Abstract
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 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.
Highlights
N2O is an important trace gas in the atmosphere, which is responsible for 5–6% of the greenhouse effect (Houghton et al, 1996), and contributes to the destruction of the ozone layer (Crutzen and Schmailzl, 1983)
High N2O concentrations were observed beyond the mouth of the Changjiang and Hangzhou Bay, especially in the bottom waters
N2O concentrations showed no significant correlation with salinity in this study (Fig. 3)
Summary
N2O is an important trace gas in the atmosphere, which is responsible for 5–6% of the greenhouse effect (Houghton et al, 1996), and contributes to the destruction of the ozone layer (Crutzen and Schmailzl, 1983). One important consequence of the increased N load is the enhanced production and emission of N2O from estuaries (Barnes and Owens, 1998; De Wilde and de Bie, 2000; Marty et al, 2001; LaMontagne et al, 2003; Garnier et al, 2006). Estuaries represent only about 0.4% of the global ocean area, Bange et al (1996) estimated they account for about 33% of the oceanic N2O emission. These estimates are rather uncertain due to high spatial and temporal variability and the limited data available, especially for the typical large river estuaries in the world. Very limited data are available for the Amazon, the Mississippi and large river estuaries in Asia
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