Biogeochemical Cycles
Course : B.Sc. Microbiology/ Bio-Technology/ Bio-Chemistry
Sem I
Sub: Environmental Science
Unit 4

What are biogeochemical cycles?
• Earth system has four parts
– Atmosphere
– Hydrosphere
– Lithosphere
– Biosphere
• Biogeochemical cycles: The chemical
interactions (cycles) that exist between
the atmosphere, hydrosphere,
lithosphere, and biosphere.
• Abiotic (physio-chemical) and biotic
processes drive these cycles
• Focus on carbon and water cycles (but
could include all necessary elements for
life). N - cycle weakly touched on!
1

Biogeochemical Cycle
• Bio- life
• Geo-earth
• Chemical- elements
• A biogeochemical cycle or substance
turnover or cycling of substances is a pathway by which
a chemical substance moves through both biotic
(biosphere) and abiotic (lithosphere, atmosphere,
and hydrosphere) compartments of Earth. A cycle is a
series of change which comes back to the starting point
and which can be repeated.

What is common amongst them?
• Each compound (water, carbon, nitrogen)
typically exists in all four parts of the Earth
System
• There are
– ‘Pools’
– Fluxes in and out of pools
– Chemical or biochemical transformations
• Transformations
– are important
– can lead to positive & negative consequences

What Sustains Life on Earth?
• Solar energy,
the cycling of
matter, and
gravity sustain
the earth’s life.
2

Two Secrets of Survival: Energy
Flow and Matter Recycle
• An ecosystem
survives by a
combination of
energy flow and
matter recycling.
Figure 3-14Figure 3-14
3

MATTER CYCLING IN
ECOSYSTEMS
• Nutrient Cycles: Global Recycling
– Global Cycles recycle nutrients through the
earth’s air, land, water, and living organisms.
– Nutrients are the elements and compounds that
organisms need to live, grow, and reproduce.
– Biogeochemical cycles move these substances
through air, water, soil, rock and living
organisms.

Water’ Unique Properties
• There are strong forces of attraction between
molecules of water.
• Water exists as a liquid over a wide
temperature range.
• Liquid water changes temperature slowly.
• It takes a large amount of energy for water to
evaporate.
• Liquid water can dissolve a variety of
compounds.
• Water expands when it freezes.

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)
Water Cycle
4

• The Water Cycle (also known as the
hydrologic cycle) is the journey water takes
as it circulates from the land to the sky and
back again.
The Sun's heat provides energy to evaporate water from the
Earth's surface (oceans, lakes, etc.). Plants also lose water
to the air (this is called transpiration). The water vapor
eventually condenses, forming tiny droplets in clouds. When
the clouds meet cool air over land, precipitation (rain, sleet,
or snow) is triggered, and water returns to the land (or sea).
Some of the precipitation soaks into the ground. Some of the
underground water is trapped between rock or clay layers;
this is called groundwater. But most of the water flows
downhill as runoff (above ground or underground),
eventually returning to the seas as slightly salty water.

The Water Cycle (also known
as the hydrologic cycle)
5

Water Cycle
• involves the processes of photosynthesis,
transpiration, evaporation and
condensation, respiration, and excretion

6

Effects of Human Activities
on Water Cycle
• We alter the water cycle by:
– Withdrawing large amounts of freshwater.
– Clearing vegetation and eroding soils.
– Polluting surface and underground water.
– Contributing to climate change.

The Carbon Cycle
All living things are
made of carbon.
Carbon is also a part
of the ocean, air, and
even rocks. Because
the Earth is a dynamic
place, carbon does
not stay still
7

• In the atmosphere, carbon is attached to
some oxygen in a gas called carbon
dioxide.
• Plants use carbon dioxide and sunlight to
make their own food and grow. The
carbon becomes part of the plant. Plants
that die and are buried may turn into fossil
fuels made of carbon like coal and oil over
millions of years. When humans burn
fossil fuels, most of the carbon quickly
enters the atmosphere as carbon dioxide.

