BEACHNET==> new article on small-period variations (1-10 min) of enterococci in diverse environments

[Meredith Nevers <mnevers@usgs.gov>]

Enterococci Concentrations in Diverse Coastal Environments Exhibit
Extreme Variability
Environ. Sci. Technol., 41 (24), 8227–8232  10.1021/es071807v

Alexandria B. Boehm

Fecal indicator bacteria (FIB) concentrations in a single grab sample
of water are used to notify the public about the safety of swimming in
coastal waters. If concentrations are over a single-sample standard,
waters are closed or placed under an advisory. Previous work has shown
that notification errors occur often because FIB vary more quickly
than monitoring results can be obtained (typically 24 h). Rapid
detection technologies (such as quantitative polymerase chain
reaction) that allow FIB quantification in hours have been suggested
as a solution to notification errors. In the present study, I explore
variability of enterococci (ENT) over time scales less than a day that
might affect interpretation of FIB concentrations from a single grab
sample, even if obtained rapidly. Five new data sets of ENT collected
at 10 and 1 min periodicities for 24 and 1 h, respectively, are
presented. Data sets are collected in diverse marine environments from
a turbulent surf zone to a quiescent bay. ENT vary with solar and
tidal cycles, as has been observed in previous studies. Over short
time scales, ENT are extremely variable in each environment even the
quiescent bay. Changes in ENT concentrations between consecutive
samples (1 or 10 min apart) greater than the single-sample standard
(104 most probable number per 100 mL) are not unusual. Variability,
defined as the change in concentration between consecutive samples, is
not distinct between environments. ENT change by 60% on average
between consecutive samples, and by as much as 700%. Spectral analyses
reveal no spectral peaks, but power-law decline of spectral density
with frequency. Power-law exponents are close to 1 suggesting ENT time
series share properties with 1/f noise and are fractal in nature.
Since fractal time series have no characteristic time scale associated
with them, it is not obvious how the fractal nature of ENT can be
exploited for adaptive sampling or management. Policy makers, as well
as scientists designing field campaigns for microbial source tracking
and epidemiology studies, are cautioned that a single sample of water
reveals little about the true water quality at a beach. Multiple
samples must be taken to gain a snapshot into the patchy structure of
microbial water quality and associated human health risk.



--
Alexandria Boehm, PhD
Clare Boothe Luce Assistant Professor
Department of Civil and Environmental Engineering
Environmental Engineering & Science
Terman Engineering Center M7
Stanford University
Stanford, CA 94305-4020
tel: 650 724-9128
fax: 650 725-3164
website: http://www.stanford.edu/~aboehm



-- 
Alexandria Boehm, PhD
Clare Boothe Luce Assistant Professor
Department of Civil and Environmental Engineering
Environmental Engineering & Science
Terman Engineering Center M7
Stanford University
Stanford, CA 94305-4020
tel: 650 724-9128
fax: 650 725-3164
website: http://www.stanford.edu/~aboehm


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Meredith B. Nevers
Aquatic Biologist
U.S. Geological Survey
Lake Michigan Ecological Research Station
1100 N. Mineral Springs Rd.
Porter, IN 46304
phone (219) 926-8336  ext. 425   fax (219) 929-5792
mnevers@usgs.gov
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