NOTES TO FACULTY

Write before discussion

Scientists are not used to asking their students to write in class, except during an exam. "Write before discussion" is an example of low-states writing - when students can write their ideas but not be graded on their work. This exercise gives students time to think and compose their ideas and questions. It is especially useful for students who need "think-time" or who are less confident about interpreting data. We so often forget that students simply need time to ponder questions we pose for discussion. This is particularly true when the questions relate to a data set students must first understand. The time allotted for this exercise depends on the students; an average time is ten minutes.

Humans have changed the global N cycle on a enormous scale, but it is difficult to get this point across to students without quickly loosing them in a morass of very large numbers. In addition, it is usually necessary to teach the N cycle so that students understand what nitrogen fixation, denitrification, nitrification, and ammonification all mean. The terms are confusing and the concepts behind them (e.g. anaerobic respiration, chemoautotrophy) are not trivial.

This figure is therefore useful for introducing the massive changes to global N dynamics as a result of agriculture and fossil fuel burning because nitrogen fixation is the only part of the N cycle specifically named.

The data associated with Figure 1 are: 80 Tg/yr (teragram =1,000,000,000,000 g) for current industrial fixation of N for fertilizers, >20 Tg/yr released to the atmosphere from burning of fossil fuels, 40 Tg/yr for leguminous crops and forages in agriculture.

A challenge in using this figure will be to help students appreciate why these huge increases in N by human activity is such a concern. One way to approach this would be to choose an effect that most interests you (e.g. the various effects on atmosphere or terrestrial and aquatic systems) and bring the point home with some detailed descriptions. For instance, as a marine ecologist I would describe effects of N loading to estuaries such as the Chesapeake Bay or Long Island Sound, including anoxia and fish kill events. You might focus on local concerns (sewage treatment plants, agriculture, acid rain) as well.

Some students will have a difficult time understanding the figure as presented because they are not used to seeing data shown in this way (stacked values). Students will understand these data much better if they rework them to create a new figure, as suggested below for an assessment. This could be done as homework or in class with students working together in small groups. They can estimate the values from Figure 1 and decide on a different way to present the data (groups can present their different approaches in small classes), or you can suggest a few approaches (e.g. stacked histograms, pie graph). This will also give students experience creating their own figures with data. These figures need not be "beautiful" Excel figures; actually sketching them by hand allows many students to engage with the data better.

Questions for Discussion:

• In Figure 1, the range for estimates of natural N fixation is about 100-about 140 Tg. Why is the range so large? How might scientists come up with these values?


• Where do the numbers in the Figure come from? How accurate do you think these numbers are - how might you know this? What do you suppose limits scientists' ability to more accurately define these numbers?


• Why is there N in fossil fuels? What is its source?


• According to Vitousek et al. use of N for agriculture in developing countries stabilized in the 1970"s and the rapid increases since then is from use in developing countries. Explain this statement and its implications in regard to regulation of global N pollution.


• They also say that more than half of all industrially fixed N for agriculture up to 1990 has been used since 1980. Explain this statement and its implications.

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Student Assessment: Replot the data.

      For some people the data in Figure 1 are graphed in a way that is difficult to understand. For homework replot the data in this figure and be prepared to present your new figure in class (use the overhead transparency or other means described by your professor). You can either make the new graph by hand by simply sketching it on a piece of paper; alternatively you can use Excel to make a more "official" looking figure. Beauty of the new graph is not important, but clarity is.


EVALUATING AN ISSUE: How do you know whether it is working?

      On-going (also called formative) evaluation of the approaches your are using is critical to the success of student-active teaching. Why try out new ideas if you don't know whether or not they are working? This is a brief overview of formative evaluation. For more information, go to the Formative Evaluation essay in the Teaching Section.

Course Goals:

      Formative evaluation only works if you have clearly described your course goals - because the purpose of the evaluation is to assess whether a particular technique is helping students reach these goals. For instance, most of us have "learn important ecological concepts and information" as a course goal. If I reviewed the nitrogen cycle in a class, for evaluation I might ask students to sketch out a nitrogen cycle for a particular habitat or system. Each student could work alone in class. Alternatively, I might ask students to work in groups of 3 and give each group a different situation (e.g. a pond receiving nitrate from septic systems, an organic agricultural field, an agricultural field receiving synthetic fertilizer). The students could draw their flows on a large sheet of paper (or an overhead transparency) and present this to the rest of the class.

The Minute Paper:

      Minute papers are very useful evaluative tools. If done well they give you good feedback quickly. Minute papers are done at the end of a class. The students are asked to respond anonymously to a short question that you ask. They take a minute or so to write their response in a 3x5 card or a piece of paper. You collect these and learn from common themes. In the next class it is important that you refer to one or two of these points so that students recognize that their input matters to you. The UW - FLAG site (www.wcer.wisc.edu/nise/cl1/flag/) gives a good deal of information about using minute papers including their limitations, how to phrase your question, step-by-step instructions, modifications, and the theory and research behind their use.