Methane efflux in relation to plant biomass and sediment characteristics in stands of three common emergent macrophytes in boreal mesoeutrophic lakes

Methane efflux was studied in stands of three emergent macrophyte species (Equisetum fluviatile, Schoenoplectus lacustris and Phragmites australis) commonly found in the littoral zone of boreal lakes. In vegetation stands with relatively low methane (CH4) emissions (<0.3 mol m(-2) (ice-free period)(-1)), the seasonal variation of CH4 efflux was better correlated with the dynamics of plant growth than variation in sediment temperature. In dense and productive vegetation stands that released high amounts of CH4 (2.3-7.7 mol m(-2) (ice-free period)(-1)), the seasonal variation in CH4 efflux was correlated with sediment temperature, indicating that methanogens were more limited by temperature than substrate supply. The bottom type at the growth site of the emergent plants significantly influenced the ratio of CH4 efflux to aboveground biomass of plants (Eff : B). The lowest Eff : B ratio was found in E. fluviatile stands growing on sand bottom under experimental conditions and the highest in P. australis-dominated littoral areas accumulating detritus from external sources. The future changes expected in the hydrology of boreal lakes and rivers because of climatic warming may impact the growth conditions of aquatic macrophytes as well as decomposition and accumulation of detritus and, thus, CH4 effluxes from boreal lakes.