Comparison of methane emissions among invasive and native mangrove species in Dongzhaigang, Hainan Island.

ABSTRACT

The strength of methane (CH4) source of mangroves is not well understood, especially when including all CH4 pathways in consideration. This study measured CH4 fluxes by five pathways (sediments, pneumatophores, water surface, leaves, and stems) from four typical mangrove forests, including Kandelia candel without pneumatophores and three species with pneumatophores Sonneratia apetala, Laguncularia racemosa and Bruguiera gymnorhiza-Bruguiera sexangula. The CH4 fluxes from sediments were 4.82±1.46mgCH4m-2h-1 for K. candel and 1.36±0.17mgCH4m-2h-1 for the other three with pneumatophores. Among the three communities with pneumatophores, S. apetala community had significantly greater emission rate than the other two (P<0.05). Pneumatophores in S. apetala were found to significantly decrease CH4 emission from sediments (P<0.01), while those in B. gymnorhiza-B. sexangula were significantly increase it (P<0.05). CH4 fluxes from waters were 3.48±1.11mgCH4m-2h-1, with the highest emission rate in the K. candel community for the duck farming. Leaves of mangroves except for those of K. candel were a weak CH4 daytime sink, but stems were a weak source. The total 72ha of mangroves in the Changning river basin emitted about 8.10Gg CH4 per year, with a weighted emission rate of about 1.29mgCH4m-2h-1. Our results suggested that mangroves are only a small methane source to atmosphere with great contribution from sediments and waters, only slight contribution from leaves and stems. Pneumatophores of different mangrove species played different roles in CH4 fluxes from sediments.