Nitrate‐Driven Eutrophication Supports High Nitrous Oxide Production and Emission in Coastal Lagoons
Henry L. S. Cheung, Mindaugas Žilius, Tobia Politi, Elise Lorre, Irma Vybernaite‐Lubiene, Isaac R. Santos, Stefano Bonaglia
Abstract
Abstract Under current circumstances, coastal lagoons are net emitters of nitrous oxide (N 2 O) to the atmosphere. We hypothesize that widespread nitrogen‐driven coastal eutrophication will enhance N 2 O production and emissions from coastal lagoons. Here, we quantified spatial and temporal patterns of sediment‐water and water‐air N 2 O fluxes in three large eutrophic lagoons in Europe. Annual sediment N 2 O fluxes ranged between −0.3 ± 0.3 (summer) and 10.6 ± 2.0 μmol m −2 d −1 (spring). In spring, conspicuous sediment effluxes were mainly supported by high nitrate concentrations (89–202 μM) and incomplete denitrification. In summer, a small sediment influx was related to nitrate limitation (0–9 μM), potentially leading to N 2 O demand for denitrification. The water‐air N 2 O fluxes were comparable with benthic fluxes, indicating that sediment was the main source of N 2 O to the atmosphere. The hypereutrophic Curonian Lagoon had the largest N 2 O emission at 4.9 ± 2.1 μmol m −2 d −1 , while the less eutrophic Oder and Vistula lagoons emitted 2.5 ± 1.0 and 2.0 ± 0.7 μmol m −2 d −1 , respectively. Our observations, combined with earlier measurements in coastal lagoons worldwide, revealed a lagoon median (Q1–Q3) N 2 O emission of 14.2 (2.7–29.8) Gg yr −1 , which is about 48% higher than previous estimates. Eutrophication driven by large nitrogen inputs is thus a significant driver of coastal N 2 O emissions globally.