Transcript Lecture #5 Biogeochemical Cycles

Lecture #5 Biogeochemical
Cycles
Unit 1: Ecology
Biogeochemical Cycles
A biogeochemical cycle is the cyclic
movement of a substance (for example,
water, carbon, nitrogen, or phosphate)
through the biotic (living) and abiotic
(non-living) environments.
Biogeochemical cycles are a key
component of ecosystems ecology.
Nature reuses
everything. All of
the matter
that cycles through
living organisms are
important in
maintaining the
health of the
ecosystem.
– Biogeochemical cycles of matter involve
biological processes, geological
processes, and chemical processes.
– As matter moves through these cycles,
it is never created or destroyed—just
changed.
* In almost all
biochemical cycles,
there is much less
of the substance in
the living reservoir
than the nonliving
reservoir.
We’re in the Driver’s Seat - Human
Activities greatly impact Many
Biogeochemical Cycles
1. The Water (hydrologic) Cycle
Plants absorb water from the soil
Water may percolate down through the
soil and eventually collect in pools
(groundwater)
Transpiration (release of water through
leaves due to the sun) and respiration
return water to the atmosphere
Precipitation (rain, snow, etc) returns
water to the soil
The Water Cycle
Only about 40% of precipitation on land comes from water
evaporated over oceans; roughly 60% comes from transpiration of
water through plants.
Freshwater Is a Precious and Often Scarce Resource
The Percentage of Available Global Freshwater is Very
Small
Human Impact on the Water
Cycle
• Withdraw large quantities of fresh water –
water diversion, groundwater depletion,
wetland drainage
• Clearing vegetation from land
– Increases runoff, reduces infiltration,
increases flooding, increases soil erosion
• Modify water quality-adding nutrients
(phosphates, nitrates)
2. The Carbon Cycle
Photosynthesis and Cell Respiration cycle
carbon and oxygen through the environment
• Carbon is fixed by plants
–
6 CO2 + 6 H2O  C6H12O6 + 6 O2
• Carbon is given off by consumers
–
C6H12O6 + 6 O2  6 CO2 + 6 H2O
• Organisms containing carbon form fossil
fuels
• Burning fossil fuels releases carbon
–
2 C8H18 + 25 O2  16 CO2 + 18 H2O
The
Carbon
Cycle
Carbon Cycle
Human Impact on the Carbon Cycle
• Burning of fossil fuels & biomass (wood)
generates huge amounts of carbon
dioxide that cannot be taken up fast
enough by the carbon sinks (oceans,
forests).
• This excess carbon dioxide contributes
to global warming, which may lead to
loss of biodiversity globally, rising sea
levels, more violent storms, and changes
in precipitation patterns.
Human Impact on Carbon Cycle
• Removal of vegetation – decreases
primary production (decreases carbon
fixation) and subsequently, biodiversity
3. The Nitrogen cycle
Atmospheric nitrogen (N2) makes up nearly
78%-80% of air.
Organisms cannot use it in that form.
Lightning and some species of bacteria
convert nitrogen into usable forms.
Nitrogen-fixing
bacteriaBacteria that live in a
symbiotic
relationship with
plants of the legume
family (e.g., soybeans,
clover, peanuts).
Nitrogen fixation-convert atmospheric
nitrogen (N2) into ammonium (NH4+)
which can be used to make organic
compounds like amino acids.
N2
NH4+
Only in certain types of bacteria and
industrial technologies can fix nitrogen.
Ammonia is further changed by other
types of soil bacteria (nitrification)
into nitrate, which is taken up by
plants and passed on to animals as
they consume the plants.
Eventually this is returned to the
nonliving reservoir when the organism
dies and decays.
The Nitrogen Cycle
Humans Play a
Major Role in the
Nitrogen Cycle
Aerial fertilization (with
nitrogen) of sugar beets.
Human Impact on the Nitrogen Cycle
• Use of synthetic nitrogen fertilizers
may stimulate algal blooms (due to
agricultural runoff), which depletes
oxygen and decreases biodiversity.
A ‘dead zone’
forms seasonally
near the area
where the
Mississippi river
dumps into the
Gulf of Mexico.
Virtually all marine
life is killed due to
the lack of oxygen
available.
VIDEO CLIP ON THE DEAD ZONE
http://oceantoday.noaa.gov/happnowdeadzone/
Human impact on the Nitrogen
Cycle Continued….
• Land management: Nitrogen-fixing
crops (legumes) add more useable
nitrogen to the soil. (Example of crop
rotation: corn, soybeans, corn,
soybeans)
– On the other hand, overplanting of
crops depletes nitrogen from soil.
Human Impact on the Nitrogen Cycle
Cont.
• Burning fossil fuels- forms nitrogen
dioxide (NO2) in atmosphere, which can
react with water to form nitric acid
(HNO3) & causes acid rain
The Phosphorous Cycle
Phosphorus - usually found in soil and
rocks in the form of calcium phosphate.
• Calcium phosphate dissolves in water
and forms phosphate ions. We can’t use
this inorganic form of phosphorous.
** Phosphorous is an important component
of DNA, bones and teeth
• Plants take up inorganic phosphate via
their roots. It is then used to build
organic phosphate .
• Consumers get organic phosphate from
plants.
• Decomposers return phosphate to soil
• Phosphate leaches into water supply
– May form new phosphate containing rock
How is this cycle unique from the others?
Answer: There is NO atmospheric phase
in the phosphorous cycle!
Phosphorous Cycle
Human Impact on the
Phosphorous Cycle
• Mining of large quantities of phosphate
rock-used for organic fertilizers and
detergents
• Runoff of wastes and fertilizers causes
accumulation in lakes and ponds killing
aquatic organisms
– leads to excessive algal growth, depletion
of oxygen, & decrease in biodiversity;
eutrophication ("over nourishment")
Take 2 minutes to summarize how
matter cycles through the biosphere,
how human activity impacts these
cycles and the effect these impacts
have on global biodiversity.