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

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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 clouds Condensation

TranspirationEvaporation

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

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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

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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

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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 ReservoirsNitrogen Reservoir

Metric tons nitrogen

Actively cycled

Atmosphere 3.9*1015 NoOcean

soluble saltsBiomass

6.9*1011

5.2*108YesYes

Land organic matter Biota

1.1*1011

2.5*1010SlowYes

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

http://www.ucmp.berkeley.edu/bacteria/nostoc.gif

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

NitrificationTwo 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

weatheringagriculture

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