ISOPRENE EMISSIONS FROM BOREAL WETLANDS IN SCANDINAVIA

Seasonal emissions of isoprene and other light hydrocarbons were measu red from both an elevated dry site (hummock) and low wet site (flark) on a Sphagnum fen in Sweden, and diurnal emissions were measured from a wet site on a Sphagnum fen in Finland. Both fens are in the southern boreal zone. Samples were taken from a Teflon chamber with stainless steel canisters, and analysis was done by gas chromatography with flam e ionization detection. Isoprene clearly dominated the flux of light h ydrocarbons, while ethene, propene, and 2-butene, as well as traces of n-butane and propane, were also observed. The isoprene emission seaso n extended from the spring thaw to the occurrence of ground frost in t he fall. The highest fluxes of isoprene were observed from wetter site s (flarks) and reached up to 2000 mu g C m(-2) h(-1), while the fluxes from the hummocks did not exceed 70 mu g C m(-2) h(-1). The fluxes of ethene and propene did not exceed 15 mu g C m(-2) h(-1). All emission s showed strong diurnal variations with zero or near-zero values at ni ght. Much of the data can be explained by temperature and light, as is the case for isoprene-emitting trees, but other factors are important . The mean normalized emission rate for the wet Sphagnum environments was 624 +/- 357 mu g C m(-2) h(-1) (photosynthetic active radiation eq ual to 1000 mu mol m(-2) s(-1), 30 degrees C). Our data indicate that in comparison with emissions from forests, the flux of isoprene from S phagnum peatlands is a significant source of volatile organic compound s to the atmosphere in boreal regions.