Tài liệu Quantifying organic carbon fluxes from upland peat

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Quantifying organic carbon fluxes from upland peat A thesis submitted to the University of Manchester for the degree of PhD in the Faculty of Engineering and Physical Sciences 2012 Do Duy Phai School of Earth, Atmospheric and Environmental Sciences List of contents Page 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 2.2.4.1 Determination of discharge………………………………………… 35 2.2.4.2 Continuous gas measurement……………………………………… 36 2.2.5 Ex-situ monitoring…………………………………………………… 37 2.2.5.1 Anaerobic incubation………………………………………………. 37 2.2.5.2 Aerobic incubation…………………………………………………. 38 2.2.5.3 Measurement of concentration and calculation of gas production… 38 2.2.5.4 Aerobic incubation of peat slurry and calculation of gas production 40 2.2.6 Separation of particle size distribution (PSD)……………………….. 42 2.2.6.1 Choosing technique………………………………………………... 42 2.2.6.2 Procedure of cleaning TFU………………………………………… 44 2.2.6.3 Preparing TFU standard solution…………………………………... 44 2.2.6.4 Testing separation ratio of TFU……………………………………. 45 2.2.7 Sample analysis……………………………………………………… 45 2.2.8 Total organic carbon…………………………………………………. 46 2.2.8.1 Prepared total carbon and inorganic carbon standards…………….. 47 2.2.8.2 Drift correction…………………………………………………….. 48 2.2.9 Freeze-dried sample…………………………………………………. 50 2.2.10 Characterization of organic matter composition - methodology development for molecular analyses………………………………………. 51 2.2.10.1 Extraction and fractionation of the sediment samples…………… 51 2.2.10.2 Gas chromatography–Mass spectrometry (GC-MS)……………... 53 2 2.2.10.3 Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) procedure adopted………………………………………………………….. 55 2.2.10.4 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 4.3.1.1 Peat sampling to quantify ex-situ gas production………………….. 93 4.3.1.2 Aerobic incubation…………………………………………………. 94 4.3.1.3 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 3 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 Final word count 34,788 4 List of Figures Page Figure 1.1 Natural carbon cycle. C reservoir masses are in gigatonnes (Gt) = 109 tonnes of carbon. Figures beside arrow denote flux rates in Gt C yr-1 from Moore et al. (1996)……………………………………….. 19 Figure 1.2 Diagram of direct and indirect greenhouse gas fluxes from an upland peat catchment………………………………………………. 21 Figure 1.3 Scenarios of potential future release GHGs from two types of upland peat: Vegetated (uneroded) and eroded peat………………... 23 Figure 1.4 Illustrative diagram of experimental design for present and future (climate change) scenarios of two peats…………………………….. 24 Figure 1.5 Illustrative diagram of the thesis……………………………………. 26 Figure 2.1 Location of Crowden Great Brook near Manchester, UK for (a) figure reproduced from ©2009 Google - Map data ©2011 Tele Atlas and (b) figure reproduced from Ordnance Survey map data by permission of Ordnance Survey, © Crown copyright………………. 27 Figure 2.2 The vegetated (uneroded) peat sub-catchment. A. photo viewed to the west of the monitoring equipment, labeled 30 in Figure 2.4. B. Schematic representation of key vegetated peat with gaseous, fluvial fluxes and high water table………………………………….. 28 Figure 2.3 The unvegetated (eroded) peat sub-catchment. A. photo viewed to the north of the monitoring equipment, labeled 50 in Figure 2.4. B. Schematic representation of key eroded peat with gaseous, fluvial fluxes and low water table………………………………………….. 28 Figure 2.4 Location of sampling points at eroded and vegetated (uneroded) sub-catchments in the Crowden Great Brook catchment. Figure adapted from Todman (2005) and reproduced from Ordnance Survey map data by permission of Ordnance Survey, © Crown copyright. Sub-catchments: the eroded peat site has a greater surface area of bare peat than the sub- catchment at the uneroded peat site which is covered by vegetation. Photos were taken in November 2008……………………………………………………... 