Peat Structure Research Articles

Simulating the long‐term impacts of drainage and restoration on the ecohydrology of peatlands

AbstractDrainage alters the carbon storage and accumulation functions of peatlands, but the long‐term effects of drainage ditches, and their restoration, on peatland development are poorly understood. Timescales of monitoring studies in ditch‐drained and restored peatlands are typically limited to a few years, and occasionally decades. In addition, experimental studies seldom monitor spatial changes in peat structure caused by ditches, despite such changes affecting water flow and water retention in peat. Ecosystem models offer an alternative to experimental studies and can help explain how complex systems such as peatlands may respond to external disturbances. Here we report on a 2‐D application of a peatland development model (DigiBog) to explore how contour‐parallel ditches, and their damming, affect the ecohydrology of peatlands over decades to centuries, using blanket peatlands as a case study. Drainage resulted in the rapid loss of peat due to increased oxic decay. The majority of these losses occurred in the first 100 years after the ditch was created, but water table dynamics were altered even centuries later. Restoration halted the loss of peat and encouraged net peat accumulation, although the amount lost in 100 years of drainage had not been replaced 200 years after the ditch was dammed. Restoration of ditches in sloping peatlands brought about more peat regrowth downslope of the restored ditch than further upslope. Our study demonstrates the potential for spatially distributed ecosystem‐scale models as tools to explore complex spatiotemporal responses to disturbance, and to support land managers in making decisions about peatland drainage and restoration.

Improved durability of lignocellulose-polypropylene composites manufactured using twin-screw extrusion

The objective of this study was to investigate the use of peat as a potential lignocellulose source in composites manufactured by twin-screw extrusion. The effects of peat decomposition rate and particle size on the mechanical properties and moisture resistance of peat-polypropylene (PP) composites under cyclic conditions were evaluated. The properties of the peat-PP composites were compared to commercial lignocellulosic fibre products, namely wood-plastic composite (WPC), medium density fibreboard (MDF) and hardboard (HB). The results show that prior cyclic freeze-thaw testing peat-PP composites had properties equal to commercial WPC, but their mechanical permanence was better after freeze-thaw conditioning. When moderately decomposed, smaller particle–size peat was used, peat-PP composites had better dimensional stability, though particle size did not affect as much as the decomposition degree. Thus, the chemical structure of peat has a greater influence on composite durability, as better water and weather resistance are achieved with peat that is more decomposed.

Land use increases the recalcitrance of tropical peat

Tropical peat carbon compound composition (CCC) is a highly understudied subject. Advanced understanding of peat CCC and carbon dynamics in differing conditions is desperately needed due to large-scale utilization of these peatlands. We studied the CCC—i.e. the hemicellulosic carbohydrate and uronic acid composition and concentrations of extractives, cellulose, acid-soluble lignin and acid-insoluble lignin—in association with peat profile depth and physical structure of peat, under representative, common land uses. Samples were gathered from an undrained forest and three sites altered 20–30 years prior to the study, which in aggregate form a continuum of increasing land-use intensity (drainage-affected forest; drained and deforested degraded open site; drained and deforested site under cultivation) in Central Kalimantan, Indonesia. Peat samples were taken from depths between 10 and 115 cm that covered mostly oxic, frequently waterlogged and permanently waterlogged, anoxic conditions. Our results demonstrated greater modification of peat properties when both vegetation and hydrological conditions were altered. The differences between sites were mainly present in the topmost peat and decreased with depth. Peat located at the surface contained more labile compounds (hemicelluloses, extractives, uronic acids, cellulose) on forest sites than at the most intensively altered open sites, where peat was enriched with recalcitrant acid insoluble lignin. The effect of drainage was evident in the drained forest site, where at the approximate median water table depth peat more closely resembled open sites in terms of the peat properties. The increased recalcitrance of peat in reclaimed areas has been a result of enhanced decomposition, reduced litter input rates and, at open sites also by repeated fires.

