Recent changes in Brazilian legislation reduced the width of riparian forest buffer needed to be preserved in private properties from 30 to 15 m or less. The consequences of these modifications can be dramatic, mainly because riparian buffer width is an important parameter for riparian forest structure and functioning. Our study assessed whether (1) macroinvertebrate family richness and Ephemeroptera, Plecoptera, and Trichoptera (EPT) family richness decrease with reduced riparian buffer width; (2) taxonomic composition and functional feeding group (FFG) composition of macroinvertebrates vary with a reduced riparian buffer width; and (3) reduced riparian buffer width similarly influence the macroinvertebrate community in different stream substrates. We selected three fragments with different riparian buffer widths (>40, <30, and <15 m) in three streams (fourth and fifth orders) in the Sinos River watershed, southern Brazil. Our results show that on all substrate types, reducing the width of the riparian buffer altered neither the macroinvertebrate richness nor EPT richness. However, EPT richness was greater in the substrates stone and gravel than leaf litter, independent of riparian buffer width. There was a significant difference in macroinvertebrate composition among riparian buffer widths. The macroinvertebrate composition and FFG differed among substrates, independent of riparian buffer width. This study showed that riparian buffer widths <15 m altered the macroinvertebrate community. A width greater than 15 m is necessary to maintain the composition and trophic conditions of macroinvertebrate families similar to those found in reference states of conservation.

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.

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