Organic carbon and microbial food web assemblages in an oligotrophic alpine lake

Picoplankton, both autotrophic (APP) and heterotrophic (HPP), ciliates and heterotrophic nanoflagellates (HNF) were counted and their biovolume measured monthly over a 3 year period in Lake Paione Superiore (LPS), a high mountain lake in the Italian alpine region. Analyses of organic carbon, particulate and dissolved, were performed at the same time. APP were negligible and picocyanobacteria almost absent. HPP showed seasonal variations, with low numbers in winter/spring and maxima of nearly 106 cell ml-1 in August/September, corresponding to 60μg C l-1. Free-living, non- pigmented flagellates showed a density range from 104 l-1 to 106 l-1 with a prevalence of cells