8

Effects of Human Activities
on Carbon Cycle
• We alter the
carbon cycle by
adding excess CO2
to the atmosphere
through:
– Burning fossil fuels.
– Clearing vegetation
faster than it is
replaced.
9

Carbon-Oxygen Cycle
• Involves the processes of respiration and
photosynthesis.
• In respiration, oxygen and glucose are combined
releasing energy and producing water and carbon
dioxide.
• In photosynthesis water and carbon dioxide along
with the energy from the sun are combined to
produce glucose (containing energy) and oxygen.
• Each process compliments the other and the
ecosystem maintains its balanced communities.

10

Nitrogen cycle
1
1

• The nitrogen cycle is the process by which nitrogen is
converted between its various chemical forms. This
transformation can be carried out through both biological and
physical processes. Important processes in the nitrogen
cycle include fixation, ammonification, nitrification,
and denitrification.
• The majority of Earth's atmosphere (78%)
is nitrogen, making it the largest pool of nitrogen. However,
atmospheric nitrogen has limited availability for biological
use, leading to a scarcity of usable nitrogen in many types of
ecosystems. The nitrogen cycle is of particular interest
to ecologists because nitrogen availability can affect the rate
of key ecosystem processes, including primary
production and decomposition.
• Human activities such as fossil fuel combustion, use of
artificial nitrogen fertilizers, and release of nitrogen in
wastewater have dramatically altered the global nitrogen
cycle.

Nitrogen Cycle
• Nitrates (used by plants)
• Build plant proteins
• Eaten by animals
• made into animal proteins
• Plants and animals die
• bacteria decay
• Ammonia (NH3)
• Nitrifying Bacteria
• Nitrates (used by plants)

12

13

14

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.
15

The biogeochemical cycle that describes the movement
of phosphorus through the lithosphere, hydrosphere, and biosphere.
Unlike many other biogeochemical cycles, the atmosphere does not
play a significant role in the movement of phosphorus, because
phosphorus and phosphorus-based compounds are usually solids at
the typical ranges of temperature and pressure found on Earth.

16

Phosphorus cycle
• Phosphates move quickly through plants and animals;
however, the processes that move them through the soil or
ocean are very slow, making the phosphorus cycle overall
one of the slowest biogeochemical cycles.
• Initially, phosphate weathers from rocks and minerals, the
most common mineral being apatite. Overall small losses
occur in terrestrial environments by leaching and erosion,
through the action of rain. In soil, phosphate is absorbed on
iron oxides, aluminium hydroxides, clay surfaces, and
organic matter particles, and becomes incorporated
(immobilized or fixed). Plants and fungi can also be active in
making P soluble.
• Unlike other cycles, P cannot be found in the air as a gas; it
only occurs under highly reducing conditions as the
gas phosphine PH3.

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
17

18

1. When rocks high in
phosphorus are exposed to
water, the rock weathers out and
goes into solution
2. autotrophs absorb this
phosphorus and use it in many
different ways,
3. then the plant is eaten by a
heterotroph and obtains
phosphorus from the plant
4. then the phosphate leaves the
body, and decomposers move
the phosphorus into the soil or
water then another plant will
absorb this phosphorus.

Effects of Human Activities
on the Phosphorous Cycle
• We remove large amounts of phosphate from
the earth to make fertilizer.
• We reduce phosphorous in tropical soils by
clearing forests.
• We add excess phosphates to aquatic
systems from runoff of animal wastes and
fertilizers.

What Sustains Life on Earth?
• Solar energy,
the cycling of
matter, and
gravity sustain
the earth’s life.

Oxygen cycle
19

Oxygen cycle
• All organisms living an animals
breathe in oxygen. Oxygen
constitutes about 20% of the
atmosphere. It is essential for
respiration. It produces energy
in living beings by the oxidation
of foods. During this process,
CO2 is released which is used
by the plants in making food
during photosynthesis. During
the process of photosynthesis,
oxygen gas is released back
into the atmosphere. Thus, this
cycle is completed.
20

Oxygen cycle
21

Oxygen cycle
• Oxygen cycle, circulation of oxygen in various forms
through nature. Free in the air and dissolved in water,
oxygen is second only to nitrogen in abundance among
uncombined elements in the atmosphere. Plants and
animals use oxygen to respire and return it to the air and
water as carbon dioxide (CO2). CO2 is then taken up by algae
and terrestrial green plants and converted into
carbohydrates during the process of photosynthesis, oxygen
being a by-product. The waters of the world are the main
oxygen generators of the biosphere; their algae are
estimated to replace about 90 percent of all oxygen used.
Oxygen is involved to some degree in all the other
biogeochemical cycles. For example, over time, detritus
from living organisms transfers oxygen-containing
compounds such as calcium carbonates into the lithosphere.

