Grade Level:
Elementary, Middle School, High School
Ecological Concepts: Abiotic,
Physical factors
Arizona Science Standards: Science as Inquiry; Life
Science
Materials:
1) Pond, stream, or aquarium
2) Loupe or magnifying lenses *
3) Chemical tests *
a) pH
b) Dissolved oxygen (DO)
c) Phosphate
d) Nitrogen
4) Rulers
5) Air and water thermometers in °C *
6) Record keeping materials
7) Sampling cups *
8) Wear boots, aqua shoes or old sneakers
* May be borrowed from SCENE.
BACKGROUND
Water is a necessity for all life on this planet. Aquatic ecosystems can be ponds, streams, lakes or oceans. Freshwater ecosystems are usually divided into still water (ponds) and flowing water (streams). Some systems encompass both still and flowing water, such as a stream with deep pools.
A variety of organisms live in freshwater, some throughout their lives, others only for certain stages, usually as immatures, or juveniles. Even in the Sonoran Desert there is naturally occurring freshwater. There are rivers and streams that flow all year long, and others, called "ephemeral," flow only during wet seasons. Ponds and pools exist as well, usually ephemerally.
In functioning aquatic systems there is a variety of plant and animal
life, the biotic
part of the system. The abiotic
component of freshwater systems is as important as the biotic. Water
temperature, pH, phosphate and nitrogen levels, dissolved oxygen,
and substrate
composition are some of the abiotic factors to consider and measure.
These must be within certain ranges for the system to be habitable
for living organisms.
GUIDED INQUIRY
Observation/Exploration Period: Have students observe
the water habitat using their eyes, magnifying
lenses, dip
nets, etc. (NOTE: Emphasize that they DO NOT
drink the water. No open water is safe.) This is open observation
time. Remind them to record their observations and any ideas or questions
that come to mind. They can use words, drawings, charts; whatever
they think is best for record keeping. They can categorize their findings
(examples: water is cold/warm, clear/murky, plants are above/below
water, strange-looking insects...) as they see fit.
Group Discussion and Question Period: Either have small groups discuss their observations and questions together first and then form one large group, or go immediately to one large group. Once in the large group, using the chalkboard or large pad of paper, record the major points that each small group has decided are characteristics of the aquatic system. Guide students to look for patterns among and between the different areas of the aquatic habitat, in particular the abiotic components they observed. As discussion continues, focus on one aspect of the abiotic features, such as water chemistry.
Some questions that might arise are: Does water chemistry vary in
different parts of the system? How much oxygen is in the water? What
other chemicals are in the water? Does water chemistry vary at different
times of the day or in different seasons?
Important aspects of guided inquiry are encouraging students
to generate multiple hypotheses,
and letting students make decisions about what data are important
and create their own data sheets.
Keeping these ideas in mind, the sample in the box below illustrates
how ONE OF MANY possible investigations around this topic might develop.
Sample
Hypothesis: Let's use the question, "Does water
chemistry vary at different times of the day or in different
seasons?" The hypothesis could be, "If the chemistry of an aquatic
system changes throughout the day and we measure the chemical
components at different times of day, then we will discover
those differences." Or, "Water chemistry changes throughout
the day because changes in temperature change water chemistry."
Sample Experiment Design: The independent
variable is time of day, morning versus afternoon/evening.
The dependent
variable is the value of the particular component
of water chemistry being measured, for example, dissolved oxygen,
phosphate, nitrogen, or pH. Since you will most likely be using
only one body of water, it will not be possible to actually
replicate
the treatment groups. To do that, you would need multiple bodies
of water, i.e., ponds. Instead, you will take at least three
measurements for the same water component in the exact same
place in the water. For example, measure the dissolved oxygen
three times at the same place and same depth in the morning
and then again in the afternoon/evening. By measuring at the
same place and depth you will be controlling
for these factors.
Note: Days with the largest changes in air temperature are the
most likely to yield larger changes in water chemistry, but
very hot days can deplete DO (dissolved oxygen) very quickly
(hence fish kills), depending on the type of water body. Unfortunately,
with an artificial, enclosed, pumped system the changes that
would be seen in a natural system may not occur in the course
of one day. Depending on the type of water system you have,
you need to consider whether to run the experiment as above,
in one day, or to take measurements in the same places but over
a longer period of time to compare seasonal effects and changes.
