Study On The Forms And Release Properties Of Organic Phosphorus In The Sediments Of The Drawdown Zone Of The South Four Lake

Nansi Lake is the largest fresh water lake in North China and the largest source of drinking water in Shandong Province.Since 2002,it has been planned as a storage lake for the eastern route of the South-to-North Water Diversion project.Therefore,the water quality of Nansi Lake is of great significance to people’s life quality and health.Phosphorus is the main nutrient element of many aquatic organisms and has been regarded as the limiting factor of water eutrophication.Since the operation of the eastern Route project,the phenomenon of total phosphorus exceeding the standard frequently occurs in the Nansi Lake area during the off-season water transfer period due to long-term exogenous input and endogenous phosphorus release from sediment.The release potential of phosphorus（i.e.,activity）depends on the form of phosphorus in the sediment.organic phosphorus（OP）is an important component of phosphorus and organic matter in the sediment,and the content,form and bioavailability of OP play an important role in phosphorus cycle.At present,most studies on sediment phosphorus pollution in Nansi Lake and its subsidence zone focus on total phosphorus（TP）and inorganic phosphorus（IP）,but little attention is paid to sediment OP.In this thesis,based on the research object of the sediment in Nansihu water-level zone,the modified Hedley continuous fractional extraction method,three-dimensional fluorescence spectroscopy（3DEEM）,Fourier infrared spectroscopy（FT-IR）,UV-Vis,scanning electron microscopy（SEM）spectroscopy（SEM）,high-throughput sequencing and other technical means were applied.The morphological distribution,influencing factors and release characteristics of organophosphorus in sediment of the water-level zone of Nansi Lake were explored in order to provide data support for controlling eutrophication of lake water.The main conclusions of the thesis are as follows:（1）The content of organophosphorus of different forms in sediment in the water-level-fluctuation zone of Nansi Lake was significantly different.The OP content of the sediment in the water-level-fluctuation zone of Nansi Lake accounted for 20.03%～45.69%of the TP content,and the average OP was 197.63mg/kg.The content and relative proportion of organophosphorus in each occurrence form were:Residual organic phosphorus（Residual-P_o,67.58%）>calcium-bound organic phosphorus（HCl-P_o,16.61%）>iron/aluminum bound organic phosphorus（Na OH-P_o,7.62%）>potentially active organic phosphorus（Na HCO₃-P_o,5.97%）>weakly adsorbed organic phosphorus（H₂O-P_o,2.22%）.The content and form of OP in sediment in the water-level zone of Nansi Lake are mainly affected by endogenous sources,which mainly come from the metabolism of bacteria and endogenous microorganisms.The risk of phosphorus release from sediment in the west bank is higher than that in the east and south banks.There was no significant difference in the spatial distribution of DOM fluorescence components at different sampling points in the Nansi Lake fluctuation zone.Aromatic proteins(P_I+P_II,56.80%)dominated the DOM in the Nansihu water fluctuation zone,while humic substances(P_IV+P_v,34.01%)were relatively low.The main components of sediment in the subsidence zone are C,Si,O,Al,Fe and Mg.Correlation analysis showed that there was a significant negative correlation between p H and phosphorus content of sediment in the subsidence zone,indicating that the increase of sediment alkalinity may lead to a higher risk of phosphorus release into water.There was a significant positive correlation between OM and OP（R²=0.719,P<0.01）,indicating that organic matter may be an important carrier of OP;Principal component analysis found that the phosphorus forms in sediment were positively correlated,indicating that the phosphorus forms in sediment in the subsidence zone had homology.（2）The richness and diversity of sediment microbial community in the water-level-fluctuation zone of Nansi Lake were higher.At the level of phylum classification,the richness of microbial communities in the sediment at different sites in the water-level zone was similar,and the differences of microbial communities were mainly reflected in the changes of relative abundance of common populations.Proteobacteria has the highest abundance in the sediment community in the water-falling zone of Nansihu Lake,while Ascomycota is the absolute dominant bacteria in the fungal community.Level,the abundance of top 20 species accounted for 22.66%～44.27%in their respective microbial community,the most advantage of bottom sediment fungal species for unclassified unclassified＿k＿Fungi,different levels of dominant fungi also exists obvious difference.Correlation analysis between microbial community structure and organophosphorus morphology at phylum and genus level showed that H₂O-P_owas significantly positively correlated with phylum NB1-j of bacteria,genus NB1-j and Mucor of fungi,and significantly negatively correlated with marmoricola of bacteria and phylum of fungi.Na HCO₃-P_owas significantly positively correlated with Geopora,Tomentella and Tausonia at the level of the fungal phylum and genus.Na OH-P_owas positively and significantly correlated with the phylum Phylum Chlorophylum,Nitroscibactertocetes,Latescibacterota,Phylum Flouscibacter,Slime Mold,and Cryptosporidium of fungi,and was significantly correlated with the genera unclassified＿o＿Polyporales,unclassified＿f＿＿Nectriaceae,Emericellopsis and Talaromyces of fungi.Na OH-P_owas significantly correlated with slime mold phylum and Talaromyces.HCl-P_owas positively correlated with the nitrifying spiral phylum and slime mold phylum of bacteria,and the genus Geopora of fungi was significantly correlated.Residual-P_owas significantly positively correlated with the genus MB-A2-108 of bacteria and highly positively correlated with the genus haliangium.（3）The alternations of wet and dry conditions could lead to significant changes in the phosphorus content in the sediment.When the sediment was submerged for the first time,the contents of TP,IP,OP,H₂O-P_o,Na HCO₃-P_oand Bio-P_odecreased by 69.00mg/kg,33.75mg/kg,35.25mg/kg,2.42mg/kg,7.12mg/kg and 8.38mg/kg,respectively.Na OH-P_ocontent increased by 1.48mg/kg.When the sediment was dried for the first time,the Na OH-P_ocontent decreased by 0.66mg/kg,while the H₂O-P_o,Na HCO₃-P_oand Bio-P_oincreased by 1.38mg/kg,9.98mg/kg and 10.715mg/kg,respectively.The releases of H₂O-P_oand Bio-P_oin the sediment at the secondary flooding stage decreased compared with those at the first flooding stage.Compared with the continuous submerged condition,the dry-wet alternating condition can increase the activity of organophosphorus in the sediment,which is more conducive to the release of phosphorus in the sediment.Moreover,the higher the dry-wet alternating frequency,the greater the release of phosphorus of various forms in the sediment.Sediment particle size,p H and OM are important factors affecting the phosphorus form and content of sediment.When the sediment is submerged,the proportion of clay will increase,and vice versa,the higher the frequency of dry-wet alternation,the smaller the proportion of clay in the sediment.The p H and OM content of the sediment in the water-level-fluctuation zone will decrease after it is submerged,whereas the OM content of the sediment will increase,and the OM content of the sediment will decrease with the alternations of dry and wet.The alternation of dry and wet would reduce the substituents in the aromatic ring of DOM.The substituents and hydrophilicity in the aromatic ring of DOM in the submerged state were higher than those in the falling dry state.The molecular weight and humification degree of DOM in the drying state were greater than those in the submerged state,and the alternation of dry and wet would increase the molecular weight and humification degree of DOM in the sediment.