Spatial Patterns of Escherichia coli Concentrations in Sediment before and after High‐Flow Events in a First‐Order Creek

Abstract

Understanding spatial patterns of Escherichia coli in freshwater sediments is necessary to characterize sediments as microbial reservoirs and to evaluate the impact of sediment resuspension on microbial water quality in watersheds. Sediment particle size distributions and streambed E. coli concentrations were measured along a 500‐m‐long reach of a first‐order creek 1 d before and on Days 1, 3, 6, and 10 after each of two artificial high‐flow events, with natural high‐flow events also occurring within the sampling periods. Spatial variability of E. coli was greater in sediments than in water within any given sampling; however, variation between sampling days was greater for water than for sediment. The mean relative difference analysis revealed temporally stable patterns of E. coli concentrations in sediments. Escherichia coli–rich locations along the reach corresponded to areas with higher organic matter and fine particle contents. Although low (k < 0.5 d−1) or negative survival rates were observed at most locations along the reach during times where no precipitation was recorded, a small number of locations showed such large concentration increase that on average the survival rate remained positive at the reach scale. The studied creek appears to have hot spots of concentration increase, where conditions for E. coli populations to increase are much more favorable than in most other locations across the reach. The effect of this increase can be seen at the reach scale but is difficult to discern without individual sampling that is dense in space and time. Core Ideas Temporally stable patterns of E. coli concentrations in sediments were observed. Reach‐average E. coli concentrations increased in sediments between high‐flow events. E. coli survival rates were generally low except in certain locations along the reach.

Microbial Water Quality: Monitoring and Modeling

“…Rich information on ARG in surface waters can be obtained from the whole genome analysis. Taggar et al (2018) assessed antimicrobial resistance in E. coli recovered from untreated surface‐water sources of dairy farms. Their whole‐genome analysis of multidrug‐resistant isolates identifies multiple ARGs, including blaCMY‐2 and blaCTX‐M‐1, that confer resistance to the critically important extended‐spectrum cephalosporins, as well as a variety of plasmids and class 1 integrons.…”

“…Sediment E. coli populations can grow between high-flow events. The rate of such growth was studied by Stocker et al (2018) in highly detailed sampling of streambed sediment across the stream reach before and after artificial and natural highflow events during 1 mo. The authors show that the increase of E. coli in sediment across the reach did occur, but this increase was due to high growth rate in several locations with elevated clay and organic matter contents.…”

“…Observations at coarser scales can reveal emerging patterns or properties that are not detectable at finer scales. Stocker et al (2018) studied E. coli concentration changes in the stream-bottom sediment after high-flow events and reported that growth of the E. coli population was pronounced at the stream-reach scale but could be easily missed with the monitoring at the "singlesample" scale.…”

Should Contact Recreation Water Quality Standards be Consistent across Hydrological Extremes?

“…This deviates from conventional thought that resuspension only occurs during high‐flow events (Jamieson et al ). Using artificial floods, Muirhead et al () and Stocker et al () demonstrated roughly two order of magnitude increases in E. coli concentrations that directly resulted from flow rate induced sediment resuspension. This is not surprising, considering that a literature review by Pachepsky and Shelton () noted that E. coli concentrations can be 1 to 2,200 times greater in sediments than in the water column.…”

“…Nonpoint E. coli sources undergo various fate and transport processes before arriving in streams (Ferguson et al ), thus affecting E. coli and pathogen quantities entering the stream. Regardless of transport mechanism, sediment provides an environmental niche where E. coli can persist for extended periods of time (Garzio‐Hadzick et al ) and potentially grow (Solo‐Gabriele et al ; Stocker et al ). This challenges water managers, as extended persistence and growth can yield E. coli populations that may not be associated with recent contamination events (Anderson et al ), thus diminishing potential relationships between E. coli concentration and human health risk.…”