eutrophication

• Eutrophication

  The process that can happen in a water body, like a river or a lake, when too many nutrients are added to the system
• Eutrophication process


  1. Fertilizers rich in nutrients like nitrate and phosphate are washed into the river or lake system

  2. Increase in nutrient concentrations in the water

  3. Nutrients are food for algae

  4. Algae grow and reproduce quickly, forming a thick green bloom in the water

  5. Algal bloom absorbs sunlight so it can't reach the bottom

  6. Plants who need this light to photosynthesis will die

  7. Algae start to die when they eat up all of the nutrients and run out of food

  8. Bacteria start to breakdown the dead plants and algae, releasing more nutrients back into the water continuing the Algal Bloom Cycle

  9. Bacteria reproduce into much larger numbers consuming oxygen as they grow and respire

  10. Water turns anoxic (without oxygen)

  11. All non-bacterial life in the water, including fish and other animals, will die
• Eutrophication happens when nutrients are added to water which causes an algal bloom, cutting off sunlight and feeding bacteria, using up oxygen in the water which becomes anoxic, causing everything living in the water to die
• Eutrophication is one reason why we need to be careful with fertilizers when we are growing crops
• Plants require several things to grow
• Things plants need to grow

  • Water
  • Sunlight
  • CO2
  • Nutrients (like nitrogen and phosphorus)
• Fertilizer


  Enriched with nutrients that plants need, mostly fixed nitrogen and phosphorus
• Plants aren't the best at soaking up every last nutrient in the soil
• It's hard to gauge just how much fertilizer a field needs, as soil quality can vary drastically over short distances
• Farmers will usually apply excess fertilizer to a given plot of land
• Excess nutrients from fertilizer


  Carried away by rain or irrigation into bodies of water
• What happens when excess nutrients enter bodies of water


  1. Algae, phytoplankton, and plants in the water grow and explode in numbers (algal bloom)

  2. Floating layer of algae blocks sunlight from reaching bottom of lake

  3. Nutrients used up, excess algae and plants die and sink to bottom

  4. Decomposers use up oxygen in water, causing animals to suffocate

  5. Positive feedback loop of more death and decomposition
• Nutrient-rich runoff can also be caused by clear-cutting and animal farms
• Eutrophication can greatly damage ecosystems and lead to a decrease in biodiversity globally