2

• Biogeochemical cycles


  The recycling of inorganic matter between living organisms and their nonliving environment
• Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during energy transformation between trophic levels
• Rather than flowing through an ecosystem, the matter that makes up organisms is conserved and recycled
• Six most common elements associated with organic molecules

  • Carbon
  • Nitrogen
  • Hydrogen
  • Oxygen
  • Phosphorus
  • Sulfur
• Forms these elements can take

  • Atmosphere
  • Land
  • Water
  • Earth's surface
• Geologic processes involved in cycling of elements


  • Weathering
  • Erosion
  • Water drainage
  • Subduction of continental plates
• Ways organisms use the six common elements

  • Hydrogen and oxygen in water and organic molecules
  • Carbon in organic molecules
  • Nitrogen in nucleic acids and proteins
  • Phosphorus in nucleic acids and phospholipids
  • Sulfur in protein structure
• The cycling of these elements is interconnected, e.g. water movement is critical for leaching of sulfur and phosphorus
• Forms of water on Earth

  • Liquid water on surface (rivers, lakes, oceans)
  • Groundwater beneath surface
  • Ice (polar ice caps and glaciers)
  • Water vapor in atmosphere
• The human body is about 60% water and human cells are more than 70% water
• 97.5% of water on Earth is salt water, over 99% of remaining freshwater is groundwater or ice, less than 1% is in lakes and rivers
• Many organisms are dependent on this small percentage of freshwater in lakes and rivers, a lack of which can have negative effects on ecosystems
• Technologies to increase water availability

  • Digging wells to harvest groundwater
  • Storing rainwater
  • Using desalination
• The supply of fresh water continues to be a major issue in modern times
• The water cycle


  1. Evaporation/sublimation of surface water

  2. Condensation into clouds

  3. Precipitation (rain, snow, hail)

  4. Surface runoff

  5. Percolation into soil

  6. Uptake by plants

  7. Transpiration

  8. Groundwater formation
• The water cycle is driven by the sun's energy
• Transpiration


  The process of water movement through a plant and its evaporation from aerial parts
• Evapotranspiration


  The combined process of transpiration and evaporation returning water to the atmosphere
• Most groundwater reservoirs (aquifers) are being depleted faster than they are being replenished
• Carbon


  The second most abundant element in organisms, by mass, present in all organic molecules and some inorganic ones
• Carbon compounds contain energy, and many have fossilized over millions of years as fossil fuels
• Since the Industrial Revolution, the demand for fossil fuels has risen, causing a drastic increase in atmospheric carbon dioxide, associated with climate change
• Two sub-cycles of the carbon cycle

  • Rapid carbon exchange among living organisms
  • Long-term cycling of carbon through geologic processes
• Biological carbon cycle


  1. Absorption of carbon dioxide by terrestrial autotrophs

  2. Absorption of dissolved bicarbonate by aquatic autotrophs

  3. Carbon passed through food chain

  4. Respiration releasing carbon dioxide
• Carbon exchange connects all organisms on Earth, the carbon in your DNA was once part of a plant or dinosaur
• Carbon reservoirs


  • Atmosphere
  • Bodies of liquid water (mostly oceans)
  • Ocean sediment
  • Soil
  • Rocks (including fossil fuels)
  • Earth's interior
• Carbon exchange between atmosphere and water

  1. Carbon dioxide dissolves in water, forming ionic compounds

  2. Some ions combine with calcium to form calcium carbonate shells

  3. Shells form sediments, becoming limestone
• Carbon storage on land

  1. Organic carbon in soil from decomposition

  2. Weathering of terrestrial rock and minerals

  3. Fossil fuels from anaerobic decomposition of plants and algae
• Carbon release to atmosphere

  1. Volcanic eruptions and geothermal systems

  2. Subduction of ocean floor sediments
• Plants and phytoplankton cannot directly incorporate nitrogen from the atmosphere
• Nitrogen fixation


  The process of converting nitrogen gas into ammonia by specialized bacteria
• Nitrogen cycle


  1. Nitrogen fixation to ammonia

  2. Nitrification to nitrites and nitrates

  3. Uptake by producers to make organic molecules
• The world's soils hold significantly more carbon than the atmosphere, for comparison
• Fossil fuels


  Anaerobically decomposed remains of plants and algae that lived millions of years ago
• Subduction


  The movement of one tectonic plate beneath another
• Carbon is released as carbon dioxide when a volcano erupts or from volcanic hydrothermal vents
• Nitrogen fixation


  The process of converting nitrogen gas into ammonia (NH3), which spontaneously becomes ammonium (NH4+)
• Nitrification


  Ammonium is converted by bacteria into nitrites (NO2-) and then nitrates (NO3-)
• Denitrification


  The process where bacteria convert organic nitrogen back into nitrogen gas
• Combustion of fossil fuels

  Releases different nitrogen oxides