Degree Of Peat Decomposition Research Articles

Late Holocene changes in the water table at an alkaline fen in Central Latvia: Their impacts on CaCO3 deposition at the fen and relation to the hydroclimate patterns of the Eastern Baltic Region

Sediments of CaCO3-precipitating alkaline fens, comprising biotic and abiotic indicators of water table changes, are among the most reliable archives for obtaining palaeohydrological data. The study uses a semiquantitative method based on a combination of selected indicators (plant macrofossils, mollusc shells, degree of peat decomposition) to estimate the relative changes in the water table position at Lustūžkalns alkaline fen, Latvia, Eastern Baltic Region. The study also aims to determine the time frames of CaCO3 deposition at the fen using loss on ignition and carbon and oxygen stable isotope records. The chronology of the three sediment sequences studied is based on the AMS radiocarbon dating of terrestrial plant macrofossils. Although the reconstructed water table positions revealed differences between the cores, the major shift from the low water tables persisting since ca. 5000 cal yr BP to the prevailing high water stands at ca. 3000 cal yr BP was common to all the sequences. The major shift observed is consistent with a change from low to high water tables in peatlands in Latvia and at numerous fens and bogs across the Eastern Baltic Region, Fennoscandia and NW Europe. Concurrent with the increase in the water tables was the onset of CaCO3 precipitation on the Lustūžkalns fen surface, which began at ca. 3000 cal yr BP and accelerated from ca. 2500 cal yr BP. The Late Holocene CaCO3 precipitation at Lustūžkalns can be attributed to the change from warm and dry conditions during the Holocene Thermal Maximum (HTM) to cooler but humid during the Late Holocene. In contrast, in Central and Western Europe, the main period of freshwater carbonate precipitation occurred during the warm and humid HTM.

Soil Cover Modifications in Vicinity of Disappearing Lakes as a Result of Climate Change

Abstract Disappearance of lakes is one of the most dangerous processes affecting the entire natural environment, including soil. This phenomenon is considered natural, resulting from climate change, however in recent decades, a significant acceleration of this process has been observed due to the direct impact of human activity. In areas directly adjacent to lakes, organic soils usually predominate. Unfortunately, wetlands are increasingly being drained and used for agricultural purposes. Under such circumstances, changes in the physical and chemical properties of these soils are often irreversible, causing their degradation. As an effect of increased mineralization, a number of typical modifications occur in soils, such as carbon loss, increased degree of peat decomposition, and changes in soil structure. Long-term dehydration has led to muck formation. Additionally, lowering of lake water uncovers previously flooded areas and increases the intensity of soil-forming processes. However, the presence of the Subaquatic qualifier in the World Reference Base for Soil Resources (WRB) suggests that sediments in shallow water bodies no more than 200 cm deep can also be classified as soils. The progressive disappearance of lakes observed all over the world is therefore a process affecting not only the reduction of water bodies, but also changes in the properties and typology of soils and vegetation cover.

The Holocene evolution of floodplain mire geosystems in the southeastern part of the Meshchera lowlands

The results of paleoecological studies of peat deposits in the area of the southeastern part of the Meshchera lowlands (Mostovoye mire) based on the analyses of peat properties, plant macrofossils, charcoal, pollen and radiocarbon dating are presented. The mire was formed in the oxbow depression on the floodplain of the Goose River around 9480 cal. yr. BP and was eutrophic throughout most of the Holocene. Drastic changes in the dynamics of the mire, namely its transition to the mesotrophic stage, characterized by a decrease in the degree of peat decomposition, occurred about 70 years ago. The results of the pollen analysis show the existence of birch-pine forests in combination with shrub thickets formed by Betula nana in the period 9480-8750 cal. yr. BP. In the subsequent stages, the vegetation cover turned to a combination of broad-leaved, birch-pine forests and riverine forests with alder. Frequent fires, both natural and anthropogenic, have favored the development of birch and pine forests over the last millennium.

