Occurrence of Aeromonas hydrophila in Limnetic Environments: Relationship of the Organism to Trophic State

The densities of Aeromonas hydrophila in various natural waters were found to be strongly correlated with a relative index proposed for use in trophic state assessments of freshwaters. No such correlation was found with the recoverable heterotrophic population of which A. hydrophila is a part. A. hydrophila was found to be seasonally distributed with maximal densities occurring during summer through early fall. It was also found to be spatially distributed within a pond with the most consistent densities occurring from 1 m depth down to that depth in the water column where the temperature reaches 16°C. The densities of the organism correlated most strongly with total phosphorus, chlorophyll a, and Secchi depth. Moderate correlations were found with dissolved phosphorus, Kjeldahl nitrogen, and dissolved organic carbon. Little or no correlation was obtained with ammonia, orthophosphate, pH, alkalinity, or dissolved oxygen. The discriminating ability that the A. hydrophila density measurements provide in the oligotrophic through mesotrophic range appears to exceed those of presently available methods. The facility and sensitivity of the enumeration method for A. hydrophila should make it a useful tool for trophic state assessments.