29 Figure 2.5 The geology of the study catchment (a) map and (b) cross section with red line representing the position of cross section. Figure reproduced from Ordnance Survey map data by permission of Ordnance Survey, © Crown copyright. Figure adapted from Todman (2005)……………………………………………………… 31 5 Figure 2.6 Peat sampling. (a) Chambered-type auger and incubation bottle with an airtight lid and two valves and (b) order of peat core samples were taken on 14 and 15 December 2009 from eroded and uneroded sites at the Crowden catchment. Numbers beside on the right of bottles are different depths of peat. Numbers on the bottles are order of samples………………………………………………… 33 Figure 2.7 Diagrammatic collecting water column and sediment samples in river water of upland peat catchment for (a) bottle with a volume of 5 L was used to take water column sample and (b) glass plates were setup to collect sediment……………………………………………. 34 Figure 2.8 Illustration of a dilution gauging curve…………………………… 35 Figure 2.9 Peat borehole. Each peat borehole has a plastic pipe, an airtight lid, switches and drill holes and a GasClam to measure CO2, CH4, O2 concentrations, temperature and atmospheric pressure every hour… 37 Figure 2.10 Measuring gas production system: (a) the GasClam (Salamander Ltd, UK), (b) operation diagram of the GasClam, (c) the GasClam was linked with a computer by a cable and controlled by a GasClam software version 2.5.6 and (d) two lines of plastic tubing were connected between the GasClam, the valves of the bottle and the hose from the nitrogen gas station………………………………….. 40 Figure 2.11 Aerobic slurry peat in OxiTop®-C bottles at 15 oC……………….. 42 Figure 2.12 Diagram separation process of particle size distribution in stream water using filter glass membrane (1.6 µm) and Tangential flow ultrafiltration (TFU) membrane plates (0.2 µm, 50 kDa and 10 kDa)…………………………………………………………………. 43 Figure 2.13 Sample analysis process for (a) peat, (b) water and (c) sediment samples of Crowden Great Brook catchment………………………. 46 Figure 2.14 Shimadzu 5050A TOC analyzer for (a) TOC analyzer and (b) automatic sampler…………………………………………………... 47 Figure 2.15 Edwards freeze-dryer. 51 Figure 2.16 Flow chart analysis of glass plate sample; TLE: total lipid extraction; Py: pyrolysis; PLFA: phospho lipid fatty acid; BSTFA: bis(-trimethylsilyl)trifluroacetamide………………………………... 53 Figure 2.17 Partial chromatogram of the total ion current of Gas chromatography–Mass spectrometry (GC-MS) chromatograms of a sediment sample: acid fraction; neutral polar fraction and neutral apolar fraction downstream of an eroded sub-catchment, the sample was taken in November 2008; ?: unknown compound……………... 54 6 Figure 2.18 Pyrolysis-Gas Chromatography-Mass Spectrometry analysis system (Py-GC-MS): (a) Pyrolyzer, (b) Gas chromatography and (c) Mass spectrometry………………………………………………. 56 Figure 2.19 Partial total ion current chromatograms of pyrolysis (700 oC): (a) normal and (b) TMAH pyrolysis of the sediment sample downstream of an eroded sub-catchment. The sample was taken in November 2008……………………………………………………... 57 Figure 3.1 Py-GC-MS products at different temperatures (300 oC, 500 oC and 700 oC) of a peat core sample in depth 0-50 cm at the eroded site…. 66 Figure 3.2 Pyrolysis - Gas chromatography - Mass spectrometry products at 700 oC of a peat sample in depth 0-50cm at the eroded site, using different amount of the samples such as 0.1 mg, 0.5 mg, 1 mg and 1.5 mg……………………………………………………………….. 67 Figure 3.3 Partial chromatogram of the total ion current of the peat core samples at 0-50 cm in depth at the (a) eroded and (b) uneroded sites. Peak symbols correspond to compounds listed in Table 3.2. 68 Figure 3.4 Percentages of six organic compound groups as defined by Vancampenhout et al. (2009) in peat at the eroded and uneroded sites. Data presented as mean of percentage of total compounds (%) and standard error (SE), n=3………………………………………... 74 Figure 3.5 Chromatograms of the total ion current of the Pd and Aq materials. Peaks correspond to compounds listed in Table 3.2……………….. 75 Figure 3.6 Percentages of six organic compound groups as defined by Vancampenhout et al. (2009) in Humic acid (Pd standard material), and dextran and alginic acid (Aq standard materials), (mean (%) ± standard error (SE) of replication analyses (n=3))………………….. 76 Figure 3.7 Classification of organic compounds in the peat into Pd and Aq…... 76 Figure 3.8 Ratio of Sphagnum contribution to the peat. I% = [I] / [I+G+S] I: 4-Isopropenylphenol); G: Guaiacol (2-Methoxy phenol); S: Syringol (2,6-dimethoxyphenol)…………………………………..... 77 Figure 4.1 Problems of in-situ and ex-situ GHG measurement. A. Environmental variable affecting subsurface GHG concentration and therefore GHG fluxes. B. Environmental variables controlled in ex-situ monitoring………………………………………………... 