Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG43] Coastal Ecosystems - 2. Coral reefs, seagrass and macroalgal beds, and mangroves

Thu. May 24, 2018 1:45 PM - 3:15 PM 201B (2F International Conference Hall, Makuhari Messe)

convener:Toshihiro Miyajima(Marine Biogeochemistry Group, Division of Ocean-Earth System Science, Atmosphere and Ocean Research Institute, The University of Tokyo), Yu Umezawa(Tokyo University of Agriculture and Technology), Atsushi Watanabe(東京工業大学 環境・社会理工学院, 共同), Tomihiko Higuchi(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Miyajima Toshihiro(The University of Tokyo), Umezawa Yu(Tokyo University of Agriculture and Technology)

2:45 PM - 3:00 PM

[ACG43-04] Carbon transport from a riverine mangrove forest on Panay Island in the Philippines

*Atsushi Watanabe1, Toshihiro Miyajima2, Maria Lourdes S.D. McGlone3, Iris Orizar3, Yoshikai Masaya1, Kazuo Nadaoka1 (1.School of Environment and Society, Tokyo Institute of Technology, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Marine Science Institute, University of the Philippines, Diliman)

Keywords:DIC, Carbon transport, Mangrove forest, Philippines

Mangrove forests are well-known for the high net primary productivity, and the significant export of fixed carbon (C) as solutes (e.g. DIC or DOC) or as particulates (POC) to adjacent coastal areas by tidal exchanges. Compilation from the world's mangrove ecosystems suggests that about 67 % of carbon is discharged as DIC to the coastal ocean, followed by 22 % as POC and 12 % as DOC. The sources of these C can be dependent on mangrove status (e.g. pristine, degraded, and regenerated) as well as catchment characteristics. But information is limited to characterize these fluxes yet. The objectives of this study, therefore, is to characterize C exports from a relatively pristine riverine mangrove forest in Katunggan It Ibajay (KII) Eco-Park on Panay Island, the Philippines, from a fieldwork conducted in September 2017.

Samples were collected and analyzed for total alkalinity (TA), dissolved inorganic carbon (DIC), the carbon isotope composition of DIC (δ13CDIC), dissolved organic carbon (DOC), particulate organic carbon (POC), and the carbon isotope composition of POC (δ13CPOC) during a 24-hr sampling at an outlet of the forest and during low tide and high tide spatial samplings in the creeks including the freshwater endmember.

TA and DIC in the freshwater were as high as 5,000 µmol kg-1, suggesting weathering of limestone in the watershed. DIC in the creeks ranged from 2,000 to 5,000 µmol kg-1. Mangrove-derived DIC (ΔDICmangrove) was calculated based on conservative mixing model between the freshwater and seawater endmembers using DIC and δ13CDIC values. ΔDICmangrove in mesohaline (salinity 5-18) and polyhaline (salinity 18-30) waters ranged from 184 to 2050 µmol kg-1 and was especially high in polyhaline waters. Majority of mangrove-derive carbon (~95%) was in the form of DIC, followed by DOC and POC in this mangrove ecosystem during the survey period. TA was also generated within the mangrove forest, suggesting groundwater or interstitial water can be a significant source of the solutes. Better understanding of groundwater flux and source organic matter signatures will be needed to further refine carbon export processes from the mangrove forest to the adjacent ecosystems.