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.