Natural Capital: Sustaining Life on Earth

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Natural Capital Sustaining Life on Earth

• Earth is an open system in terms of energy
  energy flows through an ecosystem
• All energy is ultimately in the form of heat
• Earth is a closed system in terms of matter
  matter is recycled in an ecosystem
• There is no away

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Components of Ecosystems
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Trophic Levels
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The Nitrogen Cycle
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The Nitrogen Cycle

• The most complex of the biogeochemical cycles
• N2 78 of the troposphere, chemically
  unreactive, cannot be used/absorbed directly in
  this form by multicellular plants or animals.
  Even though this is a large source of nitrogen,
  must be converted before it can be of use to
  living organisms.
• Nitrogen cycle steps nitrogen fixation,
  nitrification, assimilation, ammonification and
  denitrification

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The Nitrogen Cycle

• Nitrogen Fixation atmospheric nitrogen (N2)is
  converted to ammonia, NH3
• By cyanobacteria in soil/water and Rhizobium in
  root nodules of legumes (peas, clover, beans,
  etc.)
• Nitrification
• NH3 converted by aerobic bacteria to NO2-
  (nitrite)
• NO2- converted by bacteria to NO3-(nitrate, most
  useful form)
• Assimilation Plant roots absorb nitrates that
  are then converted into organic compounds like
  proteins and DNA. And of course, animals eat
  plants.
• Ammonification N-rich organic compounds, wastes,
  caste-off particles, dead bodies, etc., are
  converted into simpler N-containing inorganic
  compounds (e.g., NH3)
• By decomposer bacteria
• Denitrification NH3 gt NO3- and NO2- gt N2O and
  N2
• Mostly by anaerobic bacteria in waterlogged soil,
  bottom sediments of lakes, swamps, bogs and
  oceans

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Significant Human Interventions

• Internal combustion engine exhaust (i.e., fossil
  fuel burning) adds NO (nitric oxide) to the
  atmosphere when N2 reacts with O2. NO can react
  with oxygen to form NO2 (nitrogen dioxide), which
  can then react with water vapor to form HNO3
  (nitric acid), a significant component of acid
  rain.
• Farming/agriculture and cities N-rich
  fertilizers from farms and sewage from
  municipalities runs off into bodies of water.
  This stimulates the growth of algae and aquatic
  plants which then die and are broken down by
  aerobic decomposers. This aerobic decomposition
  reduces the dissolved oxygen (DO) content in the
  water, impacting fish and other aquatic animals
• Mining for N-rich minerals from the earths crust
  and soil
• Nitrogen is can be depleted from topsoil when we
  over-harvest or over-graze plants and then burn
  or clear grasslands and forests
• Cattle waste and inorganic N-fertilizers are
  broken down by bacteria into N2O (nitrous oxide).
  This is a heat-trapping gas and can contribute to
  the warming of the atmosphere.

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The Carbon Cycle (Terrestrial)
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The Carbon Cycle (Marine)
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The Carbon Cycle

• Cycles closely with hydrogen and oxygen,
  especially as an essential component of organic
  molecules (e.g., carbohydrates) and inorganic
  molecules (e.g., CO2)
• Aerobic respiration C6H12O6 6O2 gt 6 CO2 6H2O
  38 ATP
• Photosynthesis 6CO2 6H2O light energy gt
  C6H12O6 6O2
• CO2 0.036 of the troposphere (lowest part of
  atmosphere) gases, is also easily dissolved in
  H2O
• CO2 enters the atmosphere by burning fossil
  fuels, aerobic respiration and volcanic activity
• CO2 is a heat-trapping gas, and an important
  component of the earths thermostat
• More CO2 exacerbates the greenhouse effect

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The Carbon Cycle

• The oceans help regulate the CO2 in the
  atmosphere
• When oceans take in CO2, there is a cooling
  effect due to the heat-trapping ability of CO2
• Some CO2 stays dissolved in sea water
• Some is removed by photosynthesis (aquatic
  plants, algae and phytoplankton)
• Some reacts with sea water gt CO3-2 and HCO3-
  which can react with Ca2 to form CaCO3
• CaCO3 is used by marine organisms for shells and
  skeletons
• These organisms live, die, sink, are buried for
  many years, and over time, under pressure, the
  CaCO3 turns into limestone on the ocean floor

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The Carbon Cycle

• The long term storage units for carbon are the
  ocean floor (limestone) and limestone and other
  sedimentary rocks and soils on the continents
• The shorter term units are the atmosphere and
  oceans
• The average residence times of CO2 in these
  units are 3 years (atmosphere), 25-30 years
  (soils) and 1500 years (oceans)
• CO2 is released from the oceans as H2O
  temperature increases
• Warm waters cannot absorb as much CO2 as cooler
  waters
• There is a positive feedback loop between CO2
  levels and atmospheric temperatures -
  implications for global climate change

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Significant Human Interventions

• There are two major interventions that lead to
  increasing levels of CO2 in the atmosphere
• Vegetation removal/deforestation
• Fossil fuel and wood burning
• Reasons for concern
• Enhanced/magnified natural greenhouse effect
• Altered global food production due to shifting
  climate belts
• Altered wildlife habitat due to changes in
  temperature and precipitation
• Altered species interactions
• Rise in sea levels due to thermal expansion of
  water as troposphere temperature increases