Peat Column Research Articles

Reconstruction of the evolution of the lake-mire complex in the subarctic part of the Pur-Taz interfluve by spore-pollen analysis of the peat column

Reconstruction of the evolution of the lake-mire complex in the subarctic part of the Pur-Taz interfluve by spore-pollen analysis of the peat column

Application of Unsupervised Learning for the Evaluation of Burial Behavior of Geomaterials in Peatlands: Case of Lignin Moieties Yielded by Alkaline Oxidative Cleavage

Tropical Peatlands accumulate organic matter (OM) and a significant source of carbon dioxide (CO2) and methane (CH4) under anoxic conditions. However, it is still ambiguous where in the peat profile these OM and gases are produced. The composition of organic macromolecules that are present in peatland ecosystems are mainly lignin and polysaccharides. As greater concentrations of lignin are found to be strongly related to the high CO2 and CH4 concentrations under anoxic conditions in the surface peat, the need to study the degradation of lignin under anoxic and oxic conditions has emerged. In this study, we found that the "Wet Chemical Degradation" approach is the most preferable and qualified to evaluate the lignin degradation in soils accurately. Then, we applied PCA for the molecular fingerprint consisting of 11 major phenolic sub-units produced by alkaline oxidation using cupric oxide (II) along with alkaline hydrolysis of the lignin sample presented in the investigated peat column called "Sagnes". The development of various characteristic indicators for lignin degradation state on the basis of the relative distribution of lignin phenols was measured by chromatography after CuO-NaOH oxidation. In order to achieve this aim, the so-called Principal Component Analysis (PCA) has been applied for the molecular fingerprint composed of the phenolic sub-units, yielded by CuO-NaOH oxidation. This approach aims to seek the efficiency of the already available proxies and potentially create new ones for the investigation of lignin burial along a peatland. Lignin phenol vegetation index (LPVI) is used for comparison. LPVI showed a higher correlation with PC1 rather than PC2. This confirms the potential of the application of LPVI to decipher vegetation change, even in a dynamic system as the peatland. The population is composed of the depth peat samples, and the variables are the proxies and relative contributions of the 11 yielded phenolic sub-units.

Multiphase flow behavior of diesel in bog, fen, and swamp peats

Hydrocarbon fate and transport in various categories of peatlands is complicated by the botanical origin, and thus variations in the hydraulic structures and surface chemistry of its peat soils. There has been no systematic evaluation of the role of different peat types on hydrocarbon migration. Thus, two-phase, and three-phase flow experiments were performed for living and partially decomposed peat cores from bog, fen, and swamp peatlands. Numerical simulations of water drainage were performed using HYDRUS-1D, diesel-water and diesel-water-air flow using MATLAB Reservoir Simulation Toolbox (MRST). Five water table (WT) fluctuations were imposed to explore its potential to reduce residual diesel saturation in peat columns. Our results demonstrate a good match of the relative water permeability (krw) – saturation (S) relations estimated using the unsaturated hydraulic conductivity-S relation derived from HYDRUS-1D modeling of two-phase flow, and krw – S from MRST for three-phase flow, for all tested peat columns. Thus, we recommended using two-phase system based krw – S predictions if multiphase data are unavailable for peatland sites' spill management plans. We found the discharge of water and diesel both increase with increasing hydraulic conductivity, while residual water and diesel were within the range of 0.42–0.52 and of 0.04–0.11, respectively. High diesel discharge rates suggest that quick spill-response is required to manage its spread in peatlands. Up to 29% of residual diesel saturation was yielded by the five WT fluctuations, and thus we strongly recommend WT manipulation as a first step towards diesel decontamination progression in peatlands.

