1. Climate and Biodiversity
Chapter 7

2. What factors influence climate?
Section 7-1
What factors influence climate?

3. The earth has many different climates
Weather is a set of physical conditions such as temperature, precipitation, humidity, wind, speed, cloud cover, and other factors in a given area for short periods of time.
Climate is an area’s general pattern of atmospheric conditions over periods ranging from 30 to thousands of years.
Earth’s current major climate zones and ocean currents are key components of the earth’s natural capital.

4. The earth has many different climates
Climate varies in different parts of the earth primarily because global air circulation and ocean currents distribute heat and precipitation unevenly between the tropics and other parts of the world.
Three major factors determine how air circulates in the lower atmosphere:
Uneven heating of earth’s surface by the sun.
Rotation of the earth on its axis.
Properties of air, water, and land.

5. Earth’s climate zones, major ocean currents, and upwelling areas

6. Arctic Circle Tropic of Cancer Tropic of Capricorn Antarctic Circle
Labrador current
Oyashio current
North Atlantic drift
Alaska
current
California current
North Pacific
drift
Canaries current
Gulf stream
Kuroshio current
Tropic of
Cancer
North equatorial current
Caribbean current
Monsoon
Guinea current
drift
Equatorial counter current
South equatorial
North equatorial current
South equatorial current
current
Brazil current
South equatorial current
Tropic of
Capricorn
West Australian current
Peru current
East Australian current
Benguela current
Figure 7.2: Natural capital.
This generalized map of the earth’s current climate zones shows the major ocean currents and upwelling areas (where currents bring nutrients from the ocean bottom to the surface). See an animation based on this figure at CengageNOW. Question: Based on this map, what is the general type of climate where you live?
West wind drift
West wind drift
West wind drift
Antarctic
Circle
Polar (ice)
Subarctic (snow)
Cool temperate
Highland
Warm ocean current
River
Warm temperate
Dry
Tropical
Major upwelling zones
Cold ocean current
Fig. 7-2, p. 123

7. The earth has many different climates
Prevailing winds blowing over the oceans produce mass movements of surface water called ocean currents. Major ocean currents help to redistribute heat from the sun, influencing climate and vegetation, especially near coastal areas.
El Niño–Southern Oscillation, or ENSO—is an example of the interaction of land and air.
Large-scale weather phenomenon occurring every few years when prevailing winds in the tropical Pacific Ocean weaken and change direction.
Above-average warming of Pacific waters can affect populations of marine species by changing the distribution of plant nutrients.

8. Global air circulation

9. Moist air rises, cools, and releases moisture as rain
Polar cap
Cold deserts
60°N
Air cools and descends at lower latitudes.
Evergreen coniferous forest
The highest solar energy input is at the equator.
Westerlies
Temperate deciduous
forest and grassland
30°N
Northeast trades
Hot desert
Tropical deciduous forest
Warm air rises and moves toward the poles.
Solar energy
Equator 0°
Tropical rain forest
Tropical deciduous forest
Hot desert
Southeast trades
30°S
Air cools and descends at lower latitudes.
Figure 7.3: Global air circulation: The largest input of solar energy occurs at the equator. As this air is heated, it would naturally rise and move toward the poles (left). However, the earth’s rotation deflects this movement of the air over different parts of the earth. This creates global patterns of prevailing winds that help to distribute heat and moisture in the atmosphere and result in the earth’s variety of forests, grasslands, and deserts (right).
Westerlies
Temperate deciduous forest and grassland
Cold deserts
60°S
Polar cap
Fig. 7-3, p. 123

10. Energy is transferred by convection in the atmosphere

11. Heat released radiates to space Moist surface warmed by sun
LOW PRESSURE
HIGH PRESSURE
Heat released radiates to space
Cool, dry air
Condensation and
precipitation
Falls, is compressed, warms
Rises, expands, cools
Warm, dry air
Hot, wet air
Figure 7.4: This diagram illustrates energy transfer by convection in the atmosphere. Convection occurs when warm, wet air rises, then cools and releases heat and moisture as precipitation (right side and top, center). Then the cooler, denser, and drier air sinks, warms up, and absorbs moisture as it flows across the earth’s surface (bottom) to begin the cycle again.
Flows toward low pressure, picks up moisture and heat
HIGH PRESSURE
LOW PRESSURE
Moist surface warmed by sun
Fig. 7-4, p. 124

