The Effect of Temperature Oscillations and Sediment Texture on Fecal Indicator Bacteria Survival in Sediments

Abstract

Fecal indicator bacteria (FIB) inhabiting stream sediments have become a concern with regard to recreational and irrigation water quality. Sediments contain higher concentrations of E. coli and other FIB than the overlying water column. The objective of this work was to evaluate the effect of temperature oscillations on the populations of both E. coli and enterococci in sediments and the water column. The study was conducted in a microcosm system with flow-through chambers representing a small stream with two different sediment textures. Bovine manure was freshly collected and mixed with both clayey and sandy sediment. Temperatures within the chambers oscillated from 17° to 28 °C which is representative of a diurnal summer temperature range for Maryland; the control chambers were kept at 22 °C. The effect of temperature oscillations differed depending on the sediment texture. Bacterial populations in the sandy sediment immediately increased before net die-off began. Conversely, in the chambers with the clayey sediments, there was no immediate increase in concentrations in the oscillation chambers as compared to the controls. There were significantly higher populations of both E. coli and enterococci within the oscillation sandy texture chambers compared to the control constant temperature chambers; that was not the case in the clayey sediment chambers. The die-off rates in the sandy sediments were greater than those in the clayey sediments; in the latter, bacteria populations remained almost constant throughout the experiment. Temperature oscillations should be simulated in experiments designed to estimate and compare inactivation rates for fecal indicator bacteria in sediments for future inferences on microbial water quality.