RESEARCH
Assessment of the teaching of evolution by natural selection through a hands-on simulation
Lori H. Spindler, Department of Biology
University of Pennsylvania
Philadelphia, PA 19104
lori.spindler@gmail.com
Jennifer H. Doherty, Department of Biology
University of Pennsylvania
Philadelphia, PA 19104
dohertyjh@gmail.com
Assessment of the teaching of evolution by natural selection through a hands-on simulation
Lori H. Spindler, Department of Biology
University of Pennsylvania
Philadelphia, PA 19104
lori.spindler@gmail.com
Jennifer H. Doherty, Department of Biology
University of Pennsylvania
Philadelphia, PA 19104
dohertyjh@gmail.com
Teaching Issues and Experiments in Ecology - Volume 5, July 2007
RESEARCH
Evaluating course impact on student environmental
values in undergraduate ecology with a novel survey
instrument.
Robert Humston, Department of Biology
Virginia Military Institute, Lexington, VA 24450
humstonr@vmi.edu
Elena Ortiz-Barney, Department of Biology
Phoenix College, Phoenix, AZ 85013
elena.ortiz-barney@pcmail.maricopa.edu
Evaluating course impact on student environmental
values in undergraduate ecology with a novel survey
instrument.
Robert Humston, Department of Biology
Virginia Military Institute, Lexington, VA 24450
humstonr@vmi.edu
Elena Ortiz-Barney, Department of Biology
Phoenix College, Phoenix, AZ 85013
elena.ortiz-barney@pcmail.maricopa.edu
TITLE
What does agriculture have to do with climate change?
ABSTRACT PAGE
What does agriculture have to do with climate change?
ABSTRACT PAGE
The Issue
Agriculture is a major contributor of greenhouse gases, Certain management practices can substantially reduce greenhouse gas emissions, but these practices are not always economically viable for farmers.
Ecological Content
Oxidation of soil organic carbon due to agricultural management, sources of methane in agriculture, conversion of soil nitrogen to nitrous oxide, radiative forcing of greenhouse gases, carbon sequestration in agricultural soils, global warming potential from agricultural ecosystems. Other key words include carbon cycle, fertilizer, organic agriculture, no-till, carbon sources and carbon sinks.
Student-active Approaches
Turn to your Neighbor, Think Pair Share, Guided Class Discussion, Paired Think Aloud, Citizen’s Argument
Student Assessments
Short Essay, Minute Paper, Land Management Activity
Authors
Brook J. Wilke1,2 (wilkebro@msu.edu) and Justin Kunkle1,2 (kunkleju@msu.edu) 1 Michigan State University, East Lansing, MI 48824 2 W.K. Kellogg Biological Station, Hickory Corners, MI 49060
Acknowledgements
We thank numerous people at the W.K. Kellogg Biological Station (KBS), including Phil Robertson, Laurel Hartley and Sara Syswerda for inspiration, Drew Corbin for organizing years of data collection and everyone involved in the GK-12 Program, including graduate fellows and teachers. We thank the National Science Foundation and the Long Term Ecological Research network for providing funding for research and educational activities at KBS. We thank Charlene D’Avanzo for providing guidance in developing this activity and Katie Button, Jarad Mellard, Gary Mittelbach, Todd Robinson and Lindsey Walters for providing comments on earlier versions of the activity. Two anonymous reviewers were very supportive and provided excellent suggestions for revisions. This is KBS contribution #1444.
Citation
Wilke, B. J. and J. Kunkle. February 2009, posting date. What does agriculture have to do with climate change? Teaching Issues and Experiments in Ecology, Vol. 6: Issues Figure Set #3 [online]. http://tiee.ecoed.net/vol/v6/issues/figure_sets/climate_change/abstract.html
FIGURE SET HEADER for Set #1
Figure Set 1: Cultivation and Soil Carbon Losses Purpose: To teach students that cultivation of crops for food results in the oxidation of soil organic carbon, which in turn contributes a substantial amount of carbon dioxide to the atmosphere. Teaching Approach: Turn to your neighbor
Cognitive Skills: (see Bloom's Taxonomy) — Knowledge, Interpretation, Application Student Assessment: Post Lesson Assessment Essay
BACKGROUND for Set #1 (back1.html)
Background Prior to European colonization of the U.S. Great Plains, prairies were the dominant plant communities. The soils of the prairie landscapes contained relatively high amounts of organic carbon, possibly more than 50,000 kg of carbon per hectare stored in the topsoil, which is equivalent to the amount of carbon found in 20,000 gallons of gasoline (calculations based on 2.5% soil carbon, 20 cm deep topsoil and soil bulk density of 1 g / cm3). In Figure 1a, Robertson and Grace (2004) redrew this graph from Haas (1957) to show how cultivation of crops for food decreases soil carbon. Soil carbon at two sites in Kansas was measured prior to initiation of cultivation and was monitored for over 40 years to track soil carbon losses. Cultivation (tillage, fertilization, long fallow periods) resulted in the oxidation of soil organic carbon and although the two sites differed in total carbon loss, both sites exhibited a negative exponential trend. It is assumed that soil carbon eventually reaches a steady state if cultivation continues for many years.
