Hydrobiologia 457: 69–76, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 69 Biological quality of waters from an impacted tropical watershed (middle Rio Doce basin, southeast Brazil), using benthic macroinvertebrate communities as an indicator Maria M. Marques 1 & Francisco Barbosa 2,∗ 1 Ph.D. student of the Graduate Program in Ecology, Conservation and Wildlife Management, Institute of Biological Sciences, Federal University of Minas Gerais, Brazil 2 Laboratory of Limnology, Department of General Biology, Federal University of Minas Gerais, P. O. Box 486, 30161-970 Belo Horizonte, Minas Gerais, Brazil Fax: 31-499-2567; E-mail:barbosa@mono.icb.ufmg.br ( ∗ Author for correspondence) Received 29 November 1999; in revised form 21 March 2001; accepted 5 May 2001 Key words: tropical basins, water quality, macroinvertebrates, biological tool, monitoring Abstract Taking the watershed as the unit for intervention and conservation, in this study we assess water quality along a stretch of impacted watershed of considerable economic importance, the middle Rio Doce basin, using the benthic macroinvertebrate community, along with physical and chemical characteristics as parameters, for the classification of 20 sampling stations. The results showed that parameters often used in temperate regions are also useful to assess water quality in tropical ecosystems, where no specific methodology has yet been developed. In spite of a clear distinction between stations of good and bad quality, the multimetric biological analysis alone was not sensitive enough to identify intermediate conditions. Grouping similar and dissimilar stations by Cluster analysis of physical and chemical variables and biological data, however, it was possible to distinguish three categories based on the biological quality of the water: (1) stations with poor quality water; (2) stations with high quality water, and (3) stations with water of intermediate quality. Classifications of water quality of this sort will hopefully assist decision-makers in defining restoration/conservation strategies, and will provide an important tool for monitoring biodiversity and water quality in tropical watersheds. Introduction Monitoring programs for freshwater ecosystems have increasingly used benthic macroinvertebrate com- munities as an indicator (Karr et al., 1997). Rosen- berg & Resh (1993) suggested a number of ways the benthic community can be used in assessing water quality. They included changes in genetic composition of specific populations, the bioaccumulation of toxins, changes in population parameters, the appearance of deformities, the presence/absence or abundance of in- dicator species or groups, and changes in community composition and ecosystem functioning. Key com- munity parameters commonly used as measures of water quality include diversity, comparative indices of communities under different impacts, the relat- ive abundance of pollution indicator organisms, and the composition and abundance of functional feeding groups. A limited number of studies have been carried out in tropical ecosystems vital for the development of a specific regional biomonitoring protocol. An under- standing of how to assess and interpret the biological communities is still limited, and the parameters used are often those developed in temperate regions. The middle Rio Doce basin was considered by Paula et al. (1997) to be a microcosm of some of the most pressing environmental problems in Brazil.