American Journal of Climate Change
Vol.08 No.01(2019), Article ID:90680,16 pages
10.4236/ajcc.2019.81006

Organic Carbon Storage in the Tropical Peat Soils and Its Impact on Climate Change

Md. Jashim Uddin, A. S. M. Mohiuddin, Masud Hassan*

Department of Soil, Water, and Environment, University of Dhaka, Dhaka, Bangladesh

Copyright © 2019 by author(s) and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY 4.0).

http://creativecommons.org/licenses/by/4.0/

Received: December 25, 2018; Accepted: February 19, 2019; Published: February 22, 2019

ABSTRACT

Soil carbon is one of the essential elements for soil quality, holding soil nutrients for plant uptake, soil conservation, and overall the natural soil systems that are the fundamental requirements for the soil security, and food production. Moreover, Peat soils are the vital storehouses of organic carbon where there is a scope to use this carbon for mitigating climate change. In this study, we consider three major soil series of peat soils in Bangladesh: sapric peat, hemic peat, and fabric peat. Single study on the estimation of organic carbon stocks in the peat soils of Bangladesh was conducted in the 1970s. For understanding the carbon emission, we conducted the same peat soils up to 100 cm depths. The research shows that the organic carbon in peat soils in Bangladesh was about 0.12 Pg in 2018 whereas it was about 0.25 Pg during the 1970s. So, it has observed that soil organic carbon loss is alarming in the tropical country like Bangladesh and the half of the total organic carbon has already reduced by the last 50 years. These reduced carbons have huge impact on climate change and global warming. It has also found that the carbon storage percentage is higher with the increasing soil profile depth from the soil surface. So, the management should be considered not only the surface soils but also the sub-surface soils. Another relationship found between the bulk density and carbon storage is inversely proportional (r = −0.65) in the peats soils. These peat soils are losing their carbon due to the decrease of inundation level by climate change, intensive agricultural and even used as fuel for cooking purposes by the local stakeholders. There were no regulations, maintenances, laws, even the evaluation and assessment of carbon storage was not appropriately estimated in Bangladesh. By representing the carbon percentage data and their changes over times will help to develop and implement the proper mitigation action which may improve soil health, soil quality, food security, and mitigation of climate changes.

Keywords:

Peat Soils, Organic Carbon, Carbon Storage, Bulk Density, Soil Conservation, Global Warming

1. Introduction

The soils are the fundamental natural resources for the human civilization. Typical soils are mainly composed of minerals (45%), organic matter (5%), water (25%) and air (25%). However, for the peat soils, the soils organic percentage varies from 20% - 50%. Peat belongs to a group of soils called “HISTOSOLS.” Peats soils are mainly found in clay dominants soils, low land soils, and soils from mangroves forest [1] [2] [3] . The soils organic carbon storage (SOC) represents an essential function of soils that are the most effective factor for climate regulations and soil functions [1] . However, it can also be the reason for carbon emission by microbial and physiochemical activities. Additionally, the percentage of organic carbon is profoundly influencing the presence of inorganic chemical elements [4] . That is why recent attention is for the soil organic carbon storage in peat soils [5] - [18] . The carbon in soils is three times higher than that in the total carbon present in biomass and double than the total carbon present in the atmosphere. Around 1576 Pg of carbon is stored in soils whereas around 506 Pg (32%) of this carbon is found in the tropical soils [19] [20] . It has also expected that 40 percent of the carbon in soils of the tropics can be found in the forest soils [9] . However, peatlands are around 3% of the global soil, but they store around 30% of the world’s soils organic carbon [21] [22] [23] . Peatlands represent a long-term sink for atmospheric carbon dioxide [24] .

Peatlands can be found from almost all over the world, but in the tropical and subtropical region have a higher percentage. Around 88.6 Pg is stored in peatlands worldwide, whereas 68.5 Pg soil carbon (C) (77%) presents in Southeast Asia. The reported evidence of carbon emissions is found in South Asia, USA, Canada, Australia, China, Siberia, Denmark, a Caribbean island, France, Brazil, mangrove forests, and tropical grasslands that have higher emissions rate [24] - [53] . However, most of the peat soils are mainly found in the USA, Western Europe, Eastern Asia, and Central America, Tibetan grassland [52] [54] [55] . Maitra et al. studied the distribution of peat soils in Bangladesh and possible economic uses as fuel [56] . The distribution of peat soils in Bangladesh is highlighting in Figure 1. There are lots of factors that control the carbon storage in the soil including temperature, slope, and elevation. Additionally, pasturing, land use change and vegetation pattern also have considerable influences on the presence of soil organic carbon in peat soils. Land modification on peatlands results in enormous carbon instabilities by deforestation and sweltering [57] [58] .

