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Photosynthetically Available Radiation (PAR) Measurements - 2
Part 2. Measure available radiation at your water testing site

data | hook | main | background & resources | student

Author Contact Information

Barbara Schulz
BioLab.org
Seattle, Washington
bschulz@biolab.org

Overview
Students need to consider the type of radiant energy used by producers during photosynthesis. Changes or increases in the amount of radiation reaching them inhibit some photosynthesizing organisms. When thinking about organisms living in extreme environments, temperature and number of daylight hours are significant factors. When comparing ecosystems in different hemispheres, the differing amounts of radiation are also a factor.

Students are now prepared to repeat the test at the water quality testing site. Use the same protocol with lab teams to collect data. Use the same data collection sheet or have students design their own data sheets that reflect any differences the class decides is necessary. Unless the testing site has direct sunlight, students will get a reading that is somewhat less than the reading at school. Students can think about the significance of reduced PAR for producers in the streams and lakes in their own area compared with that in McMurdo Dry Valley (MDV). Students should think about how much energy is reflected back to the atmosphere on the ice-covered lakes, compared with that of their local lakes. Students should think about the depth at which photosynthetic organisms live and use PAR. For a good reference for students to look at for a better understanding of the "big picture" of solar radiation use this site: ../../weather/3_polessocold.html

  • Students will determine solar energy available at the water testing site using the same method as that used to determine solar constant

  • Students will measure energy being reflected back to the atmosphere by the water source (albedo)

  • Students will infer the amount of energy available for photosynthesis by aquatic organisms

  • Students will compare their results with those from MDV

  • Students will consider the relative importance of differing amounts of available PAR in different ecosystems at different latitudes as one limiting factor

  • Students will consider the impacts on producers of changes in the PAR values caused by the ozone hole

    Grade Level/Discipline
    11-12 Advanced or AP Biology or AP Environmental Science. Could be adapted for 9 honors biology.

    National Standards

    Pre-activity set-up

    Materials

    Time Frame

    Engagement and Exploration (Student Inquiry Activity
    What factors will you need to consider when thinking about the photosynthetically available radiation (PAR) for the ecosystem in the dry valley lakes? (Factors to make sure get mentioned include cloud cover, pollution, time of year, longitude and latitude, scatter effect as radiant energy penetrates the water, depth of water).

    What wavelengths of light do you think are included in the PAR? (400-700nm)

    How can you fairly compare the values taken at your water test site with those in the dry valleys? Can you make reasonable estimates? For honors students or advanced placement students use more in depth research as follows. Have students think about the possibility of producers getting too much PAR. The following web sites could introduce the idea of photoinhibition in areas where intense PAR occurs. Have students explore some research sites on the web and read abstracts of the research projects. One good source is the Cold Regions Research and Engineering Lab run through the U.S. Army. http://www,CRREL.usace.army.mil

    You can also access their research through the library of congress using this link. http://lcwem.loc.gov/rr/scitech/welcome.html Do a search using the letters PAR and set a data parameter and a wealth of research arcticles will appear. To read an abstract of the arcticle, click on more. There is frequently enough information in the abstract to be quite useful for students.

    Explanation (Discussing)
    Students will determine the available solar energy at the test site by repeating the experiment at that test site. Students should write a hypothesis giving a reasonable prediction of energy availability. Students will use a light probe, CBL unit and calculator held directly above the water pointing at the water to collect data Have students develop their own protocol based on the prior lab and have it approved before going to the field.

    Elaboration (Polar Applications)

    Exchange (Students Draw Conclusions)
    Students will discuss their results with lab partners and come to consensus about the meaning of the data. Students will subtract the albedo from the available energy to determine a possible amount of available energy. Students will consider the experimental error. Students will discuss the importance of doing research in the MDV and the significance of understanding the energy dynamics for living systems.

    Evaluation (Assessing Student Performance)
    Student’s lab reports will demonstrate understanding of the significance of energy to a wide variety of ecosystems.

    data | hook | main | background & resources | student