Water and carbon cycles

1. What is infiltration?

1. Water flowing over the surface
2. Water soaking into the soil from the surface
3. Water moving through rock
4. Water evaporating

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B: Water soaking into the soil from the surface. Percolation then moves water deeper into the rock.

2. Which is the largest store of water on Earth?

1. Groundwater
2. Oceans
3. Ice caps
4. Atmosphere

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B: Oceans. Oceans hold the vast majority of the Earth's water.

3. What is lag time on a storm hydrograph?

1. Total rainfall
2. The time between peak rainfall and peak discharge
3. The time for a river to dry up
4. The steepness of the falling limb

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B: The time between peak rainfall and peak discharge. Shorter lag times indicate a flashier response.

4. How does urbanisation affect a storm hydrograph?

1. Longer lag time, lower peak
2. Shorter lag time and higher peak discharge
3. No effect
4. Less surface run-off

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B: Shorter lag time and higher peak discharge. Impermeable surfaces and drains speed water to the channel.

5. What does the drainage basin water balance compare?

1. Temperature and rainfall
2. Precipitation with evapotranspiration, run-off and storage change
3. Ocean and atmospheric stores
4. River length and discharge

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B: Precipitation with evapotranspiration, run-off and storage change. It shows how water inputs are accounted for in a basin.

6. Which store of water is generally the largest globally?

1. Groundwater
2. Rivers
3. Oceans
4. Atmosphere

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C: Oceans. Oceans hold the overwhelming majority of the Earth's water.

7. Which flow moves water from the soil down into the underlying permeable rock?

1. Interception
2. Throughflow
3. Percolation
4. Stemflow

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C: Percolation. Percolation is the downward movement of water from the soil into underlying rock. Throughflow is lateral flow within the soil, and stemflow and interception happen at the vegetation level.

8. A basin receives 1000 mm of precipitation and loses 450 mm to evapotranspiration. Storage does not change. What is run-off?

1. 450 mm
2. 1450 mm
3. 550 mm
4. 1000 mm

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C: 550 mm. P = Q + E ± ΔS with ΔS = 0, so Q = P − E = 1000 − 450 = 550 mm. Adding the values (1450 mm) is a common error.

9. Why is the global water cycle closed but a drainage basin open?

1. Global water is fixed; a basin gains and loses water across its edge
2. A basin has no outputs; the global cycle loses water to space
3. The global cycle has only stores; a basin has only flows
4. Both are closed because rivers never cross a watershed

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A: Global water is fixed; a basin gains and loses water across its edge. Globally the amount of water is effectively constant, so the cycle is closed. A basin is open because precipitation enters it and discharge and evapotranspiration leave it.

10. Which human activity is most likely to reduce the groundwater store in an area?

1. Building wetland reserves
2. Removing paved surfaces
3. Pumping boreholes for irrigation
4. Planting upland forests

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C: Pumping boreholes for irrigation. Abstraction by boreholes removes groundwater faster than it is recharged, so the store falls. The other options tend to increase infiltration and recharge.