The Disturbution Of Diatom Assembles Of Nearshore Surface Sediment In Bohai Bay And Their Sedimental Enverivenment

Setting epeiric zone in both Tianjin Bay in Bohai Bay west coast and Fuzhou Bay in east coast as studying area,this study examined 40 surface sediment samples in Tianjin Bay and 8 in Fuzhou Bay and progressed diatom analysis.Indentified and found out the diatom composition,dominant species and distribution of diatom assemblages of surface sediment.With grain-size and their landform data,this study found out the sedimentary environment and the contribution of land stream and circulation toward sedimentary environment and diatom assemblages.Diatom analysis result of 8 surface sediment samples in Fuzhou Bay have been divide into 4 assemblages with Cluster analysis:assemblage Ⅰ is dominated by Par alla sulcate-Biddulphia aurita-Rhaphoneis surirella;assemblage Ⅱ is dominated by Paralla sulcate-Coscinodiscus excentrcus-Cyclotella stylorum;assemblage Ⅲ is dominated by Coscinodiscus radiates-Cyclotella stylorum;assemblage Ⅳ is dominated by Paralla sulcate-Coscinodiscus radiates-Coscinodiscus excentrcus.With grain size and landform data,we have concluded:assemblage Ⅰ is basically inlet environment with low land stream effect;assemblage Ⅲ is rocky coast environment with low land stream effect;assemblage Ⅱ and Ⅳ are inlet environment with relatively strong land stream effect.Diatom analysis result of 40 surface sediment samples in Tianjin Bay have been divide into 4 assemblages with Cluster analysis:assemblage Ⅰ is dominated by Coscinodiscus radiates-Coscinodiscus excentrcus-Cyclotella stylorum;assemblage Ⅱ is dominated by Coscinodiscits radiates-Cyclotella stylorum-Coscinodiscus excentrcus;assemblage Ⅲ is dominated by Coscinodiscus excentrcus-Coscinodiscus radiates-Coscinodiscus lineatus;assemblage Ⅳ is dominated by Paralla sulcate-Coscinodiscus excentrcus-Coscinodiscus lineatus.With grain size and landform data,we have concluded:assemblage Ⅰ is inlet environment with low land stream effect;assemblage Ⅱ is inlet environment with medium land stream effect;assemblage Ⅲ is inlet environment with strong land stream effect;assemblageⅣ is estuarine environment with strong land stream effect.Distinguishable difference can be found in percentage composition of Dictycha fibula,Thalassiosira nizschioides,genus Coscinodiscus and genus Actinocyclus in both coasts,which are pelagic diatom.Total average percentage composition of pelagic diatom in Fuzhou Bay samples is 37.65%,which figure has reached 74.01%in Tianjin Bay.This result indicates circulation with pelagic water in Tianjin Bay is more expedite,which is corresponded with regional submarine landform difference.In Fuzhou Bay sampling sites which identified fresh water diatom species,the fresh water diatom are relatively less in variety and quantity,which Epithemia turgida,Melosira granulata,Tabellaria fenestrate can be found.However,in Tian Bay sampling sites which identified fresh water diatom species,the fresh water diatom are relatively more in variety and quantity compare to Fuzhou Bay,which Epithemia hyndmanii,Gyrosigma acuminatum,Melosira granulata,Navicula cryptotenella,Navicula mediocostata,Surirella fastuosa,Synedra ulna,Tabellaria fenestrata can be found.Regular lake and marsh environmental diatom specie,is found in Fuzhou Bay,which are carried into sea while Fuzhou River flowed through tidal beach region and the same specie can not be found in Tianjin Bay.Though both coast are inlet environment,Great difference can be found,suggesting fresh water diatom species source are different in these tow region,and strongly effected by land stream in the studying area.