Trees and watertables
This activity provides opportunities for students to analyse the importance of tree in the landscape, the long-term effects of overclearing, and how science can contribute to community understanding of problems and land management practices. Students investigate the effects of a rising watertable on the soil and plants in an area.
Life and Living
5.3 Students evaluate consequences of interactions which occur between the living and non-living parts of environments.
- 6 x 250 mL beakers
- common salt (sodium chloride)
- 4 tomato seedlings
- Resource sheet 5—Trees and watertables (PDF, 89K)*
This activity starts with some simple activities that illustrate two aspects of watertable management. The first activity shows how trees can lower the level of watertables by transpiration. The second activity shows how salt below the earth can be brought to the surface by a rising watertable. Both activities encourage students to consider the consequences of management strategies. Teacher guidance will be required to enable students to make the link between the activity and its implications for watertables (see Current scientific conceptions in the 'Background' section).
A number of different plants would be suitable for this activity. It is important that the seedlings are healthy, well grown and about the same size. Students will need to be encouraged to carefully preserve as many roots as possible when removing the soil from around them.
Strategies for approaching experimental design are discussed in the sourcebook. A planning session is required to allow students to choose a problem, to design an initial experiment and to list the equipment required. Sufficient time should be given to laboratory assistants to prepare the equipment. If time allows, it is helpful for students to evaluate their initial experiments and to improve upon their original design.
Time: 30 minutes in one lesson; 30 minutes in a follow-up lesson. Open-ended investigations can take up to a week.
- Exploring phenomena
- Designing and performing experiments
Guided by the teacher, students brainstorm ideas about the effects that trees can have in a valley, and about land use practices. Questions could include:
- How much water do trees need?
- From where do trees get their water?
- What might happen to the watertable if trees are cleared?
- What reasons might people (past or present) have for clearing trees?
- What other environmental benefits do trees provide?
- How can science contribute to community understanding of these issues and improving land management practices?
Students then carry out experiments to develop a better understanding of the causes of soil salinity.
First, they set up five beakers, each containing 250 mL of water. They place one tomato seedling in each of four beakers. After 3 days (or an appropriate time for the conditions), the students remove the tomato seedlings and measure the amounts of water left in the beakers. Students calculate the difference between the remaining amounts of water in each beaker and explain the difference.
In the second experiment, students place about a millimetre of salt in the bottom of a 250 mL beaker and two-thirds fill the beaker with soil. They then fill the beaker with water to the level of the soil and leave it to evaporate. After an appropriate period of time, they make observations about the location of the salt in the beaker and draw conclusions about the role that this phenomenon may play in a catchment.
Working in groups, students discuss the questions at the end of Resource Sheet 5. Different groups can be selected to provide feedback to the whole class on particular questions.
Groups of students design experiments to test the effects of salty water on plants. Ideas for experiments could include:
- comparing the effect of salinity on a range of seedlings to identify those plants that may be more salt-tolerant
- testing the effect of different salt concentrations on the same type of seedlings.
Gathering information about student learning
Sources of information could include:
- discussion of questions
- written responses to questions.
* Requires Adobe Reader
Last updated 2 August 2010