Distribution and fluxes of methane in tropical rivers and lagoons of eastern Hainan

Methane(CH4) is an important greenhouse gas,which can influence the Earth's climate change both directly and indirectly.Distributions and fluxes of CH4 in rivers and lagoons of eastern Hainan were obtained during the survey from March 27th to April 15th in 2009.Surface waters of the three rivers(Wenchang,Wenjiao and Wanquan rivers) were over-saturated in CH4 with respect to atmospheric equilibrium [(60664±25118)%,(38582±26339)% and(9472±5594)%,respectively].Surface waters of the lagoons were also over-saturated in CH4,but at much lower levels than those in the rivers.The dissolved CH4 in the lagoons mainly come from riverine input,inputs from groundwater and fringing mangrove forest,and in-situ production;the main sinks of methane in the lagoons were oxidation and outgassing.The estimated air–water CH4 fluxes using the RC01 formula of Wenchang and Wanquan rivers were 5967.0±5142.1 and 496.2±335.9μmol.m 2.d 1,respectively.Air–water CH4 fluxes of the logoons were 528.7±625.0,441.7±473.3,26.6±21.6,and 1287.8±1453.3μmol.m 2.d 1 for Bamen bay,Bo’ao,Xiaohai,and Laoyehai,respectively.Estuaries and lagoons in eastern Hainan are persistently supersaturated in CH4,which indicates that they are net sources of atmospheric CH4.