Geochemical Journal, Vol. 45, pp. 1 to 13, 2011
Distribution of combined monosaccharides in sediments
from the Lake Rawa Danau, West Java, Indonesia:
Sources and diagenetic fate of carbohydrates in a tropical wetland
SHAFI M. TAREQ1,2* and KEIICHI O HTA 1
1
School of Environmental Science, The University of Shiga Prefecture,
2500 Hassaka-cho, Hikone, Shiga 522-8533, Japan
2
Department of Environmental Sciences, Jahangirnagar University, Dhaka-1342, Bangladesh
(Received July 4, 2009; Accepted April 21, 2010)
Monosaccharide compositions were determined for a sediment core (RD-1) collected from a tropical wetland, Rawa
Danau, West Java, Indonesia (location 6°11′ S and 105°59′ E) to assess the sources and diagenetic fate of carbohydrates in
a tropical wetland based on the acid-hydrolysis monosaccharide compositions. Total monosaccharides (TCHO; normalized to organic carbon) and individual monosaccharide abundances were variable and mostly dominated by glucose through
out all depths. The high TCHO, uneqimolar monosaccharide compositions and relatively low deoxysugars/pentoses ratio
indicated that carbohydrates were preserved under reducing conditions. The monosaccharide compositional data and diagnostic parameters show that sources of sedimentary carbohydrates changes due to changes in terrigenous plant material
which predominantly comprised of angiosperm plants. There are also few transitions between terrestrial and aquatic sources
as the most dominant source of sedimentary carbohydrates. Principal component analysis (PCA) of the monosaccharide
composition of potential source organisms and RD-1 samples revealed that sources of carbohydrates can be distinguished
from the factor loading values. A cross plot of principal component one (PC1) and two (PC2) clearly separated terrestrial
and aquatic sources since PC2 has positive values for terrestrial sources and negative values for aquatic sources. Vertical
profile of PC2 indicated few major changes in sources of carbohydrates in Rawa Danau wetland associated to changes in
local environment. Therefore, combination of monosaccharides composition to PCA is applicable for investigating the
sources and fate of carbohydrates in natural environments.
Keywords: carbohydrates, West Java, biomarker, diagenesis, wetland, vegetation changes
compounds in both aquatic and terrestrial organisms, and
represent the most abundant class of biochemical in the
biosphere. Given their ubiquity in living organisms, several researchers showed that monosaccharide composition could reflect the biological origin of organic matter
(Cowie and Hedges, 1984a; Nierop et al., 2001; da Cunha
et al., 2002). However, its application for investigating
the biogeochemical signatures of a complex source environment (e.g., tropical wetland) is limited because of some
potential problems, for example, different diagenetic reactivity and labile nature of the storage carbohydrates
(Degens and Mopper, 1975; Murayama, 1984; Hedges et
al., 1985; Guggenberger et al., 1996; Opsahl and Benner,
1999; Lallier-Vergès et al., 2008).
In a tropical lake, sources of carbohydrate are variable. Terrestrial plants and aquatic organisms are the major
sources of carbohydrates in the SOM. In addition, degradation of aquatic biota and soil materials from the lake
catchments also contribute the carbohydrates to the SOM
in the lake environment. The carbohydrates comprise
about 75 wt% of terrestrial plant tissue, where they occur
INTRODUCTION
Biogeochemical studies on sedimentary organic matter (SOM), particulate organic matter (POM), dissolve
organic matter (DOM), and humic substances in lake, river
and ocean have blossomed during the past few decades,
with numerous advances in understanding their diagenetic
fate and versatility of application being made (Keil et al.,
1989; Hedges et al., 1994; Cowie and Hedges, 1994; Ogier
et al., 2001; Benner and Opsahl, 2001; da Cunha et al.,
2002; Amon and Benner, 2003; Jia et al., 2008). Organic
matter (OM) preserved in lacustrine sediments can serve
as an information archive of environmental change as well
as the diagenetic fate of different types of compounds
(e.g., carbohydrate, lignin and hydrocarbon) through time.
