Effects of hydrological variation on the aquatic plant community in a fl oodplain palustrine wetland of southern Brazil Abstract This study analyzed macrophyte richness, biomass, and composition under fl ooding of brief duration (less than 3 days) and drawdown events over an annual cycle in a fl oodplain palustrine wetland in the south of Brazil. The study was carried out to test the hypothesis that fl oods of brief and very brief duration are not long enough to compromise the richness and the biomass of aquatic macrophytes and that the alternation between wet and drawdown phases may cause variations in the macrophyte richness and composition. A total of 26 aquatic macrophyte species were observed from April 2003 to May 2004: 13 species were observed during the wet phase, and 24 during the drawdown phase. The mean richness was higher during the drawdown phase than during the wet phase, however, the mean biomass was similar in both phases. Although macrophyte richness was not modifi ed after the three fl ooding events, mean biomass was modifi ed after two events. The number of macrophyte species of which the biomass was modifi ed after the fi rst fl ooding event increased with subsequent fl oods. These results illustrate the importance of the dynamics between brief fl oods and drawdown events to the aquatic plant community in fl oodplain wetlands in southern Brazil.

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