This is the lesson - 2 of the course; 'Foundation of Environmental Management' taught at the Faculty of Social Sciences and Humanities of the Rajarata University of Sri Lanka

1. Lesson 2 – Biogeochemical Cycles
P.B. Dharmasena
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Foundation of Environmental Management
Course code: EMGT 2114

2. Course Content
1.Concepts of Ecology and Environmental
Biology
2.Biogeochemical Cycles (C, N, P etc.)

3. Lesson 2 – Biogeochemical Cycles

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, nitrogen, water cycles (but
could include all necessary elements for life)

5. What is common amongst them?
• Typical exist in all four parts of the
Earth System
• There are ‘pools’
• Are transformed chemically or
biochemically
• There are fluxes between the pools
• Transformations are important
• Transformations can lead to
positive and negative
consequences

6. Transformations
Example of
Transformations
1. Carbon cycle:
Organic compounds
to CO2 (process:
decomposition or
fire)
2. Carbon cycle: CO2 to
organic compounds
(process:
photosynthesis)

7. Transformations
Example of
Transformations
1. Nitrogen cycle: N2
to NO3 (atmospheric
nitrogen to plant
utilizable nitrate)
(process: N-fixation)
2. Nitrogen cycle: N2
to NH3 (plant
utilizable ammonia)
(process: Haber-
Bosch Industrial N-
fixation)

8. Transformations
Examples of
Transformations
1. Water cycle: Liquid
water to water vapor
(process: evaporation
and evapo-
transpiration)
2. Water cycle: Water
vapor to liquid water
(process:
condensation)

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

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

11. 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.

12. 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.

14. 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)

15. 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.

16. Key Aspects of the Carbon Cycle
• Carbon is the skeleton of all life.
• Carbon dioxide is a critical gas:
– Taken up by plants in photosynthesis
– Released by plants and animals in respiration
– Released during decomposition (and fires)
– Greenhouse gas (greenhouse effect - your car in the
sun)
CARBON CYCLE

17. CARBON CYCLE

18. CARBON CYCLE

19. 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.

20. NITROGEN CYCLE

21. NITROGEN CYCLE

22. NITROGEN CYCLE

23. Forms of Nitrogen
1. N2 - inert gas, 78% of the atmosphere
2. NO, N20, NO2 - other gases of nitrogen, not directly
biologically important. Part of the gases found in smog.
3. NO3
- and NH4
+ -- ionic forms of nitrogen that are
biologically usable.
Losses of nitrogen from system
• In bogs, lakes (places of low oxygen), NO3
- is converted to N2
by bacteria (get their oxygen from the NO3)
• Volatilization of NH4
+ (urea) to ammonia gas (NH3) - warm,
dry conditions.
• Leaching of NO3
- (nitrate)
• Erosion
• Fire (combustion)
NITROGEN CYCLE

24. 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.

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

26. 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
Effects of Human Activities on the Nitrogen Cycle

27. Nitrogen Sources over time

28. Nitrogen Cycle: Key Points
• Nitrogen is in the
atmosphere as N2 (78%)
• N2 is an inert gas and
cannot be used by plants or
animals
• N2 can be converted to a
usable form via
– Lightening
– N-fixing plants and
cyanobacteria
– Industrial process
• Nitrogen limits plant
growth

29. PHOSPHORUS CYCLE

30. 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.

31. 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
SULPHUR CYCLE

32. 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.