Sphagnum Litter as the Most Important Genetic Horizon in the Profile of Peat Soils of Boreal Bogs

Peat soils of the taiga zone of West Siberia have historically been relatively poorly studied. In the diagnostics of peat soils, the question of the belonging of the sphagnum litter horizon to the soil profile, as well as the identification of its lower boundary, remains unresolved. In the WRB and Russian Soil Classification, sphagnum litter is considered as a vegetation cover, while in the Soviet classification it is considered as an integral part of the soil profile. The last point of view is also shared by the majority of Russian researchers. Using the material obtained in the study of peat soils in the basin of the river Kazym (subzone of the northern taiga, West Siberia), a comparative characteristic of the sphagnum litter horizon (0–20 cm) and the underlying peat horizon (20–50 cm) was carried out using three parameters: the botanical composition of peat, the degree of peat decomposition, and the color of the soil. All soils are differentiated into the litter horizon and the peat horizon by at least one parameter (5% of the profiles), but in 71% of cases, by three at once. The degree of profile differentiation into two horizons tends to increase in a series of soils formed, respectively, in oligotrophic pine-shrub-sphagnum, oligotrophic complex ridge-hollow, and mesotrophic biogeocenoses. In the overwhelming majority of oligotrophic peat soils, the transition from the litter horizon to the peat horizon is gradual, which does not allow a reproducible assessment of the boundary position in the soil profile. It is proposed to establish a fixed border of the litter horizon at 20 cm from the surface of the bog, referring it to the surface horizon of peat soil.

The Molecular Composition of Peat Organic Matter and Prospects for Its Use in Agriculture

This paper highlights the molecular composition of native peat and preparations of humic substances (HSs) isolated from permafrost hummock peatlands (Histosols) of the forest tundra zone of the European north-east of Russia. The structural and functional parameters of humic—(HAs) and fulvic acids (FAs) of the peatlands studied are determined by the combined action of cryogenic processes, species composition and the degree of peat decomposition, which reflects the climatic conditions during peat formation in the Holocene. The predominance of the proportion of HAs over FAs in the composition of peat, as well as the low acidity of FAs, makes HS-based preparations highly promising for use as organic fertilizers. The high contents of alkyl and carbohydrate fragments in the structure of the studied HSs allow us to recommend them for use in mineral loamy-textured soils.

Effect of clay with high water adsorption capacity on process of secondary consolidation of peat

Introduction. Primary consolidation of peat, underlying an embankment, is completed 3 to 5 years after its filling. It is followed by secondary consolidation, caused by removal of bound moisture from micropores. At this stage, the settlement rate depends on the degree of peat decomposition, temperature, content of various chemicals in the pore water, vibration effects, and other factors. To reduce the embankment deformation, caused by the secondary consolidation, peat is either modified by binding compounds, having filling agents, or other actions are taken to accelerate the settlement process for a short term and to decelerate it thereafter using temporary surcharge, electroosmosis and other actions.
 
 Materials and methods. The authors studied the effect of peat dehydration using clayey materials with high water adsorption capacity, such as bentonite and saponite waste generated by the diamond mining industry. 100 days oedometer tests were carried out. In the course of testing, vertical cylindrical elements, made of the above materials, were installed in the specimens. These cylindrical elements occupied about 10 % of the specimen volume.
 
 Results. Bentonite inclusions, formed without any peat extraction, had a powerful effect on development of deformations. Intensive dehydration of peat led to a 2–4 times increase in the coefficient of secondary consolidation сαε. Following 25 to 30 days of intensive settlement, the value of the cαε coefficient went down by an average of 1.5 times relative to its initial value. The effect of elements, made of saponite-containing waste, turned out to be different. The value of the cαε coefficient increased by 11 to 15 %, but 20 to 30 days later it went down by an average of 2 times relative to the initial value. Higher resistance of elements to vertical loading served as the factor preventing the development of settlement.
 
 Conclusions. Clay has a high water adsorption capacity, and its intrusion into peat results in accelerated water migration from micropores and boosts the rate of secondary consolidation. In addition to peat dehydration, secondary consolidation was accelerated by mechanical compaction in the process of adding clay into specimens followed by clay swelling.

