The Grain Size Distribution Characteristics Of Yalu Estuary And Its Response To The Change Of The Catchment

Estuary is not only a hinge that connects the river and the ocean, but also the zone suffering from various types of interface material collecting, transferring and exchanging. Since the industrial revolution, increasing human activity and exploiting resources within the catchment and the estuary, the estuarine process was greatly changed, which makes the estuarine and coastal environment experience more significant and rapid changes. The impact of catchment changes of river deltas has becoming a global issue. Yalu River is an important regional river inflowing into North Yellow Sea. Especially with the Dandong port industrial park’s construction and the development strategy of the "Five Points" in Liaoning coastal economic zone implementing, the Yalu River catchment and the deltas have suffered from mark changes. It is an ideal object that explores the small and medium-sized river basin changes in the role of global catchment-coastal interaction. Yalu River is also the boundary of China and Korea. Therefore, identifying the source of Yalu River estuary sediments, sedimentary dynamics change, sediment transport trends and the evolution of the depositional environment, woudle deepen the understanding of the material recycling process on Yalu River Estuary; and will also provide scientific guidance for the development of the natural resources and effective protection of the environment of Yalu River estuary. Furthermore, such studies are also beneficial to safeguarding national sovereignty and interests.In this paper,48surface sediments and7sediment cores were collected. Subsequently, grain size and particle size sensitive populations which from Yalu river estuary and the western tidal flat were calculated, and the surface sediments transport trends were analyzed to explore the Yalu River Estuary area’s different deposition characteristic controlled by dynamic environment of different periods, we also measure sediments age and imitate end-member constituent through Isotopic dating and end-member analysis by representative cores, then discuss the change of hydrodynamic force and sedimentary environment in the estuary area’s different sages, and explore the cores response to the basin changes(events).The results showed that:The Particle size parameters (average particle size, sorting coefficient, skewness) of Yalu River Estuary surface sediment’s variation is rather large, which adapts to different sedimentary characteristics and hydrodynamic conditions. Suffered form strong hydrodynamic in middle channel, the sediment’s average particle is larger and more sand content. In addition, the sediment’s average particle of the western channel mouth is smaller and large variation induces by morphology change. Except to the certain samples, the variation of particle size parameters in the west tidal flat is small, and the average grain diameter shows a decreasing trend from the east to the west, as well as from sea to land. The sediments upper the Niu Island of the middle channel indicate landward transport, and the sediment down from he Niu Island exhibited seaward transport. The sediments of the western channel mouth were transported southeastly. The sediments in the section of dong gou and the old channel indicate east transport, while the xin hai section and bei jing zi section were landward transported.The component of sediment cores in the western channel are mainly composed of silt, and dominated by sandy and mud layer. The parameters of grain size showed significant variations within the depth. The sediment cores of the western tidal flat mainly consist of sand and silt and shell fragments can be found in some layers. To some extent, the distribution of mean grain size change gradually in the east-to-west direction. Layer of coarse sand appears at the upper part of the cores with different thicknesses.The grain size sensitive components were identified through calculating standard devication of each grain-size class of surface sediments and sediment cores in Yalu River Estuary. The results indicate that they have two major grain-size sensitive components:the coarse component was located within2.12～3.12Φ, while the fine component was observed within6.12～7.12Φ, which show regional differences. Based on the grain size end-member analysis model, end member results of repressentative cores were obtained. Generated two or three end members respectively represent the wave dynamics, the tidal dynamics or the effect of run-off. The results also suggest that end-member component was positive correlated with their grain size senstitive components, and the trend of their grain size components were relevant with the varation of cores average grain-size.Sediment source and hydrodynamics play important roles in the estuarine areas. Anthropogenic activity within the river catchments is one of main factor that results in the variation of sedimentary characters during the recent decades. Based on the information of lithology, end members and dates of grain size parameters, dating results, we can classify the evolution of recent Yalu River estuary into five different periods.