Abstract: The surface sediment grainsize data from the Qiantang River estuary is investigated using the End-member Modeling
Algorithm and a non-parametric estimation decomposition algorithm. In order to characterize the compositional features and planar distribution patterns of different grainsize endmembers, and explore their coupling relationships with sediment provenance and environmental changes. Results show that the data obtained by algorithms have good consistency, however, the End-member Modeling Algorithm demonstrate superior performance in accurately identifying unimodal distributions of each endmember. Surface sediments of the Qiantang River estuary can be divided into five grain-size end-members: EM1 (clay and silt), EM2 (coarse silt and very coarse silt), EM3 (very fine sand and fine sand), EM4 (fine sand and medium sand), and EM5 (medium sand and coarse sand). EM1 and EM2 represent the suspended sediments transported over long distances, primarily derived from the Yangtze River (Changjiang). EM3, distributed in the estuary mouth, indicates the reworking of residual sands from the Yangtze River estuary. EM4 denotes fluvial sandy sediments transported over a relatively long distance, while EM5 represents very coarse fluvial sand transported over a short distance; both primarily originate from the upper reaches of the Qiantang River and its tributaries. This study demonstrates that for estuarine sedimentary environments with complex source-to-sink systems, the End-member Modeling Algorithm enhances the resolution and efficiency of grain-size analysis and can sensitively indicate hydrodynamic conditions, source-to-sink processes, and event deposits. Therefore, this method holds promise for application in analyzing diverse and complex source-to-sink systems and hydrodynamic conditions in similar estuarine regions worldwide.

Key words: Qiantang River estuary, sensitive grain size, end-member modeling, source-to-sink system, sedimentary process