4.10.5Additional lessons
Eutrophication — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 139 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4The Sequence of Eutrophication
Eutrophication is the enrichment of water with mineral nutrients, which leads to ecological damage.
1
Nitrates and phosphates from fertilisers or sewage enter a lake or river, often by leaching and runoff from farmland.
2
The extra nutrients stimulate rapid growth of algae and phytoplankton, forming an algal bloom on the surface.
3
The bloom blocks light, so submerged plants cannot photosynthesise and begin to die.
4
Algae and plants eventually die as nutrients run short, and decomposing bacteria multiply on the dead matter.
5
Bacterial aerobic respiration uses up dissolved oxygen, so fish and invertebrates suffocate and a dead zone may form.
6
Recovery is slow because nutrients stored in sediments continue to feed the cycle for years.
Part 2 of 4Key Concepts
These terms are used in explanations and must be linked in the correct order.
Limiting nutrient
- Limiting nutrient In many waters nitrate or phosphate limits growth, so adding it lets plant and algal numbers rise sharply.
Algal bloom
- Algal bloom A dense mass of algae at the surface that shades the water below and reduces photosynthesis by submerged plants.
Biochemical oxygen demand
- Biochemical oxygen demand The amount of dissolved oxygen consumed by microbes decomposing organic matter in a water sample.
Dead zone
- Dead zone An area of water with too little oxygen to support most animal life.
Competition
- Competition Dense algae and surface plants out-compete submerged plants for light, so light, not nutrients, becomes limiting below the surface.
Part 3 of 4Sources and Control
Eutrophication is caused by human activity and can be reduced by controlling nutrient inputs.
Sources and Control
Agricultural runoff
- Agricultural runoff Soluble fertilisers are washed from fields by rain into streams, rivers and lakes.
Sewage
- Sewage Treated or untreated sewage adds phosphates and organic matter that raise nutrient levels.
Prevention
- Prevention Apply less fertiliser, avoid applying before rain, and leave uncultivated buffer strips beside waterways.
Treatment
- Treatment Removing phosphate at sewage works reduces the nutrient load entering lakes and rivers.
Impact on use
- Impact on use Polluted water becomes unsuitable for drinking, fishing and recreation and may be costly to treat.
Part 4 of 4Exam Checklist & Tips
4.10.5 – Key Points for the Exam
- Eutrophication The enrichment of water bodies with mineral nutrients, leading to excess growth and oxygen depletion.
- Algal bloom A rapid increase in the population of algae in water.
- BOD Biochemical oxygen demand, the oxygen needed by microbes to decompose organic matter.
- Leaching Dissolved minerals being washed from soil by rain.
- Dead zone A region of a water body with too little dissolved oxygen to support most aquatic animals.
- Phytoplankton Microscopic photosynthetic organisms that float in water and form the base of aquatic food webs.
Common Mistakes
- Stating that algae use up the oxygen; the main oxygen demand comes from aerobic decomposers.
- Forgetting that the bloom blocks light, causing death of submerged plants.
- Saying fertiliser kills fish directly; the harm is indirect through oxygen depletion.
- Mixing up eutrophication with biomagnification.
Last updated:
\n