Man’s Impact on the Environment Topic

Must-Know Impact of Water Pollution

This science revision note aims to help your child

– understand upstream and downstream flow

– analyse the impact of dumping sewage into the river

– identify the concept to use when there is untreated animal waste and sewage in the water

 

But before you read on, you might want to download this entire revision notes in PDF format to print it out for your child, or to read it later.

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The map below shows a riverbank. Along the riverbank, there are a few farms and a village. The farms release animal waste into the river, while the village releases untreated sewage into the river.

Joanna took water samples from points X and Y and measured the amount of dissolved oxygen in the samples.

Which part of the river (X and Y) has less dissolved oxygen? Explain your answer.

 

STEP 1

 

Identify the factor that affects the amount of dissolved oxygen.

The difference between the two water samples is the location they were takenbefore or after the farms and village.

As stated by the question, the farms release animal waste while the village releases untreated sewage into the river.

Hence, only part Y has untreated sewage and animal waste.

(Remember to check the direction of the river flow!)

 

STEP 2

So how does animal waste and untreated sewage affect dissolved oxygen? Consider what is in the waste and sewage.

Animal waste and untreated sewage contain a lot of bacteria.

How do bacteria affect dissolved oxygen?

Bacteria use dissolved oxygen to respire and decompose the sewage released by the farms and the village, decreasing the amount of dissolved oxygen in the water.

Hence, the water along and after the farms and village would have less dissolved oxygen compared to the water before the farms and village.

Thus, Point Y has less dissolved oxygen.

(Remember to check the direction of the river flow!)

 

FINALLY, put your answer together

Question: Which part of the river (X and Y) has less dissolved oxygen? Explain your answer.

Answer: Point Y has less dissolved oxygen compared to X. The animal waste and untreated sewage released by the farms and the village contain a lot of bacteria. Bacteria use dissolved oxygen to respire and decompose. Hence, there is less dissolved oxygen in Y than in X.

You can download this revision notes so your child can revise them anytime.

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