The fate of carbon resulting from pore water exchange in a mangrove and Spartina alterniflora ecozone.

Mangrove and salt-marsh wetlands are important coastal carbon sinks. In order to quantify carbon export via pore water exchange and to evaluate subsequent fate of the exported carbon, we carried out continuous observations in a mangrove-Spartina alterniflora ecozone in the Zhangjiang River Estuary, China. The carbon fluxes via pore water exchange were estimated using ²²²Rn and ²²⁸Ra as tracers to be (2.15 ± 0.63) mol/(m²·d) for dissolved inorganic carbon (DIC) and (-0.008 ± 0.07) mol/(m²·d) for dissolved organic carbon (DOC) in the wet season and (3.02 ± 0.65) mol/(m²·d) for DIC and (-0.15 ± 0.007) mol/(m²·d) for DOC in the dry season in the mangrove-dominated creek (M-creek), while (2.52 ± 0.82) mol/(m²·d) for DIC and (0.02 ± 0.09) mol/(m²·d) for DOC in the dry season in the S. alterniflora-dominated creek (SA-creek). The negative value means that pore water was a sink of DOC in the creek. The total carbon via pore water exchange in the tidal creeks in the mangroves accounted for 41%–55% of the net carbon fixed by mangrove vegetation and was 3–4 times as much as the soil carbon accretion in the mangroves. The exported carbon in the form of DIC contributed all of the carbon outwelling from the M-creek and 79% of the carbon outwelling from the SA-creek, implying effective fixation of carbon by the wetland ecosystem. Moreover, it resulted in 54% in the dry season, 75% in the wet season of the carbon dioxide released from the M-creek to the atmosphere, and 84% of the release from the SA-creek. Therefore, quantification of pore water exchange and related soil carbon loss is essential to trace the fate of carbon fixed in intertidal wetlands. [ABSTRACT FROM AUTHOR]