A REVIEW OF CARBON-DIOXIDE GAS EMISSIONS FROM …

Journal of Oil Palm and Palm Oil Research Vol. 1, No. 1, October 2020, p. 23-39

23 This is an open access article under the CC BY-NC license (https://creativecommons.org/licenses/by-nc/4.0/)

Heru Bagus Pulunggono1, 5, Affan Cahyahusna2, Syaiful Anwar1, Basuki Sumawinata1,

Darmono Taniwiryono3, Siswanto3, Happy Wiadiastuti3, Nizam Tambusai4, Husni Mubarok4,

and Supiandi Sabiham2

1) Department of Soil Science and Land Resource, IPB University, Bogor 16680 Indonesia 2) Graduate School of IPB University, Bogor 16680 Indonesia

3) Indonesian Research Institute for Biotechnology and Bioindustry, Bogor 16128 Indonesia 4) Practitioners for Oil Palm Development in Peatlands

5) Corresponding author: [email protected]

ABSTRACT

The C loss from peatlands through CO2 flux was derived from autotrophic (root) respiration

and peat decomposition (heterotrophic respiration). The CO2 emitted into the atmosphere

was determined as a net flux, showing the difference between CO2 gas released from peat

surface and CO2 gas absorbed by oil palm trees and other crops. This paper aims to: (1)

review the current reports concerning CO2(eq) flux or emission from oil palm plantations on

drained peatlands, and (2) review the one-year research activities in relation to (i) contribution

of peat decomposition to subsidence, and (ii) emission factor of peatlands drained for oil palm

plantations. Based on review past reports, the emission of CO2 from peatlands drained for oil

palm plantations varied from 33-95 Mg ha-1 yr-1. However, emission factor used for CPO

evaluation as raw material of biodiesel was 95 Mg ha-1 yr-1, for which the use of contribution of

peat decomposition to subsidence was about 92%. One-year data observation from our

research showed the contribution of peat decomposition of subsidence of about 43.2%. The

net-flux was measured above the canopy and the result showed the average CO2 flux was

19.0 Mg CO2 ha-1 yr-1 as CO2 emission. The flux from peat decomposition was measured at

the farthest distance from the oil palm trees and the results showed the average peat CO-flux

was 29.2 Mg CO2 ha-1 yr-1 as peat CO2 emissions. The contribution of peat decomposition to

peat subsidence is 43.2%. From the results of those CO2 flux measurement we suggest that

emission factor for peatlands drained for an oil palm plantation varied from 20 to 30 Mg CO2

ha-1 yr-1. This means emission factor used for CPO evaluation was over-estimated.

INTRODUCTION

Background

In Indonesia, peatlands currently cover about 13.43 million ha, most of which are situated in

the east coast of Sumatra, west and south coasts of Kalimantan, and north and south coasts

of Papua; smaller peatlands are found in West and Central Sulawesi (ICALRD 2019). More

than 50% of peatlands in the country is claimed to be degraded lands due the development of

drainage canals for agriculture, oil palm plantations, or industrial forest plantation

A REVIEW OF CARBON-DIOXIDE GAS EMISSIONS FROM PEATLANDS TO DETERMINE THE EMISSIONS FACTOR FOR DRAINED PEATLANDS FOR

OIL PALM PLANTATIONS IN INDONESIA

https://creativecommons.org/licenses/by-nc/4.0/


http://joppor.cpopc.org/index.php/joppor 24

(HTI, Hutan Tanaman Industri). Because of the presence of seasonal variation throughout the

year (Wakhid et al. 2017; Marwanto et al. 2018), drainage canals have disturbed peat

materials causing changes in biological, physical and chemical properties of peat, and

lowered groundwater levels (GWL) particularly during the dry season. These conditions were

then claimed to be the cause of large CO2 emissions (Furukawa et al. 2005; Couwenberg et

al. 2010). However, Marwanto et al. (2019) showed that the peat layers above GWL or even

at 0-20 cm depth had high water content due to the presence of capillary action which were

able to reduce CO2 emission.

