Chapter 42 Ecosystems (Sections 42.7 - 42.10)

1. Chapter 42Ecosystems(Sections 42.7 - 42.10)

2. 42.7 The Water Cycle • 97% of Earth’s water is in its oceans • Sunlight energy drives the water cycle by causing evaporation – water vapor in the atmosphere condenses into clouds, and returns to Earth’s surface as precipitation • water cycle • Movement of water among Earth’s oceans, atmosphere, and the freshwater reservoirs on land

3. Environmental Water Reservoirs Reservoir Volume (103 cubic kilometers) • Ocean 1,370,000 • Polar ice, glaciers 29,000 • Groundwater 4,000 • Lakes, rivers 230 • Atmosphere (water vapor) 14

4. The Water Cycle

5. The Water Cycle Atmosphere Windborne water vapor Evaporation from ocean Precipitation onto the land Evaporation from land plants (transporation) Precipitation into ocean Surface and groundwater flow Land Ocean Fig. 42.8, p. 715

6. Windborne water vapor Precipitation onto the land Evaporation from land plants (transporation) Precipitation into ocean Surface and groundwater flow The Water Cycle Atmosphere Evaporation from ocean Land Ocean Stepped Art Fig. 42.8, p. 715

7. How and Where Water Moves • Precipitation that falls on any specific area of land drains into its particular watershed • A watershed may be as small as a valley that feeds a stream, or as large as the Mississippi River Basin (drains 41% of the continental United States) • watershed • Land area that drains into a particular stream or river

8. How Water Moves (cont.) • Most precipitation seeps into the ground (groundwater): • Clay-rich soils hold the most soil water and sandy soils hold the least • Water that drains through soil layers often collects in natural underground reservoirs (aquifers) • The flow of groundwater and surface water (runoff) slowly returns water to oceans

9. Key Terms • groundwater • Soil water and water in aquifers • soil water • Water between soil particles • aquifer • Porous rock layer that holds some groundwater • runoff • Water that flows over soil into streams

10. Nutrients in Water • Important nutrients such as carbon, nitrogen, and phosphorus have soluble forms that can be moved from place to place by flowing water • Runoff from heavily fertilized lawns and agricultural fields carries dissolved phosphates and nitrates into streams and lakes, causing eutrophication

11. Limited Fresh Water • Groundwater (a limited resource) supplies drinking water to about half of the United States population • Water is being drawn from aquifers faster than natural processes can replenish it (groundwater overdrafts) • In coastal aquifers, salt water moves in and replaces fresh water (saltwater intrusion) • In the US, about 80% of the water withdrawn for human use ends up irrigating agricultural fields

12. Groundwater Troubles

13. Key Concepts • The Water Cycle • Most of Earth’s water is in its oceans • Only a tiny fraction is fresh water • Evaporation, condensation, precipitation, and flow of rivers and streams moves water • Water plays a role in other nutrient cycles because it carries soluble forms of those nutrients with it

14. Animation: Threats to Aquifers

15. 42.8 The Carbon Cycle • The carbon cycle is an atmospheric cycle • Most carbon is stored in rocks – it enters food webs as gaseous carbon dioxide or bicarbonate dissolved in water • carbon cycle • Movement of carbon, mainly between the oceans, atmosphere, and living organisms • atmospheric cycle • Biogeochemical cycle in which a gaseous form of an element plays a significant role

16. 6 Steps in the Carbon Cycle • Carbon in rocks is largely unavailable to living organisms • Carbon enters land food webs when plants use CO2 from the air in photosynthesis • CO2 released by aerobic respiration returns to the atmosphere • Carbon diffuses between atmosphere and ocean; bicarbonate forms when CO2 dissolves in seawater

17. 6 Steps in the Carbon Cycle • Marine producers take up bicarbonate for photosynthesis; marine organisms release CO2 from aerobic respiration • Many marine organisms incorporate carbon into shells • Shells become part of sediments • Sediments become limestone and chalk in Earth’s crust • Burning fossil fuels derived from ancient remains of plants puts additional CO2 into the atmosphere

