The document summarizes several biogeochemical cycles, including the water, oxygen, carbon, phosphorus, nitrogen, and sulfur cycles. It describes the key processes in each cycle, such as evaporation and precipitation in the water cycle, photosynthesis and cellular respiration in the oxygen cycle, and fixation, nitrification, and denitrification in the nitrogen cycle. It also discusses how human activities like burning fossil fuels, clearing vegetation, and use of fertilizers impact these natural cycles.

1. BIOGEOCHEMICAL CYCLES

2. Biogeochemical Cycles
 Also termed as substance turnover or cycling
of substance
 It is a pathway by which a chemical
substance moves through both biotic and
abiotic compartments of Earth.
 either a gas cycle or a sedimentary cycle

3. Fig. 3-7, p. 55
Nitrogen
cycle
Biosphere
Heat in the environment
Heat Heat Heat
Phosphorus
cycle
Carbon
cycle
Oxygen
cycle
Water
cycle

4. Water Cycle

5.  Evaporation – the process of changing
water into vapor
 Condensation – the process of changing
vapor into water
 Precipitation – any form of water that falls
to the earth’s surface
 Run-off – water that moves along the
earth’s surface, it is not absorbed
 Percolation – draining or seeping of water
into the earth

6.  Capillary – when water is moved towards
the surface
 Absorption – when plants take water from
the ground
 Transpiration – water leaving the pores
from leaves on plants
 Decomposition – breaking down organic
matter, releases water to the environment

7. Oxygen Cycle

8.  Oxygen is present in our atmosphere in the
form of ozone, water vapour, pure oxygen
and carbon dioxide.
 Plants and algae perform photosynthesis
which removes carbon dioxide and adds
oxygen to the atmosphere.
 Animals perform cellular respiration which
removes oxygen from the atmosphere and
adds carbon dioxide.

9.  When plants and animals die, decomposers
uses oxygen to break down organic
material and release carbon dioxide.
 Also, water dissolves oxygen and the
aquatic life use this oxygen for
photosynthesis and cellular respiration.
Fish need oxygen in the water to perform
cellular respiration.

10. CARBON CYCLE

11.  Producers (plants and algae) use carbon
dioxide to perform photosynthesis and make
food
 Herbivores eat the plants and carnivores eat
the herbivores
 Both plants and animals respire.
 Respiration returns carbon dioxide to the
atmosphere
 Decomposers break down dead plants and
animals as well as animal waste and returns
carbon dioxide to the atmosphere or soil.

12. 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.
Figure 3-28Figure 3-28

13. Phosphorous Cycle

14.  Initially, phosphate weathers from rocks and
minerals
 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

15. 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.

16. Phosphorus
 Bacteria are not as important in the phosphorus cycle
as in the nitrogen cycle.
 Phosphorus is not usually found in the atmosphere or
in a gas state only as dust.
 The phosphorus cycle is slow and phosphorus is
usually found in rock formations and ocean sediments.
 Phosphorus is found in fertilizers because most soil is
deficient in it and plants need it.
 Phosphorus is usually insoluble in water and is not
found in most aquatic environments.

17. Nitrogen Cycle

18.  Plants use the nitrates that they absorb to make plant
proteins
 Animals get the nitrogen that they need to make
proteins by eating plants or other animals
 When plants and animals die, bacteria change their
nitrogen content to ammonia
 The nitrogen in the urine and fecal matter of animals
is also changed to ammonia by bacteria. The pungent
odour of outhouses, chicken pens, hog yards, cat
litter boxes and wet baby diapers is ample evidence
of this fact. Ammonia, in turn, is converted to nitrites
and then to nitrates by bacteria. This process is called
nitrification and completes the main part of the cycle.

19.  Ammonia, in turn, is converted to nitrites
and then to nitrates by bacteria. This
process is called nitrification and
completes the main part of the cycle.

20. 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.

21. 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

22. Nitrogen Fixation
 This is the first step of the nitrogen cycle
where specialized bacteria convert gaseous
nitrogen to ammonia that can be used by
plants. This is done by cyanobacteria or
bacteria living in the nodules on the root of
various plants.

23. Nitrification
 Ammonia is converted to nitrite, then to
nitrate
 Plant roots absorb ammonium ions and nitrate
ions for use in making molecules such as DNA,
amino acids and proteins.
Assimilation

24. Ammonification
 After nitrogen has served its purpose in living
organisms, decomposing bacteria convert the
nitrogen-rich compounds, wastes, and dead
bodies into simpler compounds such as ammonia.
Denitrification
Nitrate ions and nitrite ions are converted into
nitrous oxide gas and nitrogen gas.
This happens when a soil nutrient is reduced and
released into the atmosphere as a gas.

25. The Sulfur Cycle
Figure 3-32Figure 3-32

26. Steps of the sulfur cycle are:
 Mineralization of organic sulfur into inorganic
forms, such as hydrogen sulfide (H2S),
elemental sulfur, as well as sulfide minerals.
 Oxidation of hydrogen sulfide, sulfide, and
elemental sulfur (S) to sulfate (SO4
2–
).
 Reduction of sulfate to sulfide.
 Incorporation of sulfide into organic
compounds (including metal-containing
derivatives).

27. 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.