Diatom distribution along a tidal river in South Korea and trends with elevation and distance along the river

Abstract

The western coast of the Korean Peninsula has some of the highest tidal ranges in the world. Gomso Bay, located along the western coast of Korea, is a semi-enclosed embayment. Tidal deposits occur under most lowland rural areas along Gomso Bay. In this study, the diatom assemblage and grain size distributions of surface sediments along a tributary of Gomso Bay called Jujin Stream were examined to identify their relationships with tidal levels. Consequently, riverside sediments of Jujin Stream could be separated into four tidal level zones based on their diatom assemblage and grain size distribution. Clear diatom and grain size distribution gaps were found between the tidal (zones 1 and 2), fluvio-tidal transition (zone 3), and freshwater (zone 4) zones. The tidal zone was characterized by allochthonous marine diatom taxa. These marine taxa, and the sand content, gradually decreased in the upstream direction. Sediment in the fluvio-tidal transition zone has particularly distinctive features. Extremely high numbers of diatoms are present, which are dominated by freshwater taxa, with rare marine and marine-brackish taxa. Grain sizes in this zone increase sharply in the upstream direction. Combining diatom and grain size data can provide accurate paleo sea-level information for strongly tidal areas.