However, there have several methods and techniques that were studied for carbon sequestration including cropping pattern with or without tillage, biochars application, minerals interaction, impact of irrigation, long and short-term fertilizers application, land use changes, climatic conditions, time, pH, salinity,

Figure 1. A scheme for distribution of peat soil in Bangladesh [59] .

agricultural practices and so on [26] [29] [31] [60] - [69] . So, exploring carbon storage is very much crucial in recent days. There are no studies on the estimation of carbon stocks in the peat soils of Bangladesh in the past few decades. So, there was no adequate data for understanding the depletion rate of carbon from peat soils over the year in Bangladesh. Exploration of this resource may provide valuable information regarding their usage by estimating their storage. The research aims for estimating total carbon storage of peat soil of Bangladesh with details estimation of associated soil series. In this study, the relationship between bulk density and SOC % has been studied, finally, looking for some sustainable management practices for increasing carbon stock. It is very much urgent to take steps for preserving the peatland ecosystem and its soil security for the sake of the better environmental management.

2. Materials and Methods

Peat soils extensively recorded in the beels located in Gopalganj, hoar in Sylhet and Khulna districts [70] . Nine soil profiles were selected that covering the peatland soils of Bangladesh (Table 1). The selections of the profiles were made based on the sapric peat, hemic peat, and fabric peat. Soil color is studied in the field to recognize the nature and types of peat (Table 2). Out of nine profiles, three profiles cover Sapric peat covers three soil series: Hakaluki, Satgaon, and Sarail; hemic peat profiles cover another three soil series: Rajoir, Satla, and Mohonganj; and the fabric peat profiles covers the other three soil series: Harta, Juri, and Tarala. The soil samples were air dried with an oven at 80˚C. The samples were gently ground with rolling and passed through 0.5 mm sieve. The samples

Table 1. List of peat soils of Bangladesh with their areas and USDA names.

Table 2. Indicators that used for differentiating peat maturity in the field.

were preserved in plastic bags for carbon stock analysis. Soil organic carbon was determined by the wet oxidation method as described by Nelson and Sommers [71] . Bulk density was measured by core method as described by Blake [72] . The total soil organic carbon (TSOC) stock or storage was calculated using the equations of Batjes. [7] [73] [74] . It may be noted that the bulk density and SOC concentration (%) are the two prerequisites for estimating SOC stock or storage. Thus, the SOC storage was calculated using the following equations [7] [74] .

Total Soil Organic Carbon ( TSOC ) = SOC i × B i × D i (1)

where SOCi is the soil organic carbon content on the ith layer (g/kg); Bi is the bulk density of the ith layer (g/cc), and Di is the depth of the ith layer (cm).

3. Results and Discussion

Eswaran et al. estimated soil organic carbon contents in the soil orders at the global level [8] . He found 0.25 pg organic carbon in peat soils (Histosols) in Bangladesh [8] . So, the Histosols in Bangladesh occupy more than one million hactor, and it contains 0.25 Pg organic C (Table 3). Hussain et al. estimated that the soils of Bangladesh have a total of 2.2 Pg of organic carbon in 2002 [77] . Possibly, this is the baseline data sets of organic carbon mass in the soils of Bangladesh. SRDI Staff only provides soil organic carbon datasets on soil

Table 3. Organic carbon mass in the soils of the world and Bangladesh.

Pg = Petagram = 1 × 1015 gram (Source: [8] [77] **).

horizon/depths basis but without any bulk density data. This quantity of organic carbon present in the Histosols may be significant as a carbon sink. However, at present, these peats are used for agriculture as well as fuel where carbon is released to the atmosphere after the decomposition of peat. In the tropics, most Histosols are under forest, though most of them are cleared for agriculture and other purposes.

There has a strong relationship with the soil organic carbon storage and bulk density. So, the bulk density study is essential. The mean bulk density distribution in the Hakaluki and Rajoir soil (ranges from 0.62 - 0.63g/cc) is more or less same whereas, in Harta soil (0.53 g/cc), it is lower than the other two soils (Figure 2). Agus noted that the range of peat bulk density is generally about 0.02 - 0.30 g/cc depending on the maturity, compaction as well as the ash contents [78] . It is important to note that, Agus reported that an ideal peat soil that contains 18% - 58% carbon, where its bulk density may vary within the range 0.02 - 0.30 g/cc [78] . They also reported that on average bulk density for Southeast Asia peat lands indicates a broad range and considerable variation depending on their land uses. In Bangladesh, peatlands are mostly used for boro rice, shrimp and vegetable where there is a little scope of soil carbon sink where soil organic carbon is interlinked with bulk density.

