This article follows on from Part I: Rivers Are Perfect for Teaching Sustainability. Here's Why!
The living things found in a river or stream depend largely on limiting factors (e.g. turbidity, temperature, pH level and dissolved oxygen) and the long-term environmental conditions. If water quality is poor due to human activity for instance, certain freshwater species simply won't be able to survive and reproduce, and so won't be present in the river habitat during ecological sampling. Many freshwater invertebrates (e.g. insects, mollusks and crustaceans) in particular, especially insects in the early part of their life cycles such as mayfly and dragonfly nymphs, are highly sensitive to pollution and human-related disturbances, and thus act as useful 'bio-indicators' for ecological health and overall water quality.
Collecting freshwater invertebrates (sometimes called 'river dipping') is an easy activity to do with learners of any age from teeny tots right up to university level. For older groups in particular, I recommend doing this at two (or more) different geographical locations - one upstream and one downstream of a big urban area to make an objective comparison of ecosystem health and develop a deeper understanding of the human impacts on life underwater.
Selecting Suitable Sampling Sites
First find suitable shallow river sections with safe, easy access. Make sure that the sampling site is no deeper than knee height but preferably no shallower than your ankles.
Assessing Potential Risks
Conduct a detailed risk assessment of the sampling site and be sure to consider risks relating to weather and flash flooding.
Make sure that participants wear appropriate footwear for river dipping which attach securely and come with toe protection. In colder regions and seasons you might need rubber boots or waders.
Gather Sampling Equipment and Resources
Groups of 3-4 students work best for this activity. Each group will need the following items to carry out this invertebrate study in a river or stream:
1 x pale plastic container
1 x D-frame net
1 x paint brush
1 x pair of tweezers
1 x magnifying glass
1 x laminated species identification charts (specific to your local freshwater ecology - see below for details)
Freshwater invertebrate identification charts are typically available from conservation or environmental education organizations in your home country or geographical region. In the US, try the North American Association for Environmental Education (NAAEE). In the UK, try the Field Studies Council (FSC).
Investigating Freshwater Invertebrates
Step 1: Elicit Prior Understanding
Finding out what your students already know about your topic is the first step in any experiential learning quest. Has anyone in your group ever been river or pond dipping before? Have they ever picked up pebbles in a stream looking for creepy crawlies?
The answers to these questions can provide you with a feel of the level to pitch your lesson at and it should help inform your approach for the next 6 steps of the 7E Instructional Model.
Step 2: Engage the Learner (the 'POW')
Engage learners by grabbing the attention of the group with what’s sometimes known as 'the POW'! This could be a related game, joke, anecdote, concentration activity, story or image designed to introduce the general theme of the activity and get students interested and focused on learning more.
Top POW!: Take some river water from your sampling sites in a see-through glass or container. Ask your students to look closely at it and smell it. Does it look clean? What does it smell like? Would anyone like to swim in it?
Step 3: Explore the Concept
Ask relevant questions and introduce specific terms and concepts linked to the activity in a creative and interesting way that inspires anticipation and participation.
Ask learners what they think lives under rocks and pebbles in rivers and streams. Understanding the difference between "vertebrates" and "invertebrates" is important for this activity. Give your group a glance of the invertebrate identification charts to generate a sense of intrigue about this underwater world of tiny critters.
How might humans disturb this underwater ecosystem of small creatures?
Step 4: Explain the Activity
Now your learners are primed and ready for the main activity! Explain the instructions and logistics of the task (outlined below). Teacher expectations, boundaries and student questions or concerns should also be outlined and addressed in this step.
Get students into groups of 3-4 individuals. Issue each group with a D-frame net, a pale colored plastic container, a paint brush and a pair of tweezers.
Younger learners could simply pick up small rocks and pebbles and look underneath for creepy crawlies (a common technique called 'stone washing').
Carefully use the paint brush and/or tweezers to transfer the invertebrates into the container provided making sure not to harm them in any way.
Step 5: Elaborate On the Concept
After adequate time for students to capture as many invertebrates as possible, it's time to get them to land and classify them. Identify the invertebrates to the lowest taxonomic level possible.
The invertebrate species present in a river or stream can be used as bio-indicators to infer water quality. That's because some invertebrate species can tolerate poor water quality (e.g. segmented worms, leeches etc.) while others cannot survive unless the water quality is good (e.g. mayfly and dragonfly nymphs). This has important implications for monitoring and restoring aquatic ecosystems. For more information click here.
Step 6: Evaluate Learning Experience
This is the post activity wrap up or debriefing session. It’s the time to draw out conclusions, engage in discussion, gather feedback and guide students to join the dots and relate what they’ve learned to their own lives (or the "real world"). Ask questions such as:
- Where did you find the invertebrates? Where were the best places to look for them?
- Were you surprised how many different invertebrate species you found?
- Based on the results, do you think the water in your river or stream is clean or polluted? Why?
Step 7: Extend to Other Contexts
- How could you monitor the water quality and ecological health of your local river?
- Where does water pollution come from?
- How might you improve the water quality and ecological health of a river or stream?
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