BIO-GEO-CHEMICAL
CYCLES
Nutrient cycling in an ecosystem
Biogeochemical Cycles
(Matter moving through the environment)
• All living organisms need certain
elements/compounds for life processes
– Ex: your cells need C,H,O,P,N & S in order to live
and reproduce (make more cell)
• Cycles in nature keep these elements
“moving” from organisms to organism (and
sometimes into the atmosphere)
Biogeochemical Cycles
(Matter moving through the environment)
• The flow of a nutrient from the environment to living
organisms and back to the environment
• Main reservoir for the nutrient is in the environment
or the abiotic reservoir.
• Transfer rates to and from abiotic reservoirs are
usually lower than the rates of exchange between
and among organisms or biotic reservoirs.
• Matter is recycled through an ecosystem – not one a
way flow as with energy.
Three Main Abiotic Reservoirs
• Hydrologic cycle
– Water, (hydrogen
and oxygen)
• Atmospheric cycles
– Nitrogen, carbon, oxygen
• Sedimentary cycles
– Phosphorus and sulfur
WATER CYCLE
Water Cycle - Earth’s water supply is constantly
recycled throughout the biosphere:
Evaporation – water vapor leaves the oceans
and joins the atmosphere.
Transpiration – water vapor evaporates off of
plant leaves.
Condensation – water vapor in the atmosphere
forms clouds.
Precipitation – water vapor in the atmosphere
falls to the ground (rain.)
Carbon Cycle
• Carbon moves through the atmosphere
and food webs on its way to and from the
ocean, sediments, and rocks.
• Atmospheric carbon is mainly carbon dioxide
• Carbon dioxide is added to atmosphere
– Aerobic respiration, volcanic action, burning fossil
fuels, decomposition of organic materials
• Removed by photosynthesis
Carbon Cycle Diagram
Carbon in Atmosphere
Decomposers
break down dead
things, releasing
carbon to
atmosphere and
soil
Fossil fuels are
burned; carbon
is returned to
atmosphere
Carbon slowly
released from
these substances
returns to
atmosphere
Plants use
carbon to make
food
Plants and
animals die
Bodies not
decomposed —
after many
years, become
part of oil or coal
deposits
Animals eat
plants and
take in carbon
Carbon Cycle
Diffusion
Atmosphere
Bicarbonate,
volcanic action
carbonate
TERRESTRIAL
Marine
food ROCKS
webs
Marineweathering
Sediments
Terrestrial
Rocks
photosynthesis
Land Food
Webs
Soil Water
Peat, Fossil
Fuels
Human Impact
• Fossil fuels release carbon stores very slowly
• Burning anything releases more carbon into
atmosphere — especially fossil fuels
• Increased carbon dioxide in atmosphere
increases global warming
• Fewer plants mean less CO2 removed from
atmosphere
The Carbon Cycle
Plants
Nitrogen Cycle
What is Nitrogen?
• Nitrogen is the most abundant element
in the Earth’s atmosphere.
• Nitrogen cannot be absorbed directly by
plants and animals until it is converted
into compounds they can use. This
process is called the Nitrogen Cycle.
Nitrogen Cycle Steps
• Step 1- Nitrogen Fixation- Special
bacteria convert nitrogen gas (N2)
to ammonia (NH3) which the plants
can use.
• Step 2- Nitrification- Nitrification is
the process which converts the
ammonia into ions which the plants
can take in as nutrients.
Nitrogen Cycle Steps
• Step 3- Ammonification- After all of the
living organisms have used the nitrogen,
decomposer bacteria convert the nitrogenrich waste compounds into simpler ones.
• Step 4- Denitrification- This is the final step
in which other bacteria convert the simple
nitrogen compounds back into nitrogen gas
(N2), which is then released back into the
atmosphere to begin the cycle again.
Nitrogen in
the air
nitrogen fixing
plant
eg pea, clover plant made
animal protein
protein
root nodules
(containing nitrogen
fixing bacteria)
nitrates absorbed
dead plants & animals
urine & faeces
denitrifying
bacteria
decomposition by bacteria & fungi
ammonia
nitrates
bacteria
(nitrifying bacteria)
nitrites
bacteria
How do humans affects the Nitrogen Cycle?
• Nitric Oxide (NO) is released into the
atmosphere when any type of fuel is
burned. This includes byproducts of
internal combustion engines.
• Nitrous Oxide (N2O) is released into the
atmosphere through bacteria in
livestock waste and commercial
fertilizers applied to the soil.
How do humans affects
the Nitrogen Cycle? (cont.)
• Removing nitrogen from the Earth’s
crust and soil when we mine nitrogenrich mineral deposits.
• Discharge of municipal sewage adds
nitrogen compounds to aquatic
ecosystems which disrupts the
ecosystem and kills fish.
Phosphorus Cycle
• Phosphorus is part of phospholipids, nucleic acids,
and energy metabolism
• It is the most prevalent limiting factor in ecosystems
because it is slower moving than other cycles.
• Main reservoir is Earth’s crust; no gaseous phase (it
never enters the atmosphere – like carbon and nitrogen)
• Plants absorb phosphate from soil and phosphatizing
bacteria return it back to it’s abiotic reservoir when
they decompose organic wastes.
• Phosphates returns (moved) via weathering, volcanic
activity, ect.
Homeostasis Exists in Nutrient Cycles
• In a stable ecosystem, biogeochemical cycles
show homeostasis.
• Meaning input = output
• According to the Gaia theory by Lovelock, the
Earth (biosphere) is a self-regulating system. The
evolution of life and the planet are intimately
connected as if the earth is a big “organism”
itself.
• Human impact from clear-cutting, slash/burn,
and greenhouse gases can seriously affect the
homeostasis of the cycles!