Advanced vs. Beginning Students
The Student Instructions are written for students in introductory ecology courses with little spreadsheet experience. More advanced students can likely work with the student Excel file alone after a discussion about questions that can be addressed with the data. The Overview is also appropriate for these students; there is some additional information in the Student Instructions that might be useful as well. The 2004 Ecology paper described below would be a good paper for advanced student to read; a PDF of this paper is also included.
The time required for this Data Set depends on your students' expertise with Excel, including making bar graphs on Excel and their experience with data presentation and interpretation. The Student Instructions begin with a fair amount of background text before the detailed description of how to make the figures. To save time, ask students to read this background description ahead of time for homework.
The Overview provides good background for students, but the section of the Student Instructions titled The Kuparuk River Experiment will probably be enough of an overview with some added introduction by you. For the group work described below, you will need a computer for each three to four students (make sure the students rotate so that one student is not doing all of the work on the Excel file).
Working with the Excel File:
The Student Instructions include step-by-step procedures for making bar graphs with standard error bars. If your students are Excel novices, give them an Excel tutorial ahead of time (e.g., in a prior lab). The Resource section includes online tutorials. Many questions will arise about making graphs; since you cannot be everywhere at once, an older student can be an enormous help in this situation. The Instructions include suggestions for making simple and clear black-and-white figures; it is a good idea for you to explain this briefly.
What To Do
The Student Instructions take the students through creation of five bar graphs: Epilithic Chlorophyll, Moss, Mayflies, Fish, Temperature, and Flow. Below are some specific ideas for follow-up and different approaches:
- Divide students into groups of three or four. Instruct each group to make five same-sized figures and stack them vertically, either on the Excel file or as printed out graphs. If they work efficiently and are familiar with Excel and figure making, they should be able to do this in a 3 hour lab. Ask groups to briefly write their data interpretation, analysis, and conclusions (200-300 words) plus major questions they have. Groups can do this as homework which they will hand in. In the next session, groups can report their findings, interpretations, and questions.
- Have students work in groups as above but ask each student to write their own data description, interpretation, and questions for homework. Have groups report out as above.
- Make the first figure yourself so students can see what you are looking for; then follow either set of ideas above.
- Use the questions below as the basis for a discussion or for a homework question or two.
The flow and temperature data do not necessarily explain the biological data, but are of course potentially useful information. You will probably need to make this point.
The table below summarizes likely conclusions students will make about this Data Set and associated ecological concepts. The “misconception” column identifies common incorrect ideas your students might have related to each conclusion. It is important to be aware of students’ misconceptions because these naïve ideas can interfere with students’ learning new concepts (TIEE Glossary: Misconceptions). You can expose student misconceptions in a variety of ways — through essay or short answer written questions, class discussion, or direct questions.
|P stimulates algal growth; P limits algal growth at first.
||limiting factor, bottom-up effect, nutrient enrichment
||Primary producers won’t respond to nutrients because it is too cold.
|Cascade effect of nutrient addition on mayflies and grayling.
||cascade effect, community structure
||This reinforces the misconception of the simple linear “food chain.”
|Nutrient addition results in appearance of new moss.
||The simple addition of P can’t change community structure this much.
|Moss shades algae.
||Shading only occurs in forests with trees.
|After initial increase, algal production decreases due to grazing by mayflies.
||Primary production is limited by nutrients or grazers but not by an interaction of the two.
|Large interannual variation in all parameters.
||Such variation indicates something “wrong” with the system.
Data Interpretation and useful information
A 2004 paper by Slavik et al. published in Ecology titled "Long-term responses of the Kuparuk River ecosystem to phosphorus fertilization" (Vol. 85, No. 4, pp. 939–954) includes some of these data plus much more. Several points in this paper provide helpful additional information:
- In addition to nutrient addition from precipitation and local anthropogenic activity, global warming may result in permafrost thaw and increased on organic matter turnover and nutrient availability in the tundra. This is a nice example of unexpected effects of global warming.
- Epilithic algae were scrubbed off of randomly selected rocks with a steel brush. Insects were also removed from rocks and counted. Fish growth was measured on individually tagged fish.
- Statistical tests were paired t-tests and linear regressions.
- River temperature and flow varied with radiation input and precipitation and inter-annual differences in weather.
- The bryophyte Hygrohypnum spp., the primary moss species, was not seen the river before 1990. In later years it formed a continuous carpet of filamentous moss on parts of the river bottom in the fertilized reach. This is clearly had a large impact. Hygrohypnum replaced epilithic algae as the dominant primary producer; about 80% of NPP was driven by moss and 20% by algae (which can grow on the moss). Production of epiphytic algae growing on the moss was high. The animal benthic community composition was also altered; Chironomids (midges) changed most — from low numbers to about 40,000/m2 in ’95-’98.
- The obvious decrease in epilithic algae in the fertilized reach after 1989 is due to shading and abrasian by the moss and increased grazing pressure.
- Although the increase in moss cover impacted insects and microalgae, there is no measurable effect of moss cover increase on young or adult fish. Although Baetis abundance varied, Brachycentrus densities remained high in the fertilized reach and the large mayfly Ephemerella steadily increased in the fertilized reach (both were about 10% of Baetis biomass however). Fish may be impacted in the future as further moss growth inhibits insect drift.
- Like other stream fertilization studies, epilithic algae production in the Kuparuk River appears to have been first limited by nutrients and later by invertebrate grazing. In contrast to other studies, this changed after 8-10 years when mosses became the dominant cover in fertilized riffles.
- Slavik et al. conclude by saying "In the Kuparuk River, the impact of fertilization was more complex than a positive increase in production from one trophic level to the next. We showed how the ecosystem structure changed over time in response to nutrient enrichment. This observation emphasizes the need for long-term, whole-stream studies if we expect to predict stream response to chronic perturbation."
- * Reference Available as PDF (407 KB)
- Slavik, K., Peterson, B. J., Deegan, L. A., Bowden, W. B., Hershey, A. E., Hobbie, J. E. 2004. Long-term responses of the Kuparuk River ecosystem to phosphorus fertilization. Ecology: Vol. 85, No. 4, pp. 939–954.
Questions for Discussion
- Explain the concept of “limiting nutrients.” Why are ecologists interested in this concept?
- Why are N and P the major limiting nutrients in a wide range of habitats (not just rivers)?
- How is this research relevant to less pristine places? What are major sources of nutrient contamination elsewhere in the US?
- The chlorophyll a concentrations decrease noticeably from 1992 on and the Baetis densities are lower starting in 1989. What is the most likely explanation for these changes? Why do you think that the scientists started measuring moss cover starting in 1992 and not before that?
- Based on these data, describe what the bottom of the river in the fertilized section would look like before 1989 and after 1992? In other words, if you were snorkeling down the river what would you see on the bottom before 1989 and after 1992?
- Even though grayling eat mayflies (Baetis), years with low mayfly density don’t consistently match years with low fish biomass. What are several reasons why this might be so?
- There is considerable year-to-year variation in the fish biomass. Does this indicate an environmental problem of some sort? Why might this be so? What information would help you understand this variation better? Why does this degree of variation between years make ecological research often so difficult?
- What is the value of a long-term data set like this one? What conclusions would have been different with only a few years of data?