Carbohydrates are important as structural and storage
*Corresponding author (e-mail: [email protected])
Copyright © 2011 by The Geochemical Society of Japan.
1
Fig. 1. Map of coring site in the Lake Rawa Danau, West Java, Indonesia.
primarily in structural polysaccharides such as cellulose,
hemicelluloses and pectin (Aspinall, 1970; Sjostrom,
1981), although plankton and bacteria contain 20 to 40
wt% and 40 wt% carbohydrates, respectively, more than
half of which are storage polysaccharides (Parsons et al.,
1984; Moers et al., 1993). The suite of neutral monomers
produced upon acid hydrolysis of carbohydrates can be
useful to characterize different types of vascular plant tissue, and to determine the sources and diagenetic state of
SOM (Cowie and Hedges, 1984a). The concentration and
vertical distribution of these compounds in peat cores can
provide information on the diagenetic changes in the
depositional environment. However, few studies have
addressed the vertical variations of carbohydrates through
the peat cores in tropical areas to identify their sources
and depositional environment through time, or their fate
during early diagenesis (Moers et al., 1993).
2
S. M. Tareq and K. Ohta
The aim of the present study was to investigate the
sources and nature of the early diagenetic fate of the carbohydrate fraction in SOM from a tropical wetland, Rawa
Danau, west Java, Indonesia, in order to reconstruct the
records of major changes in the watershed vegetation and
deposition environment during the mid to late Holocene.
We also assessed biogeochemical aspects based on the
compositions of monosaccharides and their principal component analysis (PCA) parameters.
MATERIALS AND METHODS
Study area and sampling
The Rawa Danau is a low altitude lake situated 100 m
above sea level (asl) in a protected area of West Java,
Indonesia (Fig. 1). This area experiences a wet monsoon
climate with an average annual temperature of 27.5°C,
and average annual precipitation of 2650 mm, with a distinct maximum during summer. Peat formation at the
Rawa Danau began during the last glacial period (approx.
14500 y BP) in an old volcano crater. Peat deposits prevail in the central swamp area, with sequences up to 4–6
m thick just below the surface. The swamp now covers
an area of 70 km2, a major portion of which is considered
to have been developed from anthropogenic influences.
The history of human activity and vegetation changes at
the Rawa Danau is documented by Kaars et al. (2001)
and Tareq et al. (2005). The hydrology of the lake is
controlled by the topography of the surrounding areas as
well as local climatic factors. There is no continuous input of streams into the lake, and consequently the changes
in water level are controlled by the precipitation/evaporation balance. However, the lake has one surface outlet
to the southern edge of the Sunda shelf. It has a moderate
sedimentation rate (0.048 cm/y), which is comparable to
other tropical wetlands (Tareq et al., 2007).
The present study is concerned with the uppermost
peat layer which has accumulated during the mid to late
Holocene (calibrated radiocarbon ages 7428 y BP; Tareq
et al., 2007). The core (3.6 m, i.d. 10 cm) was taken using a piston corer, from the northwestern Rawa Danau
caldera (6°11′ S and 105°59′ E; Fig. 1), where thickest of
peat deposit was found. A subsurface shorter core (32 cm,
i.d. 10 cm) was also taken by a gravity corer. Both cores
were kept frozen and cut into 2 cm slices using a stainless steel hand saw. Each slice was freeze dried and pulverized by a mortar and pestle. After sieving through 300
µm, fine powder samples were stored in airtight, acidwashed brown glass vials in a freezer until analysis.
Bulk analysis
Organic carbon (OC) and total nitrogen (TN) were
determined on 5–10 mg samples after treatment with 1 M
HCl to remove carbonate. Measurements were performed
by a Thermo Quest NA 2500 NCS elemental analyzer.
