Nitrogen Fixation in River Networks: Constraints and Consequences

SCU students samplingNitrogen fixation has great potential to influence productivity, species assemblages, and food web interactions, particularly in nitrogen limited stream ecosystems.  Yet, to date, nitrogen fixation has been considered relatively unimportant in streams and its contribution remains largely unknown.  Preliminary data from the South Fork Eel River basin indicate that nitrogen fixation rates are often substantial, but highly variable in space (with drainage area) and time (seasonally and inter-annually).  

The main objective of this project is to understand how environmental gradients associated with network position and climatic variation influence spatial and temporal patterns in producer species assemblages and nitrogen fixation.  The results will lead to a better mechanistic understanding of factors that control nitrogen fixation and reveal transition points in the stream network where constraints on nitrogen fixation shift between light, grazer, and nutrient control, and how these points shift spatially up- or downstream over time.   Connecting our results with the timing and  magnitude of flooding will also aid in efforts to predict how controlsand consequences of nitrogen fixation are likely to shift in response to altered land use,fixerbottle2 precipitation patterns, and variable climatic conditions.  

This project is funded by an National Science Foundation Ecosystems Grant (DEB-0950016) and a SCU Large-Scale 3M Grant and has supported a number of SCU student research projects

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