Abstract
The Chironomidae family is one of the main groups of aquatic insects present in streams. This work aimed to investigate the influences of anthropogenic pressures and substrate types on chironomid community composition and structure. Chironomid larvae were collected during the summer of 2007 at four sites along the Vacacaí-Mirim River microbasin, chosen based on the different available benthic substrates. The organisms were identified in the laboratory at the genus level, and the density, the rarefied taxonomic richness and the Shannon diversity index were calculated. The faunal structure was subjected to an ANOVA to compare the metrics among sites and substrates. The community composition of the sites was subjected to a multivariate statistical analysis. Differences in the composition, richness, density, and diversity were observed among the sites due to differences in the levels of nutrients and solids generated by the presence of crops close to water bodies. Samples collected from sandy substrates exhibited a lower density and taxonomic richness because sand is a poorer substrate than the others that were sampled. In organic or mixed substrates with higher energy availability and better shelter conditions, the observed densities were higher. The physical and chemical conditions and the morphometric characteristics of the sites were more influential than the substrates.
Highlights
The patterns of diversity for organisms in aquatic environments have received considerable attention from researchers in recent years because, along with abiotic environmental factors, the data on these patterns can indicate the conservation status of a river, stream or other water body (Fesl 2002)
The aim of this study was to investigate the influences of anthropogenic pressures and of substrate types on chironomid community composition and structure, as well as correlate the results with the environmental characteristics of the study areas and identify the factors that most influence the local fauna
Sites A and B displayed environmental characteristics with less human influence, whereas sites C and D were influenced by areas of rice cultivation located close to the water body
Summary
The patterns of diversity for organisms in aquatic environments have received considerable attention from researchers in recent years because, along with abiotic environmental factors, the data on these patterns can indicate the conservation status of a river, stream or other water body (Fesl 2002). Immature stages of Chironomidae generally live on or in the sediment, feeding on organic detritus and associated microfauna and flora. This group occupies an important position in aquatic. Studies of the distribution of Chironomidae taxa may generate additional information that would be of use in the assessment of aquatic systems, e.g., data that indicate the influence of disturbances to the substrate, on hydrological variables and on edge vegetation, among others (Kleine and Trivinho-Strixino 2005)
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