Concepts of Biology, 2013

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544 Chapter 20 | Ecosystems and the Biosphere Figure 20.14 Dead zones occur when phosphorus and nitrogen from fertilizers cause excessive growth of microorganisms, which depletes oxygen and kills fauna. Worldwide, large dead zones are found in areas of high population density. (credit: Robert Simmon, Jesse Allen, NASA Earth Observatory) A dead zone is an area in lakes and oceans near the mouths of rivers where large areas are periodically depleted of their normal flora and fauna; these zones can be caused by eutrophication, oil spills, dumping toxic chemicals, and other human activities. The number of dead zones has increased for several years, and more than 400 of these zones were present as of 2008. One of the worst dead zones is off the coast of the United States in the Gulf of Mexico: fertilizer runoff from the Mississippi River basin created a dead zone of over 8,463 square miles. Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems including the Chesapeake Bay in the eastern United States. This OpenStax book is available for free at http://cnx.org/content/col11487/1.9
Chapter 20 | Ecosystems and the Biosphere 545 Chesapeake Bay Figure 20.15 This (a) satellite image shows the Chesapeake Bay, an ecosystem affected by phosphate and nitrate runoff. A (b) member of the Army Corps of Engineers holds a clump of oysters being used as a part of the oyster restoration effort in the bay. (credit a: modification of work by NASA/MODIS; credit b: modification of work by U.S. Army) The Chesapeake Bay (Figure 20.15a) is one of the most scenic areas on Earth; it is now in distress and is recognized as a case study of a declining ecosystem. In the 1970s, the Chesapeake Bay was one of the first aquatic ecosystems to have identified dead zones, which continue to kill many fish and bottomdwelling species such as clams, oysters, and worms. Several species have declined in the Chesapeake Bay because surface water runoff contains excess nutrients from artificial fertilizer use on land. The source of the fertilizers (with high nitrogen and phosphate content) is not limited to agricultural practices. There are many nearby urban areas and more than 150 rivers and streams empty into the bay that are carrying fertilizer runoff from lawns and gardens. Thus, the decline of the Chesapeake Bay is a complex issue and requires the cooperation of industry, agriculture, and individual homeowners. Of particular interest to conservationists is the oyster population (Figure 20.15b); it is estimated that more than 200,000 acres of oyster reefs existed in the bay in the 1700s, but that number has now declined to only 36,000 acres. Oyster harvesting was once a major industry for Chesapeake Bay, but it declined 88 percent between 1982 and 2007. This decline was caused not only by fertilizer runoff and dead zones, but also because of overharvesting. Oysters require a certain minimum population density because they must be in close proximity to reproduce. Human activity has altered the oyster population and locations, thus greatly disrupting the ecosystem. The restoration of the oyster population in the Chesapeake Bay has been ongoing for several years with mixed success. Not only do many people find oysters good to eat, but the oysters also clean up the bay. They are filter feeders, and as they eat, they clean the water around them. Filter feeders eat by pumping a continuous stream of water over finely divided appendages (gills in the case of oysters) and capturing prokaryotes, plankton, and fine organic particles in their mucus. In the 1700s, it was estimated that it took only a few days for the oyster population to filter the entire volume of the bay. Today, with the changed water conditions, it is estimated that the present population would take nearly a year to do the same job. Restoration efforts have been ongoing for several years by non-profit organizations such as the Chesapeake Bay Foundation. The restoration goal is to find a way to increase population density so the
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Concepts of Biology SENIOR CONTRIBU
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OPENSTAX OpenStax provides free, pe
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Table of Contents Preface . . . . .
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Preface 1 PREFACE Welcome to Concep
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Preface 3 Concepts in Action featur
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Chapter 1 | Introduction to Biology
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Chapter 2 | Chemistry of Life 27 2
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Chapter 2 | Chemistry of Life 29 Th
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Chapter 2 | Chemistry of Life 31 Ch
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Chapter 2 | Chemistry of Life 35 Fi
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Chapter 2 | Chemistry of Life 37 a
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Chapter 2 | Chemistry of Life 39 2.
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Chapter 2 | Chemistry of Life 47 Th
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Chapter 2 | Chemistry of Life 49 Nu
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Chapter 2 | Chemistry of Life 51 KE
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Chapter 2 | Chemistry of Life 53 so
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Chapter 3 | Cell Structure and Func
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Chapter 4 | How Cells Obtain Energy
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Chapter 5 | Photosynthesis 117 5 |
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Chapter 5 | Photosynthesis 119 Figu
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Chapter 5 | Photosynthesis 121 impo
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Chapter 5 | Photosynthesis 123 wave
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Chapter 5 | Photosynthesis 127 Afte
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Chapter 5 | Photosynthesis 133 5.2
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Chapter 6 | Reproduction at the Cel
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Chapter 7 | The Cellular Basis of I
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Chapter 8 | Patterns of Inheritance
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Chapter 9 | Molecular Biology 199 9
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Chapter 9 | Molecular Biology 217 e
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Chapter 10 | Biotechnology 225 10 |
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Chapter 10 | Biotechnology 231 Natu
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Chapter 10 | Biotechnology 245 KEY
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Chapter 10 | Biotechnology 247 REVI
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Chapter 11 | Evolution and Its Proc
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Chapter 12 | Diversity of Life 275
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Chapter 13 | Diversity of Microbes,
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Chapter 14 | Diversity of Plants 32
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Chapter 15 | Diversity of Animals 3
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Chapter 16 | The Body’s Systems 4
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Chapter 17 | The Immune System and
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Chapter 18 | Animal Reproduction an
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Appendix B 595 APPENDIX B | GEOLOGI
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Appendix C 597 APPENDIX C | MEASURE
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Answer Key 599 ANSWER KEY Chapter 1
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Answer Key 601 that extends the 3'
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Answer Key 603 I molecules expresse
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Index 605 INDEX A absorption spectr
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Index 607 density-independent regul
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Index 609 intracellular, 421 intrac
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Index 611 phototrophs, 292 phylogen
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Index 613 tropical rainforest, 565
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Concepts of Biology, 2013

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