With the increase of intense human activities, the degradation of ecosystems in tropical regions is significant. Due to the high rainfall in tropical watersheds, terrestrial substances such as freshwater, sediment, and pollutants are rapidly released into the sea, which has a significant impact on the evolution of typical ecosystems in estuaries and adjacent coastal zone. This study takes the Selangor River Catchment-Estuary-Coastal Sea System in Malaysia as the study area, and discusses the transport processes and fate of terrestrial substances after entering the sea through field observations and indoor experiments. The research results indicate that terrestrial substance delivered by Selangor River are mainly trapped in the estuary area, and the fine sediment transport seaward by the river plume and transport landward again by tidal current, resulting in the development of extensive tidal flats on both sides of the river mouth.
 

river catchment-estuary-coastal shelf continuum system; sediment transport; pollutants; river plume; Selangor river