A long-term multiparametric analysis of benthic macroinvertebrate responses to anthropogenic stressors, including a novel multimetric index for evaluating the ecological conditions of mountain rivers in Mexico

Assessing the impacts of anthropogenic pressures (e.g., urbanization, agriculture) on riparian ecosystems is key to their sustainable management. The use of multimetric indices (MMIs) based on biological assemblages for assessing such pressures has increased worldwide. Their cost-benefit advantage and the scientific rigor of their development make them efficient bioindication tools for ecosystem diagnosis and conservation. This research aimed to develop an MMI for the Basin of Mexico based on the assemblages of benthic macroinvertebrates (MIB) observed through sampling perennial rivers and springs at 77 sites over a ten-year period. Potential sites were identified from extant government maps and then visited to verify their current state or existence compared to these cartographic records. We began with 80 ecological metrics and filtered these to remove redundancy, evaluating their ability to differentiate between conserved and degraded sites, have temporal stability, adjusting their score values to natural environmental gradients using significant residual values of the MIB metrics at reference sites. Furthermore, the degree of correlation between environmental changes due to anthropogenic activities at the local and catchment scales was assessed. The final MMI was constructed based on five metrics: Total Abundance, Diptera Richness, Crawler Richness, % Scrapers, and % Temporarily Attached Organisms. The index showed significant differences when discriminating between conserved and degraded sites, as well as when responding to environmental changes at the local and catchment scales. The implemented MMI demonstrates methodological replicability, efficiency, and the potential of macroinvertebrate assemblages to be used as bioindicators in Mexico and other countries where aquatic ecosystems are under constant pressures from land-use change.