[A-CG53] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG53-P03] Fluxes of dissolved inorganic carbon and total alkalinity through porewater exchange in Lake Akkeshi

*Yasui Rina¹, Ryo Sugimoto¹, Kenta Watanabe², Atsushi Kubo³, Sayaka Tsuda³, Tomohiro Kuwae² (1.Fukui Prefectural University, 2.Port and Airport Research Institute, 3.National University Corporation Shizuoka University)

Keywords:Blue Carbon, Radium, porewater

Blue carbon ecosystems such as mangrove forests, seagrass beds, and tidal marshes, play a crucial role in absorbing atmospheric CO₂ and storing organic carbon (OC). The creation, conservation, and restoration of these habitats have gained attention as effective carbon sinks. OC assimilated through photosynthesis is decomposed via biotic and abiotic remineralization processes, a part of them being buried in sediments over long timescales. While most decomposed carbon is believed to return to the atmosphere as CO₂, some may remain in the water column as inorganic carbon ions, depending on the carbonate chemistry and chemical reactions occurring during remineralization. In this study, we investigated the outwelling of dissolved inorganic carbon (DIC) and total alkalinity (TAlk) efflux from the sediments of seagrass and tidal marsh habitats in Lake Akkeshi. Field surveys were conducted within and at the mouths of the lake as well as in the adjacent river. To trace porewater exchange between the sediment and the water column, we measured radium radioisotope as chemical tracers. As a result, short-lived Ra isotopes (²²³Ra and ²²⁴Ra) exhibited lower activity in river water and higher activity in sediment porewater. The elevated Ra activity in the lake’s surface water, compared to that in the river, indicates a significant contribution of Ra from porewater. In our presentation, we will show the porewater fluxes of DIC and Talk.