Geochemical Clues and Biological Insights: Characterizing the Importance of Salmon in Northwest Streams

Kena Fox-Dobbs, University of Puget Sound
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This page first made public: Oct 9, 2012


Salmon streams in the Northwest are local field resources that can be used to demonstrate biogeochemical connectivity. In this series of exercises students become familiar with geochemical tools used to track the presence of marine (salmon) derived nutrients in the terrestrial and freshwater ecosystems of creeks where salmon spawn. They then use a reconnaiscence fieldtrip to design project proposals to charaterize the importance of salmon in a local creek. Students present their research proposals to a mock city council in response to downstream development pressure. Finally, students are given a take-home reading and questions that address the pros and cons of hatchery raised salmon in the Northwest.

Learning Goals

  • Part 1: Familiarity with the salmon marine-terrestrial connection, and how geochemistry reveals this pattern of nutrient flow. A chance to work through terms and concepts that will appear in other parts of the activity. Concepts: marine-terrestrial spatial subsidies, nutrient cycles, salmon biology
  • Part 2: Role reversal - students are asked to design their own field-based research project - they must decide what data to collect, how to collect it, and what are the expected results. Projects connect the delivery of salmon-derived nutrients to measurable biotic and abiotic parameters within a creek ecosystem. Concepts: research design, communicating science to a broad audience
  • Part 3: Reflect on the reality of hatchery-raised salmon in the context of long-term sustainability of healthy salmon populations in South Puget Sound. Respond to specific prompts based upon reading, and independent, additional research on the topic. Concepts: sustainability and long-term ecosystem health

Context for Use

Lower to mid-level general environmental science or environmental geology course.

Timing in the course: Latter half of the course, ideally after students have experience with local flora/fauna, freshwater and riparian ecosystems, basics of biogeochemistry (specifically nutrient flow)

Classtime required: Takes one full 3-hour lab section (fieldtrip and project description), and beginning of following week lab section (~1 hr project presentations)

Take-home: Two take-home reading assignments bookend the activity (one complete before fieldtrip, and one after presentations)

Description and Teaching Materials

This activity includes a combination of independent reading and response, group discussion, partner fieldwork, and presentation of prepared proposal. I schedule it in the latter portion of the course - at which point students have been introduced to local plants, animals, and the basics of water and soil chemistry via labs and fieldtrips. The Part 1 reading (Schindler et al. 2003) provides an excellent introduction into the topic of salmon in Northwest ecosystems. I use a ~20 min discussion (largely question and answer) of the paper in lab before the fieldtrip to ensure that all students have a solid grasp on the basics of salmon biology, dynamics of marine-terrestrial nutrient subsidies, and how biogeochemistry can be used to track and identify this subsidy. The Part 2 fieldtrip gives students an opportunity to generate a question, design a scientific study to address that question, and then propose their study to a funding agency. Students have had ample experience collecting data to test hypotheses in previous labs and fieldtrips. In order to design a meaningful study for their proposal, the students must integrate knowledge gained throughout the course, and the posted scholarly articles. The proposal presentations are a chance for them to work on 'selling an idea', and packaging their plans and thoughts into a clear, concise, and convincing deliverable - a transferable skill that is valuable across disciplines. Finally, the Part 3 optional take-home exercise (reading and questions) asks that students carefully consider the pros and cons of hatchery-raised salmon in the Northwest - a debatable issue from a number of environmental perspectives.

The logistics of this activity can easily be modified to fit a specific course schedule. I assign the Part 1 reading in the first week as a take-home exercise, then lead a short discussion on the paper at the beginning of a 3-hour lab section. I then introduce the Part 2 proposal project, and we proceed directly to the field site (creek or stream) for the reconnaissance activity. I let the student pairs decide on which variables and ecosystem components they want to study once we are at the site and they have had the chance to look around. The Part 2 presentations happen at the beginning of lab section the following week - I give them 8 minutes max per pair (no questions - proposal is a stand alone document). Finally, I assign the hatchery-debate reading at the end of this lab section, and ask that it be completed the following (third) week.

PART 3 READING AND QUESTIONS (Acrobat (PDF) 224kB Aug11 11)

Teaching Notes and Tips

Some students struggle at least initially with the unstructured field component of the project, in terms of idea development and sampling design. Understanding how/what/where/when to pursue a scientific question is part of the learning process, and most pairs eventually work their way around to an interesting and achievable project idea. I generally counsel them on methodological details, once they have established the basic sampling framework.

I encourage the students to make their presentations aesthetically pleasing, and give them complete creative license. One skill that I emphasize in this project is graphic interpretation of concepts and data.


Part 1 - I ask students to answer questions from the paper, and/or pose questions to their peers. I informally keep track of who participates, and has meaningful contributions.

Part 2 - The presentations are judged by the class and me (we are the city council), and the students vote at the end of lab on which proposal should be funded - this pair gets a small reward (usually extra credit points). I then use a grading rubric to assess each proposal - general categories are background and introduction, proposed work, expected results, and concluding remarks.

Part 3 - The questions associated with the reading are straightforward, and I grade them accordingly.

References and Resources

PART 1: Schindler, D.E. et al. 2003. Pacific salmon and the ecology of coastal ecosystems. Frontiers in Ecology and the Environment. 1: 31-37.

PART 2 Supplemental papers:
Bilby, R.E. et al. 2003. Transfer of nutrients from spawning salmon to riparian vegetation in Western Washington. Transactions of the American Fisheries Society. 132:733-745,
Gende, S.M. et al. 2002. Pacific Salmon in aquatic and terrestrial ecosystems. BioScience. 52: 917-928.
Helfield, J.M and Naiman, R.J. 2001. Effects of salmon-derived nitrogen on riparian forest growth and implications for stream productivity. Ecology, 82: 2403-2409.
Reimchen, T.E. et al. 2003. Isotopic evidence for enrichment of salmon-derived nutrients in vegetation, soil, and insects in riparian zones in coastal British Columbia. American Fisheries Society Symposium. 34: 59-70.