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Environmental Detective Project

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Environmental Detective Project

A stream ecosystem is showing signs of change. Use the evidence in this project to work out what may be happening and suggest practical ways to help. Base your conclusions on evidence, and remember that one clue alone may not prove a cause.

Gather and interpret evidence

Use the scene details and the investigation records below to make careful observations.

1.A stream bank has bottles and packaging scattered along it, and several pieces of rubbish are floating in the water. Identify one possible source of pollution and describe one detail that supports your idea.

Measurement

Upstream

Downstream

Regional guide value

Nitrate (mg/L)

Water clarity (cm)

At least 30

2.Using the stream survey records, calculate how much each measurement changes between the upstream and downstream sites. Include the direction and units of each change.

3.The downstream nitrate result is above the guide value. Which conclusion is best supported by the survey?

Nitrate levels are higher downstream, so a source between the sites should be investigated.
The culvert definitely caused the nitrate increase.
The stream contains no living things.
The upstream water is more polluted than the downstream water.

4.A local resident says, “There is more green slime near the culvert, and we have seen fewer eels lately.” Give one possible ecological explanation that links these observations.

5.Match each possible pollution source to the evidence it could produce. Sources: A. farm fertiliser washed off land; B. rubbish dumped near the stream; C. road runoff entering through a drain. Evidence: 1. bottles and packaging on the bank; 2. increased nitrate and possible algal growth; 3. oil residue and road grit in the water.

A. Farm fertiliser washed off land
B. Rubbish dumped near the stream
C. Road runoff entering through a drain

1. Bottles and packaging on the bank
2. Increased nitrate and possible algal growth
3. Oil residue and road grit in the water

Test ideas and take action

Good environmental investigations use more than one clue and choose actions that address likely causes.

6.The nitrate result is 5 mg/L and the guide value is 2 mg/L. Calculate the percentage reduction needed to reach the guide value. Show your working.

7.Choose the best first investigation step before blaming a particular land user.

Repeat water tests at both sites on several days and check for other possible sources.
Announce that the nearest farmer caused the problem.
Remove all plants from the stream bank.
Ignore the results because one survey is enough to prove the stream is healthy.

8.Describe two practical actions that could reduce pollution entering the stream. For each action, state which clue or possible cause it addresses.

9.Write a short message for a local stream-care group. Include one piece of evidence from the survey, one cautious conclusion, and one next step for the group.