Transcript Bacterial concentrations in bull creek Austin, Texas

BACTERIAL CONCENTRATIONS
IN BULL CREEK
AUSTIN, TEXAS
Patrick Sejkora
Overview




Overview
Spatial Variations
Seasonal Variations
Further Work
Bull Creek




Spring fed
Drains into Town
Lake
32 mi2 watershed
Bordered by
parks
Source: LCRA 2007
Bacteria in Bull Creek


Evaluate presence of harmful waterborne
pathogens
Bacterial water quality is assessed by indicator
bacteria
 Can

indicate fecal contamination
Standards for recreation are set by TCEQ
E. coli (freshwater)
geometric mean
single sample max
Fecal coliform (all waters)
geometric mean
Single sample max
Source: TCEQ 2007
Contact recreation
(# per 100 ml)
Noncontact recreation
(# per 100 ml)
126
394
605
---
200
400
2,000
---
Statistical Tests




Select focus sites
Test spatial homogeneity of indicator bacteria
concentrations
Examine seasonal homogeneity of bacteria
concentrations
Test for correlation between bacteria concentration
and flow/precipitation
Sources of Information



Biological Information
Provided by City of
Austin
Flow data accessed
via HydroExcel
Precipitation data
from LCRA’s Hydromet
Spatial E. Coli concentrations
Examine
homogeneity of E.
coli concentrations
between sites

t-test
10000
E. coli concentration (MPN / 100 mL)

Bull Creek
District Park
1000
Loop 360 First
Crossing
100
Bull Creek at
St. Edwards
Park (above
dam)
10
1
12/18/2008
11/14/2007
10/10/2006
9/5/2005
8/1/2004
6/28/2003
Spatial E. Coli
concentrations

Identify E. coli sources

Descriptive Statistics

t-test


Homogeneous between St. Edwards
Park and Loop 360 (p=0.11)

Bull Creek District Park
nonhomogeneous with Loop 360 and
St. Edwards Park (p=3.0x10-6;
p= 1.1x10-6)
n: 25
Mean: 44
Median: 27
Standard Dev: 49
95% Confidence: 20
n: 45
Mean: 69
Median: 34
Standard dev: 44
95% Confidence: 21
t-test suggests dogs at Bull Creek
District Park could be a possible
source of E. coli
n: 57
Mean: 363
Median: 218
Standard Dev: 454
95% confidence: 121
Weekend Hypothesis

If dogs are source, E.
coli concentrations
should be statistically
higher on weekends
Observations
Mean E. coli
concentration higher on
weekends
 Nonhomogeneous


Dogs appear to be
cause of elevated E. coli
at District Park
1200
Mean E. coli Concentration (#/100 mL)

1000
800
600
400
200
0
Weekday
Weekend
p = 0.015
Seasonal Variations at Sites
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Summer is AprilOctober, winter is
November-March
Observations


Average E. coli is
higher in summer
than in winter
Hypothesis

Could swallows
be contributing
to greater E. coli
concentrations in
Summer?
1000
Mean E. coli concentration (#/100 mL)

800
600
400
200
0
Summer
-200
Winter
St. Edwards
Park
Summer
Winter
Loop 360
Summer
Winter
Bull Creek
District Park
Seasonal E. Coli
Concentrations
t-test

Observations
 Seasonal E. coli
concentrations are:
 Statistically
homogeneous at Bull
Creek District Park
 Not homogeneous at
Loop 360 or St.
Edwards Park
Winter n: 13
Summer n: 11
p = 0.04
Winter n: 24
Summer n: 13
p = 0.002
Winter n: 34
Summer n: 23
p = 0.20
Seasonal E. Coli
Concentrations
t-test
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Are seasonal E. coli
concentrations
homogeneous between
two sites?
Concentrations
homogenous between
seasons
Swallows cannot be
conclusively linked to
increased E. coli
concentrations between St.
Edwards and Loop 360
Summer
St. Edward mean: 62.6
Loop 360 mean: 886.6
p = 0.15
Winter
St. Edward mean: 24.3
Loop 360 mean: 49.0
p = 0.07
E. coli concentrations and Flow
Performed
on Bull Creek
District Park



Homogenous
yearly data
Bacteria source
affected by
stormwater
runoff
E. coli concentration (#/100 mL)

3000
2500
2000
1500
y = 21.389x + 259.58
R² = 0.0528
1000
500
Conclusions

No real trend
0
0
5
10
15
Flow (cfs)
20
25
30
E. Coli concentrations vs. Precipitation
Precipitation may
be better metric


Observations

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Causes bacteria
from dog doo to
wash into river
Better, but still
not great
Remove dry
events

Much better!
3000
3000
mL)
(#/100mL)
E. E.coli
concentration (#/100
coliconcentration

2500
2500
2000
2000
y = 2966.3x + 296.95
y = 3701.7x + 60.287
R² = 0.3061
R² = 0.7414
1500
1500
1000
1000
500
500
00
00
0.1
0.1
0.2
0.3
0.4
0.2
0.3
0.4
Precipitation
Precipitation (in)
(in)
0.5
0.5
0.6
0.6
Further Work


Nonparametric methods of comparing E. coli
concentrations over space and time
Investigate correlation between concentrations of
different indicator organisms (Fecal Coliform, Fecal
Streptococci)
Questions?
“People can come up with statistics to prove anything.
Forty percent of all people know that!”
-Homer Simpson