The effect of pore structure on ebullition from peat

AbstractThe controls on methane (CH4) bubbling (ebullition) from peatlands are uncertain, but evidence suggests that physical factors related to gas transport and storage within the peat matrix are important. Variability in peat pore size and the permeability of layers within peat can produce ebullition that ranges from steady to erratic in time and can affect the degree to which CH4 bubbles bypass consumption by methanotrophic bacteria and enter the atmosphere. Here we investigate the role of peat structure on ebullition in structurally different peats using a physical model that replicates bubble production using air injection into peat. We find that the frequency distributions of number of ebullition events per time and the magnitude of bubble loss from the physical model were similar in shape to ebullition from peatlands and incubated peats. This indicates that the physical model could be a valid proxy for naturally occurring ebullition from peat. For the first time, data on bubble sizes from peat were collected to conceptualize ebullition, and we find that peat structure affects bubble sizes. Using a new method to measure peat macrostructure, we collected evidence that supports the hypothesis that structural differences in peat determine if bubble release is steady or erratic and extreme. Collected pore size data suggest that erratic ebullition occurs when large amounts of gas stored at depth easily move through shallower layers of open peat. In contrast, steady ebullition occurs when dense shallower layers of peat regulate the flow of gas emitted from peat.

Influence of climatic and hydrological factors on structure and composition of peat from northern wetland territories with low anthropogenic impact

Northern wetlands ecosystems play an important role in the hydrological balance of neighboring areas, where they act as chemical barriers against anthropogenic and technogenic contaminations. Studied region is well known for quantity of peat deposits and the volume of peat resources. Peat can be considered as a highly informative marker for assessing change in environmental conditions. The study presents the results of the first investigation of peat samples, collected from representative ecosystems of northern wetland territories with low anthropogenic impact.Component and element composition of various peat types were studied in a relation to hydrologic, climate and sampling conditions. It was found out that organic and ash contents are more dependent on the type of the bog, than geographic location. Climatic factors are more important for the formation of bitumen. The degradation degree in peat increases proportionally to content of humates. High content of biogenic and lithogenic elements was observed in transition- and low-moor peat. The content of trace elements in peat samples do not depend on the type of the peat.The structural properties of peat were studied by the light microscopy, AFM and dynamic light scattering. It was determined that the conformation of studied peat samples is characterized by elements of asymmetry. The observed particles in the solutions exist in dynamic equilibrium with separated globular macromolecules. The size of these nanoparticles is comparable with the size of the particles of other biopolymers of similar nature.Swelling of peat in liquid water was studied. The relationship between structural specificities, origin of peat and its maximum degree of swelling was found. The degree of swelling can be used as structural-sensitive parameter in further research.

Biota and palaeoenvironment of a high middle-latitude Late Triassic peat-forming ecosystem from Hopen, Svalbard archipelago

Abstract A siliceous permineralized peat block recovered from Hopen in the Svalbard archipelago hosts a low-diversity Late Triassic flora dominated by autochthonous roots and stems of bennettitaleans and lycophytes, and parautochthonous leaves, sporangia, spores and pollen from a small range of pteridophytes and gymnosperms. Some parenchymatous bennettitalean root cells show interactions with chytrid fungi and bacteria; the remains of other fungi and fungi-like organisms are dispersed within the peat's detrital matrix. Cavities excavated through some roots and compacted detritus contain abundant coprolites probably derived from sapro-xylophagous oribatid mites, although no body fossils have yet been identified. Sparse larger coprolites containing leaf fragments attest to the presence of invertebrate folivores in the ancient ecosystem. The low-diversity flora, relatively few trophic levels and simple nutritional web, together with sedimentological aspects of the host formation and the peat structure, collectively favour accumulation of the organic mass as a fibric (root-dominated) peat within a temperate (high middle-latitude), well-aerated mire.

English

The influence of freezing on Sphagnum highly decomposed peats was estimated from their physical properties and their wettability measured in relation to the degree of desiccation. The results showed that the physical properties of peats were drastically affected by freezing, particularly improving their water availability and resulting in less , and more reversible , shrinkage after air-drying. However, contact angles measured for frozen or unfrozen peats are very similar. These results seem to indicate that the changes in physical properties are only due to a change in peat structure during freezing and are not a consequence of a change in water affinity. Nevertheless, even if freezing does not affect the wettability of materials, its influence on peat structure contributes to an improvement in their hydric properties.

A Study Of Major And Trace Element Accumulation In Humic Acids

It has been widely studied recent as well as historic accumulation of elements in peat profiles depending on intensity of anthropogenic pollution and thereby peat profiles serve as archives for research of environmental change. Peat ability to accumulate major and trace elements depends on the character of element supply, potency of metal ions to bind functionalities in the peat structure, pH reaction, oxygen presence, presence of complexing compounds, inorganic ions and many other factors. The aim of this study is to assign major and trace element distribution in humic acids (HA) for two well characterized ombrotrophic peat profiles of Eipurs and Dzelve Bog and analyse factors affecting element concentration in peat humic acids. Elemental and functional analysis of the isolated HAs was done, using total reflection X – ray spectrometry, Elemental Analyzer Model EA – 1108, Thermospectronic Helios γ UV (Thermo Electron Co.) spectrophotometer, Total acidity method.

