Global circulation models predict enhanced hydroclimatic variability in the next century, likely exceeding the range of 20th century observations. Ecologists are faced with the critical challenge of anticipating potential ecosystem responses to these changes. This proposed dissertation research will use kettlehole basins in northern Wisconsin as model systems to study the effects of past hydroclimatic variability on ecosystem structure and function. The research is designed to test the hypothesis that peatland establishment and expansion in these systems is a threshold response to climate variability, in contrast to prevailing models that suggest limited climate sensitivity. Methods will include detailed paleoecological analyses of lake and peatland sediment cores from multiple kettlehole ecosystems. Paleoecological data will be integrated with information on basin morphology and landscape position to develop a model of kettlehole ecosystem dynamics under various global climate change scenarios. The proposed project will increase our understanding of the potential for ecosystem state-shifts in response to future climate changes. Results will help resource managers anticipate potential changes in kettlehole ecosystems in the coming century, as well as changes in the ecosystem services provided by these unique systems. In addition, the predictive model developed as part of this study will be coded in open-source software and equipped with an intuitive graphical user-interface, enabling access by resource managers, educations, and students.
Project Outcome Report: Award 1011224 Project Title: Dissertation Research: The sensitivity of kettlehole ecosystems to abrupt drought induced transformation Intellectual Merit: In this project, we critically examined the processes underlying the conversion of lake to wetland in kettlehole depressions, which are common features in previously glaciated landscapes of the United States. For more than a century, the development of these ecosystems was described by a simple model of plant succession that predicted a gradual pattern of wetland encroachment from the perimeter of the basin toward the center at a constant rate, independent of basin morphology or climate change. Almost all introductory ecology textbooks describe this model. We used evidence preserved in the sediments within a northern Wisconsin kettlehole basin to reconstruct habitat changes throughout the basin since it was formed about 12000 years ago. We sampled the sediments in 21 locations throughout the basin and performed detailed physical and biological analyses, demonstrating that the pattern of wetland development was complex, inconsistent with a simple model, and related both to climate and to the morphology of the underlying basin. Our work suggests that wetland encroached into the pond during drought-induced water level drawdowns, when substrate was exposed for plant colonization. Conversely, the wetland expanded outward during times of high water levels. Major episodes of wetland expansion occurred during times of well-documented changes in climate around 5000, 3000, 2000, and 1000 years ago. These results suggest that classic model of gradual peatland development in these systems can be rejected and replaced with an episodic model wherein peatland advancement potential is explicitly linked to climate-driven basin water levels as mediated by the physical shape of the basin. By extension, our work suggests that if future climate change leads to increased moisture variability in glaciated landscapes, then abrupt conversions of kettlehole ponds into wetlands could become common. Once wetland is established, reversion to pond is highly unlikely. Broader Impacts: The results of this work have improved our understanding of climate as a driver for ecological change, particularly by identifying the processes underlying abrupt and non-linear changes in ecosystem structure and function. Furthermore, our results have large implications for modeling carbon cycling in previously glaciated landscapes, where as much as 80% of carbon storage on the landscape can be in the form of peat and pond sediments, even in heavily forested regions. The project also provided research training for one graduate student and two undergraduate students. The graduate student was able to receive specialized training, which would have otherwise been impossible, and the undergraduate students gained experience in the scientific method and methods in a wet chemistry laboratory. Finally, the developmental and carbon model produced by this work will be provided to natural resource and land managers, so that they can better plan for a future of increasingly variable climate and extreme events.
