Nitrate isotopes in catchment hydrology: Insights, ideas and implications for models

Matiatos, Ioannis; Moeck, Christian; Vystavna, Yuliya; Marttila, Hannu; Orlowski, Natalie; Jessen, Søren; Evaristo, Jaivime; Sebilo, Mathieu; Koren, Gerbrand; Dimitriou, Elias; Müller, Sasha; Panagopoulos, Yiannis; Stockinger, Michael P.

doi:10.1016/j.jhydrol.2023.130326

Cited by 5 publications

(1 citation statement)

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“…Earth’s rivers are major aquatic receiving environments of terrestrial nitrogen (N) sources transported via atmospheric deposition, agricultural runoff, hyporheic, or groundwater flow . Protecting the health of Earth’s rivers from excess N pollution requires untangling the contributions of the predominant nitrate sources, however, the nonconservative behavior of nitrate in the aquatic N-receiving environment makes source tracing a challenge owing to the coexistence of multiple biogeochemical processes that transform nitrate and other N-forms. − Microorganisms and biota mediate N transformations in rivers through stepwise oxidation and reduction processes in the water body, the riparian zone, and the water–sediment interface. , …”

Section: Introductionmentioning

confidence: 99%

Isotopes Reveal the Moderating Role of Ammonium on Global Riverine Water Nitrogen Cycling

Matiatos,

Monteiro,

Sebilo

et al. 2024

ACS EST Water

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The relationship between δ 18 O and δ 15 N in aquatic nitrate (NO 3 − ) is used to assess nitrogen (N) cycling, primarily relying on controlled laboratory tests of isotope fractionation from nitrification and denitrification. Nevertheless, laboratory findings frequently contradict the evolution of the nitrate δ 18 O/δ 15 N ratios observed in natural river systems. We investigated this disparity by using moderated regression modeling, analyzing a global data set (n = 1303) of nitrate isotopes encompassing rivers with varying NH 4 + /NO 3 − ratios and δ 18 O−H 2 O values. First, our analysis revealed that elevated δ 18 O/δ 15 N ratios (>0.6) were prevalent in rivers with high NH 4 + /NO 3 − ratios, suggesting reducing conditions that could potentially promote denitrification and/or ammonium accumulation. By contrast, lower δ 18 O/δ 15 N ratios (<0.5) predominated in rivers with low NH 4 + /NO 3 − conditions, suggesting oxidizing conditions favoring increased NH 4 + removal through nitrification. Second, when δ 18 O−H 2 O values were low, it resulted in reduced δ 18 O−NO 3− values during nitrification, which in turn lowered the δ 18 O/δ 15 N ratios. We discovered that the δ 18 O/δ 15 N ratios in nitrate were elevated in the fall, likely due to predominant processes, such as denitrification, and lower in the winter due to lower δ 18 O−H 2 O values. This global river assessment suggests a more significant influence of ammonium and the role of water oxygen in riverine N-nutrient isotope cycling than was previously considered.

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