High-frequency variability of carbon dioxide fluxes in tidal water over a temperate salt marsh

Existing analyses of salt marsh carbon budgets rarely quantify carbon loss as CO2 through the air-water interface in inundated marshes. This study estimates the variability of partial pressure of CO2 (pCO(2)) and air-water CO2 fluxes over summer and fall of 2014 and 2015 using high-frequency measurements of tidal water pCO(2) in a salt marsh of the U.S. northeast region. Monthly mean CO2 effluxes varied in the range of 5.4-25.6 mmol m(-2) marsh d(-1) (monthly median: 4.8-24.7 mmol m(-2) marsh d(-1)) during July to November from the tidal creek and tidally-inundated vegetated platform. The source of CO2 effluxes was partitioned between the marsh and estuary using a mixing model. The monthly mean marsh-contributed CO2 effluxes accounted for a dominant portion (69%) of total CO2 effluxes in the inundated marsh, which was 3-23% (mean 13%) of the corresponding lateral flux rate of dissolved inorganic carbon (DIC) from marsh to estuary. Photosynthesis in tidal water substantially reduced the CO2 evasion, accounting for 1-86% (mean 31%) of potential CO2 evasion and 2-26% (mean 11%) of corresponding lateral transport DIC fluxes, indicating the important role of photosynthesis in controlling the air-water CO2 evasion in the inundated salt marsh. This study demonstrates that CO2 evasion from inundated salt marshes is a significant loss term for carbon that is fixed within marshes.