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    TIẾN SĨ Quantifying organic carbon fluxes from upland peat

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  6. Quantifying organic carbon fluxes from upland peat

    Đề tài hoàn thành năm 2012

    List of contents
    1 General introduction 18
    1.1 Introduction and justification for research . 18
    2 Characteristics of research sites and general methods . 27
    2.1 Research sites . 27
    2.2 General methods . 32
    2.2.1 Peat sampling 32
    2.2.2 Water sampling . 33
    2.2.3 Sediment sampling 34
    2.2.4 In-situ monitoring . 35 Determination of discharge 35 Continuous gas measurement 36
    2.2.5 Ex-situ monitoring 37 Anaerobic incubation . 37 Aerobic incubation . 38 Measurement of concentration and calculation of gas production 38 Aerobic incubation of peat slurry and calculation of gas production 40
    2.2.6 Separation of particle size distribution (PSD) 42 Choosing technique . 42 Procedure of cleaning TFU 44 Preparing TFU standard solution . 44 Testing separation ratio of TFU . 45
    2.2.7 Sample analysis 45
    2.2.8 Total organic carbon . 46 Prepared total carbon and inorganic carbon standards 47 Drift correction 48
    2.2.9 Freeze-dried sample . 50
    2.2.10 Characterization of organic matter composition - methodology
    development for molecular analyses . 51 Extraction and fractionation of the sediment samples 51 Gas chromatography–Mass spectrometry (GC-MS) . 53 Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS)
    procedure adopted 55 Tetramethylammonium hydroxide (TMAH)-enhanced
    thermochemolysis Pyrolysis-Gas chromatography-Mass spectrometry
    (TMAH + Py-GC-MS) 56
    3 Characterization of peat 59
    3.1 Introduction . 59
    3.2 Aims and objectives 62
    3.3 Methods 63
    3.3.1 Peat sampling 63
    3.3.2 Sample preparation and Py-GC-MS analyses 63
    3.3.3 Determination of water content 64
    3.4 Results 65
    3.4.1 Water content of the peat 65
    3.4.2 Optimising pyrolysis (Py) temperature . 66
    3.4.3 Determining optimum mass of peat for Py-GC-MS . 67
    3.4.4 Classification using the scheme of Vancampenhout et al. (2009) 68
    3.4.5 Classification into pedogenic (Pd) and aquagenic (Aq) . 75
    3.5 Discussion 78
    3.5.1 Optimum methods for organic analysis of peat 78
    3.5.2 Environmentally relevant classification of peat composition . 78
    3.6 Conclusions 82
    4 Direct greenhouse gas fluxes from upland peat 83
    4.1 Introduction . 83
    4.2 Aims and objectives 91
    4.3 Methods 93
    4.3.1 Ex-situ gas production 93 Peat sampling to quantify ex-situ gas production 93 Aerobic incubation . 94 Aerobic incubation of peat slurry 95
    4.3.2 Gas production in-situ 97
    4.4 Results 99
    4.4.1 Ex-situ gas production 99
    4.4.2 In-situ gas production . 105
    4.4.3 Ratios of gas production . 114
    4.4.4 Changes in peat composition after 309 incubated days 115
    4.5 Discussion . 118
    4.5.1 Rates of present day GHG production . 118
    4.5.2 Rates of future GHG production 119
    4.5.3 Validation of ex-situ gas production rates 121
    4.5.4 Controls on in-situ gas production 121
    4.5.5 Changes in peat composition associated with GHG emissions 122
    4.6 Conclusions 123
    5 Indirect greenhouse gas fluxes 125
    5.1 Introduction . 125
    5.2 Aims and objectives 130
    5.3 Methods 131
    5.3.1 Sampling . 131
    5.3.2 Analysis 133
    5.3.3. Calculation . 134
    5.4 Results 136
    5.4.1 Mass flux of SsOC 136
    5.4.2 Mass flux of components of SsOC . 139
    5.4.3 Variability in composition of SsOC – PSD 143
    5.4.4 Variability in composition of SsOC – Compound classes 147
    5.4.5 SsOC composition related to processes within the catchment . 152
    5.5 Discussion . 157
    5.5.1 Mass flux of SsOC 157
    5.5.2 Mass flux of components of SsOC 159
    5.5.3 Variability in composition of SsOC – PSD 160
    5.5.4 Variability in composition of SsOC – Compound classes 161
    5.5.5 SsOC composition related to processes within the catchment . 162
    5.6 Conclusions 165
    6 General conclusions . 167
    References 172

