Sediment dynamics in the Pearl River Estuary: evolution of estuarine turbidity maximum

Abstract

Estuarine Turbidity Maximums (ETMs) represent zones where suspended particulate matter (SPM) concentrations are significantly elevated, occurring at the interface between riverine and marine environments. This has a profound influence on the biogeochemistry and biology of the estuary. The formation and maintenance mechanisms of ETMs depend on the river discharge, sediment load, tides, and estuarine morphology. In the Pearl River Estuary (PRE), hydrodynamics (river discharge, tides, and coastal current) interact with seasonal sediment load and estuarine topography to influence the sediment dynamics. The PRE is a highly variable, complex estuary. In temporal terms, it has undergone significant human-induced changes in its morphology over time, and its sea level has been rising at a rate greater than the global average. In spatial terms, various topographic units have collectively shaped the PRE. This study elucidates the physical mechanism of ETM formation and its response to the historical development and future scenarios. Investigation on the variation of stratification provides the mechanism of hydrodynamic response to morphological changes and climatic changes. Numerical modeling studies on the formation of three ETMs provide insights into different domain mechanisms. Reconstruction of past morphology and simulations under future scenarios shed light on the historical evolution and potential challenges (e.g. sea level rise, coastline change due to land reclamation or natural processes of erosion and deposition, bathymetry change due to dredging etc.) facing the PRE. The thesis aims to provide a basis for the knowledge needed by decision makers to establish science-based management strategies for estuaries under climate change and rapid coastal development.