Temporal variation in the abundance of heterotrophic bacteria in the river Cauvery and its down stream tributaries

A two year study of temporal variation in abundance of heterotrophic bacteria was carried out from February 2000 to January 2002, in the surface waters of river Cauvery, and its downstream tributaries. The data suggest that two heterotrophic bacterial communities (Free Living Bacteria, FLB and Particle Bound Bacteria, PBB) were both quantitatively and qualitatively different from each other. From the literature it is evident that in oligotrophic and mesotrophic aquatic habitats less than 1% of total bacteria can be grown on artificial media. But in the present investigation, we report that as much as 5% of the total bacteria from rivers Cauvery, Kapila, Shimsha and Arkavathy and as much as 7% from river Suvarnavathy could be grown on artificial media. The study also revealed that several environmental variables were potentially responsible for much of the temporal variation in heterotrophic bacterial abundance, particularly in river Suvarnavathy and Arkavathy suggesting the probability of stressed environment in these ecosystems. The probable causes for all such variations in these lotic ecosystems are discussed.