Impacts of land reclamation on sediment transport and sedimentary environment in a macro-tidal estuary

Abstract

During the past decades, extensive coastal areas have been reclaimed along the coastline of China, while the physical mechanisms of human pressures on estuarine-sedimentation are largely unknown. This study investigates the impacts of a land reclamation activity on estuarine sedimentation in the Yalu River Estuary (YE), China. For this purpose, we perform a multidisciplinary approach that combines rare earth element (REE) sediment records and numerical simulations. REE pattern of two sediment core samples from the main estuarine branch changed from diverse to homogenous after the early 1970s, which indicates that the estuarine sedimentary environment experienced dramatic change after the land reclamation activity completed in 1975. In order to explore physical drivers behind this change, hydro-sedimentary dynamics were simulated using Finite Volume Coastal Ocean Model (FVCOM) and an improved Track Marine Plastic Debris (TrackMPD) models. After the land reclamation, model results show that: (1) the degree of flood dominance decreased, and the tidal-choking effect was enhanced in the main branch. (2) The estuary became more well-mixed due to the stronger tidal current; (3) Suspended-sediment concentration (SSC), especially SSC in the bottom layer was increased. (4) The landward sediment flux caused by tidal pumping decreased significantly and the YE may turn into a sediment source instead of a sink if more land is reclaimed in the future. Furthermore, sediments in the main branch were likely from different sources before reclamation but became a homogenous mixture afterwards. This study qualitatively demonstrates the human-induced impacts on estuarine sedimentation using a multidisciplinary method.