DOI
https://doi.org/10.25772/H1ZV-R416
Defense Date
2019
Document Type
Thesis
Degree Name
Master of Science
Department
Environmental Studies
First Advisor
Dr. Shannon Leigh McCallister
Second Advisor
Dr. Edward Crawford
Third Advisor
Dr. Scott Neubauer
Abstract
Fluvial systems act as conduits for terrestrial carbon transport to coastal oceans. However, riverine systems not only transport allochthonous carbon, they transform and store carbon in many different ways. The different mechanisms of transformation and storage need to be considered for fluvial systems in order to accurately account for modifications to the carbon pool when developing carbon budgets. Of interest was to investigate the carbon dynamics in the James River, in Virginia, from headwaters to the tidal fresh estuary to gain a better understanding of carbon dynamics along the continuum. Sites along the river continuum were sampled for dissolved organic carbon (DOC) concentrations and used in bioassays to determine degradation dynamics along the continuum, radiocarbon analysis was used to determine the age of the DOC and POC pool available to bacteria, impoundment effect on carbon dynamics was investigated in the Appomattox River, a tributary to the James, and landcover data was used to investigate the effects of land change on aquatic carbon dynamics. Bacterial total consumption and rates were found to be highest in the headwater streams, where carbon sources have yet to undergo degradation, downstream sites consumption remained steady up to the tidal fresh estuary where degradation was minimal. Radiocarbon analyses showed older POC (5460 years old) at a site in the middle of the continuum where anthropogenic effects may have been the cause. Samples from the impoundment of the Appomattox River to form the Lake Chesdin Reservoir provided different results from the mainstem James, as DOC concentrations fluctuated throughout the continuum and the impoundment allowed for increased storage of allochthonous carbon and production of autochthonous carbon, altering the flux of carbon and nutrients downstream. As the majority of the James River watershed is forested, the increase in anthropogenic modifications downstream showed an opposite trend with the decrease in bacterial consumption further downstream, suggesting possible anthropogenic influence on bioavailability of DOC to bacteria. Rivers were once thought of as only transporting carbon downstream, however what enters rivers in the headwaters is not always the same that concludes its journey in the ocean. Thus, the many mechanisms of transformation and storage need to be assessed when accurately constructing carbon budgets.
In an Appendix, I detail modifications to the Respiratory Carbon Recovery System (ReCreS) which helped streamline sample incubation and collection. A new incubation chamber was devised with a port for a pH probe and a flat bottom for the introduction of a magnetic stir bar to reach equilibrium faster. Additionally, a new kettle lid design contained a port for a pressure gauge to prevent over pressurization during sparging. An added inline Nafion Dryer removed moisture from the gas stream before entering the vacuum line. Finally, the line was connected directly to a vacuum pump to streamline the sample collection process, removing the need to take the trapped CO2 elsewhere for processing and providing immediate recovery results.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
4-3-2020