Biogeochemical
Cycles

Objectives:
• Identify the flow on each
biogeochemical cycle.
• Explain the impact that humans
have on the
biogeochemical
cycles.

Biogeochemical cycles
• Biogeochemical cycles: The
chemical interactions (cycles) that
exist between the atmosphere,
hydrosphere, lithosphere, and
biosphere.
• Biogeochemical cycles are
components of the broader cycle that
govern the functioning of planet Earth

Biogeochemical cycles
• The transfer of matter involves biological,
geological and chemical processes; hence
the name biogeochemical cycles derives.
Biogeochemical cycles may also be
referred to as cycles of nature because
they link together all organisms and
abiotic features on earth (see Figure at
next slide). Matter is continually recycled
among living and abiotic elements on
earth.

• biogeochemical cycles facilitate the
transfer of matter from one form to
another and from one location to another
on planet earth. Additionally,
biogeochemical cycles are sometimes
called nutrient cycles, because they
involve the transfer of compounds that
provide nutritional support to living
organisms.

PathwaysofBiogeochemicalCycles
• Parts that comprise planet earth have
been categorized into four spheres
(regions). One is the sphere which has
life and it is called the biosphere (it is the
region occupied by living organisms such
as plants, animals, fungi) and the other
three spheres are largely devoid of life,
they include;

• lithosphere (region occupied by soil, land
and the earth crust), atmosphere (air and
space) and hydrosphere (areas covered
by water such as rivers, lakes and
oceans). However, where the biosphere
overlaps the lithosphere, atmosphere or
hydrosphere, there is a zone occupied by
living organisms.

Categories of biogeochemical
cycles
• Biogeochemical cycles differ in their
pathways, and on this basis the
biogeochemical cycles have been
categorized into two:
Sedimentary cycles:
Phosphorus cycle Sulfur cycle
Gaseous cycles
Carbon cycle Oxygen cycle
Nitrogen cycle Hydrological cycle

Sedimentary cycles:
• these cycles involve the transportation of
matter through the ground to water; that is to
say from the lithosphere to the hydrosphere.

Phosphorus cycle
Phosphorus is commonly found in water, soil and
sediments. Phosphorus cannot be found in air in
the gaseous state. This is because phosphorus is
usually a liquid at standard temperatures and
pressures. Phosphorus is mainly cycled trough
water, soil and sediments. However, very small
particles in the atmosphere may contain
phosphorus or its compounds. Phosphorus
moves slowly from deposits on land and in
sediments, to living organism , and much more
slowly back into the soil and water sediment. The
phosphorus cycle is the slowest one of the

Fig. 3-31, p. 77
Dissolved
in Ocean
Water
Marine Sediments Rocks
uplifting over
geologic time
settling out weatheringsedimentation
Land
Food
Webs
Dissolved
in Soil Water,
Lakes, Rivers
death,
decomposition
uptake by
autotrophs
agriculture
leaching, runoff
uptake by
autotrophs
excretion
death,
decomposition
mining Fertilizer
weathering
Guano
Marine
Food
Webs

 The cycle basically starts out in
the earth’s soil. The soil contains
phosphate and when something
grows out of the soil it should have
phosphate as well.
 When the plants grow they are
consumed by herbivore and
omnivore animals
 The animal’s waste or the animal’s
body when it dies becomes detritus.
 Detritus is non-
living organic
material. When
the detritus goes
deep into the soil,
detritivores in the
soil decompose
and become the
soil’s phosphate
and the cycle
repeats.

Sulfur cycle
• Sulfur in its natural form is a solid, and
restricted to the sedimentary cycle in this
form. It is transported by physical
processes like wind, erosion by water, and
geological events like volcanic eruptions.
However, in its compounds such as sulfur
dioxide, sulfuric acid, salts of sulfate or
organic sulfur, sulfur can be moved from
the ocean to the atmosphere, to land and
then to the ocean through rainfall and
rivers.

Fig. 3-32, p. 78
Hydrogen sulfide
Sulfur
Sulfate salts
Decaying matter
Animals
Plants
Ocean
Industries
Volcano
Hydrogen sulfide
Oxygen
Dimethyl
sulfide
Ammonium
sulfate
Ammonia
Acidic fog and
precipitationSulfuric acid
WaterSulfur
trioxide
Sulfur dioxide
Metallic
sulfide
deposits

Effects of Human Activities
on the Sulfur Cycle
• We add sulfur dioxide to the atmosphere
by:
–Burning coal and oil
–Refining sulfur containing petroleum.
–Convert sulfur-containing metallic ores
into free metals such as copper, lead,
and zinc releasing sulfur dioxide into
the environment.

Gaseous cycles
• these involve the transportation of
matter through the atmosphere.
Common example of gaseous cycles
are:

Carbon cycle
• Carbon is one of the most important
elements that sustain life on earth. Carbon
dioxide and methane gases (compounds
of carbon) in the earth's atmosphere has a
substantial effect on earth's heat balance.
It absorbs infrared radiation and hence
may contribute to global warming and
climate change.

