Biogeochemical Cycles Notes

Biogeochemical Cycles

We are all composed of elements from stars and dinosaur remains.

Outline

  • Elements and Earth
  • The carbon cycle and its evolution
  • Nitrogen cycle
  • Human effects
  • Phosphorous cycle
  • The curious role of iron
  • Humans and the carbon cycle

Origin of Elements

The amounts of elements on Earth are mostly constant.

Great Oxidation Event

  • Approximately 2 billion years ago, oxidation occurred due to photosynthesis.
  • The Great Oxidation Event (GOE) led to the construction of the aerobe niche.

Aerobic World

The aerobic world involves processes within the cell, including:

  • Electron transport chain
  • ATP Synthase
  • Citric acid cycle

The Carbon Cycle

  • Solar (or chemical) energy is used to fix Carbon.
  • Calvin Cycle.
  • Other methods.
  • Carbon is oxidized for energy.
  • Producers fix the carbon again.
  • Some carbon is removed via sedimentation and burial.

Short Term

  • Photosynthesis and Respiration.
  • Inorganic carbonates

Long Term

  • Carbonates.
  • Hydrocarbon Coal: organic sedimentary rock.

The Nitrogen Cycle

  • Nitrogen fixation: N2 \rightarrow NH4^+
  • Bacteria involved
  • NH_4^+ is used for:
    • Nucleic acids
    • Chlorophyll
    • Amino acids
    • NAD/NADH and other molecules.
  • NO_3^- can be reduced by plants.
  • Denitrification is toxic to animals.

Fixation

  • Cyanobacteria
  • Various Archaea
  • Soil bacteria
  • Root nodules
  • Legumes

Artificial N Fixation: The Green Revolution

  • N2 + 3H2 \longrightarrow 2NH_3 (Heat and pressure)
  • Invented during WWI to make explosives.
  • Modern Irrigation
  • Chemical fertilizers
  • Pesticides/herbicides
  • Plant breeding

Phosphates (and other minerals)

  • PO_4^{3-}
  • Used for:
    • Nucleic acids
    • Inorganic structures
    • Bones, shells, etc.
  • Decomposers, scavengers, detritivores break down phosphates and other minerals.

NPK Fertilizer and Changes in Land Use

  • PO_4^{3-}
  • Used for:
    • Nucleic acids
    • Inorganic structures
    • Bones, shells, etc.
  • Nutrient pollution due to:
    • Agricultural runoff
    • Fertilizer
    • Soil
    • Fecal matter

Iron, an Interesting Result of the GOE

  • Fe (Iron)
  • Fertilization of deep ocean may cause CO_2 to sink.
  • Volcanic activity.
  • Iron is often a limiting nutrient because it is barely soluble when fully oxidized and at neutral pH.

The Problem of How We’ve Adjusted These Cycles

  • CO2, CH4, N_2O are greenhouse gases.
  • Climate change is influenced by the greenhouse effect.
  • Human activities have increased the amount of greenhouse gases in the environment.
    • CO_2 – Burning fossil fuels.
    • Effects on NPP (Net Primary Production)?
    • CH_4 – Ruminants, food waste, and land use practices.
    • N_2O – Animal waste and artificial fertilizer.
  • Reduced IR emission

Solutions Relating to Nitrogen Cycling: Personal

  • Eat more legumes!
  • Reduce textile consumption
    • Cotton and wool require fertilizer.
  • Eat more mushrooms!
    • Mushrooms are grown on waste products; therefore, they do not require fertilizer.
    • They also create compost.
  • Waste less food.
  • Eat less meat
    • Fewer crops must be grown; therefore, less fertilizer is needed.
    • Less poop -> a source of N_2O emission.

Solutions Relating to Nitrogen Cycling: Societal

  • Develop organic agriculture that actually works.
  • Stop fast fashion
    • Cotton requires a lot of fertilizer.
  • Alternative animal feed stocks
    • Spirulina
  • Stop turning corn into bioethanol.