Download Cycles - Madison County Schools

CYCLES
Biosphere
Carbon
cycle
Phosphorus
cycle
Nitrogen
cycle
Water
cycle
Oxygen
cycle
Heat in the environment
Heat
Heat
Heat
Fig. 3-7, p. 55
CARBON CYCLE
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 3-28
Phosphorous Cycle
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.
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.
Nitrogen Cycle
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.
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
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.
Nitrification

Ammonia is converted to nitrite, then to nitrate
Assimilation
Plant
roots absorb ammonium ions and
nitrate ions for use in making molecules suc
as DNA, amino acids and proteins.
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.
The Sulfur Cycle
Figure 3-32
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.
