IB ESS SL 4.1 Water Systems Questions

Practise IB ESS SL 4.1 by tracing water through system diagrams and explaining how urbanisation, deforestation and agriculture alter runoff and infiltration.

Exam points

Label hydrological stores, inputs, outputs and flows on lake and global water-cycle diagrams.
Calculate changes in infiltration or sediment flow and distinguish storages from transfers.
Explain how urbanisation, deforestation and agriculture alter runoff, infiltration and water quality.

Covered syllabus points

4.1.1—Water movement drivers 4.1.2—Hydrological cycle 4.1.3—Hydrological cycle stores 4.1.4—Hydrological cycle flows 4.1.5—Human activity impacts 4.1.6—Water body steady state

[Maximum number: 11]

(a)

Outline how energy drives the hydrological cycle.

[ 4 ]

(b)

Explain, with the use of a system diagram, how human activities affect flows in the global water cycle.

[ 7 ]

[Maximum number: 7]

Explain how the hydrological cycle influences climate around the Earth.

a. evaporation/evapotranspiration is higher at regions with higher insolation;
b. evaporation absorbs heat from the atmosphere (negative latent heat flux)...;
c. ...water vapour carries (via convection currents/tropical cyclones) heat to higher latitudes/altitudes...;
d. ...condensation of vapour releases heat (positive latent heat flux) to colder latitudes/altitudes...;
e. ...stabilizing the heat deficit between Tropics and Poles;
f. condensation of vapour (as rising air cools) forms clouds...;
g. ...leading to higher precipitation (e.g. in the Equatorial Belt) / snowfall (higher altitudes/latitudes);
h. oceans/inland waters effectively store heat (positive sensible heat flux) during periods of high insolation (day/summer)...;
i. ...and release it back (negative sensible heat flux) during night/winter;
j. ...thus ameliorating regional temperature differences (seasonal/diurnal);
k. overall, oceans warm the planet (by absorbing solar radiation)...;
l. ...due to water's high thermal capacity...;
m. water masses increase humidity of adjacent region (due to higher evaporation);
n. warm ocean currents transfer heat from equator to poles / cold ocean current absorb heat from atmosphere as they move from Poles toward Equator...;
o. ...(warm currents) increasing temperatures in certain regions/e.g. Gulf Stream / (cold currents) decreasing temperatures in certain regions/e.g. Labrador current;
p. warm ocean currents also increase precipitation in coastal regions/e.g. Southwest Monsoon Current / cold ocean currents decrease precipitation in coastal regions/e.g. Peru Current...;
q. ...(warm) due to increased evaporation during the summer (period of higher insolation)/e.g. monsoons in Bay of Bengal, which is helped by...;
r. ...advection of vapor by prevailing onshore winds;
s. ...(cold currents) due to cold air holding less moisture;
t. formation of ice / increased cloud cover increases albedo, thus may stabilize global warming (negative feedback) / reduce regional temperature;
u. melting of ice / reduced cloud formation decreases albedo, thus may contribute to global warming (positive feedback) / increase regional temperature;
v. increased evaporation may contribute to global warming, as water vapour is a greenhouse gas;
w. ocean acts as a carbon sink sequestering $\mathrm{CO}_{2}$ , thus reducing global warming;

Note: Description of the tri-cellular model of air circulation should gain marks as above;
i.e. no separate mark for stating e.g. "Hadley cell". No credit for wind effects not linked to water (as, for example, in MPr).
Allow up to [2max] for reference to global warming.

[Maximum number: 2]

Figure 3: Impact of deforestation on the water cycle

Figure:Impact of deforestation on the water cycle

(a)

State one storage of fresh water not shown in Figure 3.

[ 1 ]

(b)

State one input of water into the atmosphere not shown in Figure 3.

[ 1 ]

[Maximum number: 4]

Outline how energy drives the hydrological cycle.

[Maximum number: 1]

Figure:Impact of deforestation on the water cycle

State one storage of fresh water not shown in Figure 3.

[Maximum number: 1]

Figure:Impact of deforestation on the water cycle

State one input of water into the atmosphere not shown in Figure 3.

