Date of Award
Spring 2026
Language
English
Embargo Period
5-1-2027
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
College/School/Department
Department of Atmospheric and Environmental Sciences
Program
Climate Science
First Advisor
Aubrey Hillman
Committee Members
𝐌𝐚𝐭𝐡𝐢𝐚𝐬 𝐕𝐮𝐢𝐥𝐥𝐞, 𝐌𝐚𝐫𝐤 𝐁𝐫𝐞𝐧𝐧𝐞r, 𝐃𝐚𝐧𝐢𝐞𝐥 𝐁𝐚𝐢n
Keywords
Paleolimnology; metal contamination; thermal stratification; ecological resilience; eutrophication; temperate lakes
Subject Categories
Biogeochemistry | Geochemistry | Other Earth Sciences
Abstract
Temperate lake ecosystems are increasingly stressed by multiple human disturbances, including historical land-use change, atmospheric pollution, and ongoing climate warming. While individual stressors are well studied, less is known about how their interactions influence long-term ecosystem trajectories, including recovery or transitions to novel ecological states, defined here as systems whose structure and function fall outside the range of historical variability. This dissertation reconstructs thousands of years of cumulative impacts at four Adirondack lakes by integrating geochemical proxies, biological indicators, and lake models to evaluate human-linked changes relative to natural variability.
Metal flux reconstructions reveal that the timing of metal enrichment is consistent across lakes, while the concentrations vary with disturbance history. Lakes with combined watershed disturbance and acid deposition exhibited synergistically amplified metal inputs, with Pb concentrations exceeding 300 ppm at peak enrichment, whereas minimally disturbed systems reflecting only atmospheric deposition, exhibited a third of an enrichment. Despite substantial reductions in pollution following the Clean Air Act, recovery was particularly delayed for Pb due to legacy storage in watershed soils. Notably, this study provides the first evidence of full recovery in Northeast U.S. lakes approximately 50 years after Clean Air Act implementation. Full recovery defined here as a return to background concentrations, recognizing low residual atmospheric concentrations.
To assess the role of climate forcing, we reconstructed changes from 1940 to 2024 in thermal structure and ice phenology at three lakes using an ensemble of five one-dimensional lake models. Results indicate a synchronous temperature shift in the late 1970s, characterized by accelerated warming and substantial changes in ice dynamics. Warming is concentrated in transitional months (April, May, and October), leading to an extension of stratification by 30–40 days. Ice cover duration declined by 15–18 days overall, with the greatest changes occurring in spring, extending algal growth periods.
Finally, sedimentary productivity proxies indicate some lakes have crossed critical thresholds and become locked into new ecological states, with an inability to recover. At the undisturbed lake, this shift occurred despite the absence of watershed nutrient inputs, indicating internally driven processes linked to warming, prolonged stratification, and redox-mediated nutrient recycling. These transitions were abrupt and non-linear. In contrast, lakes impacted by watershed disturbances shift to a novel ecological state driven by external nutrient inputs, followed by a later regime shift, defined as an abrupt and persistent reorganization of the system, coincident with accelerated warming.
Together, this work demonstrates that lake responses to multiple stressors reflect synergistic interactions that push systems beyond their natural range of historical variability. These findings highlight the importance of long-term records and the need for monitoring for identifying tipping points and indicate that, even after external stressors decline, internal feedbacks and hysteresis can limit recovery, reducing ecosystem resilience.
License
This work is licensed under the University at Albany Standard Author Agreement.
Recommended Citation
Hooler, Skylar, "Reconstructing Human Impacts to Assess Tipping Points in Temperate Lake Ecosystems Under Successive Stress" (2026). Electronic Theses & Dissertations (2024 - present). 460.
https://scholarsarchive.library.albany.edu/etd/460