Sedimentary Environment Characteristics And Influencing Factors Of Tidal Flats At Biliu Estuary In Liaodong Peninsula

The intertidal zone of the Biliu estuary in the Liaodong Peninsula is connected to the North Yellow Sea.Due to its proximity to the provenance and sufficient sediment supply,it has developed into a typical silt silt tidal flat.Waves,tidal currents,runoff,and coastal currents are the main dynamic factors controlling sediment transport,deposition and resuspension in this area.At the same time,the biliu estuary is a typical recessionary tidal estuary,especially in the past 40 years,the sediment from the basin has decreased sharply,which has a significant effect on the sedimentary environment of the river channel and the nearby tidal flat.Therefore,the characteristics of the sedimentary environment and its influencing factors of the tidal flat in the Biliu estuary under the dual influence of natural changes and human activities are discussed,which has important theoretical and practical significance for the study of local estuary and coastal landform evolution,coastal engineering construction and ecological environment protection.The research is based on columnar sediment collection,field observations,as well as marine hydrology,topography and other data studied by predecessors,through experimental analysis(grain size,²¹⁰Pb dating,element geochemistry and organic carbon,nitrogen),experimental analysis method correction,combined with DEM Digital methods such as elevation and remote sensing images were used to analyze the vertical distribution characteristics of multiple indicators of sediments;the particle size-standard deviation method was used to study the role of different sensitive particle size components in the evolution of the sedimentary environment;at the same time,combined with historical environmental events,such as watershed runoff The sedimentation environment characteristics and influencing factors of Biliukou tidal flat under the synergistic effect of natural factors and human activities in the past 60 years were discussed.The results show:The tidal flat columnar sediments BLH1,BLH2,and BLH3 in the coastal section outside the mouth of the Biliu River on the Liaodong Peninsula are mainly silty sand and sandy silt,with an average particle size distribution between 4.25-5.54?,and the sorting is poor to poor.The states are basically positive skewness,and the kurtosis is mostly moderately sharp to sharp.The frequency distribution curve is asymmetrical with two or three peaks and tends to the side of coarse particles,reflecting the unstable and complex depositional environment and strong hydrodynamic conditions.The change of the cumulative probability curve of each column sample is similar,with most of the jumping components,and the jumping components can be subdivided into two or three sections,indicating that the hydrodynamic conditions in this area are strong and the depositional environment is changeable.The abundance of major elements is SiO₂ and Al₂O₃,Fe₂O₃,K₂O,CaO,Na₂O,TiO₂,MgO,P₂O₅,MnO,and the proportions of the elements are basically the same as the abundance order in the respective crust.The correlation between the element and the particle size is obvious,which fully embodies the"grain control law of the element".Among the various geochemical parameter ratios of sediments,the chemical alteration index,residual coefficient,K₂O/Na₂O,and weathering leaching coefficient generally reflect the strong chemical weathering and warm and humid depositional environment.The TOC content in BLH1 is between 0.35%and 1.11%,the TN content is between 0.03%and 0.11%,and the C/N value is between 8.8 and 15.84.From the point of view of material sources,during the formation of the tidal flats of the Biliu estuary,the main material sources and supply methods of the study area are the filling of rivers with sand,the coastal current of southern Liaoning,the suspended load carried by the open sea tidal current,and the weathering products of the surrounding coastal bedrock.According to the measured data,watershed changes and human activities,the recent sedimentary environment in the study area is divided into three stages:before 1970,the river was basically in a natural state,the average particle size was relatively coarse,and the sensitive particle size components did not change significantly,TOC,TN fluctuates frequently,but the overall content is high.At this time,the forest coverage rate in the watershed is high,the intensity of human development activities is low,and the impact on the watershed is small,and the tidal flat deposition is dominated by runoff.From 1970 to 1990,the sediments were thinner than the upper section,the sorting coefficient became larger,the skewness and kurtosis values became smaller,and the TOC and TN contents decreased.Changes in runoff,sediment fluxes and their seasonal distributions into the sea also lead to a decrease in the sources of terrestrial organic matter.Especially in the 1980s,when the basin entered a period of flat water and less sand,the amount of incoming sediment dropped sharply,the river channel became thinner,and the tidal flats were enhanced by tides and waves.After1990-2010,the sediment retention effect of the reservoir was obvious,and the amount of sediment transported by runoff was significantly reduced.The same period was the flat water period,and the runoff effect showed a slight decreasing trend.The forest coverage rate of the river basin has increased,and the sediment content of the river has decreased.During the same period,industrial development and aquaculture activities along the northeast coast have increased,and the problem of eutrophication of water bodies has become increasingly prominent,resulting in an increase in the proportion of organic carbon.The runoff is further reduced,and the tidal flat deposition is dominated by tidal current and wave erosion.Analysis of factors affecting the evolution of tidal flat sedimentary environment in Biliu estuary under natural conditions(1)The rise of sea level will accelerate the movement of tidal flats to land.At the same time,due to the intensified erosion of banks and the increase of coastal engineering,the tidal flats tend to be narrowed,which will also lead to the destruction of tidal flat vegetation and the increase in the frequency of wetlands due to tidal flooding.and degenerate.(2)Changes in water and sediment fluxes and sediment sources in the basin affect the changes and development trends of the sedimentary environment.Due to the decrease of water and sediment flux and the shortage of tidal flat sediment supply,the effect of runoff is weakened,the dynamic effect of tidal current and wave is relatively strengthened,and the tidal flat erosion is intensified.In addition,tidal flat sediment is disturbed and suspended by wind and waves,and eroded by tidal flat surface,resulting in the coarsening of tidal flat sediment surface.(3)The tidal asymmetry directly affects the sedimentary environment.The high ebb tide velocity and long ebb tide duration of Biliukou tidal flat make it have strong sand carrying capacity,which aggravate coastal erosion and provide conditions for sediment migration to the sea.(4)The asymmetry of ebb and flow tide has a direct effect on the sedimentary environment.The tidal flat of Biliu estuary has high ebb tide velocity and long ebb tide duration,which makes it have strong sand-carrying capacity,intensification of coastal erosion,and also provides conditions for sediment migration to the sea.