MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14821

ABSTRACT: Seagrass ecosystems store and export significant amounts of carbon. However, the impact of this carbon export on coastal greenhouse gas (GHG) budgets remains largely unconstrained. We examined the impact of seagrass wrack deposits on summer GHG emissions from the intertidal zone of a sandy, temperate beach, hypothesizing that this natural addition of organic matter would increase GHG fluxes compared to bare sand. To test this hypothesis, we measured daytime carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes across 3 substrate cover types (sediment, wrack and sediment, or wrack only). We also measured sediment characteristics to identify potential drivers of GHG emissions from the beach. There was no consistent difference between cover types for CO₂, with sediment only fluxes differing from other treatments on just one date. CH₄ fluxes differed by date but not cover type. N₂O fluxes did not differ by cover type or date. In addition, sediment only plus wrack only fluxes were not equivalent to fluxes taken over wrack and sediment together. Compared to reported literature values from living seagrass meadows, CO₂, CH₄, and N₂O fluxes from seagrass wrack on sand were up to ~ 2×, 10×, and 25× lower, respectively. Future studies should expand on diel and seasonal factors to better quantify the role of macrophyte wrack on beach GHG fluxes.