Large methyl halide emissions from south Texas salt marshes

Abstract. Coastal salt marshes are natural sources of methyl chloride (CH₃Cl) and methyl bromide (CH₃Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH₃Br than CH₃Cl, and surprisingly high nighttime CH₃Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH₃Cl and CH₃Br.