Macroinvertebrate communities are one of the most used groups in assessments of water quality, since they respond directly to the level of contamination of aquatic ecosystems. The main objective of this study was the assessment of the water quality of the Sinos River basin (Rio Grande do Sul state, Brazil) through biotic indices based on the macroinvertebrate community ("Family Biotic Index -FBI", and "Biological Monitoring Working Party Score System -BMWP"). Three lower order streams (2 nd order) were selected in each one of three main regions of the basin. In each stream, the samplings were performed in three reaches (upper, middle, and lower), totalling 27 reaches. Two samplings were carried in each reach over one year (winter and summer). A total of 6,847 macroinvertebrates distributed among 54 families were sampled. The streams from the upper region were of better water quality than the lower region. The water quality did not change between the upper, middle and lower reaches of the streams. However, the upper reaches of the streams were of better water quality in all the regions of the basin. The water quality of the streams did not vary between the summer and the winter. This result demonstrated that water quality may be analysed in both studied seasons (summer and winter) using biotic indices. The analysis of the results allows us to conclude that the biotic indices used reflected the changes related to the water quality along the longitudinal gradient of the basin. Thus, aquatic macroinvertebrates were important bioindicators of the water and environmental quality of the streams of the Sinos River basin.Keywords: hydric resources, bioindicator, biomonitoring, water quality, biotic indices. Os arroios da bacia hidrográfica do Rio dos Sinos estão com boa qualidade da água?Os macroinvertebrados aquáticos podem responder a questão Resumo A comunidade de macroinvertebrados aquáticos é um dos grupos mais utilizados na avaliação da qualidade da água, pois respondem de forma diferente ao grau de contaminação dos ecossistemas aquáticos. O principal objetivo deste estudo foi avaliar a qualidade da água na bacia hidrográfica do Rio dos Sinos (Rio Grande do Sul, Brasil) através de índices bióticos baseados em comunidades de macroinvertebrados aquáticos (Family Biotic Index -FBI, e Biological Monitoring Working Party Score System -BMWP). Três arroios de pequena ordem (2º ordem) foram selecionados em cada uma das três principais regiões da bacia. Em cada arroio foram realizadas coletas em três trechos (superior, médio e inferior), totalizando 27 trechos. Foram realizadas duas coletas ao longo de um ano em cada trecho de arroio (inverno e verão). Um total de 6.847 macroinvertebrados distribuídos em 54 famílias foi coletado nos arroios. Os arroios da região superior da bacia apresentaram uma melhor qualidade da água do que os da região inferior. A qualidade da água não variou entre os trechos superior, médio e inferior dos arroios. Entretanto, os trechos superiores dos arroios apresentaram uma melhor qualidade ...

Understanding seasonal patterns of assembly mechanisms are key to comprehending the metacommunity dynamics of organisms inhabiting temporary habitats such as wetland macroinvertebrates. However, tests of the seasonal variation in assembly mechanisms of macroinvertebrates in wetlands with differing hydroperiods are rare, especially in the Neotropical region. We tested for seasonal patterns in the metacommunity assembly mechanisms of macroinvertebrates in small subtropical highland wetlands of southern Brazil with different hydroperiods. We also tested whether patterns varied between macroinvertebrate taxa with different dispersal modes. Macroinvertebrates were sampled in 12 wetlands classified into "short," "medium," and "long" hydroperiods (N = 4 in each category) in three seasons (fall, winter, and spring) over two full hydrological cycles (from 2012 to 2014). We assessed the role of spatial and environmental variables to metacommunity structure using distance-based redundancy analysis and variation partitioning. Environmental and spatial variables explained macroinvertebrate metacommunity structure, although their relative influence markedly changed among seasons and hydroperiods. Environmental variables were important in fall and winter, whereas spatial variables predominated in spring. Different environmental variables influenced the metacommunity structure in each hydroperiod. Environmental variables influenced active-dispersing macroinvertebrates, whereas the influence of environmental and spatial variables on passive-dispersing taxa changed among seasons. We showed that the assembly mechanisms of macroinvertebrate metacommunities show a distinct temporal dynamic among wetlands with different hydroperiods. Our findings contribute to a more complete understanding of the metacommunity structure in temporary ecosystems.