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Chapter 5
Ecosystems
and the
Physical
Environment
Cycling of Materials within Ecosystems
Basics of biogeochemical cycling
Energy flows
one way
through
ecosystems
Matter cycles
continuously
through
biotic and
abiotic
components.
MATERIAL CYCLES
• Carbon Cycle
– Begins with intake of CO2 during
photosynthesis. Carbon atoms are
incorporated into glucose and then:
• Remain in plant material until death.
– Eaten by predator
– Respiration
– Excretion
» Death (Decomposers)
Cycling of Materials within Ecosystems
Carbon cycle:
Carbon Cycle
Nitrogen Cycle
• Plants uptake inorganic nitrogen from the
environment and build protein molecules
which are later eaten by consumers.
– Nitrogen-fixing bacteria change nitrogen to a
less mobile, more useful form by combining it
with hydrogen to make ammonia - used to
build amino acids.
• Members of bean family (legumes) have nitrogenfixing bacteria living in their root tissue.
Nitrogen Cycle
– Nitrogen re-enters the environment:
• Death of organisms
• Excrement and urinary wastes
– Nitrogen re-enters atmosphere when
denitrifying bacteria break down nitrates into
N2 and nitrous oxide (N2O)gases.
• Humans have profoundly altered nitrogen cycle via
use of synthetic fertilizers, nitrogen-fixing crops,
and burning fossil fuels.
Cycling of Materials within Ecosystems
Nitrogen cycle:
Atmospheric
nitrogen (N2)
Biological
nitrogen
fixation
Nitrogen
fixation by
humans
Decomposition
Denitrification
NH3 &
NH4-
Internal
cycling
Plant & animal
proteins
Assimilation
Nitrification
NO3-
Nitrogen Cycle
Phosphorous Cycle
• Phosphorous compounds are leached from
rocks and minerals and usually
transported in aqueous form.
– Taken in and incorporated by producers.
• Passed on to consumers.
– Returned to environment by decomposition.
Cycling of Materials within Ecosystems
Phosphorus cycle:
Phosphate rocks
Excretion /
decomposition
Phosphate
mining
Erosion
Internal
cycling
Marine
organisms
Marine
sediments
Fertilizer
containing
phosphates
Animals, crops
Dissolved
phosphates
Erosion
Internal
cycling
Soil phosphates
Phosphorous Cycle
Sulfur Cycle
• Most sulfur tied up in underground rocks
and minerals. Inorganic sulfur released
into air by weathering and volcanic
eruptions.
– Cycle is complicated by large number of
oxidation states the element can assume.
– Human activities release large amounts of
sulfur, primarily by burning fossil fuels.
• Important determinant in rainfall acidity.
Cycling of Materials within Ecosystems
Sulfur cycle:
Hydrologic Cycle
• Describes the circulation of water as it:
– Evaporates from land, water, and organisms.
(Transpires from plants)
• Enters the atmosphere.
–Condenses and precipitates back to the
earth’s surfaces.
»Moves underground by infiltration or
overland runoff into rivers, lakes and
seas.
Cycling of Materials within Ecosystems
Hydrologic cycle:
Hydrologic Cycle
Hydrologic Cycle
• Solar energy drives the hydrologic cycle by
evaporating surface water.
– Evaporation - Changing liquid to a vapor below
its boiling point.
– Sublimation - Changing water between solid
and gaseous states without ever becoming
liquid.
Solar Radiation
• Visible light passes through atmosphere
undiminished.
• Ultraviolet light is absorbed by ozone in
the stratosphere.
• Infrared radiation is absorbed by carbon
dioxide and water in the troposphere.
– Albedo - Reflectivity
• Fresh clean snow
• Dark soil
• Net average of earth
90%
3%
30%
Solar Radiation
Solar Radiation
– Solar energy is unevenly distributed.
• Sun strikes the equator directly all year.
• Earth’s axis is tilted.
– Also rays of light entering the atmosphere at
the poles must pass through a deeper
envelope of air than light entering at the
equator.
– This causes the sun’s energy to be
scattered at the pole, producing lower
temperature.
Solar Radiation
Temperature Changes with Latitude
Like equator
Like at poles
Solar Radiation
Temperature Changes with Season
•Seasons are a
result of the tilt
of the earth.
•During half of
the year, the
northern
hemisphere
tilts towards
the sun, and
during the
other half
away from the
sun.
The Atmosphere
Composition
Nitrogen
Oxygen
Carbon dioxide
Argon
Water vapor
Pollutants
Helium
Etc.
78%
21%
1%
The Atmosphere
Troposphere
•Ranges in depth
from 12.5 km
over the equator
to 8.0 km over
the poles.
•All weather occurs
here.
•Composition is
relatively uniform.
•Air temperature drops
rapidly with increasing
altitude.
The Atmosphere
• Stratosphere
– Extends from troposphere to about 45 km.
