A field observation of physical environments in a mangrove forest was made in Fukido River with a surrounding mangrove swamp in Ishigaki Island, Okinawa, Japan. The characteristic flow structures are observed in creek and swamp and then found to be similar to hydraulic phenomenon in a compound meandering channel. The thermal environments in the creek and swamp are investigated by a heat budget analysis, indicating the significant importance of the heat transport by tidal current and the heat flux to swamp bottom. We also examine the sediment dynamics in detail by measuring a vertical turbulent flux of suspended sediments.
Mangrove forests in tropical and subtropical estuaries have an important role as the basis of natural ecosystems in nearshore zone. Mangrove ecosystems have recently been exposed to large human-based environmental impacts mainly caused by the reclamation in land and coastal regions. To clarify these environmental influences on ecosystems and water environments in a mangrove forest, it is desirable to realize the detailed physical processes which control several key biological and chemical processes in mangrove regions. However we have poorly understood physical environments in mangrove estuaries compared to those in template estuaries, although field surveys on the hydrodynamics and water environments in mangrove forests have been conducted (e.g., Wolanski et al., 1992; Furukawa et al., 1997). This is mainly why the mangrove estuaries are mostly located in tropical areas in less-developed countries with less research fund (Wolanski et al., 1992). Moreover the hydrodynamics and the material transports in mangrove regions are quite complex due to complicated local topography and high friction caused by densely vegetated mangrove roots.
We carried out an intensive filed survey on physical processes in a mangrove forest over about four successive tidal cycles from September 30 to October 2, 2000.