1. Chapter 42 Ecosystems (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
Atmosphere (water vapor) 14

4. The Water Cycle

5. Precipitation into ocean
The Water Cycle
Atmosphere
Evaporation from ocean
Windborne water vapor
Precipitation
onto the land
Evaporation
from land plants
(transporation)
Precipitation into ocean
Surface and
groundwater
flow
Figure The water cycle. Water moves from the ocean to the atmosphere, land, and back. The arrows identify processes that move water.
Land
Ocean
Fig. 42.8, p. 715

6. Precipitation into ocean
The Water Cycle
Atmosphere
Precipitation
onto the land
Windborne water vapor
Evaporation from ocean
Evaporation
from land plants
(transporation)
Precipitation into ocean
Surface and
groundwater
flow
Figure The water cycle. Water moves from the ocean to the atmosphere, land, and back. The arrows identify processes that move water.
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
Figure 42.9 Groundwater troubles in the United States.

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 1
photosynthesis 2 6
burning fossil fuels
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
Figure The carbon cycle. Most carbon is in Earth’s crust, where it is largely unavailable to living organisms.
Carbon enters land food webs when plants take up carbon dioxide from the air for use in photosynthesis. 1 1
Marine producers take up bicarbonate for use in photosynthesis, and marine organisms release carbon dioxide from aerobic respiration. 4
Carbon returns to the atmosphere as carbon dioxide when plants and other land organisms carry out aerobic respiration. 2
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 diffuses between the atmosphere and the ocean. Bicarbonate forms when carbon dioxide dissolves in seawater. 3
Burning of fossil fuels derived from the ancient remains of plants puts additional carbon dioxide into the atmosphere. 6
Fig , p. 716

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

21. Animation: Carbon Cycle
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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
Figure Greenhouse effect. 2
Fig , 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 Figure 42.12 Nitrogen cycle in a land ecosystem.
Land food webs
nitrogen fixation
by bacteria 1
denitrification
by bacteria 6
Waste and remains
uptake
by producers 2
decomposition by
bacteria and fungi 3
uptake
by producers 5
Figure Nitrogen cycle in a land ecosystem.
nitrification
by bacteria 4
Soil ammonium
(NH4+)
Soil nitrates
(NO3–)
Fig , p. 718

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

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

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