Program

Nitrous oxide (N2O) is an important greenhouse gas, and plays a significant role in the global climate system. Marine waters, in particular estuaries, are generally believed to be a major natural and anthropogenic source of atmospheric N2O. Dissolved N2O at different depths of 56 stations in the Changjiang (Yangtze River) Estuary and the East China Sea (ECS) were investigated from August 16 to 27 of 2016 during the strong El Nino period, and the sea-to-air fluxes of N2O were also estimated. The concentrations of N2O decreased with distance from the inner Changjiang Estuary to the open sea. N2O concentrations in the surface waters ranged from 5.9 to 100.4 nmol L-1 with an average of (7.9 ± 2.3) nmol L-1. Increased bottom N2O concentrations were observed with an average of (13.6 ± 3.8) nmol L-1. Hypoxia was well developed during this summer cruise, and the low DO area (DO < 2 mg L-1) expanded to about 23,000 km2. A region of significant bottom water hypoxia, with oxygen concentration less than 0.1 mg L-1, occurred at the north of the Changjiang Estuary, and the N2O and NO3- concentrations were reduced to 0 by strong denitrification in the water column.