Study On The Chemical Characteristics Of Carbon, Nitrogen And Phosphorus In Lake Sediments And Their Response To Different Sources Of Organic Matter

Lake is an important part of freshwater ecosystem and sediment is a major place for CNP migration and transformation.The content,distribution and stoichiometric characteristics of CNP in lake sediments significantly affect the ecological function of lake ecosystem and the material cycle of each layer.In this paper,different forms of CNP in the sediments of Dianchi lake are taken as the main research objects.Two sedimentary cores were collected in the South and North parts of Dianchi Lake in July2014.The ²¹⁰Pb radionuclide dating method was used to analyze the ages.TC,OC,IC,TN,ON,IN,TP,OP,IP,n-alkanes,and other indicators were detected.The vertical distribution rule of CNP stoichiometry and its response mechanism to different organic matter sources were studied,as well as other factors such as land use change and human activity.Through the study of this paper,we know that the source of organic matter is an important factor affecting the vertical change of carbon,nitrogen and phosphorus in sediment.The results can provide theoretical basis for further exploring the mechanism of carbon,nitrogen and phosphorus cycle and balance,and further treatment of Dianchi Lake.The main findings are as follows:?1?The difference of ages between the bottom layer and the surface layer of Dianchi lake sediment is about 100 years.Accordind to the dating results,the age span of DC-1 and DC-2?south area?,DC-4 and DC-5?north area?is 1859-2014,1888-2014,1887-2014 and 1896-2014,respectively.The mean value of deposition rate is 0.11±0.03 g cm^-2 yr^-1,0.10±0.01 g cm^-2 yr^-1,0.19±0.03 g cm^-2 yr^-1,0.19±0.04 g cm^-2 yr^-1,respectively.Different areas show different characteristics,and the depositional rate in the north of Dianchi Lake is higher than that in the south.In the vertical direction,the sedimentation rate shows a trend of increasing fluctuation,which may be related to human activities in different historical periods,especially after the 1980s,during which time the artificial influence is enhanced,and the sedimentation rate is obviously increased.?2?The concentrations and fluxes of TC,OC and IC in the sediments increase significantly with the rise of deposition age,especially after the 1980s.This indicates an increase in terrigenous material input.The concentration and vertical distribution of TN and ON are consistent with the change of TC and OC,indicating that the sources of OC and ON may be the same.ON is the main component of TN,and its concentration and deposition flux increase rapidly after 1980s.The concentration of IN is very low and its vertical distribution trend is not obvious.The increase of TN and ON fluxes could be mainly attributed to the increase of domestic sewage discharge and agricultural non-point source pollution.?3?The CNP stoichiometric ratio has significant heterogeneity among sediments due to the difference of geographical location and the source of sediment in different areas.The results of organic matter source analysis show that DC-1 and DC-4 are mainly from external sources,DC-2 and DC-5 are mainly from internal sources.On the vertical section,there is no significant difference in C/N ratio between the surface layer and the whole layer of a single sedimentary column,and there is significant difference in C/P and N/P ratio.In general,the ratio of exogenous CNP is higher than that of endogenous CNP,which reflects the regulatory effect of organic matter from different sources on the vertical change of stoichiometry.?4?There is no obvious change rule of C/N in the sediments with the change of sedimentary age.The C/P ratio and the N/P ratio in the vertical section decrease gradually with the increase of depth and finally tend to be stable,but the stage characteristics of different sedimentary columns are different.The vertical distribution of organic ratio is consistent with the total ratio.The results show that the vertical change of CNP may be mainly affected by the different mineralization and degradation of CNP.The source of organic matter,land use change,human activities and other factors will also significantly affect the CNP stoichiometric ratio in sediments.