The change of land cover in peatlands from peatswamp forest to plantation crops, in

particular oil palm plantations went through long-term processes which have been reported

by Pagiola (2000); Holmes (2000); Tjondronegoro (2004); Agus et al. (2011); and Rehman et

al. (2015). The processes were started by spontaneous migration that occurred in coastal

areas in Sumatra and Kalimantan in the 1920s and the governmental transmigration project

in 1969, followed by the presence of systematic logging through the scheme of the so called

Forest Concession Right (HPH, Hak Pengusahaan Hutan) in the 1970s. Those activities

caused the loss of natural forests which reached its peak during the years1985 to 1997, and

resulted in rapidly developing vast degraded lands. The expansion of oil palm plantations into

the degraded peatlands was started in 1990.

Environmental issues of CO2 emission from peatlands in oil palm plantations have affected

the global crude-palm-oil (CPO) trade. The standard for CO2(eq) emissions reduction from

palm oil-based biodiesel released by the Environmental Protection Agency, The United

States of America (US-EPA) in 2012, had to be more than 20% compared to the petroleum

diesel baseline. Based on the US-EPA’s calculation, however, the lifecycle of CO2(eq)

emissions from tropical peatlands associated with the palm oil-based biodiesel had reduced

the emissions to only 17%. Therefore, to verify this calculation, reviewing past studies in

more detail and analyzing the data from our research results of CO2 flux from peatlands in oil

palm plantations using chamber, subsidence and Eddy covariance methods had to be done.

Objectives of the paper

The objectives of this paper are mainly to:

1) Review the current reports concerning CO2(eq) flux or emission from oil palm plantations on drained peatlands, and

2) Review the one-year research activities in relation to (i) contribution of peat decomposition to subsidence, and (ii) emission factor of peatlands drained for oil palm plantations.

Approach

This paper presents the results of a comprehensive review of several literatures in relation to

CO2 flux or emission from oil palm plantations on peatlands in Indonesia. In order to clarify

the land use conversion of peatswamp forest to oil palm plantations, we describe the history

of land use changes in Indonesia which is claimed to be the cause of decreasing peat quality

and increasing CO2 flux/emission. The results of the reviewed literatures of CO2 emission

http://joppor.cpopc.org/index.php/joppor



were then assessed by our one-year research activities using the methods of chamber,

subsidence, and Eddy Covariance for quantifying the CO2 flux/emission from peatlands in an

oil palm plantation. Analyses of such methods based on data availability as the results of

real-time observation during the period from April 2019 to March 2020.

Peatlands and Peatswamp Forest Conversion

Peatlands in Indonesia were formerly covered by dense forests (Sabiham, 1988) that were

mainly dominated by large trees of many species growing in swampy conditions. Therefore,

peat materials which were found in the islands of Sumatra, Kalimantan, Sulawesi, and Papua

(Figure 1) were similar, very rich in wood having more or less decomposed trunks and

branches (Polak 1975). Peat

accumulation processes developed

during the Holocene period according to

the results of 14C-dating (Sabiham 1988;

Biagioni et al. 2015). These processes

yielded a unique ecosystem with highly

variable places in different

environments (Schrier-Uijl et al. 2013)

with a peat thickness of up to more than

7 m.

Figure 2 shows a model of the integrated

stratigraphic layer of peat deposits in relation

to peat ecosystem formation (Sabiham, 1988).

Thick deposits of peat have accumulated as a

consequence of low topographic relief, high

biomass production, and high rainfall (Page et

al. 2010; Dommain et al. 2011).

The occurrence of peat accumulation is due to

waterlogged conditions and, therefore, the

deposited peats are naturally in an anaerobic

condition, with various thick peat deposits and

storing very high C content (Page et al. 2011;

Biagioni et al. 2015). The accumulation rate of peat materials in the sub layer was faster

compared to that in upper layer (Sabiham 1988). Carbon storage has a global importance,

particularly in relation to CO2 gas emitted into the atmosphere.




