Materials for D.O. Team
Materials for Water Temperature Teams
Materials for pH Team
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.
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.
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.
Engaging in Argument from Evidence
Construct an argument from 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 used to explain change. (3-LS4-3)