Wetlands and Water Quality Management
Purpose: This activity
focuses on collecting data that will demonstrate to the student the importance
of wetlands for maintaining water quality. The students will develop some
hypotheses about the difference in water quality they might find if they
measure temperature, pH, nitrate and phosphorus at the inlet and outlet of a
wetland.
Summary: The students will develop hypotheses on
how the pH, temperature, nitrate and phosphorus concentrations of water will
change from the inlet to the outlet of a wetland. They will go and collect data
in the field and then graph it and determine if their hypotheses were correct.
Background:
Plants and
animals need nutrients for cellular activity to sustain life. Phosphorus and
nitrogen are essential nutrients. Plant growth depends on phosphorus
availability for it provides energy for metabolism. In many bodies of water
phosphorus can be a growth-limiting constituent. Nitrogen is usually more
abundant due to the presence of nitrogen fixing aquatic organisms. Nitrogen
fixing organisms convert N2 gas from the atmosphere into organic nitrogen. Plants sequester nitrogen in proteins
which makes nitrogen available to humans.
An overabundance
of nutrients in aquatic systems can cause excess plant growth. The process
of plant death and decay results
in removal of oxygen from the water. Wetlands due to the high biological activity can actually help
remove excess nutrients though a variety of processes. They can be taken up
by plants, which then die, and subsequently nitrogen and phosphorus are deposited
and buried in the sediments. Some microbes convert nutrients like ammonia
and nitrate into gases, which are released to the atmosphere. In some areas, wetlands have been constructed
to help with clean up of "waste water" or water that is flushed
down your toilet or that goes down your sink that goes to the wastewater treatment
plant to be cleaned up.
Some
wetlands such as bogs have no inlet and outlet. Others such as bottomlands or
in stream wetlands have an inlet and an outlet for water that moves through
them. To see how well wetlands function as nutrient sinks and how chemistry
changes in a wetland we will measure water quality parameters at the inlet and
outlet of one or more wetlands.
The
students should first formulate some hypothesis regarding what you would expect
regarding any change you might observe between the water concentrations of
nitrogen and phosphorus between the inlet and the outlet. How about temperature
and pH? What might influence the
changes in these?
Since
wetlands are natural water purifiers the students will most likely hypothesize
that nutrient concentrations should decrease. Since water in a wetland slows
down in velocity it is most likely that the temperature at the outlet will be
greater because the water is moving more slowly and warming up. What about pH? As plant material decays
in the wetland it is likely that you will generate organic acids. Microbial activity
will make H2S, which can react with water to make sulfuric acid.
These changes will most likely decrease the pH.
Materials
- Temperature probe
- Litmus paper
- Clean plastic beaker for water
sample or sample bottle or beaker.
- Distilled water for rinsing
between samples and squirt bottle.
- Nitrate water testing kit
www.hach.com
- Phosphate testing kit www.hach.com
- Wiffle or ping pong ball
- Measuring tape
- Stop watch
- Latex gloves
Procedure
1.
First
have the students develop and write out some hypotheses about water quality
from the inlet to outlet of the wetland. Then have them go and collect the
data.
2.
For a
quality control check it is a good idea to try out the pH paper with solutions
with known pH before heading to the field and to make sure everyone is
interpreting the color scheme the same way. It is also a good idea to demonstrate the tests before you
head out also to avoid confusion at the field site.
3.
In the
field use gloves to collect the water samples into a beaker or jar. Rinse the
beaker with the water to be sampled three times before filling it with water.
4.
Collect
samples from main current, away from banks and well underneath the surface of
the water. This will help ensure a well- mixed representative sample.
5.
Temperature
and pH should be analyzed in the field immediately for both can change rapidly
over time.
6.
Do
three replicates of each test.
7.
Measure
pH directly in the stream by inserting the paper and holding it there according
to instructions.
8.
Measure
temperature in the water body at the same location you measure pH.
9.
Nitrate
and phosphate should be determined according to the directions on the test
kits.
a.
