IB ESS HL 4.4 Water Pollution Questions

Practise IB ESS HL 4.4 by analysing direct tests, biotic indices and WQI evidence and evaluating pollution controls and coordinated action.

Exam points

Analyse point and non-point sources using discharge, runoff and waste evidence.
Evaluate pH, dissolved oxygen, turbidity and BOD measurements across impacted sites.
Analyse eutrophication from nutrient enrichment through oxygen loss and assess controls.
Compare biotic indices and WQI with direct tests, including what each measures and misses.
Evaluate citizen action through consumption change, monitoring, lobbying and coordinated removal.

Covered syllabus points

4.4.1—Water pollution sources 4.4.2—Plastic debris accumulation 4.4.3—Water quality measurement 4.4.4—Biochemical oxygen demand (BOD)4.4.5—Eutrophication 4.4.6—Eutrophication sequence 4.4.7—Eutrophication and ecosystem services 4.4.8—Eutrophication management levels 4.4.9 (HL)—Water pollutants 4.4.10 (HL)—Harmful algal blooms 4.4.11 (HL)—Anoxic and hypoxic waters 4.4.12 (HL)—Sewage treatment stages 4.4.13 (HL)—Indicator species 4.4.14 (HL)—Biotic index 4.4.15 (HL)—Water Quality Index (WQI)4.4.16 (HL)—Water quality guidelines 4.4.17 (HL)—Citizen action

[Maximum number: 6]

(a)

A small lake is going through the process of eutrophication. State one possible point source and one possible non-point source of nutrient pollution in the lake.
Point source:
Non-point source:

[ 2 ]

(b)

Define the term biochemical oxygen demand (BOD).

[ 1 ]

(c)

Figure:pH-tolerance ranges of freshwater organisms

The pH-tolerance chart shows the ranges over which aquatic organisms in a small lake can survive.

[ 3 ]

(i)

Use the pH-tolerance ranges of freshwater organisms: the pH tolerance ranges of trout, bass, perch, frogs, salamanders, clams, crayfish, snails and mayfly in the small lake.

State which organism(s) would still be present if the pH of the lake was reduced to 5.0.

[ 1 ]

(ii)

Use the pH-tolerance ranges of freshwater organisms: the pH tolerance ranges of trout, bass, perch, frogs, salamanders, clams, crayfish, snails and mayfly in the small lake.

Explain why the populations of remaining organisms in the lake may decline in the long term.

[ 2 ]

[Maximum number: 5]

Many countries produce large amounts of solid domestic waste. Pacific Ocean currents concentrate and trap solid domestic waste from the Pacific Rim countries and have created the Great Pacific Garbage Patch (GPGP) in the North Pacific Gyre (Figure 5).

Figure 6:Consumption and disposal of plastic waste for India and selected Pacific Rim countries

* Estimated for 2017 based on 10% growth.

(a)

Identify one reason why most plastics may be considered more serious pollutants than other forms of solid domestic waste.

[ 1 ]

(b)

Explain why the data in Figure 6 show no correlation between plastic consumption and plastic waste deposited in ocean for the countries listed.

[ 4 ]

[Maximum number: 6]

(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.

[ 1 ]

(b)

Outline an environmental problem that may result from the release of untreated sewage into a river.

[ 2 ]

(c)

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.

[ 3 ]

[Maximum number: 2]

A small lake is going through the process of eutrophication. State one possible point source and one possible non-point source of nutrient pollution in the lake.
Point source:
Non-point source:

[Maximum number: 4]

Figure 5(a): Canterbury region and the Selwyn/Waikirikiri River

Figure:Canterbury region and the Selwyn/Waikirikiri River

Figure 5(c): Agriculture within the Canterbury Plains

Figure:Agriculture within the Canterbury Plains

Figure 5(d): Cattle numbers, the Canterbury region, New Zealand, 1990–2019

Figure:Cattle numbers, the Canterbury region, New Zealand, 1990–2019

Figure:Fact file on the Canterbury region

Figure 5(b): Fact file on the Canterbury region
Canterbury is the largest region in New Zealand by area. It includes the Canterbury Plains, New Zealand’s largest area of flat land, used for intensive farming including wheat, barley, sheep and cattle (dairy and beef). The region produces the majority of New Zealand’s grains and crops.

(a)

Describe a method that could be used to monitor biochemical oxygen demand (BOD) on the Selwyn (Waikirikiri) River within the Canterbury Plains.