Peatlands covered by forests are important climatic mitigating areas as water sources,

particularly during the dry season or the occurrence of El Nino (Yule 2016). However, since

the final part of the 1960s, a majority of the Indonesian peatlands and peatswamp forests

were claimed by some environmentalists to be degraded areas due to the rapid land-use

changes, particularly into oil palm plantations, where many drainage canals were developed

and caused the emission of the formerly stored C (Pagiola 2000). Based on the results of

our review of several published-papers (Table 1), we had a difficulty to understand that forest

degradation was due to the rapid changes in oil palm plantation; in fact, primary peatswamp

forests were overall not directly converted into oil palm plantations.




The expansion of oil palm plantations into primary and secondary/ degraded peatswamp

forests in Sumatra, Kalimantan and Papua during the period 1990 to 2010 (Table 2) was in

total only 6% and 28%, respectively (Agus et al. 2011; Gunarso et al. 2013).

While its expansion into shrubs and agricultural lands was, respectively, about 26 and 40%.

Rehman et al. (2015) reported that the exploitation of peatswamp forests for oil palm

plantations in Riau and West Kalimantan was indirect and that the forest was not only

converted to oil palm plantations, but also to the other land uses. Based on an analysis of all

regions and temporal periods in both the Provinces of Riau and West Kalimantan, only 0.94%

of oil palm plantations were created on peatlands derived from primary peatswamp forests,

and about 21.55% from secondary peatswamp forest.

Important Factors Influencing CO2 Emission in Drained Peatlands

Empirical studies showed that the main factors which strongly influenced CO2 emission from

drained peatlands consisted of: (i) physical properties of peat such as bulk density, peat

porosity and ripeness, and (ii) groundwater level (GWL) movement (Husen et al. 2014;

Marwanto et al. 2018). Field evidence indicated that GWL fluctuation has a close relationship

with rainfall throughout the year (Wakhid et al. 2017).




Physical properties of peat

Bulk density (BD) of the upper-layer peat (at 0-30 cm depth) in oil palm plantations mostly

varied between 0.07 to 0.25 g cm-3 (Agus and Wahdini 2008; Hooijer et al. 2011, 2012). We

summarized that the value of peat BD measured at the beginning of the drainage canal

construction ranged from 0.07 to 0.10 g cm-3. Whereas after the drained peatlands were

used for oil palm cultivation, the peat BD increased to 0.14 and 0.25 g cm-3 depending on its

cultivation age. The change of this peat BD was the cause of peat consolidation due to water

loss through drainage systems, or compaction caused by human activities during oil palm

cultivation (Hooijer et al. 2011). This change has resulted in the increase of micro

peat-porosity and peat ripeness (Anwar 2001), causing the increase of peat moisture content

and the decrease of the emitted CO2 gas from the peat surface (Marwanto et al. 2019).

Water table/GWL movement

The high GWL occurred during the wet season and the low level during the dry season,

following a seasonal variation in precipitation (Wakhid et al. 2017). In our study, monitoring

GWL was carried out at a real time of every 60 minutes using HOBO Water Level (13 ft) Data

Logger. We also placed dip-wells at several selected locations of the planting blocks to

measure the GWL manually. Weekly measurements were taken.

Based on the results of our monitoring

during the period April 2019 to March 2020

(Figure 3), the GWL movement showed that

in the dry season (April to July 2019) the

water table generally dropped to more than

60 cm below the peatland surface, and in

August 2019, during extremely dry

conditions, it decreased to more than 80 cm.

In the wet season (September 2019 to

January 2020), however, the water table

increased to 30 cm, and sometimes to

about 20 cm, below the peatland surface.

There was a negative correlation between

GWL and peat water content (Table 3), and

this indicated that despite the lower GWL,

the peat water content at the depth of 0-20 cm was still high, meaning that peat was still

moist.




