Biogeochemical cycles Carbon cycle

1. Biogeochemical Cycles

2. Biogeochemical Cycle
• Biogeochemical cycle is a pathway by which a chemical substance
moves through both biotic (biosphere) and abiotic (lithosphere,
atmosphere, and hydrosphere) compartments of Earth.
• The term "biogeochemical" tells us that biological, geological and
chemical factors are all involved. The circulation of chemical
nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and
water etc. through the biological and physical world are known as
biogeochemical cycles. In effect, the element is recycled, although in
some cycles there may be places (called reservoirs) where the
element is accumulated or held for a long period of time (such as an
ocean or lake for water).

3. Carbon Cycle

4. How are humans affecting the carbon cycle?

5. How are humans affecting the carbon cycle?
• By cutting down trees and clearing
vegetation that naturally absorbs CO2
• Burning fossil fuels (especially coal) releases
their stored carbon into the atmosphere
• Clearing vegetation faster than it is
replaced.

6. Effects of disrupting the carbon cycle
• Global Warming – more CO2 in the
atmosphere will lead to a stronger
greenhouse effect
• Acidification of the oceans – more
dissolved CO2 in the water creates
more carbonic acid

7. • The first step of the carbon cycle in which the photoautotrophs such
as cyanbacteria, green plants, algae, and green and purple sulphur
bacteria fix carbon dioxide into organic matter using energy from
sunlight.
• Chemoautotrophs such as Thiobacillus and Beggiatoa also fix carbon
dioxide into organic matter, while metabolizing compounds such as
hydrogen sulfide for energy.

8. • In the next step, chemoheterotrophs such as animals and protozoa
eat autotrophs and may in turn be eaten by other animals.
• Thus as the organic compounds of the autotrophs are digested and
resynthesized, the carbon atoms of carbon dioxide are transformed
from organism to organism up the food chain.

9. The Carbon Cycle
The development of photosynthesis allowed microbes to tap into sunlight energy and
provided a mechanism for the first carbon cycle.
Aerobic Anaerobic
Fossil fuels
Fermentation
Photosynthesis
Respiration
Methanogenesis
CO + H O
2 2 O + CH O
2 2 Alcohols, acids,
H + CO
2 2
CH4
CH O
2

10. Where is carbon stored?

11. Where is carbon stored?
• Air – 0.037% is CO2
• Vegetation – during photosynthesis, plants convert CO2 into C6H12O6
(glucose)
• Fossil fuels – plant matter that’s been subjected to heat and pressure
• Ocean – dissolves CO2
• Marine organisms – used to make shells
• Rocks – limestone is primarily CaCO3

12. Natural Sources
of
Carbon
Sources of Carbon from
Human Activity
•Death of plants and animals
•Animal waste
•Atmospheric CO2
•Weathering
•Methane gas from cows
(and other ruminants)
•Aerobic respiration from
terrestrial and aquatic life
•Burning wood or forests
•Cars, trucks, planes
•Burning fossil fuels
such as coal, oil and
natural gas to produce
heat and energy.

13. Natural sources of CO2
• respiration
• ocean degassing
• terrestrial degassing
• wildfires
Anthropogenic sources of CO2
• fossil fuel combustion
• cement production
• land use changes
Natural sinks for CO2
• terrestrial
uptake by plants
uptake by soils
• oceanic
partitioning
biomass production
Anthropogenic sinks for CO2
• chemical production
• biological materials
Natural and anthropogenic CO2 sources and sinks

14. Fossil Fuels

15. White Cliffs of Dover

16. Carbon Reservoir Metric tons
carbon
Actively
cycled
Atmosphere
CO2
Ocean
Biomass
Carbonates
Dissolved and
particulate organics
Land
Biota
Humus
Fossil fuel
Earth’s crust
6.7 x 1011
4.0 x 109
3.8 x 1013
2.1 x 1012
5.0 x 1011
1.2 x 1012
1.0 x 1013
1.2 x 1017
Yes
Yes
No
Yes
Yes
Yes
Yes
No
Global Carbon Reservoirs

17. The carbon cycle is a good example of one that is undergoing a major perturbation
due to human activity.
Human activity has had a large impact on the atmospheric CO2 reservoir beginning with
industrialization. As a result, the level of CO2 in the atmosphere has increased 28% in
the past 150 years.
Carbon source metric tons carbon/yr
Release by fossil-fuel combustion 7 x 109
Land clearing 3 x 109
Forest harvest and decay 6 x 109
Forest regrowth -4 x 109
Net uptake by oceans -3 x 109
Annual flux 9 x 109

