Impacts of channel shifts and interannual sediment load reducing of the yellow river on the grain size characteristics of sediments in the shandong mud wedge over the past 100 years

In this study, sediment grain size of a core retrieved from Shandong mud wedge has been tested. On the basis of ²¹⁰Pb dating, the impacts of channel shifts and changes of annual sediment load of the Yellow River on the sedimentary characteristics of the remote depositional zone over the past 100 years have been studied by analyzing the temporal changes of grain size in the core, Yellow River's annual sediment load, particle size of suspended sediment in the lower reaches of the Yellow River, Yellow River estuary location, and replacement index of coastal current intensity. The results show that grain size of sediments in the study area is affected by characteristics of sediments input of the Yellow River and strength of coastal hydrodynamics. During the period 1884−1939 AD and 1947−1999 AD, the variation of grain-size characteristics in the area was mainly affected by strength of the coastal current. During the period 1939−1947 AD and 1999−2012 AD, sediments in this area were obviously coarsened, and their correlation with the coastal current intensity weakened. Such a coarsening trend of sediment is likely attributed to the insufficient sediment input of the Yellow River, because the Yellow River was cut down at the Huay-uankou during 1938−1947 AD and the annual sediment load of the Yellow River was continuous lowering since the end of the 1990s. Different from proximal depositional zone, grain-size characteristics of this remote offshore depositional area was not sensitive to the channel shifts in the lower reaches of the Yellow River. A certain delay also existed in the response of sediment grain size to the reduction of annual sediment load. The reason was that sediment in this area was subjected to resuspension and complex material mixing. Channel shifts of the Yellow River and change of sediment load were still factors that could not be ignored for evolution of sedimentary characteristics of remote depositional zone.