Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 42Ecosystems(Sections 42.7 - 42.10)

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

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

The Water Cycle

Fig. 42.8, p. 715

LandOcean

Precipitation onto the land

Surface and groundwater

flow

Evaporation from land plants (transporation)

Precipitation into ocean

Atmosphere

Windborne water vaporEvaporation from ocean

The Water Cycle

Fig. 42.8, p. 715

LandOcean

Surface and groundwater

flow

Evaporation from land plants (transporation)

Precipitation into ocean

Atmosphere

Precipitation onto the land

Windborne water vaporEvaporation from ocean

Stepped Art

The Water Cycle

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

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

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

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

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

Groundwater Troubles

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

Animation: Threats to Aquifers

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

6 Steps in the Carbon Cycle

• Carbon in rocks is largely unavailable to living organisms

1. Carbon enters land food webs when plants use CO2 from the air in photosynthesis

2. CO2 released by aerobic respiration returns to the atmosphere

3. Carbon diffuses between atmosphere and ocean; bicarbonate forms when CO2 dissolves in seawater

6 Steps in the Carbon Cycle

4. Marine producers take up bicarbonate for photosynthesis; marine organisms release CO2 from aerobic respiration

5. Many marine organisms incorporate carbon into shells • Shells become part of sediments• Sediments become limestone and chalk in Earth’s crust

6. Burning fossil fuels derived from ancient remains of plants puts additional CO2 into the atmosphere

6 Steps in the Carbon Cycle

Fig. 42.10, p. 716

Marine organismssedimentation

Earth’s crust

death, burial, compaction over millions of years

Fossil fuels

Dissolved carbon in ocean

Land food webs

diffusion between atmosphere and

ocean

aerobic respiration

Atmospheric CO2

photosynthesisburning fossil fuels

Burning of fossil fuels derived from the ancient remains of plants puts additional carbon dioxide into the atmosphere.

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.

Marine producers take up bicarbonate for use in photosynthesis, and marine organisms release carbon dioxide from aerobic respiration.

Carbon diffuses between the atmosphere and the ocean. Bicarbonate forms when carbon dioxide dissolves in seawater.

Carbon returns to the atmosphere as carbon dioxide when plants and other land organisms carry out aerobic respiration.

Carbon enters land food webs when plants take up carbon dioxide from the air for use in photosynthesis.

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2

3

4

5

11

2

3

4

5

6

6

6 Steps in the Carbon Cycle

Fig. 42.10, p. 716

Land food webs

Atmospheric CO2

photosynthesis1aerobic respiration

2

Dissolved carbon in ocean

diffusion between atmosphere and

ocean3

Marine organisms

4

sedimentationEarth’s crust

5

death, burial, compaction over millions of years

Fossil fuels

burning fossil fuels6

Stepped Art

6 Steps in the Carbon Cycle

Animation: Carbon Cycle

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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

Three Steps in the Greenhouse Effect

1. Earth’s atmosphere reflects some sunlight energy back into space

2. Some light energy reaches and warms Earth’s surface

3. Earth’s warmed surface emits heat energy• Some escapes into space• Some is absorbed and emitted in all directions by

greenhouse gases

Three Steps in the Greenhouse Effect

Fig. 42.11, p. 717

heat energy

light energy

1

2

3

Three Steps in the Greenhouse Effect

Animation: Greenhouse Effect

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

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

BBC Video: Carbon Dioxide’s Impact on Our Oceans

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

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

6 Steps in the Nitrogen Cycle

1. 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

2. Another group of nitrogen-fixing bacteria forms nodules on roots of peas and other legumes

3. Consumers get nitrogen by eating plants or one another; bacterial and fungal decomposers break down wastes and remains and return ammonium to the soil

6 Steps in the Nitrogen Cycle

4. Nitrification converts ammonium to nitrates:• Ammonia-oxidizing bacteria and archaeans convert

ammonium to nitrite (NO2–),

• Bacteria convert nitrites to nitrates (NO3–)

5. Nitrates are taken up and used by producers

6. Denitrifying bacteria use nitrate for energy and release nitrogen gas into the atmosphere

The Nitrogen Cycle

Fig. 42.12, p. 718

nitrogen fixation by bacteria

Soil ammonium (NH4

+)

uptake by producers

Land food webs

Waste and remains

uptake by producers

decomposition by bacteria and fungi

denitrification by bacteria

nitrification by bacteria Soil nitrates

(NO3–)

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2 3

4

6

5

The Nitrogen Cycle

Fig. 42.12, p. 718

nitrogen fixation by bacteria

Soil ammonium (NH4

+)

Land food webs

1

uptake by producers2

Waste and remains

decomposition by bacteria and fungi3

denitrification by bacteria6

nitrification by bacteria Soil nitrates

(NO3–)

4

Stepped Art

uptake by producers5

The Nitrogen Cycle

Animation: Nitrogen Cycle

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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

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

8 Steps in the Phosphorus Cycle

1. Weathering and erosion move phosphates from rocks into soil, lakes, and rivers

2. Leaching and runoff carry dissolved phosphates to the ocean

3. Phosphorus comes out of solution and settles as deposits along continental margins

4. Slow movements of Earth’s crust uplift deposits onto land, where weathering releases phosphates from rocks

8 Steps in the Phosphorus Cycle

5. Land plants take up dissolved phosphate from soil water

6. Land animals get phosphates by eating plants or one another; phosphorus returns to soil in wastes and remains

7. In seas, producers take up phosphate dissolved in seawater

8. Wastes and remains replenish phosphates in seawater

The Phosphorus Cycle

Fig. 42.13, p. 719

Marine sedimentsuplifting over geologic time

Marine food web

Phosphates in seawater

leaching, runoff

Phosphates in soil, lakes, rivers

excretion, death, decomposition uptake

by producers

weathering, erosion

Rocks on land

Land food webs

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2

3

4

5

67

8

The Phosphorus Cycle

uplifting over geologic time

Rocks on land

4

Fig. 42.13, p. 719

Phosphates in soil, lakes, rivers

weathering, erosion

1

Phosphates in seawater

leaching, runoff

2

Marine sediments

3

excretion, death, decomposition uptake

by producers

Land food webs

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Marine food web

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8

Stepped Art

The Phosphorus Cycle

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

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

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

Animation: Phosphorus Cycle