Methyl bromide emissions to the atmosphere from temperate woodland ecosystems

Abstract

The environmental importance of methyl bromide (CH 3 Br) arises from its contribution to stratospheric ozone loss processes and, as a consequence, its emissions from anthropogenic sources are subject to the Montreal Protocol. A better understanding of the natural budget of CH 3 Br is required for assessing the benefit of anthropogenic emission reductions and for understanding any potential effects of environmental change on global CH 3 Br concentrations. Measurements of CH 3 Br flux in temperate woodland ecosystems, in particular, are very sparse, yet these cover a large fraction of terrestrial land surface. Results presented here from 18 months of field measurements of CH 3 Br fluxes in four static flux chambers in a woodland in Scotland and from enclosures of rotting wood and deciduous and coniferous leaf litter suggest net emissions from temperate woodlands. Net CH 3 Br fluxes in the woodland varied between the chambers, fluctuating between net uptake and net emissions (À73 to 279 ng m À2 h À1 across 161 individual measurements), and with no strong seasonality, but with time-averaged net emission overall [27 AE 57 (1 SD)] ng m À2 h À1 ]. This work demonstrates that scale-up needs to be based on sufficient individual measurements to provide a reasonably constrained estimate of the long-term mean. Mean ( AE 1 SD) net CH 3 Br emissions from deciduous and coniferous leaf litter were 43 ( AE 33) ng kg À1 (dry weight) h À1 and 80 ( AE 37) ng kg À1 (dry weight) h À1 , respectively, and $ 1-2 ng kg À1 (fresh weight) h À1 from rotting woody litter. Despite the intrinsic variability, data obtained here consistently point to the conclusion that the temperate forest soil/litter ecosystem is a net source of CH 3 Br to the atmosphere.

Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

“…These measurements are broadly consistent with previous methyl bromide measurements from temperate forests and woodlands (Dimmer et al, 2001;Varner et al, 2003;Drewer et al, 2008;Rhew et al, 2010) and provide further comparative data for those few studies that examine methyl chloride and/or methyl iodide (Dimmer et al, 2001;Sive et al, 2007;Rhew et al, 2010) (Table 1). These measurements are broadly consistent with previous methyl bromide measurements from temperate forests and woodlands (Dimmer et al, 2001;Varner et al, 2003;Drewer et al, 2008;Rhew et al, 2010) and provide further comparative data for those few studies that examine methyl chloride and/or methyl iodide (Dimmer et al, 2001;Sive et al, 2007;Rhew et al, 2010) (Table 1).…”

“…The observed lack of seasonality in emissions is similar to observations by Varner et al (2003) and Drewer et al (2008) but does not reflect the observations of Rhew et al (2010) and Blei & Heal (2011) both of whom saw significant differences in litter and soil response over time with maximum net emissions (or minimum net losses) during the summer to late summer months (July and October, respectively).…”

Growing season methyl bromide and methyl chloride fluxes at a sub‐arctic wetland in Sweden

“…0.32 mm and 1.8 mm film thickness. A custom built, two-stage preconcentration unit was used prior to GC separation [Drewer et al, 2008]. The first trap was a 1=4 inch diameter by 100 mm long stainless steel tube filled with Tenax TA 60/80 mesh (Supelco, Bellefont, PA, USA).…”

Characterization of methyl bromide and methyl chloride fluxes at temperate freshwater wetlands

“…In the saltmarshes and rice paddies CH 3 Br emission rates broadly corresponded to seasonal trends in plant growth, air temperature and light intensity, indicative of a biologically-mediated process. Diurnal measurements have been made in Scottish saltmarshes [Drewer et al, 2006;Blei et al, 2010b], temperate woodland leaf litter [Dimmer et al, 2001;Drewer et al, 2008], temperate coastal marsh [Dimmer et al, 2001], temperate peatlands [Dimmer et al, 2001], Californian saltmarshes [Rhew et al, 2002], high-latitude wetlands [Hardacre et al, 2009], tropical forests [Blei et al, 2010a], and from two tropical fern species (Cyathea podophylla and Cyathea lepifera) [Saito and Yokouchi, 2006]. Of these, diurnal variation in CH 3 Br flux was observed at Scottish saltmarshes, certain temperate woodland leaf litter sampling points, high-latitude wetlands, temperate peatlands, Californian saltmarshes, the tropical ferns and some tropical plant species.…”