A Comparative Study of the Use of Organic Carbon and Loss on Ignition in Defining Tropical Organic Soil Materials

Organic soils or Histosols or peats as they are commonly referred to, are characterized by the presence of large amounts of organic soil materials (OSM), which is commonly quantified by the Walkley and Black (1934) (WB) method to determine the soil organic matter (SOM) using a correction factor of 1.724. SOM of Histosols is also identified through a combustion (loss on ignition, LOI) or elemental C-analysis (with a carbon-nitrogen-sulfur (CNS) analyzer with combustion and gas density detector). These methods were established using temperate and boreal peat deposits and here we demonstrate that tropical peat deposits require a modified approach. Typical SE-Asian tropical lowland peat pedons from rain forest and oil palm settings were sampled and the material analysed using a CNS analyzer, WB-C and LOI. The ratios for LOI:CNS-C for the 20 samples yielded values between 2.00–3.09 with a mean of 2.50 while the LOI:WB-C ratio yielded values from 1.75 to 2.58 with a mean of 1.94. A comparison of these values for topsoils and subsoils showed mean ratios (LOI:WB-C) of 1.94 and 1.89 for topsoils and subsoils, respectively. The forest samples had higher LOI:WB-C ratios than the subsoils from oil palm settings (1.94 vs 1.84). These values suggest that the standard factor of 1.724 to correct OSM to SOM for tropical soils is untenable. The values to convert CNS and WB-C values of tropical topsoils/subsoils to SOM or LOI should be 2.5 or 1.9, respectively. Our results indicate a significant difference in the soil organic carbon (SOC) of tropical lowland peats depending on the method used.     

Soil organic matter characterization of temperate peatland soil with FTIR‐spectroscopy: effects of mire type and drainage intensity

Peatlands are an important component of the global carbon cycle because they comprise huge amounts of terrestrial carbon (C). Different conditions during peat formation and secondary peat decomposition affect the quantity and composition of soil organic matter (SOM) in peats. There are few comparative studies on the chemical composition of SOM in temperate peatland soil. This study investigates compositional changes of SOM functional groups in peats and corresponding peat‐forming plants by Fourier transform infrared (FTIR) spectroscopy. Three plant samples and 29 peat samples were taken from seven temperate peatland sites with different genesis and land‐use intensity. Site‐specific differences, such as genesis of the peat, were found to be reflected in the FTIR spectra. In general, there was more variation in FTIR spectra in samples from fens than in those from bogs and peat‐forming plants. The samples from fens have a smaller C–H absorption band than those from bogs and plants, which reflects greater biochemical activity in the minerotrophic than ombrotrophic environments. In addition to peat genesis, drainage and secondary peat decomposition also affect SOM composition substantially. The larger amounts of aliphatic compounds in undrained peats could be explained by selective preservation caused by anaerobic conditions. With increasing drainage of the sites, there was a decrease in the C–H absorption that was accompanied by a relative increase in C=O absorption. These changes in absorption intensities reflect the enhanced aerobic decomposition and mineralization that accompanies drainage and land‐use intensity. However, the ‘degree of peat decomposition’, a diagnostic tool used in the field, is not reflected by OM composition determined by FTIR spectroscopy. Our results contribute to further understanding of changes in SOM composition during peat formation and processes of secondary decomposition caused by drainage.     

