stratification, or layering, occurs in many Minnesota lakes. Whether
or not a lake stratifies depends on a number of factors: the shape and
depth of the lake, the amount of wind, and the orientation of the lake
(lakes that are oriented east-west are more affected than lakes oriented
north-south). When layering occurs the upper, warmer layer is referred
to as the epilimnion,
and the colder, deeper layer is referred to as the hypolimnion.
The boundary between the layers where the rate of temperature change
is most rapid is referred to as the thermocline.
Temperature stratification is often paralleled by stratification of
other water quality measurements such as pH
oxygen. This lesson is divided into two parts. In the laboratory
part, you are challenged to develop two distinct layers of water in
a glass. In the technology application, you will determine whether or
not a specific WOW lake is stratified
during the summer.
own a cabin on a WOW lake. Your mother claims that the lake remains
stratified throughout the summer, while your father is positive that
the opposite is true. As a biology student you have decided to settle
this argument by proving whether or not the lake remains stratified
throughout the summer.
I - Laboratory Demonstration
knowledge of thermal stratification. Have you observed distinct temperature
layers in lakes? What might cause these layers? Might it be possible
to replicate these layers in a laboratory setting? How?
demonstrate thermal stratification in the laboratory? Your teacher
will supply materials.
to write a protocol for your demonstration. The protocol should provide
clear, step-by-step directions for other researchers to follow. Be ready
to explain the rationale for decisions about experimental design.
with your experimental plan. Consider variables that might affect the
outcome of the experiment. Take notes about your observations and, if
possible, repeat your experiment to substantiate the results.
Management and Analysis
your results in a way suited to your experimental design. If multiple
demonstrations were performed or if data were measured over time, a
chart or graph is helpful. For other designs a narrative analysis best
the following questions as you prepare to complete a final report:
- Did you
succeed in replicating thermal stratification in a lab? Why?
there other materials that might have aided your research?
you expect the same results if another researcher completed the experiment?
you proceed differently if repeating the experiment? Explain.
be prepared to orally present your experimental design, results, and
your interpretations of results. Which groups or designs in your class
were most successful? Why?
II - Researching Thermal Stratification in Lakes
the following questions as you prepare to research thermal stratification
in a lake:
How do your
laboratory experiences relate to a lake environment?
be more or less pronounced in a lake setting?
to demonstrate whether or not your parents' lake is stratified. Consider
what measures indicate stratification. How many measures are necessary
to decide whether or not the lake is stratified? How many dates are
necessary? Be prepared to explain your experimental design decisions.
the data necessary to decide whether or not your parents' lake is stratified.
Use as many dates and measures as you feel are necessary to prove whether
or not the lake remains stratified.
Management and Analysis
data you collected for your parents' lake. Based on your graphs, does
the lake remain stratified throughout the summer? If stratification
is evident, label each of the layers (epilimnion, thermocline, hypolimnnion).
the following questions as you prepare for your final report:
the lake remain stratified throughout the summer?
variables might affect whether or not the lake remains stratified
throughout the summer?
- How might
temperature profiles of other lakes in the region compare to the lake
monitored by RUSS?
- Why is
this type of information important to people who monitor and manage
or use our lakes?
It is time
to settle the argument. Use your graphs and knowledge of thermal stratification
to prove whether or not the lake remains stratified. Your teacher will
specify whether you should make an oral argument, written presentation,
a poster, or a multi-media presentation.