Recent studies have focused on dissolved organic matter (DOM) cycling throughout river corridors or in reservoirs, but few have explored DOM cycling in commonplace but understudied run-of-river (ROR) reservoir systems. Impoundments disrupt river flow patterns, as they increase hydraulic residence time and alter the flow of DOM downstream. During storms when the majority of DOM loading occurs, impoundments become less likely to hold DOM and will increase export of DOM downstream. In this study, we quantified DOM bioavailability and composition, carbon flux, and carbon dioxide (CO2) gas evasion in a ROR reservoir system at baseflow conditions and during a 1.5-year storm event. This study used a combination of high frequency spatial sensor data geotagged to GPS coordinates along the river to reservoir transition, and grab samples of surface water taken at two U.S. Geological Survey stream gauges and three additional sites. The landscape and shallow flow paths to ROR reservoir systems resulted in the export of both aromatic carbon and labile organic matter present within these waters, as water was mixed and exported downstream. Additionally, the reservoir was a net sink of DOC and BDOC flux, while also a source of DIC flux. Finally, CO2 evasion was magnified by high flow, with the reservoir changing from a sink to a source of CO2 to the atmosphere. ROR reservoirs may undergo "short-circuiting" during high flow, which alters DOM transformations and transport of carbon downstream. Our results provide critical insight on carbon dynamics in ROR reservoir systems and highlight the need to incorporate riverine DOM into carbon budgets, especially under variable flow conditions. / Master of Science / Recent studies have focused on dissolved organic matter (DOM) cycling through river corridors, as DOM provides energy to aquatic food webs and can be converted to carbon dioxide (CO₂) through microbial respiration. Few studies have explored DOM cycling in commonplace but understudied run-of-river (ROR) reservoir systems. ROR reservoirs are created by the implementation of a dam across a river channel and use the flow of the river to generate hydroelectric power. During storms, when the majority of DOM loading occurs, impoundments become less likely to hold DOM and will increase export of DOM downstream. In this study, we quantified DOM quality and composition, DOM transport, and carbon dioxide (CO₂) gas evasion in a ROR reservoir system at baseflow conditions and across a 1.5 year storm event. This study used a combination of high frequency spatial sensor data combined with GPS coordinates along the river to reservoir transition, and grab samples of surface water taken at two U.S. Geological Survey stream gauges and three additional sites. Results show that the landscape and shallow flow paths to ROR reservoir systems resulted in the export of both high and low quality carbon present within these waters, as water was mixed and exported downstream. Additionally, the reservoir was a net sink of DOM flux, retaining 40.7% of the total DOM loading for the storm event. Finally, CO₂ evasion was magnified by the storm event, with the reservoir changing from a sink to a source of CO₂ to the atmosphere. Our results provide critical insight on carbon dynamics in ROR reservoir systems and highlight the need to incorporate riverine DOM into carbon budgets, especially under variable flow conditions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/85021 |
| Date | 14 September 2018 |
| Creators | Ryan, Madeline Faye |
| Contributors | Biological Systems Engineering, Scott, Durelle T., Hotchkiss, Erin R., Hession, W. Cully |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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