universidade federal de minas gerais instituto de ciências biológicas ...

ABSTRACT
Studies concerning benthic communities in reservoirs have received considerable attention
due to the important participation of these organisms in ecological processes. The objective of
this study was to assess the benthic macroinvertebrate communities (taxa compositiuon,
structures and distribution) in two reservoirs in the Paraobeba River basin, a tributary from
São Francisco River: Ibirité and Serra Azul. Samples were collected every two months during
one year. The trophic level assessed in the Serra Azul reservoir presented a mean value lower
than 44 in the rainy season (oligotrophic) and 45.1 in the dry season (mesotrophic). In the
Ibirité reservoir, mean values higher than 54 were obtained in both seasons (eutrophic). Taxa
richness ranged between 0 and 14 taxa in Ibirité and between 0 and 23 in Serra Azul. The
higher richness values were found in the lotic sampling sites with higher granulometric
diversity. The indicator taxa analysis showed that, during the rainy season, Chaoboridae
(Diptera) was indicator in Serra Azul and Oligochaeta in Ibirité. Considering the lotic
sampling sites, there were no indicator taxa in both reservoirs in the rainy season. In the dry
season, Hirudinea, Oligochaeta, and Chironomidae (Diptera) were indicators in Ibirité and
Gomphidae (Odonata) in Serra Azul. In total, 54,512 organisms were collected, sorted and
identified. The most abundant taxa in the Ibirité reservoir were Oligichaeta (76.6%),
Chironomidae (17.6%), Thiaridae (1.8%), Hirudinea (1.5%), and Chaoboridae (1.2%). In
Serra Azul, Chironomidae (40%), Chaoboridae (22.7%), Oligochaeta (9.4%), Elmidae (8.4%),
Baetidae (3.1%), Leptohyphidae (2.6%), Ceratopogonidae (2.4%), Leptophlebiidae (2.1%),
Thiaridae (1.4%), and Sphaeridae (1.3%) were dominant. Comparing this study with available
data from 5 years ago, in spite of the higher total density of organisms (715,600
individual/m 2 ) in the present study, taxa richness values achieved only 9 groups in the lotic
sampling sites, presenting no significant differences from the previews study. The results
showed a bad water quality in Ibirité and a better water quality, higher taxa richness and
diversity values in Serra Azul. Reservoirs are responsible for several ecological modifications
and studies assessing the benthic macroinvertebrates bioindicators of water quality contribute
to the development of conservation and management programs.
Key-words: reservoirs, benthic macroinvertebrates, trophic level, lotic ecosystems.
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