1. The annual dynamics of methane (CH4) in a temporarily flooded meadow, mi
re bank, lacustrine sedge fen, temporarily and continuously inundated sedge
(Carex sp.) and reed (Phragmites australis) marshes were studied from June
to November in the humic mesoeutrophic Lake Mekrijarvi and in eutrophicate
d parts of the mesotrophic Lake Heposelka in the southern part of East Finl
and. The effects of water level and temperature on littoral CH4 fluxes were
determined. Vegetation zonation along the moisture gradient, and associate
d CH4 fluxes, were evaluated.
2. The CH4 flux increased along the moisture gradient from -0.2 to 14.2 mg
CH4 m(-2) h(-1), and was highest in the permanently inundated marshes. The
duration of anoxia in the sediment caused differences in the CH4 flux. Esti
mated emissions for the period 1 June 30 September in continuously inundate
d sparse reed and sedge marshes, drying sedge marsh, and lacustrine sedge f
en were 13, 11 and 6 g CH4 m(-2), respectively.
3. In continuously inundated vegetation, the fluxes were highest in late Ju
ly/early August. The seasonal CH4 flux pattern suggested that the fluxes we
re regulated by the supply of organic matter during the course of the summe
r and the water level. In the temporarily flooded zone, the seasonal CH4 fl
ux dynamics was greatly affected by changes in the lake water level, the fl
uxes being highest during the spring flood in early June.