Effects of flow reduction and spillways on the composition and structure of benthic macroinvertebrate communities in a Brazilian river reach

Abstract

Dams are a major threat to aquatic biological diversity. By altering the natural flow of rivers, dams modify fluvial habitats, making them unsuitable for the growth and reproduction of many aquatic species. The aim of this study was to evaluate the effects of a reduced flow reach (RFR) on benthic macroinvertebrate communities. Benthic macroinvertebrates were collected at six sites downstream of the Amador Aguiar Power Plant I before (lotic phase) and after (semi-lentic phase) Araguari River mean flow was reduced from 346 to 7 m 3 .s -1. Changes in macroinvertebrates richness, diversity and total biomass were not observed. Ablabesmyia, Tanytarsus (Chironomidae, Diptera), Leptoceridae and Polycentropodidae (Trichoptera) densities significantly increased the first year after flow reduction and the construction of spillways (t-test; p < 0.05). An analysis of similarity (ANOSIM) showed statistical differences in taxonomical composition despite considerable overlap in communities between the lotic and semi-lentic phases (R = 0.3; p < 0.01). In both phases, the macroinvertebrates were characterised by the dominance of groups tolerant to human disturbance (e.g., Chironomidae, Ceratopogonidae and Oligochaeta) and by the presence of the alien bivalve species Corbicula fluminea (Veneroidae), suggesting that the river was already degraded before the hydraulic modifications. Since the 1980s, the Araguari River has been continuously subjected to human pressures (e.g., cascade dams, urbanization and replacement of native vegetation by pasture and crops). These activities have led to impoverishment of biological communities and have consequently altered the ecosystem.Keywords: spillways, reduced flow, dams, benthic, anthrophic impacts.Efeitos da redução de vazão e construção de soleiras vertentes sobre a composição e estrutura de comunidades de macroinvertebrados bentônicos em um trecho de rio brasileiro ResumoAs represas constituem uma das principais ameaças à diversidade biológica. Ao alterarem a vazão natural de um rio, modificam os habitats fluviais tornando-os inadequados para o crescimento e reprodução de diversas espécies aquáticas. O objetivo deste estudo foi avaliar os efeitos de um trecho de vazão reduzida sobre as comunidades de macroinvertebrados bentônicos. Os organismos foram coletados em seis estações amostrais à jusante da UHE Amador Aguiar I antes (fase lótica) e após (fase semilêntica) a vazão média do rio Araguari (MG) ter sido reduzida de 346 para 7 m 3 .s -1. Não foram registradas mudanças na riqueza, diversidade e biomassa total dos macroinvertebrados. As densidades (ind.m -2 ) de Ablabesmyia, Tanytarsus (Diptera), Leptoceridae e Polycentropodidae (Trichoptera) aumentaram significativamente no primeiro ano após a redução da vazão e construção das soleiras vertentes (t-test; p < 0,05). Uma análise de similaridade (ANOSIM) apontou diferenças significativas na composição taxonômica, porém houve sobreposição das comunidades entre as fases lótica e semilêntica (R = 0,3; p < 0,01). Em ambas as fases a ma...

Benthic macroinvertebrates in Italian rice fields

“…All the data analyses highlighted significant differences between habitats (feeding channel and rice field), with higher diversity observed in channels; this is in agreement with the wellknown differences generally observed between fauna living in lentic and lotic habitats (Maroneze et al, 2011). Biodiversity indices stressed a significant influence of the season, which is in line with the variation of the community composition during the year according to the life cycles of different species (Barbone et al, 2012).…”

Aquatic insect community structure under the influence of small dams in a stream of the Mogi-Guaçu river basin, state of São Paulo

“…The wildlife that inhabits the stretches downstream of these impoundments has to adapt to new environmental conditions (Ward and Stanford, 1979;Pardo et al, 1998). In studies that analysed the changes resulting from the construction of small dams on the community of aquatic invertebrates, significant differences in richness and Shannon diversity were commonly not found (Chessman et al, 1987;Maroneze et al, 2011). However, after the construction of spillways, significant differences in abundance and differences in the functional feeding group structure, with the replacement of filter-collectors by gathering-collectors were observed (Maroneze et al, 2011).…”

“…In studies that analysed the changes resulting from the construction of small dams on the community of aquatic invertebrates, significant differences in richness and Shannon diversity were commonly not found (Chessman et al, 1987;Maroneze et al, 2011). However, after the construction of spillways, significant differences in abundance and differences in the functional feeding group structure, with the replacement of filter-collectors by gathering-collectors were observed (Maroneze et al, 2011). It can be inferred Pr -11 1 2 ------14 77 22 29 36 11 1 50 119 25 45 415 a that the discontinuity of small dams in the Ribeirão das Anhumas did not have an impact on the aquatic insect fauna, as the results were similar to the studies mentioned above.…”

Fish stomach contents in benthic macroinvertebrate assemblage assessments

“…ANOSIM analyses were performed with PRIMER 6.0 (Anderson et al, 2008). ANOSIM values of R > 0.75 indicate distinct groups, 0.50 < R < 0.75 indicates separate but moderately overlapping groups, 0.25 < R < 0.50 indicates separate but strongly overlapping groups, and R < 0.25 represents groups that cannot be distinguished (Maroneze et al, 2011a). A randomization process using Monte Carlo testing with 9,999 interactions was conducted to validate the R Figure 1.…”