Diploma thesis in Physics submitted by Florian Freundt born in ...

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2.3. Soil atmosphere composition 2 Theory Depth [m] 0.0 0 0.2 0.4 0.6 0.8 1 2 Jan. Feb. Mar. Apr. CO2 concentration [Vol%] 0.0 0.2 0.4 0.6 0.8 May Jun. Jul. Aug. 0.0 0.2 0.4 0.6 0.8 Sep. Oct. Nov. Dec. Figure 2.9: Monthly averaged CO2 concentration in relation to depth and its seasonal development at a mountain forest site in Japan. From Hamada and Tanaka [2001]. decreasing O2 concentrations within the soil with increasing depth, starting at the atmospheric 20.9 Vol%. The main source of CO2 lies within the soil, its spatial distribution and strength dependent on microbial diversity, organic nutrient reservoirs and temperature. The highest CO2 production takes place within the first 10 – 50 cm of soil during growing season, as shown in Figure 2.7. This corresponds to the fact that microbial biomass is one to two orders of magnitude higher close to the surface than at 2 m depth and is likely caused by the availability of nutrients [Fierer et al., 2003]. The main sink of CO2 is the atmosphere. CO2 concentrations in soil atmospheres were observed to reach up to 13.0 Vol% [Amundson and Davidson, 1990], in laboratory experiments on soil columns even up to 17.0 Vol% [Yamaguchi et al., 1967]. Due to the production zone located close to the surface, diffusive transport of CO2 exists directed both into the atmosphere as well as into deeper soil during spring and early summer, leading to increased CO2 concentrations there. The diffusive flow within the deeper soil regions changes direction in late summer and winter when microbial activity ceases. The CO2 concentration profile therefore fluctuates heavily on diurnal as well as annual scales and is closely related to the O2 concentrations, as shown in Figures 2.8 and 2.9. 30
2 Theory 2.3. Soil atmosphere composition Respiration rate K [g CO2 m-2 d-1] 8 6 4 2 0 0 Jan Mar Apr Feb Dec Nov 5 10 K0 = 1.2 May Oct Aug Jun K0 = 0.9 average soil temperature at 10 cm depth [°C] Figure 2.10: Relation between average soil temperature and daily respiration rate K of CO2 from a fallow soil. From Rowell [1997]. 2.3.2 Variability of soil respiration The dynamics of subsurface CO2 concentration can be described for modeling purposes as by Riveros-Iregui et al. [2011] based on production terms stemming from autotrophic (root respiration by carbon fixating organisms) and heterotrophic (mircobiotic organisms relying on the availability of organic carbon) activities and a diffusive transport term: ∂CCO2 nA ∂t = − ∂ ∂z � DS ∂CCO2 ∂z 15 Sep Jul 20 4 3 2 1 0 Respiration rate K [10-3 m3 CO2 m-2 d-1] � + γA(B, P AR, Θ) + γH(M, TS, Θ) (2.32) where γA describes the autotrophic and γH the heterotrophic component. B parameterizes root biomass, P AR is photosynthetically active radiation, M is soil organic matter, Θ is soil water content and TS is soil temperature. The driving force of soil respiration is microbial activity, which is highly dependent on soil temperatures. The temperature dependency of the rates K of most chemical and biological reactions is calculated by using the Arrhenius equation � K = K0 · exp − E � (2.33) RT 31
Page 1: Faculty of Physics and Astronomy He
Page 5: Measuring annual variation of soil
Page 8 and 9: CONTENTS CONTENTS 3.1 Setup of the
Page 11 and 12: Chapter 1 Introduction Understandin
Page 13: 1 Introduction Molins and Mayer [20
Page 16 and 17: 2.1. Noble gas temperatures 2 Theor
Page 24 and 25: 2.2. Physical processes and propert
Page 26 and 27: 2.2. Physical processes and propert
Page 28 and 29: 2.3. Soil atmosphere composition 2
Page 32 and 33: 2.3. Soil atmosphere composition 2
Page 35 and 36: Chapter 3 Sampling sites and method
Page 37 and 38: 3 Sampling sites and methods 3.1. S
Page 43 and 44: Chapter 4 Measuring methods 4.1 Mas
Page 45 and 46: 4 Measuring methods 4.1. Mass spect
Page 47: 4 Measuring methods 4.2. On site me
Page 50 and 51: 5.2. Temperature profiles 5 Results
Page 52 and 53: 5.3. O2 and CO2 profiles 5 Results
Page 54 and 55: 5.4. Borehole sealing 5 Results 5.4
Page 56 and 57: 5.4. Borehole sealing 5 Results Fig
Page 58 and 59: 5.5. Noble gases 5 Results 8 days,
Page 60 and 61: 5.5. Noble gases 5 Results 5.5.3 So
Page 62 and 63: 5.5. Noble gases 5 Results 5.5.4 So
Page 64 and 65: 6 Discussion This rather extreme am
Page 66 and 67: )! )! *+,-./-01234*-56-20301.7*38*9
Page 68 and 69: 6 Discussion Table 6.1: Synthetic d
Page 71: Chapter 7 Summary The results of th
Page 74 and 75: 8 Outlook Considering the manifold
Page 76 and 77: A.1. Gas sample size A Calculations
Page 78 and 79: A.3. Fractionation-Values A Calcula
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Table B.3: Noble gas volume mixing
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Table B.5: Calculated values of rel
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Table B.8: Precipitation record of
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Table B.10: Complete dataset of nob
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Appendix C Additional plots and fig
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C Additional plots and figures Figu
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C Additional plots and figures �
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C Additional plots and figures O 2
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C Additional plots and figures 4 He
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C Additional plots and figures 20 N
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C Additional plots and figures 10 1
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Appendix D Datasheets 107
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D Datasheets LogTag TREX-8 Technica
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Bibliography [Aeschbach-Hertig 1994
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BIBLIOGRAPHY BIBLIOGRAPHY [Friedric
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BIBLIOGRAPHY BIBLIOGRAPHY [Riveros-
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Acknowledegment At the end of this
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Diploma thesis in Physics submitted by Florian Freundt born in ...

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