Implementation and initial calibration of carbon-13 soil organic matter decomposition in the Yasso model

Abstract. Soils account for the largest share of carbon found in terrestrial ecosystems, and their status is of considerable interest for the global carbon cycle budget and atmospheric carbon concentration. The decomposition of soil organic matter depends on environmental conditions and human activities, which raises the question of how permanent are these carbon storages under changing climate. One way to get insight into carbon decomposition processes is to analyse different carbon isotope concentrations in soil organic matter. In this paper we introduce a carbon-13-isotope-specific soil organic matter decomposition add-on into the Yasso soil carbon model and assess its functionality. The new 13C-dedicated decomposition is straightforward to implement and depends linearly on the default Yasso model parameters and the relative carbon isotope (13C/12C) concentration. The model modifications are based on the assumption that the heavier 13C atoms are not as reactive as 12C. The new formulations were calibrated using fractionated C, 13C and δ13 measurements from litterbags containing pine needles and woody material, which were left to decompose in natural environment for 4 years. The introduced model modifications considerably improve the model behaviour in a 100-year-long simulation, where modelled δ13 is compared against fractionated peat column carbon content. The work presented here is a proof of concept and enables 13C to be used as a natural tracer to detect changes in the underlying soil organic matter decomposition.

The effects of glucose addition and water table manipulation on peat quality of drained peatland forests with different management practices

AbstractPeatlands are globally significant C storage because waterlogged conditions slow down organic matter (OM) decomposition. Changes in the water table (WT) because of global warming or drainage, consecutive vegetation succession, and enhanced root exudation causing priming may transform peatlands from C sinks to sources. We studied how glucose addition, WT, and forest harvesting affect the chemical composition of peat and decomposition rate by incubating peat columns collected from drained clear‐cut (CC) and forested (FD) peatlands. Columns were divided into high or low WT, and half were labeled with 13C to study the priming effect on peat decomposition and peat chemical quality. We measured CO2 fluxes, peat OM, and water quality. There was no detectable priming effect after glucose addition. Lowering of the WT led to increased CO2 efflux, which during the measurements averaged between 39 and 291 μg m–2 s–1. Low WT also decreased the proportion of water‐soluble OM in CC areas but not in FD areas. The proportion of recalcitrant OM in surface peat was higher in forest than in clear cut. Forest management also affected the quality of dissolved OM in soil water, with CC showing higher concentrations of recalcitrant compounds. Decomposition and OM quality were governed by forest management practices and WT manipulation. In the future, the C sink capacity of forested peatlands will be regulated by changes in WT level, forest management, and quality of OM.

Mineral inputs, paleoecological change, and Holocene carbon accumulation at a boreal peatland in the Hudson Bay Lowlands, Canada

The Hudson Bay Lowlands (HBL) is a vast contiguous peatland extending over >370,000 km2 in Canada's boreal-subarctic, and is the traditional land of the Omushkego Cree. It is currently undergoing climatic warming alongside other anthropogenic stressors, and contains a large below-ground carbon pool. Understanding how climate variability and multiple stressors impact peat accumulation in this region is critical to discerning how northern peatlands will respond to future climate and land-use changes. Pollen- and macrofossil-based paleoecological reconstructions, and analyses of aluminum (Al) and titanium (Ti) fluxes in a Holocene-aged peat core (VM375) taken from a bog in the Attawapiskat watershed were conducted to link ecosystem changes with hydroclimate and long-term carbon storage. Peat initiation is dated to 5780 cal yr B.P., coincident with land emergence driven by glacial isostatic adjustment. From 4500 to 4200 cal yr B.P., apparent rate of carbon accumulation increased, and was linked to more rapid rates of peat accretion and increases in minerotrophic indicators in the pollen record. This increase in peat accretion and shift in vegetation composition co-occur with higher rates of mineral influx as shown by Ti and Al concentrations, which may have supplied nutrients. A fen to bog transition takes place ~3300 cal yr B.P., with increases in Sphagnum spores and macrofossils, and a decline in the apparent rate of carbon accumulation relative to the earlier half of the record, where paleoecological proxies indicate treed wetland and fen stages. Since peat inception, the total carbon stock of the 260-cm peat column is 110 kg C m−2. This multi-proxy record shows an association between changing peat types and variability in apparent rates of carbon accumulation, and supports the hypothesis that mineral nutrients either supplied by surface hydrology or by eolian deposition played a role in Holocene peat carbon accumulation in eastern North American boreal peatlands.