87 Figure 4.2 Equilibration of CH4 and CO2 gas concentrations. A. Chamber equilibrates with subsurface. B. Borehole equilibrates with the section of subsurface to which it is open…………………………… 90 7 Figure 4.3 Fresh peat core samples inside the glass bottles, taken on 14 and 15 December 2009 at the eroded and uneroded sites, kept on a shelf and incubated in a cold room at 10 oC……………………………… 94 Figure 4.4 Separation of incubation bottles after 309 days…………………….. 95 Figure 4.5 Optimal amount of fresh peat for peat slurry experiment…………... 96 Figure 4.6 Peat boreholes with different depths. Each peat borehole has a plastic pipe, an airtight lid, switches and scratches and a GasClam... 98 Figure 4.7 Cumulative CH4 and CO2 production of peat soil in anaerobic incubation at 10 oC. Data presented as mean of amount (mole tonne-1) and standard errors (SE), n=3……………………………… 99 Figure 4.8 Cumulative CH4 and CO2 production of solid peat and slurry peat in aerobic and anaerobic conditions at 15 oC. Incubated time of solid aerobic and anaerobic was 333 days. Incubated time of slurry aerobic was 142 days. Data presented amount (mole tonne-1)……... 101 Figure 4.9 Eroded site in-situ continuous measurement CH4, CO2 and O2 concentrations, atmospheric pressure and soil temperature within three boreholes in the three depths in the year 2009 at the Crowden Great Brook catchment……………………………………………... 106 Figure 4.10 Uneroded site in-situ continuous measurement CH4, CO2 and O2 concentrations, atmospheric pressure and soil temperature within two boreholes in the two depths in the year 2011 at the Crowden Great Brook catchment. R2 is the coefficient of determination to show the degree of variability of CH4 and CO2 concentrations (%) due to impact of the atmosphere (mBar) on 25th January and 14th March 2011......................................................................................... 107 Figure 4.11 Relationship between gas production and environmental factors… 112 Figure 4.12 Relationship between gas production and water table. Data points were recorded every hour of continuous measurement from 05th 13th October 2009 at the eroded site………………………………… 113 Figure 4.13 Changes in peat composition in in-situ and ex-situ conditions. Fresh peat samples (t0) and incubated peat samples t309 and t142 (after 309 and 142 incubated days)…………………………………. 115 Figure 4.14 Py-GC-MS total ion current chromatogram of the peat core samples at 0-50 cm in depth at the (a) eroded and (b) uneroded sites. Red colour refers to fresh peat samples (t0) and blue colour is incubated peat core samples (t1) after 309 incubated days in anaerobic 10 oC. Peak symbols correspond to compounds listed in Table 3.2……………………………………………………………. 116 8 Figure 4.15 Percentages of six organic compound classes as defined by Vancampenhout et al. (2009) in fresh peat (t0) and incubated peat (t1) after 309 incubated days in anaerobic 10 oC at the eroded and uneroded sites……………………………………………………….. 117 Figure 4.16 Comparison of classification of organic compounds in the fresh peat (t0) and incubated peat (t1) after 309 incubated days in anaerobic 10 oC at the eroded and uneroded sites into Pd and Aq…. 117 Figure 5.1 Daily SsOC autosampler……………………………………………. 131 Figure 5.2 Typical examples of glass plates with and without material collected for (a) blank glass plate, (b) glass plates in eroded site and (c) glass plates in uneroded site. These plates had been in the stream for (b) and (c) 110 days. They were collected on 14 December 2009…………………………………………………………………. 132 Figure 5.3 Separation of sediment material on glass plate for (a) scraping off sediment on the top and bottom faces, (b) removing sediment from all faces ultrasonically………………………………………………. 133 Figure 5.4 (a) Diagram separation process of particle size distribution in stream water using filter glass membrane (1.6 µm) and tangential flow ultrafiltration (TFU) membrane plates (0.2 µm, 50 kDa and 10 kDa) and (b) Vivaflow 50 system (Viva Science, UK), master-flex pump-head (Sartorius, Germany) and TFU membrane plates……… 135 Figure 5.5 Discharge-Q (l/s) and OC UF (mg/l) concentration at the outlet of eroded and uneroded subcatchments in 2010………………………. 138 Figure 5.6 Relationship between organic carbon unfiltered (OC UF), organic carbon <0.2 µm (OC<0.2 µm) and discharge at the outlet of eroded and uneroded sub-catchments………………………………………. 139 Figure 5.7. Mass flux of SsOC, total and partitioned by PSD and compound class (Interpolation of total OC from daily samples + partitioning by average composition)……………………………………………. 