The equipment was calibrated using alanine standards,
and half of the analyses were performed in duplicate. The
deviation was estimated by evaluating the reproducibility between the duplicates and was less than 5% for both
OC and TN. Stable carbon isotope compositions (δ13C;
the Pee Dee Belemnite (PDB) scale) were determined by
an elemental analyzer/mass spectrometer (Thermo Quest
NA 2500 NCS/Finnigan MAT 252). Half of the samples
were analyzed in duplicate, with a maximum difference
of ±0.20‰. The performance of the system was evaluated by running the working standard alanine δ 13 C
(–21.56‰) and the accepted value (–21.56 ± 0.07‰) was
obtained within a sample size range of 7–100 µg carbon.
Monosaccharide analyses
The procedure used for neutral sugar analysis was
modified from previous works (Mopper, 1977; Cowie and
Hedges, 1984b; Bourdon et al., 2000). A series of experiments with various acid concentrations (0.12, 0.6, 1.2,
1.8, 2.4, 4.8 and 6 M HCl) was conducted with the peat
samples to determine the optimum conditions, i.e., the
acid concentration sufficient to release a maximum
amount of compounds but with minimal degradation. The
hydrolysis was carried out in two successive stages (Ogier
et al., 2001). The first step aimed to release
monosaccharides from the more labile polymers such as
hemicelluloses (mostly noncellulosic). The second step
was conducted by soaking the solid residue with obtained
from the first step in concentrated acid to release the
cellulosic glucose.
Pulverized samples (approx. 100 mg dry wt.) were
introduced into Pyrex tubes together with 10 ml of 1.2 M
HCl. The tubes were tightly sealed and heated for 5 hr at
100°C in a block aluminum heater placed on a digital
shaker (KS501, IKA Labortechnik). After cooling, the
samples were centrifuged (3000 rpm, 20 min). The
supernatant was subjected to analysis (mild hydrolysis
fraction). The precipitate in Pyrex tubes was soaked for
12 h at ambient temperature with 1 ml of 12 M HCl, after
which the concentrated acid was diluted to 1.2 M HCl.
The tubes were sealed and the hydrolysis was performed
under the conditions described above. This treatment is
strong hydrolysis.
In each hydrolysate, 100 µl of a solution of alditol
(0.62 mg/ml) was added as an internal standard. The
hydrolysates were first concentrated to 1–2 ml with a rotary evaporator, at a temperature not exceeding 50°C and
then evaporated to dryness at 25–30°C. The flasks containing the monosaccharides were dried for 48 hr over
KOH in a desiccator, redissolved in pyridine and transferred to a small vial. The anomeric monosaccharide mixtures were equilibrated in pyridine containing 0.2%
lithium perchlorate in closed vials for 12 hr at 50°C. A
portion of the equilibrated samples (100 µ l) was
derivatized
by
adding
100
µl
of
bis(trimethylsilyl)trifluoroacetamide (BSTFA) at 70°C for
1 hr.
The silylated monosaccharides were analyzed by using a Shimidzu 14B gas chromatograph with flame ionization detector equipped with a DB-1 fused silica capillary column (0.25 mm i.d. × 60 m), held at 300°C. A split/
splitless injector was maintained at 300°C and used in
the splitless mode (valve reopened 1 min after injection).
The oven programme was as follows: 130°C for 5 min
followed by increase to 180°C at 2°C/min, then increase
to 250°C at 3°C/min and held for 10 min. The carrier gas
was helium. Peaks were tentatively identified through
retention times and quantified using a standard mixture
of nine neutral monosaccharides, namely, lyxose, arabinose, rhamnose, ribose, fucose, xylose, mannose, galac-
Distribution of combined monosaccharides in sediments
3
Fig. 2. Test for determining optimum condition of acid hydrolysis on homogeneous samples of the Rawa Danau peat. (a) Changes
in hydrolysis time with 1.20 M HCl. (b) Changes in HCl concentrations at 5 hrs hydrolysis times. Abbreviations: Ly, lyxose; Ri,
ribose; Ar, arabinose; Xy, xylose; Fu, fucose; Rh, rhamnose; Ma, mannose; Ga, galactose; Gl, glucose.
