Transcript Biogeochemical Cycle

Chapter 5
The Biogeochemical Cycles
Botkin & Keller
Environmental Science 5e
The Geologic Cycle
• The Geologic Cycle:
– The processes responsible for formation and
change of Earth materials
– Best described as a group of cycles:
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Tectonic
Rock
hydrologic
Biochemical
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Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
Tectonic Cycle
Creation and destruction of the Lithosphere
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© 2008 John Wiley and Sons Publishers
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© 2008 John Wiley and Sons Publishers
The Rock Cycle
• The rock cycle:
– Numerous processes that produce rocks and
soils
– Depends on other cycles:
• tectonic cycle for energy
• Hydrologic cycle for water for erosion
– Rock is classified as
• Igneous – high heat, volcanic
• Sedimentary – weathering & erosion
• Metamorphic – compact, melting
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How Chemicals Cycle
•
Biogeochemical Cycle
– The complete path a chemical takes through
the four major components – or reservoirs –
of Earth’s systems
1.
2.
3.
4.
Atmosphere
Hydrosphere
Lithosphere
Biosphere
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Botkin & Keller
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© 2008 John Wiley and Sons Publishers
Biogeochemical Cycles and Life:
Limiting Factors
• Macronutrients
– Elements required in large amounts by all life
– Include the “big six” elements that form the fundamental building
blocks of life:
hydrogen
carbon
oxygen
phosphorus nitrogen
sulfur
• Micronutrients
– Elements required either in
• small amounts by all life or
• moderate amounts by some forms of life and not all by others
• Limiting factor
– When chemical elements are not available at the right times, in
the right amounts, and in the right concentrations relative to each
other
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Major Chemical Cycles
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Water (hydrologic)
Carbon
Nitrogen
Phophorus
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The Hydrologic Cycle
• The Hydrologic Cycle:
– The transfer of water from the oceans to the
atmosphere to the land and back to the
oceans. POWERED BY THE SUN !!
– Includes:
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•
•
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Evaporation of water from the oceans
Precipitation on land
Evaporation from land
Runoff from streams, rivers, and sub-surface
groundwater
• Transpiration from plants
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Human Impacts
• Withdrawal:
– Removal from society & industry faster than
recharged (overdraft)
• Increased flooding:
– Removal of wetlands & creating non-pourous
tracts
• Deforestation:
– Clearing land reduces transpiration, therefore
there is a decrease in precipitation.
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Environmental Science 5e
Botkin & Keller
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© 2008 John Wiley and Sons Publishers
Botkin & Keller
Environmental Science 5e
The Carbon Cycle
• 4th most abundant element in the
universe
• Building block of life
• Cycles through the geosphere,
biosphere, ocean and atmosphere
• Two types of cycling
– Geological carbon cycle
– Biological carbon cycle
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Geological Carbon Cycle
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How does this work?
• CO2 reacts with atmospheric water and
minerals to produce calcium carbonate.
• Calcium carbonate rock (limestone)
weathered by water – dissolves and
travels to ocean.
• Forms sedimentary layers in the ocean.
Through plate tectonics, sediments
subduct and melts.
• Carbon is released into the atmosphere
during volcanic eruption as CO2
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Biological Carbon Cycle
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Carbon Reservoirs
• Ocean – dissolved, calcium carbonate
of marine organisms shells
• Geosphere – soils, fossil fuels
• Biosphere –living organisms
• Atmosphere – 0.038% of troposphere
– (Acts as natural thermostat for Earth)
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Human impacts
• Increases Carbon
Dioxide in the
atmosphere by:
– Burning of fossil fuels
– Clear cutting of trees
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Botkin & Keller
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The Nitrogen Cycle
• The nitrogen cycle:
– Limiting factor for primary productivity
– 2 forms as nutrients: NH4 and NO3
– Conversion of N2 gas into nutrients – lightning &
nitrogen fixing bacteria
• Nitrogen reservoirs:
– Atmosphere
• 78% of Troposphere
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Common nitrogen compounds
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N2 - nitrogen gas
NH4 - ammonium
NH3 - ammonia
NO3 - nitrate
NO2 - nitrite
N2O - nitrous oxide
NO2
- nitrogen dioxide
HNO3 - nitric acid
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Steps in the Nitrogen Cycle
• Nitrogen fixation:
– N2 converted to NH4 or NH3 by bacteria
• Ammonification (mineralization)
– Decomposers turn organic material into NH4
or NH3
• Nitrification
– Bacteria convert NH4 & NH3 into NO3 for plant
uptake
• Denitrification
– Bacteria convert NH4 & NH3 into N2 & N2O
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Nitrogen fixation
• In order to be used by most living
organism nitrogen must by in the form
of NH3 or NO3.
• Nitrogen is ‘fixed’ by lightning or
bacteria.
• ‘Fixing’ allows nitrogen to be made
biologically available.
• Can be found on the roots of legumes.
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Nitrification
• Soil bacteria convert ammonia (NH4)
into a form that plants can use
– NO3
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Assimilation
• Plants absorb ammonium (NH3),
ammonia (NH4) and nitrate (NO3)
through their roots.
• Heterotrophs (or organisms that
receive energy from consuming other
organisms) obtain nitrogen from
consuming plant proteins or other
animals.
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Ammonification
• Decomposing bacteria convert dead
organisms and other waste to ammonia
(NH3) or ammonium (NH4), which can be
reused by plants
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Denitrification
• Specialized bacteria (anaerobic)
convert ammonia back to nitrates and
nitrites THEN back into nitrogen gas
and nitrous oxide, where they enter the
atmosphere.
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Nitrogen Cycle
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Additional Info
• Assimilation:
– Plants take up inorganic nitrogen (NH3 & NO3)
and convert to organic compounds (amino
acids)
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Human Impacts
• Excess Nitrates
– Animal waste, municipal
discharge
• Can promote algae
growth
• Burning of Fossil Fuels
– Released NO, NO2 and
HNO3
• Use of inorganic
fertilizers
– Increases denitrification by
anaerobic bacteria, and
therefore releases more
NO2 into the atmosphere.
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
The Phosphorus Cycle
• The phosphorus
cycle:
– Involves the
movement of
phosphorus
throughout the
biosphere and
lithosphere
– Important because
phosphorus is an
essential element for
life and often is a
limiting nutrient for
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plant growth.
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Phosphorus Reservoirs
• Ocean sediments
• Terrestrial rock
layers
– Erosion releases PO4
for producers
– Limiting factor for
primary productivity
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Guano Island
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Human Impacts
• Phosphate run-off
from
– Sewage, mining &
fertilizers
– Algal blooms
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Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers