Contribution from a eutrophic temperate estuary to the landscape flux of nitrous oxide. (15th August 2022)

• Record Type: Journal Article
• Authors: Lequy, Emeline; Asmala, Eero; Ibrom, Andreas; Loubet, Benjamin; Massad, Raia Silvia; Markager, Stiig; Garnier, Josette
• Is Part Of: Water research. Volume 222(2022)
• Publication Date: 2022-08-15
• Subjects: Greenhouse gas -- Water-atmosphere interface -- Statistical modeling -- Eddy covariance -- Roskilde Fjord; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.118874
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: We developed an approach to predict N2 O fluxes from the eutrophic Roskilde Fjord (RF). RF was a sink of N2 O during the study period. Estimated landscape N2 O fluxes fell in between the agricultural ones and the RF ones. Water quality measures and statistical modeling cost-effectively evaluated N2 O fluxes. Abstract: For mitigation of climate change, all sources and sinks of greenhouse gases from the environment must be quantified and their driving factors identified. Nitrous oxide (N2 O) is a strong greenhouse gas, and the contribution of aquatic systems to the global N2 O budget remains poorly constrained. In this study, we measured N2 O concentrations in a eutrophic coastal system, Roskilde Fjord (Denmark), and combined measurements with statistical modeling to quantify the N2 O fluxes and budget in the system over a period of six months. To do so, we collected water at 15 sampling points and measured N2 O concentrations along with physico-chemical water quality parameters, e.g. temperature, salinity, dissolved inorganic nitrogen and phosphorus, and silicon. We used mixed-effect regression models to predict N2 O concentrations in the water from water quality parameters. We then derived N2 O fluxes using well-established equations of N2 O solubility and water-atmosphere exchanges. These fluxes were then put in perspective with those measured at the landscape scale by eddy-covariance at a 96 m nearby tall tower, and to those estimated from the agricultural land next to the fjord using Intergovernmental Panel on Climate Change (IPCC) guidelines. N2 O concentrations in the Roskilde Fjord ranged between 2.40 and 8.05 nmol l −1 . The best fitting model between water parameters and N2 O concentrations in water included phosphorus and temperature. We estimated that (i) Roskilde Fjord was a sink of N2 O, with a median inward flux of -0.04 nmol m −2 s −1, (ii) while the surrounding median agricultural flux was 0.13-0.18 nmol m −2 s −1, and (iii) the median landscape flux was 0.07 nmol m −2 s −1 . All estimates of N2 O fluxes were of the same magnitude and consistent with each other. These preliminary results need to be consolidated by further research. Graphical abstract: Image, graphical abstract