[A-CG41] 沿岸海洋生態系─２．サンゴ礁・藻場・マングローブ

[ACG41-06] Quantification of drag force and material trapping ability of a planted mangrove forest in the Philippines

*吉開 仁哉¹、中村 隆志¹、Bautista Dominic²、Herrera Eugene²、岡本 拓也¹、諏訪 錬平³、灘岡 和夫¹ (1.東京工業大学　環境・社会理工学院、2.フィリピン大学ディリマン校、3.国際農林水産業研究センター　林業領域)

キーワード：マングローブ、流動抵抗、トラッピング、分散、ブルーカーボン

Mangrove forest is an important component of blue carbon ecosystem and plays a major role in climate change mitigation. The complex structures in mangroves’ above-ground roots greatly attenuate flow and trap suspended materials on their surface which promote organic matter deposition in mangrove areas. This study aims to quantify the mangrove drag force and material trapping ability in a planted mangrove forest (Bakhawan Ecopark) in Panay Island, the Philippines. Field measurement was conducted in mono-specific stands of 17-year old Rhizophora apiculata. A precise measurement of water surface slope and velocity profiling were done to quantify the mangrove drag force from the momentum balance. We also measured the projected area of the above-ground roots of R. apiculata stands to estimate the value of drag coefficient (C_D). For quantification of the material trapping ability, trapping of floating mangrove leaf litter was monitored by a video camera. The results showed that the drag force by mangroves is much higher (around ten times) than the bed shear stress. While the estimated C_D values were close to those measured in other laboratory studies, the data suggested a water depth dependence of C_D which may be attributed to the vertical variations in the above-ground root projected area. Similarly, significant changes in the leaf litter dispersal patterns and the trapping efficiency with changing water depth were observed. The results may provide the first estimates of a set of field-derived drag coefficient, dispersion, and trapping ability of a planted mangrove forest.