Nitrous oxide in the Changjiang (Yangtze River) Estuary and its adjacent marine area: Riverine input, sediment release and atmospheric fluxes

Dissolved nitrous oxide (N₂O) was measured in the waters of the Changjiang (Yangtze River) Estuary and its adjacent marine area during five surveys covering the period of 2002-2006. Dissolved N₂O concentrations ranged from 6.04 to 21.3 nM, and indicate great temporal and spatial variations. Distribution of N₂O in the Changjiang Estuary was influenced by multiple factors and the key factor varied between cruises. Dissolved riverine N₂O was observed monthly at station Xuliujing of the Changjiang, and ranged from 12.4 to 33.3 nM with an average of 19.4 ± 7.3 nM. N₂O concentrations in the river waters showed obvious seasonal variations with higher values occurring in both summer and winter. Annual input of N₂O from the Changjiang to the estuary was estimated to be 15.0 × 10⁶ mol/yr. N₂O emission rates from the sediments of the Changjiang Estuary in spring ranged from -1.88 to 2.02 μmol m^-2 d^-1, which suggests that sediment can act as either a source or a sink of N₂O in the Changjiang Estuary. Average annual sea-to-air N₂O fluxes from the studied area were estimated to be 7.7 ± 5.5, 15.1 ± 10.8 and 17.0 ± 12.6 μmol m ^-2d^-1 using LM86, W92 and RC01 relationships, respectively. Hence the Changjiang Estuary and its adjacent marine area are a net source of atmospheric N₂O.