Accumulation Characteristics Of Organic Phosphorus In Lake Sediments Of Yunnan Plateau And Responses To Basin Development

Phosphorus is one of the important factors to maintain eutrophication and cause the algae outbreak in eutrophic lakes.A large amount of phosphorus exists in the sediments of eutrophic lakes,among which organic phosphorus?OP?is an important part of lake sediments.However,due to the complexity of the structure and composition of OP,the current understanding of the biogeochemical cycle of OP in lakes is still very limited.The composition,structure and enzymatic hydrolysis characteristics of OP in sediments are closely related to the biogeochemical cycle of OP in the entire lake ecosystem.Therefore,the study used chemical sequential extraction,enzymatic hydrolysis,ultraviolet spectrophotometry?UV-vis?,three-dimensional fluorescence spectroscopy?3DEEM?,and liquid phase phosphor nuclear magnetic resonance(³¹P-NMR)to study organic phosphorus contents,composition and structure characteristics and bioavailability in sediments of Erhai Lake,Dianchi Lake and Yilong Lake in the South Plateau,the accumulation characteristics of organic phosphorus and the risk of eutrophication in lake sediments of Yunnan Plateau were analyzed from the historical perspective,the relationship between the accumulation of organic phosphorus in Yunnan plateau sediments and basin development was also discussed in order to provide scientific basis for the control of lake eutrophication and the comprehensive management of the river basin in Yunnan Plateau.Different organic phosphorus forms of columnar sediments in Erhai Lake,Dianchi Lake and Yilong Lake were quantitatively analyzed by improved Hedley sequential extraction method.The variation characteristics of organic phosphorus bioavailability in different forms of sediments were analyzed by enzymatic hydrolysis.The proportion of organic phosphorus in Yilong Lake?MOD?sediments was significantly higher than that in Dianchi Lake?LIG?and Erhai Lake?MES?.OP content in different forms of Erhai Lake and Dianchi Lake was as follows:HCl-Po>Na OH-Po>Na HCO₃-Po>H₂O-Po,while Yilong Lake was Na OH-Po>HCl-Po>Na HCO₃-Po>H₂O-Po.EHP in sediments is one of the important sources of bioavailability Po.The content of EHP in different forms was as follows:Na OH-Po>Na HCO₃-Po>H₂O-Po.The content of labile monoster P and phytate-like P obtained by all forms of organic phosphorus hydrolysis were higher than that of diester P.In the vertical distribution,the organic phosphorus content in the sediments of all lakes generally decreases with the increase of depth.The variation trend of different forms of OP was similar to TOP,in which the bioavailable Po in Erhai Lake and Dianchi Lake decreased significantly with the increase of deposition depth,while the vertical variation of bioavailable Po in Yilong Lake did not decrease significantly in the lower layer.The structures of organic phosphorus in the columnar sediments of Erhai Lake,Dianchi Lake and Yilong Lake in Yunnan Plateau were characterized by UV-vis and³¹P-NMR.The results show that The degree of OP humification and the content of aromatic ring substituents in lake sediments from Yunnan Plateau increase with the increase of depth,the molecular weight of OP in lake sediments increases from the upper layer to the lower layer,and the OP structure in lake sediments in Yunnan Plateau tends to be stable from the surface layer to the lower layer.OP with high molecular weight at the lower layer has more complex structure,more polymerizable aromatic rings and higher degree of humification,which is conducive to improving its stability and alleviating the degradation and release of bioavailable OP in sediments.,while OP in Yilong Lake sediments with low molecular weight have simple structure,low degree of humification and high molecular activity.Organic phosphorus in the sediments of Yilong Lake and Dianchi Lake came from terrestrial and biogenic sources,and the biogenic sources had a great influence,while the OP in erhai Lake was mainly influenced by terrestrial sources.³¹P-NMR technique was used to verify the organic phosphorus compositions in the sediments of Lake Dianchi and Erhai lake in Yunnan Plateau.Monoester-P and Diester-P are the main components of OP in lake sediments,and Monoester-P plays a key role in lake ecosystem.The social and economic development of lake basin has a profound influence on the accumulation of OP in sediments of Erhai Lake and Dianchi Lake.The OP extracted by Na OH-EDTA is mainly iron-aluminum bound OP,which is most active under the influence of human activities and can better reflect the changes of human activities in the basin.