Freeing the Elwha: Science Unit 2

Ecological Processes and Salmon Natural History

Lesson 7: Aspect and Soil Moisture

Guiding Question: What role do aspect, slope, sun, snow melt, blackbody absorption and elevation play in soil moisture conditions and why is soil moisture important to the structure of an ecosystem?

Overview: This lesson focuses on the role of aspect, slope, seasonal sun availability, snow melt, blackbody absorption, and elevation in soil moisture conditions. Soil moisture is one of the most important factors determining the composition of plant communities and ultimately the ecosystem structure. The amount of snowpack and the amount of time it takes to melt off each summer impacts the growing season and the ability of trees to survive. Where trees can no longer survive, alpine meadows predominate, but soil moisture conditions determine whether they are "wet" or "dry" meadows.

Time: One class period


Lesson 8: Aspect, Treeline, and Climate

Guiding Question: Trees play an important role in salmon habitat. How can an understanding of climate, aspect, soil moisture, and treeline add to our understanding of healthy river restoration?

Overview: This lesson focuses on the factors that determine the location of the treeline in different locations in the world. The elevation of treeline is affected by the combined effects of snowpack depth, minimum winter temperatures, aspect, and soil moisture conditions. Treeline varies by latitude, but is also affected by whether it is an arid, temperate, or tropical climate. In addition, in arid regions, aspect and elevation affects soil moisture conditions and determines where the transition from desert to forest occurs on sky islands. In addition, human impacts such as grazing and fires can impact the elevation of treeline.

Time: One class period.


Lesson 9: Salmon Anadromous Lifestyles

Guiding Question: Salmonids are a crucial part of the Elwha River ecosystem. How can our understanding of their life cycles help restore the Elwha River ecosystem?

Lesson Overview: Students will be introduced to the wild salmonid species of the Elwha River. After watching a power point presentation on the anadromous life styles of pacific salmonids, students will work in groups to research. Then students will compose a presentation on the lifestyle of a specific species of anadromous fish found in the Elwha River: Chinook, chum, coho, pink, sockeye, steelhead, bull trout, or Dolly Varden. Student groups will then apply their knowledge by constructing a model healthy river habitat in which their species, along with other species of salmon, can grow and thrive.

Time: Three block class periods.


Lesson 10: Salmonid Natural History

Guiding Question: How does biological evolution account for the diversity and distribution of salmonid species?

Overview: This lesson focuses on some of the natural history and stochastic events that have influenced the current distributions of salmonid fish in western North America. The relatedness of salmonid species and some of the events of the past, of which the ice age is the most important, can be examined using phylogenetic trees. This information can then be used to determine how the phylogenetic tree branched as it did. Genetic isolation, the founder effect, genetic drift, and stochasticity have all played a role in the diversification of the various species, subspecies, stocks, and runs of salmonids in western North America.

Time: One class period


Lesson 11: Habitat Requirements for Pacific Salmon

Guiding Question: Salmon are survivors; nevertheless, they have very specific habitat requirements, what are the important habitat needs of the anadromous fish of the Elwha River watershed?

Overview: This lesson focuses on the specific habitat requirements for each Pacific salmon species, as well as, other anadromous fish of the Elwha River watershed. The ecological habitat of each salmon species includes their adult range in the ocean and the specific parts of the river, and its tributaries, that are critical spawning habitat.

Time: One class period


Lesson 12: Marine-Derived Nutrient Cycling

Guiding question: How do the carcasses of dead adult salmon support young salmon and how are salmon essential to the marine food web as well as the freshwater ecosystems of the Pacific Northwest?

Overview: Discuss the marine food web related to salmon. Introduce the idea of algal blooms in the cold nutrient-rich waters of the North Pacific. Explain trophic levels, energy movement, bioaccumulation and biomagnification of nutrients and chemicals into top-level predators such as salmon. Introduce the idea of these marine-derived nutrients entering the freshwater ecosystems and becoming the basis of the freshwater ecosystem food web. Freshwater ecosystems in the Pacific Northwest tend to be oligotrohic (containing few nutrients), so these marine-derived nutrients constitute an important influx that greatly increases the productivity of these rivers.


Lesson 13: Salmon Nutrient Cycling

Guiding Question: Salmon nutrients find their way into terrestrial environments, how is it possible that trees show evidence of having derived nutrition from Salmon?

Overview: This lesson focuses on how marine-derived nutrients from salmon carcasses find their way into terrestrial environments and how scientists can track these marine-derived nutrients to analyze their importance to ecosystems today, as well as, reconstructing past ecosystem processes. Terrestrial vertebrates such as mammals and birds, as well as, insects consume salmon carcasses and then release those nutrients onto land, either by dragging the carcasses or defecating onto the forest. These nutrients then enter the soil, where they are taken up by plant roots. Once entering plant tissue, they are consumed by herbivores. Salmon nutrients have been found in every living organism investigated and up to seven miles from the stream of origin. Scientists use stable isotope N15 to track marine-derived nutrients, because this isotope is more common in marine environments than freshwater ones. Analyzing sediment layers of lakes for this isotope, scientists can reconstruct ancient salmon abundance and can make inferences to historic climate and ecological processes.

Time: One class period



This webpage was made possible in part by a grant from Washington's National Park Fund.

Last updated: April 6, 2015

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