Spatiotemporal gradients in the Paraná River-Floodplain System from a plankton functional approach

DEVERCELLI, M.; JOSÉ DE PAGGI, S.; PAGGI, J.C.; GARCÍA DE EMILIANI, M.O.

Natal

Congreso; XIII Congreso Brasileiro de Limnologia; 2011

The plankton of the Middle Paraná River System was studied in order to analyse the community driving forces and the ecological effects of different hydrological periods in the lateral dimension using a functional approach. Phytoplankton and zooplankton biomass and limnological variables (hydrological, physical and chemical parameters) were studied at the mainstem, secondary channel and two floodplain lakes during the periods 1974-1975, 1986-1988, 1997-1998 and 1999-2000, covering ordinary and extreme hydrological phases. A spatial gradient with an increasing phytoplankton and zooplankton biomass from the mainstem to the more isolated water bodies was observed. In the mainstem and secondary channel, a predominance of P and C phytoplankton functional groups, adapted to the turbulent and turbid conditions of the rivers, was found. A high diversity of functional groups, and coda composed by species with low growth rate (H1, W1, W2) were observed at the floodplain lakes. The zooplankton was characterised by the progressive increase of the larger species (cladocerans and copepods) along with the environmental gradient from low to high water residence time. The temporal gradient indicated structural changes and an inverse relationship between plankton biomass and water discharge. Drought periods favoured plankton development, except at the mainstem where the exchanges of organisms with the floodplain are essential for plankton maintenance.  In conclusion, the spatiotemporal changes of the plankton community are associated to the hydrosedimentological regime. As the lentic habitats are isolated from the lotic influence, zooplankton increases its role as phytoplankton control factor, so that biotic interactions became progressively more important in the community dynamics. FINANCTIAL SUPPORT: Proyecto PICT Bicentenario (ANPCyT-FONCyT) y Proyecto SECTeI 2010