Biogeochemical
Cycles
Connections on Earth

Solar energy, the
cycling of
matter, and
gravity sustain
the earth’s life.
Two Secrets of Survival: Energy
Flow and Matter Recycle

An ecosystem
survives by a
combination of
energy flow and
matter recycling.
Remember these laws?
• Law of Conservation of Matter – In any ordinary physical or chemical
change, matter is neither created nor
destroyed, only transformed from one
form to another.
• Law of Conservation of Energy – In any ordinary physical or chemical
change, energy is neither created nor
destroyed, only transformed from one
form to another.
Biogeochemical Cycles: Global
Recycling



These 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.
Objectives:
 Identify
and describe the flow of
nutrients in each biogeochemical
cycle.
 Explain the impact that humans
have on the biogeochemical
cycles.
Effects of Human Activities
on Water Cycle

We don’t look at the water cycle
directly because you’ve studied it
previously: however, 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.
What Sustains Life on Earth?

Solar energy, the
cycling of
matter, and
gravity sustain
the earth’s life.
Carbon Cycle
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Biogeochemical Cycles--Carbon
 Carbon
is most abundant element
on planet Earth. It is found
everywhere, in animals, plants,
organic molecules, fuels, proteins,
carbohydrates, etc.

In the atmosphere, carbon is found in
the form of carbon dioxide (CO2)
Carbon Cycle
Reactions of photosynthesis and cellular
respiration couldn’t take place without
carbon. These two reactions form a
continuous cycle.
 Two important sources of Carbon are the
ocean (since CO2 dissolves easily in H20)
Photosynthesis
: as coal,
Cellular
Respiration
:
and
rocks (such
ore and
limestone
Plants
taking
CO2 out
take that sugar and in
formed
from
dead Organisms
organisms)

of the atmosphere and
using it to produce
sugar.
the process of burning energy
release CO2 back into the
atmosphere.
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
What Sustains Life on Earth?

Solar energy, the
cycling of
matter, and
gravity sustain
the earth’s life.
Nitrogen Cycle
Biogeochemical Cycles--Nitrogen




Organisms require Nitrogen to form amino
acids, used for the building of proteins.
Proteins are important for movement,
reproduction, defense, and structure.
Nitrogen is the most common gas in the
Earth's atmosphere, comprising around
78% of it.
Unfortunately, most organisms CANNOT
use atmospheric nitrogen (N2).
Natural forms of Nitrogen Fixation
Nitrogen-fixing bacteria CAN use N2
from the atmosphere.
 Nitrogen-fixing bacteria convert
atmospheric N2 into ammonia (NH4),
nitrites (NO2) and nitrates (NO3)
which are forms of nitrogen that
plants CAN use.

Nitrogen-fixing bacteria live in the soil and in roots
of legumes.
Natural forms of Nitrogen Fixation
Lightening plays a minor part in the
fixation of atmospheric nitrogen. The
extreme heat of a lightning flash
causes nitrogen to combine with
oxygen to form nitrates.
 The fixed nitrogen is then carried by
rain to the earth, where it is used by
plants.

Synthetic Nitrogen Fixation


The Haber-Bosch process directly synthesizes
ammonia from nitrogen and hydrogen and is the
most economical synthetic nitrogen-fixation
process known.
N2 is combined with hydrogen under extremely
high pressures and moderately high
temperatures to yield an extremely high
proportion of ammonia (NH4), which is the
starting point for the production of a wide range
of nitrogen compounds, such as fertilizers used
in crop production.
Effects of Human Activities
on the Nitrogen Cycle

We alter the nitrogen cycle by:




Adding nitrogenous gases that contribute to
acid rain (through the burning of fossil fuels).
Adding nitrous oxide to the atmosphere which
can warm the atmosphere.
Contaminating ground water from nitrate ions
in synthetic/inorganic fertilizers.
Releasing nitrogen into waterways through
deforestation. (with less plants taking up the
nitrogen, it leaches into the water)
Effects of Human Activities
on the Nitrogen Cycle

Human activities
such as
production of
fertilizers now
fix more
nitrogen than all
natural sources
combined.
Other Cycles we don’t
study:
Phosphorous Cycle
Matter is neither
created nor destroyedSulfur Cycle
just changes form!
Water Cycle