The Amazonian wetlands cover a vast area subject to a monomodal flood pulse with an annual amplitude averaging 10 m, which defines an aquatic phase and a terrestrial phase of great biological importance. According to the geological origin and the catchment areas, the physical and chemical properties of the wetland will vary, being defined two major groups, the várzeas and the igapós. Although aquatic herbaceous plants do occur in the two types, higher species richness and densities are typical of the várzeas where aquatic herbaceous species, particularly C4 plants may exhibit high biomass values and net primary production - NPP about three times these of the floodplain forest. The aquatic herbaceous plants are very important in the carbon and nutrient budgets of the várzea, since through their decomposition they promote the enrichment of the aquatic system and associated floodplains, both during the aquatic and terrestrial phases of the hydrologic cycle. The major threats to herbaceous aquatic plants are related to the modification and contamination of the habitats owing to their use in economic activities as cattle and buffalo ranching and agriculture. Degradation improves the susceptibility of these systems to fire especially during the terrestrial phase, resulting in economic losses and further degradation of floodplains. Recently oil spills linked to the petroliferous activities in the region are of major concern demanding further and urgent evaluation.
Amazon River; aquatic grasses; primary production
