Impacts of Anthropogenically Driven Changes in Sediment Dynamics on Depositional Records in the Pearl River Estuary, China

Extensive research has established that both anthropogenic activities and river--tide interactions are significant factors affecting the sediment dynamics in estuarine and coastal regions. Particularly, it is considered that the narrowing and deepening of estuarine topography and decline in upstream discharge and sediment supply by anthropogenic activities (including reservoirs or dam construction, coastal reclamation, sand excavation, and channel dredging) may exert profound changes in the sediment dynamics characteristics of the Pearl River Estuary (PRE), a key region within the Guangdong-Hong Kong-Macao Greater Bay Area. To investigate the resulting impacts on sedimentary records, this study analyzed grain size distribution and loss-on-ignition (organic matter; OM) content from sediment cores collected from both eastern and western regions of the LE, the largest sub-estuary of the PRE, based on a ²¹⁰Pb-based chronological framework. The results reveal shifts in estuarine dynamics around 1994, marked by a 33 % reduction in sediment flux and amplified tidal energy, transforming the originally river-dominated estuary into a tide-dominated regime. Spatial heterogeneity in sedimentary responses was observed. In the eastern Lingdingyang Estuary (LE), sediment coarsening and improved sorting due to intensified tidal currents, while the western LE showed mixed deposition and poorer sorting linked to constrained ebb flows and sediment trapping effects. Furthermore, OM enrichment was strongly correlated with clay content, particularly in the western LE, indicating flocculation processes under tidal influence. OM accumulation increased westward but declined in the east. Our findings demonstrate that anthropogenic interventions dominate over natural processes in controlling estuarine sediment dynamics and provide essential understandings for sustainable management of the PRE and the Greater Bay Area while also offering a valuable reference for other heavily modified estuary systems worldwide.