Investigation Of Surface Sediment Diatom Assemblage And Grain Size Characteristics In Sea Area Adjacent To The Nangang Industrial Zone Of Tianjin

Setting epeiric zone in sea area adjacent to the Nangang industrial zone of Tianjin on the west coast of the Bohai Bay,this study examined 40 surface sediment samples in sea area of Tianjin progressed diatom identification and soil grain size analysis.Analyzed and identified dominant diatom species and the distribution of diatom in surface sediment.The survey area found out the sedimentary environment according to the combined with the grain size and their location data.In addition,Based on the moving path of freshwater diatoms and the change trend of percentage content,we investigated the transmission path of local water bodies adjacent to the sea area of Nangang Industrial Zone was investigated.In study area,a total of 37 species of diatoms and 25 genera were identified in 40 different glacial sediment samples.The dominant species were eucalypts Coscinodiscus spp.,Cycloella stylorum,Auliscus caelatus,Actinocyclus spp.,Thalassionema nitzschiodes,Diploneis bombus.The dominant species of diatoms generally represent the environmental characteristics of the bay in the study area.The results by diatom analysis of the 40 sediment in survey area have been segmented 3 region and 4 sub-areas with cluster analysis of SPSS 22.0,From which,Area I,The diatom combination is Coscinodiscus spp.-Auliscus caelatus-Cyclotella stylorum-Actinoyclus spp.-Surirella fluminensis.The sediment particle size is relatively coarse,the diatom species are abundant,and the diatom content of freshwater species is larger.It indicates that the sea area is affected by the rivers entering the sea on the southwest coast,and further divided into intertidal zone environments(?a)and rivers and coastal currents that are strongly influenced by rivers according to the distance from the coastline,the diatom species and content of freshwater species.A relatively complex subtidal environment(?b).Area ? The diatom combination is Coscinodiscus spp.-Auliscus caelatus-Cyclotella stylorum-Actinoyclus spp.-Thalassionema nitzschiodes,the sediment is clay silt and the sand content is more,and the hydrodynamic environment Complex.The diatom species of freshwater species are different from those of Zone? and ?.The eutrophic environment of Aulacoseira granulata and Synedra ulna diatoms are dominant,indicating that the sea area is affected.The influence of rivers,tides and human activities is greater.Area ?,the diatom combination is Coscinodiscus spp.-Auliscus caelatus-Cyclotella styloirum-Actinoycluspp.-Diploneis bombus.The sediment is clay silty sand.Sedimentary particle size is finer than ? and ? in whole,and the sand content is small.In addition,according to the percent of freshwater diatom species,this area can divided into ?a and ?b.In?a,the diatom content of the freshwater species is less than that in the I region,but the species is similar to the main species in the I region,suggesting that the sea area is affected by the coastal current and the freshwater diatoms are transported from the intertidal zone of the southwestern coast;IIIb is far away from the coastline.The diatom content of salt water is the highest and the ocean is strong.Freshwater species of diatoms have not been found,indicating that the sea area is not affected by the river and is greatly affected by the circulation in the bay.In study area,there are 29 stations which have some freshwater diatoms,accounting for 0.44%-4.03%.The characteristic distribution of this freshwater diatom tends decrease from south intertidal zone to the northeast and east in south of Nangang Industry.In north of Nangang Industry,the distribution of freshwater species tend decrease from west to east.The trend of distribution and content reduction of freshwater diatoms could be considered as the seawater movement pathway.This freshwater diatoms brought by the river which are Nanpai and Shibei rivers into the sea area are moved in two directions in south of Nangang Industry,and the first is that river flowed into sea was driven by coastal currents which flow from south to north,back south again when it was blocked by Nangang Industry,and then,it was transported to northeast in study area by the whole of currents from south to north in the bay.Second is that the water area has reached equilibrium under the meeting squeezing of rebound current which blocked by Nangang Industry and coastal current,the fresh water of Nanpai river flowed into the sea would flowed into the east of study area.In addition,the trend of freshwater species abundance decrease indicated the seawater movement from west to east in north of Nangang Industry.All in all,the completion built of NGI has changed the direction of seawater moving in adjacent area,simultaneously,this is also main reason that the difference of surface diatom changes on different sample sites.