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.
The authors thank F. Ernst, K. Dunton, I.-N. Kim and T. W. Kim (UTMSI) and Y.-T. Chen (UCB) for field support; S. Manley (CSU-LB) for data comparisons; the Bass Company and A. Nuñez (Texas General Land Office) for field site access and coordination. Research was supported by UCB, UT Austin, and the Schweppe Endowment at UTMSI. This is the University of Texas Marine Science Institute Contribution No. 1681.