Transcript Garzio-HadzickSSSAposter

Survival of E. coli Delivered with Manure to Stream Sediment
Amanda Garzio-Hadzick1, Daniel Shelton2, Yakov A. Pachepsky2, Robert L. Hill1, Andrey Guber2, Randy Rowland2, Zane Hadzick1,
1
Abstract
Concentrations of E. coli bacteria are mandated by EPA for water quality evaluation in
designating impaired surface waters, and for design of management practices to prevent
fecal contamination of water. Many of these management practices reduce runoff from
agricultural fields, implying that manure is the source of E. coli when it enters stream
water. Recent studies have shown that stream sediment acts as a reservoir and potential
source of fecal bacteria. This study was conducted to determine if (a) E. coli survival in
the presence of dilute manure (i.e., simulated runoff) was effected by sediment particle
size distribution and organic matter content, and (b) temperature affects E. coli survival in
sediments the same way as it affects E. coli survival in other environmental media.
Laboratory experiments were conducted at three temperatures (4, 14, and 24 ºC) using
stream sediment from an agricultural stream mixed with a manure slurry from the USDAARS Beltsville dairy farm. Stream conditions were statistically simulated
using innovative flow-through chambers. An oscillatory growth stage was observed
during the first 4 to 7 days at all temperatures before the exponential inactivation stage
began. The oscillation rhythm did not depend on temperature, but the population
magnitude did. The E. coli inactivation rates slowed as the temperature decreased for
the same sediment. The inactivation rates had the classical power law dependence on
temperature during the exponential inactivation stages. Increases in both sediment clay
content and in organic matter increased the initial E. coli growth and slowed the
inactivation rates. At the lowest temperature, E. coli persisted for three months in
sediment, suggesting that E. coli survival was possible in the stream sediment over
winter. Sediment provides an effective hospitable secondary habitat for manure-borne
E.coli with texture, organic matter content and temperature being the inactivation
controls.
Background
University of Maryland, College Park MD;
2 Environmental Microbial Safety Laboratory, USDA-ARS, Beltsville, MD
Laboratory Survival Study
Sediment was collected from the 3 locations along the stream and inoculated with a fresh
manure slurry. The die-off of E.coli was monitored at 3 different temperatures: 4, 14, and 24°C.
% Silt
% Clay
Particle
Density
A
Sand, Loamy
Sand
84.1 ± 0.85
11.5 ±
1.06
4.45 ± 0.29
2.61 ± 0.00
1.35 ± 0.18
0.56 ± 0.07
B
Sandy Loam,
Sandy Clay
Loam
59.9 ± 0.45
20.7 ±
0.53
19.5 ± 0.41
2.55 ± 0.01
5.14 ± 0.80
1.99 ± 0.29
C
Sand, Loamy
Sand
84.5 ± 0.19
9.59 ±
0.34
5.95 ± 0.15
2.61 ± 0.01
1.78 ± 0.12
0.64 ± 0.06
Sediment
Texture
% Sand
Organic Carbon
%
Saturated Water
Content
Flow chambers were constructed to
simulate natural flow over sediment.
E. Coli die-off curves in water above sediment
•E. coli are recommended by the EPA as indicator bacteria for fecal contamination and
are currently used to evaluate water quality.
24°C
14°C
4°C
•Sediment has been identified as reservoirs for fecal bacteria; there has been a need to
further study the relationships between E. coli and sediment.
•Sediment provides a hospitable secondary environment for E. coli due to the availability
of nutrients and soluble organic matter, and protection from predators and UV light.
•Sediment texture and organic matter content effects on E. coli survival are no not well
understood.
Preliminary Reconnaissance Monitoring
E. Coli die-off curves in sediment
Location: First order stream of a
riparian corridor bordering OPE3
field at USDA ARS Beltsville, MD
14°C
4°C
24°C
Aerial photograph of study location.
Blue circle represents location A, black
square represents location B, and red
triangle represents location C
.
Colilert-18 was used to quantify E. coli
in water and sediment
Systematic in situ sampling occurred throughout 3 week period in summer 2008
Chick’s Law (1908) was applied to the
exponential decay portion of each curve.
c  c0 e
 t
The T20 equation was then used to
calculate θ (a temperature sensitivity
parameter) and μ20 (die off at
temperature 20)
   20
The slope of the exponential decay (μ)
Sediment A Sediment B Sediment C
E. coli concentrations exponentially
decreased with increasing depth at all
locations. Most E. coli occurred in the
upper 3 cm of sediment.
Sediment A Sediment B Sediment C
4°C
-0.02566
-0.02002
-0.02384
14°C
-0.12775
-0.07528
-0.07890
μ20
0.2276
0.0967
0.1553
-0.24477
θ
1.1389
1.0936
1.1235
24°C
E. coli concentrations remained
relatively constant over time at all
locations. Time and sampling position
were found to be insignificant while
sampling location was significant.
t ( C )  20
-0.34599
-0.11986
Conclusions
• Fine-textured sediment with high organic carbon content provided the most suitable
environment for E. coli survival. This relationship was best represented by the lowest θ
value, meaning E. coli was least sensitive to temperature in finer, high organic carbon
content sediment, therefore having the slowest die-off.
• E. coli can persist in sediment for more than 3 months at 4°C, therefore they are
capable of surviving the winter months.
•The persistence of E. coli in sediment was much greater than survival in water.