APES 8.5 Eutrophication

Eutrophication

• Definition: Eutrophication is the process where water bodies become overly enriched with nutrients (primarily nitrogen and phosphorus), leading to excessive growth of algae.

  • Cultural Eutrophication: When eutrophication is caused by human activities, such as fertilizer runoff.

  • Natural Eutrophication: Occurs without human influence, generally over a long period.

Process of Eutrophication

• Nutrient Introduction: Nitrogen and phosphorus enter the water, often from runoff from fertilizers.

• Algal Blooms: The increased nutrients lead to algal blooms, which can severely diminish water quality.

• Biological Oxygen Demand (BOD): Decomposing algae consumes a significant amount of dissolved oxygen, leading to:

  • Hypoxic Zones: Areas with low oxygen saturation.

  • Anoxic Zones: Areas with extremely low or zero oxygen levels.

Effects of Eutrophication

• Decreased Oxygen Levels: As algae decompose, the process uses up oxygen, causing dead zones where aquatic life cannot survive.

• Lake Dynamics:

  • Fertilizer Pathway: Runoff from fertilizers seeps into soil, enters water systems via underground waterways, and leads to algal overgrowth.

  • Light Blockage: Excessive algal growth prevents sunlight from penetrating to the bottom, affecting other aquatic plants.

  • Bacterial Decomposition: The decomposition of algae by bacteria can lead to additional oxygen depletion.

Types of Lakes by Nutrient Levels

• Oligotrophic Lakes: Low in nutrients and algae; high oxygen levels; typically very clear.

• Mesotrophic Lakes: Intermediate nutrient levels, moderate algae, and dissolved oxygen.

• Eutrophic Lakes: High nutrient levels; often experience algal blooms and subsequent low oxygen levels.

Ecosystem Comparison

• Healthy Ecosystem: Balanced nitrogen and phosphorus levels, supports a diverse range of species.

• Eutrophic Ecosystem: High nitrogen/phosphorus; dead zones created due to oxygen depletion; less biodiversity.

Sources of Eutrophication

• Sewage: Both untreated and treated sewage can contribute to nutrient loading in water bodies.

• Detergents: Often contain phosphates that increase phosphorus levels in water.

• Combustion of Fossil Fuels: Releases nitrogen oxides (NOx), contributing to nitrogen levels.

• Fertilizers and Manures: Direct sources of both nitrogen and phosphorus.

• Runoff: General runoff can lead to excess nutrient introduction from various sources.