Reconstruction of the ecological conditions of Lake Garda (Italy) in relation with human impacts over the last two centuries.

Lake Garda is one of the four large Central European lakes included in the EuLakes Project (Reg. Nr. 2CE243P3). The main objectives are to evaluate the lake vulnerability against specific human stressors in a climate change scenario, and to promote sustainable lake management. Lake Garda is the largest lake in Italy. The deep basin (350 m) is little impacted by human activities and is suitable for reconstruction of long-term environmental variability. In contrast, the shallow basin (81 m) is strongly affected by human activities and is for this reason more suitable for studying lake eutrophication. A consistent monitoring program was started in the early 1990s. Before that, only sporadic limnological measurements are available. Lake sediment records provide a complementary source of information to extend the time span of ecological records back into the past, through the reconstruction of secular lake evolution. Radiometrical dating, geochemical (water and LOI content) and biological proxies (algal pigments and diatoms) are being analysed in one short core (56 cm) retrieved from the deepest part of the lake. Initial analyses of the sub-fossil diatom assemblages during the 20th century show two major changes. The first one, recorded around 1960, is an increase in the relative abundance of planktonic Fragilariaceae, whereas centric taxa decrease suggesting a nutrient enrichment. The second change, in mid 1940s, consists of a decrease in benthic taxa, which may be related with the intensive hydroelectrical exploitation of the catchment area. A preliminary diatom-based, quantitative reconstruction of TP concentration over the last 200 years shows good agreement with monitoring data.