    The University of Manchester

    Quantifying organic carbon fluxes from upland peat
    March 2012
    Present organic carbon fluxes from an upland peat catchment were quantified through
    measurement of in-situ direct and indirect greenhouse gas fluxes. To predict future
    greenhouse gas (GHG) fluxes, peat from eroded (E) and uneroded (U) site of an upland
    peat catchment was characterized.
    Composition of peat from E and U sites at the Crowden Great Brook catchment, Peak
    District Nation Park, UK that was characterized by Pyrolysis-Gas ChromatographyMass Spectrometry (Py-GC-MS) at 700
    C. Pyrolysis products of the peat were then
    classified using the Vancampenhout classification into 6 compound classes - viz.
    aromatic and polyaromatic (Ar), phenols (Ph), lignin compounds (Lg), soil lipids (Lp),
    polysaccharide compounds (Ps) and N-compounds (N). There was no significant
    difference in the composition between the eroded and uneroded sites within the study
    area or between peats from different depths within each site. Nevertheless, there was a
    significant difference between sites in the proportions of Sphagnum that had contributed
    to the peat. Pyrolysis products of the peat were also classified into pedogenic (Pd) and
    aquagenic (Aq) OC – the mean percentage of Pd in both eroded and uneroded peats was
    43.93 ± 4.30 % with the balance of the OC classified as Aq.
    Greenhouse gas (GHG) fluxes were quantified directly by in-situ continuous
    measurement of GHG was carried out at the E and U sites of the catchment using a
    GasClam: mean in-situ gas concentrations of CH
    4 (1.30 ± 0.04 % v/v (E), 0.59 ± 0.05 %
    v/v (U) and CO
    (8.83 ± 0.22 % v/v (E), 1.77 ± 0.03 % v/v (U)) were observed, with
    both the CH
    4 and CO
    concentrations apparently unrelated to atmospheric pressure and
    temperature changes. Laboratory measurements of ex-situ gas production - for both
    CH4 and CO
    this was higher for U site soils than for E site soils. At the U site,
    maximum production rates of both CH4
    (46.11±1.47 mMol t
    ) and CO
    2 (45.56 ±
    10.19 mMol t
    ) were observed for 0-50 cm depth in soils. Increased temperature
    did not affect gas production, whilst increased oxygen increased gas production. The
    ratios observed in-situ are not similar to those observed in the ex-situ
    laboratory experiments; suggest that some caution is advised in interpreting the latter.
    However, the maximum OC loss of 2.3 wt. % observed after 20 weeks of ex-situ
    incubation is nevertheless consistent with the long-term degradation noted by Bellamy
    et al (1985) from organic-rich UK soils.
    Indirect greenhouse gas (GHG) fluxes were quantified through the mass flux of
    suspended organic carbon (SsOC) drained from studied catchments. The SsOC was
    quantified by interpolating and rating methods. Unfiltered (UF) organic carbon (OC)
    fluxes in 2010 were calculated to be 8.86 t/km
    /yr for the eroded sub-catchment and
    6.74 t/km
    /yr for the uneroded sub-catchment. All the rating relationships have a large
    amount of scatter. Both UF OC and <0.2 µm fraction OC are positively correlated with
    discharge at the eroded site, whilst there is no discernable relationship with discharge at
    the uneroded site. SsOC is dominated by Pd type OC (95.23 ± 10.20 % from E; 92.84 ±
    5.38 % from U) far more so than in sources of the peats, suggesting slower oxidation of
    Pd (cf. Aq) OC.

    Chapter 1
    General introduction
    1.1 Introduction and justification for research
    The greenhouse effect is the process by which the presence of certain gases in the
    atmosphere traps long-wave radiation emitted from the Earth’s surface thereby making
    the Earth warm enough to support life. The gases responsible are known as greenhouse
    gases (GHGs): they include carbon dioxide (CO
    2) and methane (CH
    ). Along with other
    GHGs, they cause global mean temperature to be 15
    C rather than a modelled -18
    that it would be in the absence of an atmosphere (Mitchell, 1989). In recent decades,
    the concentration of greenhouse gases in the atmosphere has rapidly increased (IPCC,
    2007), thereby trapping increased amounts of radiation and probably causing changes in
    global climate (Schneider, 1989).
    The major GHGs contain carbon (C), CO2
    is the most important because it has a
    relatively high concentration of 388 ppm (Nolta, 2011). However, although at much
    lower concentration, CH
    4 has a GHG potential 22 times that of CO
    , and is therefore a
    significant contributor to greenhouse warming. Concentrations of both CO
    2 and CH
    are increasing yearly at approx. 1.5 ppm yr
    and 7.0 ppb yr
    respectively (IPCC, 2001).
    The concentrations of both these gases are controlled by the global carbon (C) cycle.
    Atmospheric concentrations (e.g. of CO2
    ) are controlled by cycling between
    atmosphere, ocean and earth materials; both the solid geology and its uppermost
    covering, the soil (Figure 1.1). Soils contain carbon, and are by far the largest

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