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Impacts of Metal Contamination and Reactive Nitrogen on Sediment Microbial Communities in Roadside Freshwater Ponds

Hill, Memphis (2024) Impacts of Metal Contamination and Reactive Nitrogen on Sediment Microbial Communities in Roadside Freshwater Ponds. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Human activities such as industry, agriculture, and road construction alter not only the landscape, but also ecosystem geochemistry and microbiology. In particular, metallurgical activities and fossil fuel combustion redistribute trace metals across these landscapes. Additionally, agriculture has increased environmental reactive nitrogen loadings. However, the impacts arising from this combination of pollutants on microbial communities and ecosystem services are largely unknown. The nitrogen cycle is mediated by microbial activities, and influx of reactive nitrogen can alter microbial nitrogen cycling activities. Such alterations can disrupt nutrient cycles and trophic webs. Further, microbially mediated nitrogen cycling is driven by enzymes dependent on metal cofactors. Therefore, changes in metal mixes can interfere with assimilation of these cofactors, and thus degrade enzyme functions.
Roadside ponds are ideal systems for studying the impacts of metal and nitrogen contamination mixes on both microbial community structures and nitrogen cycling functions. As road networks grow and evolve, and environmental regulations and new technologies are implemented, the source mixes of trace metal and reactive nitrogen contamination change, further complicating ecosystem impacts. Sediment records reveal details throughout road lifecycles and reflect technological changes. Microbial responses to anthropogenic nitrogen and metals are strongly influenced by variability in microbial community composition. This dissertation examines and compares nitrogen, metals, and microbes in sediment cores from two roadside ponds in contrasting environments.
Harmar Pond is an urban, temperate pond in Pennsylvania. Poudre Lake is a remote, subalpine/alpine pond in Colorado. Metal and nitrogen inputs increase in both ponds following road construction. Endmember mixing with metal-to-metal ratios confirms a shift in metal sources from industry to road runoff in both ponds, more clearly in Harmar Pond. In addition, shifts in microbial community composition are apparent in both sediment records. These shifts occur at distinct times, suggesting that community structure drivers vary. Moreover, shifts in microbial community composition and potential nitrogen cycling functions correspond to a rapid increase in nitrogen and metal fluxes coincident with road construction. Continued reconstruction of multi-proxy histories from sediment records is fundamental to comprehensive clarification of human impacts.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Hill, Memphismeh146@pitt.edumeh1460000-0002-0349-5366
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairBain, Dandbain@pitt.edudbain
Committee MemberElliott, Emilyeelliott@pitt.edueelliott
Committee MemberAbbott, Markmabbott1@pitt.edumabbott1
Committee MemberWerne, Josephjwerne@pitt.edujwerne
Date: 10 January 2024
Date Type: Publication
Defense Date: 12 September 2023
Approval Date: 10 January 2024
Submission Date: 7 December 2023
Access Restriction: 1 year -- Restrict access to University of Pittsburgh for a period of 1 year.
Number of Pages: 173
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Environmental Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: metals, nitrogen, microbes, sediment
Date Deposited: 10 Jan 2024 13:59
Last Modified: 10 Jan 2024 13:59


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