczuk et al, 2003;Stedmon et al, 2003;Alberts et al, 2004;Hitchcock et al, 2004;Jaffeé t al., 2004;Yamashita & Tanoue, 2004;ZanardiLamardo et al, 2004). However, many such studies are performed within a relatively short time frame and do not provide adequate data to assess seasonal variations in DOM sources, transport and fate.…”

Effects of recirculation of seawater enriched in inorganic nitrogen on dissolved organic carbon processing in sandy seepage face sediments

“…The C4 peak corresponds to a humic fluorophore freshly produced in the marine environment by microbial metabolism (Parlanti et al 2000; henceforth identified as Marine Humic-like). Components 1, 2 and 5 are similar to the fluorescence spectra of pure Tryptophan (C1) and Tyrosine (C2 and C5) (Coble 1996;Kowalczuk et al 2003). These three components represent a labile, bioavailable DOM fraction (Hudson et al 2007).…”

Microbial bioavailability of dissolved organic carbon from leachates of freshwater autotrophs

“…to dark tea-colored (P. illinoensis). This coloration implies that these leachates are optically different and that, as a result, they could have different degrees of reactivity (Kowalczuk et al 2003, Boyd & Osburn 2004, Coble 2007. P. illinoensis is characterized by long stems that have fewer leaves than other submerged vegetation.…”