The Responses Of Saline Lake Sediment Organic Carbon Mineralization To Temperature Increase And Nitrogen Addition In Arid Region

Lakes not only as the junction of the atmosphere,terrestrial ecosystems,and aquatic ecosystems,store abundant regional and global environmental change information,but also has the characteristics of continuous deposition,fast deposition rate,and large greenhouse gas emission flux.It is an information carrier to reveal global climate change and regional response.Saline lakes are the main types of lakes in arid regions.They are rich in potassium,lithium,magnesium and other salt resources,and are an indispensable important resource for the country and society.Temperature rise and nitrogen deposition,as the main forms of global change,have had important effects on the carbon and nitrogen cycle of terrestrial ecosystems.The research of sediments organic carbon mineralization response to warming and nitrogen deposition has mainly focused on temperate and tropical freshwater lakes,and saline lake sediments has rarely been addressed.In order to investigate the effects of warming and nitrogen deposition on the organic carbon mineralization and organic carbon components of saline lake sediments,this study takes the Ebinur,Barkol,and Dabancheng Saline Lake in Xinjiang as the research objects.Indoor culture experiment to investigate conditions of different temperatures(low temperature:5.0,10.0,and 15.7℃,high temperature:22.0,30.0,and 37.4℃)and nitrogen deposition(0 kg·ha-1·yr-1,low nitrogen addition:5,10,20 kg·ha-1·yr-1,high nitrogen addition:40,80,and 160 kg·ha-1·yr-1)conditions.The characteristics of organic carbon mineralization and organic carbon components in sediments are expected to provide basic data for predicting future climate change.The main conclusions of the study are as follows:(1)The contents of total carbon(TC),total nitrogen(TN),total phosphorus(TP),pH,Na and Mg in the sediments of Barkol are higher than Dabancheng Saline lake and Ebinur,while the contents of Al and Fe are significantly lower than those of Ebinur and Dabancheng Saline lake.The mean concentration of heavy metals(Cr,Cu,Zn,As,and Cd)in saline lake sediments is higher than the background value of Xinjiang soil.(2)During the cultivation period CH4 and CO2 emission dynamics of saline lake sediments increased first and then decreased under 5,10,and 15.7· incubation.CO2 emission dynamics of sediment CH4 decreased gradually under the treatments of 22.0,30.0,and 37.4℃.Or the trend of increasing and then decreasing;the rate of CH4 and CO2 production of organic carbon mineralization in saline lake sediments has a significant exponential correlation with temperature,and the temperature sensitivity(Q10)of CH4 and CO2 in 0-10 cm sediments is higher than 10-20 cm,CH4 emissions Q10 is higher than CO2.Under IPCC B1 scenario,compared with the current temperature,the simulated CH4,CO2 and CO2eq emissions from saline lake sediments in 2100 will increase by 13%-132%,4%-24%and 5%-35%;Temperature controls the emission of CH4 and CO2 from the sediment,and is also affected by sediment organic carbon,total nitrogen and total phosphorus.(3)Low nitrogen treatment promoted CH4 and CO2 emissions from the sediments of Ebinur and Barkol,and high nitrogen treatment inhibits CH4 emissions.Nitrogen addition increase CH4 emissions from Dabancheng Saline Lake sediments but have no significant effect of on CO2 emissions;simulated nitrogen deposition promotes N2O emissions from saline lake sediments.CH4 emissions from saline lake sediments and nitrogen,the amount of addition is a quadratic function relationship,CO2 emissions are significant negatively correlated with the amount of nitrogen added,and N2O emissions are significant positively correlated with the amount of nitrogen added.(4)There was no significant relationship between CH4 emissions from sediments treated at 5.0,10.0,15.7,and 22.0℃,and there was no significant relationship between CH4 emissions from 30.0 and 37.4 ℃ treatments.Low temperature treatment CO2 emissions are significantly related to changes in stable organic carbon,and high temperature treatment CO2 emissions are significantly related to changes in the content of all components.Under different nitrogen addition treatments,CH4 emissions are significantly correlated with changes in the composition of extremely unstable organic carbon,CO2 emissions are significantly correlated with changes in extremely stable organic carbon,stable organic carbon,and inert organic carbon.In general,warming and nitrogen deposition have increased greenhouse gas emission of saline lake sediments and reduced the stability of organic carbon pools,which are potential positive feedbacks of global climate change.