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Understanding E. coli behavior important for improving water quality

Doctoral student Sadia Salam runs water samples through a filter
Doctoral student Sadia Salam runs water samples through a filter to collect bacteria and evaluate E. coli levels in sediment in Skunk Creek in southeastern South Dakota.

Bacteria levels in many South Dakota streams are too high.

Of the more than 5,800 miles of rivers and streams assessed in the state between October 2010 and September 2015, 78 percent were impaired, meaning they were unfit for one or more of their designated uses, according to the South Dakota Department of Environment and Natural Resources 2016 Integrated Report on Surface Water Quality. The most common cause of impairment is bacteria.

To help decrease bacteria levels, South Dakota State University Assistant Professor Rachel McDaniel, a water resource engineer in the Department of Agricultural and Biosystems Engineering, and Professor Bruce Bleakley of the Department of Biology and Microbiology are studying the behavior of E. coli in sediment and in moving water. Common E. coli sources are pets, livestock, wildlife and leaky septic tanks.

Master’s student Louis Amegbletor removes a filter that collects bacteria.
Master’s student Louis Amegbletor removes a filter that collects bacteria.

“E. coli is used as an indicator organism, signaling the presence of pathogens from fecal material,” McDaniel explained. The presence of high E. coli concentrations indicates the likely presence of more dangerous fecal-borne viruses and bacteria which are hard to screen for, Bleakley added.

Through a yearly grant from the Water Resource Institute through the U.S. Geological Survey, McDaniel and Bleakley are examining how turbulence and attachment. E. coli attached to larger particles, such as sand and silt, affects the distance the bacteria travel during natural events, such as a rainstorm. The goal is to figure out how these storm events affect water quality. One master’s student has been working on this since May 2016.

“When E. coli grabs onto large particles, it tends to settle out into the stream bed faster,” McDaniel explained. “The unattached bacteria are more buoyant and travel longer distances in the water column.”

The researchers track attachment by taking water samples during a storm event. One set of data with samples taken every 30 minutes over a 5-hour period showed that only 25 percent of bacteria readily settled to the bottom. That means 75 percent of the bacteria stayed afloat for a longer time and have a greater chance of causing impairments to water quality, McDaniel explained.

Understanding how E. coli behave in streams will help scientists determine how to reduce high bacteria counts in waterways.