Task developed by Mandy Anderson, Knox Grammar, 2013
National da Vinci
Decathlon
Celebrating the Academic Gifts
of Australian Youth – Year 9/10
Science
Session 2
“The knowledge of all things is possible” Leonardo da Vinci.
Team Number
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Task developed by Mandy Anderson, Knox Grammar, 2013
The Murray-Darling River Basin:
Differing Perspectives on Water Use
The Murray-Darling River Basin (MDRB) covers over one million
square kilometres of eastern Australia. More than 2 million people
live in the basin, with an additional 1.3 million relying on its water
resources, including the city of Adelaide. The MDRB is Australia’s
most important agricultural area, generating 39% of Australia’s
agriculture income. In addition, the MDRB harbours many key
ecosystems such as wetlands, blue gum forest, floodplains, and
estuaries.
Over the past 100 years, so much water has been removed from the
rivers of the MDRB that the health of this vast river system is
1http://commons.wikimedia.org/wiki/File:Murraythreatened, putting at risk all the ecosystems and industry
catchment-map_MJC02.png
dependent upon it.
Therefore the Federal Government enacted a water management plan which came into effect
on October 20, 2012.
When the Murray-Darling Basin Management Plan was released there was a great deal of
public debate, with many different groups bringing different perspectives to the table.
1. With reference to the cartoon,
identify the different voices in the
Murray-Darling Water debate. For
each of the groups, state their main
priority in the management of the
MDRB.
(6 marks)
2http://politicalcartoonsaustralia.com/tag/burke/
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Task developed by Mandy Anderson, Knox Grammar, 2013
Soil Salinity
Much of the basin has been heavily impacted by high salt concentrations in the soil. These
salts have accumulated through 2 processes – dryland salinity and irrigation salinity.
2. Use the diagrams below to describe the processes by which soil becomes saline.
(4 marks)
Dryland Salinity
3http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/lwm_salinity_management_dryland
Irrigation Salinity
4http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/lwm_salinity_management_irrigation
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Task developed by Mandy Anderson, Knox Grammar, 2013
Water Quality
The quality of the water throughout the river system is affected by the soil salinity. The salt
leaches from the soil into the rivers and passes throughout the system downstream. It is
important that the salinity levels in the river are carefully monitored to determine whether the
water is suitable for use in agriculture, as drinking water, and to gauge the ongoing health of
riparian ecosystems.
Qualitative test: The presence of salt can be determined qualitatively by adding silver
nitrate to the water sample. If salt is present, a white precipitate of silver chloride will be
formed.
3. What is the chemical name of the most common salt found in the environment?
(1 mark)
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4. Write a balanced chemical equation for this qualitative test.
(3 marks)
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Quantitative test: A quantitative version of this same test can be conducted by adding
silver nitrate to a known mass of water and weighing the precipitate which is formed.
5. An excess of silver nitrate was added to a 5kg sample of river water. 0.235g of
precipitate was formed. Calculate the salt concentration of the water sample.
Note: the mass of one mole of silver chloride is 143.5g
The mass of one mole of sodium chloride is 58.44g
(4 marks)
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Task developed by Mandy Anderson, Knox Grammar, 2013
6. Taking water from the river system and using it for irrigation has greatly increased
soil salinity in the MDRB. Analyse the arguments for and against reducing irrigation
in the MRDB.
(8 mark)
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Task developed by Mandy Anderson, Knox Grammar, 2013
Salinity and Ecosystems
The yabby is sensitive to environmental conditions. It
is an indicator species in the MDRB. Environmental
scientists use the health of the yabby population as
another means of determining levels of water
pollution, including salinity.
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http://www.flickr.com/photos/christop/2440409492/in/photo
stream/
7. Describe how scientists can use indicator species such as the yabby to monitor water
quality.
(3 marks)
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8. Use the following description to draw a food web for the organisms in a waterhole of
the MDRB.
(3 marks)
Algae is eaten by both snails and shrimp which are both consumed by the
yellowbelly fish. The shrimp is also eaten by the gudgeon which in turn is
eaten by the yellowbelly. Yabbies eat gudgeon and are consumed by the
yellowbelly. Plankton is eaten by smelt.
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Task developed by Mandy Anderson, Knox Grammar, 2013
9. Describe the effect upon the snail population if most of the yabbies die out due to poor
water quality. Justify your answer.
(2 marks)
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10. The Murray cod is a large carnivorous fish which has almost disappeared from the
MDRB due to overfishing and habitat destruction. However, environmental scientists
are beginning to reintroduce the Murray cod into the river system. Describe how this
reintroduction would impact the other species in the waterhole food web drawn above.
(4 marks)
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END OF TASK
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