18. Natural sources of CO2
• respiration
• ocean degassing
• terrestrial degassing
• wildfires
Anthropogenic sources of CO2
• fossil fuel combustion
• cement production
• land use changes
Natural sinks for CO2
• terrestrial
uptake by plants
uptake by soils
• oceanic
partitioning
biomass production
Anthropogenic sinks for CO2
• chemical production
• biological materials
Natural and anthropogenic CO2 sources and sinks

19. The term reservoir can be used on a global scale or on a smaller scale
such as a habitat.
What are the major carbon inputs into the environment?
plant materials (through photosynthesis)
cellulose 15 – 60%
hemicellulose 10-30%
lignin 5- 30%
protein/nucleic acids 2-15%
fungal cell walls/arthropods
chitin
Carbon cycling on the habitat scale
The most complex organic polymer found in the environment is
humus.

20. Methane generation
The methanogens are a group of obligately anaerobic Archaea that can reduce
CO2 to methane (use CO2 as a terminal electron acceptor) both
chemoautotrophically or heterotrophically using small MW molecules such as
methanol or acetate.
4H2 + CO2 CH4 + 2H2O G0 = -130.7 kJ
Although much methane is microbially produced, there are other sources as
well. Methane is a greenhouse gas, 22 times more effective than CO2 in
trapping heat.
Methane utilization
In most environments, the methane produced is utilized by methanotrophic
microbes as a source of carbon and energy. The first enzyme in the
biodegradation pathway of methane is methane monooxygenase (MMO).

21. Carbon Cycle
Anaerobic Aerobic
Carbon Fixation Carbon Fixation
CO2
Respiration
And
Fermentation
Organic Matter
CH2O
Respiration
CO2
Methane Oxidation
Methanogenesis
H2
CH4

22. MARINE CARBON CYCLE
Diffusion between
atmosphere and ocean
Carbon dioxide
dissolved in
ocean water
Marine food webs
Producers, consumers,
decomposers, detritivores
Marine sediments, including
formations with fossil fuels
Combustion of fossil fuels
incorporation
into sediments
death,
sedimentation
uplifting over
geologic time
sedimentation
photosynthesis aerobic
respiration
Figure 4-29a
Page 78

23. Carbon in Oceans
• Additional carbon is stored in the ocean.
• Many animals pull carbon from water to use in
shells, etc.
• Animals die and carbon substances are deposited at
the bottom of the ocean.
• Oceans contain earth’s largest store of carbon.

24. TERRESTRIAL CARBON CYCLE
photosynthesis aerobic
respiration
Terrestrial
rocks
Soil water
(dissolved
carbon)
Land food webs
producers,
consumers,
decomposers,
detritivores
Atmosphere
(most carbon is in carbon dioxide)
Peat,
fossil fuels
combustion of wood (for
clearing land; or for fuel
sedimentation
volcanic action
death, burial, compaction
over geologic time
leaching
runoff
weathering
Combustion
of fossil
fuels

25. More notes on Carbon Cycle

26. Carbon Cycle
• Carbon moves from the atmosphere to plants.
In the atmosphere, carbon is attached to oxygen in a gas
called carbon dioxide (CO2). With the help of the Sun,
through the process of photosynthesis, carbon dioxide is
pulled from the air to make plant food from carbon.
• Carbon moves from plants to animals.
Through food chains, the carbon that is in plants moves to
the animals that eat them. Animals that eat other animals
get the carbon from their food too.

27. Carbon Cycle
• Carbon moves from plants and animals to the ground.
When plants and animals die, their bodies, wood and
leaves decay bringing the carbon into the ground. Some
become buried miles underground and will become fossil
fuels in millions and millions of years.
• Carbon moves from living things to the atmosphere.
Each time you exhale, you are releasing carbon dioxide gas
(CO2) into the atmosphere. Animals and plants get rid of
carbon dioxide gas through a process called respiration.

28. Carbon Cycle
• Carbon moves from fossil fuels to the atmosphere when
fuels are burned.
When humans burn fossil fuels to power factories, power
plants, cars and trucks, most of the carbon quickly enters
the atmosphere as carbon dioxide gas. Each year, five and
a half billion tons of carbon is released by burning fossil
fuels. Of the huge amount of carbon that is released from
fuels, 3.3 billion tons enters the atmosphere and most of
the rest becomes dissolved in seawater.
• Carbon moves from the atmosphere to the oceans.
The oceans, and other bodies of water, soak up some
carbon from the atmosphere.