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  • Title: Nitrous oxide emissions from subtropical estuaries: Insights for environmental controls and implications.
    Author: Li X, Qi M, Gao D, Liu M, Sardans J, Peñuelas J, Hou L.
    Journal: Water Res; 2022 Apr 01; 212():118110. PubMed ID: 35085843.
    Abstract:
    Estuaries are expected to contribute large nitrous oxide (N2O) emissions, however the environmental controls and implications of N2O emissions have not been well understood. Here we investigated water N2O concentrations, fluxes and sources in wet and dry seasons for 2019-2020 in five subtropical estuaries spanning hydrologic characteristics and nitrogen concentrations gradient. Water dissolved N2O concentrations and fluxes were in a range of 15.8-84.9 nmol L-1 and 0.66-22.2 µg m-2 h-1, respectively. These studied estuaries were oversaturated in N2O, with the saturations of 118-615%. Water dissolved N2O concentrations, saturations and fluxes increased significantly as nitrogen concentrations increase, whereas they did not differ significantly between the wet and dry seasons. Water N2O emissions, however, were also lower in the estuaries characterized by large discharge and water flow. N2O saturations and fluxes were determined directly by water nitrogen and oxygen concentrations and more indirectly by water temperature and velocity. The δ15N-N2O and site preference-N2O varied respectively from 2.86 to 11.31‰ and from 1.58 to 11.72‰, which overlapped the values between nitrification and denitrification. Nitrification and denitrification were responsible for 18.7-38.1% and 61.9-81.3% of N2O emissions, respectively. Indirect N2O emission factors were 0.08-0.14% and decreased with increasing total nitrogen concentrations. It is estimated that water N2O emissions in CO2 equiv could offset approximately 4.9% of average CO2 sink of China estuaries. Therefore, these results suggest that nitrogen concentrations and hydrologic characteristics together modify N2O emissions and that estuaries may be the important contributors to N2O emissions.
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