Long-term variability of the phytoplankton community in an isolated floodplain lake of the Ivinhema River State Park, Brazil

The phytoplankton community of river-floodplain ecosystems shows significant temporal fluctuations in response to hydrosedimentological regime. The aim of our study was analyze the effect of the hydrosedimentological regime of the Parani and Ivinhema Rivers on the interannual variation in the composition, biovolume and functional groups of phytoplankton in an isolated floodplain lake (Ventura Lagoon) of the Ivinhema River State Park, located in the Upper Parani River floodplain (Mato Grosso do Sul State, Brazil). Samples of phytoplankton were taken at the sub-surface of the pelagic zone of the lake from February 2000 to December 2005. A total of 132 taxa were recorded, and the species that represented greater contributions to the phytoplankton biovolume were grouped into five functional groups (FG) (H1, H2, M, MP and Y). The distribution of the FGs were linked to the high and low water periods in Ventura lagoon. Functional groups MP and Y were the highest contributors to the phytoplankton biovolume during the high water periods, whereas FGs H1, H2 and M contributed more during the low water periods. The FGs were also useful for the interannual characterization of Ventura Lagoon by taking the changes caused by climatological factors into account. There was a strong dominance of Cyanobacteria (H2 and M) in 2000 and 2001 (La Nina periods) coincident with low precipitation and low hydrometric levels of the Parani and Ivinhema Rivers and, consequently, lower water depths of Ventura Lagoon. In 2002, 2003, 2004 and 2005 (El Nino periods), when higher precipitation, higher hydrometric levels, higher discharge of the Parani and Ivinhema Rivers and an increased depth of Ventura Lagoon were observed, Cyanobacteria (H1, H2 and M) were dominant, followed by Bacillariophyceae (MP) and Cryptophyceae (Y). These results reported here corroborate the utility of using FGs as indicators of interannual and seasonal variability in floodplain lakes.