Thesis
Stormwater nitrogen retention, transformation and removal in bioretention swales during storm-interstorm period
Washington State University
Master of Science (MS), Washington State University
2019
Handle:
https://hdl.handle.net/2376/101541
Abstract
Reported nitrogen (N) retention efficiencies for bioretention swales vary widely, in part because standard N mitigation assessments cannot account for the final fate or form of retained N. Here, we apply 15N tracing to quantify not only retention of N, but also the transformation pathways of retained N during a simulated rain-event and subsequent 146 hour inter-storm period. We observed that 32-51% of 15NO− 3 retention was facilitated by transient storage in pore water, while permanent denitrification accounted for just 0.7-3.5 % at the end of the drainage period. NO− 3 held in post-storm pore water was rapidly transformed within 75 hours, such that transformation rates were within 1% of retention rates. By 151 hours from the storm’s start, less than 3% of 15NO− 3 retention could be explained by denitrification. Mesocosms were a net sink for total NO− 3 , though retention was significantly lower in one column compared to the remaining three (2%, 50-75%, respectively). Not surprising given the hydrologic goals of rapid infiltration, soil O2 levels remained near saturated levels. Physical mixing between influent water and pre-storm pore water impacts effluent mass in addition to transformation, such that net retention does not describe capture or biogeo-chemical transformation of N within a system. Future research should continue to evaluate N transformation pathways, and timescales of temporary storage in bioretention swales, as well as investigate the influence of hydrology on N cycling.
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Details
- Title
- Stormwater nitrogen retention, transformation and removal in bioretention swales during storm-interstorm period
- Creators
- Sarah E. Kintner
- Contributors
- John A. Harrison (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525298801842
- Language
- English
- Resource Type
- Thesis