- White Bucket (may need a rope unless you can submerge it in the water column where students can stand in the stream)
- Laminated poster “Salmon Habitat Needs:”
- Water temperature Best: 10-15o C (50-60o F) (salmon can overwinter in water temperatures close to freezing 0oC/32oF)
pH 6.5 to 8.5 (7.5 is ideal)
- Dissolved Oxygen Greater than 7 parts per million or ppm (mg/L)
Materials for D.O. Team
- Safety glasses
- Dissolved Oxygen Test Kit
- Disposal container for used vials
Materials for Water Temperature Teams
- Thermometer (Centigrade preferred) on a with string to lower it into the water
Materials for pH Team
- Safety Goggles
- pH Paper, a pH test kit or a pH meter
NGSS Performance Expectation
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.
- salmon can only survive well if a particular range of conditions exists for the pH and temperature of the water and the concentration of dissolved oxygen in the water.
- sample a stream and measure water quality conditions: pH, water temperature, the concentration of dissolved oxygen.
- compare their results to the range of conditions in which salmon survive well.
- argue from evidence whether salmon can survive well under the conditions they measured.
- Print out the protocols for water quality sampling and testing for each of these parameters and review them.
(The protocols for measuring pH using PH paper and for measuring the concentration of dissolved oxygen using a CHEM-ets® kit that provides a colorimetric measurement after two minutes. If you use different methods, follow those directions.)
- Create posters
- Assemble all of the materials for teams taking into consideration each team will make three measurements of each water quality parameter.
- Prepare Science Notebook page (See example.)
Note: This activity can be one station during a stream field trip to collect evidence that salmon could or could not survive well in a particular stream reach. Other stations could include Not Too Fast, Not Too Slow (measurement of velocity) and Macro-Mayhem (collecting and identifying stream macroinvertebrates as indicators of water quality.
- Divide the group into three groups and assign them the measurements of pH, dissolved oxygen, and water temperature. Each group should have at least 3 students. Explain that the pH and water temperature groups are going to make their measurement three times in three different samples of the stream.
Ask each group to assign one person as the recorder of the measurements the group makes in their science notebook.
- Demonstrate how to take a water sample using the bucket (see protocol).
- Demonstrate how to measure temperature and pH (see protocols)
- Describe the procedure for measuring dissolved oxygen, showing each element of the test kit. (see protocol)
- Give the protocols to the groups and assist them in carrying them out.
- Bring the groups back together. If there is time, have someone in each group describe what they did. Have each recorder read out their data and average values while the rest of the group writes them in their science notebooks.
- Show the group the laminated poster with the range of conditions that are best for the survival of salmon. Ask them to put a star beside their average temperature, average pH, and their dissolved oxygen (D.O.) concentration reading if they are within the range for that element of the stream habitat.
- Discuss what types of activities by people might cause higher water temperatures and thus, lower D.O. (remove trees and shrubs close to the stream that provide shade during summer) or lower or higher pH levels [dumping acidic things (such as batteries or soda) or basic things (such as bleach) into the water or letting it run off from lawns] (Fertilizer run-off from lawns adds organic matter which use up the oxygen in streams to break down.)
Draw the students’ attention to the question in their Science Notebook:
Based on your results, could salmon survive well in our stream? Yes or No & Why?
If you have time on the field trip, have a discussion about how they would answer this 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.
Significance of Stream Water Temperature for Salmon
Temperature is an easy measurement to make. It is, however, very important because it allows scientists to better understand other measurements such as dissolved oxygen and pH.
Water temperature is also important because warm water can be fatal for sensitive species, such as trout or salmon, which require cold, oxygen-rich conditions. Warmer water tends to have lower levels of dissolved oxygen (See discussion below.)
Importance of Dissolved Oxygen in a Stream for Salmon
Just like animals that live on land, animals that live in water need molecular oxygen to breathe. However, there is much more oxygen available in the atmosphere for animal respiration than in water. Roughly, two out of ten air molecules are molecular oxygen. In water, however, the ratio of oxygen molecules to every million water molecules may be as low as five or six. The amount of dissolved oxygen in the water determines what can live there. Some animals, like salmon or mayfly larvae, require higher oxygen levels than other animals like catfish or leeches.
We call the amount of dissolved oxygen the water will hold (under specific conditions) the solubility of dissolved oxygen. Factors affecting the solubility of dissolved oxygen include water temperature, atmospheric pressure, and salinity. Cold water can dissolve more oxygen than warm water. For example, at 25˚ C, dissolved oxygen solubility is 8.3 mg/L, whereas at 4˚ C the solubility is 13.1 mg/L. As temperature goes up, water releases some of its oxygen into the air. Water can hold less dissolved oxygen at higher elevations because there is less pressure. The solubility of dissolved oxygen also decreases as salinity increases.
Dissolved oxygen can be added to water by plants during photosynthesis, through diffusion from the atmosphere, or by aeration. Aeration occurs when water is mixed with air. Such mixing occurs in waves, riffles, and waterfalls. The amount of dissolved oxygen also is affected by what lives in the water. Just as photosynthesis by terrestrial plants adds oxygen to the air we breathe, photosynthesis by aquatic plants contributes dissolved oxygen to the water. Water may become supersaturated, meaning that the dissolved oxygen levels are greater than its solubility. The extra dissolved oxygen would then eventually be released back into the air or be removed through respiration.
Importance of Stream pH
pH measures the acid content of water. The pH scale (measured from 0.0 – 14.0 pH units) is a logarithmic scale of the hydrogen ion concentration. Solutions with a pH greater than 7.0 are classified as basic and ones with a pH less than 7.0 are classified as acidic. A pH of 7.0 is neutral. Each pH unit is ten times greater in hydrogen ion concentration than the next. For example, a liquid with a pH of 4.0 has 10 times the hydrogen ion concentration of a liquid with a pH 5.0. A pH of 3.0 contains 100 times the acid content of pH 5.0. For this reason, a small change in pH could have significant effects on water quality.
Most lakes and streams have pH values that range between 6.5 and 8.5. Pure water that is not in contact with air has a neutral pH value of 7.0.
pH affects most chemical and biological processes in water. pH has a strong influence on what can live in the water; aquatic organisms have certain pH ranges they prefer or require. Salamanders, frogs and other amphibian life, as well as many macroinvertebrates, are particularly sensitive to extreme pH levels. Most insects, amphibians and fish are absent in water bodies with pH below 4.0 or above 10.0. (Source: GLOBE Program website)
Prior Student Knowledge: If students go to a stream velocity station before this one, they may already have discussed how oxygen is mixed into the water through aeration when the stream is moving at relatively high velocity.
Possible Learner Misconceptions and Instructional Clarifications:
Learner Misconception: Students may over-estimate what a single sample can tell anyone about conditions in the stream which are dynamic on time scales of days and seasons
Instructional Clarification: Students are sampling a single place in the stream at a particular time. The replication of samples three times and averaging of data does help even out the sampling error but doesn’t greatly increase the time-limited nature of the sampling.
Components of Next Generation Science Standards Addressed
Engaging in Argument from Evidence
Construct an argument from evidence. (3-LS4-3)
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 used to explain change. (3-LS4-3)