%0 Journal Article
%T Predicting High-Dimensional Isotope Relationships from Diagnostic Fractionation Factors in Systems with Diffusional Mass Transfer
%J -
%D 2019
%R https://doi.org/10.1021/acsearthspacechem.8b00149
%X High Resolution Image Download MS PowerPoint Slide A dual or multiple stable isotope relationship, for example, a trajectory in a ¦Ä£¿¦Ä (or ¦Ä¡ä£¿¦Ä¡ä) space, can be used to deduce the relationship of underlying diagnostic isotope fractionation factors (¦Á) and therefore reveal the mechanism of a reaction process. While temporal data sampled from a closed-system can be treated by a Rayleigh distillation model, spatial data should be treated by a reaction-transport model. Owing to an apparent similarity between the temporal and spatial trajectories, the research community has often ignored this distinction and applied a Rayleigh distillation model to cases where a reaction-transport model should be applied. To examine the potential error of this practice, here we compare the results of a Rayleigh distillation model to a diffusional reaction-transport model by simulating the trajectories in nitrate¡¯s ¦Ä¡ä18O£¿¦Ä¡ä15N space during a simple denitrification process. We found that an incorrect application of a Rayleigh distillation model can underestimate the degree of a diagnostic fractionation to 50% but results in an insignificant difference in the regression slope of a ¦Ä¡ä£¿¦Ä¡ä trajectory when ¦Á ¡Ö 1.0. The regression slope predicted by a Rayleigh distillation model can, however, be 0.03¨C0.3 greater than predicted by a reaction-transport model when NO3¨C is involved in complex nitrogen cycling. Our reaction-transport model rarely predicts a ¦Ä¡ä18O£¿¦Ä¡ä15N regression slope > 1 for reasonable Earth surface conditions. We found that for those published cases of regression slopes > 1, many can be attributed to the grouping of multiple NO3¨C sources from independent origins. Our results highlight the importance of linking the underlying physical model to the plotted data points before interpreting their high-dimensional isotope relationships
%U https://pubs.acs.org/doi/10.1021/acsearthspacechem.8b00149