Question 1
State the largest global water store and the two largest non-ocean water stores.
[3]
Question 2
Explain how solar radiation and gravity drive movements of water in the hydrosphere.
[3]
Question 3
Figure 1 shows the approximate distribution of water among the main stores in the global hydrological cycle.
Approximate distribution of water among the main global hydrological stores; values are rounded.
| Water store | Approximate share of global water / % |
|---|---|
| Oceans | |
| Glaciers and ice caps | |
| Groundwater | |
| Surface freshwater | |
| Atmosphere | |
| Organisms |
Identify the largest water store shown in Figure 1.
[1]
Calculate the approximate percentage of global water stored outside the oceans.
[1]
Calculate how many times greater the surface freshwater store is than the atmospheric store.
[2]
Suggest why the small atmospheric store is nevertheless important to the hydrological cycle.
[1]
Question 4
Draw a systems diagram connecting the atmosphere, ocean and surface freshwater stores. Include and label evaporation, precipitation and streamflow.
[4]
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Question 5
Distinguish between infiltration and percolation.
[2]
Distinguish between advection and sublimation.
[2]
Question 6
Figures 2(a) and 2(b) represent the global hydrological cycle and the relative sizes of its water stores.
Approximate relative sizes of selected global water stores.
| Water store | Share of global water / |
|---|---|
| Oceans | |
| Glaciers and ice caps | |
| Groundwater | |
| Surface freshwater | |
| Atmosphere | |
| Organisms |
Using Figure 2(a), identify the flows numbered 4, 5 and 7.
[3]
Calculate how many times larger the glacier and ice-cap store is than the surface freshwater store.
[2]
Distinguish between infiltration and percolation.
[2]
Explain how solar radiation and gravity maintain the flows shown in Figure 2(a).
[3]
Explain why the size of a water store does not necessarily indicate the rate at which water cycles through it.
[2]
Question 7
Figure 4 is a simplified systems diagram showing one route taken by water through the hydrological cycle.
Identify flows A and B.
[2]
Distinguish between flows D and E.
[2]
Explain how solar radiation and gravity drive the route A–B–C–F shown in Figure 4.
[2]
Question 8
Figure 1 compares river responses to the same rainfall event before and after extensive urbanization of a drainage basin. The peak rainfall intensity occurred at in both cases. For this question, lag time is measured from peak rainfall to peak river discharge.
State the change in lag time following urbanization.
[1]
Explain the change in the storm hydrograph following urbanization.
[3]
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Question 9
A lake receives natural inputs totalling . Its natural outputs total .
Calculate the maximum human abstraction rate that would maintain the lake at steady state.
[2]
Calculate the rate of change of the lake's water store if abstraction is increased to .
[1]
Question 10
Explain how four properties of water support aquatic or terrestrial life.
[4]
Question 11
The town of Selvara expanded across part of the previously vegetated Luma drainage basin. Figure 1 compares river responses to the same rainfall event before and after urbanization.
Figure 1(a). Hourly rainfall and river discharge for the same 30 mm rainfall event before and after urbanization in the Luma drainage basin.
| Time after rainfall begins / | Rainfall / | Discharge before urbanization / | Discharge after urbanization / |
|---|---|---|---|
| 0 | 0 | 10 | 8 |
| 1 | 8 | 10 | 8 |
| 2 | 14 | 10 | 8 |
| 3 | 6 | 10 | 30 |
| 4 | 2 | 12 | 100 |
| 5 | 0 | 18 | 70 |
| 6 | 0 | 28 | 48 |
| 7 | 0 | 36 | 34 |
| 8 | 0 | 40 | 25 |
| 9 | 0 | 36 | 19 |
| 10 | 0 | 30 | 15 |
| 11 | 0 | 24 | 12 |
| 12 | 0 | 19 | 10 |
| 13 | 0 | 15 | 9 |
| 14 | 0 | 12 | 8 |
| 15 | 0 | 11 | 8 |
| 16 | 0 | 10 | 8 |
State the peak discharge after urbanization and the lag time between peak rainfall and peak discharge after urbanization.
