Eutrophication

Eutrophication is the process by which a water body becomes enriched with excessive nutrients, particularly nitrogen and phosphorus, leading to abnormal growth of algae and aquatic plants. This phenomenon disrupts natural ecological balance, depletes dissolved oxygen, and negatively impacts aquatic biodiversity, water quality, and ecosystem services. It is widely recognised as one of the major forms of water pollution affecting lakes, rivers, reservoirs, and coastal environments.

Causes of Eutrophication

Natural Eutrophication

• A slow, long-term process occurring over centuries as water bodies gradually accumulate nutrients through natural weathering of rocks, soil erosion, and organic matter deposition.
• Generally less harmful as it develops gradually, allowing ecosystems to adapt.

Anthropogenic (Cultural) Eutrophication

• A rapid, human-induced process resulting from activities that increase nutrient input beyond natural levels.
• Major sources include:
  • Agricultural runoff: Fertilisers and animal manure washed into water bodies.
  • Domestic sewage: Untreated or partially treated wastewater containing detergents and organic waste.
  • Industrial effluents: Discharge of nutrient-rich waste from food processing and chemical industries.
  • Urban runoff: Stormwater carrying nutrients from roads, lawns, and construction sites.
  • Aquaculture: Overfeeding and waste products from fish farms.

Process of Eutrophication

1. Nutrient Enrichment – Excessive nitrogen and phosphorus enter water bodies.
2. Algal Bloom Formation – Explosive growth of algae and phytoplankton occurs, often forming surface mats.
3. Reduction in Light Penetration – Thick algal growth blocks sunlight, limiting photosynthesis for submerged plants.
4. Oxygen Depletion – When algae die and decompose, bacterial activity consumes dissolved oxygen.
5. Death of Aquatic Life – Fish and invertebrates suffocate due to hypoxia (low oxygen) or anoxia (no oxygen).
6. Altered Ecosystem State – Biodiversity declines, water quality deteriorates, and the ecosystem may shift to a degraded, less productive state.

Effects of Eutrophication

• Ecological Impacts
  • Massive fish kills due to oxygen depletion.
  • Decline in biodiversity, with dominance of a few tolerant species.
  • Habitat destruction for aquatic plants and animals.
• Water Quality Issues
  • Bad odour, scum, and turbidity due to algal blooms.
  • Release of toxins by certain cyanobacteria, making water unsafe for drinking and recreation.
  • Increased treatment costs for drinking water supply.
• Economic and Social Consequences
  • Loss of fisheries and aquaculture productivity.
  • Reduced tourism and recreational value of lakes and rivers.
  • Damage to livelihoods dependent on clean water and healthy ecosystems.

Examples of Eutrophication

• Lake Erie (North America): Known for recurring algal blooms linked to agricultural runoff.
• Chilika Lake (India): Experienced eutrophication due to nutrient inflows from surrounding agriculture and settlements.
• Baltic Sea (Europe): Severely affected by nutrient loading, leading to widespread dead zones.

Control and Management

Preventive Measures

• Nutrient Management: Reducing fertiliser use, adopting precision farming, and promoting organic agriculture.
• Wastewater Treatment: Upgrading sewage treatment plants to remove nitrogen and phosphorus.
• Buffer Zones: Creating vegetative strips and wetlands along waterways to trap nutrients.
• Regulation and Policy: Implementing stricter controls on industrial discharge and urban runoff.

Remedial Measures

• Aeration: Artificial oxygenation of water bodies to counter hypoxia.
• Chemical Treatments: Use of compounds like alum to precipitate phosphorus.
• Algal Harvesting: Removal of excess algal biomass.
• Biomanipulation: Introducing species that can control algal growth, such as filter-feeding fish.

Significance

Eutrophication illustrates the close linkage between human activity and aquatic ecosystem health. As agricultural intensification, urbanisation, and industrialisation expand, the risk of eutrophication has increased worldwide. Effective management requires integrated approaches combining scientific monitoring, policy frameworks, community participation, and sustainable resource use.