[Maximum number: 4]

Mangrove	Seagrass	Coral reef
Provides nursery and habitat for fish and shellfish	Provides nursery and habitat for variety of species	Provides nursery and habitat which supports high biodiversity
Intercepts freshwater flow, traps sediments and absorbs nutrients	Traps sediments and absorbs nutrients from the water	Filters particulate matter from the water, increasing water clarity
Absorbs carbon dioxide and emits oxygen	Absorbs carbon dioxide and emits oxygen
Provides a source of fish and shellfish	Provides a source of fish and shellfish	Provides a source of fish and shellfish
Reduces coastal erosion		Provides coastal protection by buffering incoming waves and currents
Provides a source of wood		Provides a tourist and recreation attraction

Figure:Ecosystem goods and services in coastal marine habitats

Figure 7: Threats to biodiversity and ecosystems within the Coral Triangle
• Coral reefs and mangroves in the Coral Triangle have declined by over 40 % since the 1970s.
• Over 85 % of coral reefs are under threat from population growth and human activity.
• Mangroves have commonly been removed to make way for agriculture, aquaculture or urban development.
• Increase in unsustainable fishing practices, because of the demand for marine resources, has led to the decline of many species, such as bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares).
• Destructive fishing methods that impact marine habitats have been used throughout the region, such as use of dynamite and cyanide.
• Demand for wildlife goods such as turtle products and shark fins (used to make shark-fin soup) has caused a reduction in population numbers of some species.
• Land-based pollution from agriculture, logging, mining and urban development has damaged habitats within the Coral Triangle.

Large-scale tourism development also threatens the Coral Triangle through:
• pollution produced by tourists, such as sewage effluent, plastic waste materials
• coral trampling by snorkelers and divers
• physical damage caused by boat anchors ripping up corals and seagrass
• stress to marine wildlife caused by tourists following them too closely
• collection of wildlife souvenirs, such as corals, shellfish or turtle shells.

Climate change is a major threat to the Coral Triangle. The World Wide Fund for Nature (WWF) estimates that at current rates of global temperature increase, most coral reefs could be destroyed by 2050.

Explain how the following land-based activities could have a damaging effect on marine ecosystems within the Coral Triangle:

(a)

deforestation

[ 2 ]

identify problem [1]	its corresponding effect on marine ecosystems [1]
removal of mangroves results in loss of habitat/nursery area for young fish;	...reducing biodiversity/secondary productivity in coastal area; ...making species prone to extinction;
increase in soil/coastal erosion leading to more sediment entering the Coral Triangle;	…this blocks sunlight that coral/sea grasses/algae require;
loss of carbon sink that can lead to increase in global temperatures;	…increase in water temperatures can stress coral/reduce biodiversity;
increased carbon dioxide released into the atmosphere that contributes to ocean acidification/lowers pH;	...this adversely affects some species eg fish / reduces biodiversity; ...damages calcifying species/shellfish/corals;
without trees, runoff is no longer filtered and nutrients absorbed, thereby increasing nutrient loading within the marine ecosystem;	…this leads to eutrophication; ...this leads to algal blooms that can harm other species/reduce light to corals/seagrasses/algae; ...this leads to algal blooms that can lead to lower oxygen levels in the water (hypoxia/anoxic conditions);
removal of trees reduces water retention and increases risk of floods (overflow of freshwater) into the coastal/marine environment;	...the sudden high velocity of water could physically damage some species; ...sudden change in water salinity may kill some species;

(b)

agricultural activity.

[ 2 ]

identify problem [1]	its corresponding effect on marine ecosystems [1]
increase in nutrient/fertilizer/nitrate/phosphate pollution;	…this leads to eutrophication; ...this leads to algal blooms that can harm other species/reduce light to corals/seagrasses/algae; ...this leads to algal blooms that can lead to lower oxygen levels in the water (hypoxia/anoxic conditions);
increase in pesticide pollution;	…can harm/kill (non-target) organisms within the Coral Triangle;
increase in pollution from animal waste/manure/organic matter;	…that can block sunlight required by corals/seagrasses/algae; ...lower oxygen levels in the water;
overgrazing can increase soil erosion resulting in increased sedimentation in the reef/coastal environment;	…that can block sunlight required by corals/seagrasses/algae

[Maximum number: 1]

Figure 5: Dam storage, urban and agricultural water use, and rainfall in the Western Cape, South Africa, 2014–2018

Outline one reason for the variation in the volume of water stored in dams, as shown in Figure 5.

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