Geoscience Reference
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Conservative behavior has also been observed for the relationships among DOM absor-
bance, fluorescence, and dissolved organic carbon (DOC) concentration in many coastal
regions, where freshwater runoff controls CDOM composition. Kowalczuk et al. (
2010
)
used a six-component PARAFAC model of CDOM in the Cape Fear Estuary to deter-
mine separate relationships between DOC and optical properties for each component. They
found strong relationships between DOC concentration and absorbance, total fluorescence
intensity, and fluorescence intensity of all the individual PARAFAC components except
the tryptophan-like component. Regression coefficients varied among components, with
higher slopes and larger intercepts for the terrestrial humic-like components, although
these were both smaller than slopes and intercepts for absorbance and total fluorescence
intensity. Both carbon-specific absorbance and carbon-specific fluorescence were found
to decrease rapidly with increasing salinity. The results of this study provide a significant
improvement in the important efforts to estimate carbon export using optical sensors, both
in water and on satellites.
Extreme events such as floods and hurricanes can drastically alter the expected coastal
distributions of CDOM. Conmy et al. (
2009
) showed the influence of hurricanes to both
greatly increase and greatly decrease CDOM distributions on the West Florida shelf,
depending on storm track and thus wind direction. The composition of the CDOM over
the shelf was also altered, as blue-shifted marine CDOM replaced the terrestrial CDOM
following strong onshore winds. These events had some secondary consequences such as
increased turbidity, increased nutrients from upwelling or river discharge, and decreased
water clarity that interfere with satellite estimates of CDOM. This study highlights the
fact that seasonal dynamics of CDOM distribution and composition have ecological con-
sequences, as CDOM serves as a source of nutrients, provides UV protection, and absorbs
critical photosynthetically available radiation (PAR; Zimmerman
2003
,
2006
). A recent
study on health of nearshore corals found that CDOM absorption was higher and less
variable along intact shorelines than along developed shorelines, providing significantly
greater UV protection to corals within 5 km of the coast (Ayoub et al., 2008).
The overall observation of conservative behavior of CDOM does not preclude produc-
tion and destruction in coastal areas, rather, these processes appear to occur on time and
space scales that most studies fail to examine in detail. A few notable examples of produc-
tion of CDOM during estuarine mixing and tidal cycles can be found, in which release of
excess CDOM appears to be associated with drainage of tidal mud flats during ebb flow
(Prahl and Coble,
1994
; Gardner et al.,
2005
). A recent study in a shallow embayment in
Florida showed production of a high salinity, high CDOM water mass in the dry season
during spring tides (Milbrandt et al.,
2010
). EEM analysis confirmed that the material had
blue-shifted fluorescence characteristic of newly formed CDOM and observed concentra-
tions were eight times higher than previously reported seawater values. This new CDOM
was flushed out of the bay at ebb tide, and was replaced by lower salinity, lower CDOM
on flood tides.
Less is known of CDOM production by benthic communities such as mangroves, sea-
grasses, tidal marshes, and corals. Stabenau et al. (
2004
) reported CDOM production from