MARINE CARBON CYCLE
Slide 35Slide 35Slide 35
Diffusion between
atmosphere and ocean
Carbon dioxide
dissolved in
ocean water
Marine food webs
Producers, consumers,
decomposers, detritivores
Marine sediments, including
formations with fossil fuels
Combustion of fossil fuels
incorporation
into sediments
death,
sedimentation
uplifting over
geologic time
sedimentation
photosynthesis aerobic
respiration
Figure 4-29a
Page 78

photosynthesis aerobic
respirationTerrestrial
rocks
Soil water
(dissolved
carbon)
Land food webs
producers,
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
Combustion
of fossil
fuels
TERRESTRIAL CARBON CYCLE

Carbon Cycle Diagram
Carbon in Atmosphere
Plants use
carbon to make
food
Animals eat
plants and
take in
carbon
Plants and
animals die
Decomposers
break down dead
things, releasing
carbon to
atmosphere and
soil
Bodies not
decomposed —
after many
years, become
part of oil or
coal deposits
Fossil fuels are
burned; carbon
is returned to
atmosphere
Carbon slowly
released from
these substances
returns to
atmosphere

The Carbon Cycle

• 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
Human Impact

Nitrogen cycle
• Nitrogen gas is the most abundant
element in the atmosphere and all the
nitrogen found in terrestrial ecosystems
originate from the atmosphere. The
nitrogen cycle is by far the most important
nutrient cycle for plant life.

Effects of Human Activities
on the Nitrogen Cycle
• We alter the nitrogen cycle by:
–Adding gases that contribute to acid rain.
–Adding nitrous oxide to the atmosphere
through farming practices which can warm
the atmosphere and deplete ozone.
–Contaminating ground water from nitrate
ions in inorganic fertilizers.
–Releasing nitrogen into the troposphere
through deforestation.

Effects of Human Activities
on the Nitrogen Cycle
• Human activities
such as
production of
fertilizers now fix
more nitrogen
than all natural
sources
combined.
Figure 3-30Figure 3-30

Oxygen cycleOxygen cycle
• The oxygen cycle describes the
movement of oxygen within and between
its three main reservoirs: the atmosphere,
the biosphere, and the lithosphere. The
main driving factor of the oxygen cycle is
photosynthesis and because of this,
oxygen and carbon cycles are usually
linked and the two cycles are collectively
called oxygen-carbon cycle.

Fig. 3-26, p. 72
PrecipitationPrecipitation
Transpiration
Condensation
Evaporation
Ocean storage
Transpiration
from plants
Precipitation
to land
Groundwater movement (slow)
Evaporation
from land Evaporation
from ocean Precipitation
to ocean
Infiltration and
Percolation
Rain clouds
Runoff
Surface runoff
(rapid)
Surface
runoff
(rapid)
Photosynthesis

respiration
Rabbit eats
food, breaks
it down and
releases
CO2.
Plant uses
CO2 to
make food.
Rabbit gives off CO2,
which is taken in by the
plant.
Plant gives off O2,
which is taken in by the
rabbit.

How are photosynthesis and
cellular respiration similar?
•
• Photosynthesis uses carbon dioxide
and produces oxygen.
• Cellular respiration uses oxygen and
produces carbon dioxide.

All Animals and Other
Consumers Use Oxygen
• We use oxygen to break down simple
sugar and release energy.
• This can be done through respiration
or fermentation.
• Animals mainly use respiration.

OXYGEN-CARBON DIOXIDE CYCLE.

Hydrological cycle
• This is some times called the water cycle.
Water is the most important chemical of
life for all living organisms on earth. Water
in the atmosphere is usually in form of
vapor but condenses to liquid water and
can solidify when temperatures are 00
C to
form ice. Ninety three percent of water on
earth is in solid state mainly comprising
the ice caps and glaciers of Polar
Regions.

• The earth has a limited amount of water. That water
keeps going around and around and around and
around and (well, you get the idea) in what we call
the "Water Cycle". This cycle is made up of a few
main parts:
• Evaporation or (Transpiration)
• Condensation
• Precipitation
• Accumulation or (Collection)
• Ground Water
• Saturation
• Infiltration

• Evaporation is when the sun heats up
water in rivers, lakes or the ocean and
turns it into vapor or steam. The water
vapor or steam leaves the river, lake or
ocean and goes into the air.
Evaporation

• Water vapor in the air gets cold and
changes back into liquid, forming
clouds. This is called condensation.
• You can see this at home when you take a
shower and the windows and mirrors in
the bathroom fog up. You can also do this
by breathing on a mirror.
Condensation

• Precipitation occurs when so much
water has condensed that the air cannot
hold it anymore. The clouds get heavy
and water falls back to the earth in the
form of rain, hail, sleet or snow.
Precipitation

• When water falls back to earth as
precipitation, it may fall back in the
oceans, lakes or rivers or it may end up
on land. When it ends up on land, it will
either soak into the earth (infiltration)
and becomes part of the “ground water”
that plants and animals use to drink or it
may run over the soil and collect in the
oceans, lakes or rivers where the cycle
starts all over again.
Accumulation

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

Nature of elements transported in
biogeochemical cycles
• When living organisms die and decay, their
body structures disintegrate and may be
reduced to constituent molecules. Depending
on the region where disintegration of the
organisms occurred, the component molecular
elements then join the biogeochemical cycle.

Elements transported in the biogeochemical
cycles have been categorized as:
• 1. Micro elements – these are elements
required by living organisms in smaller
amounts. Examples of such elements include
boron used mainly by green plants, copper
used by some enzymes and molybdenum
used by nitrogen-fixing bacteria.
• 2. Macro elements – these are elements
required by living organisms in larger amounts.
Examples of such elements include carbon,
hydrogen, oxygen, nitrogen, phosphorous,
sulfur.

The importance of
biogeochemical cycles
• Biogeochemical cycles serve a variety of
functions at ecosystem level and in
ensuring survival of various organisms
including humans. Below are some of the
importance's of biogeochemical cycles.

Importance'sofBiogeochemicalCycles
• enable the transformation of matter from one
form to another.
• enable the transfer of molecules from one
locality to another.
• facilitate the storage of elements
• assists in functioning of ecosystems.
• cycles link living organisms with living
organisms, living organisms with the non living
organisms and nonliving organisms with non
living organism.
• regulate the flow of substances.

Thank you
for your
attention