FIGURE SET HEADER for Set #2
Figure Set 2: Methane Emissions from Agriculture
Purpose: To teach students that methane is a powerful greenhouse gas, and to teach the mechanisms by which agriculture contributes a substantial amount of methane to the atmosphere. Teaching Approach: Think – Pair - Share
Cognitive Skills: (see Bloom's Taxonomy) — Knowledge, Interpretation
Student Assessment: Minute Paper
BACKGROUND for Set #2 (back2.html)
Background
Although methane concentrations are much lower than carbon dioxide, per kilogram, methane is 25 times more effective at trapping heat in the Earth‘s atmosphere compared to carbon dioxide. Methane concentrations have increased by more than 100% since pre-industrial times, indicating that the increased sources due to human activity are much larger than the sinks (reaction with OH- in atmosphere and oxidation by soil bacteria). Every year, 84 Teragrams (Tg) are in excess in the Earth‘s atmosphere. Moss et al. (2000) combined literature values into one graph to show that agricultural activities contribute about half of all anthropogenic methane emissions, largely from animal digestion, waste, and rice paddies. More information about methane can be found on the U.S. EPA website: http://epa.gov/methane/. The table in this set (Table 2) was reconstructed from the Intergovernmental Panel on Climate Change (IPCC) reports from 2007, while the figure in this set is taken from Moss et al. (2000). The IPCC 2007 report, which compiled information from various scientific sources, provides detailed information about methane‘s contribution to climate change.
FIGURE SET HEADER for Set #3
Figure Set 3: Nitrogen Fertilizers Increase Nitrous Oxide Emissions
Purpose: To teach students that nitrous oxide is a very important greenhouse gas produced in soil, and that excess nitrogen fertilizer results in high levels of greenhouse gas emissions. Teaching Approach: Guided Class Discussion
Cognitive Skills: (see Bloom's Taxonomy) — knowledge, interpretation, synthesis Student Assessment: Short Essay
BACKGROUND for Set #3 (back3.html)
Background
Although the cumulative radiative forcing estimates for nitrous oxide (N2O) are lower than either carbon dioxide or methane, N2O contributes substantially to total radiative forcing by the Earth‘s atmosphere. Per unit mass, the radiative effectiveness of N2O is 298 times more than carbon dioxide, making each kilogram of N2O 298 times more relevant. The Intergovernmental Panel on Climate Change (IPCC) reported in 2007 that N2O has increased by 10% since pre-industrial time periods, but lasts in the atmosphere for approximately 114 years. In soil, bacteria produce N2O during the processes of nitrification and denitrification. During nitrification, ammonium is converted to nitrate, and N2O is a byproduct. Denitrification, the reduction of nitrate to nitrogen gas (N2), is an anaerobic process. Nitrous oxide is an intermediate product for many denitrifyers but can be the end product for some denitrifying bacteria (Robertson and Grace 2004). More information about nitrous oxide can be found on the U.S. EPA website: http://www.epa.gov/nitrousoxide/index.html. Nitrous oxide is an important greenhouse gas because of its high relative radiative effectiveness. Two factors influence relative radiative effectiveness, which are physical chemistry (including radiation absorption properties) and lifetime of a molecule in the atmosphere. Physical chemistry of a molecule determines the infrared (IR) wavelength absorbed. Gases with absorption bands in the non-visible portion of the IR spectrum, particularly between 1,000-1,200 wavenumbers, have the highest radiative forcing effect. Carbon dioxide absorption peaks occur at 2350 and 650 wavenumbers while nitrous oxide absorption peaks occur at 2,200 and 1,250 wavenumbers.
Agricultural soils high in available nitrogen are a major contributor of N2O to the atmosphere. Reactive (biologically available) nitrogen in the biosphere is twice as high as pre-industrial times, largely due to agricultural practices of fertilization and increased growth of nitrogen fixing crops (Vitousek et al. 1997). A good general source about human alteration of the global nitrogen cycle can be found on the Ecological Society of America website: http://www.esa.org/science_resources/issues.php.
