Aquatic macrophytes of Itaipu reservoir, Brazil: Survey of species and ecological considerations

In a survey of the aquatic macrophytes of the Itaipu Reservoir, we identifi ed 62 taxa in 25 families and 42 genera. The highest number taxa was observ ed for the emergent macrophytes (40 taxa). Reduced fluctuation in water lev el, increased light penetration, and sediment enrichment by nutrients and o rganic matter following the formation of the reservoir favored the appearan ce of a species-rich community of submerged macrophytes (23% of the taxa id entified). The aquatic macrophytes were found mainly near the mouths of the main tributaries of the reservoir, in shallow area of depth less than: 2 m eters. In addition to the shallow depth, the greater nutrient input from am the tributaries and relative protection from wind explained this distribut ion. Among the species found, Egeria najas merits mention for its occurrenc e in all localities sampled, with biomass values varying between 98 and 186 gDW/m(2) Some potential nuisance species such as Eichhornia crassipes, Sal vinia auriculata, and Pistia stratiotes also deserve attention since they w ere also observed to be covering large areas of Itaipu Reservoir.