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Natural methyl bromide and methyl chloride emissions from coastal salt marshes

Abstract

Atmospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, originate from both natural and anthropogenic sources. Current estimates of CH3Br and CH3Cl emissions from oceanic sources, terrestrial plants and fungi, biomass burning and anthropogenic inputs do not balance their losses owing to oxidation by hydroxyl radicals, oceanic degradation, and consumption in soils, suggesting that additional natural terrestrial sources may be important1. Here we show that CH3Br and CH3Cl are released to the atmosphere from all vegetation zones of two coastal salt marshes. We see very large fluxes of CH3Br and CH3Cl per unit area: up to 42 and 570 µmol m-2 d-1, respectively. The fluxes show large diurnal, seasonal and spatial variabilities, but there is a strong correlation between the fluxes of CH3Br and those of CH3Cl, with an average molar flux ratio of roughly 1:20. If our measurements are typical of salt marshes globally, they suggest that such ecosystems, even though they constitute less than 0.1% of the global surface area2, may produce roughly 10% of the total fluxes of atmospheric CH3Br and CH3Cl.

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Figure 1: Daytime fluxes of CH3Br, CH3Cl, CO2 and CH4.
Figure 2: Correlation between CH3Cl and CH3Br fluxes.

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Acknowledgements

We thank J. Fessenden, M. Vollmer, G. Mortyn, D. Matross and T. Tanhua for field assistance; P. Salameh and S. Walker for programming support; D. Harper for comments; and the University of California Natural Reserve System (NRS) and the Joint Powers Authority of the San Dieguito River Park for fieldwork permits. This work was supported by the NRS, the Methyl Bromide Global Coalition, NASA's Upper Atmosphere Research Program, and the NSF Graduate Research Fellowship Program.

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Correspondence to Robert C. Rhew.

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Rhew, R., Miller, B. & Weiss, R. Natural methyl bromide and methyl chloride emissions from coastal salt marshes. Nature 403, 292–295 (2000). https://doi.org/10.1038/35002043

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