Ebullition of methane from peatlands: Does peat act as a signal shredder?

AbstractBubbling (ebullition) of greenhouse gases, particularly methane, from peatlands has been attributed to environmental forcings, such as changes in atmospheric pressure. However, observations from peat soils suggest that ebullition and environmental forcing may not always be correlated and that interactions between bubbles and the peat structure may be the cause of such decoupling. To investigate this possibility, we used a simple computer model (Model of Ebullition and Gas storAge) to simulate methane ebullition from a model peat. We found that lower porosity peat can store methane bubbles for lengthy periods of time, effectively buffering or moderating ebullition so that it no longer reflects bubble production signals. Our results suggest that peat structure may act as a “signal shredder” and needs to be taken into account when measuring and modeling ebullition.

Gas bubble transport and emissions for shallow peat from a northern peatland: The role of pressure changes and peat structure

Gas bubbles are an important pathway for methane release from peatlands. The mechanisms controlling gas bubble transport and emissions in peat remain uncertain. The effects of hydrostatic pressure and peat structure on the dynamics of gas bubbles in shallow peat were therefore tested in laboratory experiments. A peat monolith was retrieved from a raised bog and maintained in a saturated state. Three distinct layers were identified from noninvasive permittivity measurements supported by soil physical properties (porosity, bulk density). Phase I of the experiment involved monitoring for the accumulation of gas bubbles under steady pressure and temperature conditions. The data showed evidence for gas bubbles being impeded by a shallow semiconfining layer at depths between 10 and 15 cm. Visible gas bubbles observed on the side of the sample box were recorded over time to estimate changes in the vertical distribution of volumetric gas content. Porosity estimates derived using the Complex Refraction Index Model (CRIM) suggest that gas bubbles enlarge the pore space when the exerted pressure is high enough. Phase II involved triggering release of trapped bubbles by repeatedly increasing and decreasing hydrostatic pressure in an oversaturated condition. Comparison of changes in pressure head and methane density in the head space confirmed that the increasing buoyancy force during drops in pressure is more important for triggering ebullition than increasing mobility during increases in pressure. Our findings demonstrate the importance of changes in hydrostatic pressure on bubble size and variations in resistance of the peat fabric in regulating methane releases from peatlands.

Effects of water table position and plant functional group on plant community, aboveground production, and peat properties in a peatland mesocosm experiment (PEATcosm)

Our objective was to assess the impacts of water table position and plant functional type on peat structure, plant community composition and aboveground plant production. We initiated a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: sedge, Ericaceae, sedge and Ericaceae- unmanipulated) in twenty-four 1 m3 intact peatland mesocosms. We measured vegetation cover, aboveground plant production, and peat subsidence to analyze interactive PFG and WT effects. Sphagnum rubellum cover increased under high WT, while Polytrichum cover increased with low WT and in sedge only PFGs. Sphagnum production was greatest with high WT, while vascular plant production was greater in low WT treatments. There was an interactive WT x PFG effect on Ericaceae production. Lowered WT resulted in significant peat surface change and increased subsidence. There were significant PFG and WT effects on net peat accumulation, with the lowest rates of accumulation, high and low WT, in sedge only PFGs. The shift in water balance leading to lowered water table position predicted with changing climate could impact plant community composition and production, and would likely result in the subsidence of peat.

A large direct simple shear device for the testing of peat at low stresses

A large direct simple shear device has been developed for the testing of peat at low normal stress. The large size allows adequate representation of the often coarse structure of peat, increases the accuracy with which small loads can be applied and diminishes device resistances to acceptably small proportions. A plane strain configuration between glass plates is used, allowing observation of the deformation field as it develops. The sample is gripped by pins along all four in-plane boundaries to reduce slippage during shear. Interesting results have been obtained in an initial series of tests. Strengths appear to be some 10% higher than those in standard simple shear tests on small-diameter samples, while the post-peak softening often measured in the latter appears to be lacking.

