Characteristics Of Organic Phosphorus And Environmental Indicators Of Lake Sediments

The eastern plain area and the Yunnan-Guizhou plateau region are the main distribution areas of freshwater lakes,and they are the most serious areas of eutrophication and the areas with the highest eutrophication risk in China.With the effective control of exogenous phosphorus load,the endogenous release of sediment phosphorus,especially organic phosphorus,provides an effective source of phosphorus for overlying water,becoming an important factor affecting the nutritional status and water quality of lakes.However,due to the complexity of the structure of organic phosphorus,at present,its understanding is still relatively limited,and different types of organic phosphorus has different biological activity,release risk and sensitivity to the environment.So,the study of the characteristics of organic phosphorus in lake sediments is of great significance for controlling the endogenous load of organic phosphorus in sediments.In this paper,the surface sediments of the Lake Erhai and the Lake Dongting,the typical mesotrophic lake in the Eastern Plain and the Yunnan-Guizhou Plateau,respectively,are selected as the research object,by means of enzymatic hydrolysis,³¹P-NMR,UV-visible spectroscopy,chemical extraction,and FT-IR techniques,the organic phosphorus in lake sediments was characterized from multiple perspectives,in order to have a more comprehensive understanding of the characteristics of organic phosphorus in lake sediments.At the same time,the characteristics of organic phosphorus in lake sediments from different regions were compared,and the relationship between organic phosphorus in sediments and environmental factors was explored,which provided a theoretical basis for lake environmental governance in China.The main conclusions are as follows:?1?The content of organic phosphorus in the surface sediments of the Lake Erhai was 315.32 mg·kg^-1,which was mainly from endogenous sources,and dominated by hydrophilic humic-acid with large molecular.Erhai has relatively higher content of organic phosphorus in sediments,but it's water quality was better,mainly because the degree of humification of organic phosphorus was relatively higher.The content of monoester phosphorus was the highest,followed by diester phosphorus?phospholipid and DNA?,and phosphonate was the least.The most abundant OP species were NaHCO₃-OP with weakly adsorbed state,followed by NaOH-OP,and less contents of HCl-OP and H₂O-OP.The content of enzymolyzed diester phosphorus in all forms of organic phosphorus was higher than that of active monoester phosphorus.Spatially,the characteristics of organic phosphorus in the central and southern lakes are similar.Compared with the central and southern lakes,the northern is less stable and releases more organic phosphorus,as a result,the content of organic phosphorus in the northern lake is lower than that in the central and southern lakes.The activity of diester phosphorus in all kinds of OP is the strongest,which is mainly affected by chl,DO and pH.Weak alkaline environment and aerobic conditions can promote the release of diester phosphorus.The increase of phytoplankton biomass promotes the accumulation of diester phosphorus.The diester phosphorus cycle between sediments-overlying water-algal is an important reason for the improvement of water quality in Erhai Lake,after exogenous pollution was controlled.?2?The content of organic phosphorus in the surface sediments of Lake Dongting is 295.72 mg·kg^-1,which is mainly from terrestrial sources,and dominated by hydrophobic humic-acid with large molecular,and has relatively higher humification degree.Spatially,the molecular weight,hydrophobicity,and humification of organic phosphorus basically decrease with the direction of the flow of water?the entered rivers?West Dongting?South Dongting?East Dongting?Dongting Lake exit?,increased stability of organic phosphorus.The content of monoester phosphorus was the highest,followed by diester phosphorus?DNA?,and the content of phosphonate was the least.Affected by external input,the content of organic phosphorus was lower in the lake than in the entered rivers and the exit.Affected by the sediment particle size and hydrodynamic conditions,the content of organic phosphorus in the western lake was the lowest.The monoester phosphorus is not strongly related to environmental factors,and is not sensitive to environmental factors.Diester phosphorus?DNA?is mainly affected by heavy metals?Fe,Al,Mn?,OM,water temperature and dissolved oxygen.Among them,the increase of heavy metal and organic matter content,the increase of water temperature,and the decrease of dissolved oxygen content are conducive to the accumulation of DNA.The spatial difference of water quality in Dongting Lake is mainly caused by the relationship between rivers and lakes,and the composition of sediment organic phosphorus has no obvious effect on it.?3?Comparative studies have shown that organic phosphorus in the surface sediments of Dongting Lake and the Erhai Lake contains monoester phosphorus,DNA and phosphonates,and the organic phosphorus has a larger molecular weight and a higher degree of humification.The organic phosphorus of Dongting Lake mainly comes from the external source and is hydrophobic,the organic phosphorus of the Erhai Lake mainly comes from the lake microorganisms and primary productivity,and is hydrophilic.the surface sediments of the The substituted species of organic phosphorous aromatic rings and the degree of humification were higher than those in Erhai Lake.Therefore,to improve the water quality of Erhai Lake,the stability of sediments should be strengthened,and the endogenous release of organic phosphorus should be reduced.At the same time,take measures to reduce the deposition of lake's native organic matter.About Dongting Lake,the improvement measures for water quality should pay more attention to the regulation of external sources.Compared with the Erhai Lake,no phospholipids were detected in the surface sediments of Dongting Lake,which was mainly caused by the different sources of organic phosphorus.The Dongting Lake belongs to the superfluous lakes affected by the relationship of rivers and lakes,but Erhai Lake belongs to the inland faulted lakes,it's flow velocity is relatively slow.The difference in hydrodynamic factors is that water quality of Dongting Lake is inferior to the Erhai Lake,but the risk of algal blooms and the accumulation of organic phosphorus in sediments are lower than that of the Erhai Lake.