CURRENT BARRIERS TO SIMULTANEOUS QUANTIFICATION OF N2 FIXATION AND DENITRIFICATION FROM OPEN-CHANNEL DIEL N2 FLUX (AND SOME IDEAS FOR BREAKING THEM)

The contribution of dinitrogen (N2) fixation to stream nutrient budgets could be better quantified with whole-reach scale rate estimates. While the opposite of N2 fixation (denitrification) can be estimated from open-channel diel N2 flux models, this approach needs refinement to account for all the ways that N2 enters, exits, or is transformed in ecosystems. Therefore, we ask: how can we more accurately estimate N2 fixation and denitrification rates from diel N2 concentrations, either by better parameterization of model unknowns or by changes to the model structure? Using syntheses of denitrification and N2 fixation rates in streams, we investigate the degree of divergence between process rates estimated with published N2 flux model structures and those derived from other methods, such as 15N tracers or acetylene chambers. We review the N2 flux and transformation pathways that are not captured in current model structures, and review ways to (a) integrate them into the N2 flux model equation, and (b) estimate rates of these processes in rivers to better constrain Bayesian model priors. Using example data, we build on published N2 flux model equations, demonstrating the impact of changes to the model structure and Bayesian priors on the fit between measured and predicted N2 concentrations. Improved N2 flux models could provide a structure to measure N2 fixation and denitrification on the same temporal and spatial scale as other reach and ecosystem-scale process measurements (eg. metabolism, nutrient uptake), building a framework to understand controls on these processes across ecosystems.

Primary Presenter: Michelle Catherine Kelly, Michigan Technological University (mckelly1@mtu.edu)

Authors:

Michelle Catherine Kelly, Michigan Technological University  (mckelly1@mtu.edu)

Megan Berberich, Michigan Technological University  (meberber@mtu.edu)

Jason Taylor, Baylor University  (jason_taylor1@baylor.edu)

Amy Marcarelli, Michigan Technological University  (ammarcar@mtu.edu)