Diversidade e biomassa de macrófitas aquáticas no Rio Ariaú, Amazonas

Abstract

Aquatic macrophyte studies are of paramount importance for the dynamics of floodplain aquatic environments, as many of these plants provide shelter for aquatic fauna, serve as food sources for various species, and act as bioindicators of trophic state. This study was conducted on the Ariaú River, in the Iranduba/AM municipality, with the aim of analyzing the structure of the aquatic macrophyte community in a section of the Ariaú River during the dry season. Six sampling points in environments with the occurrence of macrophytes were selected.The methodology used was based on the quadrat technique. At each of the six points, 10 floating quadrats of 0.25 m² were randomly sampled, totaling 60 quadrats. The plant coverage percentage in each quadrat was evaluated for the structural characterization of the community. The relative frequency of species and families was analyzed, as well as the Shannon-Weiner diversity indices and evenness (J'), as proposed by Pielou (1966). Fourteen species of aquatic macrophytes were counted and identified, distributed across 12 families, with the predominant ecological type being free-floating. The most abundant species were Eichhornia crassipes and Paspalum repens, with biomass values of 26.4 and 31.92 kg/m², respectively. The moisture content for P. repens was 93%, and for E. crassipes, 92%. The diversity index was H' = 1.58, and J = 0.58.The Principal Component Analysis (PCA) showed that at point 1, the most abundant aquatic macrophytes were Hymenachne amplexicaulis (emergent fixed), Neptunia oleracea (floating fixed), and Ludwigia helminthorrhiza (free-floating). At point 2, the greatest abundance was of Pistia stratiotes, at point 3, Ipomoea aquatica (floating fixed), at point 4, Utricularia foliosa (submerged free-floating), at point 5, Limnobium laevigatum (emergent fixed), and at point 6, the abundance was associated with Lemna minor (free-floating).The physical and chemical variables of the water—temperature, pH, and conductivity—were not associated with the abundance of aquatic macrophytes or influencing them. Analyses of these physical and chemical variables were carried out, and although the Ariaú River is a tributary of the Negro River, during the dry season, it is influenced by the Solimões River, which contributes to the occurrence of a higher number of aquatic macrophyte species that are tolerant to acidic pH.