Fulvic acid composition in degraded fenlands

Fulvic acids (FAs) from topsoil and ground water solutions were investigated to discover effects of land use and peat degradation on their molecular chemical composition and thermal properties. The FAs were extracted from three Gleysols under arable land, intensive and extensive grassland, and from three Histosols under alder forest, extensive grassland, and a natural succession in a long‐term (> 200 years) cultivated fen area. Functional groups and molecular subunits of the FAs were investigated by ¹³C Nuclear Magnetic Resonance (¹³C NMR) spectroscopy. Thermal properties and structural molecular subunits were investigated by off‐line pyrolysis, and Pyrolysis‐Field Ionization Mass Spectrometry (Py‐FIMS). The ¹³C NMR spectra showed that the FAs from topsoil solutions had smaller proportions of alkyl C (mean: —8 %) and more aromatic C (mean: + 6 %) than FAs from ground water. This clear differentiation of dissolved FAs in the soil profiles is consistent with Py‐FIMS data which have shown enrichments of lipids in ground water FAs. Furthermore, Py‐FIMS revealed that the FAs from topsoils were richer in phenols + lignin monomers, carbohydrates, as well as mostly aromatic N‐containing compounds. These molecular subunits of FAs, relatively enriched in topsoil, were also the main indicators of land use and peat degradation. For topsoil solutions, the proportions of phenols + lignin monomers and carbohydrates increased stepwise with peat degradation in Gleysols and Histosols. Correspondingly, the thermal properties indicated the incorporation of these compounds into FAs by chemical bonds of larger thermal stability. Statistical evaluation by principal component analysis of Py‐FIMS clearly supported the differentiation of FAs according to the origin from topsoils and ground water, different soil types, and land use and peat degradation. Hence, it is concluded that water soluble FAs can be utilized as objective ecological indicators for soil effects on adjacent ground and surface waters.     

ORIGIN AND COMPOSITION OF MINERAL CONSTITUENTS OF FEN PEATS FROM EASTERN POLAND

The main constituents of peat include floral remains (in a various degree of humification), peat humus, and mineral constituents of biotic and non-biotic origin. The organic content is considered to be the main parameter that decides about physical and chemical properties of peat. However, the content and composition of mineral constituents of silted (high-ash) peats may cause differences in chemical and physical properties in comparison to the unsilted (low-ash) peats. Therefore, the identification of mineral content, as well as chemical and mineral composition of inorganic constituents, is essential to predict the properties of silted peats. The aim of this study is to determine the content, composition and the origin of mineral constituents of three fens from the Lubartów Plateau (Eastern Poland).     

Effects of chemical conditions in re-wetted peats on temporal variation in microbial biomass and acid phosphatase activity within the growing season

Possible effects of chemical alterations in peat following re-wetting on their microbial characteristics are insufficiently known. Microbial biomass carbon (C_mic), nitrogen (N_mic), phosphorus (P_mic) and acid phosphatase activity were investigated in re-wetted virtually undisturbed and differently degraded peatlands (Histosols) in northeast Germany to assess re-wetting effects on microbial biomass production and phosphorus (P) cycling in one growing season. The virtually undisturbed Eutri-Ombric Histosol had the largest content of microbial biomass (C_mic: 2132 mg/kg, N_mic: 309 mg/kg and P_mic: 48 mg/kg; means of six sampling dates, upper 10 cm). Increasingly lower contents of microbial biomass were observed in the more strongly degraded peats of two Ombri-Sapric Histosols. Furthermore, the proportions of P_mic as a percent of total P (P_t) were smallest in the strongly degraded Ombric-Sapric Histosol (1.6% of P_t) and gradually larger with better peat conservation (2.6% of P_t in the moderately degraded Ombri-Sapric Histosol and 3.0% of P_t in the virtually undisturbed Eutri-Ombric Histosol). The acid phosphatase activity was always greatest in May, irrespective of peat degradation. This maximum was lower for the Eutri-Ombric Histosol (2633 μg nitrophenol/(g h)) than for the two Ombri-Sapric Histosols (3963 and 3212 μg nitrophenol/(g h)). In the two degraded peats, the temporal variation in phosphatase activity was also more pronounced. Our results, in particular the higher peak phosphatase activity combined with an incorporation of P into microbial biomass, indicate that peat degradation may enhance the phosphate input to soil solution. Thus, it is concluded that modified biological P cycling could contribute to increased risks of P losses to adjacent surface water after re-wetting of degraded peats.     

