Robert Brosa, Highland Park High School, Topeka, KS
WATER QUALITY FOR FRESHWATER ORGANISMS
Appropriate for grades 8-12.
OVERVIEW: In modern day society there are many types and sources
of pollution which directly affect the environment. One such type
of pollution, which is becoming even more predominate through the
construction of nuclear power plants, is that of thermal
pollution. Power plants use vast amounts of water which are
converted to steam by the thermonuclear reaction. This steam is
used to turn the blades of the turbines which turns the generators
producing the electricity. The hot water resulting from condensed
steam is partially cooled in specially designed towers before it
is released again into the environment by means of a reservoir or
stream. The temperature of the return water is great enough to
raise the temperature of the body of water several degrees. Such
increases in temperature could greatly affect the organisms living
in the water.
PURPOSE: The purpose of this activity is to demonstrate to
students the effect increased water temperature has on the amount
of dissolved oxygen found in water and in turn upon the gill beat
rate of fish.
OBJECTIVES: Students will be able to:
1. Describe the proper procedure for observing and recording
data.
2. Describe how to use the Winkler method for O2 determination
in water.
3. Demonstrate how to graph and interpret data.
4. Discuss what effect increased temperature has on the amount
of dissolved oxygen in water and in turn upon the gill beat
rate of fish.
ACTIVITIES: Equipment needed (for each lab group): cold aerated
pond water, 800 ml beaker, minnow, hot plate, Celsius thermometer,
ring stand, cork, stirring rod, Hach Dissolved Oxygen test kit,
data table, graph paper.
Day 1: Step #1 - Place 600 ml. of cold (50C.), well aerated pond
water into a 600 ml beaker.
Step #2 - Place minnow into beaker and set on hot plate.
Step #3 - Suspend Celsius thermometer by means of a ring
stand and cork in center of beaker.
Step #4 - Allow minnow to quiet down and take the gill
beat rate by counting the movement (beat) of the
operculum which covers the gills. Take the
count for 30 sec. and multiply by 2 to obtain
rate per minute and then record count in table
of results on work sheet. (By taking the
average of 2 or 3 counts you may be more
accurate.)
Step #5 - Turn on hot plate and heat water slowly while
gently stirring. Take a count of the next gill
beat rate when the temperature is at 100C. and
record data. (You will need to stop the
stirring when the beat rate is taken. A double
beaker with surrounding water may be used if
water heats too quickly.)
Step #6 - Repeat steps 4 and 5 at 15, 20, 25, and 30
degrees Celsius, recording your data each time.
If the minnow begins to float at the surface or
wildly thrash about immediately return to cold
water as we do not intend for it to die.
Step #7 - Take the recorded data and plot on graph: Gill
Beat Rate vs. Water Temperature.
Day 2: Step #1 - Same as step #1 above.
Step #2 - Without placing minnow into beaker use the cold
water sample and your Hach water test kit to
determine the amount of dissolved oxygen in
parts per million (ppm). Instructions are
contained within each kit. All data will need
to be recorded on your worksheet.
Step #3 - Return the amount of water lost from testing to
beaker. Place beaker on hot plate, stir gently,
and remove sample for testing when it reaches
100C.
Step #4 - Repeat Step #3 and test the amount of dissolved
oxygen at 15, 20, 25, and 30 degrees Celsius.
(If test kits are in short supply or you do not
have enough time to make a test at each 5 degree
interval, each lab group may be assigned only a
few and the data taken and averaged for the
entire class.)
Step #5 - Make a graph of Dissolved Oxygen (ppm) vs. Water
Temperature.
Step #6 - Study each of the graphs which you have made and
from your analysis write your conclusion.
RESOURCES/MATERIALS NEEDED: All explained above.
TYING IT ALL TOGETHER: The balance of nature, as we often hear,
is a very delicate one. Each organism has its own specific
tolerance levels to many different environmental and human imposed
factors. The oxygen level of water is but one of many factors
that will determine what species will be present of survive in a
freshwater ecosystem. In today's society we need to be more aware
of how we effect that balance of nature and weigh carefully the
results of our actions and decisions.
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John Kurilecjmk@ofcn.org