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THE MALAYSIAN FORESTER 2016, 79 (1 &2), 164-173
164
SOIL pH AND CARBON AT DIFFERENT DEPTH
IN THREE ZONES OF MANGROVE FOREST IN
SARAWAK, MALAYSIA
AHMAD MUSTAPHA MOHAMAD PAZI1, SECA
GANDASECA1*, NORAINI ROSLI2, AHMAD HANAFI
HAMZAH1, ALBERT EMPAWI TINDIT1 AND LAURNA
NYANGON1
1 Department of Forest Production, Faculty of Forestry, Universiti Putra Malaysia, 43400
Serdang, Selangor, Malaysia
2 Department of Forestry Science, Faculty of Agriculture and Food Sciences, Universiti Putra
Malaysia Bintulu Campus Sarawak, Malaysia
*Corresponding author:
Email: seca @upm.edu.my
Abstract: Mangrove forest is one of the potential areas for the carbon storage.
A study on carbon storage in soil was carried out in the mangrove forest at
Awat-Awat Mangrove Forest Reserve in Lawas, Sarawak, Malaysia to compare
the carbon storage potential among three different zones (seaward, middleward
and landward) and two different soil depths (0-20 cm and 20-40 cm). Standard
procedures were used to determine soil chemical properties. There are
significant differences in the carbon storage between the mangrove zones with
the middleward zone being more efficient in storing carbon. However, there
are no differences in the percentage of carbon stored at different soil depths.
Key words: Soil carbon storage, mangrove zonation, soil depth, Sarawak
INTRODUCTION
Mangrove forests are found along sheltered coastlines in the subtropical and tropical
areas. Mangrove forest provides important ecological and socio-economic functions
in the tropical coastal societies. For example, they are natural spawning and living
ground for many species of fish and crustaceans. Mangrove also gives protection
and maintenance of coastal water quality, reduction in severity of storm, wave and
flood damage and also as a nursery and feeding areas for commercial and artisanal
fishery species. In Malaysia, mangrove forest covers 564, 971 hectares of which
57% found in Sabah, 26% in Sarawak and the remaining in Peninsular Malaysia.
Most of the area had been converted to cater for developments such as plantation,
industry, building and aquaculture. All these activities give negative impacts on
mangrove ecosystem functions (Chai 1974).
Mangrove also plays an important role in global carbon cycling, since they
store a large stock of carbon as well as potential carbon sink and source to the
atmosphere (Arianto et al. 2015). A study was undertaken to compare the carbon
storage potential among three different zones; seaward site, middle zone and
landward site at two different soil depths (0-20 cm and 20-40 cm).
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165
MATERIALS AND METHODS
The study was conducted at Awat-Awat Mangrove Forest Reserve, Lawas Sarawak,
Malaysia at the latitude 04º52’2.61”N and longitude 115º13’58.14”E (Figure 1). The
forest is approximately 4.000 ha and located about 2 km from Kg. Awat-Awat, and
35 km from Lawas town in the Limbang Division. One transect line was established
from sea front towards the land. Along the transect line, three zones were identified
as A = seaward site, B = middle site and C = landward site. Six plots of 50 m x 50 m
were established with 2 plots established for each site, and further divided into 5
subplots of 10 m x 10 m; every subplot contained five 1m x1m quadrats (Figure 2).
A GPS Map 76CSx was used to record the coordinates. All dominant species inside
the plot were identified and counted. The frequency of species were calculated using
the formula of Cintron & Schaeffer-Novelli (1984) as follows:
The soil was sampled at two different depths which are D1= 0-20 cm and
D2= 20-40 cm using peat auger in 5 quadrats of 1 m x 1 m. The samples were mixed
to become one sample called bulking sample. Samples were placed into zip lock
plastic bag, labelled and transported to UPMKB soil laboratory for processing. The
samples were air-dried at room temperature, ground using pestle and mortar, sieved
to pass 2 mm sieve for further analysis. The soil pH was determined in distilled
water and 1 M KCl at a ratio of 1:2.5 soil: water or KCl using a glass electrode pH
meter (Peech 1965). Soil CEC was determined using the leaching method (Cottenie
1980) followed by steam distillation (Bramner & Mulvaney 1965). Total carbon was
determined using CHNS Analyzer (TruSpec Micro Elemental Analyzer (NCHS),
LECO, USA). The obtained data was analyzed using analysis of variance to detect
significant differences among factors while Tukey’s test was used to compare means
between zonation, plots and depths. The statistical analysis, Statistical Analysis
System version 9.2 was used (SAS 2008).
