Photochemical Release of Dissolved Organic Matter from Resuspended Salt Marsh Sediments
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Incubation experiments were conducted to determine the influence of natural sunlight irradiation on the release of dissolved organic matter (DOM) from resuspended surface sediments. The photo-release of dissolved organic carbon (DOC), dissolved nitrogen (DN), and chromophoric dissolved organic matter (CDOM) were quantified over time. During the 5–7-day incubations, 3.4–12.4 and 23–41 % of the sedimentary organic carbon (TOC) and 2.8–10.2 and 25–46 % of the solid phase nitrogen (TN) were released into DOC and DN pools from Florida and Massachusetts salt marsh sediments, respectively. The suspended, fractionated, clay-sized particles from Massachusetts released much higher DOC and DN than Florida bulk sediment. Up to 65 % of the DOC and 100 % of the DN photo-released from sediments were respired rapidly by bacteria, indicating that microorganisms play an important role in regulating the concentration of DOC and DN. The bioavailability of photo-released DOC and DN also depends largely on the biochemical nature of the DOM released from different sediments. Optical measurements confirmed that significant CDOM production was associated with the sunlight-induced DOC release. Photo-released CDOM appeared to be marine and humic-like as characterized by fluorescence and excitation–emission matrix (EEM) spectroscopy. It is estimated that photo-production of DOC from resuspended sediments could account for 10–22 % of the DOC measured in the coastal waters adjacent to the marsh systems studied. These results indicate that production of DOM from resuspended sediments due to direct sunlight irradiation could be an important source of DOC, CDOM, and secondary production in salt marshes and marsh-dominated coastal waters.
KeywordsPhotodissolution Sediment Dissolved organic matter Carbon cycle Salt marsh
We are grateful for the opportunity to work with Dr. Jaye Cable, Dr. Jennifer Cherrier, Dr. Christof Meile and their lab groups on this joint salt marsh research project funded by NSF. We thank Captain Gary Mears, Bernie Gardner, Jill Arriola, Bridget Benson and Tom Heath for their help during the field sampling. B. Benson also provided professional help with MATLAB data processing. We thank the insightful comments from two anonymous reviewers. This work was supported by the National Science Foundation (grant OCE-0928292 to RFC).
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