4.4 Water pollutionIB Environmental Systems and Societies SL: Subtopic test

1. 1
   Large amounts of plastic debris have collected in a region of the North Pacific known as the Great Pacific Garbage Patch, where circular ocean currents concentrate floating material. Much of the plastic began as single-use packaging. Seabirds and turtles swallow pieces of plastic, and larger items break down into tiny fragments called microplastics. Some organisations now place floating barriers in rivers and the ocean to collect plastic, while several countries have banned single-use plastic bags.

   (a)

   Why does plastic debris accumulate in the area known as the Great Pacific Garbage Patch?

   [1 mark]

   • APlastic is manufactured in the middle of the ocean
   • BCircular ocean currents (a gyre) concentrate floating debris in one region
   • CPlastic sinks to the surface and is dissolved by seawater
   • DMarine organisms digest plastic completely

   (b)

   Which action would remove plastics from the supply chain most directly?

   [1 mark]

   • AOrganising a beach clean-up
   • BPlacing a floating barrier in a river
   • CFitting filters to washing machines
   • DReplacing single-use plastic packaging with reusable or biodegradable alternatives

   (c)

   Outline two ways in which existing plastic pollution in aquatic environments can be cleared up.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A river receives wastewater from a food-processing factory in a town. The environment agency measures dissolved oxygen, biochemical oxygen demand (BOD), nitrate, phosphate, temperature and turbidity at several sites, and combines the results into a water quality index (WQI) for each site.

   (a)

   What is biochemical oxygen demand (BOD)?

   [1 mark]

   • AThe amount of oxygen produced by aquatic plants in daylight
   • BThe total amount of oxygen in the atmosphere above a river
   • CThe amount of dissolved oxygen required by microorganisms to decompose organic material in the water
   • DThe mass of nitrate that can be removed from the river by plants

   (b)

   A sample of river water has a very high BOD. What does this indicate?

   [1 mark]

   • AA large amount of organic material is being decomposed, so the water is likely to be polluted
   • BThe water has a very high concentration of dissolved oxygen
   • CThe water is clean and ideal for aquatic organisms
   • DNo decomposition is taking place

   (c)

   Explain why discharging organic waste into the river increases its BOD and reduces dissolved oxygen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The environment agency measured the river at a site upstream of the factory and a site downstream of its discharge. Upstream: dissolved oxygen 9.2 mg per litre, BOD 2 mg per litre, nitrate 1.2 mg per litre, phosphate 0.05 mg per litre, WQI 85. Downstream: dissolved oxygen 3.5 mg per litre, BOD 14 mg per litre, nitrate 6.8 mg per litre, phosphate 0.45 mg per litre, WQI 38. The WQI is scored from 0 to 100, with a higher score meaning better water quality.

   (a)

   Calculate the percentage change in dissolved oxygen between the upstream and downstream sites and explain how the change is linked to the change in BOD.

   [3 marks]

   (b)

   Evaluate the use of a water quality index to assess the effect of the factory on the river.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lake Erie is the shallowest and warmest of the North American Great Lakes. Phosphorus-rich run-off from farmland and wastewater from towns, much of it carried by the Maumee River, flows into its western basin. In summer, dense green blooms of algae cover large areas, the water becomes cloudy, and some bottom waters lose their oxygen. The lake supports a valuable walleye fishery, tourism and drinking water for millions of people.

   (a)

   Explain the sequence of impacts on the lake that follows an increase in nutrient inputs.

   [6 marks]

   (b)

   Evaluate management strategies for eutrophication at the three different levels at which it can be addressed.

   [6 marks]

   Total for question 4: 12 marks

End of questions