Identification of Peat Profile, Physicochemical Properties and Microstructures on Different Peat Soil Vegetation Types
Nurul Irah Fazirah Sapar1, Siti Jahara Matlan1*, Rohaya Alias2, Aniza Ibrahim3
1 Civil Engineering Programme, Faculty of Engineering, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia.
2 Faculty of Civil Engineering, Universiti Teknologi MARA Pahang, 26400 Jengka, Pahang, Malaysia.
3 Faculty of Civil Engineering, Universiti Pertahanan Nasional Malaysia, 57000 Kuala Lumpur, Malaysia.
*Corresponding Author: [email protected] Accepted: 15 February 2022 | Published: 1 March 2022
DOI:https://doi.org/10.55057/ajfas.2022.3.1.3
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Abstract: Peat commonly known as highly organic soil, is a key issue at tropical and coastal infrastructure building. As a result, understanding the peat's characteristics is critical. To investigate the characteristics of several peats in Sabah is the purpose of this study. For this study, peat samples were taken from two different locations in the Beaufort Sabah, namely Klias and Lumadan, with different land vegetation types. Field work and laboratory testing were aimed to figure out the degree of humification and peat depth, as well as the physical and chemical properties of the peat. In addition, EDX and SEM tests were conducted to study the peat's chemical composition and its microstructural characteristics. The outcome shows that Klias and Lumadan samples are under classification of hemic (pseudo-fibrous) peat, which displays H6 to H7 on the von Post scale, indicating an intermediate degree of breakdown. Both research sites show different peat depths of 4 and 4.5m, respectively. The moisture content, organic content, fibre content, specific gravity, liquid limit, and acidity of peat from Klias to Lumadan sites are found to be different. Chemical composition shows that the peat sample in Klias contains more elements of carbon compared to the Lumadan sample. The SEM result of Klias peat samples is made up of fibres that are woody, porous in nature and shows a little looser fibric arrangement. In contrast, the SEM result for Lumadan samples are lack on organic matter and fibre in soil, shows flaky granular nature and low quantity of void pores than the Klias sample. In this study, the SEM results are used to support the findings of the field and laboratory tests.
Keywords: Peat profile, physicochemical, SEM-EDX, vegetation difference, Sabah
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1. Introduction
Peat is a mushy soil with a lot of organic matter and moisture yet able to be found everywhere except at deserts and cold regions [1]. Around 1 billion acres of peat land are believed to exist in the world, accounting for around 4.5 percent of total land area [2]. Malaysia is the 9th country in the world with the most total region of peat soil, according to a global chart of total peat deposit [3]. According to the Malaysian Department of Environment and the Ministry of Energy, Science, Technology, Environment, and Climate Change [4], peat soils cover approximately 2.56 million ha (roughly 7.74 percent) of Malaysia's total land area. In Malaysia, agriculture and oil palm
plantations account for more than 60% of peatland area [5]. Sarawak has the most peat soils in Malaysia, with 1,645,585 ha, or 64.27 percent of the total peatland area, followed by Peninsular Malaysia (714,156 ha, or 27.89 percent), and Sabah (200,600 ha, or 7.83 percent). Peat deposits are mostly found around the shore. The Lower Kinabatangan River and Klias Forest Reserve contain the majority of these peats. The arrangement of peat soil areas in Malaysia is depicted in Figure 1 [4].
Figure 1: Distribution of peat soil areas in Malaysia
Peat has accumulated over the last 20,000 years, according to Hobbs [6]. Peat is made up of dead plants that decompose slowly in an acidic environment and under waterlogged conditions below the water table. Hashim and Islam [7], have found that there are two types of peat deposits that are shallow and deep peat deposits. Less than 3m thick for shallow peat, and more than 5m thick for deep peat deposit in Malaysia is. Peat is a type of soil that contains a lot of dead organic matter.
The rationale for peat accumulation is same throughout the world, but the sort of peat that forms varies owing to climate, soil type, and local vegetation [8]. According to Huat [9], the composition of peat soil changes depending on location owing to variables such as origin fibre, temperature, and humidity. Long-term geological changes encouraged soil and organic matter deposition through various phases of decomposition, culminating in the development of peat at the location.
Meanwhile, peat's tendency to decompose with time adds another layer of complexity [10]. This underlines the significance of better knowing the qualities of peat in specific places in order to avoid future difficulties.
