Modern Sedimentation Rate And Environmental Studies Deposition Bohai Bay (Tianjin Section) Coastal Waters

About two-thirds of the world’s population live in coastal area within80kilometers,about four hundred million people live in the coastline of20kilometers within the area, inshore areas as an important part of sea system, is the most frequent sea interaction, human use the sea one of the most promising places, It provides a rich marine resources for human. In recent years, this area under human disturbance, is undergoing dramatic changes. A case study of Bohai Bay, Bohai Bay geological environment is relatively fragile, semi-closed sea area belongs to the typical, the influence of large-scale human activities, exacerbated by the Gulf of Bohai environmental pressure. Therefore, to study the sedimentary environment of Bohai Bay near shore area, has the great significance to human life and productionIn this paper, Bohai Bay near shore area as the study area,through fourteen surface sediment samples to measure particle size, heavy metal and radioactivity, and3short undisturbed cores of sedimentation rate、210Pbexe and137Cs activity-depth profiles, discovery of sediment grain size fractions, heavy metal content and radioactivity in different distribution characteristics in the study area, found in different types of210Pbexe and137Cs activity-depth profiles, implement sedimentation rate measure of the modern sediment column samples, Discussed the relationship between sedimentation rate and clay content of3short undisturbed cores, analyzed the process of modern sediments of study area.The sediments were majorly silt-size and the particle size decreases southwards and eastwards in study area. The ranges of heavy metal concentrations are25.6～35.1mg/kg,44.1-67.7mg/kg and60-73.5mg/kg for Cu, Pb, Zn, respectively. The radioactivities for210Pb and137Cs are13.2-35.3Bq/kg and0.05-1.28Bq/kg, respectively. Heavy metals concentration and radioactivity decreases with the increase of particle size, and generally increases both from north to south spatially. In particular, the level of heavy metals and radioactivity in the central and southern area increases southeastwardly and eastwardly, respectively. That might be due to the fact that the fine particles are more effective in adsorbing metals than coarse particles, and the surface sediment particle size distribution can be affected by flow in Bohai bay.Two types of210Pbexe activity-depth profiles were identified:the first was Ideal-decying-type, second was Wiggling with approximate euivalent amplitude. Two types of137Cs activity-depth profiles were identified:the first was have peak and continuous137Cs curves, second was no peak and discontinuous137Cs curves.The average sedimentation rate of sediment column Zl was0.67～0.78cm/a, the average sedimentation rate of sediment column Z2was0.53～0.67cm/a the average sedimentation rate of sediment column Z1was0.91-1.12cm/a. The average sedimentation rate of3groups of sediment column samples existed slower trend since1963, t the impact of this trend is mainly affected by the material sources. The relationship between clay content of3short undisturbed cores was Z1<Z2<Z3, this may be related to the level of handling and sediment grain size composition.