Collaborative Research: Landscape Limnology of Mountain Watersheds: Nutrient Retention and Ecosystem Stability in Complex Aquatic Ecosystems

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Wayne Wurtsaugh & Michelle Baker, Utah State University in collaboration with, Brian McGlynn, Montana State University.Nutrient transport through complex watersheds is an important scientific and management problem that must be understood so that society can make appropriate management decisions to deal with the increasing levels of atmospheric and agricultural pollution threatening our water bodies. Most studies of nutrient transport have focused on single components of the watershed such as a stream or lake, but little is know about how combinations of streams and lakes that exist in watersheds influence these processes. Our work will address how interacting complexes of lakes, lake bottoms (littoral zones), streams, and their subsurface component (hyporheic zones) interact to influence nitrogen transport through watersheds in the Sawtooth Mountains of Idaho. We suggest that in simple watersheds without lakes or highly developed hyporheic zones, nutrients will runoff quickly during spring snowmelt so that little is left to fuel the growth of aquatic plants (phytoplankton, periphyton) latter in the summer. However, we expect that in complex watersheds with many lakes, the spring pulse of nitrogen will be dampened, thus providing a more stable supply of this nutrient than in simple watersheds. If nutrient delivery is stabilized, we expect that growth of phytoplankton and periphyton will also be less pulsed and thus increase ecosystem stability. We will test these ideas by measuring nutrient movement at small spatial scales with the stable isotope of nitrogen (15N), using those rates to model how nutrient transport occurs within whole watersheds, and then testing our model predictions with a whole-drainage tracer experiment and with large-scale watershed measurements of nutrient flux and algal growth in lakes and streams. To broaden the impact of our work, we will collaborate with educators to develop curricula for elementary school children, and make modules available for web-based learning.