Figure 1. Location of study site at Awat-Awat Mangrove Forest Reserve, Lawas
Sarawak
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166
Figure 2. Study plot
RESULTS
Based on zonation, Table 1 shows the taxa composition of the mangrove forest.
Rhizophora apiculata and Rhizophora mucronata dominate the middleward zone
while species of Sonneratia dominate the seaward zone; in the landward zone, both
Lumnitzera littorea and Xylocarpus granatum were found in almost the same
number.
Table 1. Mangrove species in Awat-Awat Mangrove Forest Reserve
Zone
Plot
Family
Dominant Species
Frequency
(%)
Seaward
P1
Lythraceae
Sonneratia alba
75
80
P2
Lythraceae
Sonneratia caseolaris
Middleward
P3
Rhizophoraceae
Rhizophora apiculata
100
100
P4
Rhizophoraceae
Rhizophora mucronata
Landward
P5
Combretaceae
Lumnitzera littorea
50
65
P6
Meliacecae
Xylocarpus granatum
Table 2 shows the results of selected chemical properties of different zones
at Awat-Awat Mangrove Forest in Lawas, Sarawak Malaysia. The pH in water
regardless zonation showed significant differences. The highest pH was recorded in
Plot 1 and Plot 2 (5.33a (±0.06)) which were located at seaward zone and dominated
by Sonneratia alba and Sonneratia caseolaris species. The lowest pH was
determined in Plot 3 and 4 (4.05c (±0.04)) which located at middleward zone and
dominated by Rhizophora apiculata and Rhizophora mucronata trees. The similar
result was obtained for pH in 1 M KCl and there were significant differences
irrespective of zonation. Soil CEC at different zonation were significantly different.
The highest CEC was recorded at seaward zone (19.86a (±0.79) Cmol Kg-1) while
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167
the lowest CEC was recorded at landward zone (10.32c (±0.95) Cmol Kg-1). For
carbon content, middleward zone gave the highest value.
Table 2. Selected chemical properties of different zonation at Awat-Awat
Mangrove Forest Reserve
Zonation
Plot
Dominant Species
pH
Water
pH KCl
CEC
(Cmol Kg-
1)
C (%)
Seaward
P1
Sonneratia alba
5.33a
(±0.06)
4.50a
(±0.09)
19.86a
(±0.79)
1.900c
(±0.110)
P2
Sonneratia
caseolaris
Middleward
P3
Rhizophora
apiculata
4.05c
(±0.04)
3.45c
(±0.08)
17.25b
(±1.68)
3.593a
(±0.235)
P4
Rhizophora
mucronata
Landward
P5
Lumnitzera littorea
4.48b
(±0.13)
3.78b
(±0.16)
10.32c
(±0.95)
2.301b
(±0.054)
P6
Xylocarpus
granatum
* Different alphabets within a row indicate significant different between mean of
selected chemical properties between zonation and plots using Tukey’s test at
P 0.05. Plus and minus symbols at the beginning of the number represent the
decrease and increase in each items. Values in parenthesis represent standard error
of the mean.
Table 3 shows the selected chemical properties of six different plots with
different dominant species at three mangrove zonation. The pH in water regardless
plot showed significantly differences among plots. Plot 3 and 4 was dominated with
Sonneratia alba and Sonneratia caseolaris at seaward zone obtained the higher pH
compare to other plots. Similar results were recorded on pH in 1 M KCl and showed
the significant difference between plots. Soil CEC was significantly different among
the plots, P4 and P1 recorded the highest of CEC compared to other plots. Soil
carbon content of Plot 4 and Plot 3 which was dominated by Rhizophora mucronata
and Rhizophora apiculata.
Table 4 shows the selected chemical properties of different depths at three
zones in the mangrove forest. Regardless of the zone and plot, pH in water showed
significant differences between depth 1 (0-20 cm) and depth 2 (20-40 cm) except for
middle ward zone. Soil pH in 1 M KCl showed significant differences among the
depths and depth 1 (0-20 cm) gave the highest value compared to depth 2. Soil CEC
at three zones showed no significant differences irrespective of the depth and the
same pattern was also recorded for soil carbon content.
