Terrestrial input of organic matter into lakes (such as DOC) cause brownification of the water column and may have strong effects on biological processes in lakes and their ecosystem services. However, there is today a lack of knowledge regarding the effect of DOC on the biodiversity, the composition and the metabolism of pelagic microbial communities which are key organisms of aquatic heterotrophic food webs. My main hypothesis is that the modifications of lake ecosystem properties and functions following DOC input are, especially in the pelagic habitat, related to changes in microbial communities. The metagenomics approach already provided key findings about the functional and taxonomic diversity of lacustrine microbial communities. Our aim is, thus, to apply this approach to water samples from arctic Swedish lakes discriminated by a DOC gradient. We need to use the capacity of HPC2N to process next generation sequencing datasets (from shotgun sequencing methods). Those data will be acquired by Eric Capo, post doc at the Department EMG (Umeå University) and correspond to taxonomic and functional molecular from microbial communities from swedish lakes.