PALEOECOLOGICAL CONDITIONS AND CARBON ACCUMULATION IN GENESIS OF INUNDATED MIRE OF MID-RUSSIAN UPLAND

The aim is to study of influence of the ecological conditions on the carbon accumulation at the different stages of genesis of the inundated mire.
 Materials and methods. The macrofossil analysis and the degree of peat decomposition were studied by the microscopic method, the moisture content and the dry bulk density were studied by the gravimetric method. The ash content was determined by burning, the content of organic matter was calculated by the difference between the mass of dry peat and the ash content. The carbon content (%) in peat samples was calculated based on the dry bulk density, the organic matter content and the mass fraction of carbon for each volume of peat. The rate of vertical growth of peat and intensity of peat accumulation in periods of Holocene were calculated based on the results of radioactive dating.
 The parameters of surrounding landscapes during the mire genesis were characterized by the results of the palynology analysis and the estimation of fire activity. The intensity of fires in paleolandscapes was studied by the content of coal particles in each (1 cm3) sample of wet peat.
 Results. The genesis of the Podkosmovo mire is presented by 5 stages which were took place under the stable conditions of water-mineral nutrition. The carbon accumulation in the genesis proceeded at the rate of 45.7 g/m2/year on average. At the same time, the surrounding landscapes differed in the degree of afforestation and the intensity of anthropogenic press.
 Conclusion. The moderate hydration and nutrition with mineralized waters ensure the stability of the mire development and the intensity of carbon accumulation, despite the change of surrounding landscapes under the influence of climate or human. However, the active transformation of the surrounding landscapes can have a negative impact on the functioning of the mire and reduce the intensity of carbon accumulation.

Holocene wet shifts in NW European bogs: evidence for the roles of external forcing and internal feedback from a high‐resolution study of peat properties, plant macrofossils and testate amoebae

ABSTRACTTwo conspicuous wet shifts in the peat stratigraphy of Store Mosse in southern Sweden, associated with bog‐wide changes in vegetation and degree of peat decomposition, were analysed at high resolution. The bog‐surface wetness (BSW) proxy data (organic matter bulk density, C/N ratio, plant macrofossils and testate amoebae) highlight the importance of interactions between vegetation composition, microtopography and degree of peat decomposition, and show that the bog system operated consistently during the two wet shifts (dated to c. 2700 and 1000 cal a bp) despite different internal and external conditions. A sensitive bog‐system state, associated with a degraded microtopography and well‐decomposed surface peat with low hydrological conductivity developed during sustained dry conditions, probably contributed to the large BSW amplitudes registered. Comparable bog systems are expected to operate in the same way, and regionally high sensitivity that developed in response to atmospheric circulation changes may partly explain synchronous registration of wet shifts. The wet shifts in Store Mosse were attributed to solar and volcanic forcing, respectively, and wet shifts of similar magnitude registered in other NW European bogs are likely to also have been externally forced.

Rate of Fen-Peat Soil Subsidence Near Drainage Ditches (Central Poland)

This study analyzed design depths (to), post-subsidence depths (t), shallowing magnitudes (d = to − t) and ratio values (d/t) of 12 drainage ditches in a fragment of the drained Solec fen-peat (central Poland) over a period of 47 years between 1967 and 2014. A significant decrease of the designed depth of the ditches to was shown, from the average designed value of 0.97 m to their average depth after subsidence, t = 0.71 m. The ratio (d/t) of 0.41, which is associated with the degree of organic matter decomposition, indicated medium degree of peat decomposition. The average values of bank and bottom subsidence of the ditches during the analyzed period, 1967–2014, were 0.43 m and 0.17 m, respectively. The values of the average annual rate of land surface subsidence in the vicinity of the ditches were varied and within the range of 0.09 cm year−1 to 1.70 cm year−1, with an average of 0.92 cm year−1. Two linear empirical equations were proposed to calculate the amount of subsidence and the average annual rate of subsidence of peat soil surface near the drainage ditch route, based on the knowledge of the initial thickness of the peat deposit. The results of calculations using the equations proposed by the authors were compared with calculations of the same parameters using 10 equations published in the literature. The results obtained using the proposed equations were mostly larger than those calculated with literature-published equations.

