Carbon Dioxide Release From Water-air Interface In Karst Watershed And Its Influencing Factors

Global warming is one of the most important environmental problems facing the world today.Carbon dioxide,together with trace gases such as methane,carbon monoxide,ozone and nitrous oxide,causes greenhouse effect,in which carbon dioxide accounts for the highest proportion of greenhouse gases.River system is an important link between terrestrial carbon pool and marine carbon pool,and is the main way to transport terrestrial carbon into the sea.Early studies on river carbon cycle mainly focused on transverse transport of river carbon,but less on interfacial exchange.Recent studies show that global rivers release CO₂ into the atmosphere twice as much as global rivers emit carbon into the sea.The assessment of terrestrial carbon sink capacity may be problematic due to the neglect of carbon release from rivers into the atmosphere.The low-level rivers have small fluids and respond quickly to external disturbances.They have innate advantages for understanding the carbon cycle driving process of land-water systems,evaluating the effects of human activities,and revealing the internal carbon release mechanism of rivers.An essential part of the in-depth study of the system carbon cycle.In order to analyze the CO₂release driving mechanism of rivers in karst area,the"source"and"sink"effects of atmospheric CO₂ in karst small watershed,and the influence of environmental factors and water quality parameters on CO₂ release are discussed,which provides a scientific basis for China's carbon budget calculation.In this study,the rivers and reservoir of the Aha Lake in Guiyang City,Guizhou Province were selected as research objects,and selected:Jinzhong River,Youyu River,Baiyan River,and Aha Lake for research.The flux box method and model method are used to monitor the CO₂ at the water-air interface,and the CO₂ flux at the water-air interface in the karst small watershed is analyzed.The influence of environmental factors and water quality parameters on them is explored,and the flux box method and model method are applied.For comparative analysis,the main results are as follows:?1?The average annual carbon dioxide flux at the water-air interface of Youyu River,Baiyan River,Jinzhong River and Aha Lake is greater than zero,which is the“source”of atmospheric CO₂,and the average annual release rate:Jinzhong River(690.74 mg·m^–2·h^–1)>Youyu River(439.93 mg·m^–2·h^–1)>Baiyan River(249.34mg·m^–2·h^–1)>Aha Reservoir(15.56 mg·m^–2·h^–1).?2?During the monitoring period,the measured carbon dioxide fluxes at the water-air interface of Yuyu River,Baiyan River,Jinzhong River and Lake Aha were positively correlated with water temperature and velocity.It was negatively correlated with acidity and alkalinity,dissolved oxygen and chl-a.There was no significant correlation with air temperature,wind speed,conductivity,total phosphorus and total nitrogen.?3?The pCO₂ of the Youyu River,Baiyan River,Jinzhong River and Aha Lake is higher than the air pCO₂ and is supersaturated.Annual average value of pCO₂ in water bodies:Youyu River pCO₂?389.45 Pa?>Jinzhong River pCO₂?306.68 Pa?>Baiyan River pCO₂?261.38 Pa?>Aha Reservoir pCO₂?171.25 Pa?.The seasonal variation of pCO₂ in water is:high in spring,low in summer,and between spring and summer in autumn and winter.?4?Flux box method and model method have certain correlation,but the magnitude of carbon dioxide flux at water-air interface obtained by the two methods is quite different.Among them,the higher the concentration of HCO₃^-,the closer the monitoring results of the flux box method and the model method are;the greater the pH,water temperature and flow rate,the greater the difference between the flux box method and the model method.