Review of past report on Carbon Dioxide Emission from Drained Peatlands in Oil Palm

Plantations

Several researchers reported that CO2 emissions from drained peatlands in oil palm

plantations ranged from 33 to 85 Mg CO2 ha-1 yr-1 (Table 4), with a mean of about 45 Mg. CO2

ha-1 yr-1. These CO2-emission values were obtained from the measurement based on

chamber and subsidence methods. Page et al. (2011) have calculated the annualized value

for peat C loss from oil palm plantation over a 30-year time period as a mean high emission

rate from drained peatlands for 25 to 50 years of plantation cycles, from which the result of

calculation was 95 Mg CO2 ha-1 yr-1. This was emission-factor for the peatlands drained for

oil palm plantations.

However, we considered that this proposed emission-factor was over-estimated and not

realistic because it was calculated by using a high value of the contribution of peat

decomposition to subsidence, i.e. 92%. Couwenberg et al. (2010) and Wosten et al. (1997)

proposed that the contribution of peat decomposition to subsidence was at 40 and 60%,

respectively; the other factors

which would influence subsidence were consolidation and compaction. A part of CO2 flux

from peat surface is derived from root respiration. The contribution of root respiration to the

flux from peatlands covered by <6-year and 15-year oil palm trees was calculated about 17%

(Dariah et al. 2013) and 74% (Sabiham et al. 2014), respectively. Lowering GWL increased

CO2 flux (Furukawa et al. 2005; Hirano et al. 2015) which was mostly caused by increasing

root respiration rather than by peat decomposition. Calculating the emission factor for

peatlands drained for oil palm cultivation, as showed by CO2 flux, is still a challenge.




In 2014, IPCC calculated the emission factor for organic soils based on data from many

published-papers; and the emission factor was suggested to be 40 Mg CO2 ha-1 yr-1 (Table 3).

However, direct measurements of CO2 flux based on specific locations and different methods

are important to be clarified. Annualized emission-value was used and reported in 2012 by

US-EPA as he proposed

Emission Factors for Peatlands Drained for Oil Palm Plantation:

A Review Based on CO2-flux Measurement

Three methodologies are usually used for the measurement of CO2 flux from peatlands,

namely: closed chamber, subsidence and Eddy covariance methods. The closed chamber

method is the direct measurement of C emission from peatland surface using the

conventional chamber method which is still used by many scientists (Table 4).

However, this method seems to have limitations due to the short-term measurement and the

mixture of autotrophic and heterotrophic respirations. In this study, the automated soil gas

flux system (LiCor-8100A) was used for measuring peat CO2-gas flux at the real time every

30 minutes. The strength of the subsidence method to determine the emission factor is the

fact that it has no root respiration confusion. However, this method needs other supporting

data, such as: peat BD and C content (Hooijer et al. 2011, 2012). Other information that is

most important for supporting this method is the relative contribution value of peat

decomposition to subsidence.

The last is the Eddy covariance method, that has recently been used by many researchers for

the measurement of CO2 flux in an ambient above the canopy. In this study, we used the

LiCor-7500 open path CO2/H2O gas analyzer, and measurement was conducted at the real

time of every 30 minutes. Although this instrument has high accuracy for measuring the

densities of CO2 and H2O vapor in turbulent air structures (Burba 2013), this method needs

several sophisticated tools which are very expensive. Thus, the method is mostly used for

scientific development. GWL, subsidence, and some peat physical properties were monitored

by several instruments in order to support the method of Eddy covariance.

In this review, the used data were collected from April 2019 until March 2020 observation.

The observation was conducted in an oil palm plantation in Siak Riau, at the coordinate of 0º

44’ 55.99” N and 101º 45” 14.04’ E; Lat. 0.74896 N and Long 101.75396 E, where the age of

the oil palms varied from 12 to 15 years. The review has three main objectives; first, to

analyze environmental factors which influence the flux; second, to determine the contribution

of peat decomposition to subsidence and third, to ascertain the emission factor for

peatlands drained for oil palm plantations based on CO2 flux measurement.




The influence of some important environmental factors on CO2 flux

The important environmental factors influencing the CO2 flux from peatland surface are

physical properties of peat, rainfall or precipitation, peat water content, and peat temperature

(Furukawa et al. 2005; Wakhid et al 2017). Analyses of the physical properties of peat are

focused on peat BD and available water content using the method developed by the

Department of Soil Science and Land Resource, IPB University.

