Initial development of a multi-metric index based on aquatic macroinvertebrates to assess streams condition in the Upper Isiboro-Sécure Basin, Bolivian Amazon

We developed a preliminary macroinvertebrate-based multi-metric index to assess streams biotic condition in the Upper Isiboro-Sécure basin (Bolivia). To do so we used eight local habitat descriptors and twelve metrics describing the structure and function of macroinvertebrate assemblages from 38 reference and 29 disturbed sites. Stepwise multiple linear regression procedures were first applied using the reference data to elaborate models describing metrics response to natural environmental in the absence of any significant disturbance. In a second step we used residuals distribution of each of the twelve models to select the most effective metrics in discriminating between reference and disturbed sites. These metrics were: number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), abundance of EPT, relative abundance of EPT, abundance of Chironomidae and relative abundance of Chironomidae. Finally, after converting residual values of these 5 remaining metrics into probabilities, we added values to obtain a final index score and interpreted this score as excellent, good, moderate, poor or very poor. Our final multi-metric index distinguished well between natural and human-induced variation in biological condition and showed a significant negative response to a gradient of disturbances. This type of approach could be used in the near future to develop a nation wide index by increasing regional-scale monitoring.