Phytoplankton ecology of the Lower Parana River (Argentina)
O'Farrell, I.; Izaguirre, I.; Vinocur, A.
Phytoplankton of the Lower Paraná River was studied bimonthly from April 1993 to April 1994 at six stations along 400 km length. Fluctuations in the physical and chemical variables are analysed in relation to the hydrological changes which play an important role in the functioning of large rivers with complex floodplains. Aulacoseira granulata var. granulata was the dominant alga over the entire river stretch. The subdominant taxa were also represented by centric diatoms which proved to be well adapted to flowing turbid environments. During periods of low flow, with enhanced transparency, small Chlorococcales increased in abundance. Maximum abundance of the phytoplankton and the greatest diversity were observed during spring. The absence of significant spatial changes in the structure of the phytoplankton along the studied length, reveals a sufficient constancy of environmental conditions for the planktonic dominance to be unaltered through the year.