The Macroalgae Ecological Quality Index (MEQI) in the Basin of Mexico: a proposal of aquatic bioindicators for peri-urban rivers

Abstract

We assessed macroalgal responses to anthropogenic pressures in the Basin of Mexico to examine whether these biological indicators exhibited a discriminatory and explanatory correlation with ecological quality and propose the “Macroalgae Ecological Quality Index” (MEQI). The proposal included 3 steps: i) characterization of trophic level and hydromorphological quality (HQ) in 13 sub-basins consisting of 49 sites with different degrees of conservation sampled between 2012 and 2016, ii) calculation of indicator values for 20 taxa to generate the proposed algorithm, and iii) validation of the algorithm in 26 new sites and calculation of its correlation with water quality and HQ. The ecological quality gradient to which the macroalgae responded was related to oxygen saturation, soluble reactive phosphorus, dissolved inorganic nitrogen, and hydromorphological quality. By assigning an indicator value to each group of species, we calculated the MEQI using the formula adapted from Pantle and Buck, indicating 5 different ecological quality classes. The MEQI index allowed us to establish references for good quality sites and altered sites with regards to chemical composition and structure. Therefore, the MEQI is recommended for biomonitoring in the Basin of Mexico and registering multiple environmental stressors.