12. Deep and shallow ocean currents

13. Warm, less salty, shallow current
Figure 7.5: Connected deep and shallow ocean currents: A connected loop of shallow and deep ocean currents transports warm and cool water to various parts of the earth. Question: How do you think this loop affects the climates of the coastal areas around it?
Cold, salty, deep current
Fig. 7-5, p. 124

14. Greenhouse gases warm the lower atmosphere
Greenhouse gases absorb and release heat, which warms the atmosphere, influencing the earth’s average temperatures and its climates.
The major greenhouse gases are:
Water vapor (H2O).
Carbon dioxide (CO2).
Methane (CH4).
Nitrous oxide (N2O).

15. Greenhouse gases warm the lower atmosphere
The natural greenhouse effect is a warming of the lower atmosphere and the earth’s surface.
Some of the energy that the earth’s surface absorbs from the sun is radiated into the atmosphere as heat.
Greenhouse gases absorbed some of this heat which warms the lower atmosphere, causing the greenhouse effect.

16. The earth’s surface features affect local climates
Heat is absorbed and released more slowly by water than by land, creating land and sea breezes.
Mountains interrupt the flow of prevailing surface winds and the movement of storms.
High mountains create the rain shadow effect.
Cities with bricks, asphalt, and traffic create distinct microclimates.

17. The rain shadow effect

18. Prevailing winds pick up moisture from an ocean.
On the windward side of a mountain range, air rises, cools, and releases moisture.
On the leeward side of the mountain range, air descends, warms, and releases little moisture, causing rain shadow effect.
Figure 7.6: The rain shadow effect is a reduction of rainfall and loss of moisture from the landscape on the side of mountains facing away from prevailing surface winds. Warm, moist air in onshore winds loses most of its moisture as rain and snow that fall on the windward slopes of a mountain range. This leads to semiarid and arid conditions on the leeward side of the mountain range and the land beyond. The Mojave Desert in the U.S. state of California and Asia’s Gobi Desert were both created by this effect.
Fig. 7-6, p. 125

19. How does climate affect the nature and location of biomes?
Section 7-2
How does climate affect the nature and location of biomes?

20. Climate helps to determine where organisms can live
Average annual precipitation and temperature lead to the formation of tropical (hot), temperate (moderate), and polar (cold) deserts, grasslands, and forests.
Climate and vegetation vary with latitude and elevation.
Biomes are large regions, each characterized by certain types of climate and dominant plant life.
Biomes are not uniform. They consist of a mosaic of patches, each with somewhat different biological communities but with similarities typical of the biome.

21. Average precipitation and temperature are determining factors

22. Evergreen coniferous forest
Cold
Arctic tundra
Cold desert
Evergreen coniferous forest
Temperate desert
Temperate deciduous forest
Temperate grassland
Chaparral
Figure 7.7: Natural capital.
This diagram demonstrates that average precipitation and average temperature, acting together as limiting factors over a long time, help to determine the type of desert, grassland, or forest in a particular area, and thus the types of plants, animals, and decomposers found in that area (assuming it has not been disturbed by human activities).
Tropical desert
Hot Wet
Tropical rain forest
Dry
Tropical grassland (savanna)
Fig. 7-7, p. 127

23. Biomes and climate both change with elevation and latitude

24. Tundra (herbs, lichens, mosses)
Elevation
Mountain ice and snow
Tundra (herbs, lichens, mosses)
Coniferous
Forest
Latitude (south to north)
Deciduous
Forest
Figure 7.8: This diagram shows the generalized effects of elevation (left) and latitude (right) on climate and biomes (Core Case study). Parallel changes in vegetation type occur when we travel from the equator toward the north pole and from lowlands to mountaintops. Question: How might the components of the left diagram change as the earth warms during this century? Explain.
Tropical
Forest
Tropical Forest
Deciduous Forest
Coniferous Forest
Tundra (herbs, lichens, mosses)
Polar ice and snow
Fig. 7-8, p. 127

