Sediment diatoms of Lake Garda, the largest Italian lake.

Lake Garda is the largest Italian lake. The deep basin (350 m) is relatively little impacted by human activities and is suitable for reconstructions of long term environmental variability, including climate change and its effect on lake ecology. In contrast, the shallow basin (81 m) is strongly affected by human activities and for this reason is more suitable for studies on lake eutrophication. Lake Garda is one of the four large Central European lakes included in the EuLakes Project (Reg. Nr. 2CE243P3), launched in April 2010 within the Central European Initiative. The main project aims are to evaluate the lake vulnerability against specific human stressors (e.g. nutrients, hydroelectrical exploitation) in a climate change scenario, and to promote sustainable lake management. Sediment studies will be used to determine the lake reference conditions before stronger human impact during the 20th century. The long term evolution of Lake Garda will be investigated in greater detail within a PhD program partially funded by the EuLakes project, which will focus on ecological reconstruction based on sedimentary diatom and cladocera remains. Information will be integrated by X-ray fluorescence (XRF) analyses for trace metal concentrations and Fourier transform infrared spectroscopy (FTIRS) for sediment bio-geochemistry. The reconstruction will be validated by combining palaeolimnological results with monitoring data collected during the last two decades. This contribution presents results of the analyses carried out on one short sediment core (56 cm) collected from the deepest point of Lake Garda (Brenzone) in autumn 2009. The focus is posed on changes in sub-recent diatom assemblages since the early XX century, and in particular on the increase in planktonic Fragilariaceae and concomitant decrease in centric taxa, which has been observed since the documented nutrient enrichment in Lake Garda (i.e. since the early 1970ies).