Abstract
The application and development of environmental laws governing watershed management requires identification of biological indicators, parameters and measures to establish its ecological status, for which the present study aims to characterize the ecological indicator value of stream benthic algae in an urban area of Mexico City. Six sites of the Magdalena river were studied in the most contrasting seasons: dry-warm, rainy and dry-cold. At each site the physicochemical parameters of water were recorded and 10 samples were collected: Five with visible algal growths and five with diatoms. The environmental quality of each site was determined by the trophic status and its confirmation with the richness and benthic algal diversity, through a canonical correspondence analysis and the calculation of the indicator value of species (IndVal). According to the trophic status, three groups of sites were recognized. The first group (G1) was assessed as reference of the oligotrophic conditions and presented 11 species with the highest IndVal, protruding: Encyonema silesiacum, Gomphonema parvulum, Navicula cryptocephala, Planothidium lanceolatum, Vaucheria bursata, Placoma regulare and Nostoc parmelioides. A second group (G2) was associated with 15 species considered detectors, which were tolerant to increased nutrients in at least one season, such as Diatoma mesodon and Prasiola mexicana. The third group (G3) included sites with species that had a wide range of tolerance to pollution: Fistulifera saprophila , Nitzschia minuta , Nitzschia palea , Nitzschia recta and Phormidium autumnale. The species IndVal of Magdalena River has established reference sites of good environmental quality and those that are altered by human activities, therefore they are recommended as the first step in a methodological proposal for a long-term biomonitoring through a biological index.
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