[2]
Calculate the percentage increase in peak discharge following urbanization. Show your working.
[2]
Explain how urbanization produced the changes in the storm hydrograph.
[4]
Evaluate the proposed measures for reducing flash-flood risk in the Luma drainage basin.
[4]
Question 12
The same rainfall event occurred over two drainage basins of equal area. One basin was mainly vegetated and the other was highly urbanized. Figure 2 shows the rainfall and river-discharge responses.
State the peak discharge and lag time of the urbanized basin.
[2]
Calculate the percentage by which the peak discharge of the urbanized basin exceeds that of the vegetated basin.
[2]
Explain the differences between the two hydrographs.
[3]
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Question 13
Figure 3 shows the mean annual water flows for a lake. Assume that the flow rates remain constant over the period considered.
Calculate the total natural input rate and the total natural output rate for the lake.
[2]
Determine the maximum human-abstraction rate that would maintain the lake at steady state.
[2]
Calculate the change in the lake's stored water volume over one day at the abstraction rate shown in Figure 3.
[2]
Question 14
Figure 5 shows the maximum concentration of dissolved oxygen in freshwater at different temperatures and pressures.
Calculate the percentage decrease in maximum dissolved oxygen concentration between and at an oxygen partial pressure of 1.0 atmosphere.
[2]
Describe the effect of doubling oxygen partial pressure at .
[1]
Explain how increasing water temperature could affect organisms in a freshwater ecosystem.
[3]
Question 15
Explain why the oceans currently act as a carbon sink and why the strength of this sink may decrease.
[3]
Question 16
Explain how short-term ocean carbon sequestration can cause ocean acidification.
[2]
Outline how carbon can be sequestered in the ocean over geological timescales.
[2]
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Question 17
Explain why a freshwater lake freezes from the surface downwards.
[3]
State one way in which the surface ice supports the survival of the freshwater ecosystem.
[1]
Question 18
Outline how coastal upwelling can increase marine productivity.
[2]
Outline how temperature and salinity create a deep current in the North Atlantic thermohaline circulation.
[2]
Question 19
Lake Nembi supplies water to nearby settlements. Figure 3 shows the lake's mean annual water balance. Assume that one year contains 31 536 000 seconds.
Calculate the mean annual rate available for abstraction if the lake is to remain at steady state.
[2]
Calculate the annual change in the volume of Lake Nembi at the current abstraction rate. Give the sign and units.
[3]
Explain why a water body at steady state is not a static system.
[3]
Evaluate the use of the mean annual water balance to set a sustainable abstraction limit for Lake Nembi.
[4]
Question 20
Two neighbouring agricultural drainage basins received similar annual precipitation. Basin F retained native forest, while Basin C was cleared for grazing and later used for irrigated crops.
Calculate the run-off coefficient for Basin C using annual stream run-off as a percentage of annual precipitation.
[2]
Describe two differences between the annual water balances of Basin F and Basin C.
[2]
Explain how forest clearance and livestock grazing may account for the differences in run-off and groundwater recharge.
[4]
Evaluate the proposed measures for improving the sustainability of water management in Basin C.
[5]
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Question 21
Lake Orin experiences warm summers and cold winters. Figures 5(a) to 5(c) show properties of water that influence its ecosystem.
Using Figure 5(a), distinguish between cohesion and adhesion.
[2]
Calculate the percentage decrease in oxygen solubility as water warms from to .
[2]
Explain how the properties represented in Figures 5(a) and 5(b) support aquatic life.
[4]
Explain why Lake Orin freezes at the surface while liquid water remains beneath the ice.
[3]
Suggest two reasons, other than temperature, why measured dissolved oxygen may differ from the solubility values in Figure 5(b).
[2]
Question 22
Figure 6 shows vertical profiles measured during summer in a deep, stratified lake.
