My research focus on the ecology of pelagic food webs (including zooplankton, phytoplankton and bacterioplankton) in freshwater ecosystems. Special focus within my research lies within studying the importance of organic matter (humic substances) and nutrients (nitrogen and phosphorus) for lake ecosystem productivity and food web structure. One research project studies if there are regional differences in nutrient limitation of phytoplankton growth in Swedish unproductive lakes and if such differences can be related to the atmospheric nitrogen (N) input. The project is also investigating if atmospheric N-input affects the productivity and the species composition and the succession of phytoplankton in Swedish lakes. Another project studies how the transfer efficiency of carbon and nutrients from bacteria and phytoplankton to zooplankton depend on food chain structure and carbon:nutrient stoichiometry of energy mobilizers and consumers.