Biogeochemical cycles

1. Biogeochemical Cycles
Rizwan Abbas Baho
7-12-2017

2. Definition
• Describe the flow of essential elements from
the environment through living organisms
and back into the environment.

3. ‘Fundamentals’ of biogeochemical cycles
• All matter cycles...it is neither created nor
destroyed...
• As the Earth is essentially a closed system with
respect to matter, we can say that all matter on Earth
cycles .
• Biogeochemical cycles: the movement (or cycling) of
matter through a system

4. by matter we mean: elements (carbon, nitrogen, oxygen) or
molecules (water)
so the movement of matter (for example carbon) between
these parts of the system is, practically speaking, a
biogeochemical cycle
The Cycling Elements:
macronutrients : required in relatively large amounts
“Major":
carbon , hydrogen , oxygen , nitrogen , phosphorous
sulfur

5. other macronutrients:
potassium , calcium , iron , magnesium
micronutrients : required in very small amounts, (but still
necessary)
boron (green plants)
copper (some enzymes)
molybdenum (nitrogen-fixing bacteria)

6. Water cycle
1. Reservoir – oceans, air (as water vapor),
groundwater, lakes and glaciers;
evaporation, wind and precipitation
(rain) move water from oceans to
land
2. Assimilation – plants absorb water from the
ground, animals drink water or eat
other organisms which are
composed mostly of water
3. Release – plants transpire, animals breathe
and expel liquid wastes

8. 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
increasing soil erosion.

9. Carbon cycle
1. Reservoir – atmosphere (as CO2), fossil fuels
(oil, coal), durable organic materials
(for example: cellulose).
2. Assimilation – plants use CO2 in
photosynthesis; animals consume
plants.
3. Release – plants and animals release CO2
through respiration and
decomposition; CO2 is released as
wood and fossil fuels are burned.

11. Carbon cycle
 Carbon (C) enters the biosphere during
photosynthesis:
 CO2 + H2O (carbon dioxide+ water)--->
C6H12O6 + O2 + H2O(sugar+oxygen+water)
 Carbon is returned to the biosphere in cellular
respiration:
 O2 +H2O + C6H12O6 ---> CO2 +H2O + energy

12. Nitrogen Cycle
• (Nitrogen is required for the manufacture of
amino acids and nucleic acids)
• 1. Reservoir – atmosphere (as N2); soil (as
NH4
+ or ammonium, NH3 or ammonia, N02
- or
nitrite, N03
- or nitrate
• 2. Assimilation – plants absorb nitrogen as
either NH4
+ or as N03
-, animals obtain nitrogen
by eating plants and other animals. The stages
in the assimilation of nitrogen are as follows:

13. 2. Assimilation
Nitrogen Fixation: N2 to NH4
+ by nitrogen-
fixing bacteria (prokaryotes in the soil
and root nodules), N2 to N03
- by
lightning and UV radiation.
Nitrification: NH4
+ to N02
- and N02
- to N03
-
by various nitrifying bacteria.

14. • 3. Release
• – Denitrifying bacteria convert N03
- back to N2
(denitrification); detrivorous bacteria convert
organic compounds back to NH4
+
(ammonification); animals excrete NH4
+ (or
NH3) urea, or uric acid.

16. Phosphorus Cycle
1. Reservoir – erosion transfers phosphorus to
water and soil; sediments and rocks
that accumulate on ocean floors return
to the surface as a result of uplifting by
geological processes
2. Assimilation – plants absorb inorganic PO4
3-
(phosphate) from soils; animals obtain
organic phosphorus when they plants
and other animals
3. Release – plants and animals release phosphorus
when they decompose; animals excrete
phosphorus in their waste products

17. Slide 41Slide 41Slide 41
GUANO
FERTILIZER
ROCKS
LAND
FOOD
WEBS
DISSOLVED
IN OCEAN
WATER
MARINE
FOOD
WEBS
MARINE SEDIMENTS
weathering
agriculture
uptake by
autotrophs
death,
decomposition
sedimentation settling out weathering
leaching, runoff DISSOLVED IN
SOIL WATER,
LAKES, RIVERS
uptake by
autotrophs
death,
decomposition
miningmining
excretionexcretion
Figure 4-33
Page 82
uplifting over
geologic time

18. Biogeochemical cycles of other minerals, such as
calcium and magnesium, are similar to the
phosph
orus cycle.

19. Sulfur cycle
 Component of protein
 Cycles in both a gas and sedimentary cycle.
 The source of Sulfur is the lithosphere (earth's crust)
 Sulfur (S) enters the atmosphere as hydrogen
sulfide (H2S) during fossil fuel combustion, volcanic
eruptions, gas exchange at ocean surfaces, and
decomposition.
 SO2 and water vapor makes H2SO4 ( a weak sulfuric acid),
which is then carried to Earth in rainfall.
 Sulfur in soluble form is taken up by plant roots and
incorporated into amino acids such as cysteine. It then
travels through the food chain and is eventually released
through decomposition.

20. Slide 42Slide 42Slide 42
Figure 4-34
Page 83
Sulfur
Hydrogen
sulfide
Sulfate salts
Plants
Acidic fog and
precipitation
Ammonium
sulfate
Animals
Decaying
matterMetallic
sulfide
deposits
Ocean
Dimethyl
sulfide
Sulfur dioxide Hydrogen
sulfide
Sulfur trioxide Sulfuric acid
Water
Ammonia
Oxygen
Volcano
Industries

21. Thanks
Baho