Fulvic acid coastal

Here we present one example to illustrate the utility of 15N for providing information about the source of dissolved organic nitrogen in a freshwater ecosystem. The 15N contents of fulvic acid fractions of different size varied slightly and were similar to the value for the 15N content of the synfulvic acid fraction in a eutrophic coastal pond in Antarctica (Table I) (Brown et al., 2002). Continuous production of mucilage by the chlorophyte population in the pond and diffusion of DOM from the sediments are the two main DOM sources these data suggest that the same source predominates for all of these fulvic acid fractions. 

The ratios of humic to fulvic acids in estuarine and coastal sediments range from 0.4 to 3.4, the higher values being associated with areas or sediments having a terrestrial influence (Palacas et al., 1968 Brown et al., 1972 Hue and Durand, 1973 Pelet and Debyser, 1977 MacFarlane, 1978). These values are also consistent with those from other marine and terrestrial environments (Ishiwatari, 1966 Kononova, 1975 Stuermer et al., 1978 Cronin and Morris, 1982). Other parameters measured on coastal humic substances, such as elemental composition, spectral properties, organic components, stable isotope ratios, or C ages (Pelet and Debyser, 1977 Stuermer et al., 1978 Benoit et al., 1979 Nissenbaum, 1979) are consistent with terrestrial or marine humic compounds, or a mixture of these two endmembers. 

At low pH (ca. 3-5), H2O2 can be consumed through iron cycles associated with the oxidation of fulvic acids involving the photo-Fenton reaction (reaction 8) [84]. As previously discussed, reactions (8) and (9) may be important in humic-rich natural waters at low pH such as in black-water rivers of the southeastern United States (e.g., Suwanee River, GA), but their importance in marine waters at higher pH (typically ca. pH 8.2) is unlikely except for some organic rich coastal environments (vide supra). 

The formation of soluble iron or fulvic acid chelates, represented in general as FeFA (Equation 9.8), has been shown to be responsible for soluble iron in runoff from humic-substance-rich peat bog leachate earrying iron into coastal seawater off North Scotland. ... 

Finally, a variety of zooplankton have recently been shown to produce colored (chromophoric) DOM (CDOM), a fraction of which is fluorescent (FDOM) (Steinberg et al, 2004 Urban-Rich et al, 2004, 2006). Although the nitrogenous composition of CDOM/FDOM is little known, fluorescent humic-hke material (likely fulvic and humic acids) is produced during grazing, influencing the optical characteristics of coastal waters (Urban-Rich et al, 2006). A recent culture study shows that humic-N can be a source of N for coastal phytoplankton (See et al, 2006). 

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