Distribution Of Phosphorus Forms In Sediment Of Junshan Lake And Its Influence On Lake Water Quality

Junshan Lake is a well-known freshwater lake in China and an important lake separated from Poyang Lake.It is rich in aquaculture.Studies have shown that the nutritional status of Junshan Lake has been increasing year by year.Most lakes in Jiangxi Province use phosphorus as a limiting factor.The sediments can absorb phosphorus in water bodies,but under certain conditions,they will also be released to water bodies,causing endogenous pollution.Studying the characteristics and distribution of phosphorus in the sediments of Junshan Lake,exploring the adsorption process of sediments on phosphorus,analyzing the impact of sediment phosphorus on lake water quality,can better provide a theory for the prevention and control of the eutrophication state of Junshan Lake Basis.This paper collected surface sediments and water bodies at 12 monitoring points in July and December 2020,and introduced the surface sediments at each monitoring point that were well preserved ten years ago as a reference.The phosphorus in the sediment is extracted by the SMT method.The extraction forms of the phosphorus in the sediment include total phosphorus（TP）,inorganic phosphorus（IP）,organic phosphorus（OP）,iron/aluminum phosphorus（Fe/Al-P）,calcium phosphorus（Ca-P）;perform phosphorus adsorption kinetics and adsorption thermodynamics（low concentration）experiments on sediments;evaluate the nutrient status of the water body.The measured water quality indicators include chlorophyll a（Chla）,total phosphorus（TP）,and total nitrogen（TN）,transparency（SD）,permanganate index(COD_Mn).First,understand the temporal and spatial distribution characteristics of phosphorus occurrence in the sediments of Junshan Lake,and use various data processing methods to explore the distribution differences of sediment phosphorus occurrences and the influencing factors of time changes;then study the phosphorus adsorption characteristics of the sediments in each region Analyze the relationship between the distribution of phosphorus occurrence forms in sediments and its phosphorus adsorption behavior;finally,the comprehensive nutrition index method is used to evaluate the nutritional status of the water body,and the temporal and spatial distribution characteristics of the water nutrition status are obtained,and the distribution of phosphorus occurrence forms in the sediments is explored Impact on lake water quality.The main conclusions are as follows;1.The content of TP in the sediments of Junshan Lake is 449.82～713.78 mg/kg.The relationship between the average content of phosphorus in sediments of different occurrence forms OP>IP>Fe/Al-P>Ca-P,the mass fraction of IP in TP is 41.50%～50.52%,OP accounts for 49.59%～58.50%,Fe/Al-P accounts for 31.71%～37.83%;Ca-P accounts for9.19%～16.00%.IP and OP are the main components of phosphorus in the sediments of Junshan Lake,Fe/Al-P is the main component of IP;the main sources of phosphorus in sediments are OP and Fe/Al-P,and OP is the main source.IP,OP,Fe/Al-P and TP have a good linear correlation at the level ofα=0.01.Among them,OP and TP have the highest R².The main influencing factor of the spatial distribution of sediment phosphorus is OP,followed by IP,Fe/Al-P;IP has a good positive correlation with Fe/Al-P,and has nothing to do with Ca-P.The influencing factor of the spatial distribution of IP is Fe/Al-P;OP has good correlation with IP and Fe/Al-P.2.Through the cluster analysis method,the distribution of TP in the Junshan Lake sediments can be divided into three regions,A,B,and C.The difference in TP content in each region is small.Among them,the monitoring points in area A are S7,S8,S9,S10,S11,S12;the monitoring points in area B are S3,S4,S5,and S6;the monitoring points in area C are S1,S2.The relationship between the TP content in each region is A>B>C.The IP and Fe/Al-P content of the A and B regions are higher than the C region,and the OP content and the proportion of the TP in the A region are significantly higher than the B and C regions.The difference of regional Ca-P content is small.Principal component analysis shows that the distribution difference of phosphorus occurrence in sediments is determined by IP,Fe/Al-P and OP.Compared with July,December sediment phosphorus and its occurrence form content changes less,and the spatial distribution difference is small;compared with ten years ago,the TP content in each region has a significant increase,and the spatial distribution is larger.The variation of phosphorus occurrence in different regions is also different.△TP has a good correlation with△IP and△OP,and has a certain correlation with△Fe/Al-P,indicating the main influence of temporal and spatial changes of sediment TP The factors are IP and OP,followed by Fe/Al-P;△IP has a good correlation with△Fe/Al-P,and has nothing to do with△Ca-P,indicating that the influencing factor of the temporal and spatial changes of IP is Fe/Al-P.3.The rapid adsorption process of phosphorus on Junshan Lake sediments was between the first 0 and 0.5h,and reached the adsorption equilibrium state at 24h.The maximum adsorption Q_maxin the C zone was higher than the A and B zones.The phosphorus adsorption isotherm of the sediment has a high degree of fit with the Langmuir equation,and there is desorption at each monitoring point.The EPC₀is between 0.135 and 0.210 mg/L,and the NAP content is between 15.73 and 25.62 mg/kg..The size relationship between EPC₀and NAP in each region is A>B>C.Q_maxis negatively correlated with TP,IP,OP,Fe/Al-P,and the adsorption capacity of sediments decreases with the increase of OP,Fe/Al-P;NAP,EPC₀and TP,IP,OP,Fe/Al-P is positively correlated.NAP and EPC₀can represent the pollution level of sediment phosphorus,and the release risk of sediment phosphorus mainly comes from OP and Fe/Al-P.4.The water body of Junshan Lake is mainly in mesotrophic state.The water quality in July is slightly better than that in December,and the nutritional state changes little.The relationship between the comprehensive nutrition index in each region is A>B>C,which is the same as the relationship between the phosphorus content in the sediments in each region.TP₀has a good positive correlation with TP,IP,OP,Fe/Al-P,EPC₀,NAP,and a negative correlation with Q_max,indicating that the phosphorus exchange behavior between sediments and water bodies is active,which has had an impact on water bodies.OP,Fe/Al-P is an important factor affecting water eutrophication;Chla is positively correlated with IP and Fe/Al-P.The comprehensive factors of phosphorus occurrence in sediments are OP,IP,Fe/Al-P,TP₀,Q_max,EPC₀,NAP.The phosphorus in the sediments of Junshan Lake has an important impact on the eutrophication of the water body.The release risk of phosphorus in the sediments should be paid attention to.This has a great relationship with the development of aquaculture.The degree of aquaculture and the input of related pollution should be controlled.The area should focus on prevention and control,and there is a greater trend towards eutrophication in this area.