Fig. 3. Vertical profiles of (a) total neutral monosaccharides (TCHO mg/100 mg OC), and weight % (Glucose free) of (b) Ribose,
(c) Fucose + Ribose and (d) Glucose/Ribose ratios of RD-1 core sample. Abbreviations: TP, Terrestrial plant sources; AP, Aquatic
sources.
tose and glucose. Quantification was based on one of the
major and better resolved anomer peaks given by each
studied compound. The analytical error (lyxose = 10.8%;
arabinose = 6.5%; ribose = 12%; xylose = 7.4%; rhamnose = 8.5%; fucose = 9.7%; mannose = 6.7%; galactose
= 11.1%; glucose = 5.1%) was evaluated by triplicate
analyses of the same samples, and is generally lower for
more abundant monosaccharides.
4
S. M. Tareq and K. Ohta
RESULTS
Hydrolysis: optimum condition
A series of hydrolysis experiments was carried out for
the RD1 samples under different acid concentrations
(0.12, 0.6, 1.2, 1.8, 2.4, 4.8, and 6 M HCl) and times for
hydrolysis (1, 2, 3, 4, 5, 7, and 10 hrs), as well as with
concentrated acid pretreatment prior to hydrolysis. The
Fig. 4. Relationship between relative yields of individual neutral sugars as mole % of the total and the yield of the total neutral
monosaccharides (mg/g dry peat sample) for RD-1 core sample. Values in parentheses indicate correlation coefficient. Abbreviations: Ly, lyxose; Ri, ribose; Ar, arabinose; Xy, xylose; Fu, fucose; Rh, rhamnose; Ma, mannose; Ga, galactose; Gl, glucose.
yield of individual monosaccharides obtained by treatment with 1.2 M HCl increased depending on hydrolysis
time (Fig. 2), and remained almost constant over time
between 4 and 6 hours. The yields increased depending
on acid strength to a maximum at treatment with 1.2 M
HCl. Pretreatment with concentrated HCl, prior to hydrolysis, affords more resistant cellulosic glucose and a
small fraction of mannose. As the results of the hydrolysis experiments, the hydrolysis conditions employed for
the Rawa Danau samples were 1.2 M HCl for 5 hrs, unless noted otherwise.
Monosaccharide composition
The core was divided into 24 depth sections, and the
OC, C/N ratio, δ 13C values and monosaccharide compositions were determined. Mild-hydrolysis condition
yielded a mixture of monosaccharides, and nine monosaccharide compounds were quantified and tabulated, but
strong-hydrolysis yielded mostly mannose and glucose
(Appendix 1). The concentrations of total
monosaccharides ranged from 27.38 to 159.89 mg/g dry
samples with an average value of 83.47 mg/g dry sample
and varied with core depths. The concentrations of total
Distribution of combined monosaccharides in sediments
5
nificant correlations (p < 0.01) were not observed for glucose (r 2gl = 0.44) and ribose (r2ri = 0.07).
Fig. 5. Cross plot of the first and second component scores of
PCA based on relative abundances of individual
monosaccharides to the total neutral monosaccharides of 24
sections of RD-1 core sample from top to bottom, and 20 different source organisms (Cowie and Hedges, 1984a). Abbreviations: B, bacteria; W, woody plants; nW, nonwoody plants; Pz,
phytoplankton/zooplankton; RD, Rawa Danau core samples.
monosaccharide normalized to OC content (TCHO) were
variable, and show decreasing trend with depth (Fig. 3a).
In general, mol percentages of individual monosaccharide at all depths were dominated by glucose (34.17 to
58.77%), followed by mannose (8.54 to 28.31%), xylose
(6.67 to 18.89%), arabinose (3.01 to 10.00%) and galactose (1.00 to 11.94%). Ribose was present with very low
concentration throughout the core, although the upper few
sections contained relatively higher amounts of ribose as
well as deoxysugars (fucose and rhamanose).