Impact of Forest Harvesting Intensity and Water Table on Biodegradability of Dissolved Organic Carbon in Boreal Peat in an Incubation Experiment

Boreal peatlands are vast carbon (C) stores but also major sources of dissolved organic C (DOC) and nutrients to surface waters. Drainage and forest harvesting accelerates DOC leaching. Continuous cover forestry (CCF) is considered to cause fewer adverse environmental effects. Yet, the effects of CCF on DOC processes are unrecognised. We study DOC production and quality in unharvested, CCF, and clear-cut drained peatland forests and in a non-forested alluvial sedge fen. Parallel replicate peat columns with ground vegetation are collected from the uppermost 50 cm at each site, and the water table (WT) is set to −20 or −40 cm depths on the columns. During the eight-month ex situ incubation experiment, the soil water samples are extracted monthly or bi-monthly. The samples are incubated at 15 °C for multiple 72 h incubation cycles to study pore water quality and biodegradation of DOC. The CO2 production occurs during the first three days. The DOC concentrations and the CO2 release per volume of water are significantly lower in the sedge fen than in the drained peatland forests. The WT has a negligible effect on DOC concentrations and no effect on DOC quality, but the higher WT has generally higher CO2 production per DOC than the lower WT. The results suggest that peat in the drained peatlands is not vulnerable to changes per se but that forest management alters biotic and abiotic factors that control the production, transport, and biodegradation of DOC.

Saturated hydraulic conductivity of boreal peat and its relationships with peat properties and sampling depth

AbstractThe boreal region is a significant peat‐forming area. With peat, there lie other natural resources, including mineral ores and fossil fuels needed by our economy. However, mining for mineral resources or any other activity that leads to large‐scale groundwater extraction in the near vicinity or underneath the mires can alter the water levels in the overlaying ecosystems and thus have a damaging effect on them, raising concerns about the mires' preservation. Peat itself may isolate surface vegetation from drainage caused by nearby mining when its hydraulic conductivity is sufficiently low. More is known about the hydraulic properties of the uppermost layers of the peat column, but there is very little data about deeper, generally more decomposed peat layers that may potentially act as drainage barriers. Carrying out in situ hydraulic conductivity tests in less conductive peat can be laborious and time‐consuming, and not always practical. This research aims to study and verify statistical relationships between easy‐to‐measure peat properties and hydraulic conductivity over the entire peat column, covering the knowledge deficit that is important in the context of indirect drainage effects related to mining or any other large‐scale groundwater extraction. For that, we sampled peat and conducted in situ saturated hydraulic conductivity tests in several mires in northeast Estonia to gather information about the hydraulic properties of boreal peat. Collected data were fitted with linear mixed‐effects models to link hydraulic conductivity with the degree of decomposition, dry bulk density, depth of measurement, and peatland growth phase. The results indicate that these parameters are strongly correlated with saturated hydraulic conductivity and can serve as predictors of this parameter. Constructed statistical models exhibit relatively high explanatory power and show potential usage for characterizing the hydraulic conductivity of peat. The findings of this study may be helpful in the efforts of mire conservation.

Identification of the dynamics of carbon accumulation in the Verkh-Invenskoe peatland by the method of Loss on Ignition

Abstract. The Perm Kama region is characterized by numerous promising paleoar chives, and the paleoecological knowledge of the region is uneven. Identification of the dynamics of organic carbon accumulation in peat is included in the complex of studies used to reconstruct the state of the natural environment in the past. We have studied peat deposits of the Verkh-Invenskoe bog in the western part of the region. For this, depth measurements, sampling of a peat column, and laboratory analysis of samples throughout the thickness were performed. As a result, indicators were determined: Bulk Density (further BD), Organic Matter Bulk Density (further OMBD), Loss on Ignition (further LOI), Long term average rate of carbon accumulation (LORCA). For the first time for the western part of the Perm Kama region, numerical data on the dynamics of carbon accumulation over the last 10.9 thousand years have been obtained.

