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

Abstract

Abstract. Dissolved nitrous oxide (N 2 O) was measured in the waters of the Changjiang (Yangtze River) Estuary and its adjacent marine area during five surveys covering the period of [2002][2003][2004][2005][2006]. Dissolved N 2 O concentrations ranged from 6.04 to 21.3 nM, and indicate great temporal and spatial variations. Distribution of N 2 O in the Changjiang Estuary was influenced by multiple factors and the key factor varied between cruises. Dissolved riverine N 2 O 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. N 2 O concentrations in the river waters showed obvious seasonal variations with higher values occurring in both summer and winter. Annual input of N 2 O from the Changjiang to the estuary was estimated to be 15.0 × 10 6 mol/yr. N 2 O 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 N 2 O in the Changjiang Estuary. Average annual sea-toair N 2 O fluxes from the studied area were estimated to be 7.7 ± 5.5, 15.1 ± 10.8 and 17.0 ± 12.6 µmol m −2 d −1 using LM86, W92 and RC01 relationships, respectively. Hence the Changjiang Estuary and its adjacent marine area are a net source of atmospheric N 2 O.

Nitrous oxide and methane in two tropical estuaries in a peat-dominated region of northwestern Borneo

“…Dissolved N 2 O concentrations were mostly close to atmospheric equilibrium concentrations (i.e., 100 % saturation), which is in line with other comparable studies in the tropics and subtropics (Richey et al, 1988;Zhang et al, 2010;Rao and Sarma 2013;Borges et al, 2015). High N 2 O concentrations were reported for eutrophic and hypoxic coastal waters in the western Indian continental shelf (up to 533 nmol L −1 ; Naqvi et al, 2000) and for the Peruvian upwelling (up to 986 nmol L −1 ; Arevalo-Martinez et al, 2015).…”

“…In this study, samples were not collected for salinities<4, so we cannot make this claim with certainty. However, previous studies suggest that the highest N 2 O concentrations are usually encountered at low salinities in the vicinity of the turbidity maximum (Robinson et al, 1998;Barnes and Owens, 1998;Zhang et al, 2010). On the other hand, N 2 O maximum concentrations along estuaries may also occur at intermediate salinities (de Wilde and de Bie, 2000).…”

“…The reason is obviously the missing relationship between DIN concentrations and N 2 O emissions in the studied system. Although across estuaries increasing DIN is generally associated with increasing N 2 O (Murray et al, 2015), the relationship is not linear : Zhang et al (2010) found a polynomial relationship between DIN and N 2 O across estuaries in different geographic locations. The emission factor from Mosier et al (1998), in contrast, is based on a constant N 2 O / DIN ratio.…”

“…Even though these estuaries were slightly eutrophic, the DIN concentrations were still below the average for tropical non-blackwater rivers (Baum and Rixen, 2014). For estuaries with low DIN concentrations, low N 2 O concentrations are expected (Zhang et al, 2010). Interestingly, enhanced N 2 O was measured offshore during cruise SO218.…”

Dynamics of groundwater‐derived nitrate and nitrous oxide in a tidal estuary from radon mass balance modeling

“…To date, most studies on N 2 O emissions from estuaries have focused either on net total emissions or those derived from sediment fluxes (Dong et al 2006;Zhang et al 2010) Table 2). The same study also noted significant consumption within the estuary, and so the total rate of groundwater-derived N 2 O was most likely much higher than this.…”