The relationships between the contribution of individual monosaccharides and the concentration of total
neutral sugar (TNS; mg/g dry sediments) are depicted in
Fig. 4. The relative contribution of deoxysugars (fucose
and rhamonose), lyxose, and glactose decreased with increasing the TNS yield irrespective of depths, although
those of arabinose, xylose, and mannose increased. The
negative correlations between fucose (r2fu = 0.73), lyxose
(r 2ly = 0.88), rhaminose (r2rh = 0.85), and galactose (r2ga
= 0.85) with the total neutral monosaccharide yield were
highly significant (p < 0.001, t-test). The positive correlation for arabinose (r2ar = 0.60), mannose (r2ma = 0.57),
and xylose (r 2xy = 0.59) was significant (p < 0.01). Sig6
S. M. Tareq and K. Ohta
Principal component analysis (PCA): source variations
To distinguish the sources of carbohydrates, PCA was
performed separately on the correlation matrix of the
mol% of individual and total monosaccharide for both
potential source organisms and RD-1 core samples. Results of the PCA of the monosaccharide compositions of
20 different source organisms, including terrestrial plants,
zooplankton, phytoplankton and bacteria (Cowie and
Hedges, 1984a) revealed that the sum of the first (PC1)
and second (PC2) principal components accounted for
90.8 (69.1+21.7)% of the total variance. On the other
hand, the results of the PCA of 24 depth sections from
top to bottom of the core show that the PC1 explained the
maximum amount of variance (91.2%), but the PC2 explained only 7.4%. The PCA results can be presented
graphically as factor score plots (Fig. 5). The PC1 had
positive loadings on carbohydrates of both terrestrial and
aquatic origin including microorganisms. The PC2 had
negative loadings on terrestrial plant origin and positive
loading for aquatic sources (plankton and bacteria). As
the PCA of monosaccharide compositions of the potential source organisms, PC2 is the most important component for evaluating the sources of carbohydrates by way
of terrestrial verses aquatic origin. These results indicate
distinct contrasts in the origin of the carbohydrates that
are not dependent on the sampling site or depth.
DISCUSSION
Early diagenesis
Early diagenetic processes could influence the source
signatures (Hedges et al., 1985; Hamilton and Hedges,
1988; Opsahl and Benner, 1999; Amon and Benner, 2003).
Several researchers (Degens and Mopper, 1975; Oades,
1984; Cowie and Hedges, 1984a; Ittekkot and Arian, 1986;
Nierop et al., 2001; da Cunha et al., 2002) have used
monosaccharide compositions and other parameters to
characterize the distributions of carbohydrates from different organisms as well as SOM. We used some of those
parameters as summarized in Table 1. Diagenetic alterations of monosaccharides in terrigenous OM have already
been investigated in a variety of environments (Ittekkot
and Arian, 1986; Cowie and Hedges, 1994; Hedges et al.,
1994; Benner and Opsahl, 2001). The monosaccharide
composition lead to equimolar, and the TCHO yield decreases with progress of diagenetic stage during postdeposition. The unequimolar monosaccharide compositions and relatively high TCHO yield of RD-1 core (Fig.
3a) throughout all depths suggest that the diagenetic
change is not significant in Rawa Danau. Conditions necessary for diagenesis (microorganisms, enzymatic and
*Relative values of diagnostic parameters based on neutral sugar composition of unaltered source organisms in Cowie and Hedges (1984a) and as
stated in Degens and Mopper (1975), Odes (1984), Nierop et al. (2001).
