Resuspension Of E. Coli In Sediment Laden Streams

<p>The PI proposes laboratory experiments to measure resuspension of E. coli from a sediment bed and field experiments to test the resuspension relationships developed from the laboratory results. Even though previous work suggests that sediment disturbance can account for the majority of total fecal contamination, standard water quality models do not include resuspension of fecal bacteria as a source. The PI previously showed that including interactions between the sediment and the water column can improve predictions of microbial concentrations, but because most models that include resuspension of bacteria either specify a resuspension rate or calibrate as a function of only discharge, better ways to predict resuspension are needed. The main benefit of the proposed work is the ability to identify, control, and isolate the parameters affecting resuspension so that relationships to predict resuspension can be developed and tested. The objectives of the proposed work are to (1) measure the resuspension of E. coli in controlled laboratory experiments, (2) develop relationships to predict resuspension of attached and unattached E. coli as a function of properties of the flow and sediment, and (3) assess the relationships with data collected in the field. They hypothesize that (a) the resuspension rate of attached E. coli will be proportional to the resuspension rate of sediment because the attached fraction in the water column will be the same as that in the sediment bed and (b) resuspension of unattached E. coli will occur at lower shear stresses than for attached E. coli. These hypotheses are encapsulated in a physically based, quantitative framework proposed to predict resuspension. The intellectual merit of the proposed research comes from the ability to isolate and control important parameters affecting resuspension. Laboratory experiments with flow over three types of sediment will provide the first measurements of E. coli resuspension in which flow rates and sediment properties are varied systematically. Data from the laboratory experiments will be used to test and develop physically based relationships to predict resuspension of E. coli as a function of properties of the flow, sediment, and organisms. To test the formulas derived from laboratory experiments in the field, resuspension rates computed from a mass balance applied to a reach of Squaw Creek in Ames, IA will be compared to the predictions. The resulting physically based relationships will be important for reducing the parameterization of water quality models, and the laboratory experiments will provide information over a range of conditions that will help to guide the application of our results in water quality modeling. Preliminary results, as well as previous work on sediment resuspension, show that the flume experiments will be useful for studying resuspension of E. coli. The broader impacts include training a graduate student and undergraduate student; conducting outreach to schools; mentoring a new assistant professor; helping the Iowa Department of Natural Resources, which is responsible for developing total maximum daily loads, to incorporate the research results into watershed scale water quality models to develop more realistic load allocations; and collaborating with the Ames Water and Pollution Control District, which is considering adding disinfection to the wastewater treatment plant in Ames, Iowa. Careful measurements and improved models of the fate and transport of E. coli in streams will improve predictions of conditions where a risk to human health is likely and the implementation of land management practices to reduce bacterial pollution in the nation?s water bodies.</p>