Summer vertical profiles in a deep stratified lake.
| Depth / m | Temperature / | Dissolved oxygen / | Nitrate / |
|---|---|---|---|
| 0 | 22 | 9.2 | 0.3 |
| 10 | 21 | 9.0 | 0.4 |
| 20 | 20 | 8.7 | 0.5 |
| 30 | 15 | 7.2 | 1.1 |
| 40 | 10 | 5.4 | 2.1 |
| 50 | 6 | 4.0 | 3.0 |
| 60 | 6 | 3.4 | 3.6 |
| 80 | 6 | 2.6 | 4.3 |
| 100 | 6 | 2.0 | 4.8 |
Identify the depth range of the thermocline.
[1]
Describe the changes in dissolved oxygen and nitrate concentration between 10 m and 100 m depth.
[2]
Explain the contrasting dissolved oxygen and nitrate profiles shown in Figure 6.
[4]
Question 23
Figures 7(a) and 7(b) show changes in anthropogenic carbon emissions, ocean carbon uptake, sea-surface temperature and mean surface-ocean pH between 2000 and 2020.
Figure 7(b): Changes in global mean sea-surface temperature anomaly and mean surface-ocean pH, 2000–2020.
| Year | Sea-surface temperature anomaly / | Mean surface-ocean pH |
|---|---|---|
| 2000 | 0.40 | 8.11 |
| 2005 | 0.55 | 8.10 |
| 2010 | 0.70 | 8.08 |
| 2015 | 0.90 | 8.06 |
| 2020 | 1.10 | 8.05 |
Calculate the percentage of anthropogenic carbon dioxide emissions absorbed by the oceans in 2020.
[2]
State the change in mean surface-ocean pH between 2000 and 2020.
[1]
Explain how ocean uptake of carbon dioxide may cause the pH trend shown in Figure 7(b).
[2]
Suggest two reasons why the percentage of emissions absorbed by the oceans could decline if the trends continue.
[2]
Question 24
Figure 2 compares ocean stratification under historical conditions and under conditions of surface warming and increased freshwater input from melting ice.
Explain how surface warming and melting ice intensify ocean stratification.
[3]
State one possible ecological or environmental consequence of intensified stratification.
[1]
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Question 25
Researchers investigated carbon uptake and seawater chemistry in the fictional Pelagos Sea between 1980 and 2020.
Calculate the percentage of annual anthropogenic carbon emissions absorbed by the Pelagos Sea in 1980 and in 2020.
[3]
Describe the relationship between carbon emissions and ocean uptake shown in Figure 6(a).
[2]
Explain how ocean uptake of atmospheric carbon dioxide causes the pH change shown in Figure 6(b).
[3]
Distinguish between short-term and long-term ocean carbon sequestration shown in Figure 6(c).
[2]
Evaluate the claim that ocean uptake can continue to offset increasing anthropogenic carbon emissions indefinitely.
[4]
Question 26
Seasonal stratification and coastal upwelling occur in the Maruva coastal water body. Figures 7(a) to 7(c) show conditions during summer.
Figure 7(a): summer vertical profiles in the Maruva coastal water body.
| Depth / m | Water layer | Temperature / | Dissolved oxygen / mg L | Nitrate / mg L |
|---|---|---|---|---|
| 0 | Warm mixed layer (0–20 m) | 24 | 8.0 | 1 |
| 20 | Thermocline (20–60 m) | 23 | 8.5 | 1 |
| 40 | Thermocline (20–60 m) | 14 | 5.5 | 5 |
| 60 | Thermocline (20–60 m) | 9 | 3.0 | 10 |
| 100 | Cool deep layer (>60 m) | 7 | 2.0 | 14 |
Summer coastal conditions during periods with and without upwelling.
| Measure | Non-upwelling | Upwelling |
|---|---|---|
| Mean surface temperature / | 22 | 15 |
| Surface nitrate / | 1 | 9 |
| Chlorophyll-a / | 2 | 8 |
| Fish catch / tonnes boat week | 3 | 7 |
Identify the depth range of the thermocline and calculate the mean temperature decrease per metre across it.
[3]
Explain the dissolved oxygen and nitrate profiles shown in Figure 7(a).
