quantifying organic carbon fluxes from upland peat

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 General introduction………………………………………………………… 18 1.1 Introduction and justification for research…………………………… 18 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 2.2.10.3 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 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 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 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 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 General conclusions………………………………………………………… 167 References……………………………………………………………………… 172 Final word count 34,788 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 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 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 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, 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 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 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