O que as algas têm a dizer sobre o rio Negro? O uso de algas perifíticas como bioindicadoras de qualidade ambiental do baixo rio Negro, Manaus-AM

Abstract

Taxonomic and ecological information on periphytic algal assemblages along rivers in the Amazon region is scarce and inconclusive. The use of these assemblages as bioindicators for water quality assessment of these rivers, especially the Negro River, is practically nonexistent. In this thesis, we sought to analyze the ecological preferences of the species that compose the periphytic algal assemblage of the lower Negro, elucidate taxonomic questions about two species widely reported for this sampling region and, pioneeringly, evaluate the bioindicator potential of the inventoried species, by considering their ecological preferences and calculating specific indices for these assemblages. With this purpose, an anthropogenic influence gradient (LAI = low anthropogenic influence area, IAI = intermediate anthropogenic influence area, HAI = high anthropic influence area) was previously established for the lower Negro River, in which 12 stations were distributed, where abiotic (pH, dissolved oxygen concentration, temperature, electrical conductivity, turbidity, nitrate, nitrite, total phosphorus and orthophosphate) and biotic (periphytic algal assemblage structure) variables were sampled during four consecutive weeks at two flood periods (2013 and 2014). After treatment and analysis of samples (abiotic and biotic), exploratory analyses (CCA, PCA, Pearson Correlation and Cluster Analysis), inferential statistical analyses (Multiple Regression and Analysis of Variance), index calculation (diatom-based and soft algae-based) and indicator species value calculation were conducted, with the goal of answering the questions raised based on the objective of this thesis. Results showed a promising potential of periphytic algae for water quality evaluation of the lower Negro River. Among the 15 diatom-based indices tested, five (IPS, EEC, TDI, IDP, EPI-D) showed significant relationship with the abiotic variables, demonstrating their ability to infer about water quality at the lower Negro River. The five indices mentioned above were satisfactorily associated with the pollution gradient. The soft algaebased index (PIT) did not show significant relationship with abiotic variables, which may indicate a better fit of diatom indices to this sampling region. However, it is important to note that this index also showed a satisfactory fit to the previously established pollution gradient. It was possible to reveal the indicator species for each sampling region. The species most strongly associated with eutrophic environments were Luticolla goepertiana, Luticola permuticoides, Discostella cf. Stelligera, Batrachospermum spp., Oedogonium spp., Rhizoclonium riparium, Stigeoclonium tenue, Spirogyra spp. The species indicating mesotrophy were Eunotia aff. subarcuatoides and again Spirogyra spp. And the species most strongly associated with oligotrophic environments were Actinella brasiliensis and Peridinium umbonatum. This set of results indicates the potential of periphytic algae to infer about the lower Negro River water quality, besides showing the immediate need of including protocols that consider these assemblages in environmental impact studies of aquatic environments, since these assemblages’ responses offer much more reliable, realistic and integrated information about the ecological state of the environment, showing, not only the situation at the moment of sampling, but also possible polluting events that occurred at other times in that environment. Nevertheless, caution is needed when considering indices, due to difficulties associated with these species’ taxonomic and ecological issues that remain far from fully elucidated for the Amazon. This makes the contribution of studies such as the one carried out for this thesis even more relevant, in view of the latent need to develop effective and reliable methods for assessing water quality in Brazil, especially, in the Amazon. In addition, from the results presented above during the development of the thesis it was possible to identify and describe a new diatom species (Bacillaryophyta), Eunotia amazonica, widely distributedin the sampling area, still with respect to the taxonomic results, was possible, through analysis of the samples, propose two new combinations within the genus Gomphonema (Gomphonema frequentis and G. frequentiformes).