The response of sedimentary record to catchment changes induced by human activities in the western intertidal flat of Yalu River Estuary, China

The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores, along with the hydrologic data and human activities in the catchment. The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea, which could be divided into three stages as 1958–1970, 1971–1990 and 1991–2009. Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes. There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010, i.e., 1940–1950, 1951–1980, 1981–1990 and 1991–2010. The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980, whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990. Despite the further reduction of the water and sediment input into the sea from 1990 to 2009, this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly, the significantly increased silt contents of the sensitive component.