Biogeochemical Cycles

Introduction to Biogeochemical Cycles

  • Definition: Biogeochemical cycles refer to the pathways in which chemical nutrients move through biological (biotic) and non-biological (abiotic) components of ecosystems.
  • Components:
    • Bio: Living organisms
    • Geo: Inorganic molecules (e.g., rocks, air, water)
    • Chemical: Interactions among elements

Types of Nutrients

  • Macronutrients: Required in large amounts, essential for all biological life.

    • Examples:
    • Carbon
    • Hydrogen
    • Oxygen
    • Nitrogen
    • Phosphorus
    • Sulfur
    • Additional Macronutrients: Potassium, Calcium, Magnesium

  • Micronutrients: Required in smaller amounts but still vital.

    • Examples:
    • Iron
    • Manganese
    • Copper
    • Zinc
    • Sodium

Carbon Cycle

  • Importance: Carbon forms the basis for life on Earth. It is stored in the atmosphere, land, and water.
  • Photosynthesis: Converts inorganic atmospheric carbon into organic carbon used by plants.
  • Steps of the Carbon Cycle:
    1. Atmosphere to Plants: Carbon dioxide from the atmosphere is absorbed by plants during photosynthesis to form organic compounds.
    2. Plants to Animals: Carbon moves through the food chain as animals consume plants.
    3. Plants/Animals to Soil: When organisms die, carbon is returned to the soil as they decompose.
    4. Living Things to Atmosphere: Respiration releases carbon dioxide back into the atmosphere.
    5. Atmosphere to Oceans: Carbon dioxide is absorbed by oceans, dissolved in water, contributing to the aquatic carbon cycle.
  • Increasing CO2 Concentration:
    • Caused by organic breakdown during respiration, oil and coal extraction, fuel combustion, and land-use changes.

Nitrogen Cycle

  • Stages:

    • Nitrogen fixation
    • Nitrification
    • Assimilation
    • Ammonification
    • Denitrification

  • Processes:

    1. Nitrogen Fixation: Conversion of N2 (nitrogen gas) to NH4+ (ammonium) by nitrogen-fixing bacteria, lightning strikes, and industrial processes.
    2. Nitrification: Conversion of ammonia to nitrite (NO2-) and then to nitrate (NO3-) by nitrifying bacteria.
    3. Assimilation: Uptake of nitrogen compounds from soil by plants for protein synthesis.
    4. Ammonification: Decomposition of nitrogen-containing organic matter releases ammonia.
    5. Denitrification: Conversion of nitrate back to N2 gas by denitrifying bacteria, usually in low-oxygen environments.

Phosphorus Cycle

  • Characteristics:
    • Phosphorus is primarily found as mineral in phosphate rocks and is a sedimentary cycle (no gas phase).
  • Processes:
    • Erosion and mining release phosphates into soils/water.
    • Plants absorb phosphates, which move to animals through food chains.
    • Return to soil occurs via waste and decomposition.
  • Eutrophication: Excess phosphates from fertilizers lead to algal blooms.
  • Alterations to Cycle: Occur from deforestation and agricultural fertilizer use.

Sulfur Cycle

  • Importance: Sulfur is vital for vitamins, proteins, and hormones, impacting climate and ecosystem health.
  • Sources: Majority stored in rocks/minerals; weathering releases sulfur.
  • Processes:
    • Sulfur interacts with air forming sulfate (SO4) and is absorbed by plants.
    • Animal consumption moves sulfur through the food chain.
    • Decomposition returns some sulfur to soil as sulfate.
    • Natural Sources: Volcanic eruptions, organic matter breakdown, water evaporation.

Hydrologic Cycle

  • Definition: The cycle of water storage, transport, and transformation in the atmosphere-earth system.

  • Importance: Shapes weather, supports plant growth, and sustains life.

  • Water Reservoirs:

    • Oceans: 97%
    • Polar Ice/Glaciers: 2%
    • Groundwater: 0.7%
    • Lakes: 0.01%
    • Atmosphere: 0.001%
    • Others: Soils, Rivers/Streams

  • Transport Methods: Evaporation, Transpiration, Precipitation, Infiltration, Percolation, Runoff, Interflow.

  • Transformations:

    • Liquid to Gas (evaporation)
    • Gas to Liquid (rainfall)
    • Solid to Liquid (snowmelt)

References

  • Nathanson, J.A. 1997. Basic Environmental Technology. Prentice-Hall, Inc.
  • Tayo, G. T., et al. 2004. Fundamentals of Environmental Science. Trinitas Publishing, Inc.
  • Various web sources concerning biogeochemical cycles.