Phytosociological survey as a baseline for environmental status assessment: the case of hydrophytic vegetation of a deep volcanic lake.

Freshwater ecosystems are strongly endangered throughout Europe as they suffer from ongoing human pressure, pollution and eutrophication. Assessment and monitoring species and habitats is essential to address conservation efforts and evaluate the results of conservation policies. Thus, European Habitats Directive (92/43/EEC) and Water Framework Directive (2000/60/EC) ask for monitoring actions. Nevertheless, knowledge about hydrophytic vegetation of volcanic lakes in Central Italy is still lacking, incomplete or not updated. Herein, we analysed phytosociological data collected in 2010/2012 along six transects performed at Martignano Lake, a small volcanic lake 30 km NW from Rome, where aquatic vegetation was not previously studied. Overall we detected 17 species in 84 relevès: seven species belong to charophytes and ten are vascular plants; species richness for relevès ranges from one to eight; maximum macrophyte growing depth was recorded at 15,3 meters. The presence of eight communities were detected, three belonging to Charetea fragilis (Charetum asperae, Charetum polyacanthae, Charetum globularis) and five to Potametea pec- tinati (Potametum denso-nodosi, Potamo-Myriophylletum spicati, Potametum pectinati, Ceratophylletum demersi, Najadetum minoris). Limnologi- cal water variables and structural patterns of aquatic vegetation can be considered similar to patterns of other European calcareous deep-water lakes, from the Scandinavian Peninsula to the Balkans. Thus, to assess ecological condition of Martignano Lakes, the Reference Index method developed for German lakes was applied. Results indicated a good status of conservation for Martignano Lake even if, maximum growing depth revealed a negative trend in the last decades. We argue that Reference Index can be a useful method for Central Italy deep volcanic lakes.