Rainfall or precipitation, peat water content, and peat temperature were measured at the real

time of every 30 minutes by using the respective related-instruments as the accessories of

Eddy covariance. The measurement of rainfall was monitored using the rain gauge

(TR-525USW Texas Electronic). Peat water content data was collected by using Stevens

Hydra Probe II-A (Soil Moisture Probe), while peat temperature monitoring was conducted

using Soil Temperature Sensor of LiCor-7900-1. The collected data using the respective




instruments, including soil temperature, were then downloaded and transferred into the Excel

Program, and then calculated using the Software Soilflux-Pro (Burba 2013).

Environmental factors that strongly influence CO2 flux in ambient above canopy are air

temperature and evapotranspiration (ETP). Air temperature monitoring was carried out by

using the 14-Plate Radiation Shield RM Young, an instrument of Humidity and Temperature

Sensor, as one of the Biomet System Packages consisting of four components of radiation

measurement and self-calibrating heat flux measurement for tower application. Monitoring

of ETP is based on the H2O gas measurement results using Li-Cor 7500 CO2/H2O Analyzer.

The collected data were analyzed using Software Eddy-Pro.

The results of analyses of BD, peat water content at pF 2.54 and 4.2, available water content,

peat water content at the layer of 0-20 cm, rainfall, and ETP are shown in Table 5.

This table shows that the average peat BD at 0-20 cm depth is 0.134 ± 0.023 g cm-3, and it

then decreased with increasing peat depth. Peat BD in the dry season was relatively lower

than that in wet and transition seasons. The average daily rainfall was 4.14 mm.

Based on water contents at pF 2.54 and 4.2, the average available water in peat at the depth

of 0-20 cm could be calculated and the result showed the value of 3.2 ± 1.6% (v/v). According

to peat-water content at the layer of 0-20 cm (Table 5), peat above GWL would be in wet

conditions although GWL was sometimes lowered to 100 cm below the peat surface. By

calculation with peat BD of 0.134 g cm-3, the relative water content by weight is about 292.5%

(w/w). So, the water content in one hectare (at 0-20 cm peat depth) was calculated to be

about 585.0 Mg water ha-1 or about 58.5 mm.

Based on the calculation results of ETP (Table 5), the total water in peat that is needed for

supporting daily crop transpiration and daily peat evaporation from the depth of 0-20 cm was

about 3.66 ± 0.75 mm day-1. Because the average total-water content in peat at the same

depth is 39.2% (v/v) and its availability is 3.2% (v/v), so the total available water that could be




used to support daily evaporation and transpiration is (3.2/39.2 x 58.5) mm or 4.78 mm day-1.

The total available water in peat is the sum of daily rainfall and available water, which is (4.78

+ 4.14) mm or 8.92 mm day-1. By comparing this against daily ETP (of about 3.66 mm day-1),

there is a surplus of water content in the 0-20 cm peat layer of about 5.26 mm day-1. This

means that peat layers above GWL could be considered as peat in a moist condition

throughout the year. Marwanto et al. (2019) reported that the moist peat in the top layer is

able to significantly decrease the released CO2 flux from the sub layers.

Contribution of peat decomposition to subsidence in relation to CO2 flux

Studying the relationship between CO2 flux and peat decomposition as one of the sources of

flux was not easy to implement in the field due to some difficulties in handling the flux

observation without the effect of root respiration. In order to solve such a problem, we

followed the research approach of Sabiham et al. (2014) and Dariah et al. (2013) with some

modification. Each of the four automated soil-gas-flux (automatic chambers of LiCor-8100A)

was placed at the selected oil palm tree as observation points (Figure 4), where the distance

from the center of the tree trunk to each automated chamber was 1.5, 2.5, 3.5, and 4.5 m.

Oil palm roots, as one of the sources of CO2 flux, was observed in detail by Sabiham et al.