Rearrangement of bacterial community structure during peat diagenesis

The relationship between microbial diagenesis of Sphagnum peat (SP) and reed-sedge peat (RSP) and the spatial organization of peat bacterial communities was studied. Peats were aerobically incubated at 18-22 °C for 4 months. Changes in molecular composition of peat organic matter were monitored with solid-state ¹³C NMR, and the respective amount of functional groups was determined by integration of corresponding peaks. No abiotic peat transformation was detected. SP diagenesis caused about a 4% loss of parent materials with a similar yield of ketones, phenols, aromatic, and carbonyl compounds; whereas about 20% of RSP carbohydrates, along with ketones and methoxyl compounds were gradually transformed into carbonyl and aliphatic compounds. SP and RSP substantially varied in bacterial composition. To address spatial community structure, bacterial populations were dissected by a differential elution technique into three fractions based on the degree of their attachment to peat. Community composition was surveyed with T-RFLP (HhaI, MspI, and RsaI). The fragments were further attributed to freely-dispersed (FD), particle-associated (PA), or omnipresent (OMN) bacterial fractions. In both peats, bacterial communities have gradually shifted with the progress of diagenesis. In SP, numbers of exclusively FD or PA bacteria slightly decreased while in RSP their numbers more than doubled after 4-month incubation, and the number of OMN bacteria respectively decreased. The substantially greater changes in the spatial structure of RSP bacterial community compared to SP were consistent with the chemical transformations detected in these peats suggesting the diagenesis-driven divergence of RSP bacterial community into FD and PA sub-communities.     

New classification systems for tropical organic-rich deposits based on studies of the Tasek Bera Basin,Malaysia

Most schemes in common use for field and laboratory classification of peats were developed in boreal and humid temperate regions and do not recognize the distinctive features and specific uses of tropical peats, such as those of the Tasek Bera Basin in tropical Peninsular Malaysia. The important aspects of peat texture (morphology of constituents and their arrangement) and laboratory ash content (residue after ignition) need modification to be valuable for classifying these and other tropical peat deposits. In the Tasek Bera Basin, most of the deposits would not be considered as peat according to some classification schemes, even though most have C contents >25%. We propose a new three-group (fibric, hemic, sapric) field texture classification applicable to tropical organic deposits, which is similar to the system of the US Soil Taxonomy. The classification is based on the following factors: (1) visual examination of the morphology of the peat constituents (texture); and (2) estimates of fiber content and matrix (finest fraction of peat consisting of highly humified organic matter and inorganic material). The classification is applicable to all organic deposits with <65% ash (i.e., >35% loss on ignition). We also present a new laboratory classification of organic soils based on ash and C content. The US Soil Taxonomy classifies organic soils as having more than 12–18% organic C, depending on clay content. Ash content and these limits for organic soils allow the discrimination of four main groups: peat, muck, organic-rich soil/sediment and mineral soil/sediment. Peat is defined as having an ash content of 0–55%, muck 55–65%, organic-rich soil/sediment 65–80% and mineral soil/sediment 80–100%. The peat class is further subdivided into very low ash (0–5%), low ash (5–15%), medium ash (15–25%), high ash (25–40%) and very high ash (40–55%) subclasses.     

Sequentially extracted phosphorus fractions in peat‐derived soils

Phosphorus (P) forms were sequentially extracted from peat derived soils (Eutric Histosols and Gleysols) at eight sites in Saxony‐Anhalt (Germany) to disclose general differences in P pools between mineral and organic soils and to investigate effects of peat humification and oxidation in conjunction with land use and soil management on the P status of soils. Overall 29 samples providing a wide variety of basic chemical properties were subjected to the Hedley fractionation. The Histosol topsoils contained more total P (P_t) (1345 ± 666 mg kg^—1) than the Gleysol topsoils (648 ± 237 mg kg^—1). The predominant extractable fractions were H₂SO₄‐P (36—63 % of P_t) in calcareous and NaOH‐P_o (0—46 % of P_t) in non‐calcareous Histosols. These soils had large pools of residual P (13—93 % of P_t). Larger contents and proportions of P_o and of labile P fractions generally distinguished organic from mineral soils. Regression analyses indicated that poorly crystalline pedogenic oxides and organic matter were binding partners for extractable and non‐extractable P. Intensive management that promotes peat humification and oxidation results in disproportional enrichments of labile P fractions (resin‐P, NaHCO₃‐P_i, and NaHCO₃‐P_o). These changes in P chemistry must be considered for a sustainable management of landscapes with Histosols and associated peat derived soils.     

Morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra

The morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra are characterized. The soils developing in the areas of barren peat circles differ from oligotrophic permafrost-affected peat soils (Cryic Histosols) of vegetated peat mounds in a number of morphological and physicochemical parameters. The soils of barren circles are characterized by the wellstructured surface horizons, relatively low exchangeable acidity, and higher rates of decomposition and humification of organic matter. It is shown that the development of barren peat circles on tops of peat mounds is favored by the activation of erosional and cryogenic processes in the topsoil. The role of winter wind erosion in the destruction of the upper peat and litter horizons is demonstrated. A comparative analysis of the temperature regime of soils of vegetated peat mounds and barren peat circles is presented. The soil–geocryological complex of peat mounds is a system consisting of three major layers: seasonally thawing layer–upper permafrost–underlying permafrost. The upper permafrost horizons of peat mounds at the depth of 50–90 cm are morphologically similar to the underlying permafrost. However, these layers differ in their physicochemical properties, especially in the composition and properties of their organic matter.     

Hydrophysical Properties of the High-Ash Lowmoor Peat Soils

The water retention curve (WRC), density, botanical composition, and ash contents were determined for high-ash lowmoor peat soils (Rheic Sapric Histosols) developing on the floodplain of the Yakhroma River (Moscow oblast) from the herb–hypnum and hypnum peat enriched in carbonates, agromineral peat soils (Rheic Drainic Sapric Histosols (Mineralic)), and peat soils developed from woody peat underlain by herb, sedge, and woody peat layers (Rheic Sapric Histosols (Lignic)). The WRC was determined by capillarimetric method in the range of water pressure from 0 to 80–90 кPa. For the studied peat soils, the WRC represents a close to linear dependence of the water content on the water pressure in semilogarithmic scale. In contrast to mineral soils, a characteristic point of the air-entry pressure is virtually absent on the WRC of peat soils. The WRC of peat largely depended on their density: denser peat samples were characterized by a higher water content at the same water pressure, which attests to the increased water retention capacity. An increase in the degree of decomposition of peat and its ash content also leads to the rise in the water retention capacity, but the effect of these factors is considerably smaller than the effect of peat density.     

Effect of sewage sludge on nitrogen availability in peat

Summary We studied the effect of incubating peat with lime and sewage sludge in small proportions on biological activity and N mineralization. The peat response was dependent on pH and, in acid peats, on mineralization capacity. In acid peats, the addition of sewage sludge inhibited biological activity. Only the most eutrophic peats (Herbosa) responded with accelerated mineralization. The addition of lime to acid peats favoured organic matter mineralization, shown by a greater CO₂ release. The best results were obtained by adding lime and sewage sludge together. In saline peats, the best N levels were obtained without incubation.     

Microbial Biomass and Its Structure in Karst Peats of Tula Oblast

Eurasian Soil Science - Microbial biomass and its structure in karst peats (Eutric Fibric Histosols), Dystric Fibric Histosols) in Tula oblast were studied by luminescent microscopy. The microbial...     

Water Repellence of Cultivated Organic Soils

Abstract

A range of cultivated organic soils was studied with respect to water repellence. All soils were wettable above a water content of approximately 30-50 % (v/v). Below this critical content, most soils showed a varying degree of water repellence. Well decomposed peat had lower infiltration rates than moderately decomposed peat. Lightly crushing the peat soil before measurement increased the infiltration rate compared with an undisturbed soil sample. In tests with aqueous ethanol of different molarity, peat soils showed greater repellence than gyttja soils. All moss peat layers were extremely water repellent and fen peats slightly less repellent. Water repellence did not occur on gyttja clay and marl gyttja.     