Impacts of vegetation and palaeohydrological changes on the n-alkane composition of a Holocene peat sequence from the Upper Vistula Valley (southern Poland)

PurposeThe analysis of n-alkanes in palaeoenvironmental studies of peatlands is mainly limited to ombrogenous peatlands which are a rare feature in the environment. Using n-alkane and plant macrofossil analysis, we have tracked changes in the environment in the valley of a large Central European river. We tested the possibilities for applying such studies to low-moor bogs which are the most commonly occurring type of bog in the world.Materials and methodsRepresentative peat samples were taken from two profiles in a peatland located in the Vistula Valley (southern Poland), and they were analysed for the occurrence and distribution of biomarkers. The distribution of n-alkanes was determined using gas chromatography-mass spectrometry (GC–MS). The botanical composition of the samples was determined by analysis of plant macrofossil remains, and the degree of peat decomposition was also determined.Results and discussionSamples of low-moor peat were characterised by a prevalence of medium- and long-chain n-alkane homologues, which is typical for higher plants. The variable values of the CPI, CPI (25–31), and the C23/C25 ratio have provided information on the stages of formation of the Zapadź bog. The source of n-alkane differentiation is vegetation change related to palaeohydrological dynamics and palaeoenvironmental conditions within the peatland.ConclusionsWe have shown that analysis of n-alkanes can be successfully used in low-moor bogs as a complement to palaeobotanical and palaeozoological methods. The bringing together of these types of research enables changes in the ecosystems of large river valleys to be tracked.

9000 years of changes in peat organic matter composition in Store Mosse (Sweden) traced using FTIR‐ATR

Store Mosse (the ‘Great Bog’ in Swedish) is one of the most extensive bog complexes in southern Sweden (~77 km2), where pioneering palaeoenvironmental research has been carried out since the early 20th century. This includes, for example, vegetation changes, carbon and nitrogen dynamics, peat decomposition, atmospheric metal pollution, mineral dust deposition, dendrochronology, and tephrochronology. Even though organic matter (OM) represents the bulk of the peat mass and its compositional change has the potential to provide crucial ecological information on bog responses to environmental factors, peat OM molecular composition has not been addressed in detail. Here, a 568‐cm‐deep peat sequence was studied at high resolution, by attenuated reflectance Fourier‐transform infrared spectroscopy (FTIR‐ATR) in the mid‐infrared region (4000–400 cm–1). Principal components analysis was performed on selected absorbances and change‐point modelling was applied to the records to determine the timing of changes. Four components accounted for peat composition: (i) depletion/accumulation of labile (i.e. carbohydrates) and recalcitrant (i.e. lignin and other aromatics, aliphatics, organic acids and some N compounds) compounds, due to peat decomposition; (ii) variations in N compounds and carbohydrates; (iii) residual variation of lignin and organic acids; and (iv) residual variation of aliphatic structures. Peat decomposition showed two main patterns: a long‐term trend highly correlated to peat age (r = 0.87), and a short‐term trend, which showed five main phases of increased decomposition (at ~8.4–8.1, ~7.0–5.6, ~3.5–3.1, ~2.7–2.1 and ~1.6–1.3 ka) – mostly corresponding to drier climate and its effect on bog hydrology. The high peat accumulation event (~5.6–3.9 ka), described in earlier studies, is characterized by the lowest degree of peat decomposition of the whole record. Given that FTIR‐ATR is a quick, non‐destructive, cost‐effective technique, our results indicate that it can be applied in a systematic way (including multicore studies) to peat research and provide relevant information on the evolution of peatlands.

Stages of soil development in the coastal zone of a disappearing lake\u2014a case study from central Poland

PurposeThe aim of this study was to estimate the impact of lake disappearance, groundwater table fluctuations, and some aspects of human pressure on stages of soil cover development in the catchment of Lake Rakutowskie.Materials and methodsResearch was conducted in soil chronosequence composed of eight soil profiles located in 785-m-long transect. Soils were sampled every 10 cm. Physical and chemical properties were determined with the use of disturbed and undisturbed samples. Radiocarbon dates were obtained for the bottom part of peat in each soil profile. The mineral composition of selected soil samples was determined using the X-ray diffraction (XRD) method. Additionally, the hydrological conditions were continuously monitored from July 27, 2013 to September 23, 2014.Results and discussionAn increased rate of shallow lakes overgrowth and final disappearance is a commonly observed process in the European lowlands. This paper presents and discusses the influence of changes in the range of the Lake Rakutowskie wetlands complex (central Poland) and water level fluctuations on soil cover transformation in the immediate vicinity of the lake. Five major phases of soil cover development (from Subaquatic Histosols (Limnic) to Hypereutric Regosol (Drainic, Humic)) were hypothetically reconstructed based on detailed studies of soil physical and chemical properties, mineral composition, water level fluctuations, and radiocarbon dating. The degree of peat decomposition in the studied profiles increased with the distance from the contemporary lake surface. Along with the progressive dehydration and mineralization of organic soils, their physical and chemical properties deteriorated, which is visible, e.g., in soil structure, and mineral and chemical composition (especially TOC and TN). Obtained radiocarbon ages of selected samples indicate that the oldest peat layers developed about 5856 cal BCE (6970 ± 70 14C BP), while the youngest were deposited about 1074 cal CE (980 ± 40 14C BP)–1573 cal CE (300 ± 35 14C BP). Hydrological studies indicate a progressive process of lake disappearance.ConclusionsThe process of soil cover transforming of the studied area takes place relatively quick, mainly recently due to the influence of human activity. Based on these results, it can be predicted that the lake will most likely disappear in a relatively short time, and the soil cover will be entirely in the fifth phase (P5) of evolution.

