Cross-channel and vertical variation in diversity and abundance of phytoplankton in the Lower Paraná River, Argentina
O'Farrell, I.; Vinocur, A.; Lombardo, R. J.
The vertical and cross-channel distribution of phytoplankton and some environmental parameters from two sites of the Lower Paraná River with heterogeneous channel morphology (San Nicolás and San Pedro Cities) were analysed. Sampling was done at 2-monthly intervals between April 1993 and April 1994. Centric diatoms, mainly represented by Aulacoseira granulata and its varieties, dominated the phytoplankton; green algae were subdominant. Highest algal densities and species diversity were found in late winter-early spring, strongly related with higher transparency and lower water discharge. No stratification was observed in the water column, whereas cross-channel contrast was found in the phytoplankton structure and in some physical and chemical variables, attributable to the margins difference in channel depth, bank morphology and floodplain. At San Nicolás the algal composition was different for both margins, while San Pedro presented a much more homogeneous distribution of phytoplankton across the channel. The ordination of samples based on species density reveals the difference between low and high waters periods, as well as the separation of the left margin samples from the middle of the channel and right margin samples.