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168
Table 3. Selected chemical properties of different plots at Awat-Awat Mangrove
Forest
Zonation
Plot
Dominant Species
pH Water
pH KCl
CEC
(Cmol Kg-1)
C %
Seaward
P1
Sonneratia alba
5.38a
(±0.12)
4.57a
(±0.18)
22.92b
(±0.41)
1.714f
(±0.136)
P2
Sonneratia caseolaris
5.27b
(±0.03)
4.43b
(±0.05)
16.80c
(± 0.60)
2.087e
(±0.156)
Middleward
P3
Rhizophora apiculata
4.70c
(±0.04)
3.35c
(±0.14)
10.33e
(±0.40)
2.683b
(±0.068)
P4
Rhizophora mucronata
4.25d
(±0.04)
3.36d
(±0.08)
24.17a
(±1.08)
4.503a
(±0.209)
Landward
P5
Lumnitzera Littorea
4.21e
(±0.11)
4.01e
(±0.15)
12.58d
(±1.37)
2.302c
(±0.052)
P6
Xylocarpus granatum
3.89f
(±0.22)
3.55f
(±0.28)
8.05f
(±0.89)
2.300d
(±0.099)
* Different alphabets within a row indicate significant different between mean of
selected chemical properties of different plots using Tukey’s test at P 0.05. Plus
and minus symbols at the beginning of the number represent the decrease and
increase in each items. Values in parenthesis represent standard error of the mean.
(No Tukey test in the Table)
Table 4. Selected chemical properties of different depths at Awat-Awat Mangrove
Forest.
Zonation
Plot
Depth
pH Water
pH KCl
CEC
(Cmol (+)/Kg-
1)
C %
Seaward
P1
D1
(0-20 cm)
5.50a
(±
0.08)
4.83a
(±0.09)
21.10a
(±0.95)
2.143a
(±0.179)
P2
D2
(20-40 cm)
5.15b
(±0.04)
4.17b
(±0.04)
18.62a
(±1.17)
1.657b
(±0.074)
Middleward
P3
D1
(0-20 cm)
4.04a
(±0.04)
3.76a
(±0.07)
18.88a
(±2.68)
3.760a
(±0.389)
P4
D2
(20-40 cm)
4.06a
(±0.08)
3.13b
(±0.01)
15.62a
(±2.05)
3.427a
(±0.273)
Landward
P5
D1
(0-20 cm)
4.97a
(±0.04)
4.42a
(±0.02)
11.66a
(±1.43)
2.317a
(±0.081)
P6
D2
(20-40 cm)
3.99b
(±0.13)
3.14b
(±0.14)
8.94a
(±1.17)
2.286a
(±0.077)
* Different alphabets within a row indicate significant different between the mean of
selected chemical properties of different depth using Tukey’s test at P 0.05. Plus
and minus symbols at the beginning of the number represent the decrease and
increase in each item. Values in parenthesis represent standard error of the mean.
(No mention of Tukey test in the Table).
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169
Figure 3 shows the interaction between depth and plot on soil pH in water.
Regardless of the plot, depth 1 (0-20 cm) showed the highest values of pH in water
compared to depth 2 (20-40 cm). The same pattern also was obtained in soil pH in 1
M KCl (Figure 4). The mean depth 2 is more acidic compared to depth 1. Figure 5
shows the interaction between depth and plot on soil CEC. Regardless of plot, depth
1 gave higher value than depth 2 and significantly different among plots except on
soil depth on CEC at plot 3 and plot 5 which showed no significant difference. For
soil carbon content, only soil depth on P1, P2 and P4 differed significantly (Figure
6).
Figure 3. Interaction between depth
and plot on soil pH in water.
Figure 4. Interaction between depth
and plot on soil pH in 1 M
KCl.
Figure 5. Interaction between depth and
plot on soil CEC
Figure 6. Interaction between depth
and plot on soil carbon
* Different alphabets within a line indicate significant difference between mean of
selected chemical properties between the depths using Tukey’s test at P 0.05.
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170
Figure 7 shows the comparison between zonation (seaward, middleward and
landward) on selected soil chemical properties. Soil pH in water in the seaward zone
was the highest. The same pattern was also recorded for soil pH in 1 M KCl. Soil
CEC seaward also obtained the highest result and significantly different among the
zones. For soil carbon content, middleward zone gave the highest value and
significantly different from landward and seaward zones.
Figure 7. Comparison between zonation (seaward, middleward and landward) on
selected soil chemical properties at mangrove forest.
* Different alphabets within a line indicate significant difference between mean of selected
chemical properties between the depths using Tukey’s test at P 0.05
DISCUSSION
There are six dominant species of mangrove forest trees belonging to four families
were identified in Awat-Awat Mangrove Forest Reserve along the mangrove
zonation. Those species was dominated at certain zonation of mangrove forest such
as on seaward, middleward and landward zones. Species composition was attributed
to the ability of plant species to tolerate soil salinity, nutrient, wave energy and
flooding conditions that vary within as well as among mangrove zonation (Wibisono
& Sualia 2008).
