Massive sedimentation of fine sediment with organic matter and enhanced benthic–pelagic coupling by an artificial dyke in semi-enclosed Chonsu Bay, Korea

► We assess the impact of an artificial dyke on the organic carbon cycle. ► Massive organic matter is deposited near dyke by change of tidal circulation. ► Organic C oxidation rate in sediment near dyke was two times higher than out of bay. ► The nutrient benthic fluxes were four to six times higher than those outside bay. To assess the impact of an artificial dyke in Chonsu Bay (CBD) on the organic carbon (Corg) cycle, we measured excess 210Pb activities, Corg and nitrogen content in sediment cores. The Corg oxidation rates (Cox) on the surface sediment and benthic nutrient fluxes were also quantified with an in situ benthic chamber. The higher excess 210Pb inventory, Corg and nitrogen in cores near the CBD indicated lateral transport and local, massive deposition of particulate matter due to tidal circulation altered by artificial dyke construction. The Cox in sediment near the CBD was about twice as high as that out of the bay, suggesting the importance of benthic remineralization of organic matter. The benthic fluxes of dissolved inorganic nitrogen and phosphate were four to six times higher than those outside the bay, corresponding to 141% and 131% respectively, of the requirements for primary production.