A lot of scientific effort is now being focused on how plants and animals will respond to a warming climate. This is critically important, but very difficult because there are many other global changes occurring at the same time. For example, humans have widely spread large amounts of nitrogen and phosphorus, which are important fertilizers. But what effects excess nutrients that are deposited mainly on land but then wash into aquatic ecosystems will have as the world warms is not clear. So studies are needed that examine how multiple global changes like these interact at the same time. The goal of this research project is to explore how freshwater ecosystems respond to warming and nutrient enrichment simultaneously. The research is important because nutrient enrichment may drastically alter the effects of warming on streams and rivers and so the results should be useful as society tries to adapt to warmer conditions. Results will also inform ecological theory that attempts to use basic principles for understanding how species and ecosystems may respond to global change. An education program will be an integral part of this project and will include the development of film documentaries, student podcasts, and the more traditional training of undergraduate and graduate students, as well as research technicians.
This project will be conducted in a geothermally active region of southwestern Iceland, where streams exhibit a wide range in ambient temperature without significant differences in background chemistry that would otherwise influence results. The research team will use the differences in natural temperature between streams to examine how nutrient supply and temperature together influence the ecology of streams and rivers. The first objective is to quantify effects of warming and nutrients on the origin and fate of carbon and nitrogen (e.g., ecosystem productivity, nutrient uptake, and nitrogen-fixation). The team will then combine ecosystem-scale nitrogen and phosphorus additions with controlled streamside channel experiments to examine how the influence of warming on the ecology of streams and rivers is affected by nutrient supply, and whether short-term responses to warming differ from those observed in natural ecosystems over longer periods. Responses of these ecosystem-level processes should also shape how energy and materials flow through food webs from algae to trout. The second objective is to quantify the interactive effects of temperature and nutrients on the routes of energy and materials through river and stream food webs. Food web responses to nutrients between streams of varying temperatures will be tracked using a combination of stable (i.e., non-radioactive) isotope tracer additions, secondary production measurements, and flow food web analyses. This research will provide much needed information about how two dominant global change drivers, warming and nutrient enrichment, interact to influence biodiversity and ecosystem function in an important freshwater habitat.
