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BIOGEOCHEMICAL CYCLES
‘Fundamentals’ of biogeochemical cycles
• All matter cycles...it is neither created nor destroyed...
• As the Earth is essentially a closed system with
respect to matter, we can say that all matter on Earth
cycles .
• Biogeochemical cycles: the movement (or cycling) of
matter through a system
by matter we mean: elements (carbon, nitrogen, oxygen) or
molecules (water)
so the movement of matter (for example carbon) between these
parts of the system is, practically speaking, a biogeochemical
cycle
The Cycling Elements:
macronutrients : required in relatively large amounts
"big six":
carbon , hydrogen , oxygen , nitrogen , phosphorous
sulfur
other macronutrients:
potassium , calcium , iron , magnesium
micronutrients : required in very small amounts, (but still
necessary)
boron (green plants)
copper (some enzymes)
molybdenum (nitrogen-fixing bacteria)
6 of the most important cycles
are the water, carbon, nitrogen,
sulfur, phosphorus and oxygen.
WATER HYDROLOGIC
CYCLE
Condensation
Rain clouds
Transpiration
Transpiration
from plants
Precipitation to
land
Precipitation
Runoff
Surface runoff
(rapid)
Evaporation
Precipitation
Evaporation
from land
Evaporation
from ocean
Precipitation to
ocean
Surface
runoff
(rapid)
Infiltration and
Percolation
Groundwater movement (slow)
Ocean storage
HYDROLOGIC CYCLE
CONNECTS
ALL OF THE
CYCLES
AND
SPHERES
TOGETHER
HUMAN IMPACTS TO
WATER CYCLE
1. Water withdrawal from streams, lakes and
groundwater. (salt water intrusion and groundwater
depletion)
2. Clear vegetation from land for agriculture, mining,
road and building construction. (nonpoint source
runoff carrying pollutants and reduced recharge of
groundwater)
3. Degrade water quality by adding nutrients(NO2, NO3,
PO4) and destroying wetlands (natural filters).
4. Degrade water clarity by clearing vegetation and
increasing soil erosion.
Water Quality Degradation
MARINE CARBON CYCLE
Diffusion between
atmosphere and ocean
Carbon dioxide
dissolved in
ocean water
photosynthesis
Combustion of fossil fuels
aerobic
respiration
Marine food webs
Producers, consumers,
decomposers, detritivores
incorporation
death,
into sediments sedimentation
uplifting over
geologic time
sedimentation
Marine sediments, including
formations with fossil fuels
Figure 4-29a
Page 78
TERRESTRIAL CARBON
CYCLE
Atmosphere
(most carbon is in carbon dioxide)
Combustion
of fossil
fuels
volcanic action
photosynthesis
Terrestrial
rocks
weathering
combustion of wood (for
aerobic
clearing land; or for fuel
respiration
Land food webs
producers,
consumers,
decomposers,
detritivores
Soil water
(dissolved
carbon)
leaching
runoff
death, burial, compaction
over geologic time
sedimentation
Peat,
fossil fuels
Explain
Natural Sources
of
Carbon
•Death of plants and animals
•Animal waste
•Atmospheric CO2
•Weathering
•Methane gas from cows
(and other ruminants)
•Aerobic respiration from
terrestrial and aquatic life
Sources of Carbon from
Human Activity
•Burning wood or forests
•Cars, trucks, planes
•Burning fossil fuels
such as coal, oil and
natural gas to produce
heat and energy.
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.
14
CO2 emissions from fossil fuel
(billion metric tons of carbon equivalent)
13
High
projection
12
11
10
Low
projection
9
8
7
6
5
4
3
2
1
0
1850
1900
1950
Year
2000
2030
Figure 4-30
Page 79
Slide 38
IMPORTANCE OF CARBON
CYCLE
CARBON IS THE BACKBONE
OF LIFE!
The Nitrogen Cycle
Sources
•
•
•
•
•
•
Lightning
Inorganic fertilizers
Nitrogen Fixation
Animal Residues
Crop residues
Organic fertilizers
Forms of Nitrogen
•
•
•
•
•
•
•
Urea  CO(NH2)2
Ammonia  NH3 (gaseous)
Ammonium  NH4
Nitrate  NO3
Nitrite  NO2
Atmospheric Dinitrogen N2
Organic N
Global Nitrogen Reservoirs
Nitrogen
Reservoir
Metric tons
nitrogen
Actively cycled
Atmosphere
3.9*1015
No
Ocean 
soluble salts
Biomass
6.9*1011
5.2*108
Yes
Yes
Land  organic
matter
 Biota
1.1*1011
2.5*1010
Slow
Yes
Roles of Nitrogen
• Plants and bacteria use nitrogen in the
form of NH4+ or NO3• It serves as an electron acceptor in
anaerobic environment
• Nitrogen is often the most limiting
nutrient in soil and water.
Nitrogen is a key element for
• amino acids
• nucleic acids (purine, pyrimidine)
• cell wall components of bacteria (NAM).
