Reduced riparian zone width compromises aquatic macroinvertebrate communities in streams of southern Brazil.

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.

Structure of potamoplankton along a gradient of preservation of riparian vegetation in subtropical streams.

Water quality in lotic and lentic systems is greatly influenced by the land use in the adjacent areas. This study was conducted in order to assess whether different degrees of preservation of riparian forest (from well preserved with 30m wide up to degraded with < 5 m wide) influence potamoplankton community structure. The study was conducted in three streams in the upper region of the Rio dos Sinos basin, at four sampling sites, with different width of the forest. Samplings were gathered for abiotic and biological analysis in winter (August 2010) and summer (January/February 2011). The analysis of environmental and biotic variables indicated that seasonality was the main determinant of biomass patterns, regardless of the width of riparian vegetation. The potamoplankton community of the studied streams responded to environmental conditions, although lack of significant difference among the different degrees of riparian vegetation preservation has been observed. Increasing trends on biomass, richness and diversity of species, and higher concentrations of total phosphorus and nitrogen in the non-preserved areas might indicate that the different gradients of preservation of riparian vegetation are related with the water quality in subtropical streams and consequently with the potamoplankton structure.