Study On Greenhouse Gas Emission Characteristics And Dissolved Inorganic Carbon Sources In The Yarlung Zangbo River

Rivers,which connect the continents with the oceans,are important channels for the transportation of surface materials.In terms of hydrological and geological scales,the basin carbon cycle is an important part of the global carbon cycle and plays an important role in indicating the global carbon cycle and climate change,but the hydrological conditions restrict the carbon flux and affect the basin carbon cycle.Mountain rivers are hot spots for greenhouse gas emissions,but so far there have been few studies on CO₂,CH₄ and N₂O emissions from mountain rivers,which have not been paid attention to in previous studies.Therefore,the greenhouse gas emissions from mountain rivers may be underestimated.Based on the above research background,this experiment selected the Yarlung Zangbo river in Tibet as the research area.Through the collection of time and space samples in the Yarlung Zangbo river basin,fixed-point samples were collected in May2017 and September 2017 for the section of the Yarlung Zangbo river.In order to explore the spatial and temporal distribution characteristics of CO₂,CH₄ and N₂O concentrations in the Yarlung Zangbo river,a large river on the plateau,and its influencing factors,and to provide a theoretical basis for the release of greenhouse gases in mountain rivers and make contributions to the exploration of inorganic carbon sources in plateau rivers.Based on the test results and analysis,the following conclusions are drawn:（1）The content of CH₄ in the Yarlung Zangbo river is 2.3⁸64.9 nmol·L^-1 and the content of N₂O is 8.2²3.7 nmol·L^-1 in the Yarlung Zangbo river.There is no significant difference between the content of CH₄ in the low-flow season and that in the high-flow season（p=0.1120）,but the content of N₂O in the low-flow season is significantly higher than that in the high-flow season（p=0.0173）.The release rates of CH₄ and N₂O in Yarlung Zangbo were 4.3¹1.1 mg C·m^-2·d^-1 and 0.16⁰.37 mg N·m^-2·d^-1,and the emissions were 1.88⁴.59 Gg C·y^-1and 0.07⁰.16 Gg N·y^-1,respectively,accounting for 1.25³.06‰and 2.17⁴.96‰of the CH₄ and N₂O in global rivers respectively.（2）The partial pressure of CO₂ in the Yarlung Zangbo river basin has obvious characteristics of low-flow season and high-flow season.The partial pressure of CO₂ in high-flow season is lower than that in low-flow season,and the partial pressure of CO₂in the middle and upper stream is obviously higher than that in the lower stream.The average pCO₂ in dry season was 813?atm,and the average pCO₂ in wet season was690?atm.The water-air interface CO₂ release rate in Yarlung Zangbo river basin was106⁴296 mg C·m^-2·d^-1,and the average annual release rate was 1864 mg C·m^-2·d^-1,which was the source of atmospheric CO₂.The main reason for the high CO₂ in the upstream river may be from the groundwater rich in DIC,so there is a high partial CO₂pressure in the upstream water.In the basin rainfall effect,the hydrological condition is the primary control factor affecting the change of pCO₂,and the correlation analysis of the oversaturated apparent oxygen consumption and CO₂ shows that the biological aerobic respiration has a relatively low impact on the pCO₂ of Yarlung Zangbo river.CO₂,CH₄ and N₂O emissions from weak mountain rivers need to be taken seriously,and global river GHG emissions may therefore need to be reassessed.（3）The proportion of DIC from carbonate rocks in low water period was46.4%⁹9.8%,with an average of about 86.3%;The proportion of DIC from carbonate rocks in high water period was 72.3%⁹6.1%,with an average of about 83.4%.The release of CO₂ mainly comes from the dissolution of carbonate minerals and soil CO₂,The average proportion of the former in low-flow season and high-flow season is 86.3%and 83.4%respectively,and the highest proportion can reach 99.8%.so it is possible that the one is geologic old an important way of carbon released into the atmosphere.