(2014). They found that, in the top layer, of the four root sizes with diameters <0.5; 0.5-2.5;

2-5-5.0; >0.5 mm, only the root density of the first two sizes had significant negative

correlation with the distance of the

observation points. This indicated the

presence of a gradual decrease in the root

densities with increasing distance. Both

oil-palm root densities at 4.5 m from the tree

trunk were nearly zero, meaning that no

flux occurred from root respiration, and thus,

flux was only released by peat

decomposition. Harianti et al. (2017)

reported similar results which showed that

the total active oil-palm’s roots at the upper

layer of peat were decreased with increasing

distance from the oil palm tree.

The subsidence of peatlands in the study

area was measured at the 3-selected planting blocks having oil palm trees with the respective

ages of <10, 10-15, and >15 years. The measurement was conducted using an iron pipe

stick with a diameter of two inches. At each block, two subsidence sticks, with an iron ring

as a reference point of the peat surface when the measurement started, were driven into the

peat vertically until a 1.0 m-depth in the mineral soil substratum. The results (Table 6)

indicated that the lowest peat flux of 0.08 ± 0.06 Mg CO2 ha-1 day-1 was found at the

observation point farthest from the oil palm tree. The flux then sharply increased closer to the

observation point nearest to the oil palm tree, reaching the highest flux of 0.23 ± 0.13 Mg ha-1

day-1 or 84 Mg CO2 ha-1 yr-1.

During the wet season, the peat CO2 flux of 0.15 ± 0.09 Mg CO2 ha-1 day-1 was lower than that

in dry season that was shown by the value of 0.21 ± 0.08 Mg CO2 ha-1 day-1. This clearly




indicated that with the increasing peat water content due to relatively high rainfall and high

GWL, the peat CO2 flux would significantly decrease, and this was substantiated by Pearson’s

correlation test shown in Table 3.

The average peat CO2-flux from all observations was 0.17 ± 0.09 Mg CO2 ha-1 day-1 or 62.1

Mg CO2 ha-1 yr-1. In accordance with Sabiham et al. (2014) and Harianti et al. (2017) who

reported that no active roots could be found at the distance farthest from oil palm tree, in this

study there were no active roots at the distance of 4.5 m from the oil palm tree. Therefore, the

lowest CO2 flux of 0.08 ± 0.06 Mg CO2 ha-1 day-1, occurring at the observation point farthest

from the oil palm tree, could be considered as the flux derived from peat decomposition.

Based on the results of subsidence measurement (Table 6), the lowest rate of subsidence

(1.65 cm yr-1) occurred at the planting block covered by oil palm trees <10-years old. The rate

increased with the increasing age of the oil palm tree. The highest rate (3.19 cm yr-1) was

found in the planting block with oil palm trees aged more than15-years old. The average

subsidence rate from all measurements during a one year period was 2.47 cm yr-1.

Following the analysis results of the subsidence rate and the CO2 flux measured from the

observation point farthest from the oil palm tree, the contribution of peat decomposition (CPD)

to the subsidence could then be calculated by using the following equation:

CPD = (A)/(P) x 100%

where

(A) Actual CO2 flux (Mg CO2 ha-1

yr-1

) is the flux measured by using the automated soil gas flux system (LiCor-8100A) at the farthest point from the oil palm tree.

(P) Potential CO2 flux (Mg CO2 ha-1

yr-1

) is the flux resulting from the calculation of the subsidence

rate per year (dm) x 1,000,000 dm2 x BD (kg dm

-3) x C-organic (%) x 44/12




The actual CO2 flux derived from peat decomposition was 0.08 Mg CO2 ha1 day-1 or about

29.2 Mg CO2 ha-1 yr-1. Whereas the potential CO2 flux that could be obtained depended on

the value of the subsidence rate, peat BD, and C-organic content, was determined by using

the following calculation: 0.247 dm x 1,000,000 dm2 x 0.134 kg dm-3 x 55.64/100 x 44/12 =

67,52 Mg CO2 ha-1 yr-1.