Deep peat fire persistently smouldering for weeks: a laboratory demonstration

Background Peatlands are becoming more vulnerable to smouldering fires, driven by climate change and human activities. Aims This work explores the persistent burning, propagation, and emission of the deep peat fire. Methods Laboratory experiments are conducted with a 1-m deep peat column, and smouldering fires are initiated at different depths. Key results We found localised burning and multi-directional smouldering fire spread in deep peat layers. The smouldering temperature first decreases with depths up to −40 cm (from around 550 to 350°C) and then remains at about 300°C in the deeper layers. High moisture content can slow down in-depth fire propagation and reduce the burning duration. Conclusions Peat fire can burn in deep layers for weeks, and its combustion is incomplete with small mass loss, because of a limited oxygen supply and low smouldering temperature. Measuring the carbon monoxide concentration near the surface can detect underground fire and monitor its intensity. Implications This work helps reveal the underlying mechanism of the in-depth smouldering wildfires in peatland and supports future larger-scale peat fire experiments in the field.

Is bog water chemistry affected by increasing N and S deposition from oil sands development in Northern Alberta, Canada?

Nitrogen and sulfur emissions from oil sands operations in northern Alberta, Canada have resulted in increasing deposition of N and S to the region’s ecosystems. To assess whether a changing N and S deposition regime affects bog porewater chemistry, we sampled bog porewater at sites at different distances from the oil sands industrial center from 2009 to 2012 (10-cm intervals to a depth of 1 m) and from 2009 to 2019 (top of the bog water table only). We hypothesized that: (1) as atmospheric N and S deposition increases with increasing proximity to the oil sands industrial center, surface porewater concentrations of NH4+, NO3−, DON, and SO42− would increase and (2) with increasing N and S deposition, elevated porewater concentrations of NH4+, NO3−, DON, and SO42− would be manifested increasingly deeper into the peat profile. We found weak evidence that oil sands N and S emissions affect bog porewater NH4+-N, NO3−-N, or DON concentrations. We found mixed evidence that increasing SO42− deposition results in increasing porewater SO42− concentrations. Current SO42− deposition, especially at bogs closest to the oil sands industrial center, likely exceeds the ability of the Sphagnum moss layer to retain S through net primary production, such that atmospherically deposited SO42− infiltrates downward into the peat column. Increasing porewater SO42− availability may stimulate dissimilatory sulfate reduction and/or inhibit CH4 production, potentially affecting carbon cycling and gaseous fluxes in these bogs.

Mercury dynamics in the pore water of peat columns during experimental freezing and thawing

Biogeochemical processes in northern peatland ecosystems are influenced by seasonal temperature fluctuations that are changing with the climate. Methylmercury (MeHg), commonly produced in peatlands, affects downstream waters; therefore, it is important to understand how temperature transitions affect mercury (Hg) dynamics. We investigated how the freeze-thaw cycle influences belowground peat pore water total Hg (THg), MeHg, and dissolved organic carbon (DOC). Four large, intact peat columns were removed from an ombrotrophic peat bog and experimentally frozen and thawed. Pore water was sampled across seven depths in the peat columns during the freeze-thaw cycle and analyzed for THg, MeHg, and DOC concentrations. Freezing results showed increased concentrations of THg below the ice layers and limited change in MeHg concentrations. During thawing, THg concentrations significantly increased, whereas MeHg concentrations decreased. Limited bromide movement and depth decreases in THg and DOC concentrations were associated with increased bulk density and degree of humification in the peat. The experiment demonstrates the effects of the freeze-thaw cycle on Hg concentrations in northern peatlands. Changes to freeze-thaw cycles with climate change may exacerbate Hg cycling and transport processes in peatland environments.

Carbon storage change and \u03b413C transitions of peat columns in a partially forestry-drained boreal bog

Background and aimsIn forestry-drained peatlands, drying leads to changes in C cycling which could affect peat δ13C. Furthermore, the δ13C profile of the entire peat column may reveal effects of earlier climatic periods.MethodsWe measured peat δ13C and C inventories in adjacent peat profiles, two collected from undrained and two from the drained side of a bog that was partially ditch-drained 37 years earlier. The cores were sliced into 10-cm subsamples for analyses; matching of the profiles based on surface levelling, peat stratigraphic correlation and a horizontal ash layer found in both profiles.ResultsSurface subsidence of 30 cm was observed in the dried site and the uppermost 160 cm in the undrained site contained an excess of 5.9 kg m−2 of C compared with the corresponding strata of the ditch-drained site. The δ13C values increased but markedly only in the thin surface layer of the drained site, indicating low δ13C of the missing C (ca. –30‰). In the deeper strata, dating to Mid-Holocene, high dry bulk density, C%, N%, humification index and low C/N ratio were connected to low δ13C of peat.ConclusionsDrainage of 37 years increased δ13C values in the upper peat profile of the drained bog and led to the selective loss of 13C depleted C. Results indicate that C balance studies can be aided by C isotope analyses. Low δ13C values in the peat profile indicate the existence of a wet fen stage during the moist and warm period during Mid-Holocene.

