Download Nitrogen and Carbon Cycle

Unit 4 –
Nutrient
Cycles in
marine
ecosystems
Nitrogen and
Carbon Cycle
The Nitrogen Cycle
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78% of troposphere is N2, 0% utilized in respiration
Present in proteins, moves through food chain
Most complex cycle
Disrupted by
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Burning fuel (releases nitric oxides)
Increased use of fertilizer
Removal from topsoil
Addition to aquatic ecosystems
Conversion of Atmospheric Nitrogen
to usage nitrogen
N2
Soil
Acid soil
bacteria
NH3
NH4
Nitrogen Cycle
• N2 gas is modified by nitrogen fixing bacteria
into ammonia (NH3) (nitrogen fixation)
• Bacteria turn nitrogenous waste and detritus
into ammonia (ammonification)
• NH3 is converted into nitrite (N02) which is
used to produce nitrate (N03) (nitrification)
• Other bacteria convert nitrite into gas which
enters the air (denitrification)
5 steps
1. Nitrogen fixation: N2 converted to NH3
Ammonia…combustion, volcanism, lightening and
industrial processes.
Nitrogenase: nitrogen fixing cyanobacteria employ this
enzyme in aquatic environments. Bacteria live beneath
oxygen proof slime on the roots of certain plants and
inside special nodules on the roots of
lugumes(beans)…Rhizobium
2. Nitrification: the conversion of NH3 ammonia or
ammonium NH4+ to Nitrate NO3-.
Performed by soil nitrifying bacteria.
3. Assimilation: Plant roots absorb nitrate, or ammonium
and assimilate the nitrogen of these molecules to into
plant proteins and nuclei acids.
*** When animals consume plants they assimilate amino
acids and make proteins.
4. Ammonification: Conversion of biological nitrogen
compounds into ammonia.
• Nitrogen waste such as urea and uric acid.
• Nitrogen waste decomposes and is released into the
abiotic environment.
• Ammonifying bacteria carry on this process.
5. Denitrification: reduction of nitrate to gaseous N2 . Live
were there is no free oxygen. Found deep in the soil near
the water table.
Human Impact on the Nitrogen Cycle
• Nitrogen cycle is being altered by nitrogen fertilizer
produced from nitrogen gas for agriculture…141 million
tons
LAND…RIVERS…OCEANS…DEAD ZONES!!!
• Leach into groundwater.
• Nitrous oxides from cars make photochemical smog.
• Form nitric acid deposition acidifying lakes and streams.
Cycling of Materials within Ecosystems
Nitrogen cycle:
Atmospheric
nitrogen (N2)
Biological
nitrogen
fixation
Nitrogen
fixation by
humans
Decomposition
Denitrification
NH3 &
NH4-
Internal
cycling
Plant & animal
proteins
Assimilation
Nitrification
NO3-
The Carbon Cycle
• Key role in Earth’s thermostat
– Absorbed by ocean, utilized by plants in
photosynthesis, humans in digestion
– Sinks (storage) in lithosphere (largest reservoir –
limestone and other sedimentary rock),
hydrosphere (ocean), atmosphere (CO2) and in the
biosphere (dead animals, wood, plants…)
– Released by fires, decomposition, volcanoes, and
human respiration
Carbon Dioxide Cycle
1. .037% Atmosphere
2. Present in the ocean as carbonate, bicarbonate and other
forms
3. Present in rocks
PHOTOSYNTHESIS “fixes” CO2 into complex sugar
compounds.
Photosynthesis= biotic + abiotic = sugar!!!
Sea Floor
Covered with the remains of phytoplankton kilometers
thick…
The ocean is the greatest carbon dioxide sink on the planet.
Limestone that becomes land via uplift will deteriorate and
return carbon to the carbon cycle.
Fossil Fuels.
1. By-product of the carbon cycle.
2. Vast deposits of carbon compounds
3. Remains of ancient organisms
Can be returned to the atmosphere by
burning…COMBUSTION… 
Rapid oxidation of
organic molecules 
Global Warming
1. Before the industrial revolution in 1850 carbon dioxide
was in a steady state.
2. Less than half of the carbon that is release remains in the
atmosphere…vegetation on land and the ocean
3. ½ of the CO2 is unaccounted for!!!
4. The rise of CO2 in the atmosphere caused by humaninduced changes
Cycling of Materials within Ecosystems
Carbon cycle: