Mangrove is an important coastal carbon sink. In order to evaluate the behavior of carbon, we carried out a series of observations in a mangrove wetland in the Zhangjiang River Estuary, China. The carbon fluxes via pore water exchange were estimated using ²²⁸Ra as tracer to evaluate dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) during winter in the tidal creek. The results show that the total carbon via pore water exchange in the tidal creeks in the mangroves accounted for about half of the net carbon fixed by mangrove vegetation and was several times as much as the soil carbon accretion in the mangroves. In addition, the exported carbon in the form of DIC contributed all of the carbon outwelling from the creek, implying effective fixation of carbon by the mangrove ecosystem. Therefore, quantification of pore water exchange and related soil carbon loss is essential to trace the fate of carbon fixed in mangrove wetlands.

mangrove,carbon outwelling,pore water exchange,228Ra