Methane emissions from boreal and tropical forest ecosystems derived from in-situ measurements

Abstract

Methane is a climatologically important greenhouse gas, which plays a key role in regulating water vapour in the stratosphere and hydroxyl radicals in the troposphere. Recent findings that vegetation emits methane have stimulated efforts to ascertain the impact of this source on the global budget. In this work, we present the re-5 sults of high frequency (ca. 1 min −1) methane measurements conducted in the bo-real forests of Finland and the tropical forests of Suriname, in April–May, 2005 and October 2005 respectively. The measurements were performed using a gas chro-matograph – flame ionization detector (GC-FID). The average of the median mixing ratios during a typical diel cycle were 1.83 µmol mol −1 and 1.74 µmol mol −1 for the 10 boreal forest ecosystem and tropical forest ecosystem respectively, with remarkable similarity in the time series of both the boreal and tropical diel profiles. Night time methane emission flux of the boreal forest ecosystem, calculated from the increase of methane during the night and measured nocturnal boundary layer heights yields a flux of (3.62±0.87)×10 11 molecules cm −2 s −1 (or 45.5±11 Tg CH 4 yr −1 for global boreal 15 forest area). This is a source contribution of circa 8% of the global methane budget. These results highlight the importance of the boreal and tropical forest ecosystems for the global budget of methane. The results are also discussed in the context of recent work reporting high methane mixing ratios over tropical forests using space borne near infra-red spectroscopy measurements.