Download Methane exchange in a boreal forest estimated by gradient method

Methane exchange in a boreal forest estimated by gradient method
E. Sundqvist1, M. Mölder1, P. Crill2, N. Kljun3,4, A. Lindroth1
1
Department of Physical Geography and Ecosystem Science, Lund University
Department of Geological Sciences, Stockholm University
3
Department of Geography, Swansea University
4
Centre for studies of Carbon Cycle and Climate interactions (LUCCI), Department of
Physical Geography and Ecosystem Science, Lund University
2
Forests are generally considered to be net sinks of atmospheric CH4 because of oxidation
by methanotrophic bacteria in well-aerated forests soils. However, emissions from wet
forest soils, and sometimes canopy fluxes, should also be considered when quantifying
the CH4 budget of a forest. We used a modified Bowen ratio method and combined eddy
covariance and gradient methods to estimate net CH4 exchange at a boreal forest site in
central Sweden. Results show that the site is a net source of CH4. This is in sharp contrast
to soil and leaf chamber measurements indicating that the site is a net sink. Wetter soils
within the footprint are thought to be responsible for the discrepancy. We found no
evidence for canopy emissions per se. However, the diel pattern of the CH4 exchange
with minimum emissions at daytime correlated well with GPP, which supports an uptake
in the canopy, as was recently observed with branch chamber measurements on shoots
from different tree species from the same site.