Soil chemical properties among the zonation showed significant differences
between seaward, middleward and landward zones. Soil pH in water and 1 M KCl
in every zonation of this mangrove forest, were acidic with the range of 4.05 to 5.33
and showed significant difference among the zonations. A similar pattern was
recorded on pH in KCl 3.45 to 4.50. The most acidic one was found in a middleward
zone at plot 3 and 4 where Rhizophora mucronata and Rhizophora apiculata were
dominant. This is because soil pH decreases with increasing distance from the water
edge. In general, the soils of mangrove are neutral to slightly acidic due to sulphur-
reducing bacteria and the presence of acidic clays, but in Malaysia there are
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171
mangroves with very acidic brackish waters due to the aeration of soil sulphates,
forming the sulphuric acid (Arianto et al. 2015). Since seaward zone is nearest to
the sea and situated at a lower level than middleward and landward zones, it is likely
that seaward zone is more affected by seawater than freshwater. Seawater is
probably one of the factors in determining soil pH of the mangrove forest (Chapman
1976). Soil CEC and carbon content also showed a significant difference among the
zonations. The values of CEC and carbon content increasing toward the landward
zonation indicating an increase in organic matter and its decomposition.
Selected soil chemical properties of different plots were different due to the
dominance of different mangrove species. Soil pH in water and 1 M KCl at Plot 1
and Plot 2 were higher compared to other plots ((5.38a(±0.12) and 4.57a(±0.18).
This is due to the high organic matter decomposition processes tends to occur
towards inland since it was occupied with trees and have a favourable condition to
sustain forest communities (Kusamana et al. 1992). The seaward zone which is
easily flooded during tides might have its organic matter being washed away. A high
total CEC and carbon content in soil maybe due to dominant species such as
Sonneratia alba, Sonneratia caseolaris, Rhizophora apiculata, Rhizophora
mucronata, Lumnitzera littorea, and Xylocarpus granatum. These species contribute
high litter falls on the forest floor and the accumulation of these litter falls is
normally trapped by dense and large roots of the species during tidal inundations.
The decomposition processes induced by microorganisms lead to high carbon
accumulation and consequently a greater H+ is generated contributing to soil acidity.
A similar observation was reported by Rambok et al. (2010).
Soil depth shows a significant difference on soil chemical properties between
depth 1 and depth 2. In terms of pH in water and 1 M KCl, depth 1 gave the highest
values and the statistical mean comparison and show the significant difference
between depth 1 and 2 except for pH in water in Plot 2. Soil CEC and carbon
content belong to different depths, depth 1 obtained the higher value and the
statistical mean comparison show there is no significant difference between depth 1
and 2. This is because mangrove ecosystems are typically waterlogged, have little
aeration and a heavy load of organic material decomposing at a slow rate at the
different areas of mangrove (Linn & Doran 1984). However, mangrove soil has a
different profile and it influenced by water levels.
The result of soil chemical properties on mangrove forest revealed that the
soil is acidic and significantly different among all plots. The differences are due to
zonation patterns of the mangrove within the study area. Each area was occupied or
dominated by different species, soil texture, soil organic material and
microorganisms content (Feller & Sitnik 2011). Seaward zone obtained high pH
(water and KCl) and CEC, and these can be attributed to low organic matter present
because of flushing by tides. This also explains why organic matter at the soil
surface (0-20 cm) is lower on the seaward area. As for the landward area, the finding
was contradictory, where the total carbon and CEC were found to be high. These
findings were comparable to other studies by Rambok et al. (2010).
CONCLUSION
The study showed that the middleward zone and different dominance demonstrates
significant values of selected soil chemical properties (pH, CEC and Carbon)
compared to other zonation at Awat-Awat Mangrove Forest Reserve, Lawas,
Sarawak Malaysia. In term of depths, upper soil (0-20 cm) has the higher value of
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pH and CEC compared to the lower soil (20-40 cm). The middleward zone of
mangrove forest has shown signs of storing carbon. But, further studies are needed
to verify mangrove potential as carbon storage as many other factors may also
influence.
ACKNOWLEDGEMENTS
We wish to thank Universiti Putra Malaysia for funding this project. The
contribution and assistance from the Sarawak Forestry Department, Miri Forestry
Department and all staff of the Department of Forestry Science and Department of
Crop Science are greatly appreciated.
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