142 Figure 5.8 PSD of OC under different discharges (Q) at the eroded site. The discharge (l/s) and the organic carbon (OC) concentration (mg/l) appear beneath each column. Discharge increases approximately linearly along the x-axis. The thumbnail graphs show relative Q five days prior to sampling, also OC (mg/l)……………………….... 144 Figure 5.9 PSD of OC under different discharges (Q) at the uneroded site. The discharge (l/s) and the organic carbon concentration (mg/l) appear beneath each column. Discharge increases approximately linearly along the x-axis. The thumbnail graphs show relative Q five days prior to sampling, also OC (mg/l)………………………… 145 9 Figure 5.10 PSD of OC under different seasons at the eroded and uneroded site. The discharge (l/s) and the total carbon concentration (mg/l) appear beneath each column………………………………………... 146 Figure 5.11 Relative composition of SsOC to in-situ peat at the eroded site….. 148 Figure 5.12 Relative composition of SsOC to in-situ peat at the uneroded site.. 149 Figure 5.13 Relative Pd and Aq compositions of SsOC to in-situ peat at the eroded site…………………………………………………………... 150 Figure 5.14 Relative Pd and Aq compositions of SsOC to in-situ peat at the uneroded site………………………………………………………... 151 Figure 5.15 Mass of OC in different days in-situ on top and bottom faces of glass plates at the (E) eroded and (U) uneroded sites………………. 154 Figure 5.16 Composition of OC in sediment on (T) top and (B) bottom faces of glass plates at the (E) eroded and (U) uneroded sites. The T and B faces and days in-situ appear beneath each column……………… 154 Figure 5.17 Average percentage of total organic compounds in peat, suspended and deposited sediment. Ar-aromatics and polyaromatics, Ph-phenols, Lg-lignin compounds, Lp-soil lipids, Ps-polysaccharide compounds and N-compounds………………….. 155 Figure 5.18 Average percentage of total Pd and Aq compositions in peat, suspended and deposited sediment…………………………………. 156 Figure 5.19 Illustrative diagram of hysteresis. A. clockwise hysteresis and B. anti-clockwise hysteresis……………………………………………. 162 10 List of Tables Page Table 2.1 Sub-catchments, area and elevation for each sampling point containing continuous monitoring equipment. Average data of water table height were measured at the eroded site from 29 September to 13 October 2009……………………………………… 28 Table 2.2 Typical TOC sample sequence for automatic sampling ASI 5000A... 49 Table 3.1 Water content (% weight of dry peat) of the peat core layers, data present the mean ± standard error (SE) of three replication samples. 65 Table 3.2 List of Py-GC-MS compounds found in the fresh and incubated peat core samples, containing average retention time (RT), molecular weight (MW), major ion and molecular formula (MF). Peak signs correspond to those of Figure 3.3…………………………………... 69 Table 4.1 Effects of depth and site (eroded and uneroded) on rates of CH4 and CO2 at 10 0C using analysis of variance (ANOVA): Two-Factor with replication (P<0.05)…………………………………………… 100 Table 4.2 Gas production rates (mMol t-1 d-1) from peat incubated for 309 days (A) and subsequent to changed conditions 333 days (B); 60 days and 142 days (C). Data presented as mean of rates of triplicate samples ± SE (standard errors), n=3………………………………... 103 Table 4.3 Average concentration of gas (% v/v) of in-situ continuous measurement at the eroded and uneroded sites at Crowden Great Brook………………………………………………………………... 110 Table 4.4 Effects of seasons on in-situ concentration (% v/v) of CH4 and CO2 using analysis of variance (ANOVA): Single factor (P<0.05)……... 111 Table 4.5 Ratios of in-situ and ex-situ gas production from eroded and uneroded peat at the Crowden Great Brook catchment…………….. 114 Table 4.6 Gas production rates of CH4 and CO2 of peat in anaerobic condition. 118 Table 5.1 OC UF and OC <0.2 µm fluxes in different periods at the outlet of eroded and uneroded sub-catchments in Crowden Great Brook catchment…………………………………………………………… 137 Table 5.2 Mass fluxes of SsOC of different size fractions and compound classes in 2010 at the outlet of eroded and uneroded subcatchments. Ar-aromatics and polyaromatics, Ph-phenols, Lglignin, Lp-lipid, Ps-polysaccharide compounds and N-compounds. Pd-pedogenic, Aq-Aquagenic………………………………………. 