부산대학교 도서관

Groundwater nitrate‐N isotopes (δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$) 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− ${{\text{NO}}_{3}}^{-}$ for riparian zones affected by relict milldams and road salt salinization. Contrary to natural, undammed conditions, groundwater δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$ values declined from the upland edge through the riparian zone and were lowest near the stream. Groundwater δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$ values increased for low electron donor (dissolved organic carbon) to acceptor NO3− $\left({{\text{NO}}_{3}}^{-}\right)$ ratios but decreased beyond a change point in ratios. Groundwater δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$ 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− ${{\text{NO}}_{3}}^{-}$ can provide valuable insights into process mechanisms and can serve as "imprints" of anthropogenic activities and legacies. Plain Language Summary: Human activities and their legacies can alter our environment and the imprints can last for a long time. Here, we show the groundwater stable nitrogen isotopes can provide new and unexpected insights into nitrogen processing and cycling in riparian zones affected by dams and road salt salinization. Using such metrics/indicators we can investigate the changes in process mechanisms and the thresholds at which they change. This knowledge will help us better manage environments impacted by human landuse. Key Points: Groundwater N isotopes revealed altered riparian N processing due to milldams and salinizationGroundwater δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$ values changed along the riparian transect and in response to electron donor to acceptor (DOC:NO3− ${{\text{NO}}_{3}}^{-}$) ratiosLow groundwater δ15N‐NO3− ${{\text{NO}}_{3}}^{-}$ values were attributed to suppression of denitrification due to persistent anoxic conditions and salinization [ABSTRACT FROM AUTHOR]