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Applied and Environmental Microbiology, December 1999, p. 5628-5630, Vol. 65, No. 12
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Seasonal Enumeration of Fecal Coliform Bacteria
from the Feces of Ring-Billed Gulls (Larus delawarensis)
and Canada Geese (Branta canadensis)
K. A.
Alderisio* and
N.
DeLuca
New York City Department of Environmental
Protection, Bureau of Water Supply, Quality, and Protection,
Division of Water Quality Control, Valhalla, New York 10595
Received 27 April 1999/Accepted 1 October 1999
 |
ABSTRACT |
Water suppliers have often implicated roosting birds for fecal
contamination of their surface waters. Geese and gulls have been the
primary targets of this blame although literature documenting the fecal
coliform content of these birds is quite limited. To determine the
actual fecal coliform concentrations of these birds, fecal samples from
249 ring-billed gulls and 236 Canada geese in Westchester County, N.Y.,
were analyzed over a 2-year period. Results indicate that gull feces
contain a greater average concentration of fecal coliform bacteria per
gram (3.68 × 108) than do goose feces (1.53 × 104); however, average fecal sample weights of the geese
were more than 15 times higher than those of the gulls.
| |
TEXT |
The enumeration of fecal coliform
bacteria (FC) has been widely used as an indicator of fecal pollution
in drinking water supplies and is relatively quick and inexpensive to
monitor (1). The New York City Department of Environmental
Protection (NYC DEP) monitors its water supply for FC in many streams,
lakes, and reservoirs throughout the watershed. Often in the past, FC concentrations in the Kensico Reservoir in Westchester County, N.Y.,
became elevated in the autumn and winter periods, coincident with the
increased roosting of ring-billed gulls (Larus delawarensis) and Canada geese (Branta canadensis) (9). It
appeared that the birds were adversely affecting the water quality,
considering the numbers of birds, location of overnight roosting, and
length of stay; however, the quantitative impact could not be
determined since the potential FC loading of these birds was not known.
The promulgation of the Surface Water Treatment Rule in 1991 required NYC DEP to comply with FC concentration regulations, and as a result, a
study of the relationship between waterfowl presence and fecal coliform
concentrations in the reservoir was implemented. Bird counts were
performed in different areas of the reservoir, and results indicated
that sample sites associated with large numbers of roosting waterfowl
showed a significant correlation with elevated fecal coliform levels
(r = 0.50, P = 0.01), whereas samples
from sites with no waterfowl present often contained counts of <1
FC/100 ml (9). In 1992, a formalized and benign waterfowl mitigation program was implemented and the seasonal FC elevation at the
Kensico Reservoir attributable to birds was largely eliminated.
Some investigators have determined the FC concentration of gull feces;
however, it was done in other countries or in captivity or collection
was short-term (5, 7). Others have associated the FC impact
of waterfowl with the degradation of water supplies but have not
directly enumerated levels of FC in bird feces (2, 3, 6,
10). This study was designed to document the possible impact of
the bird feces on the water quality of the Kensico Reservoir by
determining the FC loading potential of the birds.
Sample collection.
Known grazing areas for the gulls and geese
in Westchester County, N.Y. were visited on a regular basis for sample
collection. Droppings were collected in situ immediately after
defecation by the birds was observed. Feces were collected with sterile
1-ml tuberculin syringes and forceps and placed into sterile,
preweighed 50-ml centrifuge tubes with screw caps. Caution was used so
that any surrounding material from the ground or grass area of
defecation was not gathered. When notable interference was likely, the
sample was passed over and not collected. Tubes were labeled, placed in
a cooler with ice packs, and returned to the laboratory for processing
within 4 h of the time of collection. Physical descriptions of the
feces were also noted (e.g., solid, liquid, color). Samples were
collected from 249 ring-billed gulls and 236 Canada geese over the
course of 2 years, from September 1995 to September 1997.
Sample analysis.
All 485 fecal samples were analyzed
independently. Fecal samples were analyzed for overall average
concentration and weight, as well as potential seasonal variation for
both bird species. Tubes were weighed upon arrival to the laboratory,
and the net weights of the samples were determined. To be consistent,
the weight of each fecal sample was multiplied by nine to determine the
amount of sterile buffered water to be added to each tube to yield a
101 dilution. Ten-fold serial dilutions were performed, up
to 107. Some of the goose samples were not analyzed in
their entirety for FC concentration, since portions of the feces
occasionally had to be removed to include the buffer. Centrifuge tubes
were shaken vigorously and then vortexed for 2 min, and aliquots of 10-fold serial dilutions were pour plated with mFC agar (Difco) onto
15- by 100-mm petri dishes (1). Samples were inverted and
incubated in a water bath at 44.5°C for 24 ± 2 h
(1).
