Long-term environmental changes in the Geum Estuary (South Korea): Implications of river impoundments

We investigated a sediment core collected from the Geum Estuary through sedimentological and geochemical analyses. Three lithological units were classified based on sedimentological characteristics. Unit 1 and Unit 3 were geochemically distinct, while Unit 2 was the transitional phase between them. The geochemical results suggest that the contribution of terrestrial organic carbon (OC) to the sedimentary OC pool in the coarse-grained Unit 1 was lesser than that of fine-grained Unit 3. The excess activity (²¹⁰Pb_ex) and the sedimentation rate indicate that Unit 1 corresponded to 1977 Common Era (CE). Since the first dam construction on the Geum River began in 1975 CE, the deposition of Unit 1 in the Geum Estuary is likely associated with river impoundments, which reduce the delivery of fine-grained sediment and terrestrial OC to the estuary. This study highlights the role of river impoundments in altering the sedimentary OC and thus the sedimentary environment in the estuary.