Transcript Biogeochemical Cycles

Biogeochemical Cycles
Something to think about…
• A handful of elements combine to form the
building blocks of all known organisms.
• Organisms cannot manufacture these
elements and do not “use them up,” so where
do essential elements come from?
Objectives:
• Identify the elements of Life
• Identify and describe the flow of elements
(“nutrients”) in each biogeochemical cycle.
• Explain the impact that humans have on
the biogeochemical cycles.
Two Secrets of Survival: Energy
Flow and Matter Recycling
• An ecosystem
survives through
a combination of
energy flow and
matter recycling.
• Unlike the one-way
flow of energy, matter
is recycled within and
between ecosystems.
• As matter moves
through these cycles,
it is never created or
destroyed —
just changed.
Why is it important that matter is
recycled?
• They are required to build and maintain an
organism
Elements of Life
Essential Elements
• 24 elements are required for life
• Macronutrients are required in LARGE
quantities
– carbon, hydrogen, nitrogen, oxygen,
phosphorus, and sulfur.
• Micronutrients are required in
small/medium quantities, or not at all in
some organisms
– Copper, sodium, iodine
How does matter move through the
biosphere?
• A biogeochemical cycle is the complete
path a chemical takes through the Earth’s
four major reservoirs:
• atmosphere
• hydrosphere (oceans, rivers, lakes,
groundwaters, and glaciers)
• lithosphere (rocks and soils)
• biosphere (plants and animals)
• Chemicals enter storage compartments - sinks
Biogeochemical Cycles in Ecosystems
• Biological Processes
– any and all activities performed by living organisms;
includes eating, breathing, “burning” food, and
eliminating waste
• Geological Processes
– include volcanic eruptions, the formation &
breakdown of rock, and major movements of matter
within and below the surface of the earth
• Chemical / Physical Processes
– include the formation of clouds and precipitation, flow
of running water, and the action of lightning
Hydrologic (Water) Cycle
Carbon Cycle
• Carbon is vital for
life but is not
abundant
• Enters biological
cycles through
photosynthesis to
produce organic
forms of carbon
Carbon Cycle in a Pond
Fossil Fuels
• Lack of oxygen or low
temperatures may
prevent decomposition
of dead organisms
• Burial in sediments over
thousands or millions of
years transforms the
stored organic carbon
into coal, oil or natural
gas
Global Carbon Cycle
Nitrogen Cycle
Nitrogen Cycle
• Essential for manufacturing proteins and
DNA
• Although 80% of atmosphere is molecular
nitrogen, it is unreactive and cannot be
used directly
• Nitrogen fixation converts nitrogen to
ammonia or nitrate
Nitrogen Fixation
• Some organisms have a symbiotic
relationship with nitrogen fixing
bacteria
• Found in root nodules in some
plants, or in the stomach of some
herbivores
• Nitrogen fixation also occurs through
lightning and industrial processes
Denitrification
• When organisms die, denitrifying
bacteria convert organic nitrogen to
ammonia, nitrate, or molecular nitrogen
Nitrogen Cycle
Global Phosphorus Cycle
Phosphorus Cycle
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No gaseous phase
Slow rate of transfer
Released by erosion of exposed rock
Absorbed by plants, algae, and some
bacteria
Exported from terrestrial ecosystems by
runoff to oceans
May be returned through seabird guano
Phosphate Mining
• Impact on
landscape by
open-pit mining
Sulfur Cycle In a Forest Ecosystem
Includes gaseous forms (sulfur dioxide and
hydrogen sulfide);cycles much faster than calcium
Calcium Cycle in a Forest Ecosystem
Soluble in water and easily lost through runoff
Remember…
• Biogeochemical cycles of matter pass the
same atoms and molecules around again
and again.
• If you interrupt the
cycling, how does
this affect the
ecosystem?
Case of the missing carbon!
– Analysis shows contribution of 8 .5 bill. tons
into the atmosphere but less than ½ stays
there…where does it go?
– 7 billion from fossil fuels and 1.5 billion from
deforestation
Case of the missing carbon!
– Appears oceans are acting as carbon sinks as are
forests and grasslands.
– But which area is more critical, and which one
dominates.
– Will these blessings last?
• If they stop functioning we could face drastic changes
even before 2050.
Case of the missing carbon!
– Global tests of CO2 show less in the north than the south
despite larger northern outputs
– Why is this the case?
– If land plants are doing the work then there should be a
corresponding oxygen increase.
– If it is dissolving in the oceans then there should be no
added oxygen.
Case of the missing carbon!
– Results (best guess):
• Ocean is soaking up 2.4 billion tons globally
• Land plants do the most work in the northern
hemisphere
– Forests literally breath in the carbon but appetite changes
dramatically due to season, amount of sunlight, rainfall, and
age of forests
• Marine organisms undergo photosynthesis as well
• So that leaves about 2.9 units unaccounted for between
these groups.
Case of the missing carbon!
– Biggest threats:
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Decline in forest growth
Killing of ocean phytoplankton due to rising sea temperatures
Death of forests due to spread of disease and insects
Melting permafrost layer
Land clearing for development and agriculture
Ofcourse continued output of carbon from fossil fuel burning