Importance of CDOM Distribution and Photoreactivity in a Shallow Texas Estuary |
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| Authors: | G Christopher Shank Kevin Nelson Paul A Montagna |
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| Institution: | (1) Marine Science Institute, University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA;(2) Harte Research Institute, Texas A&M University Corpus Christi, 6300 Ocean Drive, Unit 5869, Corpus Christi, TX 78412, USA |
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| Abstract: | This study examined freshwater discharge of dissolved organic matter (DOM) to the shallow Lavaca–Matagorda (LM) Bay estuarine
system along the central Texas coast and investigated whether chromophoric DOM (CDOM) photochemical reactions have the potential
to stimulate microbial activity within LM estuarine waters. Dissolved organic carbon (DOC) concentrations ranged from 3 to
10 mg C l−1 and CDOM levels (reported as a
305) ranged from 8 to 77 m−1 during April and July, 2007, when the LM system was experiencing very high freshwater inputs. DOC and CDOM levels were well-correlated
with salinities > 3, but exhibited considerable variability at salinities < 3. CDOM photobleaching rates (i.e., decrease in
a
305 resulting from exposure to solar radiation) for estuarine samples ranged from 0.014 to 0.021 h−1, corresponding to photobleaching half-lives of 33–50 h. Our data indicate when Matagorda Bay waters photobleach; dissolved
organic carbon utilization is enhanced perhaps due to enhanced microbial respiration of biologically labile photoproducts
(BLPs). Net ecosystem metabolism calculations indicate that most of the LM system was net heterotrophic during our study.
We estimate that BLP formation could support up to 20% of the daily microbial respiratory C demand in LM surface waters and
combined with direct photochemical oxygen consumption could have an important influence on O2 cycles in the LM system. |
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