Abstract
Nitrogen pollution to streams is altering the nitrogen cycling in unknown ways, causing challenges for predicting nitrogen fixation fluxes within aquatic ecosystems. Increasing nitrate pollution decreases the amount of nitrogen fixation occurring in streams. However, the relationship between stream nitrate concentration and the rate of nitrogen fixation is unknown. We predict that lower nitrate streams will have the highest rates of nitrogen fixation. Additionally, there will be much more energy produced in streams with nitrogen fixation compared to the amount required to fix the nitrogen. We estimated whole-stream gross primary production and nitrogen fixation fluxes using the diel change in dissolved nitrogen and oxygen gases compared to the expected dissolved gas saturation. Our whole-stream method is preferable to chamber estimates to understand the relationship between energy requirements for nitrogen fixation and gross primary production, but additional data is needed to distinguish between relationship types and make our measurements generalizable.
Featured photo by Intermountain Forest Service, USDA Region 4 Photography on Flickr. https://flic.kr/p/jbTRUj