Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2010
Publication Date: 9/1/2010
Citation: Kyung Hwa, C., Pachepsky, Y.A., Joon Ha, K., Guber, A.K., Shelton, D.R., Rowland, R.A. 2010. Release of Escherichia coli from the bottom sediment in a small first-order creek: Experiment and Modeling. Journal of Hydrology. 391(3-4):322-332. Interpretive Summary: E. coli concentrations in surface water are commonly used to evaluate the microbiological water quality and water suitability for irrigation and recreation. Streambed sediments are known to be reservoirs of E. coli bacteria. However, attempts to monitor and model the impact of re-suspension of E. coli from sediments on water quality are hampered by the extreme variability of E. coli concentrations and release rates from sediments. We created an artificial high flow event in the first order creek, during which flow and E. coli concentrations were measured using automated samplers, Based on this data, a model was developed that accurately predicted both flow rates and E. coli concentrations for the whole stream. The results of this work are important for irrigation and recreation water quality evaluations, in that they allow for improved interpretations of microbial water quality monitoring data. Specifically, the model provides estimates of the relative contributions of E. coli in re-suspended sediments vs E. coli in runoff to changes in water microbial quality caused by rainfall events.
Technical Abstract: E. coli release from streambed sediments may substantially affect microbial water quality. Models of E. coli release and transport commonly use a single set of parameters for the whole stream or reservoir, yet little is known about the magnitude and sources of the variability of parameters of the streambed bacteria release. The objectives of this work were (a) to obtain and compare parameters of streambed E. coli resuspension in three stream reaches with distinctly different bottom sediment textures, and (b) to see whether the modeling of streambed E. coli resuspension with reach-specific parameters could provide substantially better accuracy than modeling with a single set of parameters. Sediment particle size distributions and the streambed E. coli concentrations were measured along a small first order creek in the USDA-ARS OPE3 experimental watershed in Maryland. Afterwards, 80 m3 of water were released into the creek at a rate of 60 L per second in four equal allotments separated by 1 to 3 min intervals. Flow rates and E. coli concentrations were monitored with automated samplers at the ends of the three reaches with a total length of 630 m. A high concentration of streambed E. coli (“hotspot”) resuspended within the first reach caused a pulse of high E. coli concentrations that propagated along the creek without substantial attenuation; inputs of sediment-borne E. coli from the next two reaches were relatively small. The E coli transport model utilized one-dimensional flow and included the Saint-Venant and advective-dispersive equations. The calibrated roughness coefficient values were comparable for the three reaches, whereas the critical stress and the entrainment rate differed among reaches by a half order and an order of magnitude, respectively. Overall, better accuracy was observed when the model contained reach-specific parameters. Additional research is needed to understand which and how sediment properties affect parameters of streambed E. coli release into the water column.