IB ESS SL 4.4.3 Water Quality Measurement Questions
Interpret physical, chemical and biological indicators of water quality.
- Syllabus
- First assessment 2026
- Course
- ESS SL
- Level
- SL
Exam points
- identify physical, chemical and biological water-quality indicators and methods, including transparency or turbidity, dissolved oxygen, BOD, pH, nutrients, coliforms, probes and biotic indices
- explain how representative repeated sampling across sites and times can monitor pollution and aquatic change, and interpret measurements or graphical data such as sewage-related turbidity, coliforms, nutrients and oxygen
- apply and evaluate a water-quality monitoring method using evidence, comparing direct measurements with biological indicators and considering reliability, objectivity, cost and ecological coverage
IB ESS SL 4.4.3 Water Quality Measurement Questions question 1
Question (a)
(a)
Figure:Coliform bacteria one day after untreated sewage release
Using Figure 11(b), estimate the highest concentrations of coliform bacteria (in units/100 mL) found in the St Lawrence River one day after the untreated sewage was released.
Question (b)
(b)
Figure:Coliform bacteria before untreated sewage release
Figure:Untreated sewage release into the St Lawrence River
Montreal:
In November 2015, the City of Montreal discharged between 5 and 8 billion litres of untreated sewage into the St Lawrence River.
• It was called “FlushGate” in the Canadian news.
• Citizens were warned to avoid contact with the water.
• River pollution levels returned to normal within 4 to 10 days.
• The Mayor of Montreal described it as the “most environmentally-friendly solution”.
Quebec:
In November 2016, the City of Quebec discharged 110 million litres of untreated sewage into the St Lawrence River.
Nationally:
• 25 % of Canadians do not have access to sewage or wastewater treatment centres.
• 205 billion litres of untreated sewage are released into Canadian rivers and oceans each year.
With reference to Figures 10, 11(a) and 11(b), describe a method to monitor the impact of the release of untreated sewage into the St Lawrence River ecosystem.
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