[A-CG40] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG40-P03] Construction of an artificial outlet channel affects organic carbon accumulation in a coastal lagoon

*Kenta Watanabe¹, Tomohiro Kuwae¹ (1.Port and Airport Research Institute)

Keywords:organic carbon storage, seagrass meadows, saltmarshes, coastal construction, age-depth modelling

Organic carbon (C_org) storage is one of the important functions of vegetated coastal ecosystems for mitigating the adverse effects of climate change. The artificial alteration of landforms by coastal constructions would impact on habitats, hydrological conditions, and sediment loads. However, how the coastal constructions change C_org accumulation in vegetated coastal ecosystems is poorly understood. In this study, the sediment profiles of geological and biogeochemical characteristics were measured in Komuke Lagoon, Hokkaido. Stable isotope ratios and ²¹⁰Pb profiles were used to investigate the origin of C_org and sediment age. We showed that C_org accumulation rates and the origin of accumulated C_org significantly changed after the construction of an artificial outlet channel. C_org accumulation was enhanced, the contribution of terrestrial-derived C_org decreased, and that of microalgae- and seagrass-derived C_org increased after the coastal construction at the site. These findings indicate that the construction of an artificial outlet channel alters the frequency of seawater exchange and affects habitat types and C_org accumulation.