Fluxes of dissolved methane and nitrous oxide in the tidal cycle in a mangrove in South China

Mangroves are carbon sinks that are believed to contribute to carbon neutrality; however, they are also considered to be partly offset by their emissions of methane (CH4) and nitrous oxide (N2O). In this study, dissolved CH4, N2O and other hydrological parameters over the tidal cycle in the Golden Bay mangrove (GBM), Beihai, Guangxi, are investigated during the dry season and wet season. The concentration and flux of dissolved N2O and CH4 in the GBM have distinct seasonal variations under the influence of the tidal cycle, and the concentration and flux in the dry season were higher than those in the wet season, with GBM as a weak source of N2O and a strong source of CH4. The fluxes of N2O and CH4 were 119 +/- 370 mu mol m(-2) yr(-1) and 87.2 +/- 48.6 mmol m(-2) yr(-1) respectively during tidal coverage. The emission of CH4 through the water-atmosphere interface offsets 22.5 % of the total carbon sequestration of GBM. Owing to the potential increase in N2O emissions caused by possible exogenous nitrogen input and the transport of dissolved CH4 from mangroves to coastal water, uncertainty remains in assessing the capacity of blue carbon sinks in mangroves.