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Water-air gas exchange of CO2 and CH4 in coastal wetlands
Book chapter

Water-air gas exchange of CO2 and CH4 in coastal wetlands

Judith A. Rosentreter
Carbon Mineralization in Coastal Wetlands, pp.167-196
Estuarine and Coastal Sciences Series, Volume: 2, Elsevier Inc, 1st
2022
DOI: https://doi.org/10.1016/B978-0-12-819220-7.00003-0

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Abstract

Blue carbon Carbon dioxide Gas transfer Global warming potential Mangroves Methane Saltmarshes Seagrasses Switchover times Water-air fluxes
This chapter discusses carbon dioxide (CO2) and methane (CH4) gas exchange at the water-air interface in coastal wetlands. The existing literature was reviewed to report the magnitude of CO2 and CH4 water-air fluxes in mangrove, saltmarsh, and seagrass ecosystems. Based on available data, mangrove waters show a large range of CO2 (13–9726mgCO2m−2day−1) and CH4 water-air fluxes (−1.1–1169mgCH4m−2day−1) and are generally a source of CO2 and CH4 to the atmosphere. Similarly, saltmarsh waters are predominantly water-air sources of CO2 (mean: 2823±332mgCO2m−2day−1) and CH4 (−1.5–1510mgCH4m−2day−1). In contrast, seagrass waters can act as a source or sink of CO2 (−3168–3041mgCO2m−2day−1) and are likely a source of CH4 to the atmosphere (1.9–4.9mgCH4m−2day−1). High spatial and temporal variability and the large range of fluxes are linked to tidal regimes, seasonality, vegetation coverage, and complex biogeochemical processes that occur in coastal wetland sediments and waters. Various direct and indirect drivers are described that can control CO2 and CH4 concentration gradients, transport pathways, and fluxes from sediments to the water column and ultimately to the atmosphere. Finally, the three most commonly used methods to determine water-air gas exchange in coastal waters are reviewed, which are the chamber method, the gradient flux method, and the eddy-covariance technique. Using appropriate methods, more research is needed for a better assessment of long-term and large-scale gas exchange in dynamic coastal wetland waters, to quantify more accurately present and to predict future greenhouse gas trends and potential “blue carbon” offsets in mangrove, saltmarsh, and seagrasses on regional and global scale.

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