Trophic evolution of Lake Garda in the last 200 years as outlined by paleolimnological studies

Lake sediments of Lake Garda have been studied within the EU EuLakes project (Nr. 2CE243P3). The results are being used to determine the lake reference conditions before stronger human impact. The deepest lake basin (350 m depth) is less impacted by human activities and is suitable for reconstruction of long term environmental (and climatic) variability and its effects on lake ecology. The shallower basin (81 m) is strongly affected by tourism and agriculture, and thus is more suitable for studies on lake eutrophication. The aim of this contribution is to evaluate the vulnerability of Lake Garda respect to specific human stressors (e.g. nutrients, hydroelectrical exploitation) in a climate change scenario. The palaeolimnological approach adopted focusses on changes in sub-fossil diatoms in two pelagic sediment cores and on diatom-based TP reconstruction. The core collected at 350 m shows two discontinuities. The deepest one dates in the 1940s and consists in a decrease in benthic taxa, which may be related to the hydroelectric exploitation of the catchment area. The second discontinuity in early 1960s coincides with the increase in Fragilariaceae respect to centric taxa, as a result of nutrient enrichment. The core from the shallower basin does not show discontinuities, though sub-fossil diatoms show a decrease in both mesotrophic Fragilariaceae and Cyclotella spp. since the 1960s. Reconstructed lake TP concentrations confirms the trends in decadal limnological data