Nitrate-
HACH 14161-00 range is 0 to 10 mg/L.
i. Put on gloves!
ii. For this test first fill one of the
color viewing tubes with the liquid to be analyzed. Stopper and shake
vigorously. Empty and repeat.
iii. Fill the tube to the mark with the
sample.
iv. Open one NitraVer 6 nitrate reagent
powder pillow. Add to the sample to be tested. Stopper and shake for three
minutes. Allow sample to sit undisturbed for 30 seconds. Unused Cadmium should sink to the
bottom.
v. Pour the prepared sample into the
other viewing tube so that the cadmium remains in the first tube
vi. Open one NitraVer 3 reagent powder
pillow. Add the contents to the sample. Stopper the tube and shake for 30 seconds.
A red color will develop if nitrate is present. Insert the tube in the opening
closest to the center of the container. After 10 minutes (but not more than 20)
you can make the reading.
vii. Rinse the cadmium metal from the color viewing tube used in
step iii. Fill to mark with original water sample and place it in the opening
nearest the side of the box.
viii.
Hold
the box up to the light and rotate the disc to obtain a color match. Read the
number through the scale window and multiply by 4.4 to get the results as mg/L.
b.
Phosphate
HACH 2250-01 low range
i. Put on gloves!
ii. Rinse the square bottle several
times with the water to be analyzed.
iii. Fill the square mixing bottle to the
20-ml mark with the water to be tested.
iv. Open one PhosVer 3 reagent pillow
powder. Add the contents to the bottle and swirl around to mix. Allow 2 minutes
for color development. If phosphate is present a blue violet color will appear.
v. Fill one sample tube with the
prepared sample and the other tube with the untreated sample.
vi. Insert the treated sample in the
hole closest to the center of the box.
vii. Orient viewer toward a light source
and be careful not to spill the sample.
viii.
Rotate
the disc to get a color match. Record the reading in the scale window and
divide by 50 to get mg/L phosphate.
10. Record all values on a data sheet
for each site.
11. Velocity can be determined by
placing something buoyant in the water like the wiffle ball and measuring the
distance it travels over a certain amount of time. Measure off a distance
parallel to the direction of flow. Drop the wiffle ball in the water and
measure how long it takes for it to travel the distance. Calculate the velocity
as follows:
Velocity (feet/minute) = Distance traveled / Time
At
the TMWRF constructed wetlands we will actually measure the volume of water
moving
through
the system as a function of time so we can calculate the amount of water
treated per
day.
We will collect water in a gallon jug and time the collection to get
gallons/minute.
12. Use the summary sheet to describe what was going on in
the wetlands in terms of water chemistry. Have them write up a scientific
report following the scientific method.
Name__________________________________
Date______________ Time_____________
General information
Site description
Sample location
Weather
Description of vegetation
Quantitative Water Quality
|
Wetland
location |
Planted
inlet |
Planted
outlet |
Unplanted
inlet |
Unplanted
outlet |
|
pH |
|
|
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|
|
Temperature |
|
|
|
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|
Nitrate |
|
|
|
|
|
Phosphate |
|
|
|
|
Amount of water moving through the wetland as a function of
time. Gallons/ minute
Area of the wetland
Hypothesis
Method
to test the hypothesis
Summary of field data
Site description
Date and time data was collected
Environmental conditions
Detailed description of wetland including vegetation, surface area and amount of water being treated .
Data summary
|
Sample location |
TEMP |
PH |
Nitrogen |
Phosphorus |
Volume treated |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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|
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|
|
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Discuss the difference in pH and temperature between the inlet and outlet of the wetland and potential reasons for the difference.
Percent removal of nitrogen and phosphorus. Calculate the amount of nutrients being removed
(Concentration at the outlet- concentration at the inlet)/ Concentration at the inlet *100= Percent removed
Is there a difference in the % removal for the different wetland types?
Resources
A world in our backyard: A wetlands educational and stewardship program. Video by Bill Nye
www.envmedia.com/catalog/products/a_world_backyard.html. Printed material 144 pages with information and activities
Wow! The Wonders of Wetlands. Book with activities and handouts from Environmental Concern Inc. 201 Boundary Lane, P. O. Box P, St. Michaels, MD 21663
410-745-9620
Vocabulary Words
Wetland
hydric soil
nitrogen
phosphorus
pH
scientific
method
hypothesis