Assessment of applying VLF geophysical method to determine the peat deposit thickness

Peat deposits accumulate large reserves of carbon and play an important role in formation of global climate, biosphere, and hydrological conditions. High degree of knowledge of peat reserves is one of the prerequisites for scientifically based and economically viable wetland management. For economically efficient commercial activity, an enterprise developing a peat deposit must be confident in the availability of sufficient and high quality commercial peat reserves. Therefore, the topic of studying the thickness of peat deposits is quite relevant. The paper analyzes the experience of using the geophysical method called VLF ("very low frequency") to study the thickness of peat deposits. The method consisted of using a VLF receiver to measure the properties of VLF emitted by the peat deposit and the underlying mineral ground. The study was carried out at the Beloe Lake peat deposit in the Tukayevsky district of Tatarstan, at three peat areas of different depths: deep-lying (over 3 m), intermediate (1.5 – 3 m), and shallow (up to 1.5 m). The depth was confirmed by direct measurements in the wells. Low-frequency (VLF) measurements were carried out along the geophysical paths at each area of the peat deposit. The data were processed using the NAMEMD (Noise Empirical Decomposition) method and converted to resistivity and depth values using the specialized software. The study showed that the resistivity differs significantly between the areas of deep-lying and shallow peat. The resistivity varies depending on the peat thickness and the thickness of the buried wood horizons. In the horizons of deep-lying peat, the resistivity is strongly influenced by the degree of peat decomposition, its natural density and moisture. The presence of peaks and their height on the data interpretation plots characterizes the number and thickness of the horizons of buried wood in the peat deposit. With increasing depth of peat occurrence, the resistivity increases significantly. However, in the shallow areas, it does not show differences, being characteristic for the deep-lying peat area. This proves that the VLF method works correctly in peat layers and is capable to indicate the peat thickness, the number and thickness of the buried wood horizons.

Vertical distribution of PAHs during the evolution of permafrost peatlands of the European arctic zone

A range of polycyclic aromatic hydrocarbons has been identified, and regularities of their vertical distribution in the peatland of hummock-hollow complexes in the southern tundra – forest tundra and northern tundra – southern tundra ecotones of the European Arctic zone have been determined. Benzo[ghi]perylene, naphthalene, pyrene, fluorene, phenanthrene, benzo[b]fluoranthene and benzo[a]pyrene are displayed most in the peatlands under study. Regarding the peatland profile the vertical polyarene distribution is similar – in 150–175 cm permafrost layers (site 1) and 50(70)–210(250) cm layers (site 2), and on the border between the active layer and permafrost 35–50(60) cm (site 1) and 30(42) – 50 cm (site 2) a significant increase of HCO-accumulated PAHs weight fraction is observed. PAHs content maximums in tundra peatland horizons are associated both with 4-, 5- and 6-nuclear structures at both sites under the analysis, and with a larger amount of 2- and 3-nuclear polyarenes in the peatlands on the northern tundra-southern tundra ecotone. Aeration-exposed seasonally thawing peatland layers are subject to continuous formation of primarily light 2- and 3-nuclear PAHs of natural origin resulting from microbiological decomposition of plant residues, which are subsequently involved in equilibrium cycles of chemical and biochemical transformation, with their total capacity remaining almost unchanged and constituting ⁓200–500 ng/g. Owing to low productivity of plant communities and absence of tree vegetation in the seasonally thawed layer, accumulation of the sum of 4-, 5- and 6-nuclear PAHs weakens significantly. One can detect dependencies between individual PAHs and the botanic composition of peat through higher weight fraction of 4-, 5- and 6-nuclear polyarenes being lignin transformation products generated more as the share of tree vegetation grows. The PAHs composition is a paleoclimatic marker reflecting adequately both changing paleovegetation stages and the degree of peat decomposition.

