Nitrous oxide emissions from water bodies was a no-negligible contribution to nitrous oxide budgets in a subtropical forest catchment

Inland water was considered an important sources of nitrous oxide (N2O) production and emissions. However, assessment of indirect emission factors (EF5r) and contribution of different water body N2O on N2O budgets remains challenging, and results are uncertain due to limited data availability. In this study, floated chamber and boundary layer model method were conducted on four diurnal days, and two year observations at high temporal resolution in a subtropical forest catchment in Southeast China. The results showed that there was clearly diurnal characteristics of N2O emissions, and the CC98 model was more fit for estimating stream N2O emissions. The N2O fluxes from different water body was in the order: ponds (35.99±33.58 μg m^-2 h^-1) > main stream (17.09±4.48 μg m^-2 h^-1)> tributary (14.78±12.79 μg m^-2 h^-1). All of their EF5r (0.050%±0.058% to 0.249%±0.456%) were significantly higher than the IPCC 2006 default value 0.025%, suggesting that N2O emissions from China and world inland water may be grossly underestimated. Multiple regression model selected the dissolved oxygen and NH4-N concentrations as the crucial factors influencing the N2O emission fluxes from streams, whereas dissolved oxygen and NO3-N in ponds. Although the water body's surface area only occupied 2% in this catchment, where the N2O emissions fluxes were approximately contribute 1.4% of N2O budget in whole catchment. These findings will draw attentions to the role of inland water N2O productions and emissions in the contributions of N2O budgets, especially in the large scale N2O estimated.