From Figure 3, it has been clear that the carbon storage has been increased along with the depth of peat soil that is very different from floodplain soil or general soil profiles. The soil profiles are different from other soil structure. The soil organic carbon storage percentage is getting higher with increasing the depth from the soil surface up to 100 cm of the soil profile. However, from the 60 - 80 cm and 80 - 100 cm, the carbon storage has been increasing significantly which is higher than overall soil carbon storage (Figure 3). So, it should make sure for the management not only just the upper surface but lower sub-surface as well. There has a strong relationship between bulk density and soil organic carbon percentage. The relationship is inversely proportional (Figure 4). With increasing the soil organic carbon shows the lower bulk density.

Figure 2. Bulk density (g/cc) of major, studied peat soil up to 100 depth (Harta, Hakaluki, and Rajoir).

Figure 3. The distribution of soil carbon storage in the major peat soils in Bangladesh with the soil profile depth.

Figure 4. The relationship between the bulk densities with the soil organic carbon percentages of different peat soil.

That means denser soil have more susceptibility to store carbon for having lower air content and their structure. Their relationship is a limited negative correlation (r = −0.67).

SOC distribution in the Harta soils ranges from 10.09 to 21.53 percent from the surface to 100 cm depth, and the mean SOC is 15.03 percent. SOC distribution in the Hakaluki soils ranges from 6.63 to 15.01 percent from the surface to 100 cm depths, and the mean SOC is 11.18 percent. SOC distribution in the Rajoir soils ranges from 12.10 to 28.20 percent from the surface to 100 depths, and the mean SOC is 20.66 percent. So, the SOC distribution in the peat soils of the study site ranges from 11.18 to 20.66 percent (Figure 5). It is important to note that Agus et al. reported that the peat soil that contains 18% - 58% carbon [78] . They also reported that in Southeast Asia, SOC in peatlands varies in a broad range and considerable variation depends on their local land uses and land covers. In Bangladesh, peatlands are mostly used for agricultural purposes where there is a considerable loss of SOC rather than sink. On the other hand, there is no forest cover in the peatlands of Bangladesh as such diversified use of peatland is limited.

SOC storage in the Harta soils varies from 11.27 to 17.76 Kg/m2, and the low storage is about 70.35 Kg/m2. The rice-shrimp integrated cultivation mainly dominates Harta soils. SOC storage in the Hakaluki soils varies from 9.00 to 15.01 Kg/m2, and the low storage is about 61.7 Kg/m2. Hakaluki soils are used for the cultivation of boro rice, and in the dry season, these are used for grazing grassland. SOC storage in the Rajoir soils varies from 19.75 to 26.21 Kg/m2, and the low storage is about 115.56 Kg/m2. Rajoir soils are used for the cultivation of boro rice, and it becomes waterlogged almost for the whole year. So, it was found that SOC storage in the study sites varies from 61.7 to 115.56 Kg/m2 (Figure 5). The variation in the SOC storage possibly due to their land use, inundation level, and land cover variations.

From Figure 5 and Table 4, we can observe that overall carbon storages are present almost in all studied soil series. However, Satla, Harta, and Rajoir contain large peatland than others. However, the carbon stock is evenly distributed almost all soil series of Bangladesh.

Globally around 1576 Pg of carbon is stored in the soil, where 506 Pg of carbon stored in the tropical soils. It has also reported that around 684 - 724 Pg of carbon present in the upper 30 cm, 1462 - 1548 Pg of carbon present in the upper 100 cm, and 2376 - 2456 Pg of carbon present in the upper 200 cm of soil profile from the surface [7] . Whereas, in peat soils in Bangladesh holds around

Table 4. Carbon stock (Pg) across the peat soils of Bangladesh at 100 cm depths.

Figure 5. Distribution of soil organic carbon (SOC) storage and SOC % in different peat soils.

0.25 pg in the 1970s and whereas 0.12 Pg found in 2018. So, it has been estimated that around 50% of organic carbon is released in the environment that have a substantial negative impact on the environment. So that, it hypothesized that, after 40 years, around 50% of SOC demolish unless taken proper management techniques. Other experiments have shown that deforestation can result in 20% to 50% loss of this deposited carbon, mostly through erosion and effect of deforestation. Alongside, one of the major determinant factors of SOC storage depends on the soil types. As, in sandy soil, SOC % is lower, whereas peat soil or clay soil have higher % of SOC [79] . Soil organic carbon storages vary from 6.63 to 28.20 percent with a variation of bulk density from 0.30 to 0.91 g/cc in different soil series under major peat soils of Bangladesh.

