Increasing occurrences of human infectious disease outbreaks arising from environmental pathways highlights the need to better understand the fate and persistence of pathogenic bacteria in the open environment. A risk shared by both developed and undeveloped population centers is exposure to water that has been contaminated with fecal bacteria such as Escherichia coli. To date, the majority of research on E. coli and other fecal bacterial constituents has emphasized understanding their biochemistry, genomics, and host specificity in a clinical or laboratory setting. Much less is known about factors that influence the presence, abundance, persistence, and survival of E. coli and other fecal bacteria in non-host associated environments such as aquatic ecosystems. The purpose of this study was to investigate seasonal patterns in presence and abundance of E. coli, in six urban lakes in and around the city of Lubbock, Texas, USA. Specific objectives of the study were to (1) document long-term seasonal patterns in abundance of E. coli in small urban lentic ecosystems over a continuous three-year period, (2) identify environmental factors, including effects of migratory Canada geese (Branta canadensis) and artificial aeration devices that might influence E. coli abundance, and (3) determine if patterns in E. coli abundance through time were similar for individual lakes. Water samples were collected monthly for 36 consecutive months from each of six study lakes, three of which contained artificial aeration devices (fountains). Standard procedures were used to determine presence and abundance of E. coli as well as for determination of nutrient concentrations of all samples. Stepwise multiple linear regression models were constructed to determine which environmental variables had the greatest influence on E. coli abundance in both summer and winter seasons.
Results/Conclusions
Analyses revealed that E. coli is present in the urban lakes of Lubbock, Texas year-round and typically exceeds the established bacterial loading threshold for recreational waters. Final regression models for both seasons most frequently contained pH and dissolved oxygen as primary predictor variables and explained between 17.4% and 92.4% of the total variation in E. coli abundance. Lakes that contained city installed fountains were found to have a substantially higher oxygen concentration during summer and also contained a consistently lower abundance of E. coli. We conclude that solar irradiation in synergy with pH and dissolved oxygen is the primary control mechanism for E. coli in study lakes and that fountains act to help control the abundance of fecal bacteria within these systems.