The existence of organic matter in the soil has been shown to affect the quality of the soil's geotechnical and engineering properties [11]. Peat soils are considered problematic soils owing to their unpredictability due to their low shear strength and high compressibility. As a result, peat soil is regarded as unfit for use as a foundation. Several researchers have investigated the physical and engineering properties of soft or peat soil stabilization [2, 7, 12-18]. The physical and chemical properties, as well as morphological characteristics of organic soils and peat soils have been
discussed by a limited number of researchers [19-23]. The majority of these studies, however, have been conducted in Peninsular Malaysia and Sarawak, with little research on the physicochemical features of peat or highly organic soil from Sabah [24]. As a result, the current study focuses on the physicochemical properties and microstructural characteristics of peat soil samples from Sabah in order to acquire a better understanding of their behavior.
2. Materials and Methods
2.1. Sampling Location
Throughout this work, disturbed soil samples were collected from two distinct locations and tested for physicochemical parameters at depths ranging from 0.5m to 1.0m below ground level.
Furthermore, the chemical composition and microstructural properties of diverse peat soil samples were investigated using Energy-Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Micrographs (SEM). Figure 2 depicts the collection sites, which are labelled Klias Site (5°19'34.3"N, 115°40'22.1"E) and Lumadan Site (5°17’11.2”N, 115°40’52.6”E), along with differences in local vegetation. Klias is made up of oil palm trees, whilst Lumadan is made up of rubber and agarwood trees (i.e., Gaharu).
Figure 2: Klias and Lumadan on a map in Beaufort, Sabah, with different land vegetation types
2.2. Field Survey and Observations
In accordance with the von Post scale [25], the Klias sample comes into the H6 to H7 humification range, while the Lumadan sample falls into the H6 humification group. The plants' remains were also found to be quite pasty and had lost several of its distinguishing features, but some could still be identified. Karlsson and Hansbo [26] classified this peat as hemic (pseudo-fibrous) peat, which has a von Post scale of H6 to H7, indicating an intermediate degree of decomposition. Groundwater levels were measured in the field at both research sites in mid-January and early August 2020.
Groundwater levels at both study sites suggest that it is shallow, ranging from 0.2 to 0.6 meters below the ground surface. Local meteorological conditions, which endure rainy and dry seasons
throughout field investigations, are thought to influence groundwater level fluctuations in these places [39].
Furthermore, the thickness of the peat layer at the Klias and Lumadan study sites is assessed at 4 and 4.5m depths, respectively, using the peat sampler method. According to Hashim and Islam [7], shallow peat deposits are usually less than 3 meters thick, whereas deep peat deposits in Malaysia are more than 5 meters thick. Consequently, peats in this research are categorized as intermediate deposit thickness. The measured thickness of the peat layer at the Klias and Lumadan sites are shown at Figure 3.
(a)
(b)
Figure 3: Measurement of peat thickness at two study sites: (a) Klias (b) Lumadan
2.3. Sample Preparation and Laboratory Testing Procedure
Refer to standard procedures, all laboratory tests are carried out. Moisture content (BS1377: Part 2: 1990, Clause 3.2), organic content (BS1377: Part 3: 1990, Clause 4.0), fibre content (ASTM D1997-91), specific gravity (BS1377: Part 2: 1990, Clause 8.3), liquid limit (BS1377: Part 2: 1990, Clause 4.3), and pH value (BS1377: Part 3: 1990, Clause 9.0) are among the physical and chemical characteristics tests performed in the laboratory. The peat soil samples were first dried, ground, and sieved before being utilized for various physical property tests.
The Energy-Dispersive X-ray Spectroscopy (EDX) test is used to assess the basic chemical composition of peat samples. The tests were carried out using Quantax 200, Bruker brand equipment. From the test, images, graphs, and element analysis are produced. Scanning Electron Micrographs (SEM) were used to examine the microstructural features of Klias and Lumadan peat samples. For the SEM test, Hitachi S-3400N Variable Pressure equipment was employed.
Micrographs of both samples were taken at magnifications of 20µm.
3. Results and Discussion
Table 1 below presented the basic characterization of peat samples from the Klias and Lumadan sites. The values in the table correspond to the average value based on several lab trials.
