Ecosystems

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Ecosystems

• Biogeochemical Cycles

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KEY CONCEPT 1

• Ecosystems consist of nonliving (abiotic) and
  living (biotic) components.

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KEY CONCEPT 2

• An ecosystem survives by a combination of energy
  flow and matter recycling.

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KEY CONCEPT 3 Earth is a Closed System!
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BIOGEOCHEMICAL CYCLES ABIOTIC CYCLES

• GLOBAL RECYLING - A closed pathway where matter
  cycles from the nonliving environment to living
  and then back again for reuse.
• Key feature- nutrients recycle through the
  earths air, land, water, and living organisms.
• Nutrients are the elements and compounds that
  organisms need to live, grow, and reproduce.
• The overall rate of nutrient movement is limited
  most by decomposition.
• The rate of nutrient loss is a key characteristic
  in any ecosystem.

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Plants
Overview of Nutrient Cycling
Consumption
Herbivore
Assimilation
Feces or urine
Death
Death
Detritus
Uptake
Soil nutrient pool
Decomposer food web
Loss to erosion or leaching into groundwater
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Water Cycle
Condensation
Rain clouds
Transpiration
Evaporation
Transpiration from plants
Precipitation to land
Precipitation
Precipitation
Evaporation from land
Evaporation from ocean
Surface runoff (rapid)
Precipitation to ocean
Runoff
Surface runoff (rapid)
Infiltration and Percolation
Groundwater movement (slow)
Ocean storage
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Water Cycle

• Causes wind currents
• There are strong forces of attraction between
  molecules of water.
• 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.
• Water expands when it freezes.

Water has greatest influence of all non-living
components
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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.

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Carbon Cycle

• Combustion
• Burning- CO2
• Fossil fuels hydrocarbons
• Volcanic Action
• Forest Fires

• Photosynthesis and Cellular respiration
• O2 ? ? CO2

• Erosion
• CaCO3 ? shells ? limestone

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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
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Greenhouse gases
Methane
Carbon dioxide
Nitrous oxide
Water
Sulfur hexafluoride
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Most Important Greenhouse Gases
GHGs Source Examples Water H2O Oceans,
rivers, plants, soil Carbon Dioxide CO2
Combustion of fossil fuels, plant
respiration, oceans, volcanoes Methane
CH4 Mining operations, combustion,
animals, wetlands, landfills Other GHGs
Nitrous oxide (N2O), Ozone (near surface), Learn
more about GHGs http//www.epa.gov/climatechange/
emissions/index.html
http//www.for.gov.bc.ca
Source U.S. EPA 2005
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Nitrogen Cycle

• Availability of Nitrogen is a limiting factor for
  primary productivity

• 78 N gas in atmosphere
• unusable

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Nitrogen Cycle

• Ammonification
• Decomposition by bacteria during decay

• Bacteria can fix nitrogen which means they
  break apart nitrogen gas and convert it into
  ammonia or ammonium.

• Assimilation
• Absorption and incorporation of nitrogen by plants

These nodules are called rhyzomes. They are
where the nitrifying bacteria reside. They have
a symbiotic relationship with the plant

• Nitrification
• Ammonia to nitrates and nitrites by bacteria
• Then can be assimilated by plants

• Denitrification
• Denitrifying bacteria convert nitrates back into
  N2

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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.

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Effects of Human Activities on the Nitrogen Cycle

• Human activities such as production of
  fertilizers now fix more nitrogen than all
  natural sources combined.

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Phosphorous Cycle

• No gaseous component (from land to sediment and
  back to land only)
• Erosion ?releases phosphate? soil ?plants
• Decomposers ?phosphate ? soil
• Deposited in oceanic sediment ? unavailable for
  years
• Fertilizers, run off containing animal wastes,
  and sewage ?aquatic ecosystems

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The Phosphorous Cycle
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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.

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The Sulfur Cycle
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Effects of Human Activities on the Sulfur Cycle

• We add sulfur dioxide to the atmosphere by
• Burning coal and oil
• Refining sulfur containing petroleum.
• Converting sulfur-containing metallic ores into
  free metals such as copper, lead, and zinc
  releasing sulfur dioxide into the environment.

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Acid Precipitation

• Rain, snow or fog that has a pH value of less
  than 5.6 because of the carbon dioxide from air
  dissolved in it
• Any rainfall has a pH value less than 5.6 is
  defined as acid rain

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Acid Precipitation

• When gas pollutants e.g. sulfur dioxide, nitrogen
  dioxide dissolve in rain water, various acids are
  formed.

CO2 H2O ? H2CO3 (carbonic acid) SO2
H2O ? H2SO3 (sulphorous acid) NO2 H2O ? HNO2
(nitrous acid) HNO3 (nitric acid)
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CAUSES OF ACID RAIN
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