Variation of deposition rate and evolution of depositional environment in the Modaomen estuary of Pearl River in the past 100 years indicated by grain size and ²¹⁰Pb_ex

As one of the important estuaries of the Pearl River system, Modaomen estuary is an ideal area to study the impact of human activities on the depositional environment of river estuaries. However, due to the difficulty in determining the sedimentary age, the relevant studies are scarce. Therefore, we studied the evolution and control mechanism of depositional environment in the last hundred years and determined the age and deposition rate of a core in Modaomen estuary shoal thru ²¹⁰Pb dating technique in combination of grain size characteristics and grain size end element analysis. Results show that the sediments of the core are mainly from the Xijiang River runoff and the reinput sediment by offshore tidal current, and influenced by the inshore particle input. Besides, the depositional environment in this area have been changed significantly in the 1970s. The deposition rate in Modaomen increased from 0.53 cm/a (before 1970s) to 1.68 cm/a (after 1970s) with increases in the variation coefficient of every grain-size component, coarse grain fraction, and material input from runoff and inshore supply, and with decrease of tidal material input, which is probably related to the change in sediment discharge from Xijiang River and intensified human activities including reclamation in Modaomen since 1970s.