2012 Annual Report
1a.Objectives (from AD-416):
The overall objective of this project is to improve our understanding of and ability to predict the transport and fate of pathogenic microorganisms at various spatial scales (from pore to plot scale).
1b.Approach (from AD-416):
Laboratory experiments will be designed to test specific hypotheses with regard to mechanisms controlling pathogen transport and fate in the environment. The specific experimental approaches and techniques will depend on the research question. For example, we may use measurements of electrophoretic mobility, hydrophobicity, surface charge density, enzyme treatment, FTIR, and TEM imaging to examine surface properties of pathogens that influence their interaction in the environment. We may use batch, micromodel systems, DLVO calculations, pore-scale flow and transport simulation techniques, and saturated and unsaturated column experiments to examine mechanisms of pathogen transport, retention, and survival. Information collected from laboratory studies will be used to refine and improve the predictions of models for pathogen transport and fate. Existing models for pathogen transport and survival will be modified to simulate field scale behavior.
Laboratory and numerical studies were continued to investigate the transport and fate of E.coli D21g and coliphage fX174 in saturated soils with preferential flow under different solution ionic strength (IS=1, 5, 20, and 100 mM) conditions. Complementary transport experiments were conducted in homogeneous sand columns to identify controlling transport and retention processes, and to independently determine model parameters for numerical simulations in the heterogeneous experiments. Results from homogeneous and heterogeneous transport experiments demonstrate that retention of E. coli D21g and fX174 increased with IS, while the effect on E. coli D21g in finer sand was much greater than in coarse sand. The importance of preferential flow on microbe transport was found to be enhanced at higher IS, even though the overall transport decreased. However, the contribution of preferential flow was much higher for E. coli D21g than fX174.
Researchers from the ARS and University of California at Riverside (UCR) coordinate the work schedules and objectives for all personnel that are funded through this SCA and meet with them on a regular basis to discuss progress. UCR provides ARS with a SCA budget on a monthly basis. The objectives of the SCA and parent project complement each other. For example, one objective of the parent project, "Develop managment practices to minimize the transport of pathogens from concentrated dairy and beef cattle operations to water resources" directly relates to our experiments examining pathogen transport during overland flow. Preferential transport of pathogens will also occur during overland flow and this has been studied as part of the SCA research described above.