Distribution Characteristics Of Phosphorus And Nitrogen Forms In The Sediments In Bohai Bay Offshore

The distribution characteristics of nitrogen and phosphorus forms in the sediments of Bohai Bay Offshore were studied by the sequential extraction method,quantify the biologically available phosphorus,estimate the nitrogen load in the sediments,discuss contributors of total organic,and briefly evaluated the pollution degree of nitrogen and phosphorus in the sediment.Provide scientific and technological support and basic data for the environmental governance and restoration of Bohai Bay.The main conclusions can be summed up as follows:A modified sequential extraction method was used for divide the occurrence of phosphorus in the study area,namely:Loosely adsorbed inorganic phosphorus?Lsor-P??Occluded phosphorus?Oc-P??Fe/Al adsorbed phosphorus?Fe/Al-P??Authigenic apatite+Ca CO₃-bound inorganic phosphorus?Ca-P??Detrital apatite phosphorus?De-P??Organic phosphorus?OP??Portland phosphorus?SIF-P?.The total phosphorus?TP?in surface sediments varied from 112.4 to 277.1?g/g,the average was 190.7?g/g.Its spatial distribution is characterized by first increasing and then decreasing from west to east,which is mainly influenced by terrestrial inputs and hydrodynamic conditions.The concentration of different forms of phosphorous followed the following order:Lsor-P<Ca-P<Fe/Al-P<SIF-P<Oc-P<OP<De-P,obviously,De-P is the main form,accounting for 53.95%of the whole phosphorus form.Affected by factors such as the properties and sources of phosphorus forms,the spatial distribution characteristics of each phosphorus form are different.The TP in columnar sediments varied from 25.2 to 655.0?g/g.Stations 8#and 11#first decrease and then increase with the increase of deposition depth,while station 2#shows a tendency to fluctuate and increase.De-P is also the main phosphorus form in columnar sediments,and the vertical distribution of each phosphorus form is different due to the influence of sedimentary environment and other factors.The bioavailable phosphorus?BAP?in surface sediments of this investigated area varied from 77.0 to 173.4?g/g,with an average of 129.3?g/g.The average proportion of the whole phosphorus form is 34.3%,basically showing the distribution characteristics of nearshore>far shore.The BAP vertical variation?0?20 cm?is:81.4?140.3?g/g,with an average proportion of 33.0%.The BAP at different research sites presents different vertical distribution trends,which are mainly controlled by Oc-P and OP.It is also affected by factors such as hydrodynamic conditions.The TN in surface sediments of this investigated area varied from 680.0 to 1550?g/g,with an average value of 1145?g/g.Affected by the water content of the sediments and TOC,the spatial distribution characteristics is near shore higher than low shore.The TF-N varied from 144.5 to 233.2?g/g,with an average of 193.1?g/g.The overall distribution is basically near shore>far shore.Among the transformable nitrogen forms,IEF-N is the main form,and CF-N is smaller,the spatial distribution is relatively even.The content of IMOF-N is varies greatly,and the overall spatial distribution characteristics increase and then decrease;the content of OSF-N presents the distribution characteristics of near shore>far shore,depending on the source of sediments,Influence of factors such as particle size.In the columnar sediment samples,the TN content ranged from 630.0 to 1340?g/g.The average content of stations 8#and11#were 958.8?g/g and 798.6?g/g,respectively.The content in the surface layer was greater than that in the deep layer,and the content in the deep layer remained stable.The vertical variation range of TF-N content is 23.54?312.5?g/g,and different vertical variation trends reflect the difference in sedimentary environment.The transformable nitrogen forms have different vertical distribution characteristics due to different depositional environments.According to the average content of nitrogen forms in the sediments?0-10cm above the columnar sediments?,the TF-N load in the Bohai Bay sediments is calculated to be 36.33×10⁶kg.The source of organic matter in the study area is mainly affected by the combination of marine self-generating and terrestrial sources.According to the Manual for sediment quality assessment formulated by Ontario Environment and Energy?1992?,TP is at a safe level,and TN is at the lowest level.Through appropriate mathematical statistics,the environmental background value ranges of TN and TP in the study area are 825.8?1782.4?g/g and 130.4?311.5?g/g,respectively.The background area method is used to analyze the pollution degree of TN and TP in the sediments.Factors and comprehensive evaluation results show that:5#,7#,8#,12#stations are currently in the lightly polluted stage and should be taken seriously.