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Human Impact on Environment

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Human Impact on Environment

Read the case study and use the data to investigate how people affect ecosystems. Answer in complete sentences where appropriate. For multiple-choice questions, select one answer unless the question says otherwise.

A changing catchment

Kōwhai Stream flows through a farming valley in Aotearoa New Zealand. A patch of native forest beside the stream was cleared for pasture. Cattle sometimes entered the water, and rain washed soil and fertiliser from paddocks into the stream. Downstream, researchers recorded algal growth and fewer sensitive aquatic invertebrates. The community fenced the stream, planted native trees along its banks and worked with farmers to reduce fertiliser loss. The measurements below were taken before and three years after the work began.

Measure

Before restoration

Three years after

Nitrate concentration (mg/L)

4.0

2.5

Water clarity (cm)

Invertebrate score (index)

Investigate the evidence

Use the case study and monitoring results for Questions 1–10.

1.Which activity in the case study is the most direct source of excess nitrate entering the stream?

Planting native trees beside the stream
Fertiliser washing off paddocks in rain
Fencing cattle away from the water
Monitoring aquatic invertebrates

2.Choose the best explanation for why clearing native vegetation beside a stream can harm the ecosystem.

It removes habitat and reduces the vegetation that can trap sediment and shade the water.
It increases the number of native plant species in the catchment.
It prevents all rainwater from reaching the stream.
It makes fertiliser harmless to aquatic organisms.

3.Calculate the percentage decrease in nitrate concentration, from 4.0 mg/L to 2.5 mg/L. Show your calculation.

4.Describe two patterns in the monitoring results after restoration began. Include figures from the table.

5.Explain one way excess fertiliser can cause algal growth, and describe a possible effect of that growth on aquatic organisms.

6.Identify one limitation of using these measurements alone to conclude that the restoration work caused all the improvements.

7.Match each restoration action to its most likely ecological benefit.

Fence cattle away from the stream
Plant native trees along the banks
Reduce fertiliser loss from paddocks

Adds habitat, stabilises soil and provides shade
Reduces trampling, bank damage and direct faecal contamination
Lowers nutrient runoff into the stream

8.True or false: An increase in the invertebrate score from 4 to 7 is evidence that conditions may have improved for aquatic life, but it does not prove that every species recovered.

TrueFalse

9.Complete the causal chain using the terms in the word bank: more sediment, loss of bank vegetation, reduced light, soil entering the stream. Word bank: reduced light; soil entering the stream; loss of bank vegetation; more sediment.

10.Recommend one further action the community and farmers could take to reduce human impacts on Kōwhai Stream. Explain how it would help.