Date of Award

Spring 5-6-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Aria Amirbahman

Second Committee Member

Stephen Norton

Third Committee Member

David Courtemanch

Additional Committee Members

Rachel Hovel

Shaleen Jain

Abstract

The Influence of anthropogenic activities on lake water quality is well documented, but how those influences interact with the effects of natural features, such as watershed geology or lake morphometry, has been less explored. Further, some aspects of lake condition are influenced by factors that are not lake or watershed specific, but occur across large regions, such as weather patterns. All these factors may be interrelated in some instances, which can complicate lake condition assessments which have the purpose of determining how lakes are being affected by human activities. This dissertation investigates how lake assessments can integrate the interactions among natural features of lakes, their watersheds, and anthropogenic influences. Chapter 1 discusses the variety of factors that may affect lake condition and how those influences may confound lake condition assessments. Chapter 2 details the creation of a hydrogeomorphic lake classification, based on ecoregions and lake depth, that partitioned lakes into groups that share similarities in background water quality condition. In chapter 3, a logistic regression model is described that uses maximum depth and relative lake area beneath the epilimnion to predict which low-nutrient lakes (total phosphorus < 15 μg/L) may exhibit naturally-occurring anoxia. In chapter 4, water clarity patterns from different types of reference lakes (detailed in chapter 2) were modeled to allow for comparisons between yearly water clarity values in non-reference lakes and a reference baseline that shifts over time. Cumulative precipitation during the lake stratification season was the primary driver of yearly differences in background lake water clarity. In chapter 5, methods were developed to measure the effect of anthropogenic shoreland disturbance on the condition of littoral habitat. Multi-metric indices based on various habitat measures were established that determine if the littoral habitat is different from a natural reference condition. Chapter 6 summarizes the research in this dissertation and offers potential foci of future lake research in Maine. The overall goal of this dissertation was to advance our collective understanding of how lakes may be variably affected by natural and anthropogenic factors, thereby allowing for better-informed lake assessments and the development of more comprehensive, achievable lake management goals. The research presented herein underscores the importance of considering the interactions of multiple cross-scale factors when evaluating lake condition, especially those related to landscape traits that influence runoff water chemistry, natural lake-specific features such as basin morphometry, large-scale weather patterns, and localized shoreland development.

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