The influence of Carex aquatilis and Juncus balticus on methane dynamics: A comparison with water sourced from a natural and a constructed fen

As fen peatlands have been heavily disturbed by resource extraction in northeastern Alberta, Canada, fen construction has been completed. In order to optimize biogeochemical function of future constructed fens, it is beneficial to understand methane (CH4) cycling of newly constructed fens, and how revegetation strategies influence CH4 dynamics. Here, we investigate the effects of two vascular species used for fen construction on CH4 dynamics. A factorial greenhouse experiment using peat columns and a laboratory incubation experiment were used to understand differences in CH4 production, emissions, pore water concentration, and oxidation between Carex aquatilis Wahlenb. and Juncus balticus Willd. The experiment also considered how water sourced from the constructed fen influenced CH4 dynamics compared to natural rich fen water. Higher pore water CH4 concentration and potential CH4 production were found at C. aquatilis columns, possibly associated with higher labile carbon throughout the column. In columns with J. balticus, evidence to support radial oxygen loss reducing CH4 concentration and production was found. Water sampled from peat columns with constructed fen water had higher Fe (all cation forms), Mn (all cation forms), SO42−, and NO3− compared to columns with rich fen water, which corresponded to lower CH4 emissions and pore water concentration. Results from this study could be used to inform revegetation designs of future constructed fens that consider greenhouse gas emissions, including CH4, as a reclamation goal.

MOISTURE RELEASE OF TROPICAL PEAT SOILS AS DECREASING WATER TABLE

Hydro-physics of peat soils varied with their peat decomposition degree. One of the important hydro-physics is ability of the peat soil to release water as decreasing water table. Potential of water availabilty to crop growth is evidently related to this behaviour. The present study was conducted to understand modes of moisture release of peat soils as decreasing water table. Water tables were simulated using a hanging column method. The water table was arranged at levels of 0, 10, 20, 30, 50, and 100 cm below peat column surfaces. Potential of moisture release or in oppositely potential of moisture retention could be modelled with the 3 parameter equation. Highly decomposed peat characterized by higher bulk density and lower total porosity stored less water but retained more water.

Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw.

Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long-term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2 ) and methane (CH4 ) to the atmosphere, but how much, at which time-span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant-soil systems (mesocosms) allowed us to simulate permafrost thaw under near-natural conditions. We monitored GHG flux dynamics via high-resolution flow-through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10-15cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74±0.49 vs. 0.84±0.60g CO2 -Cm-2 day-1 ; with vegetation: 1.20±0.50 vs. 1.32±0.60g CO2 -Cm-2 day-1 , mean±SD, pre- and post-thaw, respectively). Radiocarbon dating (14 C) of respired CO2 , supported by an independent curve-fitting approach, showed a clear contribution (9%-27%) of old carbon to this enhanced post-thaw CO2 flux. Elevated concentrations of CO2 , CH4 , and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost-carbon feedback by adding to the atmospheric CO2 burden post-thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre- and post-thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales.

Sodium transport and attenuation in soil cover materials for oil sands mine reclamation

