Overview
This lecture explains the phosphorus cycle, detailing how phosphorus moves between reservoirs and the environmental impacts of human activity on this cycle.
The Phosphorus Cycle: Overview
- The phosphorus cycle describes the movement of phosphorus between sources (rocks, sediments) and sinks (soils, water bodies).
- Phosphorus movement is much slower than in the carbon or nitrogen cycles.
Major Reservoirs and Processes
- Main reservoirs of phosphorus are rocks and phosphorus-containing sediments.
- Weathering releases phosphate from rocks and sediments through wind and rain.
- Phosphate is carried by runoff into soils and aquatic ecosystems.
- There is no gaseous phase of phosphorus, which slows its cycle.
Biological Importance of Phosphorus
- Phosphorus is essential for ATP (energy), DNA, and bone and teeth strength in animals.
- Plants absorb phosphorus from soil; animals obtain it by eating plants or other animals.
Human Impact and Synthetic Sources
- Humans mine phosphate rocks for fertilizers and detergents.
- Runoff from agriculture and household wastewater adds phosphorus to water bodies.
Recycling and Return to Soil
- Decomposition and waste return phosphorus from dead matter and excretion to the soil.
- This forms a mini-loop similar to that in the nitrogen cycle.
Sedimentation and Geological Uplift
- Excess phosphate in water precipitates out, forming sediments on the waterbed (sedimentation).
- Over time, sediments are compressed into sedimentary rock.
- Geological uplift exposes new phosphorus rocks to weathering, restarting the cycle.
Environmental Impact: Eutrophication
- Excess phosphorus (and nitrogen) in water causes eutrophication, leading to algal blooms.
- Algal blooms block sunlight, killing underwater plants.
- Bacteria decomposing dead plants and algae use up oxygen, causing "dead zones" with little aquatic life.
- Positive feedback loop: less oxygen leads to more deaths, more decomposition, and further reduced oxygen.
Key Terms & Definitions
- Phosphorus Cycle โ movement of phosphorus through rocks, soils, water, and living things.
- Weathering โ breakdown of rocks, releasing phosphate.
- Assimilation โ absorption of phosphorus by plants.
- Sedimentation โ formation of solid phosphate deposits at the bottom of water bodies.
- Geological Uplift โ movement of rock layers to the surface by tectonic activity.
- Eutrophication โ nutrient enrichment of water, causing excessive algae growth and oxygen loss.
- Positive Feedback Loop โ a process that accelerates itself due to its outcomes.
Action Items / Next Steps
- Practice: Use a model of the phosphorus cycle to describe how phosphorus moves between two reservoirs.
- Review phosphorus cycle diagrams and the effects of human activities on nutrient cycles.