Date of Award:

8-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Michelle A. Baker

Committee

Michelle A. Baker

Committee

Andrew M. Ray

Committee

Brooke B. Osborne

Committee

Janice Brahney

Committee

Erin N. Rivers

Abstract

Humans have greatly affected streams and rivers worldwide through urbanization, agriculture, and water use. The purpose of my dissertation is to increase our understanding of various human impacts on rivers. In chapter two, I aim to determine whether there are differences in greenhouse gas (GHG) emissions between a natural river and manmade canals. I did this by measuring the emissions and dissolved concentrations of three of the most prevalent GHGs, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). I found that most of the sites I studied were emitting CO2 and CH4 to the atmosphere, but that the canals had higher rates of emissions. I also found that different environmental variables affected GHG emissions in the canals and the river. Yet, despite differences in site type, salinity and amount of carbon (C) and nitrogen (N) in the water were usually associated with higher GHG concentrations and emissions.

In my third chapter, my objective was to determine whether watershed protections can successfully preserve the water quality and the amount of water flowing in the Yellowstone River. While large areas of land have been protected worldwide, there is a lack of evidence to determine whether these protections are effective. My analyses showed that salinity and nutrient concentrations (N and phosphorus (P)) have remained low and stable compared to a similar but unprotected river. However, I found that high and low flows have been becoming more extreme over the past century, and that the date of peak flow is occurring earlier in the year. Together, these results suggest that watershed protections may be effective means of preserving water quality, but do not protect rivers from climate-induced changes to flow.

In the fourth chapter, I use a laboratory experiment to investigate the relationship between salinity and C cycling, which was observed in chapter two. I used two methods to estimate the amount of C being consumed by microbes relative to the amount of C being respired by them as CO2, called C use efficiency (CUE). I found that microbial CUE is resilient to moderate salt stress, and microbial growth is stimulated by even modest salinity increases. These results provide evidence that in a laboratory setting salt loading does not lead to higher levels of CO2 production in sediments and instead may modestly increase sediment C storage.

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