Nutrient Cycling

Overview of Nutrient Cycling

  • Discussion on limiting nutrients, particularly nitrogen and phosphorus.
  • Focus on nutrient cycling's importance and components, specifically the nitrogen and phosphorus cycle.
  • Introduction to pools and fluxes, differentiating movement (physical transport) and transformations of elements (chemical transformations).

Nutrient Cycles

  • Definition: Nutrient cycles are comprehensive representations of nutrient forms and processes mediating transformations between those forms.
  • Distinction from nutrient dynamics, which studies all processes transporting and transforming nutrients.
  • Nutrient cycles are nested within nutrient dynamics, controlling what forms are moved and how.

Key Components of Nutrient Cycles

  • Recognition that nitrogen and phosphorus are key limiting nutrients in ecosystems, especially in streams.
  • Importance of understanding nitrogen cycling for ecological studies and nutrient availability.

The Nitrogen Cycle

Forms of Nitrogen

  • Two main types: organic and inorganic forms.
  • Example of different forms process:
    • N₂ gas: Predominant form (70% of atmosphere), has a strong triple bond.
    • Nitrogen fixation: Process by which certain organisms (with specialized cells, e.g., heterocysts) convert N₂ into biologically available forms.
    • Converts N₂ to NH₄⁺ (ammonium) through biological fixation.
    • Nitrification: Conversion of NH₄⁺ into NO₃⁻ (nitrate), which can be taken up by organisms.
  • Internal cycling includes:
    • Ammonium (NH₄⁺) being mineralized from dead organisms or waste.
    • Nitrate being taken up by plants or denitrified back to N₂ gas (using nitrate as an electron acceptor).
  • Mention of efficiency in anaerobic conditions with nitrate as an electron acceptor compared to oxygen.

Movement of Nitrogen

  • External sources affecting nitrogen availability:
    • Atmospheric deposition (e.g., auto emissions).
    • Loss through leaching or off-gassing.
  • An example cycle visual:
    • N₂ gas → Nitrogen fixation → NH₄⁺ → Nitrification → NO₃⁻ → Plant uptake → Animal consumption → Mineralization → Back to NH₄⁺ or denitrification back to N₂ gas.
  • Comparisons of availability:
    • NH₄⁺ is generally more available than NO₃⁻ for various organisms.

The Phosphorus Cycle

Phosphorus Cycle Characteristics

  • Unlike nitrogen, phosphorus has no gas phase in its cycle.
  • Sources include:
    • Weathering of rocks, which releases phosphate into soils and water bodies.
  • Cycle involves:
    • Uptake by plants from soils.
    • Returns to soil through decomposition of organic matter from plants and animals.
  • External sources include:
    • Mining and fertilizers contribute to phosphorus availability.
    • Animal waste contributes organic phosphorus that decomposes into available forms.

Movement and Availability of Phosphorus

  • Phosphorus binds easily to sediments, affecting its bioavailability.
  • Distinction between total phosphorus and biologically available phosphorus:
    • Soluble reactive phosphorus and phosphate are more bioavailable forms.
    • Total phosphorus often includes bound forms that are inaccessible for organisms.
  • Ammonium does not bind to sediments as strongly as phosphorus.

Additional Context and Recommendations

  • Acknowledgment that more comprehensive classes on nitrogen cycles or nutrient cycling exist for deeper understanding.
  • Suggestion to take courses in biochemistry or ecosystem ecology for enhanced knowledge on nutrient uptake dynamics and cycling dynamics.
  • Mention of further discussion to come in future lectures concerning nutrient uptake dynamics and additional components of cycles.