Chapter 7

Essential Environment: The Science behind the Stories (3rd Edition)

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7 Environmental Systems and Ecosystem Ecology Chapter Objectives This chapter will help students: Describe the nature of environmental systems Define ecosystems and evaluate how living and nonliving entities interact in ecosystem-level ecology Compare and contrast how carbon, phosphorus, nitrogen, and water cycle through the environment Explain how plate tectonics and the rock cycle shape the earth beneath our feet Lecture Outline I. Central Case: The Gulf of Mexico’s “Dead Zone” A. In 2002, the dead zone grew to its largest size ever—22,000 square km (8,500 square miles). B. The dead zone is a region in the Gulf of Mexico so depleted of oxygen that it cannot support marine organisms, a condition called hypoxia. C. The change from productive fishery to dead zone has occurred in the last 30 years. The spread of the hypoxic zone threatens the Gulf’s fishing industry, one of the most productive fisheries in the United States. D. Scientists studying the dead zone have determined that fertilizer runoff from midwestern farms is a major cause. E. Other important causes include urban runoff, industrial discharge, fossil fuel combusion, and municipal sewage. II. Earth’s Environmental Systems A. Systems show several defining properties.
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1. A system is a network of relationships among a group of parts, elements, or components that interact with and influence one another through the exchange of energy, matter, and/or information. 2. Systems receive input, process it, and produce output. 3. Sometimes a system’s output can serve as input to that same system in a circular process called a feedback loop. a. In a negative feedback loop, output driving the system in one direction acts as input that moves the system in the other direction. b. In a positive feedback loop, the output drives the system further toward one extreme. 4. The inputs and outputs of a complex natural system often occur simulta- neously, keeping the system constantly active. If they are in balance, it is called a dynamic equilibrium. 5. Processes in dynamic equilibrium contribute to homeostasis, where the tendency of the system is to maintain stable internal conditions. 6. It is difficult to fully understand systems by focusing on their individual components because systems can show emergent properties, characteristics that are not evident in the system’s components. 7. Systems rarely have well-defined boundaries, so deciding where one system ends and another begins can be difficult. 8. A closed system is isolated and self-contained, having no interactions with other systems. This does not occur in nature but is a useful way to begin considering a simple version of a system. 9. An open system exchanges energy, matter, and information with other systems. All systems on Earth are open systems. B.
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Chapter 7 - 7 Environmental Systems and Ecosystem Ecology...

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