Surface peat structure and chemistry in a tropical peat swamp forest

Background and Aims Tropical peat swamp forests (PSF) are great stores of terrestrial carbon and host unique biodiversity. Despite their importance for carbon accounting, the peat characteristics are sparsely studied, and the effect of microtopography on peat properties has not been reported before.

Sorption characteristics of peat of Brunei Darussalam V: removal of Congo red dye from aqueous solution by peat

Peat collected from Panaga, Brunei Darussalam, shows strong affinity towards the adsorption of Congo red (CR) dye from aqueous solution. The adsorption capacity of Bruneian peat under optimized conditions of shaking time, settling time, and medium pH is determined to be 10.1 mg g−1 at equilibrium. Adsorption of CR on Bruneian peat follows monolayer adsorption with small contribution to multilayer formation qualifying the validity of the Redlich–Peterson model, which is further supported by error function determination. In addition, changes in peat structure and surface were studied using scanning electron microscopic and X-ray fluorescence techniques. Kinetics studies were in agreement with the pseudo-second-order model and the adsorption reaction proceeds according to intra-particle diffusion.

Impact of Heat Treatment on the Structure and Properties of Tomsk Region Peat

Botanical composition of terrestrial peat and fen peat with decomposition degree (R) ranging from 25% to 45% has been studied and technical analysis has been carried out. The effect of heat treatment on peat group composition alteration was evaluated. The peculiarities defined by the preliminary heat treatment were revealed. Optical properties of peat were studied by IR spectroscopy. Conclusions about the degree of heat treatment influence on the physicochemical properties of peat were made.

The effect of peat structure on the spatial distribution of biogenic gases within bogs

AbstractNorthern peatlands are a large source of atmospheric methane (CH4) and both a source and a sink of atmospheric carbon dioxide (CO2). The rate and temporal variability in gas exchanges with peat soils is directly related to the spatial distribution of these free‐phase gases within the peat column. In this paper, we present results from surface and borehole ground‐penetrating radar surveys – constrained with direct soil and gas sampling – that compare the spatial distribution of gas accumulations in two raised bogs: one in Wales (UK), the other in Maine (USA). Although the two peatlands have similar average thickness, physical properties of the peat matrix differ, particularly in terms of peat type and degree of humification. We hypothesize that these variations in physical properties are responsible for the differences in gas distribution between the two peatlands characterized by (1) gas content up to 10.8% associated with woody peat and presence of wood layers in Caribou Bog (Maine) and (2) a more homogenous distribution with gas content up to 5.7% at the surface (i.e. <0.5 m deep) in Cors Fochno (Wales). Our results highlight the variability in biogenic gas accumulation and distribution across peatlands and suggest that the nature of the peat matrix has a key role in defining how biogenic gas accumulates within and is released to the atmosphere from peat soils. © 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.

Männyn kylvö ja luontainen taimettuminen vanhoilla ojitusalueilla – turvemaiden uudistamisen erityispiirteitä

Artificial and natural seeding of Scots pine in old drainage areas – Unique features of forest regeneration on peatlands The aim of this dissertation was to investigate site characteristics unique to nutrient-poor, forestry-drained peatlands from the standpoint of establishing the second post-drainage generation of forest. Specifically, the effects of ground vegetation succession, surface peat structure and composition, water table level, and peat water retention capacity on the regeneration success of Scots pine after articial and natural seeding were examined. As Sphagnum moss cover declines and moss species typical of upland soils increase in abundance, seedbed receptivity of forestry-drained sites gradually becomes weaker. Thus, in order for natural regeneration to succeed in old drainage areas, some means of soil preparation is necessary, at the very least scarification. Depending on the progression of vegetation succession, a raw humus layer originating from plant litter may also have developed in the forestry-drained area. Following the disappearance of Sphagnum cover, the presence of raw humus most notably reduces seedbed receptivity in old drainage areas. After final felling, changes in the ground layer of vegetation often occur quite slowly especially on dwarf shrub and Vaccinium vitis-idaea drained peatland site types, provided that the water table level does not rise too high. The total coverage of vegetation in scalps decreased and succession markedly slowed when the water table level corresponded to that of a well drained site. Maintenance drainage carried out concurrently with soil preparation in the regeneration area is thus an effective measure when attempting to retard the invasion of vegetation onto scalped surfaces. In mounded areas, relatively large, over 25 cm high mounds remained free of vegetation for a long time, particularly when they had been created from deeply dug, highly decomposed peat. Due to the inherent variation in the water table level (in scalps and rotavated furrows) and sensitivity of the peat to desiccation (in mounds), forest regeneration via artificial or natural seeding is highly susceptible to weather conditions. In a growing season characterized by average rainfall and temperature, the regeneration result tends to be better in mounded than scalped regeneration areas. Such is the case particularly in years when the fluctuating water table level in a scalped regeneration area rises too high during late summer. From the seedling regeneration aspect, this problematic variation in the water level of scalps is a more probable scenario than excessive desiccation of the surface peat in mounds during an average growing season. Scalps, on the contrary, are ideal seedbeds during dry and warm growing seasons when excess drying of mounds is most likely to occur.

