Composite Analysis for Escherichia coli at Coastal Beaches

["Shannon Briggs" <briggssl@michigan.gov>]

J. Great Lakes Res. 33(2):335-341.
Internat. Assoc. Great Lakes Res., 2007
http://www.iaglr.org//jglr/db/view_contents.php?pub_id=2513&mode=view&table=yes&topic_id=&mode=toc&volume=33&issue=2
 
Composite Analysis for Escherichia coli at Coastal Beaches

Erin E. Bertke, U.S. Geological Survey, 6480 Doubletree Avenue,
Columbus, Ohio, 43229-1111

ABSTRACT: At some coastal beaches, concentrations of fecal-indicator
bacteria can differ substantially between multiple points at the same
beach at the same time. Because of this spatial variability, the
recreational water quality at beaches is sometimes determined by
stratifying a beach into several areas and collecting a sample from each
area to analyze for the concentration of fecal-indicator bacteria. The
average concentration of bacteria from those points is often used to
compare to the recreational standard for advisory postings.
Alternatively, if funds are limited, a single sample is collected to
represent the beach. Compositing the samples collected from each section
of the beach may yield equally accurate data as averaging concentrations
from multiple points, at a reduced cost. In the study described herein,
water samples were collected at multiple points from three Lake Erie
beaches and analyzed for Escherichia coli on modified mTEC agar (EPA
Method 1603). From the multiple-point samples, a composite sample (n =
116) was formed at each beach by combining equal aliquots of well-mixed
water from each point. Results from this study indicate that E. coli
concentrations from the arithmetic average of multiple-point samples and
from composited samples are not significantly different (t = 1.59, p =
0.1139) and yield similar measures of recreational water quality;
additionally, composite samples could result in a significant cost
savings.

KEYWORDS: Beach, composite, E. coli, monitoring, recreation.


 

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