E. coli release from streambed to water column during base flow periods: a modeling study

Authors: PARK, YOUNGEUN - Us Forest Service (FS); Pachepsky, Yakov; HONG, EUNMI - Orise Fellow; Shelton, Daniel; Coppock, Cary

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2016
Publication Date: 12/28/2016
Citation: Park, Y., Pachepsky, Y.A., Hong, E., Shelton, D.R., Coppock, C.R. 2016. E. coli release from streambed to water column during base flow periods: a modeling study. Journal of Environmental Quality. 46(1):219-226.

Interpretive Summary: Microbial quality of water is evaluated by measuring concentrations of the indicator bacterium, E. coli. Prior research has shown that E. coli are distributed between the water column and sediments. During high low events (rainfall) bottom sediments can be resuspended, resulting in E.coli concentrations increased by orders of magnitude in the water column. There have been indications that E. coli from sediment may increase concentrations in the water not only during high flow events but also during base flow, or low flow, events. We tested this hypothesis with data on flow and bacteria concentrations in a creek in Southern Pennsylvania. A substantial E. coli influx into the creek water column was found during the base flow period. Consequently, the microbial quality of the water was unsatisfactorily independent of any other processes (e.g. runoff). This finding indicates that there may be a disconnect between management practices regarding animal waste and manures on the one hand, and microbial quality of water on the other hand, unless sediment-borne E. coli contributions to the water column are taken into account. Results of this work will be of use for a wide range of environmental professionals concerned with microbial quality of water from freshwater sources.

Technical Abstract: Microbial quality of stream water is important for recreation, irrigation, and other uses. It is usually evaluated by concentrations of fecal indicator bacteria (FIB) such as E. coli. Streambed sediments have been shown to harbor large FIB populations that could be released into the water column during high-flow events when sediments are resuspended. The objective of this work was to investigate the hypothesis that FIB release occurs also during base flow. As the starting point, we used data from a previous study conducted at the Little Cove Creek, PA, where E. coli release from bottom sediments was modeled using the watershed-scale water quality model SWAT. Further analysis of the results showed that the base flow concentrations were underestimated, suggesting that there is release of E. coli into the water column during base flow periods. We hypothesized that the active release was proportional to E coli concentrations in the sediment, while the passive release was proportional to both concentrations in sediment and groundwater flow. Rates of both types of E. coli release were calibrated for three creek reaches with data from 2008. Model performance was substantially improved when both passive and active release were accounted for, i.e. model simulations were more accurate. The active impact appeared to be preferable. Consequently, release of E. coli from streambed sediments during periods of base flow means that water column E. coli concentrations are dependent not only on land management practices, but also on in-stream processes during base flow periods. This dependence needs to be evaluated before using E. coli to evaluate the impact of land management practices on watersheds.