Incubated plates were observed for the optimum number of CFU, between
30 and 300 colonies per plate (1), and blue colonies were
counted from the appropriate dilution with the aid of a Quebec colony
counter. Final results were calculated as
w/CFU(d) = 1/x, where
w is the weight of the fecal sample, CFU is the number of colonies counted, d is the dilution factor, and x
is the number of fecal coliforms per gram (wet weight) of feces.
Quality control consisted of routine sterility procedures recommended
by Standard Methods for microbiological analyses (
1).
Duplicates were performed on 58 separate samples that were collected
at
times spread out over the duration of the study. No data were
rejected
based on paired data, although one point failed the rule
of Hugh Error
based on the log difference between the duplicates.
The average log
difference was 0.1, which is the relative precision
of this technique.
Criteria for counting FC followed those of
the manufacturer (Difco) and
consisted of counting all blue colonies,
since over 93% of the blue
colonies that develop on mFC medium
at the elevated temperature of
44.5 ± 0.2°C are reported to be
FC (
4). Over 250 blue colonies were verified by using blood
agar and MacConkey agar,
followed by biochemical identifications
(API 20E; bioMerieux
Vitek).
The data show that the average fecal sample weights were relatively
consistent within each bird type over the 2 years studied,
with the
exception of the winter of 1997, when the average weight
of goose
samples was 30% lower than the average from all seasons
(Table
1). The winter of 1997 was extremely mild
and may have
somehow influenced the average fecal weight for that
season. Fecal
sample weights collected from 171 geese ranged from 0.44 to 25.4
g, with a mean of 8.35 g per goose fecal sample.
Individual samples
collected from 249 gulls ranged from 0.01 g to
an unusually high
2.49 g, with a mean of 0.48 g per gull
fecal sample. There were
no significant differences in the seasonal
averages for the gull
fecal sample weights, which ranged from 0.42 to
0.54 g. Weights
documented in this study should be considered
conservative since
some goose and gull fecal samples were not collected
in their
entirety.
Concentration data indicate that the ring-billed gull feces contain a
greater concentration of FC/gram than those of the Canada
geese. Over
the course of the 2 years, the 249 gull samples averaged
3.68 × 10
8 FC/g of feces while the 236 goose samples averaged
1.53 × 10
4 FC/g (Table
2). Average FC concentrations of the gull
feces
for the eight consecutive seasons studied ranged from 5.84 × 10
7 to 1.52 × 10
9 FC/g of feces. The
seasonal averages were all within the same
order of magnitude,
suggesting a fairly stable FC concentration
in the gull feces.
Conversely, the goose fecal results were more
variable. The FC
concentrations for the eight seasons of goose
samples varied from an
average of 4.50 × 10
3 to 2.42 × 10
7
FC/g (wet weight) of feces, with seasonal averages ranging from
5.15 × 10
4 to 1.21 × 10
7 FC/g (wet
weight) of feces, demonstrating less stability in their
concentrations
than the gull samples. The difference in variability
may be explained
by the different eating habits of these birds,
the goose being more of
a grazer than an omnivore. The lowest
average goose FC concentration
occurred during the winter of 1997,
corresponding with the season with
the lowest average goose fecal
weight.
In all, the data indicate that the feces from these birds, especially
the gulls, contain what can be considered significant
numbers of FC per
gram. Considering the average weights and FC
concentrations of the gull
and goose feces examined, they can
potentially contribute approximately
1.77 × 10
8 and 1.28 × 10
5 FC per
fecal deposit to the surface water, respectively. The
potential FC
impact of these birds is relative to the numbers
and types of birds, as
well as the duration and time of day that
the birds roost on the
surface water and their defecation rates.
These investigators
additionally collected several old, sun-dried
fecal samples from docks
adjacent to the reservoir and found significant
numbers of viable FC
bacteria. Samples were analyzed in the same
fashion as the fresh feces
except that additional buffer was used
to facilitate pipetting of the
sample. The dried "cakey" feces
from five geese yielded a range of
FC concentration, from 8.2
× 10
2 to 3.0 × 10
5/g. This indicates that runoff from bird feces may also
impact
water supplies, even if the birds do not roost overnight on the
water. Most significantly, it appears that hundreds or thousands
of
birds roosting on the surface water, especially near intakes
to
aqueducts, would have an adverse effect on the microbiological
quality
of the water. This point is further proven in that counts
of FC in the
Kensico Reservoir decreased significantly once the
NYC DEP Waterfowl
Mitigation Program was implemented (
8).
| |
ACKNOWLEDGMENTS |
We gratefully acknowledge the work of Michael Usai, Bryce McCann,
and Christopher Nadareski for their persistent and patient efforts in
collecting fecal samples in all types of weather.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: New York City
Department of Environmental Protection, 465 Columbus Ave., Valhalla, NY
10595. Phone: (914) 773-4423. Fax: (914) 773-0365. E-mail: kalderi{at}valgis.dep.nyc.ny.us.
| |
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Applied and Environmental Microbiology, December 1999, p. 5628-5630, Vol. 65, No. 12
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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