[4]
Using Figures 7(b) and 7(c), explain how upwelling affects biological productivity and fish catch.
[3]
Evaluate how stronger and more persistent stratification could affect the Maruva ecosystem and fishery.
[4]
Question 27
Figure 8 shows selected properties of water masses in a simplified North Atlantic thermohaline circulation system. The meltwater scenario represents increased melting of land ice.
Calculate the increase in density as present-day surface water moves from lower latitudes to the high-latitude sinking region.
[1]
Explain why the present-day high-latitude water sinks despite having a lower salinity than the lower-latitude surface water.
[2]
Predict how the increased meltwater input shown in Figure 8 would affect deep-water formation and the North Atlantic conveyor belt.
[2]
Explain one possible climatic consequence and one possible ocean-system consequence of a weaker conveyor belt.
[2]
Question 28
The following questions concern hydrological flows and flood-risk management within drainage basins.
Distinguish between transfers and transformations in the hydrological cycle, using one example of each.
[4]
Explain how deforestation may alter water flows and flood risk within a drainage basin.
[7]
Using named examples, evaluate the claim that restoring vegetation is the most effective way to manage flood risk within drainage basins.
[9]
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Question 29
An aquifer receives renewable recharge at a mean rate of . Its natural groundwater outflow is and water is currently abstracted at . For the calculations in part (a), assume that these rates remain constant and that one year contains seconds.
Calculate the maximum abstraction rate that would maintain the aquifer at steady state and the annual change in its stored water volume at the current abstraction rate. Show your working.
[4]
Explain why the calculated steady-state abstraction rate may not be environmentally sustainable.
[7]
Using named examples, evaluate strategies for achieving sustainable groundwater use.
[9]
Question 30
Outline how the global hydrological cycle operates as a system.
[4]
Explain how irrigated agriculture and urbanization may alter stores and flows in the hydrological cycle.
[7]
Using named examples, to what extent can deliberate manipulation of hydrological flows provide sustainable water security?
[9]
Question 31
The North Arven Sea forms part of a global thermohaline circulation system. Researchers monitored surface conditions and deep-water formation between 1990 and 2020.
Figure 8(b): Surface conditions and circulation in the North Arven Sea, 1990–2020.
| Year | Surface temperature / C | Practical salinity | Deep-water formation / Sv | Northward heat transport / PW |
|---|---|---|---|---|
| 1990 | 6.0 | 35.1 | 18 | 1.20 |
| 2000 | 6.4 | 35.0 | 17 | 1.16 |
| 2010 | 6.9 | 34.7 | 14 | 1.05 |
| 2020 | 7.5 | 34.4 | 11 | 0.92 |
State the two water properties that drive thermohaline circulation and describe how each affects density.
[3]
Calculate the percentage decrease in deep-water formation between 1990 and 2020.
[2]
Analyse the relationships among temperature, salinity, deep-water formation and heat transport shown in Figure 8(b).
[4]
Explain how evaporation, rivers and melting ice can have opposing effects on deep-water formation in the North Arven Sea.
[2]
Evaluate the possible environmental significance of the observed weakening of circulation.
[3]
Question 32
Explain how four properties of water support life.
[4]
Explain how seasonal stratification can produce vertical differences in temperature, dissolved oxygen and mineral nutrients in a deep lake.
[7]
Using named examples, evaluate the claim that maintaining natural mixing processes is essential for the sustainability of aquatic ecosystems.
[9]
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Question 33
Distinguish between an ocean carbon sink and ocean carbon sequestration.
[4]
Explain the short-term and long-term pathways of carbon after atmospheric carbon dioxide enters the ocean.
[7]
Using named examples, to what extent can ocean carbon uptake be relied upon to limit anthropogenic climate change?
[9]
Question 34
Explain how temperature and salinity differences drive thermohaline circulation.
[4]
Explain how global warming may affect ocean stratification, upwelling and thermohaline circulation.
[7]
Using named examples, evaluate the environmental significance of climate-driven changes to ocean circulation.
[9]
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