Nutrient loading impacts on culturable E. coli and other heterotrophic bacteria fate in simulated stream mesocosms

Authors: GREGORY, LUCAS - Texas Water Resources Institute; KARTHIKEYAN, R - Texas A&M University; PETERSON-AITKENHEAD, J - Texas A&M University; GENTRY, T - Texas A&M University; WAGNER, K - Texas Water Resources Institute; Harmel, Daren

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2017
Publication Date: 10/6/2017
Citation: Gregory, L.F., Karthikeyan, R., Peterson-Aitkenhead, J., Gentry, T.J., Wagner, K.L., Harmel, R.D. 2017. Nutrient loading impacts on culturable E. coli and other heterotrophic bacteria fate in simulated stream mesocosms. Water Research. 126:442-449.

Interpretive Summary: Understanding bacteria persistence in streams and lakes is important when making management decisions to improve instream water quality. Routinely, bacteria fate and transport models that rely on published bacteria death/growth relationships are used to inform such decision making. The objective of this work was to evaluate bacteria response to applied nutrients. Re-created artificial streams were established in the laboratory and filled with water and sediment from a small, 3rd order southeastern Texas stream. Treatments consisted of low or high nutrient doses above ambient water concentrations operated at low or high flow rates. Two types of bacteria concentrations were quantified in water and sediment over 22 days. No significant differences in death/growth relationships were observed among fecal bacteria (E. coli) in water or sediment, and only fecal bacterial in sediment showed any growth response. However, other bacteria exhibited a pronounced growth response in water and sediment within 24 hours of nutrient addition but did not differ significantly from the control conditions. Significant growth/death relationship differences between E. coli and other bacteria in water were identified but did not differ significantly in sediment. Results indicate that nutrient addition does affect microbial activity instream, but competition from other bacteria appears to prevent any potential E. coli growth response.

Technical Abstract: Understanding fecal indicator bacteria persistence in aquatic environments is important when making management decisions to improve instream water quality. Routinely, bacteria fate and transport models that rely on published kinetic decay constants are used to inform such decision making. The objective of this work was to evaluate bacteria response to applied nutrient amendments. Re-created stream mesocosms were established in laboratory-based, repurposed algae raceways filled with water and sediment from a small, 3rd order southeastern Texas stream. Mesocosm treatments consisted of low (10x) or high (50x) nutrient doses above ambient water concentrations operated at low (0.032 m/s) or high (0.141 m/s) flow rates. Escherichia coli and heterotrophic bacteria concentrations were quantified in water and sediment over 22 days. No significant differences in kinetic constants were observed among E. coli in water or sediment, and only E. coli in sediment showed any growth response. Heterotrophic plate counts revealed a pronounced growth response in water and sediment within 24 hours of nutrient addition but did not differ significantly from control mesocosms. Significant kinetic constant differences between E. coli and heterotrophic bacteria in water were identified (p<0.01) but did not differ significantly in sediment (p>0.48). Results indicate that nutrient addition does affect microbial activity instream, but competition from heterotrophic bacteria appears to prevent any potential E. coli growth response.