ED037-0033
Tidal Exports of Dissolved Organic Carbon from a Coastal Salt Marsh Complex

Monday, 14 December 2020
Poster
Sophie Kuhl1, Meagan Eagle Eagle2, Kevin D Kroeger3, Aleck Zhaohui Wang4, Omar I. Abdul-Aziz5, Jianwu Tang6, Mohammed T. Zaki5 and Neil K Ganju7, (1)Brown University, Providence, RI, United States, (2)USGS, Woods Hole Coastal and Marine Science Center, Woods Hole, MA, United States, (3)USGS, Woods Hole, MA, United States, (4)Marine Chemistry and Geochemistry, Woods Hole, MA, United States, (5)West Virginia University, Civil and Environmental Engineering, Morgantown, WV, United States, (6)MBL, The Ecosystems Center, Woods Hole, MA, United States, (7)U.S. Geological Survey, Woods Hole, MA, United States
Abstract:
Coastal wetlands play an important role in carbon cycling at the global scale, with coastal vegetation removing atmospheric CO2 and sequestering carbon into anoxic soils and biomass. Carbon not retained within the wetland system outwells to the coastal ocean with tidal exchange driving lateral fluxes of dissolved carbon between these two reservoirs. This study evaluates lateral fluxes of dissolved organic carbon (DOC) within the Sage Lot Pond salt marsh complex in Waquoit Bay on the southern coast of Cape Cod, Massachusetts. From November 2012 to December 2016, high-frequency sensor measurements of biogeochemically important parameters were taken in a tidal creek that drains a portion of the marsh, and DOC fluxes were calculated at five-minute intervals based on an emergent power law scaling-based predictive model that utilized creek water temperature, pH, fDOM, and measured water flux. DOC fluxes were quantified for over ~1,000 complete tidal cycles. DOC fluxes increase concurrently with higher tides, due to enhanced flooding of the marsh surface and subsequent flushing of accumulated DOC from marsh porewaters. DOC flux was greatest in the summer (50.2% of total flux), followed by spring (23.1% of total flux), fall (21.6% of total flux) and winter (5.1% of total flux) seasons likely coincident with plant growth and soil respiration. During neap tidal cycles (16.1% of tides), the marsh platform did not flood and flux was close to zero (only 7.8% of total flux). 81.4% of the total flux occurred during frequent, moderate amplitude tidal cycles that were sufficient to flood the marsh surface. Extreme flux events did occur when the water levels were much greater than MHHW (2.5% of tides), accounting for 11.4% of the total flux. In all, we observed a yearly lateral DOC export from the marsh of 84.7 g C m-2 yr-1. Exports of marsh-derived organic material to the adjacent estuary are likely an important source of carbon and other nutrients.
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