Analysis of benthic macroinvertebrates and biotic indices to evaluate water quality in rivers impacted by mining activities in northern Chile L’analyse des macroinvertébrés benthiques et indices biotiques pour évaluer la qualité de l’eau dans les rivières touchées par les activités minières dans le nord du Chili

Catchments in the semiarid regions are especially susceptible to environmental perturbation associated with water scarcity, hydrological variations and overuse by anthropogenic activities. Using multivariate analysis to relate environmental and biological data, and diversity and biotic indices (ChBMWP, ChIBF), we analyzed the macroinvertebrate composition of 12 rivers of the semiarid region of northern Chile. A non-metric multidimensional scaling for macroinvertebrate taxa and a principal component analysis for environmental variables strongly separated upstream sites (e.g. Vacas Heladas and Malo Rivers), which presented low pH and high dissolved metal concentrations, from other sites. Effectively, CCA showed that metals and low pH, associated with the altitudinal gradient, determined the distributional patterns of macroinvertebrates in the Elqui catchment. The causes of these particular conditions could be related to geological processes and human impact. The biotic indices applied to the sampling sites corroborated and reflected these characteristics, with La Laguna and Turbio Rivers showing a diverse macroinvertebrate community and moderate to good water quality, and the Claro River showing favorable conditions for the development of aquatic biota, indicating its better quality relative to other stations. To the middle and low part of the basin, a change in the composition of the community was observed, with species that suggest an impact by an increase in organic matter, due to agricultural activities and urban settlements concentrated in this area. Our results suggest that macroinvertebrate taxa in northern Chile may be exceptional species, adapted to unfavorable geochemical conditions, and emphasize the need for protection of the semiarid basins of the region. Les bassins versants des régions semi-arides sont particulièrement sensibles aux perturbations de l’environnement associées à la rareté de l’eau, aux variations hydrologiques et à la surexploitation par les activités anthropiques. Utilisant une analyse multivariée pour relier les données environnementales et biologiques, la diversité et des indices biotiques (ChBMWP, ChIBF), nous avons analysé la composition des macroinvertébrés des 12 rivières de la région semi-aride du nord du Chili. Une mise à l’échelle multidimensionnelle non métrique pour des taxons de macroinvertébrés et une analyse en composantes principales des variables environnementales, séparent fortement les sites amont (par exemple Vacas Heladas et rivières Malo), qui présentent un pH faible et des concentrations élevées de métau