Human Impact to the Environment Practice Test

Scientists compare two explanations for fish deaths in a pond near a construction site.

Claim 1: Land clearing increased sediment runoff, making the water cloudier and stressing fish. Claim 2: The fish deaths happened because the pond is getting older, and human activity is unrelated.

Evidence:

• After heavy rains, turbidity (cloudiness) in the pond rose from 5 NTU to 40 NTU during weeks when soil was exposed at the site.
• A silt fence was installed; after similar rains, turbidity peaked at 12 NTU.
• Fish deaths were reported during the highest turbidity weeks.

Which claim is best supported by the evidence?

A river runs through farmland where irrigation withdrawals have increased.

Claim: Increased irrigation withdrawals have contributed to lower river flow and warmer water in summer.

Evidence (summer averages):

• Water withdrawn for irrigation increased from 10 to 18 million m³ per summer over 12 years.
• Average river flow at a downstream gauge decreased from 55 to 38 m³/s.
• Average summer water temperature at the same site increased from 18°C to 21°C.

If the irrigation withdrawals continue to increase at a similar rate, which prediction is most consistent with the evidence (noting that predictions depend on evidence strength)?