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Chapter 5
The Biogeochemical Cycles
Botkin & Keller
Environmental Science 5e
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
Botkin & Keller
Environmental Science 5e
Chemical Reactions
• Chemical reaction:
– The process in which new chemicals are
formed from elements and compounds
through chemical change
Botkin & Keller
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
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:
carbon
oxygen
hydrogen
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
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:
•
•
•
•
Tectonic
Hydrologic
Rock
Biochemical
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
Tectonic Cycle
• Tectonic cycle:
– Involves creation and destruction of the solid
outer layer of Earth, the lithosphere
• Plate tectonics:
– The slow movement of these large segments
of Earth’s outermost rock shell
– Boundaries between plates are geologically
active areas
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
Tectonic Cycle: Plate Boundaries
• Divergent plate boundary:
– Occurs at a spreading ocean ridge, where plates are
moving away from one another
– New lithosphere is produced (seafloor spreading)
• Convergent plate boundary
– Occurs when plates collide
• Produces linear coastal mountain ranges or continental
mountain ranges
• Transform fault boundary
– Occurs where one plate slides past another
• San Andreas Fault in California
Botkin & Keller
Environmental Science 5e
The Hydrologic Cycle
• The Hydrologic Cycle:
– The transfer of water from the oceans to the
atmosphere to the land and back to the
oceans. Includes:
•
•
•
•
Evaporation of water from the oceans
Precipitation on land
Evaporation from land
Runoff from streams, rivers, and sub-surface
groundwater
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 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
– Rock is classified as
• Igneous
• Sedimentary
• Metamorphic
Botkin & Keller
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
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
The Carbon Cycle
• Carbon is the element that anchors all
organic substances
• The carbon cycle:
– Carbon combines with and is chemically and
biologically linked with the cycles of oxygen
and hydrogen that form the major compounds
of life
Botkin & Keller
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
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
The Carbon Cycle:
Unanswered Issues
• The Missing Carbon Sink
– Substantial amounts of carbon dioxide
released into the atmosphere but apparently
not reabsorbed and thus remaining
unaccounted for
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
The Carbon-Silicate Cycle
• The carbon-silicate cycle:
– A complex biogeochemical cycle over time scales as
long as one-half billion years.
– Includes major geological processes, such as:
•
•
•
•
Weathering
Transport by ground and surface waters
Erosion
Deposition of crustal rocks
– Believed to provide important negative feedback
mechanisms that control the temperature of the
atmosphere.
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers
The Nitrogen Cycle
• The nitrogen cycle:
– Cycle responsible for moving important nitrogen
components through the biosphere and other Earth
systems
– Extremely important because nitrogen is required by
all living things
• Nitrogen fixation:
– The process of converting inorganic, molecular
nitrogen in the atmosphere to ammonia or nitrate
• Denitrification:
– The process of releasing fixed nitrogen back to
molecular nitrogen
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 plant growth.
Botkin & Keller
Environmental Science 5e
Botkin & Keller
Environmental Science 5e
© 2008 John Wiley and Sons Publishers