18. 6 Steps in the Carbon Cycle

19. 6 Steps in the Carbon Cycle Atmospheric CO2 photosynthesis 2 1 burning fossil fuels 6 aerobic respiration diffusion between atmosphere and ocean 3 Land food webs Dissolved carbon in ocean 4 Fossil fuels death, burial, compaction over millions of years Marine organisms Earth’s crust sedimentation 5 1 Carbon enters land food webs when plants take up carbon dioxide from the air for use in photosynthesis. 1 Marine producers take up bicarbonate for use in photosynthesis, and marine organisms release carbon dioxide from aerobic respiration. 4 Many marine organisms incorporate carbon into their shells. After they die, these shells become part of the sediments. Over time, the sediments become carbon-rich rocks such as limestone and chalk in Earth’s crust. 5 Carbon returns to the atmosphere as carbon dioxide when plants and other land organisms carry out aerobic respiration. 2 Carbon diffuses between the atmosphere and the ocean. Bicarbonate forms when carbon dioxide dissolves in seawater. Burning of fossil fuels derived from the ancient remains of plants puts additional carbon dioxide into the atmosphere. 3 6 Fig. 42.10, p. 716

20. Atmospheric CO2 photosynthesis 2 1 burning fossil fuels 6 aerobic respiration diffusion between atmosphere and ocean 3 Land food webs Dissolved carbon in ocean 4 Fossil fuels death, burial, compaction over millions of years Marine organisms Earth’s crust sedimentation 5 6 Steps in the Carbon Cycle Stepped Art Fig. 42.10, p. 716

21. Animation: Carbon Cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

22. Carbon, the Greenhouse Effect,and Global Warming • Atmospheric CO2 and other “greenhouse gases” help keep Earth warm enough for life through the greenhouse effect • greenhouse effect • Warming of Earth’s lower atmosphere and surface as a result of heat trapped by greenhouse gases

23. Three Steps in the Greenhouse Effect • Earth’s atmosphere reflects some sunlight energy back into space • Some light energy reaches and warms Earth’s surface • Earth’s warmed surface emits heat energy • Some escapes into space • Some is absorbed and emitted in all directions by greenhouse gases

24. Three Steps in the Greenhouse Effect

25. Three Steps in the Greenhouse Effect light energy heat energy 3 1 2 Fig. 42.11, p. 717

26. Animation: Greenhouse Effect

27. Global Warming • Human-induced increase in atmospheric greenhouse gases correlates with global climate change • Current atmospheric CO2 is the highest in 420,000 years –and climbing • global climate change • A rise in temperature and shifts in other climate patterns

28. Key Concepts • The Carbon Cycle • Most of Earth’s carbon is tied up in rocks, but organisms take carbon up from water or the air • Carbon dioxide is one of the atmospheric greenhouse gases that help keep Earth’s surface warm • Increasing carbon dioxide in the air is the most likely cause of climate change

29. BBC Video: Carbon Dioxide’s Impact on Our Oceans

30. 42.9 The Nitrogen Cycle • Nitrogen moves in an atmospheric cycle (nitrogen cycle) • Atmospheric nitrogen (N2 or gaseous nitrogen) is Earth’s main nitrogen reservoir, but most organisms can’t use N2 • nitrogen cycle • Movement of nitrogen among the atmosphere, soil, and water, and into and out of food webs

31. Bacteria and Nitrogen Conversions • Only certain bacteria can make nitrogen available to other organisms, or return N2 to the atmosphere • nitrogen fixation • Bacteria use nitrogen gas (N2) to form ammonia (NH3) • nitrification • Bacteria convert ammonium (NH4+) to nitrates (NO3-) • denitrification • Bacteria convert nitrates or nitrites (NO2-) to nitrogen gas

32. 6 Steps in the Nitrogen Cycle • Nitrogen fixing cyanobacteria in soil, water, or lichens break bonds in N2 and form ammonia, which is ionized in water as ammonium (NH4+) and taken up by plants • Another group of nitrogen-fixing bacteria forms nodules on roots of peas and other legumes • Consumers get nitrogen by eating plants or one another; bacterial and fungal decomposers break down wastes and remains and return ammonium to the soil

33. 6 Steps in the Nitrogen Cycle • Nitrification converts ammonium to nitrates: • Ammonia-oxidizing bacteria and archaeans convert ammonium to nitrite (NO2–), • Bacteria convert nitrites to nitrates (NO3–) • Nitrates are taken up and used by producers • Denitrifying bacteria use nitrate for energy and release nitrogen gas into the atmosphere

34. The Nitrogen Cycle

35. The Nitrogen Cycle Land food webs nitrogen fixation by bacteria denitrification by bacteria 1 6 Waste and remains uptake by producers decomposition by bacteria and fungi uptake by producers 2 3 5 nitrification by bacteria 4 Soil nitrates (NO3–) Soil ammonium (NH4+) Fig. 42.12, p. 718

36. denitrification by bacteria 6 Waste and remains uptake by producers decomposition by bacteria and fungi uptake by producers 2 3 5 nitrification by bacteria 4 Soil nitrates (NO3–) The Nitrogen Cycle Land food webs nitrogen fixation by bacteria 1 Soil ammonium (NH4+) Stepped Art Fig. 42.12, p. 718

37. Animation: Nitrogen Cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

38. Human Effects on the Nitrogen Cycle • Manufactured ammonia fertilizers increase the concentration of hydrogen ions (H+) as well as nitrogen • Nutrient ions bound to soil particles get replaced by H+, and essential nutrients leach away in soil water • Nitrogen runoff also pollutes aquatic habitats • Burning fossil fuels releases nitrous oxide, a greenhouse gas that also contributes to acid rain • Nitrogen in acid rain has the same effects as fertilizers

39. 42.10 The Phosphorus Cycle • Most phosphorus is bonded to oxygen as phosphate (PO43– ) in rocks and sediments – and moves in a sedimentary cycle • phosphorus cycle • Movement of phosphorus among Earth’s rocks and waters, and into and out of food webs • sedimentary cycle • Biochemical cycle in which the atmosphere plays little role and rocks are the major reservoir

40. 8 Steps in the Phosphorus Cycle • Weathering and erosion move phosphates from rocks into soil, lakes, and rivers • Leaching and runoff carry dissolved phosphates to the ocean • Phosphorus comes out of solution and settles as deposits along continental margins • Slow movements of Earth’s crust uplift deposits onto land, where weathering releases phosphates from rocks

41. 8 Steps in the Phosphorus Cycle • Land plants take up dissolved phosphate from soil water • Land animals get phosphates by eating plants or one another; phosphorus returns to soil in wastes and remains • In seas, producers take up phosphate dissolved in seawater • Wastes and remains replenish phosphates in seawater

42. The Phosphorus Cycle

43. The Phosphorus Cycle Land food webs Rocks on land 1 weathering, erosion excretion, death, decomposition uptake by producers 5 6 leaching, runoff 2 7 Phosphates in seawater Marine food web Phosphates in soil, lakes, rivers 8 3 uplifting over geologic time 4 Marine sediments Fig. 42.13, p. 719

44. Land food webs Rocks on land excretion, death, decomposition uptake by producers 5 6 leaching, runoff 2 7 Phosphates in seawater Marine food web 8 3 uplifting over geologic time 4 Marine sediments The Phosphorus Cycle 1 weathering, erosion Phosphates in soil, lakes, rivers Stepped Art Fig. 42.13, p. 719

45. Phosphates and Eutrophication • Phosphorus is often a limiting factor for plant growth • Phosphate-rich droppings from seabird or bat colonies are used as fertilizer • Phosphate-rich rock is also mined for this purpose • Water pollution from high-phosphate fertilizers, detergents, or sewage can cause eutrophication

46. Key Concepts • Nitrogen and Phosphorus Cycles • Plants take up dissolved forms of nitrogen and phosphorus from soil water • Nitrogen is abundant in air, but only certain bacteria can use the gaseous form • Phosphorus has no major gaseous form; most of it is in rocks

47. Too Much of a Good Thing (revisited) • Water treatment systems can remove phosphates from household wastewater with additional treatment and cost • Phosphate-rich runoff from lawns usually goes into waterways without going through a treatment plant • The most effective and economical way to keep aquatic ecosystems healthy is to avoid using phosphate-rich products when substitutes are available

48. Animation: Phosphorus Cycle