Methyl bromide and methyl chloride fluxes from temperate forest litter

Methyl halide fluxes were measured from fine (nonwoody) litter samples at a temperate deciduous forest site in Scotland on 16 occasions over more than a year and at a coniferous forest site. The resulting mean (±1 sd) CH3Br and CH3Cl fluxes were 4.1 ± 3.7 ng kg−1 h−1 and 0.98 ± 0.62 μg kg−1 h−1, respectively, for dry mass leaf litter and 5.7 ± 6.3 ng kg−1 h−1 and 0.47 ± 0.14 μg kg−1 h−1 for dry mass needle litter. Temporal variations of net fluxes from leaf litter were significantly greater than spatial variations suggesting seasonality in the fluxes. The mean CH3Cl/CH3Br mass ratio of fluxes was ∼200 (to 1 sig. fig.), an order of magnitude larger than the ratio of their estimated global turnovers. Temperate forest litter may be a moderate net source of CH3Cl globally but a negligible source of CH3Br. These statements refer to the nonwoody litter component only.