Índice de integridade ecológica para ecossistemas lóticos da região nordeste do Rio Grande do Sul

Abstract

The use of benthic macroinvertebrates has emerged as an important component to assessment of aquatic ecosystems biological integrity. Several indices based on benthic communities have been proposed in Brazil, demonstrating the need to expand the knowledge about the use of biotic communities in the assessment of the lotic ecosystems quality. This study aims to present a new biological index to examine the ecological integrity of mountain streams from Rio Grande do Sul, based on benthic macroinvertebrate communities and the conductivity measurement. The study was based on samplings performed during the period of 2002 to 2011, in 35 streams in the regions Campos de Cima da Serra and Encosta Superior Nordeste, including the cities of Antônio Prado, Cambara do Sul, Caxias do Sul, Itati, São Francisco de Paula, São Marcos and Três Forquilhas The data used in the Integrity Ecological Index (IEI) development included 88 samples and 1495 cases, and allowed the evaluation of the ecological amplitude of 38 taxa. The coefficient of variation was used to determine which physical and chemical measures are best to differentiate the water courses ecological quality. Linearized regression analysis (Stepwise) were performed to determine which physicochemical parameters show the best relation with the structure of the communities. The parameters conductivity and Chemical Index, indicated by this analysis, were used to estimate the ecological valence of taxa. The association between taxa (Euclidean distance) was used to determine the indicator groups. With the results of these analyzes was possible to assign scores to the macroinvertebrates and to the conductivity values, according to their indication on an environmental gradient. A classification system of ecological integrity was formulated, considering these scores, to indicate the degree of environmental impact in mountain streams of the studied region. When compared to the Chemical Index, the IEI showed a larger number of affected sites, demonstrating to be more sensitive in the assessment of ecological integrity. The IEI could be a useful tool to help managers assess environmental risk in mountain stream ecosystems. [resumo fornecido pelo autor]