Ecosystem Scale Measurements of Methyl Halide Fluxes from a Brackish Tidal Marsh Invaded with Perennial Pepperweed (Lepidium latifolium)

Natural methyl chloride (CH3Cl) and methyl bromide (CH3Br) emissions from coastal marsh ecosystems may constitute a significant proportion of stratospheric chlorine and bromine, which catalyze ozone depletion. Current inventories involve substantial uncertainties associated with up-scaling plot-scale footprints (i.e., ≤ 1m2).  Here we present net ecosystem flux measurements of methyl halides from a brackish tidal marsh on the west coast of the United States between April 2016 and June 2017 using the relaxed eddy accumulation method.  The measurement footprint encompasses a large part of the studied tidal marsh, including roughly 20 vascular plant species, open water and soil surfaces.  On the annual scale, ecosystem methyl halide emissions showed the strongest relationships to temperature and the growth cycle of halophyte vegetation, whereas on diurnal timescales, fluxes correlated the most with evapotranspiration. The maximum seasonal emissions occurred during the flowering season of L...