[ 3 ]

a. Water samples could be taken at various points along the river;
b. Water could be tested for BOD by taking samples and measuring oxygen concentration at start / initial oxygen concentration is measured in the sample;
c. Incubate samples for ( 5 days at $20^{\circ} \mathrm{C}$ ) in the dark;
d. Measure reduction in oxygen concentration after 5 days;
e. Example of method e.g. dissolved oxygen can be measured using an oxygen probe/test kit/titration;
f. Testing could be repeated at different time intervals (and compared to previous results);

(b)

Outline one disadvantage of using BOD measurements as an assessment of pollution.

[ 1 ]

[Maximum number: 1]

Pollutant	Unit	2011	2012	2013	2014	2015
Nitrate	kt	32.80	32.60	31.30	37.10	32.90
Phosphate	kt	4.50	4.40	4.00	4.80	4.40
Lead	kg	186.18	215.91	201.00	41.21	3.57
Arsenic	kg	28.09	21.34	15.11	8.00	11.04
Mercury	kg	1.72	0.49	0.64	0.10	0.33
Cadmium	kg	12.44	17.90	17.45	0.58	0.70
Chromium	kg	508.68	460.10	438.05	266.65	93.59

Figure 9(d): Pollutants in wastewater discharged into Beijing rivers, 2011-2015

With reference to Figure 9(d), identify the year in which eutrophication was most likely to have occurred.

[Maximum number: 6]

With reference to natural cycles and human activities, outline the process of eutrophication.

[Maximum number: 4]

Figure Diagram showing the expanse of the Mississippi River basin draining into the Gulf of Mexico

Figure Pie charts showing sources of nutrients delivered to the Gulf of Mexico from the Mississippi River

Explain how nutrient pollution could impact aquatic food production in the Gulf of Mexico.

[Maximum number: 7]

Evaluate two strategies for preventing eutrophication.

Strategy: [1max]
a. Avoid use of inorganic fertilisers by education / switch to organic fertilisers via taxes/laws;
Pros: [2max]
b. Eliminates origin of problem;
c. Organic fertilisers may be gained cheaply from natural waste;
d. Organic fertilisers provide slow release of nitrates/phosphates;
e. Education should have long-term impacts, especially if addressed to young generations;
f. Reduces GHG emissions/energy use during manufacturing of synthetic fertilizers;
Cons: [2max]
g. May reduce productivity;
h. Involves a change of farming practice that may not be popular;
i. Leads to inflation/passing higher prices to consumers;
j. Educational programs/laws/taxes need to be enforced effectively;
k. Taxes/laws may be unpopular/considered coercive;

Strategy: [1max]
l. Plant buffer zones to prevent agricultural run off;

Pros: [2max]
m. Prevents nitrates/phosphates from entering nearby water bodies;
n. Increases biodiversity of farmlands;
o. Low cost solution;
p. Reduces soil erosion;

Cons: [2max]
q. Requires considerable labour in short term;
r. Takes up space that could be used for more crops;
s. Heavy rainfall may overwhelm the buffer zone;
t. Does not eliminate origin of pollution;

Strategy: [1max]
u. Phosphate stripping/nitrate removal at sewage/domestic wastewater treatment facilities;
Pros: [2max]
v. Prevents phosphates/nitrates from reaching water bodies / completely removes from water;
w. Biological removal decreases sludge production;
x. Physical removal recovers phosphorus for re-use;
y. Some methods of phosphate stripping are considered cost-effective / fit for LEDCs, too;
Cons: [2max]
z. Chemical precipitation/removal results in more toxic sludge;
aa. Usually require high initial investment / high operational costs / large-scale facilities;
bb. Require continuous monitoring / high expertise;

Note to examiners: Credit any valid advantage or disadvantage of up to two valid strategies. If more than two strategies are evaluated, credit the two that gain the more marks and ignore the other strategies.
Do not credit similar evaluative KSs for both strategies (e.g MPm & MPv will get mark once, but allow both MPb & MPt).
Do not credit restoration strategies.

To get the strategy mark, there should be a little more than just naming;
especially for strategies like "construction of a dam" or "scrubbers reducing NOx" there should be outline of how these strategies would prevent eutrophication. Still allow ECF.

[Maximum number: 1]

With reference to Figures: Probability of lead exposure for condors by diet and Figure: Lead and non-lead bullets after impact:

State the term for a species that is used to measure pollution levels.

[Maximum number: 7]

Describe methods that could be used to assess the impact of an industrial effluent on the biotic index of a river.

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Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Question 2

Question (a)

Question (b)

Question 3

Question (a)

Question (b)

Question (c)

Question 4

Question 5

Question (a)

Question (b)

Question 6

Question 7

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Question 9

Question 10

Question 11