Biogeochemical Cycles and Terrestrial Ecosystems

Biogeochemical Cycles

  • Biogeochemical cycles are discussed, with a focus on carbon, nitrogen, phosphorus, sulfur, and oxygen.
  • Terrestrial ecosystems (biomes) are introduced.

Reminders

  • Lecture assignment 9 and makeup lecture assignment are due next Friday.
  • The issue with images in assignment 9 has been resolved.
  • A final exam example will be presented on Thursday, May 8 at 2:00 PM.
  • Lab will be in the stream this week.

The Carbon Cycle

  • Carbon is a major ingredient of all organic molecules.
  • The atmosphere is a major carbon reservoir.
  • Fossil fuels also serve as a carbon reservoir.
  • The carbon cycle operates globally.
  • CO2 is fixed during photosynthesis.
  • Carbon fixation is the transformation of carbon from CO2 (inorganic form) to an organic molecule.
  • Net ecosystem productivity is the rate of carbon fixation minus the rate of carbon waste.

Global Carbon Cycle

  • Most of Earth’s carbon is buried in sedimentary rock and is not easily accessible.
  • The relationship between Photosynthesis, Respiration, Atmosphere, Diffusion, Decomposition, Deforestation, Combustion, Fossil fuels, Rivers, Runoff, Vegetation, Oceans and Sedimentation rates are demonstrated using numerical values.
  • Photosynthesis: 120
  • Respiration: 60
  • Atmosphere: 750
  • Diffusion: 92
  • Decomposition: 91
  • Deforestation: 1-2
  • Combustion: 5-6
  • Fossil fuels: 5-6
  • Rivers: 0.5
  • Runoff: 0.5
  • Vegetation: 560
  • Oceans: 38,000
  • Sedimentation: 60

Carbon Dioxide Concentration Fluctuation

  • Carbon dioxide concentration fluctuates throughout the day.
  • The relationship between Hours and Height (m) is demonstrated with a graph.

Carbon Cycle in the Ocean

  • The ocean's carbon cycle involves several pumps:
    • Biological pump: Involves phytoplankton, zooplankton, bacteria, and deep consumers, transferring organic carbon from the surface to the deep ocean.
    • Carbonate pump: Formation of sediments from dead organisms, leading to carbon sequestration.
    • Physical pump: Deepwater formation and ventilation (upwelling) influence CO2 distribution.

The Nitrogen Cycle

  • Nitrogen is a limiting factor in the synthesis of proteins and nucleic acids.
  • Two abiotic reservoirs:
    • Atmosphere
    • Soil
  • Nitrogen fixation converts atmospheric nitrogen into a biologically usable form: N2→ammonia(NH3)N2 → ammonia (NH3)
  • Ammonification converts ammonia to ammonium (NH4+)(NH4+)
  • Plants uptake ammonium.
  • Nitrogen fixation is performed by:
    • Bacteria that live symbiotically in the roots of some plants.
    • Free-living bacteria in soil or water.

Nitrogen Cycle Details

  • Key processes in the nitrogen cycle include:
    • Fixation: Conversion of atmospheric nitrogen to ammonia.
    • Nitrification: Conversion of ammonia to nitrites and nitrates.
    • Assimilation: Uptake of nitrogen by plants.
    • Ammonification: Decomposition of organic matter into ammonia.
    • Denitrification: Conversion of nitrates back to atmospheric nitrogen.

Numerical data for nitrogen cycle rates:

  • The amounts of nitrogen involving Fixation in lightning, Denitrification, Biological fixation, Recycling, Human activities, River flow
    Oceans, Land plants, Internal cycling, Soil organic N, Groundwater, Permanent burial are indicated with numerical values.
  • Fixation in lightning < 3
  • Denitrification 110
  • Denitrification ≤ 200
  • Biological fixation 15
  • Recycling 30
  • Biological fixation 140
  • Human activities
  • River flow 36
  • Oceans
  • Land plants 1200
  • Internal cycling
  • Soil organic N 8000
  • Groundwater
  • Internal cycling
  • Permanent burial 100

The Phosphorus Cycle

  • Phosphorus is needed for:
    • Nucleic acids
    • Phospholipids (in cell membranes!)
    • ATP (adenosine triphosphate)
    • Vertebrate bones and teeth
  • The phosphorus cycle does not have an atmospheric component.
  • Rocks are the primary source of phosphorus for terrestrial ecosystems.

Phosphorus Cycle Details

  • Key Processes:
    • Weathering: Releases phosphate from rocks.
    • Uptake: Plants absorb inorganic phosphate from the soil.
    • Consumption: Animals obtain phosphorus by eating plants or other animals.
    • Decomposition: Returns phosphorus to the soil.
    • Sedimentation: Phosphorus accumulates in sediments over time.

Sources of Phosphorus

  • Origins from:
    • Agricultural fertilizers
    • Runoff of animal waste from livestock feedlots
    • Outflow of sewage treatment plants
    • Human waste
    • Dishwasher detergents
  • Results in:
    • Heavy growth of algae and cyanobacteria in aquatic ecosystems, causing algal blooms.

The Sulfur Cycle

  • Has both sedimentary and gaseous phases.
  • Sedimentary phase:
    • Longer duration.
    • Involves organic and inorganic deposits.
    • Sulfur is released by weathering and decomposition.
    • Pyritic rocks containing FeS weathered or uncovered by humans (during coal mining).
  • Gaseous phase:
    • Sulfuric gases circulate on a global scale.

The Oxygen Cycle

  • Atmosphere is the major source of oxygen.
  • Generated by two processes:
    • Breakup of water vapor: 2H2O→O2+4H+2 H2O → O2 + 4 H+
    • Photosynthetic production
  • Oxygen is also biologically exchangeable in various molecules that are transformed by living organisms.

Global Biogeochemical Cycle of Oxygen

  • Net primary production, Respiration and decay, Surface organic matter, Weathering and Burial details are demonstrated with their respective numerical values.
  • Atmosphere 3.7×1073.7 \times 10^7
  • Net primary production 8384
  • Respiration and decay 8384
  • Surface organic matter 2.4×1052.4 \times 10^5
  • Weathering 16
  • Burial 16
  • Reduced constituents of the crust 16×10816 \times 10^8