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To discuss the role of rivers in nature

Module by: Siyavula Uploaders. E-mail the author

NATURAL SCIENCES

The earth and beyond

Rivers and their catchment areas

EDUCATOR SECTION

Memorandum

Assignment 10:

1. Assignment clear in module. Assignment can lead to an exhibition of collected samples, photos and notebooks.

Follow-up visit for cleaning up is recommended.

Assignment 11:

Listen at least to Wendy Oldfield's song "Acid Rain". Learners take the lead and answer the following question:

"Which environmental issues are addressed and what solutions do we have for the problems?"

Assignment 12:

Help the learners with a framework, e.g.

  • The river as an environment wherein plants and animals can live
  • light
  • visibility
  • oxygen
  • no poison
  • protection against temperature changes
  • Life in a river (above-mentioned environment)
  • types of plants
  • types of animals
  • mutual dependence of plants and animals

LEANER SECTION

Content

ACTIVITY: To discuss the role of rivers in nature [LO 1.1, LO 1.2]

IN THE LEARNING UNIT DEALING WITH FOSSILS WE SAW THAT THE DRY KAROO USED TO BE A MARSHLAND THAT COVERED APPROXIMATELY THREE-QUARTERS OF THE SURFACE AREA OF SOUTH AFRICA. IT IS CLEAR THAT FRESH WATER HAS PLAYED AN IMPORTANT ROLE IN THE LIVES OF PLANTS AND ANIMALS AS WELL AS PEOPLE FOR MILLIONS OF YEARS.

A RIVER IS MORE THAN WATER!

  • Rain absorbs carbon dioxide and oxygen when it travels through the atmosphere. While it travels down a mountain slope, tiny plant particles from the vegetation are also caught up in it. In this way water takes up sufficient soluble nutrients to sustain animals that live in water, as well as plants.
  • Rivers are generally endangered. The fact that people need water for survival, places a great deal of pressure on rivers to meet this need and to carry away waste material.
  • Rivers are not drainage conduits for the removal of waste: they are complex systems.
  • Different plants and animals exist along the different reaches of a river. These organisms utilise the natural materials contained in the river in the natural process of their lives. This ensures that the water in the river is purified continually. Rivers are also able to absorb much pollution.
  • This unique characteristic of rivers is largely destroyed by excessive pollution, damming up of water and canalisation.
  • The Department of Water Affairs and Forestry acknowledges that rivers are living systems that should be conserved. Healthy rivers are attractive features that provide us with water and make it possible to save money. The capacity for self-purification that is observed in rivers can make it possible to save thousands of rand that would have to be spent on building purification projects, provided that we protect this capacity.
  • Rivers need people to protect their interests and to fight for them.

River catchment areas

  • The catchment area of a river, is the area between the mountain peaks where the river has its source and the coast where the river mouth is. The area that is drained by a single river forms its catchment area.
  • The characteristic feature of any river is determined by the activities (human and natural) that take place in the catchment area. All the water that is precipitated as snow, dew, mist and rain in any particular catchment area flows together in a river. Only a very small quantity of this water is lost through evaporation.

Figure 1
Figure 1 (graphics1.png)

A catchment area

  • The sizes of catchment areas vary greatly. Most of South Africa's large storage dams get their water from such mountain catchment areas.
Figure 2
Figure 2 (graphics2.png)

There is a close relationship between soil conservation and the use of water from catchment areas. Dense vegetation prevents soil erosion to a large extent. Where the vegetation is removed, especially on steep slopes, rainwater flows fast and the danger that a flash flood can occur is increased. This happened in 1981, when a flood caused serious damage to Laingsburg. When fertile topsoil is removed, storage dams and river mouths become silted up as the soil is deposited in these places.

The fynbos kingdom, which is unique to the Western Cape, is threatened by urbanisation, planting of forests and deforestation in the catchment areas. It is important to protect catchment areas. Most of the plants in the fynbos kingdom are small, hardy and spiky to reduce loss of water during the dry summer months. Some well-known plants from this kingdom are the Ericas, Proteas and the Restios, which are grass-like members of the reed family.

  • Invader plants like pine trees have been planted in many places in the catchment areas. Amongst other things, pine trees, together with hakea and Australian acacia species, disturb the natural balance of the river ecosystems of the Western Cape.

FACTORS THAT AFFECT THE QUALITY OF THE WATER IN THE RIVERS.

  • All of us must share the responsibility of using water resources responsibly. Every person can make a contribution by becoming involved in our own communities. In this way we can also assist governing bodies and make it easier for them to function.
  • All of us need inland water for personal use and we must remember that overpopulation and mismanagement of our limited resources is not a new problem. The Greek philosopher Plato was already complaining about environmental degradation two thousand years ago.
  • POLLUTION refers to any substance that has a harmful effect on the natural environment. The pollutants might be in the atmosphere, or may occur in water that flows through any part of the catchment area. Pollutants may be very difficult to identify and control.
  • ARTIFICIAL FERTILISERS are used by farmers to ensure bigger harvests. These nutrients are washed away in rivers. This encourages the growth of algae, which reduces the amount of oxygen in the water.
  • RUBBISH like tins and plastic bags block up small streams.
  • SEWERAGE water is rich in organic substances and nutrients that also reduce oxygen levels in the water during decomposition. This destroys many species of life that occur in rivers.
  • HEAT POLLUTION is caused by pumping warm water into rivers and lakes.
  • TOXIC CHEMICALS and heavy metals build up in living tissue and increase over time. This inevitably leads to the death of numbers of plants and animals.
  • SOLID WASTE MATERIALS like soil particles from eroded land, mining activities, coal, dust and builder's rubble also flow along down streams. This suffocates water creatures and their eggs, block up the gills of fish and buries food sources.
  • SALINISATION indicates an increase of natural minerals in water or in the soil. Fresh water becomes saltier when minerals like sodium, potassium, magnesium, chloride, etc. build up in the water because of evaporation. Global calculations show that one million hectares of soil become unsuitable for agricultural use annually because of salinisation.
  • Rivers do have the capacity to be restored, but the degree of pollution plays an important role in the extent to which complete restoration is possible.

Figure 3
Figure 3 (graphics3.png)

“Self-restoration” of a river

Table 1
z Problems Serious problems On the way to recovery Clear water
Much lifeMuch oxygenNo smellClean water Fungi developLittle oxygenSlightly smellyGrey or dark water Organisms that do not need oxygenNo oxygenA smell of rotten eggsBlack water A little sign of lifeA little oxygenSlightly smellyWater becoming clearer Much lifeSufficient oxygenNo smellClear water

  • A river can regain its original unpolluted condition provided that it is not diverted into a canal and that interference by people is not too serious.

ASSIGNMENT 10

Go for a walk along a river. What do you observe? Collect samples of shells, feathers, plants, etc. from along the route, but take care to avoid doing damage. Find out whether some parts of the river are more polluted than other parts and whether there are parts that have been restored after being exposed to pollution.

  • Write notes in a notebook, take photographs and present your findings to the class.

If you identify an area where the levels of pollution are high, you could also return to it and launch a cleaning operation.

Figure 4
Figure 4 (graphics4.png)

ASSIGNMENT 11

Listen to the song “Acid Rain” by Wendy Oldfield. There are more songs that have messages concerning the environment. Draw up a list of such songs and have a class discussion on the issues that are addressed in them.

ASSIGNMENT 12

  • Write a composition (280 words) on life in a polluted river.

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Assessment

Learning Outcome 1:The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

Assessment Standard 1.1: We know this when the learnerplans investigations;

Assessment Standard 1.2: We know this when the learnerconducts investigations and collects data.

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