Climate-induced ecological change in subarctic lakes - Evidence from biological archives, long-term monitoring, and contemporary field studies

Sammanfattning: Northern lakes have a unique flora and fauna and are sensitive ecosystems that experience rapid rates of change. Multiple environmental changes are currently affecting these lakes, including climate-induced oligotrophication, with nutrient levels decreasing in waters throughout the Scandinavian mountain range. In this thesis I have studied multiple lakes and used approaches that span over multiple time scales to study energy flows and community composition of primary producers and consumers in northern lake food webs, and how these respond to climate-induced environmental changes. Paleolimnological analyses showed that northern lake food webs have been closely connected to long-term climate fluctuations, and catchment vegetation during the last 5800 years. And further, that benthic primary production was the predominating carbon source to zooplankton biomass during warmer and drier conditions while pelagic primary production predominated during colder and wetter periods. Time-series analysis of contemporary data showed clear evidence of the current oligotrophication in all of the lakes with dramatic decreases in water concentrations of total phosphorus. Food web responses were, however, weaker than expected likely owing to a large dependence on benthic primary productivity in these systems. The results from a study on within- and among-lake variability in δ13C and δ15N, for primary producers and consumers, showed that within- and among-lake stable isotope variability were similar. Which indicates that small-scale, within-lake processes, can be equally important as catchment-scale processes for stable isotope composition of primary producers and consumers.