Riverine N2O concentrations, exports to estuary and emissions to atmosphere from the Changjiang River in response to increasing nitrogen loads.

This study investigated the variations of dissolved N₂O and emissions over diurnal and seasonal temporal scales in 2009, as well as the time series of riverine N₂O export to estuary and emission to atmosphere in response to increasing anthropogenic nitrogen loads in the Changjiang River. For the diurnal study, N₂O concentrations ranged from 0.26 to 0.34 and from 0.44 to 0.52 μg N-N₂O L^-1 in August and October 2009, respectively. The dissolved N₂O was supersaturated with a mean value of 197%. Studies on N₂O emissions, also taken in August and October, ranged from 2.67 to 11.6 and from 6.72 to 15.2 μg N-N₂O m^-2 h^-1, respectively. For the seasonal study (June through December 2009), N₂O concentrations ranged from 0.34 to 0.72 μg N-N₂O L^-1 and were supersaturated in all the samples (average 212%). N₂O emissions ranged from 1.87 to 40.8 μg N-N₂O m^-2 h^-1. Our study found no significant differences in diurnal patterns of N₂O saturation but detected significant difference in seasonal patterns of N₂O saturation: higher during summer while lower during autumn and winter. We found a significant relationship between dissolved N₂O and river nitrate, which can predict the variation of N₂O concentrations in the River. The net production of N₂ ranged from 0.01 to 0.47 mgN-N₂L^-1. These excess N₂ values were significantly correlated to the N₂O production and are suggestive of denitrification in me river. Applying the Global News model to the river system using measures taken during the 1970 to 2002 period, we estimated N₂O emissions to atmosphere increased from 330 to 3650 ton N-N₂O yr^-1. During that same 1970-2002 period, N₂O exports to estuary increased from 91 to 470 ton N-N₂O yr^-1. Taken together, the findings reported here suggest that both the river N₂O concentrations and emissions would increase in response to rising anthropogenic nitrogen loads. Our study showed that the mean emission factor based on the ratio of the total N₂O flux to NOJ" flux is four times greater than the value of 0.0025 obtained with the methodology recommended by the Intergovernmental Panel on Climate Change. Thus, our findings reflect the open river channel rapid exchange of gases with the atmosphere. [ABSTRACT FROM AUTHOR]