Therefore, the contribution of peat decomposition to the 2.47-cm subsidence of peat surface

per year is:

(29.2 / 67.52) x 100% = 43.2%

Emission factors for peatlands drained for oil palm plantations

There are two CO2 fluxes that must be carefully considered: (i) CO2 fluxes released from the

peat surface as the total fluxes derived from root respiration and peat decomposition, and (ii)

net CO2 flux in the ambient above canopy (Burba 2013). The net flux can be defined as the

flux resulting after the total flux from the peat surface was reduced by CO2 sequestration.

Therefore, the total CO2 flux from the peat surface should not be used as an emission factor.

The results shown in Table 6 indicate that the average net CO2 flux during the dry season

(0.044 ± 0.077 Mg CO2 ha-1 day-1) was lower than that in the wet season (0.059 ± 0.066 Mg

CO2 ha-1 day-1). This indicates the present high absorption of CO2 occurred during the dry

season. In relation to the daily net flux, Figure 5 shows that the average flux in the day time

(09:00 to 17:00) was lower than that in the night. This means that there is an occurrence of

CO2 sequestration through photosynthesis.

From the one-year observation, the average net CO2 flux was 0.052 ± 0.074 Mg CO2 ha-1

day-1, while the average CO2 flux from the peat surface was 0.17 ± 0.09 Mg CO2 ha-1 day-1. In

this micro scale of the environment, the sequestration of CO2 by oil palm trees and understory

cover crops can be calculated simply, of which the result is about 0.118 Mg CO2 ha-1 day-1.

Fig 5. Measurement of net CO2-flux above canopy using LiCor-7500 CO2/H2O gas

analyser that installed to the tower having the height of 19 m




The average CO2 flux derived from respiration, calculated from each observation point at the

respective distance of 1.5, 2.5, and 3.5 m from the oil palm tree, was 0.12 Mg CO2 ha-1 day-1.

These results indicate that the total CO2 flux from respiration was overall sequestrated.

Therefore, in order to determine the emission factor for peatlands drained for oil palm

plantations, it might be more feasible to consider:

1) Net CO2 flux for a micro scale of peatland environment in oil palm plantations, having a value of 0.052 Mg CO2 ha-1 day-1, or about 19.0 Mg CO2 ha-1 yr-1 as net CO2 emission.

2) CO2 flux from peat decomposition, having the value of 0.08 Mg CO2 ha-1 day-1, or about 29.2 Mg CO2 ha-1 yr-1 as the CO2 emission of peat.

Based on this consideration, we propose that the emission factor for peatlands drained for oil

palm plantations to be in the range of 20 to 30 Mg CO2 ha-1 yr-1.

CONCLUSION

The main factors which strongly influence the CO2 emission from drained peatlands are peat

water content and water table movement which are closely related to rainfall throughout the

year. Having surplus water content, the peat layers above GWL, the top peat layers in

particular, are always in a moist condition. The emission of CO2 from the peat surface is

mainly derived from root respiration and peat decomposition. The contribution of peat

decomposition to peat subsidence is 43.2%. Peat CO2 emission from root respiration is about

43.8 Mg CO2 ha-1 yr-1, which is equal to the sequestrated CO2 of about 43.1 Mg CO2 ha-1 yr-1.

This indicates that all emission from root respiration is absorbed by the oil palm trees and

other crops grown in the plantation. Thus, it is not feasible to use the total emission from the

peat surface to determine the emission factor.

CO2 emissions measured above the canopy and from peat decomposition are the best to be

used as emission factors for peatlands drained for oil palm plantations, which range from 20

to 30 Mg CO2 ha-1 yr-1.

ACKNOWLEDGEMENT

We thank the Board of Directors of BPDP-KS for the financial support which made our

research possible. We do believe that the research would not have been successful without

the help of friends and colleagues in the Soil Laboratory of the Department of Soil Science

and Land Resource, IPB University who did all or part of the research activities.

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Appreciation. This manuscript was reviewed for JOPPOR by Prof. Dr Kukuh Murtilaksono,

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Physical Land Resources, IPB University.


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