Reclamation soil covers are used in oil sands mine closure to support vegetative growth over tailings. Geochemical processes within these covers may impact solute transport during upward migration of oil sands process-affected water (OSPW) from the underlying tailings. In this study, we examined the geochemical processes controlling Na transport and attenuation within the peat and clay-till cover soils at Sandhill Fen in northern Alberta, Canada. We analyzed soil core samples collected along transects of this 54-ha pilot-scale oil sands mine reclamation wetland. The geochemical (Na, Ca, Mg, K, Cl, SO4, HCO3) and isotopic (δ2H, δ18O) compositions of extracted pore water were analyzed statistically to identify OSPW and fresh surface water within the cover. Depth-dependent trends in pore water sodium concentrations were not apparent, suggesting that the soil cover had been fully flushed by a mixture of OSPW and fresh surface water used to flood the fen. Relative concentrations of Na, Ca and Mg were used to define the extent of cation exchange within the clay cover. Complementary laboratory column experiments showed that cation exchange removed up to 50% of dissolved Na as the first pore volume of simulated OSPW passed through the peat and till. However, Na attenuation by these materials declined rapidly and was limited after 4 (peat) to 7 (till) pore volumes of OSPW flushing. Reactive transport modeling confirmed that cation exchange was the dominant control on Na attenuation and corresponding Ca and Mg release within the till and peat columns. Mineral precipitation-dissolution reactions also influenced dissolved Ca and Mg concentrations and, therefore, indirectly impacted Na attenuation. Overall, this study helps constrain the geochemical processes controlling Na transport and attenuation in oil sands reclamation soil covers exposed to OSPW, and indicates that the attenuation of Na from OSPW by these covers is short-lived.

Stable carbon isotopic composition of peat columns, subsoil and vegetation on natural and forestry-drained boreal peatlands

ABSTRACTWe studied natural and forestry-drained peatlands to examine the effect of over 34 years lowered water table on the δ13C values of vegetation, bulk peat and subsoil. In the seven studied sites, δ13C in the basal peat layer was 1.1 and 1.2 ‰ lower than that of the middle-layer and surface layer, respectively. Furthermore, there was a positive correlation between the δ13C values of the basal and surface peat layers, possibly due to carbon (C) recycling within the peat column. In the same mire complex, natural fen peat δ13C values were lower than those of the nearby bog, possibly due to the dominance of vascular plants on fen and the generally larger share of recycled C in the fens than in the bogs. Furthermore, natural and 51 years previously drained fen and bog, on the opposite sides of a ditch on the same mire complex, showed no significant differences in δ13C values. Plant δ13C values were lower, while δ13C values of subsoil were higher in the drained than in the natural site of the fen.

Thule Inuit environmental impacts on Kangeq, southwest Greenland

Palaeoecological investigations of a rapidly eroding coastal midden and an adjacent peat bog on the island of Kangeq in southwest Greenland have provided new information on environmental change and human impact associated with Thule Inuit occupation. Palynological and palaeoentomological datasets have been produced through the 14th to the 17th centuries AD. The pollen and sedimentary data provide evidence for peat formation, increased frequency of the northern annual herb Koenigia islandica (Iceland purslane) from the end of the 15th century AD, and a decline in shrub pollen over the same period. These changes are interpreted as local responses to Little Ice Age cooling. No clear signal for human impact on the vegetation was revealed in the pollen record, and there was little macroscopic charcoal recovered from either of the sedimentary contexts that were examined; microscopic charcoal evident in the peat column is probably evidence for domestic fires. The insect remains suggest periodic patterns of disposal on the midden and provide information on natural environments in the vicinity. Fossil fly puparia (Diptera) are associated with decaying animal materials and perhaps indicate waste produced from the skinning of marine mammals and birds as opposed to butchering. The faunas contrast with results from the Saqqaq site of Qeqertasussuk and several Norse farms.

Natural Downward Smouldering of Peat: Effects of Inorganic Content and Piled Bed Height

The ash thickness formed above the combustion front of peat, which is affected by the inorganic content and the piled bed height of peat column, plays both positive and negative effects on peat smouldering fires. This work investigated the effects of the inorganic content and the piled bed height (5, 10 and 20 cm) on the natural downward smouldering mechanism of peat, both experimentally and numerically. It was observed that the char formation and char oxidation processes are stable and dominant during the downward smouldering. The spread rate of the pyrolysis front was found to decrease almost linearly with the inorganic content, while the spread rate of the char oxidation front was less dependent on the inorganic content and the piled bed height at higher inorganic content. The spread rate of the char oxidation front levelled off when the ash layer above the char layer was thick enough, which was also well-predicted by a 1-D numerical model. The model also predicted the nonlinearly increasing peak temperature and decreasing downward spread rate with depths in experiments. This work provides a better understanding of the multiple role of inorganic content in peat smouldering fires, especially for the fires in the in-depth peat layer with abundant inorganics in natural peatlands.