Murrells Inlet Estuary Microbial Source Tracking Study
Cara Schildtknecht, Jeff Barley, Dr. Adam Leaphart, and Dr. Susan Libes (Coastal Carolina University)
Background
Results and Conclusions
Elevated levels of E. coli were identified by the Murrells Inlet Volunteer Monitoring Program. On land sources of E. coli were identified and
investigated with a microbial source tracking study to determine whether the contamination was human-sourced.
SCDHEC sets
TMDL for
shellfish in
Murrells Inlet
2005
2010
Volunteer
Monitoring
Program
(VMP)
initiated
VMP identifies
sites with
elevated E.
coli levels
2014
2015
Microbial
source
tracking study
conducted
The study revealed higher fecal bacteria concentrations and higher turbidity levels during rain events than during dry events. There is minimal
evidence to attribute the elevated bacteria concentrations to human sources. Because significant contributions of fecal bacteria were found at all
sites, further source tracking upstream should be performed to identify the source of contamination. Additional genotypic assays should be performed
to determine the source of fecal bacteria such as for dogs, birds, and other wildlife, including raccoons.
Present
Implement
management
practices to
intercept
contaminants
Ongoing
assessment of
water quality
by VMP
2016
Methods
Five sample sites were selected including three identified by the volunteer monitoring as having elevated levels of fecal bacteria concentrations as
well as two upstream sites. Water and sediment samples were collected during three dry and three wet events during the summer and fall of 2015
when fecal bacteria concentrations were expected to be highest. Samples were then analyzed for tracers including human-sourced Bacteroides
(BacHum), Bacteroides (GenBac), E. coli and total coliforms, fecal coliforms, caffeine, turbidity, and salinity.
HS-4
HS-5
Harrelson’s Seafood
Restaurant at HS-VM
HS-2
HS-1
HS-VM
HS-3
HS catchment
HS-6
HS-3
HS-VM
BB catchment
BHR catchment
BB-VM
BHR-2
BHR-3
BHR-1
BHR-4
BHR-VM
Figure 2: Results for E. coli concentrations for sediment and water samples and turbidity levels for water samples. Uncertainty estimates of 46%
for E. coli in water and 2.8% for turbidity are based on average relative percent difference between field duplicates. Orange bars represent the
infrequent cases where dry weather concentrations were greater than the wet weather concentrations. Red values exceed class SFH criteria.
BHR-5
Sewage lift station
at BHR-VM
Sewage lift station
at BB-VM
Image of BB-VM. White pole is stilling well for a water level
logger used to obtain hydrographs for each sampling event.
BHR-VM
BHR-1
Figure 1: Map of Murrells Inlet with sampling sites with maps and photographs of each of the catchments. Phase I sites are in yellow.
Potential Phase II sites are in green. Red lines are subwatershed boundaries. Blue lines are stormwater infrastructure.
Figure 3: Analysis results for tracers of human-sourced bacteriodes (GenBac), bacteroides (BacHum), and caffeine.
Acknowledgements
This project is funded by Georgetown County and could not have been completed without the Murrells Inlet Volunteer Monitoring Program.