Nitrate—nitrogen from agricultural fields and other sources—represents a serious threat to water quality, as it promotes algae blooms and declining oxygen levels in rivers and other water bodies.
Riparian zones along rivers can potentially remove nitrate because groundwater in these areas interacts with plants and bacteria. Both plants and bacteria consume nitrate, but while plants store the nitrogen locally in their tissues, some forms of bacteria convert the nitrate into nitrogen gas that is released to the atmosphere and hence removed as a concern for water quality. This latter process is known as denitrification.
Lutz et al.  make a significant advance in the ability to separate denitrification from other nitrogen cycling processes with a novel use of stable, or non-radioactive, isotopes of nitrogen and oxygen. As bacteria consume nitrate the concentration of heavier versus lighter isotopes changes. By combining this isotope information with measured concentrations of nitrate, the authors develop a simple mathematical model to distinguish nitrate removal to the atmosphere from processes that store nitrate.
The new model can be generally applied to gain insight on processes of nitrogen removal from groundwater in riparian zones, and thereby overcome a major challenge for making and interpreting environmental measurements.
Citation: Lutz, S. R., Trauth, N., Musolff, A., Van Breukelen, B. M., Knöller, K., & Fleckenstein, J. H. . How important is denitrification in riparian zones? Combining end‐member mixing and isotope modeling to quantify nitrate removal from riparian groundwater. Water Resources Research, 56, e2019WR025528. https://doi.org/10.1029/2019WR025528
D. Scott Mackay, Editor, Water Resources Research