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.
CBET-0967845 Project dates: June 1, 2011 to May 31, 2014 Harmful microorganisms are the leading cause of impairments in the 300,000 miles of rivers and shorelines and 5 million acres of lakes that do not meet U.S. water quality standards, but predicting the risk of bacteria to public health and allocating load reductions fairly requires accurate models of the key processes of fate and transport. The high concentrations of bacteria in suspended sediment and bed sediment suggest that the understanding of interactions between pathogens and sediment must be improved so that risks to public health can be properly evaluated. Even though sediment disturbance can account for the majority of total fecal contamination, standard water quality models used to determine reductions to pollutant loads do not include resuspension of fecal bacteria as a source. The goal of the proposed work is to improve prediction of fecal indicators in streams. The objectives are to Measure the resuspension of E. coli in controlled laboratory experiments Develop relationships to predict resuspension of attached and unattached E. coli as a function of properties of the flow and sediment Assess the relationships with data collected in the field Equations were developed to predict the resuspension of E. coli as a function of properties of the stream flow and bottom sediments. The equations were adopted from sediment transport theory but modified to represent E. coli present in stream bottom sediments. The physical basis of these equations allows for modification to represent a range of sediment characteristics, flow conditions, and streambed pathogen concentrations. These equations were applied to a range of conditions to examine the impacts of resuspension over different flows and varying sediment:water E. coli ratios as published in the Journal of the American Water Resources Association in 2013. The equations were tested in the field with monitoring data collected in the Squaw Creek watershed, near Ames, Iowa. During the experiment samples of the streambed sediment and the overlying water column were collected on a weekly basis and also each hour during a storm event. The water samples were analyzed for E. coli concentrations in the stream bed sediments and the overlying waters. Results show that E. coli levels in the water column increased by several orders of magnitude during the event. The E. coli levels in streambed sediment also varied considerably. During high flow conditions, a smaller proportion of small particles in streambed sediment were observed, which coincided with reduced levels of E. coli in the streambed sediment. The project lead was Dr. Michelle Soupir, an associate professor in the Agricultural and Biosystems Engineering Department at Iowa State University. Four graduate students, two K-12 teachers, two NSF REU summer interns, and many undergraduate research assistants contributed to the success of this project. Six peer-reviewed journal articles have been published and two additional manuscripts are under review. The work has been presented at 14 conferences as posters or oral presentations. We also provided opportunities for exposure of environmental engineering principals to young people from diverse backgrounds including an Aquatic Ecology Home School Class and through the Science Bound Program at Iowa State University. Science Bound is Iowa State University’s precollege program designed to prepare ethnic minority students for degrees and careers in STEM fields. These activities included analyzing water, soil, and manure samples for E. coli and discussing management practices that might decrease the transport of E. coli to streams and lakes.
