Chamber Method Measurement Of Greenhouse Gas Emissions From Typical Terrestrial Ecosystems Of China: Method Research, Application And Results Discussion

It is a fact that the increase of concentration of greenhouse gases in the atmosphere is a cause of the global climate change. CO₂ and CH₄, which increased very fast during the past years, are carbonaceous gases. These compounds are correlated with the development of industry and agriculture. So, carbon budget and global carbon cycle have to be the hottest portion of global climate change research. China is the largest region of Eurasia and has various ecosystems, any change of this region will affect whole global climate. So in situ measurement of carbon flux from China typical terrestrial ecosystems is crucial for carbon budget research. To develop a unified and effective measuring system is the key point to obtain first hand data of China terrestrial ecosystems greenhouse gas emissions. With an improved gas chromatography and static chamber, we set up a measuring system for greenhouse gases emission based on decade?ˉs year work of our lab. Performance tests show that the static chamber/ GC system is suitable for monitoring emissions of the main greenhouse gases in the terrestrial ecosystem since it is easy to use, efficient, constant and reliable. The system is installed in 16 field experimental stations of the Chinese Ecosystem Research Network (CERN) and to carry out the large project of the knowledge innovation program ?°Study on Carbon Budget in Terrestrial and Marginal Sea Ecosystems of China-CBESTC?± of the Chinese Academy of Sciences, with scientific management, united format of database and standard criterion for data quality. The improvements of GC are: Using difference of injection time to finish analyzing of CH4 and CO2; with back-flush and separately sweeping technique to achieve continuous analyse of N2O; and expanding two electrical driving switches into four gas-driving channels; selecting suitable separation columns and oven temperature to combine these separate analyzing systems in same gas chromatography. The combined system is able to simultaneously measure CH4, CO2 and N2O in an air sample in 4 minutes. It?ˉs a breakthrough to apply assembled static chamber to observe trace gases exchange ratio between soil surface and atmosphere. Advantage of the assembled chamber is that the height of chamber is adjustable according growth of plant. Results of test show that the chamber is suitable for observing flux of terrestrial greenhouse gases with low detection limit. The measuring error of the assemble chamber/GC system is less than 10%, far smaller than error caused by temporal and spatial difference. Management of the carbon flux research net with chamber/GC is scientific and reasonable. All stations are applying unified sampling strategy, data analysis technique and database format which designed by Sub-Center of Atmospheric Science of Chinese Ecosystem Research Network (SCAS-CERN). SCAS-CERN is in charge of the technique support, data management and data quality control (QA/QC). After data QA and QC, those data will be return to stations and database will be open to researchers of the whole research group. There are a lot of consideration to assure the representative and veracity of flux measurement. Observing results show that the main factors to affect soil respiration rate of terrestrial ecosystems are temperature, humidity and organic carbon content. As for natural ecosystems such as forest, grassland and wetland, temperature is the dominated factor of soil respiration rate; soil humidity and organic carbon content determine the rate of respiration when temperature is appropriate; in some degree, soil respiration of temperature sensitivity ( Q10 ) covers the contribution of water content and organic carbon to soil respiration. The soil respiration of the wood land of natural forest is larger than reform forest and the south forest lager than the north. With decreasing of water depth, the soil respiration of wetland is increasing; annual respiration efflux of wetland is enhanced with the annual temperature. There is a minimum water temperature for CH4 emission rate of lakes in south china, and CH4 emission rate is correlated with water temperature above this temperature. IVThe minimum temperature is different with spatial difference.