Genetic fecal indicators : environmental behavior and associated health risks
- Microbial source tracking (MST) markers that target bacterial DNA from the feces of particular animal hosts have been developed over the past two decades. Scientists, regulators, and managers are interested in using MST markers to better understand the problem of microbial contamination at recreational beaches. Certain knowledge gaps exist, however, that hinder our ability to interpret environmental measurements of MST markers. The goal of the research in this dissertation is (1) to characterize the fate and transport of the gull-associated MST marker, both absolutely and relative to Enterococcus (ENT), the standard fecal indicator; (2) to investigate through-beach transport as a pathway by which the gull marker and ENT reach the surf zone; and (3) to predict the health risks of swimming in water contaminated with a gull MST marker, or with a mixture of gull and human MST markers. Chapter 2 presents a study measuring the decay rates of a gull marker and ENT in beach sand and seawater. Indicator concentrations were measured over time in laboratory microcosms filled with natural beach sand and seawater. We found differences in the decay rates among indicators. Therefore, the ratio of indicators from a given contamination event will vary depending on how much time has elapsed since the event. Chapter 3 examines whether seawater circulating through nearshore sand can carry fecal indicators from sand to the surf zone. Laboratory column studies and numerical modeling were used to estimate transport rate coefficients. These transport rate coefficients, as well as decay rate coefficients from Chapter 2, were then input to a field-scale model to calculate transport distances. We found that through-beach pathways only allow the transport of fecal indicators over short distances. In Chapter 4, a Quantitative Microbial Risk Assessment (QMRA) is presented that predicts the probability of illness from swimming at a beach with gull fecal pollution. Monte Carlo simulations were carried out to find risk distributions for different concentrations of the gull MST marker. We found that risk is only elevated above a threshold level at beaches with very high gull impact. Chapter 5 is another QMRA, that examines the risk associated with swimming in water with both gull and human sources. We found that the source of the human marker matters: at all concentrations of the human marker, risk is much greater from a sewage source than a treated effluent source. In addition, we found that at a beach with both gull and human MST markers, the risk is determined by the human marker.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Civil and Environmental Engineering.
|Luthy, Richard G
|Luthy, Richard G
|Statement of responsibility
|Submitted to the Department of Civil and Environmental Engineering.
|Thesis (Ph.D.)--Stanford University, 2016.
- © 2016 by Kendra Irene Brown
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...