The following research themes can be used to construct hypotheses
that will lead students to explore the extent of
bacterial contamination in your region, what the causes are and how to
decontaminate the water.
Research Themes and Associated Activities
- Geographic Source Tracing
Have students select sampling sites that are close
to suspected sources of bacterial contamination, such as water bodies
that collect runoff from lawns where pets live or near a farm.
Have the students try to estimate the types and numbers of animals
living in the area. Collect samples from sites that are far from
these sources and thus should have cleaner water. Plot the
results on a bar graph with the location on the x axis.
Alternatively, plot the results on a map with concentration values in
a circle located over the sampling site. Compare all the results
to see if they exceed US EPA or state water quality criteria.
- Effects of Stormwater Runoff
Have students collect samples within a few hours
after a rainfall. Compare the results to samples taken from the
same site during dry conditions (no rain for at least 48 hours).
If several rainfall events can be sampled, have students collect
rainfall information, using a simple plastic rain gauge.
Calculate the percent increase in bacterial numbers by computing the
difference in bacterial concentrations before and after a rain
effect. This value can also be ratioed to the depth of the
rainfall to facilitate comparison of samples collected after different
rain events. Compare all the results to see if they exceed US
EPA or state water quality criteria.
- Effects of Resuspension
You will need a piece of PVC pipe 8" in
diameter and 4 to 5 feet tall to perform this activity. First
collect a sample from the site to serve as the control. Then
place the pipe firmly into the sediment of a river or ditch or marsh
to create a water-tight seal. Pick a location where you have no
more than 2' of water in the pipe. Muddy sediments will yield
more bacteria than sandy ones. Use a yardstick to measure the
height of the water in the pipe. Use the yardstick to stir
the water for about 30 seconds - this simulates the effect of boat
wake or strong winds. Unless you have very long arms, you will
need to tape your sample container to the yardstick to collect a
sample. You will collect some sediment in your container.
When you return to the lab, shake the container for 30 seconds and let
it settle 10 minutes. Use only the top clarified part of your
sample so that your filter remains relatively sediment
free. This requires that you pour carefully. Measure
the volume of the remainder of your sample so that you can determine
how much water was passed through the filter. You can compute
the effect of resuspension in two ways. First, calculate the
percent increase in bacteria as the difference between the bacteria
concentrations before and after resuspension. Second take this
difference and multiply it by the height of the water in the pipe in
units of cm. This will yield the flux (or flow) of bacteria from
the sediments in units of CFU per square centimeter.
Resuspension experiments can be conducted at sites that are expected
to be clean as compared to those that are close to bacteria sources
(such as marinas and boat landings). Use a bar graph to display
the results with the control and treatment on the x axis.
Collect nine samples from a site known to have high
bacteria numbers (you might have to sample within a few hours of a
rain event). Analyze three samples immediately to serve as a
control. Compute the average concentration of the control.
Hold three (unopened samples) at 28oC to simulate high
summer temperatures (use a drying oven) and three (unopened samples)
at 4oC to simulate cold winter temperatures (use a
refrigerator). Analyze these samples after 24 hours.
Compute the average concentration after exposure to high temperatures
and the average concentration after exposure to low
temperatures. Compute the percent declines in bacterial
concentrations for each treatment using the difference between the
average treatment concentration and that of the control.
Use a bar graph to display the results with the control and treatment
on the x axis.
Collect nine samples from a site known to have high
bacteria numbers (you might have to sample within a few hours of a
rain event). Analyze three samples immediately to serve as a
control. Compute the average concentration of the control.
Hold three (unopened samples) in the dark at room temperature (25oC)
for 24 hours. Use a grow light to simulate sunlight and expose
three (unopened samples) for 18 hours of light and 6 hours of dark to
simulate the effect of sunlight. Make sure that the light is not
elevating the temperature of the samples. Analyze these samples
after 24 hours. Compute the average concentration after exposure
to no sunlight and the average concentration after exposure to
sunlight. Compute the percent declines in bacterial
concentrations for each treatment using the difference between the
average treatment concentration and that of the control.
Use a bar graph to display the results with the control and treatment
on the x axis.
Collect twelve samples from a site known to have
high bacteria numbers (you might have to sample within a few hours of
a rain event). Analyze three samples immediately to serve as a
control. Compute the average concentration of the
control. Carefully open three samples and add 1.5 grams of table
salt to each container to simulate the effects of brackish water
(approximately 10 parts per thousand salinity). Carefully close
each container. Add 3.0 grams of salt to the last three
containers to simulate seawater (approximately 30 parts per thousand
salinity). Leave three samples unopened to serve as secondary
control (0 ppt salinity). Hold all nine samples in the dark at
room temperature (25oC) for 24 hours and then
analyze. Compute the average concentrations after exposure to 0
ppt, 10 ppt, and to 30 ppt salinity. Compute the percent
declines in bacterial concentrations for each treatment using the
difference between the average treatment concentration and that of the
control. Use a bar graph to display the results with the
control and treatment on the x axis.
Collect nine samples from a site known to have high
bacteria numbers (you might have to sample within a few hours of a
rain event). Analyze three samples immediately to serve as a
control. Compute the average concentration of the control.
Carefully open three samples and add 1 gram of sterile potting soil to
each container to simulate the effects of adsorption onto
sediments. Carefully close each container. Leave
three samples unopened to serve as secondary controls (no soil).
Hold all six samples in the dark at room temperature (25oC)
for 24 hours and then analyze. Compute the average
concentrations after exposure to no soil and 10 ppt soil.
Compute the percent declines in bacterial concentrations for each
treatment using the difference between the average treatment
concentration and that of the control. Use a bar graph to
display the results with the control and treatment on the x axis.
Collect twelve samples from a site known to have
high bacteria numbers (you might have to sample within a few hours of
a rain event). Analyze three samples immediately to serve as a
control. Compute the average concentration of the
control. Hold three samples for 24 hours by storing in the
incubator and then analyze. Compute the average
concentration. Hold three samples for 36 hours and three samples
for 48 hours and then analyze. Plot the average concentrations
with time on the x-axis. This simulates the death of pathogens
once they leave the intestines of their hosts.
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