The Effect of Weir Opening on Physiochemical Properties in the Geum Estuary of Republic of Korea

Abstract

Deteriorated river water quality affects estuarine environments due to river and estuary linkages. Thus, river water quality improvement could play a pivotal role in the maintenance of estuarine ecosystem functions. The South Korean administration opened river weirs to restore river ecosystems and announced that this helped restore habitats and improve water quality. Despite these reported positive results in the rivers, little research has been conducted on the effects of weir opening on estuaries linking to rivers. We investigated the physicochemical properties of the Geum Estuary during the initial weir opening (2018) and stabilization (2021) periods. The results indicated that the NO3− inputs from rivers to estuaries decreased from 2018 to 2021 by 19~68%; however, the trends of [NO3−] in estuarine water columns in nearby estuary dams fluctuated between 2018 and 2021. No change in NO3− pollutant sources was observed from 2018 to 2021. Unlike [NO3−], [PO4−] and [SiO2] were higher in 2021; thus, large amounts of previously accumulated PO4− and SiO2 within the weirs might have been released from the river into the estuary. This supply of PO4− could enhance estuarine phytoplankton growth, where PO4− is a limiting factor for primary production due to excessive inputs of NO3− from rivers. Therefore, dredging the accumulated sediment within weirs should be considered prior to opening them to prevent the release of PO4− and SiO2 into estuaries.