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Fecal contamination of water from a dog park and water potential
changes affecting bacterial survival.
Garfield, Lynell & Walker, Mark
Abstract.
Land use may result in runoff to surface waters, and with
increased urbanization, the proportion of rainfall and snowmelt
occurring as runoff is increased by impervious surfaces. Fecal
matter from companion animals may enter waterways and cause
microbial contamination in drinking and recreational waters. This
research included two studies, a field study at Lake Tahoe that
examined the links between a heavily used dog exercise area and
microbial water quality, and a laboratory study that looked at
effects of evaporation on indicator organism populations losses
through time. The 14 month field study measured fecal accumulation
and distribution on land and E. coli levels in a creek passing
through the site. This study utilized Inverse Distance Weighting to
estimate fecal loading on site, and membrane filtration to test
microbial water quality. Results showed localized loading with an
estimated 45.4 kg dry mass accumulation over the study period.
Results also showed lower E. coli levels downstream from the park
than upstream, with a one-sided Wilcoxon Signed-Rank test (P =
.000+), presumably due to an on-line sedimentation basin on the
creek in the park.
Based on results of the field study, a laboratory study examined
survival of indicator organisms in feces, specifically the
relationship of evaporation to microbial survival. Canine feces were
used to make a standardized sterile matrix, which was inoculated
with E. coli, ATCC strain 25922. An environmental chamber study
examining fecal bacteria degradation in canine feces evaluated
bacterial degradation rates at evaporation conditions of 0.08, 0.21,
and 0.29 in/day. With the data fitted to Chick’s law, estimates of
decay coefficients corresponded to results of -.07, -.22 and
-.23/hr, respectively. Linear regression analysis gave R2 values of
0.69, 0.82, and 0.83, respectively (P = .000+). High and medium rate
studies were not statistically different from one another, but
significantly different from the low rate study. Control studies
showed that high temperatures add to bacterial degradation rates,
and that E. coli survival in feces is mostly limited by water
potential. We measured changing water potential with water content
losses and created a moisture release curve for canine feces. The
data corresponded to previous research stating E. coli would not
survive conditions below ~ -22.4 MPa water potential.
Authors: Lynell@clearmountainstream.com 775-784-4882; mwalker@cabnr.unr.edu
775-784-1938
But, what does it mean?
Dog poop contributes bacteria to nearby surface waters under wet
conditions (no surprise there). Under dry weather conditions,
particularly hot conditions, the bacteria die in the poop and do not
pose much of a threat to nearby surface waters ... unless you step
in it and wash your shoes off in those waters.
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