141 11 Table 5.3 Average PSD (% SsOC). The data presented as mean of percentage and relative standard deviation (RSD), n=9………………………… 143 Table 5.4 Average compound class composition (% SsOC). The data presented as mean of percentage and relative standard deviation (RSD), n=9………………………………………………………….. 147 Table 5.5 Ranges of OC fluxes in the literature, along with notes on the catchments studied and the source of data………………………….. 158 12 Abstract The University of Manchester Do Duy Phai PhD Quantifying organic carbon fluxes from upland peat 21st 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 oC. 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 CH4 (1.30 ± 0.04 % v/v (E), 0.59 ± 0.05 % v/v (U) and CO2 (8.83 ± 0.22 % v/v (E), 1.77 ± 0.03 % v/v (U)) were observed, with both the CH4 and CO2 concentrations apparently unrelated to atmospheric pressure and temperature changes. Laboratory measurements of ex-situ gas production - for both CH4 and CO2 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-1 day-1) and CO2 (45.56 ± 10.19 mMol t-1 day-1) were observed for 0-50 cm depth in soils. Increased temperature did not affect gas production, whilst increased oxygen increased gas production. The CH4/CO2 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/km2/yr for the eroded sub-catchment and 6.74 t/km2/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. 13 Declaration I declare that no portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning. 14 Copyright Statement The following four notes on copyright and the ownership of intellectual property rights must be included as written below: i. The author of this thesis (including any appendices and/or schedules to this thesis) owns certain copyright or related rights in it (the “Copyright”) and s/he has given The University of Manchester certain rights to use such Copyright, including for administrative purposes. ii. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has from time to time. This page must form part of any such copies made. iii. The ownership of certain Copyright, patents, designs, trade marks and other intellectual property (the “Intellectual Property”) and any reproductions of copyright works in the thesis, for example graphs and tables (“Reproductions”), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and commercialisation of this thesis, the Copyright and any Intellectual Property and/or Reproductions described in it may take place is available in the University IP Policy (see http://documents.manchester.ac.uk/DocuInfo.aspx?DocID=487), in any relevant Thesis restriction declarations deposited in the University Library, The University, Library’s regulations (see http://www.manchester.ac.uk/library/aboutus/regulations) and in The University’s policy on Presentation of Theses. 15 Acknowledgments The author would like to thank very deeply all supervisors Drs. Clare H. Robinson, Bart E. van Dongen, Stephen Boult and Prof. Dave Polya for their kind and helpful advice throughout the study period and during preparation of this thesis. Thanks also go to Drs. Peter Morris, John Gaffney and Alison Jackson for their help with field and laboratory work. Thanks are also due to Paul Lythgoe, Alastair Bewsher and Cath Davies, in the Manchester Analytical Geochemistry Unit of the School of Earth, Atmospheric and Environmental Sciences for their practical help and advice in the laboratory. My thanks also to the staff of the John Rylands library for their kind help. I thank my parents, brothers, sister, my wife and kids for their morale support and encouragement in my study. I thank as well my colleagues and official staff of the Soils and Fertilizers Research Institute (SFRI) - Vietnam Academy of Agricultural Sciences (VAAS) and Vietnam International Education Development (VIED) - Ministry of Education and Training (MOET) who regularly kept in touch with me during this PhD programme. Finally my thanks to the Vietnamese government - “Key programme of development and application of biotechnology to agricultural field and rural development up to 2020” of the Ministry of Agriculture and Rural Development (MARD) through the coordinator organization Vietnam International Education Development (VIED) Ministry of Education and Training (MOET) and The University of Manchester Overseas Research Scholarship (ORS) for their financial support for this PhD programme and during writing the thesis. Thank you. 16 Abbreviations Aq Ar C CSD DIW DOC DO E EC EPS GC-MS GHG HA IPCC Lg Lp N OM OC PSD Py-GC-MS Pd Pd:Aq Ph Ps Q RSE