The Preliminary Study On The Distribution Of Diatoms From The Main Body Of Water In Beijing

Background: Beijing belongs to the Haihe River Basin.There are five major river systems—Daqing River System,Yongding River System,Beiyun River System,Chaobai River System and Jiyun River System—from west to east.There are 425 rivers of the drainage area of over 10 square kilometers and their total length is 6400 km approximately.In addition,there are also 17 with a certain amount of lakes and 18 large and medium-sized reservoir waters.Such a huge area of the water can beautify the natural environment of capital,but also make many wading accident happen.Therefore a lot of corpses were found in the water in Beijing each year.In these bodies,some belong to accidental or Dutch act,belonging to homicide or postmortem submersion into the water is not uncommon.In response to these cases,forensic workers must determine whether the deceased was drowned or died.And investigators would judge whether the position of the body found is the location of drowning or not.In forensic practice,the status of diatom test as a "gold standard" for identification of drowning remains unchanged,which is of great significance in the identification of drowning or postmortem water entry and the presumed location of drowning.Due to the environment of waters is different and a great variety of diatom and different sources of diatoms is not the same,so the quantitative distribution of diatoms from the lung,liver,kidney and marrow of corpses can help to identify the location and time of drowning by comparison with diatoms from field water and diatoms in different time periods in the waters.At persent,the study on the distribution of diatoms from the main body of water in Beijing is half-baked.Objective: 1.Research the quantitative distribution of diatoms and calculate the percentage of a particular genus in the main body of waters—19 rivers,16 lakes,12 reservoirs—in Beijing.2.Compile the database and atlas of diatom species in the main body of waters in Beijing.To provide assistance to the Beijing public security organs and relevant departments in the determination of diatom species in the case of water bodies and the identification of the location of the dead bodies in the water.Methods: the Lefort aqua regia digestion method detecting diatom in main waters of Beijing.1.69 different sampling sites(19 rivers,16 lakes,12 reservoirs)were sampled by us from April 2016 to March 2017.2.The water samples were digested at each sampling point and then observed by scanning electron microscopy.Statistics of diatom species in each water sample.Compile the database that include the atlas of diatom species.Results: 1.21 diatom genera,including Aulacoseira,Stephanodiscus,Cyclotella,Coscinodiscus,Thalassiosira Cleve,Navicula,Diatoma De Candolle,Gyrosigma Hassall,Fragilaria,Amphiprora Ehrenberg,Nitzschia Hassall,Cocconeis Ehrenberg,Caloneis Cleve,Tabellaria Ehrenberg,Cymbella Agardh,Achnanthes Bory,Diploneis Ehrenberg,Surirella Turpin,Amphora Ehrenberg ex Kützing,Gomphonema,Synedra Ehrenberg,were found in all samples.They are from 2 classes.The typical diatom samples were taken for scanning electron microscopy,and the abundance of diatoms in different waters was statistically analyzed.2.10 diatom genera,including Cyclotella Kützing ex Brébisson,Stephanodiscus,Navicula Bory,Nitzschia Hassall,Synedra Ehrenberg,Aulacoseira,Fragilaria Lyngbye,Achnanthes Bory,Gomphonema Ehrenberg,Cymbellaceae Agardh,were found in Jingmiyin channel.Conclusion:The characteristics of diatom distribution in the main waters of Beijing were investigated.The atlas of diatom scanning electron microscope(SEM)and the database of species composition in Beijing were established.On this basis,the forensic workers in Beijing will be able to effectively complete the diatom species comparison.By using the high resolution images of the diatom species detected in the scanning electron microscope and compared with the diatom map in the database,the forensic workers can determine whether the diatom species are consistent.This is very helpful for the diagnosis of drowning in water bodies and the location of the bodies falling into the water.