LELAND STANFORD JUNIOR UNIVERSITY, THE
Current assessment of microbial pollution in recreational waters involves measurement of fecal indicator bacteria (FIB) as proxies for human pathogens. FIB concentrations display diurnal variability such that the time the sample is collected dramatically impacts the measured concentration, which could make the difference between compliance and noncompliance with water quality standards. Also, it is not known whether the concentrations of actual pathogens, and thus associated health risk, also experience such fluctuations. Thus, it is critical to obtain information on the processes that control these diurnal fluctuations for FIB and human pathogens. Sunlight is believed to be the major cause of the diurnal fluctuation in FIB. The goal of this project is to develop predictive tools for assessing the sunlight-mediated inactivation of fecal indicator organisms and human viruses under a range of environmental conditions prevalent in natural waters. The specific research objectives involve a coordinated effort by a multidisciplinary team to study sunlight-mediated inactivation in the field, the laboratory, and via modeling. Field work will be conducted at one ocean beach in California and a freshwater beach on Lake Superior. These sites, which differ in salinity as well as the concentration of sensitizer molecules, will be compared with data from a third site for which we already have completed the field work. Field experiments will be used to develop empirical relationships between environmental conditions and inactivation rates of FIB and human viruses. Laboratory experiments will be used to develop a mechanistic understanding of the processes that control inactivation, and to understand the nature of observed differences between organisms and field sites. Field and laboratory data will be combined to develop a model that predicts inactivation rates for any water given easily obtainable environmental. Broad dissemination of the results of this study will be accomplished through publication of peer-reviewed research papers, participation in a conference focused on beach water quality, and direct interaction with policy makers and beach managers. Information gleaned from this study on natural waters will also be extendable to understanding sunlight-mediated inactivation of organisms in other engineered and natural systems, such as solar disinfection of drinking water and waste stabilization ponds. This work will promote teaching, training and learning, as the PIs will involve students in all aspects of the research and will integrate the results obtained into their classroom instruction.