Terrestrial (>54.1) vs. Aquatic (<16.9)
Terrestrial (<1.41) vs. Aquatic (>3.97)
Terrestrial (<2.75) vs. Aquatic (>11.87)
Terrestrial plant (>50) vs. Aquatic (<20)
Gymnosperm (<17.02) vs. Angiosperm (>23.76)
Gymnosperm (>3.67) vs. Angiosperm (<0.89)
Woody (<15.16) vs. Nonwoody (>20.73)
Woody (>13.73) vs. Nonwoody (>19.14)
Terrestrial plants (<0.50) vs. Microbial (>2.00)
and diagenetic indicator
Total carbohydrate per 100 mg organic carbon
Weight percentage of ribose (glucose free basis)
Combined weight percentage of ribose and fucose (glucose free basis)
Glucose/ribose
Weight percentage xylose (glucose free basis)
Molar ratio of mannose and xylose
Combined weight percentage of arabinose and galactose (glucose free basis)
Combined weight percentage of arabinose and lyxose (glucose free basis)
(Rhmanose + Fucose)/(xylose + arabinose)
∑TCHO/100 mg OC
% Ri
% (Ri+Fu)
Gl/Ri
% Xy
Ma/Xy
% (Ar+Ga)
% (Ar+Ly)
DeoxyS/C5
Inferences
Definitions
Parameters
geochemical) in a sub-aqueous environment become
unfavorable under the reducing condition of Rawa Danau
and the terrigenous OM had not undergone substantial
degradation after entering the lake sediments.
Molecular analyses can also be useful to evaluate the
early diagenesis of carbohydrates (Amon and Benner,
2003). In a continental aquatic ecosystem, pentose is
mainly derived from vascular plants (da Cunha et al.,
2002). Simultaneous decomposition of plant-derived
monosaccharides and production of microbially producing monosaccharides can be estimated by the ratio between deoxysugars and pentoses (DeoxyS/C5) which also
reflects early diagenetic trend of sedimentary carbohydrates. The vertical distribution of these ratios with depths
showed that DeoxyS/C5 is variable (Fig. 6a), and no obvious general increasing or decreasing trend is observed
with depth except elevated values at few sections of the
core. These elevated values might indicate variation of
sources rather than diagenetic conditions. The lack of such
a trend with depth and the high total monosaccharide content support that carbohydrates (after loss of more labile
portions) remained diagenetically unaltered in subaqueous tropical wetland. In addition, if preferential degradation of carbohydrates has occurred, the residue of the
SOM be relatively enriched in 13C-depleted biomolecules
(e.g., lignin and free lipids). But, the δ13C values do not
show any obvious trend with depth (Fig. 6b), and the small
scale excursions are related to other factors such as changing sources and climatic conditions (e.g., water availability, humidity, and temperature).
The carbohydrates preservation in a tropical lake might
Table 1. Definition of different carbohydrate diagnostic parameters*
Fig. 6. Vertical profiles of (a) Fucose + Rhmanose; Deoxy/
Arabinose + Xylose; C5 and (b) δ13C (‰ PDB) of RD-1 core
sample. δ13C data obtained from Tareq et al. (2007).
Distribution of combined monosaccharides in sediments
7
be related to lignin distribution. The peats in Rawa Danau
are highly lignified (8.66 to 31.31 mg/100 mg OC; Tareq
et al., 2004), which greatly reduces the digenetic activities by inhibiting the decay of associated polysaccharides
(Hedges et al., 1985; Kuder et al., 1998; references
therein), possibly by shielding them from extracellular
hydrolytic enzymes (Crawford, 1981). The tropical terrestrial plants contain abundant tannin that could preserve
during early stages of peat formations (Wilson and
Hatcher, 1988), and also inhibit the effectiveness of some
microbial enzymes (Moers et al., 1994). Thus, the carbohydrates in the Rawa Danau peat core remains relatively
unaltered after loss of the relatively more labile portions,
and can be useful as biological source indicators.
Sources of carbohydrates: aquatic plankton, bacteria, and
woody and non-woody plants
The yield of carbohydrate (normalized to OC) from
terrestrial plant tissue is higher than that of aquatic organisms or bacteria (Kögel-Knabner, 2002). The vertical
profile of the TCHO exhibited decreasing trend with core
depth with an average value of 396 µg/mg OC (Fig. 3a).
