Human activities are threatening biodiversity in freshwaters leading to irreversible alterations in ecosystem processes. One of the most important processes for the functioning of small-forested streams is the decomposition of allochthonous plant litter, which constitutes the major source of nutrients and energy for freshwater food-webs. Microbial decomposers, namely fungi and bacteria, and invertebrate shredders play a critical role in this process by degrading plant material. In the Functional Ecology group we are mainly concerned with: 1) the impacts of global change (e.g. global warming, eutrophication, riparian diversity loss) on aquatic biodiversity and decomposition of plant litter in freshwaters; 2) the impacts of metals, PAHs and nanoparticles on freshwaters at the community-, population- and cellular-level, with focus on fungi and invertebrates; 3) the relationship between biodiversity and the functioning of detritus food-webs in freshwaters and 4) the application of molecular tools, such as denaturing gradient gel electrophoresis (DGGE), cloning and DNA barcoding to assess diversity of microbial decomposers on plant-litter decomposing in freshwaters.