Study On The Marine Sedimentary Environment Evolution Of The Southern Of Laizhou Bay Under The Impact Of Port Projects

Human activities have significantly impact on coastal environmental due toabundant resources, dense population and developed marine economy. Coastal area ofLaizhou bay is a typical marine environment under the interaction of nature andhuman factors. Surface sediments are mainly composed by silt and the water depth inthe south of study area is relatively shallow with characteristic of low-lying. Marinesedimentary environment of Laizhou bay is evolving under the influence of the largeport projects in recent years. The evolution of the marine depositional environments inthe study area is studied, and analyzed the impact of marine environment under theconstruction of Weifang port. Therefore, it has theoretical and practical significance inprotecting the surrounding marine environment and developing the marine resourcesreasonably.In this paper, characteristics of surface sediment distribution, transport trends,transport fluxes, sediment evolution, hydrodynamic environment changes, modernsediment rate and geochemical characteristics are studied based on147surfacesediment samples, chart data, observed current data, and two columnar sedimentsamples in the study area. Marine sedimentary environment evolution of the southernof Laizhou bay under the impact of port projects are systematically analyzed on thebasis of measured data and the main results are as follows.Distribution characteristics of surface sediment types in the study area are obviousstrip and parallel to the shoreline, and the sediment types are sand, silty sand, sandysilt and clayey silt in proper order. Contour of particle size are parallel to the shorelineand gradually smaller from the shore to the sea in general. Sediment distribution iseffected by the port in the nearshore, and the sediment curves are bending to the shorenear the port. Surface sediment is tapering on both sides of the port and especially inthe west side. Distribution of surface sediment is mainly affected by sedimentprovenance, wave tide and port projects in the study area.Hydrodynamic in the nearshore area is strong, and is relatively stable in the openwaters of the north side of Weifang port. Sedimentary environment is relatively weak on both sides of the ports. Surface sediments are mainly transported from theshoreline to the offshore area in the southwest side of the study area; Surfacesediments are mainly transported from the east to the west along the coast line in theeast side of the port, and part of the sediments is accumulated in the east of WeifangPort; meanwhile, surface sediments are mainly transported to the north in thenorthwest side of the study area, and this is mainly affected by fine grained sedimentstransported from the Yellow River delta.Compared with1984, results of chart analysis show that the shoreline of2002inthe current estuarine fills to the sea under the effect of suspended sediments from theYellow River, meanwhile, shoreline of the south Laizhou bay shows little change. Theshoreline of the Yellow River estuary appeared retreat from2000to2009because ofriver diversion, reduce amount of sediment discharge and depositional environmentchanges. Shoreline near the Weifang port changes significantly between1984and2007with characteristic of formation of a large number of new artificial shoreline.Depth contour of-5meters constantly advance to the sea and the total distance was at1500~3000meters in the past30years. In general, it was silting in near Weifang portand its’ adjacent waters during1984and2002. The average deposition rate was about2cm/a. The deposition rate was accelerated during2002and2007, where the netamount of siltation was at1.92×108m3and the average deposition rate was about7cm/a. There is a certain degree of siltation around Weifang Port and it is obvious inthe east and west side of the jetty.The surface sediments are mainly composed by silty sand and it is coarser in theshallow waters around Weifang port. Sedimentary layer above230cm in WF1holeand218cm in WF2hole was deposited after1855. A thin layer of fine grainedsediments from the Yellow River were deposited in the study area under the stormsurges and other extreme conditions, and the deposition rate was about0.3~0.5cm peryear during this period. Construction of Weifang port projects in1997and2007havea great impact on the sedimentary environment of the surrounding waters, and thedeposition rate is significantly increased. The average annual deposition rate is at5.1cm and3.5cm in WF1and WF2core between1997and2007. Content of heavymetals Ni in sediments of study area above200cm was increased slightly withdeposition of sediment, while there is no obvious change in the content of Pb. Itshows that the content of heavy metals in sediments was less affected by human activity and there is no significant heavy metals accumulation in the study area.