The TCHO distribution pattern and average value reflect
contributions from both productions of terrestrial plants
and aquatic production. The decreasing trend of TCHO
with depth might be related to a stepwise loss of more
labile portions, terrestrial source variations, in situ
diagenesis and other factors. There are few peaks in the
vertical profile of TCHO due to transitions between terrestrial and aquatic sources as the most dominated source.
Weight percentage of ribose and sum of ribose and
fucose (% (Ri+Fu), on glucose free) can also distinguish
between carbohydrates of aquatic and terrestrial sources
(Table 1). Aquatic organisms and microbes contain significantly higher levels of these monosaccharides than
terrestrial plants where they occur as minor components
(Ogier et al., 2001), and extracellular microbial slimes
which may survive early diagenesis to some extent (de
Leeuw and Largeau, 1993). The vertical distributions of
ribose and % (Ri+Fu) indicate that the principal source
of carbohydrate at the Rawa Danau changes between productions of terrestrial plants and aquatic organisms except in the top few sections (50 cm) where ribose (wt%)
and the “% (Ri+Fu)” are relatively high (Figs. 3b and c).
Such high values are attributed to the microbial activity
at the top section due to recent changes of lake water level.
This is in agreement with lignin phenol data of the same
core. The acid/aldehyde (Ad/Al) ratios of both vaniyll and
syringyl phenol groups are highly variable in the upper
50 cm (Tareq et al., 2004). Furthermore, the glucose/ribose (Gl/Ri) ratios, varied between 8.5 and 99.1 with an
average value of 52.8, also indicate that the major sources
of carbohydrates in the SOM are vascular plants (Fig. 3d).
The aquatic organisms (plankton) might be enriched in
8
S. M. Tareq and K. Ohta
Fig. 7. Ternary plots of (sum of Arinose, Xylose, Mannose, and
Glucose) – (sum of Fucose, Rhamnose, Ribose, Galactose, and
Lyxose) – Total neutral monosaccharides (TCHO mg/100 mg
OC) composition of the Rawa Danau peat samples, and 20 different types of source organisms (Cowie and Hedges, 1984a).
Abbreviations: B, bacteria; W, woody plants; nW, nonwoody
plants; Pz, phytoplankton/zooplankton; RD, RD-1 core samples.
glucose due to the presence of starch-like storage
polysaccharides depending on season (Cowie and Hedges,
1984a) which might skew the Gl/Ri ratio. The possibility
of such effect is, however, very small because starch-like
polymers disappear within short time after deposition, and
do not affect the Gl/Ri ratio in the long run. The Gl/Ri
values increasing with depth due to the refractory nature
of cellulose, shows a remarkable biological stability of
plant-derived cellulose reflecting the specific nature of
hydromorphic environments such as peat lands, compared
to aerobic soil environments. The ratios of total glucose
and noncellulosic glucose ranges from 1.45 to 5.85 with
an average value of 2.92 (Table 1; the values >1 indicate
presence of cellulose), which also corroborated with the
above discussion.
Correlations between the contributions of various
monosaccharide monomers and the TNS divide the nine
aldose derivatives into two groups depending on their
correlation coefficient values (r 2 ) and trends; (1)
deoxysugars (rhamanose and fucose), galactose, ribose,
and lyxose decrease with TNS, and have significant negative correlations (values: –0.7 to –1) except ribose (principal sources are microorganisms and aquatic production),
Fig. 8. Vertical profiles of weight % (Glucose free) of (a) Xylose, (b) Mannose/Xylose ratios, (c) Arabinose + Galctose and (d)
Arabinose + Lyxsoe of core RD-1 core sample. Abbreviations: A, Angiosperm plants; G, Gymnosperm plants; W, Woody plants;
nW, Non-woody plants.
