Study On The Variation Characteristics Of CO₂ And CH₄ Fluxes In The Main Stream And Typical Tributaries Of Wanzhou Section Of The Three Gorges Reservoir

In recent years,some scholars have pointed out that reservoirs may be the net source of greenhouse gas emissions.The release of greenhouse gases from reservoirs has gradually become one of the core issues in the international academic debate.Therefore,the research on reservoir greenhouse gas emissions has attracted more and more attention from scholars around the world.In this study,the main stream and the typical tributary（Pengxi River）of the Wanzhou section of the Three Gorges Reservoir were studied.The main environmental factors（water temperature,p H,DO）and biogenic substances（DOC,DIC,DTN,DTP,etc.）and surface sediment biogenic materials（TOC,TP,TN）difference characteristics;at the same time,the main stream,tributary surface and bottom water body CO₂,CH₄ concentration and water-air interface CO₂,CH₄ flux are monitored monthly,To explore the characteristics and influencing factors of the difference between the concentration and flux of CO₂ and CH₄ in the main stream and tributaries.The main conclusions are as follows:（1）Water blooms exist in tributaries（Gaoyang,Huangshi）,and environmental factors（water temperature,p H,DO）and biogenic substances（DOC,DIC,DTN,DTP,etc.）in surface water and bottom water show significant differences;main stream（Wanzhou）Relevant indicators in surface water and bottom water did not show obvious differences.（2）Average CO₂ concentration in surface water:tributary（Gaoyang,Huangshi）<main stream（Wanzhou）,average CO₂ concentration in bottom water:tributary（Gaoyang,Huangshi）>main stream（Wanzhou）.The average flux of CO₂ at the water-gas interface:tributary（Gaoyang,Huangshi）<main stream（Wanzhou）.During the monitoring period（April-September）,the CO₂ concentration in the main stream（Wanzhou）and the tributaries（Gaoyang,Huangshi）was basically saturated,releasing CO₂ to the atmosphere,showing the characteristics of CO₂"source",of which the tributary was only in July（Gaoyang,Huangshi）The CO₂ flux at the water-air interface is negative,indicating that the water body absorbs CO₂ in the atmosphere,showing the characteristics of CO₂"sink".（3）The CO₂ concentration in the tributaries（Gaoyang,Huangshi）was significantly negatively correlated with water temperature,p H and DO,and positively correlated with DOC and DTP;the CO₂ flux at the water-air interface was significantly negatively correlated with water temperature and significantly positively correlated with DTP and CO₂concentration.The CO₂ concentration in the main stream（Wanzhou）was significantly negatively correlated with p H and positively correlated with DIC,DOC and NH₄⁺-N;the CO₂ flux at the water-air interface was significantly positively correlated with NH₄⁺-N and CO₂ concentration.（4）The average concentration of CH₄ in the surface water body:tributary（Gaoyang,Huangshi）>main stream（Wanzhou）,the average concentration of CH₄ in the bottom water body:tributary（Gaoyang,Huangshi）>main stream（Wanzhou）.The average CH₄ flux at the water-gas interface:tributary（Gaoyang,Huangshi）>main stream（Wanzhou）.During the monitoring period（April-September）,the CH₄ concentration in the main stream（Wanzhou）and the tributaries（Gaoyang,Huangshi）was saturated,releasing CH₄ into the atmosphere,showing CH₄“source”characteristics.（5）The CH₄concentration of tributaries（Gaoyang,Huangshi）was significantly positively correlated with water temperature and p H,and the CH₄ flux at the water-gas interface was significantly positively correlated with CH₄ concentration.The CH₄concentration in the main stream（Wanzhou）was significantly positively correlated with p H,DIC and DOC,and the CH₄ flux at the water-gas interface was significantly positively correlated with the CH₄concentration.