Sample Prediction: Levels of dissolved oxygen,
phosphate, nitrogen, and pH will change from morning to night.
Record Results: Using the test kit for water
chemistry, measure the dissolved oxygen, phosphate, nitrogen,
and pH levels and record the values for morning and afternoon
or evening. If conducting this experiment over different seasons
rather than at different times of day, try to conduct the tests
at the same time of day, and record the values of the same abiotic
components each time.
Sample Analysis of Data and Presentation: Make
a separate bar
graph for each water chemical, with the time of
day listed on the horizontal axis and the raw number values
on the vertical axis. For students who can divide, calculate
the average
water chemical value for each time period. Graph the average
number on the vertical axis. If the water chemistry is tracked
over seasons, make a line
graph with time on the x-axis and averages on the
y-axis.
Discussion: Was your hypothesis supported?
If yes, go on to test other hypotheses. If not, why not? What
did happen? Why? This is a great opportunity to revise your
hypothesis and do another test. |
MORE:
(1) Elementary:
(a) Measure water depth and temperature in various
places in the pond. Take several temperatures in the same place
at the same depth and average the results. Compare to temperature
averages from other sites in the pond. Measure air temperatures
in shade and sun and see how these values compare to water temperatures.
(b) Take same measurements in an artificial pond
and a natural pond; compare. Try to compare ponds that are similar
in size, depth, and type of location (i.e., shaded, not shaded).
(2) Middle School:
(a) Find
the mean,
median,
mode
and range
of the data.
(b) If the aquatic system is a stream, determine
the water
velocity (V) in meters per second. Calculate V in different
parts of the system. Examine possible correlations
with other abiotic or biotic features (See
Biotic Components of Ponds activity).
(3) High School:
(a) Calculate the variance
and standard
deviation of the averaged data.
(b) Perform a T-test
comparing chemistry in two different parts of the system. (T-test
is a standard statistics test comparing means
of two treatment groups). Perform an ANOVA
when comparing three or more treatment groups.
(c) Test for a correlation
between two variables, e.g., dissolved oxygen levels and abundance
of aquatic insects (See
Biotic Components of Ponds activity). Draw a scatter
plot and calculate the sample correlation
coefficients.
(d) Measure water depth and width, use to calculate
stream
flow or discharge, Q.
References:
Edelstein, Karen. 1999. Pond and Stream Safari. A guide to the
ecology of aquatic invertebrates. Cornell Cooperative Extension.
Cornell University, Media and Technology Services Resource Center,
7 Cornell Business & Technology Park, Ithaca, NY 14850 Dist_Center@cce.cornell.edu
Hall, Jody S. 1998. Organizing Wonder: Making Inquiry Science
Work in the Elementary School. Heinemann. ISBN 0-325-00045-X
Hunken, Jorie. 1994. Ecology for All Ages: Discovering nature
through activities for children and adults. The Globe Pequot
Press. ISBN 1-56440-138-3.
Ruef, Kerry. 1998. The Private Eye: (x5) Looking, Thinking by
Analogy. The Private Eye Project. P.O. Box 646 Lyle, WA 98635
www.the-private-eye.com
ISBN 0-9605434-1-4
LaMotte Company. 1994. The Pondwater Tour: Hands-on test kit
and mini curriculum for exploring lakes, streams and ponds.
LaMotte Company, P.O. Box 329, Chestertown, MD 21620. (800) 344-3100.
Canterbury Environmental Education Centre, UK. Website of pond activities
and organism identification. www.naturegrid.org.uk/pondexplorer/pond1.html
Institute for Inquiry Web Site. "Created in response to widespread
interest in inquiry-based science instruction, the Exploratorium
Institute for Inquiry provides workshops, programs, on-line support,
and an intellectual community of practice which afford science reform
educators a deep and rich experience of how inquiry learning looks
and feels." www.exploratorium.edu/IFI
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