25. The earth’s major biomes

26. Arctic tundra (cold grassland)
Tropic of Cancer
Equator
High mountains
Polar ice
Arctic tundra (cold grassland)
Temperate grassland
Tropic of Capricorn
Figure 7.9: Natural capital.
The earth’s major biomes—each characterized by a certain combination of climate and dominant vegetation—result primarily from differences in climate (Core Case study). Each biome contains many ecosystems whose communities have adapted to differences in climate, soil, and other environmental factors. People have removed or altered much of the natural vegetation in some areas for farming, livestock grazing, obtaining timber and fuelwood, mining, and construction of towns and cities. (Figure 3, p. S33, in Supplement 8 shows the major biomes of North America.) See an animation based on this figure at CengageNOW. Question: If you take away human influences such as farming and urban development, what kind of biome do you live in?
Tropical grassland (savanna)
Chaparral
Coniferous forest
Temperate deciduous forest
Temperate rain forest
Tropical rain forest
Tropical dry forest
Desert
Fig. 7-9, p. 128

27. There are three major types of desert
Deserts have low annual precipitation often scattered unevenly throughout the year. The sun warms the ground during the day and evaporates water; heat is quickly lost at night.
Tropical deserts are hot and dry most of the year, with few plants.
Temperate deserts have high daytime temperatures in summer and low in winter. Sparse vegetation is mostly cacti and other succulents.

28. There are three major types of desert
Cold deserts have sparse vegetation, cold summers and precipitation is low.
Desert soils take from decades to centuries to recover from disturbances such as off-road vehicle travel because deserts have slow plant growth, low species diversity, slow nutrient cycling, and very little water.

29. Typical variations in annual temperature (red) and precipitation (blue) in deserts

30. Stepped Art
Fig. 7-10, p. 129

31. There are three major types of grasslands
Grasslands occur mostly in the interiors of continents in areas too moist for deserts and too dry for forests.
Grasslands are not taken over by shrubs and trees because of seasonal droughts, grazing by large herbivores, and occasional fires.

32. There are three major types of grasslands
The three main types of grassland:
Tropical (e.g. savanna): Savanna contains widely scattered clumps of trees and is usually warm year-round with alternating dry and wet seasons
Temperate (e.g. short-grass and tall-grass prairies):Temperate grassland winters can be very cold, summers are hot and dry, and annual precipitation is fairly sparse and falls unevenly through the year.
Cold (e.g. cold grasslands or arctic tundra): Cold grasslands, or arctic tundra, are bitterly cold, treeless plains.
Permafrost forms when frozen underground soil exists for more than two consecutive years.

33. Typical variations in annual temperature (red) and precipitation (blue) in grasslands

34. Stepped Art
Fig. 7-11, p. 131

35. Intensively cultivated cropland

36. Some components and interactions in an arctic tundra ecosystem

37. Long-tailed jaeger Grizzly bear Caribou Snowy owl Mosquito Arctic fox
Horned lark
Willow ptarmigan
Dwarf
willow
Figure 7.13: This diagram shows some of the components and interactions in a tropical rain forest ecosystem. When these organisms die, decomposers break down their organic matter into minerals that plants use. Colored arrows indicate transfers of matter and energy between producers; primary consumers (herbivores); secondary, or higher-level, consumers (carnivores); and decomposers. Organisms are not drawn to scale. See an animation based on this figure at CengageNOW.
Lemming
Bacteria
Mountain
cranberry
Fungi
Moss campion
Producer
to primary consumer
Primary to secondary consumer
Secondary to higher-level consumer
All producers
and consumers
to decomposers
Fig. 7-13, p. 133

38. There are three major types of forests
Forests are lands dominated by trees.
The three main types of forest:
Tropical: Found near the equator with a warm and wet climate; ideal for a wide variety of plants and animals.
Dominated by broadleaf evergreen plants keep most of their leaves year-round. There is little vegetation on the forest floor because the dense tree-top canopy blocks most light from reaching the ground.
Very high net primary productivity and an incredible high level of biological diversity.

39. There are three major types of forests
Cover about 2% of the earth’s land surface but are estimated to contain at least 50% of the earth’s known terrestrial plant and animal species
Temperate:
Cool temperatures slow decomposition, so have a thick layer of slowly decaying leaf litter which is a storehouse of nutrients
Cold: northern coniferous (cone-bearing) and boreal.
Winters are long and extremely cold. Plant diversity is low, decomposition is slow.

