Thesis
Overabundant macrophyte growth alters ecosystem function in a lowland river
Washington State University
Master of Science (MS), Washington State University
05/2020
DOI:
https://doi.org/10.7273/000004124
Handle:
https://hdl.handle.net/2376/125157
Abstract
Macrophytes in flowing water provide habitat, dissolved oxygen (DO), and other benefits to aquatic animals, but can also degrade habitat when they become dense and abundant. The lower Yakima River in eastern Washington, USA, is dominated by a native macrophyte, water stargrass (Heteranthera dubia (Jacq.) MacMill.), which may be creating conditions harmful to native salmonids that rely on the river for migration, spawning, and rearing. In this portion of the river, nighttime DO levels during low flow periods often fall below critical levels for salmonids, and water stargrass may be largely responsible. However, not all the specific impacts of this macrophyte have been tested, and some ecological conditions that promote its establishment remain uncertain. I reviewed the literature regarding macrophytes in aquatic systems to provide a broader perspective on their ecological effects and key factors that control their colonization. I then related that literature to the specifics of the Yakima River to generate hypotheses about macrophyte dynamics in this system. Based on the literature review, I hypothesized that water stargrass respiration is largely responsible for the DO minima and that its canopy may be creating zones of localized DO depletion. I tested the first hypothesis by measuring metabolic rates in habitats with and without water stargrass, using clear, open-bottom chambers. To determine whether there are localized canopy effects, I collected continuous DO measurements with paired DO loggers in areas with and without dense water stargrass beds. Water stargrass habitats had significantly greater net ecosystem production (NEP), community respiration (CR), and gross primary production (GPP) (mean difference ± 95% CI: 5.95 ± 1.65, 5.58 ± 2.03, and 11.50 ± 3.22 mg O2 m-2 h-1, respectively). Based on coverage estimates, water stargrass was responsible for 86.7% of NEP, 91.5% of CR, and 90.6% of GPP at the reach scale. Continuous DO data from water stargrass and non-water stargrass habitats showed no meaningful difference in diel DO patterns, likely because the river is well-mixed. My results suggest water stargrass could be responsible for the critically low DO minima and that non-water stargrass areas do not currently provide salmonids refuge from low DO.
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Details
- Title
- Overabundant macrophyte growth alters ecosystem function in a lowland river
- Creators
- Aaron Christopher Pelly
- Contributors
- Sarah Roley (Advisor) - Washington State University, School of the Environment (CAS)
- Awarding Institution
- Washington State University
- Academic Unit
- School of the Environment (CAS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Identifiers
- 99900890782401842
- Language
- English
- Resource Type
- Thesis