Vascular plants affect properties and decomposition of moss-dominated peat, particularly at elevated temperatures

Abstract. Peatlands, storing significant amounts of carbon, are extremely vulnerable to climate change. The effects of climate change are projected to lead to a vegetation shift from Sphagnum mosses to sedges and shrubs. Impacts on the present moss-dominated peat remain largely unknown. In this study, we used a multiproxy approach to investigate the influence of contrasting vascular plant types (sedges, shrubs) on peat chemistry and decomposition. Peat cores of 20 cm depth and plant material (Sphagnum spp., Calluna vulgaris and Eriophorum vaginatum) from two ombrotrophic peatlands in the Italian Alps with a mean annual temperature difference of 1.4 ∘C were analyzed. Peat cores were taken under adjacent shrub and sedge plants growing at the same height above the water table. We used carbon, nitrogen and their stable isotopes to assess general patterns in the degree of decomposition across sampling locations and depths. In addition, analytical pyrolysis was applied to disentangle effects of vascular plants (sedge, shrub) on chemical properties and decomposition of the moss-dominated peat. Pyrolysis data confirmed that Sphagnum moss dominated the present peat irrespective of depth. Nevertheless, vascular plants contributed to peat properties as revealed by, e.g., pyrolysis products of lignin. The degree of peat decomposition increased with depth as shown by, e.g., decreasing amounts of the pyrolysis product of sphagnum acid and increasing δ13C with depth. Multiple parameters also revealed a higher degree of decomposition of Sphagnum-dominated peat collected under sedges than under shrubs, particularly at the high temperature site. Surprisingly, temperature effects on peat decomposition were less pronounced than those of sedges. Our results imply that vascular plants affect the decomposition of the existing peat formed by Sphagnum, particularly at elevated temperature. These results suggest that changes in plant functional types may have a stronger impact on the soil carbon feedback in a warmer world than hitherto assumed.

Peat decomposition proxies of Alpine bogs along a degradation gradient

The carbon sink function of peatlands is the result of a relatively small imbalance between biomass production and decay and proposed to be sensitive to changes in environmental conditions. Thus, peat decomposition plays a decisive role in determining the future carbon balances of peatlands under changing climatic conditions and increasing human pressure. To evaluate the effects of peatland degradation on the degree of decomposition in light of deviating site histories and to reveal interrelations between different indicators, we analysed peat depth profiles of physicochemical peat decomposition proxies across nine study sites in two valley bogs in the Eastern Alps, Austria. For this purpose, we divided 1 m peat cores sampled at the nine sites into 4 cm sections and analysed these peat samples for bulk density, loss on ignition, pH value, carbon and nitrogen content and ratio, stable carbon and nitrogen isotope signatures, and five humification indices based on Fourier transform infrared spectroscopy. Besides, we regularly measured water levels and incubated litter bags over two years. Peat characteristics were found to be relatively homogenous across the treeless and only slightly degraded sites. At these sites, depth profiles followed similar patterns with strongly increasing decomposition in the uppermost layers and the highest degree of peat decomposition at 40–56 cm depths for most proxies. Thus, our findings suggest that even apparently only slightly degraded sites were distinctly affected by past drainages. In contrast to the open peat bog sites, the degree in peat decomposition was distinctly higher at tree-encroached sites and at long-term drained former peat-cutting sites. Both, the distinct difference in the degree of decomposition between the two peatlands and the inverse decomposition depth trends, i.e., more decomposed peat overlying less decomposed layers, highlight the importance of secondary decomposition on the depth profiles and the strong effects of site histories on the current degree of peat decomposition. The results of two-year litter bag incubations of four vascular plant species revealed distinct differences in species-specific litter decomposition rates and considerable differences for same species between the two investigated bogs. The strong interrelations between different humification indices underline the simultaneous effects of proceeding decay on the different chemical properties of the peat. Besides, humification indices were strongly related with other physical and chemical properties of peats and highest loadings on the principal component 1 that accounted for 41% of the total variance of the dataset were found for four different humification indices, bulk density and nitrogen contents. We conclude that the selective preservation of aliphatic, acid and aromatic groups during peat decomposition are well suited to elucidate small-scale differences in the degree of decomposition and to strongly interrelate with established indicators as bulk densities.

