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Ecosystems
Chapter 47 Part 2
47.7 Carbon Cycle
 In the carbon cycle, carbon moves though all
food webs, to and from its major reservoirs
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Earth’s crust: 66 to 100 million gigatons
World ocean: 38,000 to 40,000 gigatons
Fossil fuel reserves: 4,000 gigatons
Detritus in soil: 1,500 to 1,600 gigatons
Air: 766 gigatons (mostly as CO2)
Biomass: 540 to 610 gigatons
Movements of Carbon
 Most of the annual cycling of carbon occurs
between the ocean and the atmosphere
• Some CO2 in surface waters is converted to
bicarbonate (carbon-oxygen cycling) and moved
by ocean currents to deep ocean reservoirs
 Photosynthesis, aerobic respiration,
decomposition, and formation of carbonate
sediments all contribute to the carbon cycle
Carbon Cycling
Carbon Cycling
Animation: Carbon cycle
Deep Ocean Reservoirs
Humans Are Altering the Carbon Cycle
 Each year we withdraw 4 to 5 gigatons of fossil
fuel from environmental reservoirs; and put 6
gigatons more carbon into the air than can be
recycled to ocean reservoirs
 Excess CO2 entering the atmosphere may be a
factor in global climate change
47.8 Greenhouse Gases, Global Warming
 Greenhouse effect
• Radiant energy from the sun is absorbed by
Earth’s surface and radiated back as heat
• Gases in the upper atmosphere trap heat like a
greenhouse, and radiate it back to Earth
• Greenhouse gases: carbon dioxide, water, nitrous
oxide, methane, chlorofluorocarbons (CFCs)
The Greenhouse Effect
Animation: Greenhouse effect
Atmospheric Observations
 Atmospheric CO2 fluctuates annually with
patterns of photosynthesis
 Average concentrations of CO2 and other
greenhouse gases are increasing
 Human activities – mainly burning of fossil fuels
– increase greenhouse gases
Increasing Greenhouse Gases
Global Warming
 Global warming
• A long-term increase in temperature near Earth’s
surface, currently about 1.8°C (3.2°F) per century
 Scientists expect far-reaching effects
• Melting glaciers and rising sea levels
• Altered global precipitation patterns, droughts and
flooding, more intense hurricanes
Changes in Global Mean Temperatures
Fig. 47-17a, p. 853
Fig. 47-17b, p. 853
Fig. 47-17c, p. 853
Fig. 47-17d, p. 853
Fig. 47-18, p. 853
The Shrinking Antarctic Ice Shelf
Fig. 47-24a, p. 859
Fig. 47-24b, p. 859
47.9 Nitrogen Cycle
 Gaseous nitrogen (N2) makes up about 80
percent of the lower atmosphere
• Most organisms can’t use gaseous nitrogen
 The nitrogen cycle starts with nitrogen fixation
• Nitrogen-fixing bacteria convert N2 in the air to
ammonia (NH3), then to ammonium (NH4+) and
nitrate (NO3-), which plants easily take up
Other Nitrogen Inputs Into Ecosystems
 Ammonification
• Bacteria and fungi make additional ammonium
available to plants when they break down
nitrogen-rich wastes and remains
 Nitrification
• Bacteria convert ammonium to nitrite (NO2-), and
then to nitrate, which plants easily take up
Losing Nitrogen from Ecosystems
 Denitrification
• Denitrifying bacteria convert nitrate or nitrite to
gaseous nitrogen (N2) or nitrogen oxide (NO2)
 Ammonium, nitrite, and nitrate are also lost from
land ecosystems in runoff and by leaching
Nitrogen Cycle in a Land Ecosystem
gaseous nitrogen
in atmosphere
food webs on land
nitrogen fixation
fertilizers
excretion, death,
uptake by autotrophs decomposition
ammonia, ammonium in soil
nitrogen-rich
wastes, remains
in soil
ammonification
loss by leaching
nitrification
uptake by autotrophs
loss by
denitrification
nitrate in soil
nitrification
nitrite in soil
loss by
leaching
Fig. 47-19, p. 854
Animation: Nitrogen cycle
Disruptions by Human Activities
 Deforestation and conversion of grassland to
farmland causes nitrogen loss
• Plant removal increases erosion and leaching
 Synthetic ammonium fertilizers increase soil
acidity and encourage ion exchange
• Calcium and magnesium ions are washed away
 Burning fossil fuels releases nitrogen oxides
• Contribute to global warming and acid rain
Nitrogen Oxides:
Some Effects of Air Pollution
47.10 The Phosphorus Cycle
 Phosphorus cycle
• A sedimentary cycle that moves phosphorus from
its main reservoir (Earth’s crust) through soils and
sediments, aquatic habitats, and bodies of living
organisms
Phosphate and the Phosphorus Cycle
 Phosphorus in rocks is mainly phosphate (PO43-)
• Water moves phosphate through ecosystems
 Phosphorus is a limiting factor on plant growth
• Taken up by plants only in ionized form
• Required for ATP, phospholipids, nucleic acids
• Depleted when forest is converted to farmland
The Phosphorus Cycle
mining
excretion
fertilizers
guano
agriculture
uptake by
autotrophs
marine
food webs
uptake by
autotrophs
weathering
dissolved in
ocean water
leaching, runoff
dissolved in
soil water,
lakes, rivers
death,
decomposition
sedimentation
land
food webs
death,
decomposition
settling out
weathering
uplifting over
geologic time
marine sediments
rocks
Fig. 47-21, p. 856
Animation: Phosphorus cycle
Eutrophication: Too Many Nutrients
 Eutrophication
• Nutrient enrichment of any ecosystem that is
otherwise low in nutrients; often a form of nutrient
pollution from agricultural runoff or sewage
 Eutrophication of a lake can cause excessive
algal growth, oxygen depletion, and fish kills
Eutrophication
 Phosphorus is often the limiting factor in aquatic
ecosystems
nitrogen,
carbon
added
nitrogen,
carbon,
phosphorus
added
Fig. 47-22, p. 857
47.5-47.10 Key Concepts
Cycling of Water and Nutrients
 The availability of water, carbon, nitrogen,
phosphorus, and other substances influences
primary productivity
 These substances move slowly in global cycles,
from environmental reservoirs, into food webs,
then back to reservoirs
Animation: Carbon dioxide and
temperature
Animation: Effect of air pollution in
forests
Animation: Food webs
Animation: Greenhouse gases
ABC video: MTBE Pollution
ABC video: Bottle Backlash
ABC video: Carbon Offsets
ABC video: International Report: Cooling
the Planet
ABC video: Endangered species
threatened by rain
ABC video: Water Pollution threatens
Millions
Video: Bye-bye, blue bayou
Video: Cliff nesters