Date of Award

2025

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Environmental Engineering (PhD)

Administrative Home Department

Department of Civil, Environmental, and Geospatial Engineering

Advisor 1

Brian Barkdoll

Advisor 2

Xinyu Ye

Committee Member 1

Cory McDonald

Committee Member 2

Amy Marcarelli

Committee Member 3

Noel Urban

Abstract

The central theme of this dissertation is ecological scaling, which examines how small, localized features, such as beaver ponds, contribute to large-scale watershed processes and how different modeling approaches at various scales reveal distinct insights. Through a combination of probabilistic modeling and high-resolution empirical research, this work demonstrates that small ponded systems, particularly those created by beavers (Castor canadensis), serve as critical biogeochemical control points, whose contributions to sediment and nutrient dynamics have been historically underestimated.

In Chapter 1, I contextualize this research within the broader fields of freshwater ecology, watershed modeling, and ecological restoration. I introduce the theoretical basis for a dual-scale approach: one that recognizes the importance of fine-scale temporal variability in understanding nutrient cycling while also making the case for simplified, probabilistic models that enable large-scale ecological inference.

In Chapter 2, I present a Monte Carlo modeling framework used to estimate the historical density and ecological function of beaver dams across the contiguous United States. Results indicate that approximately 14.2 million beaver dams once retained 25.15 km³ of sediment and 1.08 million metric tons of phosphorus while supporting nearly 47,800 km² of wetland habitat. These findings affirm that beavers were once ecosystem architects at continental scales, capable of significantly shaping water quality and hydrology through their cumulative impacts.

In Chapter 3, I analyze high-frequency spatial and diel data collected from a single beaver pond to assess the dynamics of phosphorus cycling. The study reveals that soluble reactive phosphorus (SRP) concentrations vary by up to 20 µgP/L over 24-hour cycles and across pond zones. These fluctuations are likely driven by photosynthetic alkalinization, alkaline phosphatase activity, and acropetal nutrient transport, biologically mediated processes not commonly included in conventional models of internal loading. These results suggest that ponds are highly dynamic systems that do not conform neatly to lentic or lotic classifications.

In Chapter 4, I synthesize these findings and argue for a flexible, scale-explicit modeling framework in aquatic ecosystem research. Rather than viewing complex and simplified models as mutually exclusive, I propose that each scale of analysis contributes different but complementary insights. The large-scale modeling work reveals the historical ecological magnitude of beaver activity, while the small-scale observations show how local biological processes mediate nutrient cycling. I also emphasize the need for temporally resolved sampling in aquatic systems, as single-time-point sampling would have failed to detect the biogeochemical variability documented in this study. Collectively, this dissertation supports growing calls in freshwater science and restoration ecology to reintegrate beaver-mediated processes into watershed management, and it provides both empirical and theoretical contributions to the study of cross-scale

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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