Estudo da assembleia de Chironomidae (Diptera) para avaliação ecológica de riachos de baixa ordem, Minas Gerais

Abstract

The use of organisms in evaluations of aquatic ecosystems enables understanding the structure and functional processes of these systems. By calculating metrics of the assemblage of Chironomidae (Diptera) from remanso and corredeira mesohabitats, this study allowed identification of the state of preservation of nine low-order streams belonging to the Marmelos stream sub-basin, located in the municipality of Juiz de Fora, Minas Gerais, Brazil. The first chapter reports the results of two experiments. The first investigated the succession of Chironomidae from samples collected in bags containing Picramnia sellowii leaves, incubated in remansos and corredeirasof three streams in forested areas for 120 days. The changes in the composition and structure of the fauna were attributed mainly to the leaf mass loss and physical heterogeneity of the detritus, especially when the leaf decomposition reached 50% (60 days), at which point the greatest richness of taxa was observed. After 30 days, the dominance of larvae of Stenochironomus possibly contributed to the greater physical fragmentation of the leaf litter. The absence of a relationship between non-mining Chironomidae and fungal biomass indicated that many larvae use the leaves only as substrate. Between the two mesohabitats, there was weak variation in the faunal composition. The second experiment, which compared the Chironomidae fauna in the bags containing leaves after decomposition for 60 days between streams in forested areas versus those in areas affected by organic pollution, detected a clear difference in the composition of taxa between the two environments. The Chironomidae metrics had a strong relation with the environmental variables that distinguished preserved and impacted streams, suggesting the use of this method to assess the environmental conditions of streams. The second chapter investigates whether the metrics of the Chironomidae assemblage differ between remansos and corredeirasin response to different land uses (forest, pasture and urban) in low-order streams, in the dry and rainy seasons. It was found that the taxon composition of both mesohabitats and seasons was the metric with greatest sensitivity to land use, suggesting that the use of this metric of one or the other mesohabitat or season of the year for the biomonitoring enables obtaining results that are less influenced by the natural variability of the environment and reduces the time for processing of the samples. The third chapter investigates the taxonomic concordance of benthic groups identified at different taxonomic levels. Genera of Chironomidae and genera of Ephemeroptera, Plecoptera and Trichoptera (EPT) were found to be concordant in the dry and rainy seasons. The same was found for the genera of Chironomidae and species of Oligochaeta. Families of macroinvertebrates were concordant with Chironomidae genera and EPT genera only in the dry season. Similar responses to the environmental variables were attributed to the concordance between groups, while the proximity of the streams resulted in absence of an influence of the spatial variables. The numerical resolution of Chironomidae genera in both seasons was found to be effective, while this only occurred for the Oligochaeta species in the dry season. The percentage of information lost (>15%) indicates caution in using data on the presence/absence of these groups, suggesting use of this type of investigation only for rapid assessments in environments with marked differences in their preservation conditions.