Inamdar, S., M. Peipoch, M. Sena, B, Joshi, M.M. Rahman, J. Kan, E.K. Peck, A. Gold, T.L.E. Trammell, and P.M. Groffman. 2024. Geophysical Research Letters 51(5): e2023GL106888.
DOI/Permalink (Open access)
Abstract
Groundwater nitrate-N isotopes (δ15N-NO3−) have been used to infer the effects of natural and anthropogenic change on N cycle processes in the environment. Here we report unexpected changes in groundwater δ15N-NO3− for riparian zones affected by relict milldams and road salt salinization. Contrary to natural, undammed conditions, groundwater δ15N-NO3− values declined from the upland edge through the riparian zone and were lowest near the stream. Groundwater δ15N-NO3− values increased for low electron donor (dissolved organic carbon) to acceptor (NO3−) ratios but decreased beyond a change point in ratios. Groundwater δ15N-NO3− values were particularly low for the riparian milldam site subjected to road-salt salinization. We attributed these N isotopic trends to suppression of denitrification, occurrence of dissimilatory nitrate reduction to ammonium (DNRA), and/or effects of road salt salinization. Groundwater δ15N-NO3− can provide valuable insights into process mechanisms and can serve as “imprints” of anthropogenic activities and legacies.
