Use of the thermotolerant Aeromonas group for the trophic state classification of freshwaters

Abstract

Data obtained from 68 lakes surveyed in the United States showed a highly significant correlation between the densities of a specific group of autochthonous, heterotrophic bacteria, thermotolerant aeromonads and the trophic state of fresh waters. This measurement provides a sensitive, accurate and facile descriptor of limnetic water quality and shows strong correlations with certain other commonly employed physical, chemical and biological parameters used in this regard. The best correlations were obtained with Secchi depth ( r = −0.70 ), total phosphorus ( r = 0.72 ) and chlorophyll α ( r = 0.67 ). An even stronger correlation was obtained with a trophic index derived from these three parameters ( r = −0.84 ). Alternatively, total heterotrophic bacterial populations, as enumerated by epifluorescence microscopy, were very poorly correlated with all the individual trophic state measurements, and the indices derived from them. An analysis of correlation coefficients for trophic state parameters and indices used for this study indicated that the level of thermotolerant aeromonads was one of the most discriminating single parameters for defining trophic state. The economy of the measurement, coupled with its facility, makes it an exceptionally promising technique for assessing the degree and rate of fresh water eutrophication.