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

Abstract. 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 seasonal variations with high values occurring in summer and spring. 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 20.8±7.8 nM. The average annual input of N2O from the Changjiang to the estuary and its adjacent area was estimated to be 15.8×106 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 suggest that sediment can act as either a source or a sink of N2O in the Changjiang Estuary. The annual sea to air N2O fluxes from the Changjiang Estuary were estimated to be 6.8±3.7, 13.3±7.2 and 14.9±8.3 μmol m−2 d−1 using LM86, W92 and RC01 relationships, respectively. The annual sea to air N2O fluxes from the adjacent marine area were estimated to be 8.5±7.8, 15.3±13.5 and 17.4&plusmn15.7 μmol m−2 d−1 using LM86, W92 and RC01 relationship, respectively. Hence the Changjiang Estuary and its adjacent marine area is a net source of atmospheric N2O.