However, Germany, Netherland, Poland, and Ukraine are using more than 50% of the total peat soil for agricultural practices. Other countries like Finland, Iceland, Britain, China, Russia, Malaysia, Bangladesh, India, and Thailand are also using it as an agricultural purpose. Peat soils are highly used for agricultural food production all over the world due to high level of soil fertility. The below table highlighting the total peat land and peat land used for food production by different region of the world (Figure 6). Due to agricultural intensification and intense tillage, the storage carbon can easily degraded and expose to the environment that leads to climate changes. From the below figure we can predict that the use of peat soils for food production is highly correlated with the total peat soils.

Supply of flesh organic biomass in the subsoil will help to slow down the mineralization of ancient organic soil. So that, land and agriculture management should be in a way that can add some green biomass to secure microbial food supply that can help to minimize the mineralizing the organic soil which stored in the long period [80] . Liming can increase food production and plant growth that may lead to store atmospheric carbon to the soil carbon. However, the main problem is helping to increased microbial activity that may release SOC to the environment. However, in the net calculation, it has been observed in several studies, application of liming helps to store SOC [81] . So, application of liming

Figure 6. Distribution and agricultural used of peat soils by different countries from all over the world.

could be a possible option for mitigating climate change. Limited grazing could be another strategy for storing the SOC. The sarjan procedure is practiced in medium-high to medium lowland. In this case, the land is divided into several subplots between the two subplots. The optimum size of the plot is 800 cm 150 cm. Each type of land use requires its specific depth of the water table. Water table control is not only needed for agriculture purpose but also to restore the hydrology in degraded peatlands. These differences in subsidence rates have also repercussions for the operation and maintenance of the water management system: the more profound the water tables, the higher the subsidence, thus the shorter the period after which the drainage canals have to be deepened to avoid waterlogging. Depending on the season, the water management system has to perform different functions: during the rainy season removal of excess water is required but during the dry system water conservation is needed. Furthermore, water table control is needed to maintain favorable growing conditions for the crops or to avoid excessively dry conditions (fire prevention). Water table control is difficult because water management requirements change from season to season. Thus adjustable control structures are needed. Especially in the dry season, when evaporation exceeds rainfall, the water tables will fall, and this deficit cannot be supplemented by irrigation as this would require pumping. Water table control is needed either to create right conditions for agriculture or to restore degraded peat domes. Thus structures either have to been piled or floated. Pile structures have the disadvantage that after a few of years the surrounding area will have subsided and the structures end up “hanging” in the air and no longer suitable for water table control. “Floating” structures have unit weight more or less the same as that of the surrounding peat: these structures will thus subside at the same rate as the surrounding peat area. Peat has a high permeability thus the structures cannot achieve much head difference (the difference between upstream and downstream water level) and thus hinders to store much water. They will mainly act as an extra barrier to flow (=increase flow resistance). Discharge requirements fluctuate significantly over the year as rainfall varies considerably. In the rainy season, flow can be exceptionally high, and these extreme discharges should not result in overtopping the banks and the water control structure as this will result in severe erosion.

4. Conclusion

The study has provided the present carbon storage measurement of nine soil series under major peatland of Bangladesh from 0 to 100 cm depth from the surface. Presently, about 125.02 kha land contains 0.12 Pg carbon stock in Bangladesh whereas the amount was 0.25 Pg in the 70s. So, in the last five decades, it has almost lost 50% of carbon stock in a country like Bangladesh. It can also assume that other tropical and subtropical regions also face emission of huge carbon over a long period due to low or no management that leads to rapid global warming and climate changes. Additionally, in peat soils, there has a limited negative correlation (r = −0.65) found between bulk density and soil organic carbon percentage. So, bulk density is one of the important factors for storing soil organic carbon in peat soil. The bulk density should be controlled for storing and management of soil organic carbon. Furthermore, it has also observed that peat soils are used as agricultural land almost all over the world that leads to high release to organic carbon in the atmosphere. These phenomena lead rapid mineralization of organic carbon from the soil. So, it should be minimized to control climate change. Possible management option of peat soils is also discussed briefly. It should include proper characterization, estimation, assessment, and regulation over the time to maintain sustainable environment.

Conflicts of Interest

There is no conflict of interest among the authors.

Cite this paper

Uddin, Md.J., Mohiuddin, A.S.M. and Hassan, M. (2019) Organic Carbon Storage in the Tropical Peat Soils and Its Impact on Climate Change. American Journal of Climate Change, 8, 94-109. https://doi.org/10.4236/ajcc.2019.81006

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