Streams are ecosystems organized by disturbance. One of the most frequent disturbances within a stream is elevated flow. Elevated flow can both stimulate ecosystem processes and impede them. Consequently, flow plays a critical role in shifting the dominant stream function between biological transformation and physical transportation of materials. To garner further insight into the complex interactions of stream function and flow, I assessed the influence of elevated flow and flow disturbances on stream metabolism. To do so, I analyzed five years of dissolved oxygen data from an urban- and agriculturallyinfluenced stream to estimate metabolism. Stream metabolism is estimated from the production (gross primary production; GPP) and consumption (ecosystem respiration; ER) of dissolved oxygen. With these data, I evaluated how low and elevated flows differentially impact water quality (e.g., turbidity, conductivity) and metabolism using segmented metabolism- and concentration- discharge analyses. I found that GPP declined at varying rates across discharge, and ER decreased at lower flows but became constant at higher flows. Net ecosystem production (NEP; = GPP - ER) reflected the divergence of GPP and ER and was unchanging at lower flows, but declined at higher discharge. These C-Q patterns can consequently influence or be influenced by changes in metabolism. I coupled metabolism-Q and C-Q trends to examine linked flow-induced changes to physicochemical parameters and metabolism. Parameters related to metabolism (e.g., turbidity and GPP, pH and NEP) frequently followed coupled trends. To investigate metabolic recovery dynamics (i.e., resistance and resilience) following flow disturbances, I analyzed metabolic responses to 15 isolated flow events and identified the antecedent conditions or disturbance characteristics that most contributed to recovery dynamics. ER was both more resistant and resilient than GPP. GPP took longer to recover (1 to >9 days, mean = 2.5) than ER (1 to 2 days, mean = 1.1). ER resistance was strongly correlated with the intensity of the flow event, whereas GPP was not, suggesting that GPP responds similarly to flow disturbances, regardless of the magnitude of flow event. Flow may be the most frequent disturbance experienced by streams. However, streams are exposed to a multitude of other disturbances; here I also highlight how anthropogenic alterations to streams – namely, burying a stream underground – can change biogeochemical function. This thesis proposes novel frameworks to explore the nexus of flow, anthropogenic disturbances, and stream function, and thereby to further our understanding of the complex relationship between streams and disturbances. / Master of Science / A stream is defined by its flowing water. Flow brings the nutrients, organic matter, and other materials necessary to the algae and bacteria within the stream as well as the invertebrates and fishes they sustain, and is consequently integral to in-stream biology and ecology. However, elevated flow is also one of the most frequent disturbances experienced by streams. Elevated flow dilutes or enriches concentrations of water quality parameters, moves the water faster, reduces the amount of time essential nutrients are available to organisms within streams, and scours the algae and bacteria on stream bottoms. Here, I analyzed five years of data from an urban- and agriculturally-influenced stream and estimated stream metabolism to explore the influence of flow on stream biology, chemistry, and ecology. Stream metabolism is a process that reflects the respiration and photosynthesis of bacteria and algae, estimated from the production and consumption of dissolved oxygen. The primary research objective of my thesis was to investigate how changing flow impacts metabolism, by: (1) examining how low and high flows impact metabolism differently, and (2) studying the response and recovery of metabolism following multiple flow disturbances. Flow not only influences in-stream biology and processes, such as stream metabolism, but also changes the water quality of the stream (e.g., conductivity, pH, turbidity). To examine the interconnection between flow-induced changes to water quality parameters and metabolism, I measured how low and high flows impacted water quality and then compared water quality-flow relationships with metabolism at low and high flows. I found that metabolic processes and related water quality parameters were frequently coupled. Next, to test how water quality might also influence the response and recovery of metabolism after a flow disturbance, I examined whether prior environmental conditions (e.g., temperature, light) or the magnitude of the flow disturbance influenced metabolic response and recovery. I found that the size of the flow disturbance did change a critical piece of stream metabolism. Flow is not the only prevalent disturbance streams face: increasingly, streams are being altered by ongoing urban and suburbanization. Therefore, to highlight the full suite of disturbances to streams caused by human modification, I wrote a public science communication piece documenting the biological, chemical, and ecological ramifications of burying streams underground. Ultimately, this thesis proposes new frameworks to more adequately explore the complex relationships between water quality, stream ecology, and disturbances.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/101660 |
| Date | 02 July 2019 |
| Creators | O'Donnell, Brynn Marie |
| Contributors | Biological Sciences, Hotchkiss, Erin R., McLaughlin, Daniel L., Barrett, John E. |
| 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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