40. Typical variations in annual temperature (red) and precipitation (blue) in forests

41. Stepped Art
Fig. 7-14, p. 134

42. Specialized plant and animal niches are stratified in a tropical rain forest

43. Black-crowned antpitta45
Emergent layer
Harpy eagle 40 35
Toco toucan
Canopy 30 25
Height (meters) 20
Understory
Wooly opossum 15
Figure 7.15: This diagram illustrates the stratification of specialized plant and animal niches in a tropical rain forest. Filling such specialized niches enables species to avoid or minimize competition for resources and results in the coexistence of a great variety of species. 10
Brazilian tapir
Shrub layer 5
Black-crowned antpitta
Ground layer
Fig. 7-15, p. 135

44. Components and interactions in a temperate deciduous forest ecosystem in North America

45. Metallic wood-boring beetle and larvae
Broad-winged hawk
Hairy woodpecker
White oak
White-footed
mouse
White-tailed
deer
Metallic wood-boring beetle and larvae
Mountain
winterberry
Shagbark hickory
Black racer snake
Figure 7.16: This diagram shows some of the components and interactions in a tropical rain forest ecosystem. When these organisms die, decomposers break down their organic matter into minerals that plants use. Colored arrows indicate transfers of matter and energy between producers; primary consumers (herbivores); secondary, or higher-level, consumers (carnivores); and decomposers. Organisms are not drawn to scale. See an animation based on this figure at CengageNOW.
May beetle
Long-tailed weasel
Fungi
Wood frog
Bacteria
Producer
to primary consumer
Primary to secondary consumer
Secondary to higher-level consumer
All producers
and consumers
to decomposers
Fig. 7-16, p. 136

46. Mountains play important ecological roles
Mountains are steep or high-elevation lands where dramatic changes in altitude, slope, climate, soil, and vegetation take place over a very short distance.
About 1.2 billion people (17% of the world’s population) live in mountain ranges or their foothills, and 4 billion people (57% of the world’s population) depend on mountain systems for all or some of their water.
Many mountains are islands of biodiversity surrounded by a sea of lower-elevation landscapes transformed by human activities.

47. Mountains play important ecological roles
Important ecological roles include:
Contain the majority of the world’s trees
Provide habitats for endemic species
Have sanctuaries for species that can migrate and surviving in higher altitudes if they are driven from lowlands by human activities or a warming climate..
Mountains play a critical role in the hydrologic cycle by serving as major storehouses of water.

48. How have human activities affected the world’s terrestrial ecosystems?
Section 7-3
How have human activities affected the world’s terrestrial ecosystems?

49. Humans have disturbed most of the earth’s land
About 62% of the world’s major terrestrial ecosystems are being degraded or used unsustainably.

50. Major human impacts on terrestrial ecosystems

51. Natural Capital Degradation
Major Human Impacts on Terrestrial Ecosystems
Deserts
Grasslands
Forests
Mountains
Large desert cities
Conversion to cropland
Clearing for agriculture, livestock grazing, timber, and urban development
Agriculture
Timber and mineral extraction
Destruction of soil and underground habitat by off-road vehicles
Release of CO2 to atmosphere from burning grassland
Figure 7.18: This diagram illustrates the major human impacts on the world's deserts, grasslands, forests, and mountains (Concept 7-3). Question: For each of these biomes, which two of the impacts listed do you think are the most harmful?
Hydroelectric dams and reservoirs
Conversion of diverse forests to tree plantations
Overgrazing by livestock
Depletion of groundwater
Air pollution blowing in from urban areas and power plants
Damage from off-road vehicles
Oil production and off-road vehicles in arctic tundra
Land disturbance and pollution from mineral extraction
Soil damage from off-road vehicles
Pollution of forest streams
Fig. 7-18, p. 138

52. Natural Capital Degradation
Major Human Impacts on Terrestrial Ecosystems
Large desert cities
Deserts
Destruction of soil and underground habitat by off-road vehicles
Depletion of groundwater
Land disturbance and pollution from mineral extraction
Grasslands
Conversion to cropland
Release of CO2 to atmosphere from burning grassland
Overgrazing by livestock
Oil production and off-road vehicles in arctic tundra
Forests
Clearing for agriculture, livestock grazing, timber, and urban development
Conversion of diverse forests to tree plantations
Damage from off-road vehicles
Pollution of forest streams
Mountains
Agriculture
Timber and mineral extraction
Hydroelectric dams and reservoirs
Air pollution blowing in from urban areas and power plants
Soil damage from off-road vehicles
Figure 7.18: This diagram illustrates the major human impacts on the world's deserts, grasslands, forests, and mountains (Concept 7-3). Question: For each of these biomes, which two of the impacts listed do you think are the most harmful?
Stepped Art
Fig. 7-18, p. 138

