Terrestrial carbon in aquatic ecosystems: experimental tests of the subsidy-stability hypothesis

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Ecosystems are spatially linked by the flux of materials and energy. Over the past decade there has been growing appreciation that the movement of resources across the landscape can act to subsidize populations in local habitats. In addition, theory suggests that resource subsidies may act to stabilize food webs and ecosystems, but these predictions remain largely untested. This study will examine the effects of terrestrial-derived dissolved organic carbon (DOC) on the stability of aquatic ecosystem metabolism. Traditionally been viewed as a low quality resource, it is now recognized that terrestrial DOC inputs are a resource subsidy for bacteria that can determine whether recipient aquatic ecosystems function as sources or sinks of atmospheric carbon dioxide. The first goal of this project is to describe the shape, magnitude, and direction of subsidy-stability relationships using a set of whole-pond experiments that manipulate the supply rate of terrestrial DOC. The second goal of this project is to identify the mechanisms by which terrestrial DOC influences aquatic ecosystem stability. Specifically, the project will assess whether DOC affects ecosystem stability by modifying nutrient cycling, altering temperature dynamics, or by altering interaction strengths among different groups of microorganisms. The objectives of this project will be assessed using a combination of autonomous sensor technology to quantify ecosystem metabolism and temperature variability, radioisotope assays to measure nutrient cycling, and molecular techniques to evaluate changes in the metabolic activity of microbial communities. At a global scale, the export of terrestrial DOC to aquatic ecosystems is increasing due to a combination of factors, including atmospheric deposition, climate variability, and shifting land use. The tools and approaches developed in this proposal will address this phenomenon and help scientists and managers predict how changes in DOC loading affect ecosystem functioning and water quality under existing and future climate scenarios. This project has a significant education and outreach component that will foster interactions among the Kellogg Biological Station (KBS), Michigan State University (MSU), and rural Michigan K-12 school districts. Specifically, the project will continue an ongoing collaboration that will introduce concepts of ecological stability, microbial diversity, and biogeochemical cycling into the high-school classroom. The project will also provide interdisciplinary research training in the fields of ecosystem science, quantitative ecology, and molecular biology for undergraduate students, a graduate student, a high school teacher, and postdoctoral researcher.