Table 1: Peat Properties of Klias and Lumadan Sites Parameter Unit Klias Site Lumadan Site
Moisture Content % 673.99 630.35
Organic Content % 99.42 56.63
Fibre Content % 67.03 61.28
Specific Gravity - 1.22 1.57
Liquid Limit % 171 158
pH of Peat - 3.0 3.5
3.1. Physical Properties of Peat
The moisture content of Klias samples is higher than that of Lumadan samples, resulting in an average range of 630 to 674 percent for the areas (Table 1). The ground water level in the research locations, which is at a depth of 0.2 m to 0.6 m below the ground, influences the high value of moisture content. The natural water content of East Malaysian peat, according to Huat [9], ranges from 200 to 2207 percent. As an outcome, the results of this study's samples from the Klias and Lumadan locations are within the typical peat soil moisture content.
Organic content is essentially plant waste and vegetative stuff whose accumulation rate is greater than its degradation rate. The value in Table 1 is illustrated in several places of peat in Beaufort, and it appears to fluctuate in the average range of 56 to 99 percent. Klias samples were likewise found to have greater organic material than Lumadan samples. These findings reveal that the organic content of peat increases with the soil wetness rate in the research area. In addition, the characteristics of distinct plants—where the Klias site comprises of oil palm while the Lumadan site consists of rubber trees and agarwood (i.e., Gaharu)—could be factors influencing the outcomes. According to Huat et al. [27], biochemical processes take place for vegetative components that accumulate with the help of water, sunshine, internal temperatures, macro and microbes, and anaerobic circumstances, ultimately culminating in the synthesis of a percentage of organic matter. These characteristics are thought to vary by country or region and are influenced by deposits, fibre sources, temperature, and humidity [28]. The Klias and Lumadan samples can be classified as peat or highly organic soil, according to the definitions of the various disciplines [27, 29].
Fibre in peat masses has a big impact on shear strength and soil compressibility characteristics.
Refer to the results table, the fibre content in Klias and Lumadan peat samples appears to range between 61 and 67 percent on average. The fibre content of Klias samples was found to be higher than that of Lumadan samples. Based on the amount of fibre in the peat, ASTM D1997 [30], it can be determined that the Klias and Lumadan samples were moderately degraded, commonly known as hemic peat, with fibre content ranging from 30 to 67 percent.
Soil mineralogy is the key determinant of soil specific gravity [31]. The specific gravity of peat samples collected from the Klias and Lumadan sites are shown in Table 1. According to the findings, the specific gravity of peat samples collected at the Klias site is lower than that of peat samples collected at the Lumadan site, with average values of 1.22 and 1.57, respectively. This is
due to the greater fibre content of Klias samples. These findings are also supported by Huat, Asadi, and Kazemian [28], who found that when the amount of organic material increases, the specific gravity of peat or organic soils decreases. Prior research [32-35] indicates that the specific gravity of tropical peat typically ranges from 1.0 to 1.7. The specific gravity of several types of peat was also determined by Paul et al. [10], and it ranged from 1.22 to 2.36. As a result, the findings of this study agree with previous findings.
Table 1 also includes the results of the liquid limit testing. Klias samples had a higher liquid limit value than Lumadan samples, with an average value of 171 and 158 percent, respectively. Klias samples have a slightly higher liquid limit value than Lumadan samples because the soil includes more fibre, resulting in a higher water absorption capacity. This conclusion statement is supported by Kolay et al. [20]. Besides, the moisture and organic content of the Klias samples were greater. According to Huat, Asadi, and Kazemian [28], as organic content increases, so does the liquid limit. According to Paul et al. [10], the variation in liquid limit values ranges from 69 to 413 percent for different types of peat. As a result, the findings of this study agree with previous studies.
3.2. Chemical Properties of Peat
A soil's acidity or alkalinity is measured by its pH, which is a chemical property. The acidity of peat is determined by rock types, plant species, oxygen availability, and humic acid concentration [36]. Table 1 shows the pH value of peat at the Klias and Lumadan sites. The result shows that the pH value of peat for the area is in the average range of 3.0 to 3.5. In summary, the pH value of peat samples from the Klias site is lower than that of peat samples from the Lumadan site. As a result, Klias samples are more acidic, which may be due to their organic content. According to various observations [37, 38], the peat samples from the Klias and Lumadan locations have the same pH value as the average peat soil.
Based on spot analysis for the Klias peat sample, the chemical elements identified by EDX were Carbon (57.72%), Nitrogen (2.73%), Oxygen (12.76%), Iron (0.74%), and Gold (26.05%) in accordance with the 100% by weight shown in Table 2 and Figure 4(b). Carbon was the most abundant element discovered in the Klias peat sample. By comparing the Klias peat with Lumadan peat, it was found that the Klias peat sample did not have elements such as Aluminum, Silicon, and Potassium.