53. What are the major types of aquatic systems?
Section 7-4
What are the major types of aquatic systems?

54. Most of the earth is covered with water
About 71% of the earth’s surface is covered with salty ocean water.
One global ocean, divided it into four large areas by geographers.
Atlantic Ocean.
Pacific Ocean.
The largest; contains more than half of the earth’s water and covers one-third of the earth’s surface.
Arctic Ocean.
Indian Ocean.

55. The ocean planet

56. Land–ocean hemisphere
Figure 7-19 The ocean planet: The salty oceans cover 90% of the planet’s ocean hemisphere (left) and nearly half of its land-ocean hemisphere (right). (Concept 7-4).
Ocean hemisphere
Land–ocean hemisphere
Fig. 7-19, p. 139

57. Most of the earth is covered with water
Aquatic life zones are the aquatic counterparts of biomes
Distribution of aquatic organisms is determined largely by the water’s salinity—the amounts of various salts such as sodium chloride (NaCl) dissolved in a given volume of water.
Zones are classified into two major types:
Saltwater or marine life zones: Oceans and their bays, estuaries, and other coastal systems.
Freshwater life zones: Lakes, rivers, streams, and inland wetlands.

58. Most of the earth is covered with water
Four major types of aquatic organisms:
Plankton are weakly swimming and free-floating. Types include:
Phytoplankton: photosynthesizers, includes many types of algae.
Zooplankton: plankton that feed on other plankton.
Ultraplankton: huge populations of photosynthetic bacteria.
Nekton are strong-swimming consumers such as fish, turtles, and whales.

59. Most of the earth is covered with water
Benthos are bottom dwellers. Examples include:
Oysters, which anchor themselves to one spot.
Clams and some worms, which burrow into the bottom.
Lobsters and crabs, which walk on the sea floor.
Decomposers (mostly bacteria), which break down organic compounds in the dead bodies and wastes of aquatic organisms.

60. Most of the earth is covered with water
Key factors determining the type and number of organisms at various depths include:
Water temperature.
Dissolved oxygen content.
Availability of food.
Availability of light and nutrients required for photosynthesis.

61. Section 7-5
Why are marine aquatic systems important and how have we affected them?

62. Marine ecosystems

63. Oceans provide vital ecological and economic services
Enormous reservoirs of biodiversity with three major life zones: The coastal zone, open sea and ocean bottom.
The coastal zone
Warm, nutrient-rich, shallow water that extends from the high-tide mark on land to the edge of the continental shelf.
Makes up less than 10% of the world’s ocean area while containing 90% of all marine species and is the site of most large commercial marine fisheries.
Have high net primary productivity due to ample sunlight and plant nutrients that flow from land.

64. Major life zones and vertical zones in an ocean

65. Water temperature (°C)
High tide
Coastal Zone
Open Sea
Low tide
Depth in meters
Sea level
Photosynthesis 50
Euphotic Zone
Estuarine Zone
100
Continental shelf
200
500
Bathyal Zone
Twilight
1,000
1,500
Water temperature drops rapidly between the euphotic zone and the abyssal zone in an area called the thermocline .
Abyssal Zone
2,000
3,000
Figure 7-21 This diagram illustrates the major life zones and vertical zones (not drawn to scale) in an ocean. The actual depths of these zones vary by location. Available light determines the euphotic, bathyal, and abyssal zones. Temperature zones also vary with depth, shown here by the red line. Question: How is an ocean like a rain forest? (Hint: see Figure 7-15.)
Darkness
4,000
5,000
10,000 5 10 15 20 25 30
Water temperature (°C)
Fig. 7-21, p. 141

66. Estuaries and coastal wetlands are highly productive
Estuaries are where rivers meet the sea, forming partially enclosed bodies of water where seawater mixes with freshwater as well as nutrients and pollutants from streams and runoff from the land.
Associated coastal wetlands are areas covered with water all or part of the year.
Coastal wetlands are in temperate zones.
Mangrove forests are in tropical zones.
Some of the earth’s most productive ecosystems.