FIGURE SET HEADER for Set #4
Figure Set 4 homepage Carbon Sequestration in Agricultural Soils
Purpose: To teach students that degraded agricultural soils can sequester carbon, and that there are certain management strategies that can maximize carbon storage in soil. Teaching
Approach: Paired Think Aloud
Cognitive Skills: (see Bloom's Taxonomy) — Knowledge, interpretation, synthesis Student Assessment: Short Essay
BACKGROUND for Set #4 (back4.html)
Background
Many agricultural fields in temperate regions have been cultivated for hundreds of years. In these fields, much of the carbon stored in soil has been lost to the atmosphere due to enhanced decomposition during cultivation (See Figure Set 1). Under conventional crop management, soil carbon loss eventually levels out & remains at a steady state at approximately 50% of original carbon levels. However, certain management strategies can slowly increase soil carbon content back towards original levels, which is called soil carbon sequestration. This can occur when net primary productivity due to plant growth exceeds respiration of organic carbon by soil biota. See Schlesinger (1999 – pdf included) or Post and Kwon (2000) for more information about carbon sequestration on agricultural soils. A simple explanation of carbon sequestration can be found at the U.S. EPA website: http://www.epa.gov/sequestration/local_scale.html. The data on soil carbon sequestration in Figure 4 were collected from a Long Term Ecological Research (LTER) Experiment at the W.K. Kellogg Biological Station in southwest Michigan. In this experiment, six ecosystems were established in 1989 and compared from 1989 to 1999 to characterize their ability to sequester carbon in the soil. These systems were compared to conventionally tilled (physically turned over) agricultural fields in which soil carbon concentrations were hypothesized to remain relatively unchanged over time. The first three ecosystems were cultivated with annual crops, in a corn-soybean-wheat rotation.
o The “Conventional” ecosystem received both soil tillage and pesticides to control weeds and was fertilized to maximize crop yields.
o “Organic” refers to an ecosystem that received no fertilizer or pesticides, but tillage was used to control weeds and legume (nitrogen fixing) cover crops were used as nitrogen fertilizer sources.
o “No-Till” refers to an ecosystem in which the soil was not disturbed after the start of the experiment in 1989. Instead, weeds were controlled using pesticides.
The last three agroecosystems contained perennial plants and no tillage.
o “Alfalfa” is a perennial nitrogen fixing plant that is grown for animal feed. Alfalfa was planted in 1989 and the above ground growth was cut and removed from the fields 3-4 times per year. Although perennial, alfalfa was replanted every 5-7 years to maintain vigorous growth, as older plants died and weeds invaded the fields.
o Successional communities are those that are left fallow and receive no human induced disturbances. “Early Successional” ecosystems were last tilled in 1988, but were left undisturbed, except for occasional burning to prevent trees from growing in the experimental plots.
o “Poplar trees” were first planted in 1989, and were harvested after 10 years of growth. Trees were cut and used as biofuel for electricity generation. After harvest, the trees re-sprouted and will be harvested a second time for the same purposes.
FIGURE SET HEADER for Set #5
Figure Set 5: Global Warming Potential – Temperate Agriculture
Purpose: To teach students that land management can affect the amount of greenhouse gas emissions from temperate agricultural production and that cessation of agriculture results in net sequestration of greenhouse gases in the soil. Students will play roles of various citizen groups to identify ways in which agricultural land management can affect a variety of different people around the world.
Teaching Approach: Citizens Argument
Cognitive Skills: (see Bloom's Taxonomy) — Knowledge, interpretation, analysis, synthesis Student Assessment: Land Management Activity
BACKGROUND for Set #5 (back5.html)
Background
Agriculture and climate change are inextricably linked, as was shown in Figure Sets 1-4. Not only will climate change affect agricultural crop production, but agriculture is a primary source of several greenhouse gases. As shown in Figure Set 1, cultivation of undisturbed soils results in the loss of soil carbon. The production of nitrogen fertilizer, burning of fossil fuels by machinery and lime applications also emit carbon dioxide to the atmosphere. Fertilized agricultural soils contribute a substantial amount of nitrous oxide to the atmosphere. Methane oxidation in soil is lower in agricultural soils compared to adjacent forested areas. All of these factors must be examined simultaneously to understand the cumulative global warming potential of agroecosystems. Many agricultural soils in temperate regions have been cultivated for many years. In these fields, much of the carbon stored in soil has been lost to the atmosphere due to enhanced decomposition during cultivation (See Figure Set 1). Soil carbon loss eventually levels out and remains at a steady state under conventional crop management. However, soil carbon content can actually increase under certain crop management strategies, including conservation tillage, cover crop planting and perennial crop growth. Likewise, other management strategies such as reducing fertilizer applications can reduce the amount of greenhouse gases emitted during management activities. Taken together, the net global warming potential can be calculated for different agroecosystems. Negative global warming potential values indicate net decreases in atmospheric heat trapping potential and positive global warming potential values indicate net increases in atmospheric heat trapping potential. The global warming potential (GWP) of five agroecosystems in the Long Term Ecological Research Experiment at the W.K. Kellogg Biological Station in SW Michigan were compared from 1989 – 1999 (Table 5). In this experiment, five ecosystems were compared from 1989 to 1999 for their total contribution to global warming. The first three ecosystems were cultivated with annual crops, in a corn-soybean-wheat rotation.
o The “Conventional Agriculture” ecosystem received both soil tillage and pesticides to control weeds and was fertilized to maximize crop yields.
o “No Till Agriculture” refers to an ecosystem in which the soil was not disturbed after the start of the experiment in 1989. Instead, weeds were controlled using pesticides.
o “Organic Agriculture” refers to an ecosystem that received no fertilizer or pesticides, but tillage was used to control weeds and legume (nitrogen fixing) cover crops were used as nitrogen fertilizer sources.
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