IB ESS HL 4.4.6 Eutrophication Sequence Questions
Trace nutrient enrichment, algal growth, oxygen depletion and ecosystem change.
- Syllabus
- First assessment 2026
- Course
- ESS HL
- Level
- HL
Exam points
- outline the eutrophication sequence and distinguish nutrient inputs from natural cycles, agricultural fertilizer runoff and domestic wastewater
- explain how excess nutrients cause algal growth, reduced light and photosynthesis, oxygen depletion through decomposition, hypoxia, organism death and possible positive feedback
- analyse and evaluate the sequence using map, lake or coastal evidence, considering long-term effects on tolerance, reproduction, food webs, ecosystem services and human activities
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IB ESS HL 4.4.6 Eutrophication Sequence Questions question 1
[Maximum number: 6]
With reference to natural cycles and human activities, outline the process of eutrophication.
eutrophication is an increase in nutrients in an aquatic ecosystem;
nutrients added from decomposing biomass / natural run-off from surrounding areas (natural cycles);
seasonal temperature inversion/turnover/upwelling currents bringing nutrients to surface (natural cycles);
similarly run-off from agricultural land/artificial fertiliser/fertilisers/slurry adds nutrients to water (human activities);
domestic waste water contains phosphates and nitrates/detergents/non-treated sewage(human activities);
Marking guidance:
[3 max] for causes and [2 max] if only natural or human causes are mentioned. both human and natural eutrophication leads to increase in biomass of algae initially/rapid algae growth;
the algae increase turbidity/lower the light penetration to underwater plants;
increased death of algae/underwater plants leads to increase in DOM/bacteria;
increased bacteria increase BOD which leads to lowered oxygen content of water/causes hypoxia;
lowered oxygen leads to stagnation/anaerobic bacteria/death of many organisms;
human induced eutrophication happens a lot faster than natural eutrophication/on a bigger scale;
[4 max] for outline of eutrophication
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