Sulphur Cycle
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
22

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.

What do you think?
• Does life on earth control earth’s life-
sustaining processes or does life merely
influence these life-sustaining process?

Images:
1.http://www.centerforecopsychology.org/images/image2.jpg
2.http://image.slidesharecdn.com/biogeochemicalcycles-130609103318-
phpapp02/95/biogeochemical-cycles-4-638.jpg?cb=1370792062
3.http://en.harunyahya.net/resimleri/sites/4/62/the-food-cycle.jpg
4.https://lh4.ggpht.com/dA7aCeK4Br2RGMjqXu9HZILHd_q9twMzmEelevDnHZ
piVVGUMsHvzaZQjyb5yIun8qYMTg=s151
5.http://www.mrnorton.com/Podcasts/Digital%20Posters%202009-2010/4th
%20Period/Water/WaterCycleKS.JPG
6.https://lh4.ggpht.com/FplaEfmu-0A-YXbsAaD9rpGOSlNaOEP-
F34VVXcCtu8Ltue6oJEZdjeZCHfaZAC4BEMw=s132
7.https://s-media-cache-
ak0.pinimg.com/236x/00/a9/44/00a94471151401ace96c0168ca2e3798.jpg
8.http://www.quia.com/files/quia/users/repasy_p/nutrientcycles/carboncycle3
9.https://lh5.ggpht.com/vZipErPS3JNmvN22fRti9pMhh8vEBJ-
O4ALE3Ve5_fIZ63s1H1koVzp-26FSag-if0Bf=s85
10.https://lh6.ggpht.com/AgnYsZWsI7fVbul3Qs7GlllRviZzoYdKKsKmqNc9UwJ
6Q3r6UkTKQD_Byb1_LsoT7ENl1tI=s115
References

Images:
11.https://lh5.ggpht.com/yySasAxNRgtCSUaGuHkCktWqCMVmvTpLf080fKAToyoTE-
uYM9oMYbu55RGxdOS4yAJX=s125
12.https://lh5.ggpht.com/U7_wf-Kxz6ehM3WQmyqoQWAXsgGRysvLGxwNwMv-
GdF1pYZAPkBmi-5rZVpPWsDu8Tv38w=s142
13.http://figures.boundless.com/3398/raw/nitrogen-cycle.svg
14.http://s3.amazonaws.com/slideserve/thumb1/1_2621771.jpg
15.https://lh5.ggpht.com/NngoBf5fWd5Y26CWNFBk2T44SoRWV_VCc8J-67K7R8o1uckHs-
yUP2zkcEIQvLl-XaNMM8g=s87
16.http://i1.wp.com/gnosticwarrior.com/wp-content/uploads/2013/09/Phosphorus-cycle-with-
peeing-dude.png?zoom=2&resize=400%2C341
17.https://lh4.ggpht.com/FUijUdc3LKSstNE83iXl5kjt0szD8Tepw9fj9s12dOp-
Ch0d6wz_UFxoeq24ynu7EtNjd8I=s134
18.https://lh6.ggpht.com/pZmflvLmgicH0ttp5zZWVF7GYjm4E0RdMe7ufp8oEomHOLZzvDexi
wtI1YsXAA25BMgUgA=s136
19.http://www.keepbanderabeautiful.org/oxygen-cycle-i.jpg
20.https://lh6.ggpht.com/6CHiLGb9q0vmq8c-
VmxlEButeSis9sRHtTuXWV_WNLcnKuvwMdBQ_51P4BEclZ6iXmdTgNU=s99
21.https://lh3.ggpht.com/t3En7f5lp-
jig_lvYJdqdNBYD2r4wAO1FJtD5A3gUrWvpUmJagCpOvMzcbxR1SBpSY42=s127
22.https://lh6.ggpht.com/DfIiPQ_NOrLm__b0zBiD0waD0RGfvoIraT6B7GmXkfE6-
Ra_aDaucMF2wJcK8sR5zs9HMQ=s145
References

Books:
1.Environmental studies by R.Rajagopalan
2.Environmental Science by Richard T Wright & Bernard J
Nebel
References