Isotopic constraints on active nitrification in a eutrophic artificially oxygenated lake: Implications for nitrate regeneration and nitrous oxide production

作者：Alessandra Mazzoli, Claudia Frey, Cameron M. Callbeck, Jakob Zopfi, Teresa Einzmann, Chiara Piantoni, Tim J. Paulus, Moritz F. Lehmann · 发表于：Limnology and Oceanography · 年份：2026 · DOI：10.1002/lno.70281 · 被引用次数：1 · 研究领域：Aquatic Ecosystems and Phytoplankton Dynamics、Marine and coastal ecosystems、Isotope Analysis in Ecology

Abstract Nitrification is a key process in the aquatic nitrogen (N) cycle, but its products, nitrate (NO 3 − ) and nitrous oxide (N 2 O), contribute to eutrophication and greenhouse gas emissions, particularly in eutrophic lakes. Variations in in‐lake N cycling and N 2 O production pathways, as a function of seasonality and artificial oxygenation, remain poorly understood. We investigated nitrification in the artificially oxygenated eutrophic Lake Baldegg, by analyzing NO 3 − and N 2 O concentrations and isotope ratios, and measuring ammonium oxidation rates via 15 N tracer incubations over one year. An N isotope mass‐balance model revealed that nitrification sustained only 5.3 ± 0.7% of total NO 3 − consumption in the epilimnion, where external N loadings were influential, and considerably more in the hypolimnion (81.6 ± 18.5%) during stratification. Dual NO 3 − isotope signatures (Δδ 18 O : Δδ 15 N ~ 1.5–1.73) and associated negative NO 3 − isotope anomalies confirmed epilimnetic nitrification, though external inputs partly obscured this signal. During stratification, relatively high hypolimnetic nitrification rates correlated with organic matter export, and seemed linked to sediment resuspension and artificial oxygenation. While sedimentary denitrification/DNRA dominated hypolimnetic NO 3 − reduction (with negligible effects on δ 15 N‐NO 3 − and δ 18 O‐NO 3 − ), transient suboxic conditions enabled water column denitrification during stratification (24.1–30.2% of the total...