The Variations Of Water And Sediment Discharge Of The Rivers Along The East Coast Of Liaodong Peninsula During The Past Millennium:Simulation,Reconstruction And Driving Mechanism Analysis

The water and sediment discharge to the coastal ocean is a significant issue in study of catchment-coast interactions.Under the background of increasing global climate change and human activities in the basin,Analysis of the quantity,mechanism and main control factors of the river discharge to coastal zone at different time scales that can promote understanding the sediment transport path and quantitative interpretation the characteristics of the continental margin sedimentary sequence.Meanwhile,which is of great benefit to strengthen understand evolution of coastal landform and ecosystem development.In two decades,large international research projects,such as the land sea interaction plan(LOICZ),the STRATFORM of the United States and the MARGIN S2S in the Papua Bay and the North Island of New Zealand have paid close to the rivers discharge to coastal ocean.In this paper,the Hydrotrend v.3.0 hydrological model is used to simulate the variations of water and sediment discharge of the 5 rivers along the east coast of Liaodong Peninsula during the past millennium on the basis of collecting information on the topography,geology,human activities,historical data and measured hydrological records.And then,3 scenarios(climate change(M1),human activity(M2),climate change and human activity(M3))were set up to quantify the effects of climate change and human activity.Main conclusions are drawn as follows:(1)In the past 1000 years,Water discharge of east coast of Liaodong peninsula are the same(27.88km3/y)driven by M1 and M3 scenarios,the climate change is the dominant factor of runoff change,and human activities almost does not affect the total runoff in study area.In 1000-1450 and 1851-2012 years,the east coast of Liaodong Peninsula belongs to the warm and humid interglacial period,annual water discharge are 28.28 and 29.71 km3/y,while study area enters the dry cold ice period in the 1451-1850 years that made the runoff reduce to 26.67km3/y.climate change causes fluctuation range of runoff is 5.7%-11.4%.The contribution percentage of the runoff has changed little under the impact of climate change.The Yalu is the main river supplying water to coastal ocean,with about 90%of the runoff from the the Yalu River basin.Therefore,in the absence of reservoir interception,the sediment discharge into the sea in this period will reach 11.33Mt/y.(2)The fluctuation range of the sediment load is between 4.3%-12.1%driven by climate change(M1).In the past 1000-2012 years,the sediment load to sea under the three modes of M1,M2 and M3 was 5.59,6.05 and 6.02Mt/y respectively.This shows that human activity is the dominant factor in the change of sediment discharge into the sea.On the one hand,1751-1940 years,human activities caused serious soil loss in the study area,5 rivers total sediment yield reached 7.9Mt/y,an increase of nearly 36.2%smaller than 5.8Mt/y in 1000-1750 years;On the other hand,1941-2012 years,under the impact of forest destruction and reservoir interception,the total amount of sediment into the coastal zone in Eastern Liaoning Peninsula reduced to 3.21Mt/y,far less than the natural state of the 5.8Mt/y.In the same period,the increase of soil and water loss was 5.05Mt/y,while the interception rate of the reservoir was as high as 8.12Mt/y.Therefore,if there is no reservoir interception,the sediment discharge into the sea in this period will reach 11.33Mt/y.Different river basins have different intensity and times point of human activity impact,resulting in the study area of different river water and sediment flux contribution ratio also exists on the change of time.In the 1000-1940 years,88%of the total sediment discharge is from the Yalu River,but in 1941-2012 years,only 30%of total sediment discharge is from the Yalu River(Huanggou station)under the influence of the reservoirs.The other 70%sediment loads came from the Ai river and other small rivers along the east of Liaodong peninsula.(3)Under the combined influence of climate change and human activities,the frequency of floods and floods is changing.In the past 1000-1750 years,the YaLu river(Huanggou)and Ai river were less affected by human activities,and the flood frequency changed from the impact of climate change:In 1451-1750 years(LIA),The frequency of floods in the two basins decreased by 7.4%and 5.8%respectively due to climate change comparing with that of the 1000-1450.Influenced by climate change and human activities in the past 1751-2012 years,the frequency of flood frequency changes in the the Yalu River has been complicated:flood frequency of two basins increased from 14%and 15%in 1751-1850 years to 16%and 17%in 1851-1940 years.In the past 1941-2012 years,the frequency of floods in two basins increased by 5%and 16.8%respectively in different forms of human activities.During the same period,the frequency of flooding in the entire the Yalu River basin was about 32%.After the establishment of the three Bay Reservoir in Ai river in 2010,the flood frequency of the entire the Yalu River basin will be reduced to about 20%.