Abstract
Using the 16S rRNA and mcrA genes, we investigated the composition, abundance and activity of sediment archaeal comm unities within 18 high-mountain lakes under contrasted metal levels from different origins (bedr ock erosion, past-mining ctivities and atmospheric depositions). Bathy archaeota, Eury archaeota and Woesear c haeota were the major phyla f ound at the meta-comm unity scale, representing 48%, 18.3% and 15.2% of the archaeal ommunity respectively. Metals were equall y important as physicochemical variable sin explaining the assemb lage of arc haeal communities and their ab undance. Methanogenesis appeared as a process of central importance in the carbon cycle within sediments of alpine lakes as indicated by the absolute ab undance of methanogen 16S rRNA andmcrA gene transcripts (10 5 to 10 9 copies g -1 ). We sho wed that methanogen ab undance and activity were significantl y reduced with increasing concentrations of Pb and C d, tw o indicators of airborne metal contami-nati ons. Considering the ecological importance of methanogenesis in sediment habitats, these metal contaminations may have system wide implications even in remote area such as alpine lakes. Overall, thiswork was pioneer in integrating the effect of long-range atmospheric depositions on archaeal communities and indicated that metal contamination might significantl y compromise the contribution of Archaea