Document Type

Thesis

Date of Degree Completion

Summer 2019

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Clay Arango

Second Committee Member

Jason Irwin

Third Committee Member

Paul James

Abstract

Headwater streams are important for the biological integrity of river systems because they represent most of the length of the hydrological network and control the downstream flow of energy and nutrients to larger river systems. Headwater streams are culturally and economically important because they, directly or indirectly, support recreationally important anadromous and resident fisheries. Managing fish in these systems often requires time-consuming population counts, but fish biomass might be related to overall stream productivity, which can be measured relatively easily using models to estimate stream metabolism. The goal of my study was to relate whole-stream metabolism to fish biomass in 10 different headwater streams on the eastern slopes of the Cascade Mountains in Kittitas County, Washington. I estimated fish biomass on two occasions using a multiple-pass removal population estimate multiplied by the average fish mass, and I estimated ecosystem metabolism on three occasions using the single station method with a diel oxygen curve and inverse modeling. I estimated the critically important air-water gas exchange values based on stream slope, using an empirical relationship from a previously published study. Gross primary production across sites and sampling periods ranged from 0.01 to 0.71 g O2 m-2 d-1, varied by sampling period, and increased with stream depth. Ecosystem respiration ranged from 4.55 to 24.29 g O2 m-2 d-1, and increased with stream depth and slope. Fish were mostly cutthroat trout (Oncorhynchus clarkii lewisi), and biomass ranged from 0 to 8.38 g m-2, increasing with colder water especially under more open canopies, and differing by catchment, but there was no relationship with ecosystem metabolism. Overall stream metabolism predictors were limited to model inputs, owing in part to extremely limiting levels of photosynthetically active radiation and dissolved inorganic nitrogen, and the air water gas-exchange estimations were likely inaccurate. Metabolism metrics and trout biomass did not relate with photosynthetically active radiation, dissolved inorganic nitrogen, soluble reactive phosphorus, dissolved organic carbon, or other physical attributes of these streams. I demonstrated that these methods are not adequate to relate stream metabolism to trout biomass in headwater streams.

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