Nitrogen Cycles
•
•
•
•
•
Ammonification/mineralization
Immobilization
Nitrogen Fixation
Nitrification
Denitrification
Ammonification or Mineralization
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
Mineralization or Ammonification
• Decomposers: earthworms, termites, slugs,
snails, bacteria, and fungi
• Uses extracellular enzymes  initiate
degradation of plant polymers
• Microorganisms uses:
• Proteases, lysozymes, nucleases to degrade
nitrogen containing molecules
• Plants die or bacterial cells lyse  release of
organic nitrogen
• Organic nitrogen is converted to inorganic
nitrogen (NH3)
• When pH<7.5, converted rapidly to NH4
• Example:
Urea
NH3 + 2 CO2
Immobilization
• The opposite of mineralization
• Happens when nitrogen is limiting in the
environment
• Nitrogen limitation is governed by C/N ratio
• C/N typical for soil microbial biomass is 20
• C/N < 20 Mineralization
• C/N > 20 Immobilization
Nitrogen Fixation
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
Nitrogen Fixation
• Energy intensive process :
• N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 +
16ADP + 16 Pi
• Performed only by selected bacteria and
actinomycetes
• Performed in nitrogen fixing crops
(ex: soybeans)
Microorganisms fixing
•
•
•
•
•
Azobacter
Beijerinckia
Azospirillum
Clostridium
Cyanobacteria
• Require the enzyme
nitrogenase
• Inhibited by oxygen
• Inhibited by
ammonia (end
product)
Rates of Nitrogen Fixation
N2 fixing system
Rhizobium-legume
Nitrogen Fixation (kg
N/hect/year)
200-300
Cyanobacteria- moss
30-40
Rhizosphere
associations
Free- living
2-25
1-2
Immobilization is the opposite of which process in the cycle?
A) Mineralization
B) Nitrification
C) Immobilization
D) Nitrogen Fixation
E) Denitrification
What process takes place when nitrogen is limiting in the environment?
A) Mineralization
B) Nitrification
C) Immobilization
D) Nitrogen Fixation
E) Denitrification
Which has the highest rate of nitrogen fixation?
A) Rhizobium-legume
B) Cynaobacteria-moss
C) Rhizosphere associations
D) Free-living
E) Azobacter
Applications to wetlands
•
•
•
•
•
Occur in overlying waters
Aerobic soil
Anaerobic soil
Oxidized rhizosphere
Leaf or stem surfaces of plants
Bacterial Fixation
• Occurs mostly in salt marshes
• Is absent from low pH peat of northern
bogs
• Cyanobacteria found in waterlogged
soils
Nitrification
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
Nitrification
Two step reactions that occur together :
• 1rst step catalyzed by Nitrosomonas
2 NH4+ + 3 O2  2 NO2- +2 H2O+ 4 H+
• 2nd step catalyzed by Nitrobacter
• 2 NO2 + O2  2 NO3
• Optimal pH is between 6.6-8.0
• If pH < 6.0  rate is slowed
• If pH < 4.5  reaction is inhibited
In which type of wetlands do
you thing Nitrification occurs?
Denitrification
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
Denitrification
• Removes a limiting nutrient from the
environment
• 4NO3 + C6H12O6 2N2 + 6 H20
• Inhibited by O2
• Not inhibited by ammonia
• Microbial reaction
• Nitrate is the terminal electron acceptor
PHOSPHOROUS CYCLE
mining
excretion
FERTILIZER
GUANO
agriculture
uptake by
autotrophs
MARINE
FOOD
WEBS
weathering
DISSOLVED
IN OCEAN
WATER
uptake by
autotrophs
leaching, runoff
DISSOLVED IN
SOIL WATER,
LAKES, RIVERS
death,
decomposition
sedimentation
death,
decomposition
weathering
settling out
uplifting over
geologic time
MARINE SEDIMENTS
ROCKS
LAND
FOOD
WEBS
HUMAN IMPACTS TO
PHOSPHOROUS CYCLE
1. Humans mine LARGE quantities of phosphate rock to use in
commercial fertilizers and detergents. Phosphorous is NOT
found as a gas, only as a solid in the earth’s crust. It takes
millions to hundreds of millions of years to replenish.
2. Phosphorous is held in the tissue of the trees and vegetation, not
in the soil and as we deforest the land, we remove the ability for
phosphorous to replenish globally in ecosystems.
3. Cultural eutrophication – ad excess phosphate to aquatic
ecosystems in runoff of animal wastes from livestock feedlots,
runoff of commercial phosphate fertilizers fro cropland, and
discharge of municipal sewage.
IMPORTANCE OF
PHOSPHOROUS CYCLE
• 1.Phosphorous is an essential nutrient of both plants and
animals.
• 2. It is part of DNA molecules which carry genetic
information.
• 3. It is part of ATP and ADP) that store chemical
energy for use by organisms in cellular respiration.
• 4. Forms phospholipids in cell membranes of plants
and animal cells.
• 5. Forms bones, teeth, and shells of animals as calcium
phosphate compounds.
SULFUR CYCLE
Water
Sulfur trioxide
Acidic fog and
precipitation
Sulfuric acid
Ammonia
Oxygen
Sulfur dioxide
Ammonium
sulfate
Hydrogen
sulfide
Plants
Volcano
Dimethyl
sulfide
Industries
Animals
Ocean
Sulfate salts
Metallic
sulfide
deposits
Decaying
matter
Sulfur
Hydrogen
sulfide
HUMAN IMPACTS TO
SULFUR CYCLE
Approximately 1/3 of all sulfur emitted into
atmosphere comes from human activities.
• 1. Burning sulfur containing coal and oil to
produce electric power (SOx = acid deposition).
• 2. Refining petroleum – (SOx emissions)
• 3. Smelting to convert sulfur compounds of
metallic minerals into free metals (Cu, Pb, Zn)
• 4. Industrial processing.
IMPORTANCE OF SULFUR
CYCLE
1. Sulfur is a component of most proteins and some vitamins.
2. Sulfate ions (SO4 2- ) dissolved in water are common in
plant tissue. They are part of sulfur-containing amino
acids that are the building blocks for proteins.
3. Sulfur bonds give the three dimensional structure of amino
acids.
4. Many animals, including humans, depend on plants for
sulfur-containing amino acids.
The Oxygen cycle
“GOOD OZONE UP HIGH”
PHOTOCHEMICAL SMOG
“BAD OZONE DOWN LOW”
OZONE DEPLETION