- Explain to students that they will talk about water’s ability to clean itself:
- What is the self-purification capacity of a river? (River’s ability to clean itself)
- How can water in a river clean itself? (There are various natural processes related to self-purification capacity: biological processes through food chains, physical processes, such as filtration, and chemical processes, such as oxidation).
- What kind of natural biological processes are related to the self-purification capacity of a river? (Organic pollution, such as sewage, are nutrients for microorganisms, which transform dead organic matter into inorganic matter that are nutrients for plants. Therefore, the growth of plants and algae is intensified, which also intensifies a reproduction of various animal species, since they have plenty of food. Of course, this is possible only if the water is not too much polluted).
- How can one see that a river has a high self-purification capacity? (The most important measures to define a high degree of river’s ability to clean itself are: (1) well-aerated water with high level of oxygen that microorganisms in the river need for breathing, and (2) wide riparian zone with plants and active connection to other wetlands)
- Take a field trip to the nearest rivers and streams. Observe the river, its banks and its riverbed. Discuss the river’s ability to clean itself. Then fill out Worksheet “Self-purification capacity of a river”.
- Make several field trips to different parts of a river and its tributaries or find another river or stream. For each of them, fill out the Worksheet “Self-purification capacity of a river”. Make a comparison of all of them. What did you learn?
Activity adapted from Vahtar, M., Zdešar, M., Kompare, B., Urbanc-Berčič, O., (2005): Kako se reka očisti? – Priročnik za učitelje 3. Book collection Vodni detektiv. ICRO Domžale, Domžale, Slovenia, p.38.