マングローブ林堆積物における有機物とメタンの動態

概要

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CH_4 is one of the most important greenhouse gas. In tropical and subtropical coastal region, mangroves are actively fixing CO_2 by photosynthesis and regarded as a significant CO_2 Sink. On the other hand, it is known that mangrove sediment releases CH_4 to atmosphere. Due to O_2 deficiency in the sediment, which is caused by redundant supply of organic matter and seawater flooding the sediment. Although CH_4 released from natural wetland occupies 20% for all of CH_4 production, pathway and condition of the CH_4 production are still unclear. In this work, we study behavior of organic matter in mangrove sediment, in particular accumulation of organic matter and CH_4 release, at the mouth of Fukido River, Ishigaki Island, Okinawa Prefecture. Although pH was the optimum condition for methanogenesis bacteria (pH 6.4-7.4), redox potential was very high (+185 - +240mV). Total organic carbon in sediment was 6.2±2.7% for sediment dry weight, which shows that this mangrove forest stores much abundant carbon in sediment. The CH_4 release rate in vitro experiment was 118μmol m^<-2>day^<-1>. This value is negligible compared with total organic carbon reduction rate (2.1mol m^<-2>day^<-l>). This suggests that CH_4 produced by decomposition of organic matter is minor or that CH_4 is immediately oxidized in sediment.
静岡大学の論文