Photochemical Release of Dissolved Organic Matter from Resuspended Salt Marsh Sediments

Abstract

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.