Study On Greenhouse Gases Fluxes At The Water-air Interface Of Rivers In Qinghai Lake Basin

Inland river ecosystems play an important role in the global carbon cycle.However,the impact of the greenhouse gas exchange flux of the water-gas interface of plateau mountain rivers on the global carbon and nitrogen cycle still needs in-depth research,especially the measured data on the greenhouse gas exchange flux of small rivers in the plateau mountain area are relatively scarce,which may lead to a serious underestimation of the importance of rivers in the global carbon cycle.In addition to being the water source of several major rivers in Asia（such as the Yangtze River,Yellow River and Yarlung Zangbo River）,the Tibetan Plateau is also home to numerous small rivers.However,a few studies have focused on the impact of greenhouse gas exchange fluxes at the water-air interface on the global carbon and nitrogen cycle in the plateau mountain rivers.Clarifying the magnitude of greenhouse gas release in rivers in the plateau basin can provide basic data for related studies of greenhouse gas release in rivers in the permafrost of the Qinghai-Tibet Plateau,and also provide data support for the control of carbon emissions during the construction of the Qinghai-Tibet Plateau National Park Group.Therefore,this study takes Buha River and Shaliu River,the two largest rivers entering Qinghai Lake Basin,as the research objects,and conducts multi-frequency sample collection on them from October 2020 to August 2021.Headspace-gas chromatograph is used to quantify the exchange fluxes of CH₄,CO₂and N₂O at water-gas interface,and combines the environmental factor data of sampling points.The temporal and spatial characteristics of carbon and nitrogen release,influencing factors and temperature potential were analyzed systematically.The results show that:（1）The seasonal differences of greenhouse gas fluxes at the water-air interface of the two rivers in Qinghai Lake Basin were significant.The CH₄,CO₂and N₂O exchange fluxes showed that the seasonal distribution of spring thaw period was much higher than that of summer wet period and winter early freezing period（P<0.05）.The fluxes of CH₄,CO₂and N₂O at the river water-gas interface showed similar diurnal variation trends.The exchange fluxes of the three greenhouse gases dropped to the lowest value at 00:00,and then fluctuated and peaked at about 17:00 p.m.（2）The exchange fluxes of CH₄,CO₂and N₂O at the water-air interface in Buha River were significantly higher than those in Shaliu River.In terms of spatial variation within rivers,the Buha River and Shaliu River show similar spatial variation trends,and the exchange fluxes of CH₄,CO₂and N₂O at sampling points in the upper and middle reaches of permafrost cover are higher than those in the lower reaches of the freeze-thaw erosion area.（3）By sorting out the environmental factors affecting the greenhouse gas exchange fluxes at the river-water interface,it is found that the exchange fluxes of CH₄,CO₂and N₂O are positively correlated with the wind speed and TDS in the river,and significantly negatively correlated with the salinity of the water body.Meanwhile,the greenhouse gas exchange fluxes at the river water-gas interface during the thaw period have an obvious altitude effect.（4）The mean exchange fluxes of CH₄,CO₂and N₂O at the water-air interface in Qinghai Lake Basin were 192.45±221.30μmol·m^-2·d^-1,123.26±128.53 mmol·m^-2·d^-1,101.27±44.19μmol·m^-2·d^-1,respectively.The results showed that the river water in Qinghai Lake Basin was the source of greenhouse gas,and the warming potential（GWP）of greenhouse gas in Qinghai Lake Basin was 1.06 kg CO₂m^-2·a^-1.（5）The existence of permafrost in the study area complicates the issue of greenhouse gas exchange fluxes at the water-air interface.Comparing the emission fluxes of CH₄,CO₂and N₂O at the water-air interface in this study with other greenhouse gas exchange fluxes in rivers affected by permafrost,it can be seen that the greenhouse gas fluxes at the water-air interface in Qinghai Lake Basin are at a low value.However,the contribution of CO₂emission to GWP value is the largest in the rivers around the Arctic,and CH₄contribution to GWP value is relatively greater in the Qinghai Lake Basin.Considering that the greenhouse effect of CH₄and N₂O is 25 and298 times that of CO₂on the centennial scale,climate warming will more significantly promote the net emission of CH₄and N₂O from rivers in Qinghai Lake Basin,thus producing a positive feedback effect on climate warming.