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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
Slide 34Slide 34Slide 34
Figure 4-28Page 76
Precipitation toland
Transpirationfrom plants
Runoff Surface runoff(rapid)
Evaporationfrom land Evaporation
from ocean Precipitation toocean
Ocean storage
Surfacerunoff(rapid)
Groundwater movement (slow)
Rain cloudsCondensation
Transpiration
Evaporation
PrecipitationPrecipitation
Infiltration andPercolation
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
Slide 35Slide 35Slide 35
Diffusion between atmosphere and ocean
Carbon dioxidedissolved in ocean water
Marine food websProducers, consumers,
decomposers, detritivores
Marine sediments, includingformations with fossil fuels
Combustion of fossil fuels
incorporation into sediments
death, sedimentation
uplifting over geologic time
sedimentation
photosynthesis aerobic respiration
Figure 4-29aPage 78
TERRESTRIAL CARBON CYCLE
Slide 36Slide 36Slide 36
photosynthesis aerobic respirationTerrestrial
rocks
Soil water(dissolved
carbon)
Land food websproducers, 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 timeleaching
runoff
weathering
Figure 4-29b Page 79
Combustion of fossil
fuels
Explain
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.
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.
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Figure 4-30Page 79
Year
1850 1900 1950 2000 20300
2
3
4
5
6
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CO
2e
mis
sio
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fro
m f
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sil
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(bil
lio
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etr
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on
s o
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arb
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eq
uiv
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nt)
1
Highprojection
Lowprojection
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
Biomass6.9*1011
5.2*108
YesYes
Land organic matter Biota
1.1*1011
2.5*1010
SlowYes
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
R-NH2
NH4 NO2
NO3NO2
NO
N2O
N2
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
R-NH2
NH4 NO2
NO3NO2
NO
N2O
N2
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 Nitrogen Fixation (kg N/hect/year)
Rhizobium-legume 200-300
Cyanobacteria- moss
30-40
Rhizosphere associations
2-25
Free- living 1-2
Immobilization is the opposite of which process in the cycle?A) MineralizationB) NitrificationC) Immobilization D) Nitrogen FixationE) Denitrification
What process takes place when nitrogen is limiting in the environment?
A) MineralizationB) NitrificationC) Immobilization D) Nitrogen FixationE) DenitrificationWhich has the highest rate of nitrogen fixation?A) Rhizobium-legumeB) Cynaobacteria-mossC) Rhizosphere associationsD) Free-livingE) 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
R-NH2
NH4 NO2
NO3NO2
NO
N2O
N2
Nitrification
Two step reactions that occur together :
• 1rst step catalyzed by Nitrosomonas2 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
R-NH2
NH4 NO2
NO3NO2
NO
N2O
N2
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
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GUANO
FERTILIZER
ROCKS
LAND FOOD WEBS
DISSOLVED IN OCEAN
WATER
MARINE FOOD WEBS
MARINE SEDIMENTS
weathering
agriculture
uptake by autotrophs
death, decomposition
sedimentation settling out weathering
leaching, runoff DISSOLVED IN SOIL WATER,
LAKES, RIVERS
uptake by autotrophs
death, decomposition
miningmining
excretionexcretion
Figure 4-33Page 82
uplifting over geologic time
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
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Figure 4-34Page 83
Sulfur
Hydrogen sulfide
Sulfate salts
Plants
Acidic fog and precipitation
Ammonium sulfate
Animals
Decaying matterMetallic
sulfide deposits
Ocean
Dimethyl sulfide
Sulfur dioxide Hydrogen sulfide
Sulfur trioxide Sulfuric acidWater
Ammonia
Oxygen
Volcano
Industries
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
