Thesis
Stream nitrogen fixation in photosynthetic and non-photosynthetic species
Washington State University
Master of Science (MS), Washington State University
05/2020
DOI:
https://doi.org/10.7273/000004095
Handle:
https://hdl.handle.net/2376/124927
Abstract
Biological nitrogen (N) fixation, the microbial conversion of N2 gas to ammonia, makes N biologically available to food webs. While widely studied in lakes and marine environments, many questions remain regarding stream N fixation such as the relative contributions of various N-fixing organisms, particularly heterotrophic bacteria. As N fixing taxa are often abundant in low-N streams, N fixation is potentially an important N source in these systems. In low-N streams in the Cascade Mountains (Washington, USA), three groups of N fixers predominate: cyanobacteria (Nostoc paramelioides) colonies that house a midge symbiont, cyanobacteria without a midge symbiont, and heterotrophic sediment bacteria. N fixation was measured with the acetylene reduction assay and a 15N2 calibration in 7 streams. Cyanobacteria N fixation rates were relatively low (average of 4.17 [mu]g N m-2 hr-1) compared to other mountain streams. Rates were not significantly different among types of N fixers. However, sediment rates (average of 10.27 [mu]g N m-2 hr-1) were higher than reported rates measured only with acetylene reduction, suggesting that sediment N fixation importance has been previously underestimated. Sediment N fixation rates increased with total phosphorus (TP). Surprisingly, cyanobacterial N fixation rates increased with dissolved inorganic N (DIN), though DIN was less than 0.085 mg/L at all sites. These results suggest that cyanobacteria require a minimum amount of N to support their growth and consequently their ability to fix N.
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Details
- Title
- Stream nitrogen fixation in photosynthetic and non-photosynthetic species
- Creators
- Erica A. H. Bakker
- 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
- 99900890787101842
- Language
- English
- Resource Type
- Thesis