8.5 - Eutrophication

Question 1

Eutrophication Process

Answer 1

• B/c they’re limiting nutrients in aq. ecosystems, extra input of N & P lead to eutrophication (excess nutrients) which fuels algae growth
  1. Algae bloom covers surface of water, blocking sunlight & killing plants below surface
  2. Algae eventually die-off; bacteria that break down dead algae use up O2 in the water (b/c decomp. = aerobic process)
  3. Lower O2 levels (dissolved oxygen) in water kills aquatic animals, especially fish
  4. Bacteria use up even more O2 to decompose dead aq. animals
  5. Creates pos. feedback loop: less O2 → more dead org. → more bacterial decomposition → less O2

Question 2

Cultural Eutrophication

Answer 2

• Anthropogenic nutrient pollution (N & P) that leads to eutrophication
  - Algae bloom due to increase of N/P → decreased sunlight → plants below surface die → bacteria use up O2 for decomp. → hypoxia (low O2) & dead zones
• Major N/P sources:
  1. Discharge from sewage treatment plants (N/P in human waste & phosphates in soaps/detergents)
  2. Animal waste from CAFOS
  3. Synthetic fertilizer from ag. fields & lawns

Question 3

Oligotrophic Waterways

Answer 3

• Waterways with low nutrient (N/P) levels, stable algae population, and high dissolves oxygen
• can be due to lack of nutrient pollution, or age of the body of water
• Aquatic ecosystems naturally undergo succession
  - sediment buildup on bottom (benthic zone) leads to higher nutrient levels
  - overtime ponds naturally shift from oligotrophic to mesotrophic to eutrophic

Question 4

Dissolved Oxygen and Dead Zones

Answer 4

• Decrease in dissolved oxygen (hypoxia) is what causes a dead zone
• all aquatic life requires DO (Dissolved oxygen) in water for respiration
• As DO decreases, fewer species can be supported
  - Most fish required at least 3.0 ppm too survive, 6.0 ppm to reproduce