Natural (15)N(15)N abundances constrain fixed nitrogen loss.

Natural abundances of the rare 15 N15 N isotopologue of N2 directly reveal widespread nitrogen loss across diverse aquatic environments, with values indicating significant nitrogen removal.

• Why it matters: Understanding fixed nitrogen loss is crucial for grasping global nitrogen cycling and productivity, yet current methods rely on indirect proxies or ex situ experiments, limiting accuracy.
• What they did: The study measured 15 N15 N isotopologue abundances in various aquatic systems, exploiting the distinct isotopic signatures of biological N2 production sources to distinguish them.
• The result: Findings show that 15 N15 N measurements uncover extensive nitrogen loss previously hidden by physical gas accumulation and nitrogen fixation, providing a direct framework for constraining nitrogen loss in aquatic systems.