Macroinvertebrate biomonitors of Eastern Amazon headwaters – our latest Ph.D. success!

Congratulations to Lenita Sousa da Silva who successfully defended her Ph.D. thesis Biomonitoring of headwater streams in the Caeté river basin (Pará) using benthic macroinvertebrates on Wednesday 27 February 2019. The examining committee members were Breno Eduardo da Silva Barros (Federal Rural University of Amazonia), Cleidson Paiva Gomes (Federal Institute of Pará), Tatiane do Nascimento Medeiros Rodrigues and Marcus E. B. Fernandes (both from the Federal University of Pará). Her average grade was 9.6 (Excellent).

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Lenita taking stream measurements with Ismael Sander during an RHDI survey in 2016. Photo: Benedito Oliveira.

Lenita’s thesis was divided into a General Introduction, three specialized chapters and a General Conclusion. The first chapter looked at assessing ecological integrity in ten headwater streams in the Caeté basin (Pará, Northern Brazil) using macroinvertebrate families and functional groups, water quality parameters and a Riparian Habitat Diversity Index (RHDI) based on Callisto et al. (2002). The RHDI scores classify streams with increasing riparian habitat diversity, as impacted (least diverse, most impacted) through altered to natural (most diverse, least impacted). Macroinvertebrate structure was distinct in streams classified as natural, but was similar in both altered and impacted streams. Thus, even moderate impacts on riparian habitat are associated with a fauna similar to that of impacted streams. Numbers of macroinvertebrate families, especially Ephemeroptera, Plecoptera and Trichoptera (EPT), were higher in natural streams. The RHDI score correlated positively with the number of EPT families and percent Shredders, and negatively with Berger-Parker dominance and chironomid abundance. In altered and impacted streams, tolerant taxa, mainly Chironomidae and Tubificidae, and percent Predators predominated. In natural streams, percent gravel, dissolved oxygen concentration, pH and organic matter content were higher, whereas in altered and impacted streams, turbidity and percent sand were higher. The use of EPT and Chironomidae, along with RHDI scores and classes, facilitates rapid and reliable monitoring of eastern Amazon headwaters and may be generally applicable to low-order streams in other tropical regions.
In the second chapter, two biological indices based on macroinvertebrates, the Biological Monitoring Working Party (BMWP), modified by Junqueira and Campos (1998) and the Family Biotic Index (FBI), devised by Hilsenhoff (1988), were assessed for their performance in evaluating water quality in six headwater streams in the Caeté basin. The BMWP index distinguished water quality in natural streams from that in altered and impacted streams, but was unable to differentiate between the latter two classes. The FBI index performed better, distinguishing among different water quality classes within each of the three RHDI levels, and highly correlated with the RHDI numerical score. Higher organic matter content, percent gravel and dissolved oxygen concentrations were associated with higher biological water quality, whereas turbidity and conductivity were higher where biological water quality was lower. As the Family Biotic Index appears to be more responsive to subtle changes in the macroinvertebrate fauna, its use is recommended in biological water quality monitoring programmes in Eastern Amazon streams where the aquatic fauna is relatively diverse.
The third chapter describes for the first time in eastern Amazon headwater streams, the effect of small dams on macroinvertebrate assemblage structure and water quality. Five streams without dams (stream habitat) were compared with five streams with dams (reservoir habitat) in the Caeté basin. Macroinvertebrate diversity was lower in reservoirs, where temperature, conductivity and turbidity were high, and tolerant taxa (Chironomidae, Chaoboridae and Tubificidae) were abundant. In stream habitat, where dissolved oxygen and pH were higher, macroinvertebrate diversity and the abundance of sensitive taxa, such as EPT and Elmidae, were greater. As riparian habitat removal, declining water quality and small dam construction are widespread in the Eastern Amazon, regulation, management and conservation measures need urgent implementation in order to maintain headwater stream function in the region.

Key words: Bioindicators, benthic macrofauna, first-order streams, ecological integrity, riparian habitat, water quality, small dams, environmental impact.

Callisto M., Ferreira W., Moreno P., Goulart M. and Petrucio M. (2002). Aplicação de um protocolo de avaliação rápida da diversidade de habitats em atividades de ensino e pesquisa (MG-RJ). Acta Limnologica Brasiliensia 14: 91-98.

Hilsenhoff W. L. (1988). Rapid field assessment of organic pollution with a family-level biotic index. Journal of the North American Benthological Society 7: 55-68.

Junqueira, V. M. and Campos S. C. M. (1998). Adaptation of the BMWP method for water quality evaluation to Rio das Velhas watershed (Minas Gerais, Brazil). Acta Limnologica Brasiliensia 10: 125-135.

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