What Is This Study About? And, Why Go to Iceland?

Nostoc - a nitrogen-fixer
found in Hengill streams

One of our study streams in Iceland  -
rich with nitrogen-fixers

Nitrogen fixation is the conversion of nitrogen gas in the atmosphere into a usable form for protein synthesis and growth of a unique group of organisms called cyanobacteria. By bringing this essential nutrient into the ecosystem, these organisms may affect productivity, species composition, food web interactions, and rates of nutrient cycling in rivers, and ultimately how whole ecosystems respond to changes in temperature. The relationship between nitrogen fixation rates and temperature is therefore important for understanding how freshwater ecosystems, with a complexity of interacting species, will respond to climate warming and thus, this study will help us to make more informed climate change predictions.  The Hengill region of Iceland is an ideal location to do this work because we can isolate temperature as our variable of interest in an intact ecosystem with its resident species, and separate it from other environmental variables including light and nutrient availability.   The Hengill region is geothermally active, and as a result, spring-fed rivers emerge from the ground at dramatically different water temperatures, depending on the extent to which the water has heated underground.  In Iceland, we will study 13 comparable rivers that span a 25 degree Celsius temperature gradient, while the water chemistry, underlying geology, and light availability remain consistent across streams.  This will allow us to determine how temperature alone influences nitrogen fixation rates, and how nitrogen fixation itself feeds back on other critical biological processes including photosynthesis and respiration rates, species composition, and the physiological demand for essential nutrients by algae and microorganisms that inhabit the river.  Ultimately, this project will help us to better understand how in-stream nitrogen fixation influences carbon cycling at the ecosystem scale, and how both are likely to respond to changes in temperature.