Soil Erosion and Conservation: A Policy Debate - Prof. T. Dunne, Assignments of Environmental Science

Download Soil Erosion and Conservation: A Policy Debate - Prof. T. Dunne and more Assignments Environmental Science in PDF only on Docsity! ESM 203: Earth System Science Homework 4 Tom Dunne 27 November 2007, due 6 December 5:00 pm Carl Legleiter (via e-mail to Carl) Soil Erosion, Soil Conservation: The Policy Debate The readings for this homework exercise are in the course reader and on the web page. They provide an introduction to an important policy debate that is emerging in this nation and within international funding and development agencies. This exercise asks you to explore six short papers on the subject and to articulate the major issues being debated. (1) The first paper by Douglas [1990] gives many (out of many more) examples of erosion accelerated by land use and sedimentation that occurs on a scale large enough to cause significant problems for societies. (2) The next paper, by the ecologist Pimentel and his students [Pimentel et al., 1995], extends the concern about erosion’s effects on natural resources and water quality, and tries to quantify the associated economic costs. The authors also argue that the cost of soil conservation measures to reduce erosion across the US would be much less than the estimated costs of the erosion. (3) The follow-up commentary by the economist Crosson [1995] raises questions about Pimentel’s estimates of costs and benefits and the authorities they quote. (4) In 1999, the geomorphologist Trimble [1999] reported a long-running empirical study of soil loss from a single catchment, and used his results to motivate another questioning of Pimentel’s claims . . . (5) . . . thus prompting the embattled Pimentel to mobilize an ally (Skidmore) from the US Department of Agriculture to defend the proposition that soil erosion is an important threat to the nation [Pimentel and Skidmore, 1999]. (6) Trimble and Crosson [2000] then joined forces to ask what is myth and what is reality in this debate over the appropriate level of concern and investment about the environmental damage caused by soil erosion. Homework assignment Read the various estimates and opinion pieces, and summarize the key points of the debate. What are the differences of opinion? What kinds of evidence do the two sides use? What does each side propose, or imply, that government should do about the problem? Is there a compromise position, or should we ‘believe’ one or the other? If we accept a compromise, what should be DONE? Write a brief report in the form of a talk on the status of the debate for an agency committee, which is deciding whether the agency should act in one way or the other (for example, whether to continue, discontinue, or expand subsidies for national soil conservation programs.) Make the report very focused. Don’t just tell us everything you have discovered about soil erosion. You are designing a talk, which in less than half an hour has to inform a non-technical decision-making body, which will make a decision soon. Work out the material in your group. Find a spare room with a blackboard and discuss the critical points to create the outline of an argument that everyone can see. Practice developing an exact position. Summarize your points from the blackboard. Assign a lead writer to produce the first draft. Help this person as much as possible by each agreeing to write one paragraph on an exactly defined topic from the blackboard outline. Write the paragraph promptly. (It will never be easier than immediately after that meeting.) Then all of you should review and polish it before submitting NO MORE THAN TWO pages. We want just one report from each group. Remember that we want to be affected. Tell us what to do and why. ********************************************************** BUT, “Whoa!”, you say. What’s all this discussion about prediction of soil erosion by computer models? Are these like global climate models? The most widely used of these models (and increasingly the only model used) is called the Universal Soil Loss Equation (USLE), developed by the US Department of Agriculture in the 1950-70s, and clung to with increasing desperation by that agency and every other agency that needs to make predictions by a rapid, convenient (data-sparse) means for public policy. If you use one of the water quality models to predict concentrations of sediment and associated contaminants in streams for Total Maximum Daily Loads or similar regulatory fantasies, the sediment prediction originates from the USLE buried deep in visually appealing software. The coefficients required for the equation are revised every few years by US DA on the basis of judgments of experienced soil conservation specialists, so the equation is now called the R(evised)USLE, and you can access it on the web in the form of a calculator. In order to avoid viewing the RUSLE as a Wizard of Oz, it is revealing to use it for a simple hand calculation. Background and instructions for doing so can be found in the document on Soil Erosion Prediction, a chapter from an old textbook by Dunne and Leopold (1978) that you can download from the ESM203 homework website. Use it to make and report the following exercise before you address the policy debate outlined above. There is much talk about using corn for biofuel, and the agricultural community across the Midwest is already expanding the area seeded to corn. Some of the land that can be used for corn (or other biofuel) production has been withdrawn from cropping in recent decades through a government-subsidized program that pays farmers not to plant in order to reduce soil erosion and water pollution from lands that are most vulnerable to accelerated erosion. Your agency asks you to make a rough estimate of the degree to which erosion might be accelerated and water pollution intensified if marginal croplands are used for biofuels. Since the USLE/RUSLE is the only method that can be used quickly, and it is already widely used for similar planning and assessments, you decide to use it to make a sample calculation --- realizing that other degrees of complexity could be introduced later in the form of more sites, more soils, seasonality of rainfall and cropping, etc. You choose a site in the far southwestern corner of Iowa (reason for choice will become