Chapter 4
Biogeochemical Cycles
What IS a “biogeochemical cycle”?
 BIO
= “life”
 GEO = “earth”
 CHEMICAL = “elements – C, O, N, P, S
• a cycling of nutrients (water, carbon, oxygen, nitrogen,
phosphorus, sulphur) from the abiotic components of the
ecosystem (water, air, soil, rock) through the biotic
components (plants, animals, fungi, bacteria)
Objectives:
 Identify
and describe the flow of nutrients in
each biogeochemical cycle.
 Explain
the impact that humans have on the
biogeochemical cycles.
Objectives:
 Identify
and describe the flow of nutrients in
each biogeochemical cycle.
 Explain
the impact that humans have on the
biogeochemical cycles.
What Sustains Life on Earth?
• Solar energy,
the cycling of
matter, and
gravity sustain
the earth’s life.
Figure 3-7
Two Secrets of Survival: Energy
Flows and Matter Cycles
 An
ecosystem
survives by a
combination of
energy flow (from
Sun to Earth) and
matter cycling.
 Remember: the
Earth is a
CLOSED system
Figure 3-14
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’s Unique Properties
 There
are strong forces of attraction between
molecules of water. (due to H bonds)
 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. (due to polar nature of water)
 Water expands when it freezes.
THE HYDROLOGIC (WATER) CYCLE
Condensation
Rain clouds
Transpiration Evaporation
Transpiration
Precipitation
to land
from plants
Precipitation
Runoff
Surface runoff
(rapid)
Precipitation
Evaporation
from land Evaporation
from ocean
Precipitation
to ocean
Surface
runoff
(rapid)
Infiltration and
Percolation
Groundwater movement (slow)
Ocean storage
Fig. 3-26, p. 72
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.
Fig. 3-27, pp. 72-73
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
 photosynthesis =
 CO2
Figure 3-28
THE NITROGEN CYCLE
THE NITROGEN CYCLE
Effects of Human Activities
on the Nitrogen Cycle
 We



alter the nitrogen cycle by:
Adding nitrous oxide to the atmosphere from
vehicles and factories which contributes to acid
rain.
Contaminating ground water from nitrate ions in
inorganic fertilizers.
Releasing nitrogen into the troposphere through
deforestation (less N assimilated by trees).
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 3-30
THE PHOSPHORUS CYCLE
mining
excretion
Fertilizer
Guano
agriculture
uptake by
uptake by weathering
autotrophs
autotrophs
leaching, runoff
Dissolved
Land
Marine
Dissolved
in Soil Water,
Food
Food
in Ocean
Lakes, Rivers
Webs
Webs
Water
death,
death,
decomposition
decomposition
weathering
sedimentation
settling out
uplifting over
geologic time
Rocks
Marine Sediments
Fig. 3-31, p. 77
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 – excess phosphorus causes algal
blooms
Algal blooms
THE SULPHUR CYCLE
Sulfur
trioxide
Water
Acidic fog and
precipitation
Sulfuric acid
Ammonia
Oxygen
Sulfur dioxide
Ammonium
sulfate
Hydrogen sulfide
Plants
Dimethyl
sulfide
Volcano
Industries
Animals
Ocean
Sulfate salts
Metallic
sulfide
deposits
Decaying matter
Sulfur
Hydrogen sulfide
Fig. 3-32, p. 78
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
Assignment: Put the 6 cycles
together on one poster!
Draw the hydrologic, carbon, oxygen,
nitrogen, phosporus and sulphur cycles onto
one piece of poster paper.
 Include the required terminology
 Follow the criteria on the rubric provided
 Assessment will be done by performance
(explanation of the cycles by the group)

The Gaia Hypothesis:
Is the Earth Alive?
 Some
have proposed that the earth’s various
forms of life control or at least influence its
chemical cycles and other earth-sustaining
processes.


The strong Gaia hypothesis: life controls the
earth’s life-sustaining processes.
The weak Gaia hypothesis: life influences the
earth’s life-sustaining processes.