Publication
Global patterns of nitrate isotope composition in rivers and adjacent aquifers reveal reactive nitrogen cascading
Publisher:
Springer Science and Business Media LLC
Date:
03-2021
DOI:
10.1038/S43247-021-00121-X
Abstract: Remediation of nitrate pollution of Earth’s rivers and aquifers is h ered by cumulative biogeochemical processes and nitrogen sources. Isotopes ( δ 15 N, δ 18 O) help unravel spatiotemporal nitrogen(N)-cycling of aquatic nitrate (NO 3 − ). We synthesized nitrate isotope data ( n = ~5200) for global rivers and shallow aquifers for common patterns and processes. Rivers had lower median NO 3 − (0.3 ± 0.2 mg L −1 , n = 2902) compared to aquifers (5.5 ± 5.1 mg L −1 , n = 2291) and slightly lower δ 15 N values (+7.1 ± 3.8‰, n = 2902 vs +7.7 ± 4.5‰, n = 2291), but were indistinguishable in δ 18 O (+2.3 ± 6.2‰, n = 2790 vs +2.3 ± 5.4‰, n = 2235). The isotope composition of NO 3 − was correlated with water temperature revealing enhanced N-cascading in warmer climates. Seasonal analyses revealed higher δ 15 N and δ 18 O values in wintertime, suggesting waste-related N-source signals are better preserved in the cold seasons. Isotopic assays of nitrate biogeochemical transformations are key to understanding nitrate pollution and to inform beneficial agricultural and land management strategies.