Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geography, Geology, and Anthropology

Abstract

The Midwest region of the United States is a global agriculture center and home to nearly 70 million people. As a result of ongoing climate change, the area is already experiencing changes in hydroclimate. Precipitation has increased in the region every decade since the 1970s. It is projected that these changes will continue to increase in the future in both severity and occurrence, particularly in the form of extreme hydroclimate events. Hydroclimate has varied in the regions past; however, a lack of high-resolution paleoclimate records for the region limits our understanding of past hydroclimate variability. Lakes are sensitive to changes in climate at the local and regional scale. As a result, they can be used as indicators of hydroclimate variability in the Midwest. This study focused on diatom assemblages from a 2,000yr record of Clear Lake, located in north-central Iowa. The goals of this study were to 1) assess shifts in dominant diatom species throughout the record and relate these shifts to local and regional variation in hydroclimate, 2) determine if the lake showed a response to known periods of recent climatic variations during the Medieval Climate Anomaly (MCA; 950–1250CE) and Little Ice Age (LIA; 1300–1800CE), 3) determine if the lake responded to landscape change as a result of anthropogenic influence, and 4) understand how this record is explained by the hydroclimate dipole, which has been proposed by recent findings. This study found that diatoms at Clear Lake clearly responded to hydroclimatic change throughout the 2,000 year history, particularly through the connection of the lake to adjacent wetland areas. We infer that in the earliest part of the record, the lake level was higher. Benthic diatom abundances were higher in this part of the record indicating shallower habits were more common than today, likely the result of elevated precipitation that flooded the lake into adjacent wetlands. Lake level likely decreased through time, evidenced by benthic abundances that generally showed a decreasing trend throughout the record. Additionally, the lake showed a response to the MCA and the LIA, similar to that of other Midwestern lakes. During the MCA, lake level increased somewhat as a result of increased precipitation. However, during the LIA, lake level was lower, which was the result of inferred droughts, which have been observed in other regional records during the LIA.

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