Decomposition of organic matter in peat soil in a minerotrophic mire

Decomposition of organic materials, oxygen consumption, and carbon dioxide emission were investigated in Masukata mire, a small minerotrophic mire in central Japan. We selected three dominant community types in the mire, a Sphagnum palustre community, a Phragmites australis community, and an Alnus japonica community, for the decomposition study sites. Decomposition rates were measured in the field by examining mass loss of peat and cellulose for 6 months. The oxygen consumption rate was measured in the field using a closed chamber equipped with an oxygen electrode. The carbon dioxide emission rate of the peat was measured by an infrared gas analyser in the laboratory under controlled conditions. Results of these measurements were tested by correlation analysis. The rate of mass loss of peat positively correlated with the CO₂ emission rate. The cellulose decomposition rate showed significant differences among community types, and it had significant positive correlation with the oxygen consumption rate. Although oxygen consumption measurement is not generally used to estimate peatland soil respiration, the oxygen consumption method can be used for predicting long-term decomposition rate according to different vegetation types within a short time.     

An evaluation of the functional significance of peat microorganisms using a reciprocal transplant approach

Our current knowledge on the relevance of microbial diversity and composition for the recovery and maintenance of soil biological processes is rudimentary, partly because experimental substantiation of the importance of community composition to function is scarce. Guided by this gap, we devised a reciprocal transplant experiment to examine the functional behaviour of different microbial communities exposed to two structurally distinct peats. Sterile peat samples representing two types, one humified (sedge) and the other dominated by coarse plant material (fibric), were inoculated with a 10⁻¹, 10⁻³, 10⁻⁵, or 10⁻⁸ dilution of either the same or reciprocal peats. After 5 months of incubation, we used a nucleotide-analog technique to label the active bacterial taxa in samples receiving the 10⁻¹ and 10⁻⁸ dilutions. We assessed both the peats' functional potential (respiration and nutrient-acquiring and lignin-degrading enzyme activities) and the structures of active and total bacterial communities (PCR-DGGE). In general, we found a decline in respiration rates and increase in enzyme activities with increasing dilution level, but the effect of dilution on bacterial richness was weak. The bacterial community structure and richness depended on both the inoculum source and the peat type. The activity of enzymes involved in nutrient acquisition depended mainly on the soil type, while the lignin-degrading activity was influenced by differences in community composition between peat types. Neither active bacterial populations nor respiration were significantly influenced by peat type or inoculum source. Our results suggest that the relationship between microbial community composition and function is not only related to the taxonomic breadth of the taxa that perform a given function, but may also be shaped by interactions between microorganisms in the inoculum source and the substrate being colonized.     

THE PRESERVATION OF PEAT MONOLITHS FOR PERMANENT DISPLAY

Techniques for preparation and preservation of peat soil monoliths for display purposes are described. Impregnation with a low molecular weight polyethylene glycol polymer has been found to be extremely effective in stabilising the natural structural features of peats.     

Specific features of the development of soils of hydromorphic ecosystems in the northern taiga of Western Siberia under conditions of cryogenesis

Differently directed and heterochronous cryogenic processes have contributed to the contrasting soil cover patterns and spatial heterogeneity of the properties of soils in hydromorphic ecosystems of the discontinuous permafrost zone of the northern taiga in Western Siberia. Frost heave and permafrost thawing within ecosystems of highmoor bogs have led to the development of specific cryogenic landforms, such as flat-topped and large peat mounds. A set of cryogenic soils is developed in these ecosystems; it includes different variants of cryozems, gleyzems (Cryosols), and peat soils (Histosols). The distribution of these soil types is controlled by the local topography and thawing depth, other factors being insignificant. Alternation of peat horizons of different types and ages, whirl-like patterns of horizon boundaries, considerable variations in the thickness of soil horizons, and inversions of soil horizons under the impact of frost cracking, frost heave, and cryoturbation are typical of the considered soils. Thawing depth is the most significant factor affecting the thickness of organic horizons, the soil pH, and the degree of decomposition of peat. As a result of the upward movement of bog ecosystems under the impact of frost heave, peat soils are subjected to considerable transformation: peat horizons undergo mineralization, and the thickness of organic horizons decreases; in some cases, eluvial–illuvial differentiation of the mineral horizons takes place, and peat podzols are developed. However, the opposite process of the return of the soils to the bog stage of pedogenesis with peat accumulation may take place in any time in the case of activation of thermokarst processes.     

