Assessing the sensitivity of kettle ecosystems to climatic and anthropogenic disturbances

Human-induced global change raises important questions about ecosystem resilience to external perturbations. Kettle peatlands have been underutilized in studies of ecosystem response to climatic and anthropogenic disturbance due to a widely accepted hypothesis that their development is gradual, climate-independent, and driven purely by autogenic succession. In this dissertation, I review the scant data underpinning this hypothesis and present alternative conceptual models in which peatland development is driven by climate and mediated by surficial geology. These hypotheses were tested at two sites using paleoecological techniques. Fallison Bog records a complex developmental history that included both terrestrialization and paludification. Episodes of peatland establishment centered on 5000, 3200, 2000, 1000, 700, and 400 cal yr BP. Review and synthesis of published data revealed significant temporal correlations between peatland development in Fallison Bog and in 75 cores collected from 37 basin-filling peatlands across the Great Lakes Region (r = 0.70), suggesting a common climatic driver. A spatially explicit model of whole-system carbon accumulation was developed for Fallison Bog. Model results indicate accumulation of ∼ 6655 t of carbon during the Holocene, 66% of which accumulated in peat within the last 5000 years. Results from Titus Bog indicate that peatland establishment episodes centered on 800, 650, and 400 cal yr BP. Each establishment event coincided with or immediately followed a multidecadal drought recorded in regional climate reconstructions. Data suggest little change on the floating peatland until European settlement around 1850 A.D. Analysis of recent peat deposits at Titus Bog indicate that deforestation of the surrounding uplands resulted in dust deposition on the peatland surface, increasing nutrient availability and initiating a cascade of ecosystem-level changes. Plant communities shifted from Sphagnum-dominance to vascular-plant-dominance, including increased recruitment of Pinus strobus onto the peatland. Testate amoeba communities shifted toward those adapted to highly variable micro-environmental conditions, and likely reflect broader changes in microbial communities. These results demonstrate that indirect and often overlooked human disturbances can lead to dramatic structural and functional alterations of carbon-rich wetlands. Collectively, this work demonstrates the sensitivity of kettle peatlands to outside disturbances and highlights their potential vulnerability to external disturbances.