4.4C Eutrophication Notes

1. Eutrophication is the process by which a body of water becomes enriched with nutrients, particularly nitrates (NO₃⁻) and phosphates (PO₄³⁻), leading to excessive growth of algae and aquatic plants.
2. This enrichment disrupts aquatic ecosystems, often resulting in oxygen depletion, loss of biodiversity, and decline in water quality.

Causes of Eutrophication

1. Eutrophication can occur naturally (over centuries) or artificially due to human activity (cultural eutrophication).
2. Anthropogenic (human-induced) eutrophication occurs much faster.
   1. Agricultural Runoff: Fertilizers applied to crops wash into rivers and lakes during rain, introducing nitrates and phosphates.
   2. Sewage Discharge: Untreated or partially treated domestic waste adds organic matter and nutrients.
   3. Detergents: Phosphate-based detergents contribute to nutrient loading.
   4. Industrial Effluent: Factories may release nitrogen compounds and organic pollutants.

The Process of Eutrophication

1. Nutrient Enrichment: Runoff or discharge introduces nitrates and phosphates into the water.
2. Algal Bloom: Rapid growth of algae and cyanobacteria due to increased nutrient availability.
3. Light Limitation: Dense algal layers block sunlight, reducing photosynthesis in submerged plants.
4. Plant Death: Submerged macrophytes die due to lack of light.
5. Decomposition: Dead algae and plants decompose, consuming dissolved oxygen.
6. Oxygen Depletion: Decomposition leads to hypoxia (low O₂) or anoxia (no O₂).
7. Biodiversity Loss: Fish and other aerobic organisms die or migrate; anaerobic bacteria dominate.
8. Toxic Gas Production: Anaerobic decomposition produces CH₄ (methane), NH₃ (ammonia), and H₂S (hydrogen sulfide).

Impacts on Ecosystem Services

1. Fisheries

1. Hypoxia causes fish kills or migration.
2. Surface-dwelling species like carp dominate, reducing biodiversity.
3. Fish caught in eutrophic waters may contain toxins.
4. Economic losses occur as fishermen travel farther offshore or catch declines.

2. Recreation

1. Algal scum and foul odors reduce enjoyment of water-based activities (swimming, boating, fishing).
2. Dense macrophyte growth blocks navigation and access.
3. Tourist income declines.

3. Aesthetic and Cultural Value

1. Murky, green water and decaying biomass destroy scenic beauty.
2. Bad odors from H₂S reduce public appreciation.
3. Cultural and spiritual connections to clean water bodies are lost.

4. Health Impacts

1. Nitrate-rich water can cause blue baby syndrome (methemoglobinemia) in infants.
2. Cyanobacteria (blue-green algae) release toxins that contaminate drinking water and shellfish.
3. Some toxins are heat-stable and cannot be removed by boiling.
4. Long-term nitrate exposure may increase the risk of gastric cancer.

Management of Eutrophication

1. Reducing Human Activities that Produce Pollutants

1. Fertilizer management: Use organic or slow-release fertilizers, apply in small doses, and avoid before rainfall.
2. Crop management: Practice crop rotation and intercropping with nitrogen-fixing plants.
3. Detergent control: Promote phosphate-free detergents.
4. Public awareness: Campaigns on responsible washing, gardening, and waste disposal.

2. Reducing Release of Pollutants

1. Wastewater treatment: Use nutrient-stripping methods to remove nitrates and phosphates.
2. Buffer zones: Establish vegetation strips along rivers to trap runoff.
3. Wetlands restoration: Natural wetlands absorb excess nutrients and improve water quality.
4. Regulation: Implement and enforce environmental laws limiting nutrient discharge.

3. Removing Pollutants and Restoring Ecosystems

1. Dredging: Removes nutrient-rich sediments from lake bottoms.
2. Aeration: Increases oxygen levels and supports aerobic decomposition.
3. Bioremediation: Use aquatic plants or algae to absorb nutrients, then harvest them.
4. Chemical treatment: Add alum (aluminum sulfate) to coagulate nutrients for easier removal.
5. Restocking: Reintroduce native species once water quality improves.