九龙江河口沉积物中硫酸盐还原与甲烷厌氧氧化:同位素地球化学证据

Sulfate reduction and methane anaerobic oxidation: isotope geochemical evidence from the pore water of coastal sediments in the Jiulong Estuary

通过沉积物柱孔隙水中甲烷,SO42-,Cl-,δc(34S-SO42-)、δc(13C-CH4)的垂直分布特征,研究了硫酸盐还原和甲烷厌氧氧化(anaerobic oxidation of methane,简称AOM)过程在九龙江河口沉积物中的分布规律。测定结果显示两个站位(J-A和J-E)间隙水中SO42-浓度随深度增加快速减小,分别在55和130 cm深度附近消耗殆尽,而惰性的Cl-浓度随深度没有减小的趋势;孔隙水中硫酸盐的硫同位素组成随着深度增加明显偏重。这些结果表明两个站位沉积物上部(55和130 cm)存在明显的硫酸盐还原作用。孔隙水中甲烷浓度在硫酸盐-甲烷过渡带(sulfate-methane transition,简称SMT)随着深度减小急剧增大,与此同时甲烷碳同位素组成也相应偏重,表明两个站位沉积物下部产生的大量甲烷在SMT附近被AOM消耗。沉积物中SMT分布深度与上覆水盐度存在明显的正相关,反映了研究区上覆水盐度变化所导致的硫酸盐浓度改变是控制九龙江河口沉积物中SMT深度的关键因素。

The spatital distrubution of sulfate reduction and anaerobic oxidation of methane（AOM） was investigated in the Jiulong estuarine sediment based on the concentration profiles of geochemical parameters,including sulfate,methane,δc（34S-SO2-4）,δc（13C-CH4） and chlorine in pore water.Sulfate concentrations in pore water decrease remarkably with the depth.The sulfate is consumed completely at depth intervals 55 and 130 cm at two stations（J-A and J-E）.There is no significant change for chloride concentration through the depth of the cores.The δ34S values of sulfate increase with the depth in both cores.It is suggested that sulfate reduction occurs within the upper 55 and 130 cm in the sediment at Stas J-A and J-E,respectively.Methane concentrations sharply increase at the depth of sulfate-methane transition（SMT）,and the δc（13C-CH4） values become heavier due to the AOM.Overall,these data suggest methane is consumed mainly by anaerobic oxidation at the SMT.There is obvious positive correlation between the depth of the SMT and the salinity of overlying water at two stations.It is assumed that the depth of the SMT is mainly controlled by the gradient of sulfate which is controlled by the salinity of the overlying water in the Jiulong Estuary.