Collaborative Resarch: Terrestrial Support of Lake Food Webs: A Multi-Isotope Approach

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The support of animals in ecosystems ultimately comes from two sources: primary production within an ecosystem (e.g. newly grown plant material) or primary production imported from other ecosystems (e.g. inputs of terrestrial material to an aquatic system). In lakes, it is well known that external inputs are large compared to internal primary production, but how these materials support lake food webs is less well documented. Deuterium is a stable isotope of hydrogen and deuterium content of terrestrial and aquatic primary producers is significantly different. Carbon and nitrogen stable isotope ratios, while less well contrasted, are also helpful, when coupled with deuterium, in discriminating sources of consumer support. Thus, integrated analysis of hydrogen, carbon and nitrogen stable isotopes can distinguish the use of internal versus external primary production by lake animals and microbes. In this proposal the PIs will use measurements of the stable isotopes carbon, nitrogen, and hydrogen along with a new modeling approach to test hypotheses about variation in terrestrial subsidies of aquatic consumers and how these vary among different types of lakes. The multi-isotope approach will also be applied to a whole lake nutrient fertilization experiment to test differences in the support of benthic versus pelagic consumers by external organic matter. This research will directly measure variation in the support of consumers by external materials and contribute to understanding the drivers of variation among ecosystems in these processes. Several undergraduates and 2 graduate students will receive training through this research in ecosystem ecology, limnology, modeling, and stable isotope methodology. Results from this research will contribute directly to courses taught by the PIs. The stable isotope model to be utilized in this study is a tool that will be of interest to other researchers. The model which runs on open access software will be made available through our website along with documentation, tutorials, and test data. In addition, the PIs propose to sponsor a half-day workshop at a national meeting on modeling methods in isotopic studies. Providing a multi-isotope model approach to the larger research community will be a significant component of the Broader Impacts of this project.