Transcript Slide 1

Vertical Microbial Transport via Water Flow Through Beach Sediments
M. Phillips, H. M. Solo-Gabriele, A. Reniers, T. Kiger, A. Shah
Center for Oceans and Human Health
Rosenstiel School of Atmospheric and Marine Science, University of Miami
Introduction
Results
Summary
Dislodge-able Bacteria Released Quickly
Sampling
4.0%
Percentage of Total CFUs Removed
 Enterococci are used by the EPA to test recreational waters for
human fecal contamination
 Can also grow in beach sediments and contaminate water
without point source of sewage
 Process by which microbes are transported from the sediment
into the water column has not been widely studied
Methods
One large
experimental core
and three small cores
were sampled per
sampling event
3.5%
3.0%
7/21/2009
8/25/2009
2.5%
8/28/2009
11/2/2009
2.0%
11/9/2009
11/23/2009
1.5%
12/8/2009
12/17/2009
1.0%
1/12/2010
1/23/2010
0.5%
0.0%
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Conclusions
600
Volume Eluted (mL)
Release Pattern Did Not Differ With Direction of Flow
Flow-Through Columns
Up-Flow Column
2.0%
Percentage of Total CFUs Removed
 Determine the contribution of vertical entrainment in
transporting enterococci into the water column
 Determine if enterococci are transported into the water column
in a predictable manner
Results suggest some other parameter controls percentage of
enterococci released
Biofilms could be this parameter
Rain events fundamentally alter the amount of bacteria
quantified from sand
Run off and/or different states of cultivability in enterococci
could explain difference
2.5%
Objectives
Down-Flow Column
Only 10% (on average) of total enterococci in experimental core
were dislodged and washed off
98% of dislodge-able enterococci released within one pore water
volume (400mL)
Direction of flow and flow velocity have no effect on percentage
of enterococci released
Mild correlation seen between hydraulic conductivity and
percentage of enterococci released
No correlation seen with any other physical or chemical
parameters
Up Flow Mean (Dashed Stdv)
Down Flow Mean (Solid Stdv)
1.5%
1.0%
Recommendations
0.5%
Experimental
0.0%
0
Site Description
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600
Volume Eluted (mL)
Hydraulic Conductivity Correlated with Percent
Bacteria Removed
 Hobie Beach, Virginia Key, Florida
 No point source of sewage
 Closed 4.6 days per year due to microbial
water quality violations
 Epidemiological studies have shown
illness correlated to bathing at Hobie Beach
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y = 0.011x - 0.0306
R² = 0.5065
Experiments and Analysis
Hydraulic Conductivity (cm/sec)
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Acknowledgements
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This work was funded by NSF (#OCE0432368/0911373) and NIEHS (1 P50 ES12736)
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Sterile water was driven through experimental cores via
pressure created by head differential
Water samples were collected from eluent that had passed
through the core
Water samples were then
analyzed for enterococci via
Membrane Filtration
(EPA Method 1600)
Microbes from sand (before
and after) also quantified
Moisture Content, Volatile
Organic Content, Grain Size Analysis, Porosity and Flow Rate
also measured
Hydraulic conductivity (measure of difficulty for flow to pass
through sediment) was calculated using Darcy’s Law
Future work should quantify biofilms along with bacteria to
establish correlation
Microscopy can be used to determine if enterococci in different
culturable states are present in sand samples
Since vertical entrainment produces no predictable release of
bacteria, other physical forces such as shear should be examined
for possible use in a predictive model
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Percentage of Total Bacteria Removed
Explosive Growth After Rain Event
One experimental Core was collected during heavy rain
Quantity of enterococci and percentage released significantly
higher than other cores
Rain Core vs Means of Other Cores
Average
Rain Core
CFU/g Dry Sand Before
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458
CFUs Washed off Core
659
204600
% Removed from Core
11%
40%
*CFU- Colony Forming Unit, the functional unit for measuring bacteria
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