Sedimentary Environment Changes And Events Response Of Liao River Estuary Entrance Shoal In Nearly 50 Years

This paper shows grain-size, elements content characteristics and chronological framework of a sediment core collected in Liao River entrance shoal (location N40°53’0.16", E121°46’3.22"), analyses the reason of annual variation of the grain-size, elements content characteristics, and discusses the events response. The main conclusions are as follows:1. By analyzing 137Cs dating results, a chronological framework was built from 1963 to 2015. The sedimentary rate from 1963 to 1986 was 4.56cm/a, from 1986 to 2015 was 4.14cm/a, which suggested the rapid accumulation in the estuary area.2. Elements content characteristics show shoal sediment is terrigenous. Si has an enrichment tendency in coarse material. Al, Mn, Fe, Mg and most trace elements have an enrichment tendency in fine material. K, Na, Ba, Sr are easily migrated during weathering, while Rb is stable.3. With the limit of the chronological framework, grain-size and elements content can indicate sedimentary environment changes and events which were influenced by the coupling effect of natural changes and human activities:(1) A big difference occurs in frequency distribution curves of grain-size above the depth of 205cm (1969AD) comparing to these under the depth of 205cm, which indicates tidal current has became another important hydrodynamic force in the shoal area after Panshan dam was built in 1968. After the closure of Liao River in 1998, sediments of shoal became more fine, which indicated that runoff no longer affected sedimentary process, and tidal current and longshore current became the main hydrodynamic forces.(2) According to the abrupt change characteristics of grain-size and elements content, single-year flood and successive annual floods were identified.