Table 3 and Figure 5(b) show the chemical elements that are found in the Lumadan sample by using EDX. The components that were identified are Carbon (45.80%), Oxygen (17.82%), Aluminum (10.08%), Silicon (8.42%), Potassium (0.94%), Iron (0.87%) and Gold (16.08%). The ratio stated is in accordance with 100% by weight. The major element is Carbon, although the percentage amount is slightly lower than in the Klias peat sample. Aside from the elements Carbon, Oxygen, and Iron, both Klias and Lumadan samples contain the element Gold (Au). Previous research has found that the amount of Au in peat-forming vegetation agrees with this mechanism [40]. Plants have a higher gold content than the peat made from them, according to this information. Given that the domed peat bog is predominantly supplied by atmospheric precipitation, as well as capillary ground water uptake and nutritive matter extraction from the underlying soils by the plant root system, it is plausible to conclude that ground water is the primary source of gold. Plants take ionic gold from the water horizons beneath them.
Table 2: Chemical components found in Klias peat sample by using EDX
Element Weight, % Atomic, %
Carbon 57.72 80.86
Nitrogen 2.73 3.28
Oxygen 12.76 13.42
Iron 0.74 0.22
Gold 26.05 2.23
(a) (b)
Figure 4: SEM image and chemical composition of peat soil samples from the Klias study site
Table 3: Chemical components found in Lumadan peat sample by using EDX
Element Weight, % Atomic, %
Carbon 45.80 66.65
Oxygen 17.82 19.46
Aluminum 10.08 6.53
Silicon 8.42 5.24
Potassium 0.94 0.42
Iron 0.87 0.27
Gold 16.08 1.43
(a) (b)
Figure 5: SEM image and chemical composition of peat soil samples from the Lumadan study site
2 4 6 8 10 12 14
keV 0
10 20 30 40 50
cps/eV
C
N O
Fe Fe
Au
Au Au
Au
2 4 6 8 10 12 14
keV 0
2 4 6 8 10 12 14 16 18 20 22 24 cps/eV
C
O Al
Si
K K
Fe Fe
Au
Au Au
Au
3.3. Microstructural Characteristics of Peat
Figures 4(a) and 5(a) shows SEM images of peat soil samples from the Klias and Lumadan study sites. Klias soil samples, as shown in Figure 4(a), are fiber-rich, woody, and porous in nature. Klias samples have fibric patterns that are slightly loose that result in bigger voids that appear as dark gaps. Moreover, the remnants of cell walls, small stems, and rootlets in the Klias sample are fairly considerable. In other words, the Klias sample has a more porous space structure since its soil has more fibrous and organic content. Peat is more compressible and porous in nature due to the presence of highly perforated particles [20].
Lumadan samples have fewer organic materials and fibre than Klias samples, as well as a flaky granular texture and fewer empty pores, as seen in Figure 5(a). The presence of flaky structures in the SEM image indicates that the peat has low shear strength and a high compressibility [21]. The SEM results in this study describe the microstructures of hemic peat (pseudo-fibrous), which refers to the intermediate degree of breakdown between H6 and H7 with different land vegetation types.
4. Conclusions
The peat profiles, physicochemical parameters, and microstructural properties of peat soil samples from Klias and Lumadan in Beaufort, Sabah, are investigated in this study. The following are some of the study's conclusions:
1) Klias and Lumadan peats were classified as hemic (pseudo-fibrous) peats, with von Post scales ranging from H6 to H7 indicating an intermediate degree of decomposition. The depth of the peat profile varies according to the study site.
2) According to the results of moisture content, organic content, fibre content, specific gravity, liquid limit, and acidity, peat physical qualities differed from Klias to Lumadan locations.
The difference in peat physical qualities between Klias and Lumadan sites is attributable to each area's own unique mix or difference in vegetation composition, resulting in distinct features.
3) The chemical composition of the peat samples at both study sites reveals that the elements present are influenced by the type of soil plants, groundwater level, and local climate conditions.
4) According to microstructural investigation, peat samples have slightly varied features. The Klias samples are made up of fibres and appear to be woody and porous, whereas the Lumadan samples resemble flaky granular peats. These features help to describe the decomposition properties of peats.
Acknowledgement
This research would not have been possible without the financial support granted by Universiti Malaysia Sabah (Grant Code: GUG0384-2/2019).
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