• Air temperature is stable
• -45deg C to -75 degC (part closest to Earth)
• Fraction ozone is 1000x more than in the
troposphere.
• Absorbs UV
• Steady wind
• Relatively calm
The Atmosphere
• Mesosphere
– Middle Layer.
• Minimum temperature is about - 138o C.
• Thermosphere
– Extends from 80-500 km.
• Ionized and thin air
–Ionosphere - Lower Thermosphere
»Aurora borealis (northern lights)
• high temperatures. (-1000 deg C+)
• Absorbs UV and X-ray
The Atmosphere
Atmospheric Circulation
Circulation
spawned
by heating
/ cooling
Prevailing
winds
Generated by
pressure
differences
and Coriolis
effect
The Atmosphere
The Coriolis Effect
The
influence of
Earth’s
rotation
which tends
to turn fluids
towards the
right in the
Northern
Hemisphere
and towards
the left in the
Southern
Hemisphere.
Coriolis effect
How does the airplane fly?
Coriolis effect
• Deflects air in North hemisphere to right
• Deflects air in South hemisphere to left
• Currents flow clockwise in the North and
counter-clockwise in the South.
• Most noticed in higher latitudes.
Other Winds
•
•
•
•
Prevaling winds
Polar easterlies
Westerlies
Trade
The Global Ocean
Patterns of Circulation in the Ocean
•Surface
winds cause
ocean
currents
(gyres).
The Global Ocean
Patterns of Circulation in the Ocean
Influenced by:
1) Coriolis Effect
2) Land Masses (freer to move in the S. Hemisphere)
The Global Ocean
Vertical Mixing of Ocean Water
•Cold salty
water is
more
dense that
warmer
water.
•As a
result,
warm less
salty water
floats
above the
colder
water.
Ocean Conveyor Belt
El Nino Southern Oscillation
(ENSO)
• Large pool of warm surface water in Pacific
Ocean moves back and forth between
Indonesia and South America.
– Most years, the pool is held in western
Pacific by steady equatorial trade winds.
• Every three-five years the Indonesian low
collapses and the mass of warm surface
water surges back east.
The Global Ocean
Ocean Interactions with the Atmosphere
ENSO
alters the
climate in
many
areas
remote
from the
Pacific
Ocean.
The Global Ocean
Ocean Interactions with the Atmosphere
Coastal Upwelling – deep waters come to the surface due
to strong trade winds bringing nutrients.
This decreases
during El Niño
Increases
during La Niña
El Nino Southern Oscillation
– Weak trade winds, expand warm mass of water, currents slow,
prevents upwells
– Devastates S. Hemi fishing industry
– Nutrient poor waters
– Some species thrive, ie shrimp and scallops
– During an El Nino year, the northern jet stream pulls moist air
from the Pacific over the US.
• Intense storms and heavy rains.
– During intervening La Nina years, hot, dry weather is often
present.
– Pacific Decadal Oscillation - Very large pool of warm water
moving back and forth across the North Pacific every 30 years.
Weather and Climate
• Weather - A description of physical
conditions of the atmosphere.
• Climate - A description of the long-term
weather pattern in a particular area.
– Weather and climate are primary
determinants of biomes and ecosystem
distribution.
Weather and Climate
Precipitation: any form of water that falls
from the atmosphere
• Driest place on earth
– Atacama Desert in Chile = 0.05 cm / year
• Wettest place on earth
– Mount Waialeale in Hawaii = 1200 cm / year
Weather and Climate
Rain shadows
Mountains cause air to rise . As the air rises it takes moisture with it, which
forms a cloud when temperatures decreases (with greater elevation), and
precipitation occurs. As the air moves down the other side of the mountain it
is warmed. This decreases the chance of precipitation.
Insert Fig 5.19 b
Weather and Climate
Severe weather events:
1) Tornados: form when a mass of cool dry air collides with
warm moist air
Frequency of tornados annually per 100,000 km2
Tornado Alley (US)
40
Sydney, Australia
8
United Kingdom
1
Bangledesh
0.6
Source: University of Wyoming, Department of Atmospheric
Science
Weather and Climate
Severe weather events:
2) Tropical cyclones
Atlantic Ocean = hurricanes
Pacific Ocean = typhoons
Indian Ocean = cyclones
Weather and Climate
But, all are the same severe weather event:
• hurricane
• typhoon
• cyclone
Internal Planetary Processes
Plate tectonics: study of the movements of plates
Internal Planetary Processes
Plate boundaries
Internal Planetary Processes
Plate boundaries
Internal Planetary Processes
Volcanoes
Most volcanoes occur
along subduction zones
Internal Planetary Processes
Volcanoes
Some occur along
spreading zones
Few, such as Hawaiian
Islands, not associated
with plates.
Internal Planetary Processes
Earthquakes
• caused by release of built up stress,
typically along faults
• movement releases seismic waves
Typical side effects include:
1) Landslides
2) Tsunamis