Optional:
Vocabulary
Students who demonstrate understanding can:
3-LS4-3. Construct an argument with evidence that in a particular habitat some organisms can survive well, some survive less well, and some cannot survive at all.
Tell, or remind, the students the question they are trying to answer: Could salmon survive well here? Then ask them how the insects in the stream might be important to salmon and at what stage of their lives. (Remind them that insects that are big enough to see with their naked eye are called “macro,” and because they have no spine, or vertebrae, they’re called “macroinvertebrates. These are the right size for salmon fry and juveniles to eat; adults don’t eat anything after they enter their spawning streams.)
Explain that they will be gathering evidence about not only whether there is some food for young salmon in the stream by sampling the macroinvertebrates that are part of the salmon food web. Certain species of macroinvertebrates that young salmon and other predators eat can only live where the water is not polluted and there’s plenty of dissolved oxygen. They are considered Indicator Species of “good” or “neutral” water quality required by salmon. Other macroinvertebrates are quite tolerant of pollution and require less oxygen. If students find those species in the stream, it means that the water quality is poor, likely too poor for salmon to find food and survive. Check to see if they understand the concept of an indicator. (One analogy would be a dipstick used to check the level of the oil in a car. The oil level won’t tell you about how every part of the car is doing, but cars don’t run well when they’re low on oil. A stream ecosystem doesn’t run well when it’s low on oxygen and certain types of macroinvertebrates that are the food for a diversity of predators.)
Indicators of Good Water Quality (Sensitive or Intolerant To Pollution)
Organisms easily killed, impaired or driven off by bad water quality include:
Indicators of neutral water quality (Somewhat Tolerant To Pollution)
Organisms with the ability to live under varying conditions. You may find them in good or poor quality water:
Indicators of poor water quality (Tolerant to Pollution):
Organisms capable of withstanding poor water quality.
Macroinvertebrates that can survive at a lower dissolved oxygen level because they can come to the surface to get oxygen through a breathing or "snorkel" tube or carry a bubble of air with them around their bodies or under their wings. Several species of macroinvertebrates are indicative of water systems with lower dissolved oxygen levels and include aquatic worms and leeches. Lower dissolved oxygen levels are often associated with polluted waters while higher levels indicate good quality water.
After the students have completed their observations and notes, have them return all the equipment and then RETURN THE INSECTS TO THE CREEK.
Ask students to share their results in terms of whether they found species that fit into each of the three categories for water quality. Remind them that salmon need a water quality index of good or neutral to survive well.
Draw their students’ attention to the question on page 13 of their Science Notebook:
Based on your results, could salmon survive well in our stream? Yes or No & Why?
If you have time, have a discussion about how they would answer the question. Ask students to explain their answers by providing evidence to answer the “Why?” If there isn’t enough time for this discussion during the field trip, tell them to write their answers when they’re back in their classroom.
This field trip activity was developed for the Anchorage School District Watershed Education Program. The field trip program supplements a 4th grade STEM Kit on the theme of Interdependence and a focus on Anchorage watersheds and salmon.
Macroinvertebrates are relatively easy to collect and observe. They are important indicators of water quality for salmon and stream food web that supports salmon because certain species are indicators of intolerant to organic pollution (sewage and other waste materials that require oxygen to decompose) and to other types of pollution that are also toxic to salmon.
Common macroinvertebrate species can be separated into three categories as indicators of water quality as good, neutral, or poor. Salmon can survive well where the water quality is good or neutral but not where the water quality is poor.
Prior Student Knowledge: Salmon and insect life cycles, food chains and webs
Possible Learner Misconceptions and Instructional Clarifications:
Learner Misconception: Students can tell if a stream is “clean” through observations of litter or debris in a stream.
Instructional Clarification: Pollution is defined as something introduced into the stream that doesn’t occur naturally. Even natural substances, however, such as heat or organic wastes that use up available oxygen during decomposition, can change the conditions for life in the stream. Many types of litter and debris are not toxic to salmon or other life in the stream, but substances that dissolve into the water, like pesticides that wash off lawns, can be very toxic. Sampling macroinvertebrates in the streams provides a way to determine how “clean” the water is in terms of pollutants that affect the survival of salmon and the food web they depend on in a way that visual observations of whether or not a stream “looks clean” can’t.
Learner Misconception: If students find only small numbers and a few species of macroinvertebrates that indicate good or neutral water quality, this is evidence the stream is likely polluted or poor quality.
Instructional Clarification: Using macroinvertebrate diversity and tolerances to pollution an indicator of stream health is highly dependent on the timing and location of sampling because macroinvertebrate populations fluctuate seasonally and each species has different habitat preferences in the stream. The presence of any tolerant and sensitive species an indicator they can survive under the current water quality conditions in the stream. Low abundance of food, however, could affect salmon survival or growth rates.
Engaging in Argument from Evidence Construct an argument with evidence. (3-LS4-3)
LS4.C: Adaptation
For any particular environment, some kinds of organisms survive well, some survive less well, and some cannot survive at all. (3-LS4-3)
Cause and Effect
Cause and effect relationships are routinely identified and can be used to explain change.