RAISED BOG PEAT HUMIC ACID ELEMENTAL COMPOSITION: TRENDS OF CHANGES AND RELATED FACTORS

Peat deposits can be considered as archives of environmental changes and indicators of anthropogenic pollution. The character of element accumulation, the potential of metal ions to bind functional groups in the peat structure, the pH reaction, the presence of oxygen, the complex- ing compounds and inorganic ions are the main factors governing peat ability to accumulate major and trace elements. The aim of this paper has been to study the major and trace element accumu- lation in humic acids (HAs) in two well-characterized ombrotrophic peat profiles of Eipurs Bog and Dzelve Bog in Latvia and analyse factors affecting the element concentrations in HAs with reference to peat properties. The analysis of major elements (e.g., Ca, Fe, K, Mg, Na) and trace elements (e.g., As, Cd, Co, Cr, Cu, Ni, Pb, Se, Zn) was performed by total reflection X-ray fluo - rescence spectrometry. Thise c paper demonstrates that HAs are significant for several elements, however, they are not the dominant factor affecting the element accumulation. The concentration of trace elements in peat and in peat HAs depend not only on human-induced pollution (determin- ing elevated concentrations of trace elements in upper layers of the bog). The study has revealed that for the accumulation of several toxic trace elements in peat (for instance, As, Pb and others) natural processes are of key importance.

Influence of physical and chemical properties on the low‐frequency complex conductivity of peat

ABSTRACTOrganic layers are heterogeneous in space and their composition changes over time. This poses challenges to ecohydrologists, subsurface hydrologists and ground engineers in characterizing subsurface peat structures and predicting their behaviour over time. Peat deposits can be characterized by performing electrical surveys, provided that the complex conductivity of peat is understood and connected to its physical and chemical properties. Low‐frequency (0.1–1000 Hz) induced polarization measurements were carried out to investigate the correlation between the chemical and physical properties of several peat samples and their electrical properties. A Cole‐Cole model was fit to the peat spectra to obtain the model parameters and study their relationship with the sample properties. All the samples were characterized by analysing their degree of humification, water content, organic content, cation exchange capacity, pH and conductivity of the pore‐fluid. Two significant correlations between physical, chemical and electrical properties are found. The peat bulk conductivity is directly correlated with the pore fluid conductivity, whereas the degree of humification of peat shows an inverse correlation with the phase angle. This study presents results that have implications for peatland characterization with frequency dependent or single frequency analysis of induced polarization measurements.

Chemico-geomechanical sensitivities of tropical peat to pore fluid pH related to controlling electrokinetic environment

Peat is an accumulation of partially decayed vegetation with high noncrystalline content (humus), which is formed in wetland systems. Chemico-geomechanical sensitivities of a fibrous (very slightly decomposed) and a sapric (highly decomposed) peat to peat-water pH gradients in terms of resulting effects on cation exchange capacity (CEC), zeta potential (ζ), particle density, liquid limit (LL), particle size distribution, dry density–moisture content relationship, permeability, and undrained shear strength (Su) have been investigated. The specimens were treated for a 20-day period under acidic and basic conditions. It was found that in both fibrous and sapric peat, the CEC and ζ decreased; the LL, permeability, Su, and the optimum moisture content (OMC) increased, and the grain size distribution became skewed toward larger particles because of acidic conditions, while basic conditions had a contrary effect. The sensitivities of the fibrous peat to peat-water pH gradients were not of such intensity as were observed in the sapric peat because of the naturally inherited peat structure, degree of decomposition, ion change capacity, particle size, surface charges, and specific surface area. Our results are important, in that they confirm the link between the degree of peat humification and the chemico-geomechanical sensitivities of the peat to peat-water pH gradients.