67. Estuaries and coastal wetlands are highly productive
Sea grass beds consist of plants that grow underwater in shallow marine and estuarine areas along most continental coastlines.
Coastal aquatic systems provide vital ecological and economic services such as:
Help maintain water quality in tropical coastal zones by filtering toxic pollutants, excess plant nutrients, and sediments, and by absorbing other pollutants.
Provide food, habitats, and nursery sites for a variety of aquatic and terrestrial species.
Reduce storm damage and coastal erosion by absorbing waves and storing excess water produced by storms and tsunamis.

68. Estuary in Madagascar

69. Coral reefs are storehouses of biodiversity
Underwater structures that are built primarily of limestone and form in the clear, warm coastal waters of the tropics and subtropics.
Highly productive ecosystems that are dazzling centers of biodiversity.
Reefs form from massive colonies of polyps that secrete limestone.
Coral reefs result from a mutually beneficial relationship between the polyps and single-celled algae called zooxanthellae that live in the tissues of the polyps.

70. Coral reefs are storehouses of biodiversity
Ecological services provided by coral reefs include:
Act as natural barriers that help to protect 15% of the world’s coastlines from erosion caused by waves and storms.
Provide habitats for about 25% of all marine organisms.
Produce about 10% of the global fish catch.
Provide fishing and ecotourism jobs for some of the world’s poorest countries.

71. Coral reefs are storehouses of biodiversity
Coral reefs are easily damaged because they grow slowly, are disrupted easily and require specific water conditions.
Coral bleaching occurs when stresses such as increased temperature cause the symbiotic zooxanthellae to die. Without food, the coral polyps die, leaving behind a white skeleton of calcium carbonate.

72. A healthy coral reef and a bleached one

73. Coral reefs are storehouses of biodiversity
Ocean water is becoming more acidic as it absorbs some of excess carbon dioxide from the atmosphere. The CO2 reacts with ocean water to form a weak acid, which can slowly dissolve the calcium carbonate that makes up the corals.
Almost 45–53% of the world’s shallow coral reefs have been destroyed or degraded by coastal development, pollution, overfishing, warmer ocean temperatures, increasing ocean acidity, and other stresses.

74. The open sea and the ocean floor host a variety of species
The open sea occurs beyond the edge of the continental shelf and is divided into three vertical zones largely on the basis of the penetration of sunlight.
The euphotic zone is the brightly lit upper zone, where drifting phytoplankton carry out about 40% of the world’s photosynthetic activity.
The bathyal zone is the middle zone, which gets little sunlight and therefore does not contain photosynthesizing producers.
The lowest zone, called the abyssal zone, is dark and very cold; it has little dissolved oxygen.

75. Human activities are disrupting and degrading marine ecosystems
About 45% of the world’s population and more than half of the U.S. population live along or near coasts.
Major threats to marine systems from human activities include:
Coastal development, which destroys and pollutes coastal habitats.
Runoff of nonpoint source pollution such as fertilizers, pesticides, and livestock.
Point-source pollution such as sewage from passenger cruise ships and spills from oil tankers.

76. Human activities are disrupting and degrading marine ecosystems
Overfishing, which depletes populations of commercial fish species.
Use of trawler fishing boats, which drag weighted nets across the ocean bottom and destroy habitats.
Invasive species, some introduced by humans, that can out compete populations of native aquatic species and cause economic damage.
Climate change which is warming the oceans and making them more acidic; this could cause a rise in sea levels during this century that would destroy coral reefs and flood coastal marshes and coastal cities.

77. Major threats to marine ecosystems by humans

78. Section 7-6
What are the major types of freshwater systems and how have human activities affected them?

79. Water stands in some freshwater systems and flows in others
Freshwater life zones include standing bodies of freshwater such as lakes, ponds, and inland wetlands, and flowing (lotic) systems such as streams and rivers.
Lakes are large natural bodies of standing freshwater formed when precipitation, runoff, streams and rivers, and groundwater seepage fill depressions.
Oligotrophic (poorly nourished) lakes have a small supply of plant nutrients, causing them to look crystal clear.

