| Wetland is the ecosystem with the highest carbon density on the earth's land surface and plays an important role in the global carbon cycle,as a special type of ecosystem on the Qinghai-Tibet Plateau,the alpine wetland is very sensitive to climate change due to its special geographical location at"low latitude and high altitude",which makes the alpine wetland extremely valuable.This study takes the Longbaotan wetland in the central part of the Qinghai-Tibet Plateau as the research object,the altitude of Longbaotan is over 4100 m,it has been in the ice-sealing period from november to may of the following year,the soil is frozen and wetland is covered with snow,greenhouse gas emissions are low and difficult to measure.Therefore,during the growth season from may to november in 2017 and 2018,we used a portable greenhouse gas analyzer to observe the CH4 and CO2 fluxes in different areas of the Longbaotan wetland,in order to analyzer the temporal and spatial variation of CH4 and CO2 fluxes,understand the relationship between relevant environmental factors and soil greenhouse gases,and assessment of greenhouse gas emission differences and uncertainties in Longbaotan wetland.The research results and preliminary conclusions are as follows:?1?The daily variation of greenhouse gases shows that the wetland area?WA?and transition area?TA?in the Longbaotan wetland are sources of CH4 emissions.During the growing season?July-September?,the daily variation of CH4 flux is the monopeak curve,the peak appears in the afternoon?14:00—15:00?,In the flat area?FA?,the daily variation characteristics are not obvious,and the value is negative,which is expressed as the"sink"of CH4.Wetland area?WA?,transition area?TA?and the flat area?FA?are all CO2 emission sources.The daily average value of CO2emissions is flat area>transition area>wetland area.In summer?July and August?,the daily variation of CO2 emission flux is the monopeak curve,and the daily variation characteristics of other months are less obvious.?2?The data of the two observation periods showed that the CH4 and CO2 fluxes in the three areas had significant seasonal variation,the peaks of CH4 emissions in wetland area and transition area occurred in the summer in 2017 and mostly in autumn in 2018.The peak of CH4absorption flux in flat area appears in summer,?August?in 2017 and 2018.The average CH4fluxes in wetlands,transition and flat areas are 971.5,763.56 and-9.73?g?m-2?h-1 respectively.The seasonal variation patterns of CO2 emission fluxes during the two observation periods are similar,peak emissions in early spring and summer,low emissions in autumn.The CO2 emission flux has the same spatial variation law,that is,the order of CO2 emission flux is flat area>transition area>wetland area,and the mean fluxes of the two observation periods are 700.57,619.60 and 415.42 mg?m-2?h-1 respectively.?3?Pearson correlation analysis between greenhouse gases and environmental factors showed that CH4 flux in different areas of Longbaotan wetland was significantly correlated with soil temperature at 0.05 level in 2017,while the correlation between CH4 flux and soil temperature in different areas in 2018 is weak at 0.05 level.Combined with Q10 value,the sensitivity of CH4 flux in wetland to soil temperature in 2017 was higher than that in 2018,indicating that the response of CH4 flux to soil temperature during the two observation periods existed larger difference.The CO2 emission fluxes of the two observation periods were negatively correlated with soil moisture at 0.05 level,it indicates that the size of CO2 emissions along the wetland water level distribution gradient shows a negative correlation with the water level.The CO2 emission fluxes in different areas of the two observation periods are significantly positively correlated with soil temperature at 0.05 level,indicating that the soil temperature is an important factor affecting CO2 emissions.?4?During the two observation period,the cumulative order of CH4 annual cumulative emissions is wetland area>transition area>flat area,and its annual cumulative emissions are7.791,5.992,-0.08 g?m-2,respectively.There was a significant difference at 0.05 level in cumulative CH4 emissions from the wetland and transition areas.The annual cumulative emissions of CO2 are in the flat area>transition area>wetland area,and their annual cumulative emissions are 6384.6,5051.0,4360.6 g?m-2,respectively.The annual CO2 accumulation between the three areas is not significant difference at 0.05 level.On the scale of 100 years,the warming potential of greenhouse gas?CH4+CO2?is the largest in the flat area,the transition area is the second,the wetland area is the smallest,and the three areas are generally the source of greenhouse gases,which can enhance the warming trend. |
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