Descriptive and Statistical Assessment of Escherichia coli in a Suburban Lake for Management Purposes Open Access

Abstract

INTRODUCTION Current research efforts focus on contamination in water bodies with obvious risk of exposure and economic impact, such as larger lakes with beaches. Improved surveillance methods increasingly link small scale outbreaks to recreational freshwater. This linkage has implications for lake management. A small neighborhood lake in suburban Georgia is the focus of this investigation into environmental predictors of Escherichia coli (E. coli). The study will address four aims: 1) determine if E. coli concentrations exceed recommended standards for recreational water, 2) assess correlations between variables to determine likely predictors of E. coli levels 3) develop a predictive model that may be used to 4) inform future lake management decisions.

METHODS Data was compiled from publicly available sources including Georgia Adopt-A-Stream, National Oceanographic and Atmospheric Administration Climate Data Online, National Aeronautics and Space Administration Earth Observatory, and community-hired contractor lake service reports. E. coli counts were collected from three sites: the inflowing creek, the outflow edge of the lake, and the outflow creek. Associations between environmental factors were assessed by Pearson and Spearman correlations to determine parameters for a predictive model for E. coli in Lake Avondale. Environmental variables considered include air temperature, conductivity, dissolved oxygen (DO), fecal coliform, insolation, month, pH, season, sampling site, and water temperature. Multivariate linear regression and logistic regression models were developed to investigate the relationships of environmental factors with the dependent variable, E. coli concentration and presence, respectively.

FINDINGS Multivariate linear regression found conductivity, log-transformed precipitation, and sampling site predict log-transformed E. coli. Investigation of interaction terms resulted in an over-specified model of E. coli concentration by conductivity, sampling site, insolation, pH, log-precipitation, water temperature, dissolved oxygen, season, interaction between dissolved oxygen and season. Logistic regression found conductivity and dissolved oxygen predict E. coli presence. Limitations include small sample size and convenience sampling at irregular intervals across space and time. Results suggest key environmental factors such as precipitation, conductivity, and dissolved oxygen be considered or controlled during lake management decisions. For a community actively engaged in the management of a local lake concerns regarding water quality are valid. Extending that concern to questions of health risks while perhaps not a dire concern is a reasonable discussion to promote evidence-based lake management.

Table of Contents

Chapter I: Introduction 1

Background 1

Problem

Statement 5

Purpose Statement 6

Specific Aims 6

Significance Statement 6

Research Question 7

Hypothesis 7

Ethics 7

Chapter II: Literature Review 8

Recreational Water-Associated Outbreaks 8

Pathogens of Interest 9

Enteric Bacteria 9

Protozoan Parasites 10

Enteric Viruses 11

Other Pathogens 11

Indicator Organisms 12

Sources of Contamination 12

Measures of Microbial Water Quality 13

Coliform Bacteria 13

E. coli 13

Conductivity 14

Dissolved Oxygen 15

Insolation 15

pH 16

Temperature 16

Transparency and Turbidity 17

Exposure 17

Water Quality and Dogs 18

Lake Management 18

Factors of Importance 18

Nutrients 19

Pesticides 20

Metals 20

Buffer Region 20

Color 21

Algae and Fish 21

Canada Geese and Other Waterfowl 22

Precipitation 24

Upper Ocmulgee River Watershed 24

Bess Walker Park, Avondale Estates 25

Lake Management in Bess Walker Park 25

Fauna of Bess Walker Park 26

Geese of Bess Walker Park 26

Pesticides and Bess Walker Park 27

Results of Studies Investigating the Problem - Interrelationships Between Variables 28

Risk Assessment 29

Current problem and relevance to target population 30

Chapter III: Manuscript 31

Abstract 31

Introduction 32

Methods 34

Data Sources 34

Data Analysis 36

Results 39

Descriptive

Results 39

Correlation

Results 40

Linear Regression Results 41

Logistic Regression Results 43

Discussion 43

Conclusion 48

Chapter IV: Conclusion and Recommendations 50

Conclusions 50

Recommendations

for Lake Avondale 50

Recommendations for Future Studies 51

Extended Discussion of Canada Geese 52

Volunteer Data Collection 53

Public Health Implications 53

Chapter V. Report to the Community 54

Tables and Figures 56

Table 1: Descriptive statistics of continuous environmental factors 56

Figure 1: Comparison of E. coli concentration by sampling site 57

Table 2: Yearly compliance with EPA monthly E. coli regulation 57

Table 3: Monthly compliance with EPA monthly E. coli regulation for recreational 58

Figure 2: Comparison of environmental variables across the three sampling sites 59

Table 4: Results of simple linear regression analysis of environmental variables with log-transformed E. coli to assess bivariate association 60

Table 5: Comparison of multivariate linear models for predicting E. coli concentrations in Lake Avondale based on environmental factors 60

Table 6: Correlation matrix comparing environmental parameters using correlation coefficients and the associated p-values 61

Table 7: Parameter estimates for the full eight--variable predictive linear regression model of log-transformed E. coli in Lake Avondale 62

Table 8: The parameter estimates for the reduced model based on backwards selection from the eight-variable predictive model of log-transformed E. coli 62

Table 9: The parameter estimates for the reduced model with potential outliers identified by jackknife residuals, removed 62

Table 10: Parameter estimates for the reduced nine-variable predictive linear regression model including investigation of interaction terms 63

Figure 4: Numbers of geese relocated annually from Lake Avondale, Avondale Estates, Georgia 63

References 64

Appendix 75

Appendix A: Acronyms 75

Appendix B: Definitions of Terms 76

Appendix C: Regulations on Fecal Coliforms and E. coli .77

Appendix D: Estimated Water Ingestion During Water Recreation Activities 78

Appendix E: Proportions of Microbial Etiologic Agents Associated with Recreational Water Outbreaks 79

Appendix F: Key Water Quality Concerns for Selected Lake Uses 80

Appendix G: Data Sources 81

Appendix H: Map of Plan for Bess Walker Park 82

Appendix I: Locations of Sampling Sites 83

Appendix J: Extended Site Description 85

Appendix K: Monthly Precipitation Data 86

Appendix L: Photos from Lake Avondale 87

Appendix M: Relative Location of Lake Avondale 88

About this Master's Thesis

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School	Rollins School of Public Health
Department	Environmental Health
Degree	MPH
Submission	Master's Thesis
Language	English
Research Field	Environmental Health
Keyword	Escherichia coli Lake management Water quality
Committee Chair / Thesis Advisor	Kirby, Amy, Emory University
Committee Members	Tolbert, Paige, Emory University Levy, Karen, Emory University Warren, Camilla, EPA, Lake Avondale Advisory Board
Partnering Agencies	Georgia state or local agency (not a health department)

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