Abstract
Geometric mean concentrations of fecal indicator bacteria E. coli and enterococci are commonly used to evaluate the microbial quality of irrigation, recreation, and other types of waters, as well in watershed-scale microbial water quality modeling. It is not known how the uncertainty of those geometric mean concentrations depends on the time period between sampling. We analyzed data collected under baseflow conditions from three years of weekly and several daily sampling campaigns at Conococheague Creek in Pennsylvania. Standard deviations of logarithms of geometric mean concentrations were computed over weeks, months, and seasons. The increase in standard deviations from weekly to seasonal time scale was on average about 0.1 and 0.2 for log(E. coli) and log(enterococci), respectively, and in most cases was statistically significant. This may need to be accounted for when evaluating the uncertainty of measurements for modeling purposes and in risk assessment of microbial water quality.
Highlights
Geometric mean concentrations of fecal indicator bacteria E. coli and enterococci are commonly used to evaluate the microbial quality of irrigation, recreation, and other types of waters, as well in watershed-scale microbial water quality modeling
Studies of the uncertainty of geometric means of indicator bacteria concentrations have a substantial history in the research addressing health issues (i.e. Gronewold et al.[6]; Heberger et al.7), no data are available on the effect of time scale over which the geometric mean was computed on the uncertainty in the value of this geometric mean
The work of Muirhead and Meenken[8] presents the only known to us exemption; the authors examined the differences of temporal variability under baseflow condition at different relatively short time scales and observed the increase in variability with the increase of time scale
Summary
Geometric mean concentrations of fecal indicator bacteria E. coli and enterococci are commonly used to evaluate the microbial quality of irrigation, recreation, and other types of waters, as well in watershed-scale microbial water quality modeling It is not known how the uncertainty of those geometric mean concentrations depends on the time period between sampling. The increase in standard deviations from weekly to seasonal time scale was on average about 0.1 and 0.2 for log(E. coli) and log(enterococci), respectively, and in most cases was statistically significant This may need to be accounted for when evaluating the uncertainty of measurements for modeling purposes and in risk assessment of microbial water quality. Food and Drug Administration (FDA) has suggested to use generic Escherichia coli (E. coli) and enterococci as indicators of fecal contamination for recreational water and irrigation water[4] Both regulatory agencies use the geometric mean of those indicator bacteria concentrations. The objective of this work was to evaluate and compare the temporal variability of the geometric mean concentrations of E. coli and enterococci in a creek at weekly, monthly, and seasonal time scales for the intensively monitored large creek in Pennsylvania with multiple water uses
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
