Author ORCID Identifier

https://orcid.org/0000-0001-6589-5990

Date Available

12-11-2024

Year of Publication

2024

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

Advisor

Dr. Michael M. McGlue & Dr. Kevin M. Yeager

Abstract

Investigation of past lake environments forms the discipline of paleolimnology. Paleolimnological studies seek to evaluate geophysical, geochemical, and ecological proxies and indicators contained within lake sediment archives. Using these potential stores of high-resolution environmental information, questions regarding climate, biological, and geochemical changes experienced by a lake and its watershed can be investigated. This dissertation research utilized lake sediment records from two lakes within North America to study different aspects of environmental change. This dissertation consists of three separate studies presented in three chapters.

Chapter Two presents a retrospective environmental assessment of Jackson Lake, Wyoming to investigate the impacts of dam emplacement. Dam emplacement occurred in ~1916 CE and drastically altered Jackson Lake’s surface area, morphology, and relationship with the inflowing Snake River, yet the consequences for nutrient dynamics and algae in the lake are unknown. Paleoecological (diatoms) and geochemical datasets were developed on a well-dated sediment core and compared with regional hydroclimate data, to assess patterns of limnological change. Diatom assemblages prior to dam installation were characterized by high relative abundances of plankton that thrive under low nutrient availability. Following dam construction, diatom assemblages shifted to planktic species that favor more nutrient-rich waters. Elemental abundances of sedimentary nitrogen and phosphorous support the interpretation that dam installation resulted in a more mesotrophic state in Jackson Lake after ~1916 CE. The results of the study highlight the sensitivity of algal composition and productivity to changes in nutrient status that accompany outlet engineering of natural lakes by humans.

Chapter Three presents a paleoenvironmental reconstruction of Jackson Lake, Wyoming encompassing the Late Quaternary tectonic and hydroclimate history. This study presented new high-resolution seismic reflection data and sediment cores from Moran Bay, which is adjacent to the active Teton fault on the southwestern lake margin. Seismic data showed stacked clinoform deposits, best explained by increased accommodation in Moran Bay around ca. 10 ka aligning with earthquakes on the Teton fault previously identified in terrestrial and lacustrine paleoseismic records. Seismic records were used to reconstruct previous Holocene water levels of ~2,046, ~2,049, ~2,053, and 2063 m asl. Sediment core records revealed a complex depositional history of evolving stream networks and varying stream discharge driven by regional seismic activity and climatic changes. Together, the seismic and core data records indicate a complex and dynamic Holocene lacustrine evolution controlled by fault motion and water level changes.

Chapter Four presents the sediment accumulation and carbon burial rates of West Okoboji Lake, Iowa over the last ~100 yrs. We used new data from multiple 210Pb-dated sediment cores and lake floor sediment samples to determine carbon burial rates. Our lake-wide dataset shows that carbon burial within West Okoboji Lake has varied spatially and temporally. Prior to 1940 CE, the primary locus of organic carbon burial was centered around Browns Bay; the average lake-wide sedimentation rate was 0.1 g m-2 yr-1 and organic carbon burial was 69 g C m-2 yr-1. After 1940 CE, sedimentation and organic carbon burial rates increased to 0.27 g cm-2 yr-1 and 200 g cm-2 yr-1, respectively. In addition, the locus of organic carbon burial shifted to the lake’s central deepwater depocenter by 1960 CE, where it has persisted to the present day. The chief driver for the changes in rates of sedimentation and organic carbon burial is interpreted to result from anthropogenic landscape modifications around 1940–1960 CE. This period witnessed the growth of lake margin communities, urbanization, and agricultural activities.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.504

Funding Information

The research was funded and supported by the U.S. National Science Foundation award EAR-1932808, the University of Wyoming-National Park Service field station, the Overcash Family Fund for Field Research, and the Pioneer Endowment at the University of Kentucky.

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