The effect of environmental factors on bacterial populations and community dynamics in high rate oxidation ponds

The effect of environmental factors on different bacterial populations and cultivable heterotrophic bacteria community dynamics in an experimental high-rate oxidation pond (HROP) was studied. After 24 months of weekly and bimonthly sampling, the relationships between bacteriological and environmental variables at the outflow of the HROP were modeled. Path analysis applied to the in-situ data provided evidence of very different behavioral models according to bacteriological variables and the scale of sampling. The fecal coliform and fecal streptococci distributions showed seasonal cycles, with low summer and high winter abundances. Solar radiation, water temperature, pH and chlorophyll a concentration were the main environmental variables affecting the temporal dynamics of these bacterial populations, the effects of which were different on each bacterial group. No cyclic behavior was found for Aeromonas spp. whose abundances were irregular and closely related to water temperature and chemical oxygen demand. The temporal dynamic of the cultivable heterotrophic bacteria community was found to be independent of the majority of the model's predictive variables, indicating its maturation as an endogenous community in the high-rate pond ecosystem. These results suggest that fecal-indicator bacteria are controlled by different processes occurring in the high-rate pond than are the Aeromonas spp. and aerobic heterotrophic bacteria.