SsOC SE TFU TOC U v/v Aquagenic Aromatics and polyaromatics Carbon Chemical Data Systems Deionised water Dissolved organic carbon Dissolved oxygen Eroded Electrical conductivity Extracellular polymeric substances Gas Chromatography-Mass Spectrometry Greenhouse gas Humic acid Intergovernmental Panel on Climate Change Lignin compounds Lipids N-compounds Organic matter Organic carbon Particle Size Distribution Pyrolysis-Gas Chromatography-Mass Spectrometry Pedogenic Pedogenic to aquagenic ratio Phenols Polysaccharide compounds Discharge Relative standard error Suspended organic carbon Standard error Tangential flow ultrafiltration Total organic carbon Uneroded Volume per volume 17 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 (CO2) and methane (CH4). Along with other GHGs, they cause global mean temperature to be 15 oC rather than a modelled -18 oC 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, CH4 has a GHG potential 22 times that of CO2, and is therefore a significant contributor to greenhouse warming. Concentrations of both CO2 and CH4 are increasing yearly at approx. 1.5 ppm yr-1 and 7.0 ppb yr-1 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 18 terrestrial carbon reservoir (Gorham, 1991) and therefore an important component of the C cycle (Figure 1.1). 9 Figure 1.1 Natural carbon cycle. C reservoir masses are in gigatonnes (Gt) = 10 tonnes of -1 carbon. Figures beside arrow denote flux rates in Gt C yr from Moore et al. (1996). The natural cycling of C can be disrupted by anthropogenic activities. Burning fossil fuel is the most well known: global CO2 emissions from burning fossil fuels from 1950 to 1991 were 4550 million tonnes of C (Wigley & Schimel, 2000). However, changes in soil because of changes in land management may be equally or more important. During the period from 1850 to 2000, globally, carbon flux from changes in land use and management released an estimated 156 Pg of C into the atmosphere (Houghton, 2003). Changes in rice paddies from drying to flooding in the process of cultivation leads to anaerobic soils and the release of CH4 (Neue et al., 1996). In addition, there are changes in drainage of soils which lower the water table extending aerobic conditions downward and increasing oxidation of C releasing CO2 (Evans et al., 1999) . 19 Such changes in soil will have most impact when soils with high carbon content are affected. Soils with very high C content are known as histosols and, of these, peats have the highest C content (>50%) (Baldock & Nelson, 1999; Brady, 1990). Peats cover 4 x 106 km2 of the global ice-free land area (Gorham, 1991; Wilding, 1999), and they cover 3.46 x 106 km2 in the arctic/tundra (Vitt, 2006) and 0.36 x 106 km2 in tropics (Andriesse, 1988). Many of these peats are fairly inaccessible, which has limited confidence in estimating their GHG emissions. Besides the inaccessibility, peats in upland areas are also subject to hydrometeorology characterised by low frequency, high intensity events, such as storms, which are likely to make representative measurement of GHG emissions even more difficult, because of lacking equipment. GHG fluxes from peat are likely to be a significant contributor to atmospheric concentrations, and these fluxes are not well quantified in upland environments. The aim of this research is to quantify present and to attempt to predict under a possible climate change scenario, using an increase of 5 oC in temperature and a fall in water table, GHG fluxes from upland peat in the United Kingdom. Quantification of present GHG fluxes being both an important aim in itself but also necessary in order to predict future changes associated with land management changes. Present and future GHG fluxes from upland peat are both direct; those to atmosphere from in-situ intact primary peat, and indirect; those from transported and dispersed peat (Figure 1.2). The present direct flux of GHG can be quantified by making measurements in in-situ peat, while prediction of GHG fluxes requires ex-situ peat to be manipulated experimentally to model changing environmental factors. However, prediction of future fluxes is also possible from in-situ peat because spatial variability in natural peat allows field-scale experiments; eroded peat is a field-scale model of the future as climatic warming is expected to dry peat and make it more liable to erosion 20
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