Shrubland fluxes of methyl bromide and methyl chloride

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH3Br and CH3Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH3Cl and CH3Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH3Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of