Phytoplankton association patterns in the deep southern subalpine lakes (Part 1)

Since the first meetings, usually held in Pallanza, of the Working Group on Deep Lakes (GlaP, Gruppo Laghi Profondi) the idea to compare the phytoplankton assemblages in deep southern subalpine lakes gradually grew up. We recognise that this isn’t a new idea: since the papers by Pietro Pavesi (1877, 1879 a, b, 1883) and Rina Monti (1929) until the most recent years (i.e. Ruggiu 1983; Ambrosetti et al. 1992) similar comparisons have been already done. However, we feel that the analysis presented in this and the next issue of Journal of Limnology will offer many new subjects: the study is not only a comparison of taxonomic lists, but is focused on phytoplankton assemblages and their seasonal dynamics; the data from the different lakes have been collected during the same time period, with similar periodicity and fully comparable sampling techniques and strategies; the methods used to analyse the samples and to treat the data are the same. Due to the full comparability of the data collected, it has been possible to study the seasonal dynamics of the phytoplankton assemblages in the whole subalpine lake district, across a trophic, geographic and climatic spectrum. Moreover, the analysis described here was a useful tool for recognising a common succession pattern in the southern deep subalpine lakes. We are confident that this collection of papers on the phytoplankton in the deep southern subalpine lakes can represent a starting point towards the possibility to answer questions as: what kind of changes should we expect in the phytoplankton assemblages following future increases or decreases of the nutrient loads? Which are the environmental conditions favouring the growth and, eventually, the bloom of certain algae (i.e. cyanobacteria)? What species assemblage could be the most typical in the subalpine lake district?