Date of Award:

5-2022

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Janice Brahney

Committee

Janice Brahney

Committee

Dennis Newell

Committee

Diego Fernandez

Abstract

Freshwater lakes around the world have suffered from the increasing occurrence of harmful algal blooms in recent decades. One of the most pressing reasons water quality managers try to address harmful algal blooms is that some of the species that occur with them produce toxins which can affect humans, pets, and wildlife. In many lakes, the nutrient phosphorus controls whether these harmful algal and bacterial species can occur. Therefore, efforts to control harmful algal blooms often center around reducing inputs of phosphorus from a variety of sources within the watershed. Scientists and water quality managers have long been challenged by the problem of determining the extent of phosphorus pollution in lakes, and to what degree human activity has changed the phosphorus aspect of aquatic ecosystems. We studied the historical phosphorus record of Utah Lake in north-central Utah, USA, which has been plagued by harmful algal blooms in recent years, by taking sediment cores from four different locations around the lake. We first analyzed the CaCO3 component of one Utah Lake core for trends in phosphorus concentration over time. This approach is based on the co-precipitation of CaCO3 with phosphorus, which scales with concentrations of phosphorus in the lake water. Next, we separated the total phosphorus of samples from four different sediment cores into five different forms by extraction and analyzed each extraction to establish trends in the different fractions of phosphorus that occur in lake sediments. In order to correlate phosphorus trends with important events in the lake’s ecological history, we performed cesium and lead isotope analyses, assigning years to the various depths of these sediment cores. These analyses together support our hypothesis that phosphorus concentrations have increased in the lake due to human activity. Nearly all of the phosphorus fractions from each of the four cores increase in more recent years, agreeing with the analyses focused on CaCO3 grains from one specific core which showed an increase in phosphorus beginning around the middle of the 19th century. We recommend applying the principles of our CaCO3-phosphorus analysis performed here in other lakes with CaCO3-P-rich sediments to better understand their ecological histories.

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