Participation of Plants in the Formation of Polycyclic Aromatic Hydrocarbons in Peatlands

The composition of polycyclic aromatic hydrocarbons (PAHs) in vegetation of natural hummocky peatlands in the forest-tundra subzone of the Komi Republic and its possible impact on the composition of polyarenes in peat were assessed. The content of polyarenes was estimated by the method of highly efficient liquid chromatography. The accumulation of polycyclic aromatic hydrocarbons was the highest in Polytrichum strictum, Betula pubescens, and shoots of Picea abies and smaller in Betula nana L., Salix lapponum L., and Carex limosa L. with the domination of low-molecular-weight PAHs. We did not reveal dibenz[a,h]anthracene and benzo[ghi]perylene in plants: they could be the products of soil-forming processes. It is shown that distribution patterns of PAHs in the permafrost-affected soils of peat mounds (Hemic Folic Cryic Histosols) and in the soils of open-water mire pools (Fibric Floatic Histosols) are similar. Small quantities of low-molecular-weight polyarenes were normally accumulated in the seasonally thawed layer. The content of heavy structures (mainly, benzo[ghi]perylene) strongly increased at the contact with permafrost and then slightly decreased in the underlying permafrost. The composition of PAHs in the active layer mainly depended on composition of polyarenes in plants. At the contact with permafrost, the active synthesis or release of high-molecular-weight compounds took place. The influence of the composition of PAHs in plants on their composition in peat greatly depended on the degree of peat decomposition. Reasoning from the natural model of peat formation in open-water mire pools, the composition of polyarenes in the upper peat horizons of such sites was affected by recombination of low-molecular-weight hydrocarbons in Sphagnum riparium and Eriophorum sp. In the course of long-term soil development, the decomposition of complex organic compounds in plant tissues (particularly, in Eriophorum sp.) results in the formation of heavy PAHs with a simultaneous increase in the content of low-molecular-weight polyarenes.

Microbiological Characteristics of Bare Peat Circles on Flat-Topped Peat Mounds in the North of Western Siberia

A destructive peat horizon Tmd of bare peat circles on flat-topped peat mounds in the north of Western Siberia differs from peat horizons (T) of typical peat soils in its higher density, water content, and comminution of peat residues; lower microbial biomass; low mineralization and hydrolase activities; low physiological diversity of hydrolytic bacteria; and specific composition of the fungal complex with an uncharacteristically high proportion and quantity of psychrophilic yeasts Leucosporidium drummii. Specific respiration rate and hydrolase activity in the Tmd and T horizons are relatively close, which indicates that, in general, the metabolic activity of microorganisms decomposing the organic matter of peat and increasing the degree of peat decomposition remains unchanged in the soils of bare peat circles.

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.

Hydrophysical properties of ombrotrophic peat under drained peatlands

Understanding the processes that control the retention and flow of water in peat soils is critical to the effective management of such soils from both agricultural and ecological perspectives. The water retention properties of peats collected from rubber-cultivated, oil palm-cultivated, and abandoned (uncultivated) areas in the vicinity of Kanamit Barat Village, Pulang Pisau District, Province of Central Kalimantan were characterized using the van Genuchten equation. Based on the parameters of α indicating a change in the water content as water potential changes and n indicating the rate of decreasing water content as water potential becomes more negative, the more decomposed peats in the rubber cultivated peatland lost their water relatively slowly at small negative pressure heads, while less decomposed peats in the oil palm-cultivated and abandoned peatlands lost their water more quickly. This reflects difference of pore-size distribution among different land uses of peatlands. The total volume of water retained by the unsaturated layers in the rubber-cultivated peatland was lower than that in the oil palm-cultivated and abandoned areas. Also, the residual water content was higher in the rubber-cultivated peatland compared to the oil palm-cultivated and abandoned areas. This implies that the proportion of the maximum volume of water being removed decreases as a result of agricultural activities in peatlands. This evidence shows that the moisture state of peat soil is greatly influenced by the degree of peat decomposition and water table fluctuation. K e y w o r d s: drainage, moisture retention, residual porosity, tropical peatland