Overview
This lecture covers the phosphorus cycle, highlighting how phosphorus moves through natural and synthetic sources, why it is a limiting nutrient, and environmental concerns like eutrophication.
Phosphorus Cycle Overview
- The phosphorus cycle describes the movement of phosphorus between sources (reservoirs) and sinks in the environment.
- Main phosphorus reservoirs are rocks and sediments.
- The cycle is much slower than the carbon or nitrogen cycles.
Steps in the Phosphorus Cycle
- Weathering of rocks releases phosphate, which is then transported to soil or water by wind and rain.
- Phosphorus exists mainly in solid form as phosphate; there is no gaseous phase.
- Plants absorb phosphates from soil; animals obtain phosphorus by eating plants or other animals.
- Decomposition and animal waste return phosphorus to soil, creating a "mini-loop" in the cycle.
Human Impact and Synthetic Sources
- Humans mine phosphate rocks and use them in fertilizers, detergents, and cleaners.
- Runoff from agriculture and household waste introduces extra phosphorus into water bodies.
Sedimentation and Geological Uplift
- Phosphates that do not dissolve form solid sediments at the bottom of water bodies (sedimentation).
- Over time, sediments compress into sedimentary rocks, which can be uplifted by tectonic activity, exposing new phosphorus sources.
Eutrophication and Consequences
- Excess phosphorus and nitrogen from runoff cause eutrophication (nutrient overload in water).
- Eutrophication leads to algae blooms, blocked sunlight, and plant death.
- Decomposition of dead algae uses up oxygen, causing fish kills and potentially creating dead zones.
- This creates a positive feedback loop, making the problem worse.
Key Terms & Definitions
- Weathering — Breakdown of rocks by wind and rain, releasing phosphorus as phosphate.
- Phosphate — The form of phosphorus available for plant uptake.
- Eutrophication — Over-enrichment of water with nutrients, causing excessive algae growth and oxygen depletion.
- Sedimentation — Formation of solid phosphate sediments at the bottom of water bodies.
- Positive feedback loop — A process where an effect amplifies its own cause, worsening the situation.
Action Items / Next Steps
- Practice FRQ: Use a visual model to describe how phosphorus moves between two reservoirs in the cycle.