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Algae Blooms Investigation

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Algae Blooms Investigation

A monitoring team at a New Zealand lake wants to find out whether extra nutrients and warmer water help algae grow. Use the evidence below to plan a fair test, interpret results and suggest ways to protect waterways.

What is happening in the water?

Read the field note. An algae bloom is a rapid increase in algae in water. Algae are tiny organisms; some are useful food for aquatic life, but a very large bloom can block light. When large amounts of algae die and decompose, that process can use oxygen in the water. Some blooms can also produce toxins, so people should follow local health advice and avoid contact with water where a warning is posted.

1.Which statement best describes an algae bloom?

A rapid increase in algae in a body of water
A kind of water plant that always grows as a single flower
A sudden increase in fish numbers
Water becoming clear after rain

2.Give two ways a very large algae bloom may affect a lake ecosystem, according to the field note.

Plan a fair investigation

Finn and Ruben propose testing how nutrient level affects algae growth. They will use identical clear containers, the same volume of lake water, equal light and the same temperature. They will add different measured amounts of nutrient solution and record algae growth after seven days.

3.What is the variable Finn and Ruben deliberately change, and what should they measure as the result?

4.Why should the containers receive the same volume of water and the same amount of light?

5.Choose the best comparison container for their test. Explain your choice.

A container with no added nutrient solution, kept under the same conditions
A container with extra nutrient solution kept in a warmer place
A container with a different volume of water and less light
No comparison container is needed

6.Name one safety or care rule the team should follow when handling lake water or algae.

Read the results

A class tested three nutrient levels at the same temperature and light level. They estimated algae growth on day 7 using a scale: 0 = no visible growth, 5 = very heavy growth. Each treatment was repeated three times.

Nutrient level

Low

Medium

High

Growth scores (three repeats)

1, 1, 2

2, 3, 3

4, 4, 5

7.Which nutrient level had the greatest algae growth overall? Use a result from the table as evidence.

8.The team repeated each treatment three times. How does repeating a test help make the evidence more useful?

9.Can this investigation prove that high nutrient levels always cause algae blooms in every lake? Explain why or why not.

Apply the science

Rain can wash nutrients from fertiliser, animal waste or other sources into streams and lakes. Warm, still conditions can also favour rapid algae growth. These factors can make a bloom more likely, but they do not make one certain.

10.A lakeside monitoring team reports warm weather and high nutrient readings after heavy rain. Is a bloom impossible, unlikely, likely or certain? Give one reason.

11.Suggest two practical actions that could reduce nutrients washing into waterways. For each, explain briefly how it could help.