九州大学学術情報リポジトリ
Kyushu University Institutional Repository
Study on Soil CO2 Emission and Its Effects on Balance in Global Carbon Circulation
サルマワティ
http://hdl.handle.net/2324/2236185
出版情報：九州大学, 2018, 博士（工学）, 課程博士 バージョン：
権利関係：
（様式２）
氏 名 ：
サルマワティ
論 文 名 ：
Study on Soil CO
2Emission and Its Effects on Balance in Global Carbon
Circulation (土壌 CO
2放散と全地球的な炭素循環への影響に関する研究) 区 分 ： 甲
論 文 内 容 の 要 旨
The unbalance in global carbon cycle due to high energy consumption of fossil fuels results in a rising greenhouse gases, especially carbon dioxide (CO2) in the atmosphere, and induces the global warming and climate change. One of the solutions to reduce its impacts on the environment and human beings is believed to be the CO2 capture and geological storage (CCS) that returns CO2 to underground where originally fossil fuels reserved. However, a monitoring system for CO2 leakage is required to obtain agreement of residents near the CO2 geological storage site. CO2 gas leakage coming up to the surface is identified by increasing of CO2 gas flux on the surface over the base line of the natural soil CO2 emission generated by microorganism activity in the soil layer. However the natural CO2 emission has a characteristics changing with climate conditions, such as soil temperature and moisture related to seasonal atmospheric temperature and rain fall.
Therefore, it is important to determine annual baseline characteristics of the natural CO2 flux emitted from the surface.
In this study, the long-term measurement of soil CO2 flux was conducted to investigate the characteristics of the natural CO2 flux for the environmental factors. The CO2 soil flux was measured continuously using the monitor newly developed for any kind of weather conditions for analyzing the effects of environmental parameters. Furthermore, the increasing rate of global soil CO2 emission rate from onshore surface was estimated against increasing rate of surface soil temperature rise expected to be 1 to 2 ºC.
This thesis is consist of 5 chapters as follows:
Chapter 1 presents the background and objectives as well as the outline of the study. Moreover, an overview about the climate change and its impact on our social life is reviewed, and increasing CO2
concentration in the atmosphere with increasing global temperature and why CCS is the best option to reduce the impact are discussed here as well. The challenges in the CCS technology are also described here to lead a necessary of the soil CO2 flux monitoring on the surface.
Chapter 2 focuses on the brief introduction about the soil CO2 flux, its important role for global carbon cycle generally and baseline identification at CO2 geological storage sites specifically. The processes involve, mathematical model and environmental parameters that affect it are briefly explained here as well. In this research, the closed-chamber method and concentration-gradient methods were applied for soil CO2 flux measurements performed irregularly at the test field in Ito Campus, Kyushu University. For the case of manual closed-chamber method, the CO2 flux was measured by trapping CO2 gas emitted from soil in the closed hemisphere-chamber set manually on the surface and analyzing time-gradient of CO2 concentration in
the chamber over a time (3min.). On the other hand, concentration-gradient method was used to estimating soil CO2 flux using the Fick’s first law based on the vertical CO2 concentration up to 1.0 m in soil depth which profile follows the logarithmic trend. As a result, it was revealed that the measurement results of soil CO2 flux using two methods agree with each other in the range of 0.0025 to 0.010 mol/m2/h measured in the soil temperature 6 to 20 °C.
Chapter 3 describes results extending to long-term continuous measurement by considering the advantages and disadvantages of the two soil CO2 flux measurement methods applied in the previous chapter. A new automated continuous-monitor named “Automated and Continuous Monitoring System for Surface CO2 flux (ACMS-SCO2)” was developed to carry the long-term measurement of the soil CO2 flux in the field. The ACMS -SCO2 was constructed in this study using electric devices, such as CO2 sensor (sensitivity: 1ppm), soil temperature sensor (sensitivity: 0.1°C), high-sealing electric butterfly-valve, process control system, etc., to meet the closed chamber method. It has an ability to measure the soil CO2 flux continuously under any climate conditions and it is easy to modify other sensors. In this chapter as well, long-term measurement using ACMS -SCO2 was carried out at the test field. The results reveal that the soil CO2 flux is ranged from -0.0006 to 0.025 mol/m2/h. Its pattern has the best correlation with soil temperature pattern observed at 5 cm of soil depth, and it also follows trend along the year. It was confirmed that the soil CO2 flux increases exponentially for soil temperature below 30 in not raining condition. Different behavior is observed when the soil temperature is higher than 30ºC, it tends to decrease as the soil temperature increases. Moreover, the effect of the rainfall mostly reduced the soil CO2 flux up to 95% after the rain and the slight negative fluxes (in some cases) were measured after the heavy rain. Furthermore, for the condition that soil temperature and water saturation are lower than 30ºC and less than 90% the threshold line for judging possibility of CO2 leakage by monitoring soil CO2 flux at CO2 storage site has been proposed based on the maximum line identifying the normal soil CO2 flux from natural soil layer.
Chapter 4 discusses about an estimation of the soil CO2 flux response to the global warming in atmospheric air temperature. The increasing rate of global soil CO2 emission was estimated from the characteristics that soil CO2 flux has an exponential correlation to soil temperature based on 71 datasets of the soil CO2 flux collected from 23 literature studies including present study. The data were analyzed to find the response of global warming around 1 to 2 °C during next 20 years with increasing of 1°C in soil temperature considering the climate zone and measured temperature-range. Finally, it has been concluded that the soil CO2 emission measured in subtropical and temperate climate zone were estimated to increase 10.3% in average versus 1°C increase in soil temperature regardless vegetation, climate conditions and soil characteristics.
Lastly, Chapter 5 presents the conclusions of this study including the possibility of the future work.
