Date of Award:

8-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Erin Rivers

Committee

Erin Rivers

Committee

Timothy Walsworth

Committee

Janice Brahney

Abstract

Water quality is declining in freshwater lakes around the world due to environmental change and anthropogenic activities that threaten the physical, ecological, and geochemical integrity of freshwater ecosystems. Excess N and P in lakes can cause eutrophication, a major driver of water quality impairment that leads to excessive algal growth, or harmful algal blooms (HABs), and poses risks to recreation, fisheries, and public drinking water. Water level fluctuations in lakes are expected to become more frequent and intense as climate change increases periods of drought and alters precipitation patterns, and fluctuations may stimulate biogeochemical reactions in littoral sediments that add or remove bioavailable nutrients and impair water quality in lakes. This study assessed the effect of drying and rewetting on nitrogen cycling in littoral sediments at Utah Lake, a shallow, hypereutrophic lake in Utah, USA.

Nitrogen fluxes were assessed during dry summer conditions and transitional fall conditions in three field sampling campaigns across three zones (saturated, littoral, and upland) with different hydrologic histories. Sediment and water samples were analyzed for bioavailable nutrients (sediment nitrate, and sediment ammonium) and sediment nitrogen cycling (denitrification, mineralization, nitrification, and microbial biomass C and N). Our results showed considerable variability across zones. High levels of sediment ammonium were found in the lake zones and in winter across all zones, while high levels of nitrate and rates of mineralization were found in the upland zones. Carbon availability sediment moisture, and pH strongly influenced these results. We hypothesize that if lake levels decrease and more sediments are exposed, there is potential for bioavailable nutrients to leach into the groundwater and contribute to internal nitrogen loading.

The results of this study will contribute to the creation of an internal nutrient loading budget of Utah Lake. With this data, we will better understand the relationships between external and internal nutrient loading to Utah Lake. From there, the most significant sources of nutrients to the lake will be identified and we can begin to reduce nutrient loads in order to manage eutrophication.

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