RESUMO
The phytoplankton structure and dynamics were analysed in relation to abiotic variables in Paso de las Piedras Reservoir, Argentina. Phytoplankton driving forces were explored using a functional approach. A total of 15 functional groups were identified among which D, P, HI, F, J and C were the most important. A Canonical variate analysis indicated that the categorization of the species in functional groups and its relationship with the temporal species clustering was not a random result. In the redundancy analysis, temporal ordination dynamics of functional groups was well described by the distribution of samples. Remarkable shifts in composition and biomass of phytoplankton occurred in agreement with changes in temperature, N:P ratio and transparency. The group succession could be summarized as: P/J [early summer]->P/ HI [late summer]->P [early autumn]-"P/F [late autumn]-"C [early winter]-"D [late winter]-"Y [early spring]-"D [early spring]->P [late spring]. The majority of the associations detected were typical of eutrophic-hypertrophic systems. With the exception of HI, the groups that most contribute to biovolume were those characteristics of mixed aquatic environments, i. e., non-stratifying lakes or deep, well-mixed epilimnia of stratifying lakes. The diversity indices, in terms of functional groups, were low, meaning that a small number of traits were present and/or that there was an inequitable distribution