Midsummer spatial variation in methane efflux from stands of littoral vegetation in a boreal meso‐eutrophic lake

Abstract

Summary 1. Spatial variation of methane (CH 4 ) efflux from the littoral zone of a meso‐eutrophic boreal lake was studied with a closed‐chamber technique for three summer days in 22 vegetation stands, consisting of three emergent and three floating‐leaved species. 2. Between‐species differences in CH 4 emission were significant. The highest emissions were measured from the emergent Phragmites australis stands (0.5–1.7 mmol m −2 h −1 ), followed by Schoenoplectus lacustris > Equisetum fluviatile > Nuphar lutea > Sparganium gramineum > Potamogeton natans . Within‐species differences between stands were not significant. 3. In P. australis stands, the stand‐specific mean CH 4 emission was significantly correlated with solar radiation, probably indicating the role of effective pressurised ventilation on CH 4 fluxes. The proportion of net primary production emitted as CH 4 was significantly higher in P. australis stands (7.4%) than in stands of S. lacustris and E. fluviatile (both 0.5%). 4. In N. lutea stands, CH 4 efflux was negatively correlated with the mean fetch and positively with the percentage cover of leaves on the water surface. There were no differences in CH 4 efflux between intact N. lutea leaves and those grazed by coleopteran Galerucella nymphaeae . In S. graminaeum and P. natans stands, CH 4 effluxes were not related to any of the measured environmental variables. 5. For all vegetation stands, the biomass above water level explained about 60% of the observed spatial variation in CH 4 emission, indicating the important role of plants as gas conduits and producers of substrates for methanogens in the anoxic sediment.