80. Water stands in some freshwater systems and flows in others
Eutrophic (well-nourished) lakes have a large supply of nutrients needed by producers, causing them have high productivity and look murky brown or green.
Cultural eutrophication occurs when human inputs of nutrients from the atmosphere and from nearby urban and agricultural areas accelerate eutrophication.

81. Freshwater systems provide many important services

82. Typical distinct zones of life in fairly deep temperate-zone lakes

83. Littoral zone Limnetic zone Profundal zone Benthic zone Painted turtle
Blue-winged teal
Green frog
Muskrat
Pond snail
Littoral zone
Plankton
Active Figure 7-28 There are typically distinct zones of life in any fairly deep temperate-zone lake. See an animation based on this figure at Question: How are deep lakes like tropical rain forests? (Hint: See Figure 7-15)
Limnetic zone
Profundal zone
Diving beetle
Northern pike
Benthic zone
Yellow perch
Bloodworms
Fig. 7-28, p. 146

84. The effect of nutrient enrichment on a lake

85. Freshwater streams and rivers carry water from the mountains to the oceans
Surface water becomes runoff when it flows into streams or lakes.
A watershed, or drainage basin, is the land area that delivers runoff, sediment, and dissolved substances to a stream or lake.
The downward flow of water from mountain highlands to the sea typically takes place in three aquatic life zones characterized by different environmental conditions:
The source zone, the transition zone, and the floodplain zone.

86. Three zones in the downward flow of water

87. Lake Glacier Rain and snow Headwaters Rapids Waterfall Tributary
Flood plain
Oxbow lake
Salt marsh
Delta
Deposited sediment
Ocean
Source Zone
Transition Zone
Figure 7-30: There are three zones in the downhill flow of water: the source zone, which contains mountain (headwater) streams; the transition zone, which contains wider, lower-elevation streams; and the floodplain zone, which contains rivers that empty into larger rivers or into the ocean.
Water
Sediment
Floodplain Zone
Fig. 7-30, p. 147

88. Freshwater inland wetlands are vital sponges
Inland wetlands are lands covered with freshwater all or part of the time and located away from coastal areas.
Marshes (mainly grasses, reeds, and few trees).
Swamps (dominated by trees and shrubs).
Prairie potholes (depressions carved out by ancient glaciers).
Floodplains (receive excess water during heavy rains and floods).
Seasonal wetlands (remain under water or are soggy for only a short time each year).
Arctic tundra (wet in summer).

89. Freshwater inland wetlands are vital sponges
Inland wetlands provide a number of free ecological and economic services, which include:
Filtering and degrading toxic wastes and pollutants.
Reducing flooding and erosion by absorbing storm water and releasing it slowly, and by absorbing overflows from streams and lakes.
Maintaining stream flows during dry periods.
Helping to recharge groundwater aquifers

90. Freshwater inland wetlands are vital sponges
Helping to maintain biodiversity by providing habitats for a variety of species,
Supplying valuable products such as fishes and shellfish, blueberries, cranberries, wild rice, and timber, and
Providing recreation for birdwatchers, nature photographers, boaters, anglers, and waterfowl hunters.

91. Human activities are disrupting and degrading freshwater systems
Dams and canals alter and destroy terrestrial and aquatic wildlife habitats along rivers and in their coastal deltas and estuaries by reducing water flow and increasing damage from coastal storms.
Flood control levees and dikes built along rivers disconnect the rivers from their floodplains, destroy aquatic habitats, and alter or reduce the functions of nearby wetlands.
Cities and farms add pollutants and excess plant nutrients to nearby streams, rivers, and lakes. This can cause explosions in the populations of algae and cyanobacteria, which deplete the lake’s dissolved oxygen. Fishes and other species may then die off, which causes a major loss in biodiversity.

92. Human activities are disrupting and degrading freshwater systems
Many inland wetlands have been drained or filled to grow crops or have been covered with concrete, asphalt, and buildings.
More than 50% of the inland wetlands in the continental United States have been lost which has increased flood damage in the United States.

93. Three big ideas
Differences in climate, based mostly on long-term differences in average temperature and precipitation, largely determine the types and locations of the earth’s deserts, grasslands, and forests.
Saltwater and freshwater aquatic systems cover almost three-fourths of the earth’s surface, and oceans dominate the planet.
The earth’s terrestrial and aquatic systems provide important ecological and economic services, which are being degraded and disrupted by human activities.