Multimetric analyses for assessing pollution in the Lerma river and Chapala lake, Mexico

Abstract

Techniques for monitoring the water quality should have low costs and consider several parameters in order to obtain more efficient analysis of data. This study proposes an application of a multimetric system for the bioassessment of the contamination during dry (May), rainy (July) and post-rainy conditions (November) in the main stream of the LermaChapala basin. It included seven physiochemical determinations for the Water Quality Index (WQI), an Extended Biotic Index (EBI) based on the macrobenthos communities and the application of bioassays on sorghum seeds. The results indicated that according to the levels of the WQI there was a big difference between the river and the lake; during the dry season, the river figures in the scale of polluted to highly polluted, including its entrance to Chapala Lake, the rest of the lake was placed within the interval between low pollution and acceptable. In rainy and post-rainy periods, the river improved and was found within the range of polluted to not very polluted, in the mean time the entire lake was mantained within not very polluted and acceptable. According to the IBE, which was only applied to the river, the upper basin was placed within the range of polluted to severe pollution, while the intermediate and lower basin maintained their highly polluted conditions; for rainy and post-rainy seasons, the conditions improved smoothly. According to the WQI, EBI and the bioassays on dry conditions, the most polluted area in the river was the intermediate basin.