Photochemical and Microbial Degradation of Chromophoric Dissolved Organic Matter Exported From Tidal Marshes

Wetlands export chromophoric dissolved organic matter (CDOM) to estuaries, where CDOM is removed and transformed through biotic abiotic process, subsequently impacting nutrient cycling, light availability, ecosystem metabolism, phytoplankton activity. We examined the bioavailability photoreactivity of exported from four Chesapeake Bay tidal marshes across three seasons along an estuarine salinity gradient using incubation treatments: 14-day microbial (MD), 7-day combined photochemical/microbial (PB + MD), after photobleaching (MD PB). absorption at 300 nm (aCDOM300) carbon (DOC) concentrations showed strong seasonality, with minima in winter, but quality (absorption spectral slopes, fluorescence component ratios) was less variable seasonally. PB MD over 7 days decreased aCDOM300 (−56.0%), humic-like (−67.6%), DOC (−17.8%), increased slope ratio SR (=S275–295/S300–350) (+94.8%), suggesting a decrease molecular weight. Photochemistry dominated treatment. Photoreactivity greater during winter marsh/watershed versus down-estuary sites, likely due previous exposure. Prior marsh-exported CDOM, resulting loss DOC, increase (−6.0%, −5.9%, +18.4% change, respectively, incubations, vs. −2.8%, −5.5%, +2.6% incubations). marsh downstream major wastewater treatment plant greatest bioavailability. This highlights significance human activity on biogeochemical cycles.