1. Chapter 3
Biogeochemical Cycles
Big Question
Why Are Biogeochemical Cycles Essential
to Long-Term Life on Earth?

2. • 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).

3. • Chemicals enter storage compartments - sinks
• Amount that moves between compartments is the flux

4. 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

5. Geological Cycle
• The formation and change of Earth materials
through physical, chemical, and biological
processes

6. The Tectonic Cycle
• Lithosphere is comprised of several plates
floating on denser material
• Plates move slowly relative to each other –
plate tectonics

7. • Divergent plate boundaries occur at spreading
ocean ridges
• Convergent plate boundaries occur when
plates collide

8. Biogeochemical Cycles in Ecosytems
• Begins with inputs from reservoirs such as
atmosphere, volcanic ash, stream runoff, ocean
currents, submarine vents
• Chemicals cycle through physical transport
and chemical reactions (e.g. decomposition)
• All ecosystems “leak” chemicals to other
ecosystems.

9. Carbon Cycle
• Carbon is vital for
life but is not
abundant
• Enters biological
cycles through
photosynthesis to
produce organic
forms of carbon

10. Carbon Cycle in a Pond

11. • Large inorganic carbon reservoir in oceans
• Dissolved CO2 is converted to carbonate and
bicarbonate
• Transferred from land by rivers and wind

12. Fossil Fuels
• Decomposition of dead organisms may be
prevented by lack of oxygen or low
temperatures
• Burial in sediments over thousands or millions
of years transforms the stored organic carbon
into coal, oil or natural gas

13. Global Carbon Cycle

14. Global Carbon Cycle

15. 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

16. 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.

17. 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.

18. 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.

19. Case of the missing carbon!
– Biggest threats:
• 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

20. 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

21. 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

22. Denitrification
• When organisms die, denitrifying bacteria
convert organic nitrogen to ammonia,
nitrate, or molecular nitrogen

23. Global Nitrogen Cycle

24. Phosphorus Cycle
• 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

25. Global Phosphorus Cycle

26. Phosphate Mining
• Impact on
landscape by
open-pit mining