Applicability of thermal methods for characterization of peats and plants

Differential thermogravimetric (DTG) and differential thermal analysis (DTA) curves were obtained for some peat materials and peat-forming plants. Four peats were selected on the basis of botanical composition and degree of decomposition. Granulometric fractions and holocellulose preparations from the peats were also analyzed.

The DTG curves showed three main regions of weight loss: the first at 275°–325°C the second at 360°–460°C and the third at 500°–560°C. The first region with a peak at 300°C was by far the most important. It was associated with cellulosic materials which may reflect the degree of decomposition. The size of the 300°C peak could be used for measuring holocellulose in peats, and this might be a valid substitute for chemical means for that measurement, specially in more decomposed peats.

The nature of the 300°C peak did not change significantly with changes in particle size, although the position of the 420°C peak was shisfted toward lower temperatures as particle size decreased. The original features of the peats were generally retained in the separates. Even though the predominance of residues from one species of plants in a particular peat did not greatly influence the shape of the DTG curves, some generalizations concerning the botanical sources of peats were obtained.

In a comparison of DTG and DTA methods, the former appears to provide more useful information on the chemical make-up and on the degree of decomposition of peats.     

FTIR spectroscopy can be used as a screening tool for organic matter quality in regenerating cutover peatlands

Vegetational changes during the restoration of cutover peatlands leave a legacy in terms of the organic matter quality of the newly formed peat. Current efforts to restore peatlands at a large scale therefore require low cost and high throughput techniques to monitor the evolution of organic matter. In this study, we assessed the merits of using Fourier transform infrared (FTIR) spectra to predict the organic matter composition in peat samples at various stages of peatland regeneration from five European countries. Using predictive partial least squares (PLS) analyses, we were able to reconstruct peat C:N ratio and carbohydrate signatures with reasonable accuracy, but not the micromorphological composition of vegetation remains. Despite utilising different size fractions, both carbohydrate (<200 μm fraction) and FTIR (bulk soil) analyses report on the composition of plant cell wall constituents in the peat and therefore essentially reveal the composition of the parent vegetational material. The accuracy of the FTIR-based PLS models for C:N ratios and carbohydrate signatures was adequate to allow for their use as initial screening tools in the evaluation of the present and future organic matter composition of peat during monitoring of restoration efforts.     

Implications of soil substrate and land use for properties of fen soils in North-East Germany Part I: Basic soil conditions,chemical and biological properties of topsoils

Abstract

The objective of the paper was to analyse the implications of the origin of peat (muck) soil substrate, the current type of land use and the state of anthropogenic soil development for the topsoil properties of fens. Chemical and biological properties of peat soils of the Rhin-Havelluch lowland and the Uckermark rural landscape were analyzed. The unit water content according to Ohde and the ash content were utilized to characterize the anthropogenic development status of peat topsoils. Several chemical properties were significantly influenced by soil substrate, in particular by the proportion and kind of the mineral component. The substrate was associated with the hydrological type of mire and the soil development state. TOC/N ratio and microbial activity were increased in cases of high lime spring mires and moorshified low ash peat. The proportion of easily soluble organic carbon increased, whereas the sulphur content decreased with the soil development state. The nitrogen content and the proportions of oxalate soluble iron and aluminium reached maxima in the moorshified state. The type of land use (grassland, forest) significantly influenced the topsoil pH and the proportion of oxalate soluble phosphorus. Soils under forest were clearly determined by topsoil acidification.