The Sedimentary Characteristics And Sedimentary Environments Of The Surface Sediments In Lake Xihu,Dali

Lake is an important part of ecosystem,which plays an important role in regulating regional climate,maintaining regional ecosystem balance and breeding biodiversity.Lakes are sensitive to global change and record climate and environment changes faithfully.By studying lake sediments,we can reconstruct the past paleoclimate and paleoenvironment.The surface sediments of lakes reflect the characteristics of modern environment,and the impact of human activities on lakes can also be reflected in the sediments.Lake Xihu plays an important role in the local social development and maintaining the ecological environment of the lake area.With the development of social economy,a series of problems have arisen in Lake Xihu,such as eutrophication,lake shrinkage and ecosystem degradation,which seriously affect the ecological and economic functions of the lake.Therefore,42 surface sediment samples were collected in this paper.Through the analysis of grain size,loss on ignition,magnetic susceptibility and water quality,the material source,lake environment and pollution of Lake Xihu were discussed.The main conclusions are as follows:?1?The clay content of the surface sediment of Lake Xihu is 16.7⁴2.1%,the average value is 29.5%.The silt content is 56.6⁷9.3%,the average value is 65.2%.The sand content is 0.2²1.3%,the average value is 5.1%.The silt is the dominant particle size.The input of exogenous materials has a great influence on the spatial distribution of particle size in the western lake area,and the hydrodynamic conditions have an influence on the spatial distribution of particle size in the eastern lake area.?2?The content of organic matter is 13.11⁴5.92%,the average is 22.29%.The content of carbonate is 7.53²6.58%,the average is 15.69%.The content of organic matter increased with the deepening of water depth,and the internal contribution of organic matter was larger.The carbonate content is negatively related to organic matter and water depth,and the higher carbonate content in the northwest may be the input of exogenous carbonate.?3?The magnetic susceptibility of the surface sediments in Lake Xihu is2.2×10^-898.5×10^-88 m³/kg,with an average of 24.75×10^-88 m³/kg.The magnetization value of the western lake area is higher than that of the eastern lake area,because the western lake area receives a large number of foreign materials,and the foreign magnetic minerals are mostly deposited in the western lake area,while the foreign material input of the eastern lake area is less,and the high organic matter content will also dilute the magnetization.The percentage frequency susceptibility of the western lake area increases from north to south with the deepening of water depth.?4?The?¹³C value of the surface sediments in Lake Xihu is-31‰^-27‰,and the average value is-29‰.?¹⁵N value is 1‰⁷‰,average value is 5‰.C/N ratio is13¹9,average value is 19.According to?¹³C value and C/N value,the organic matter in the western lake area comes from land-based organic matter,aquatic plants and phytoplankton,while the organic matter in the eastern lake area comes from aquatic plants and phytoplankton,and the contribution of reed is greater.The?¹⁵N value of Lake Xihu indicates that the nitrogen comes from nitrogen fertilizer,manure and domestic sewage.Submerged plants,emergent plants and nitrogen fixing cyanobacteria affect the?¹⁵N value.?5?The TN content in the surface sediment of Lake Xihu is 4833.24¹1915.85mg/kg,the average content is 7275.589 mg/kg.The TP content is 590.43¹656.05mg/kg,the average content is 1071.91 mg/kg.The TN and TP contents in the surface sediments of Lake Xihu are high,and the organic pollution is serious.The physical and chemical properties of the water and human activities will promote the potential of endogenous release of nutrients.