Nah Eun Kim Master's Thesis Defense Ecological Sciences and Engineering Forestry and Natural Resources Tipping Points Conceptual Models and Applications in the Great Lakes Basin Wednesday, April 18, 2012 3:00 p.m. ABE Building, Room 301 ABSTRACT Humans have left their imprints on natural landscapes since the beginning of evolutionary time. The influence of man on planet Earth is undeniable, observable in changes in the atmosphere, lithosphere, and hydrosphere. Our alterations to the globe have become so pervasive that they have ushered in an era fittingly named 'the Anthropocene'. As the drivers of the Anthropocene, we continue to exert a disproportionately large influence on the abiotic and biotic aspects of our terrestrial and aquatic ecosystems. The accumulation of our actions have triggered extensive die-offs of mega flora and fauna, and the destruction of important habitats both onshore and offshore, many of which are referred to as "hot spots" of biodiversity. On a more regional to local scale, the effects of mankind are self-evident with the widespread degradation of critical landscape components such as air quality, soil fertility, and hundreds of thousands of stream miles. While there are countless causes to these problems-some of which are natural-the recurring perpetrator behind the disintegration is human land use and land cover (LULC) change. Conventional anthropogenic LULC change, such as urbanization, catalyzes many alterations within the landscape that exacerbate conditions for the degradation of natural systems, such as streams and lakes. For example, alterations in the local or regional hydrology trigger changes within the flow patterns of streams and the composition of materials (i.e. contaminants) that enter waterways. All of these interactions imply the strong interconnections and feedbacks between natural systems and human institutions which are characteristic of complex systems. Ecologists have studied natural ecosystems using the framework of complex systems in an attempt to understand the effects of change-both natural and human-caused-on ecosystems. Complex systems are characterized as possessing multiple levels of organization within which feedbacks and nonlinear behaviours occur which, in turn, large changes occur from comparatively small forcings. This kind of nonlinear behavior is commonly referred to as the 'tipping point'. As homage to the pervasive and often negative effects of anthropogenic land use change on the natural systems which sustain us, my thesis will explore how freshwater systems are affected by human land use using a complex systems approach. More specifically, this thesis will attempt to address how complex system approaches can be used to understand how anthropogenic stressors affect freshwater river ecosystems in the U.S. Great Lakes basin. Chapter 1 will provide a general overview of the many anthropogenic effects on the Great Lakes region, with a focus on human land use change. Chapter 2 will lay out a conceptual framework for tipping points that will be applied in Chapter 3, which will identify land use-stream quality tipping points within Michigan, Wisconsin, and Illinois streams. Chapter 4 is a collection of fact sheets that emphasize the effects of common nonpoint source pollutants that run off from anthropogenic land uses. Christal Musser Program Coordinator Ecological Sciences and Engineering Interdisciplinary Graduate Program Purdue University Young Hall, Room 948 155 S. Grant Street West Lafayette, IN 47907 765-494-2102 musser@purdue.edu<mailto:musser@purdue.edu> http://www.purdue.edu/ese<http://www.purdue.edu/dp/ese>