Trace gas fluxes from tidal salt marsh soils: implications for carbon–sulfur biogeochemistry

Abstract

Abstract. Tidal salt marsh soils can be a dynamic source of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as sulfur-based trace gases such as carbon disulfide (CS2) and dimethylsulfide (DMS) which play roles in global climate and carbon–sulfur biogeochemistry. Due to the difficulty in measuring trace gases in coastal ecosystems (e.g., flooding, salinity), our current understanding is based on snapshot instantaneous measurements (e.g., performed during daytime low tide) which complicates our ability to assess the role of these ecosystems for natural climate solutions. We performed continuous, automated measurements of soil trace gas fluxes throughout the growing season to obtain high-temporal frequency data and to provide insights into magnitudes and temporal variability across rapidly changing conditions such as tidal cycles. We found that soil CO2 fluxes did not show a consistent diel pattern, CH4, N2O, and CS2 fluxes were highly variable with frequent pulse emissions (> 2500 %, > 10 000 %, and > 4500 % change, respectively), and DMS fluxes only occurred midday with changes > 185 000 %. When we compared continuous measurements with discrete temporal measurements (during daytime, at low tide), discrete measurements of soil CO2 fluxes were comparable with those from continuous measurements but misrepresent the temporal variability and magnitudes of CH4, N2O, DMS, and CS2. Discrepancies between the continuous and discrete measurement data result in differences for calculating the sustained global warming potential (SGWP), mainly by an overestimation of CH4 fluxes when using discrete measurements. The high temporal variability of trace gas fluxes complicates the accurate calculation of budgets for use in blue carbon accounting and earth system models.