Identifying the impacts of anthropogenic alterations on estuary using biogeochemical characteristics-Nakdong estuary, Korea

Abstract

In estuaries, biogenic silica (BSi) content of sediment is typically controlled by dissolved silica (DSi) in riverine flows. Change in DSi flux could result in variation of nutrient ratio in estuarine waters, which may influence the planktonic communities and aquatic food webs potentially. Nakdong estuary dam was installed in mid 1980s and the phytoplankton composition might have been modified after the installation. In order to determine damming effect in Nakdong estuary, sediment cores were collected in 2015 and 2017 at tidal flats of Nakdong estuary. 210-Pb dating was conducted for each cores. The sedimentation rates in both cores were 1.0~2.5cm/yr, indicating that both sediment cores include the period of Nakdong estuary dam construction. Especially, sand content in sediment core of Eulsuk tidal flat showed decreasing trend after Nakdong estuary dam construction. In addition, C/N ratio of sediment core collected in Jinwoo-do tidal flat was abruptly decreased at 45cm depth. BSi content and BSi/TOC(total organic carbon) ratio were also decreased after dam construction, indicating that DSi flux reduction and its effects on phytoplankton composition. Therefore, BSi/TOC ratio could be is a useful tool for tracking phytoplankton composition change because sedimentary BSi content and TOC content are used as indicators of diatom productivity and total primary productivity respectively.