(2) arabinose, xylose mannose and glucose increase with
TNS and have moderate positive correlations (values: 0.5
to 0.7) except glucose (principal sources are terrestrial
plants). Based on these two groups and TNS, a ternary
plot of 24 sections of the entire core of the Rawa Danau
with the monosaccharide compositional data of microorganism, plankton, and different terrestrial plants, as reported by Cowie and Hedges (1984a), was constructed
(Fig. 7). The ternary plot showed variable composition
and carbohydrates mostly derived from terrestrial plants
except in few sections as reflected in the other parameters.
Angiosperm-derived hemicellulose is characterized by
high concentration of xylose units, although this macromolecule derived from gymnosperm is relatively rich in
mannose. These distributions of the xylose and mannose
in hemicellulose from different vascular plants have already been used to distinguish between softwood and
hardwood plant sources (Cowie and Hedges, 1984a;
Hedges, 1990). The vertical profile of xylose (wt%) of
Rawa Danau core indicated few transitions of terrestrial
vegetation (Fig. 8a) between gymnosperm and angiosperm
while the most dominating vegetation is angiosperm.
These transitions are also reflected in the vertical profile
of Ma/Xy ratio (Fig. 8b). This is consistent with the vegetation changes inferred by lignin phenol data of the same
core, which has a positive correlation (r2 = 0.48) between
Ma/Xy and lignin phenol vegetation index (LPVI) (Tareq
et al., 2004). LPVI was calculated according to Tareq et
al. (2004): LPVI = [{S(S+1)/(V+1)+1} × {C(C+1)/
(V+1)+1}]; where V, S and C are vanillyl, syringyl and
cinnamyl phenols respectively and expressed in % of the
sum of eight vanillyl, syringyl and cinnamyl phenols. The
LPVI records information about the vegetation changes
since gymnosperm, angiosperm and nonwoody plants
have different compositions of V, S and C phenol groups.
Thus Ma/Xy ratio is more effective than absolute abundance of individual monosaccharide (xylose) and could
be used to study vegetation changes between gymnosperm
and angiosperm.
Non-woody plant materials are typically rich in pectin compared to woody plant materials. Pectin is mainly
composed of arabinose, galactose, and hexauronic acids
(Sjostrom, 1981; Kögel-Knabner, 2002). Thus, the combined weight percentage of arabinose and galactose can
be used to separate non-woody plant sources among all
terrestrial plant sources. Cowie and Hedges (1984a) also
showed that the combined weight percentage of the lyxose
and arabinose can completely distinguish the non-woody
sources. The vertical profiles of these two parameters do
not show any clear changes of carbohydrate sources in
the Rawa Danau during the accumulation periods (Figs.
8c and d). The values of these two parameters varied between woody and non-woody range with small scale excursions. This might be due to the fact that pectins are
minor components, and highly soluble in neutral water
compared to hemicelluloses and cellulose. Thus, this
chemical nature influenced the burial process of terrestrial carbohydrate in a lake such as the Rawa Danua.
Implication at Rawa Danau by PCA
In PCA, the first factor accounts for the maximum
Distribution of combined monosaccharides in sediments
9
Fig. 9. Vertical distribution of the second principal component
(Solid line: PC2) and lignin phenol vegetation index (broken
line: LPVI) of RD-1 core sample with boundary line for terrestrial plant sources and aquatic origin. Detail explanation of
LPVI data obtained in Tareq et al. (2004). Abbreviations: TP,
Terrestrial plant sources; AP, Aquatic production/organisms
sources; G, Woody gymnosperm; g, Non-woody gymnosperm;
A, Woody angiosperm.
amount of variance and subsequent factors explain successively smaller quantities of the original variance. The
number of principal components, which were used for interpretation of results, was determined based on
eigenvalues. This study retains only factors with
eigenvalues that exceed one. This criterion was proposed
by Kaiser (1958), and is probably the one most widely
used (Davis, 1987; Reyment and Joreskog, 1993).
A cross plot of PC1 and PC2 with PCA data of different source organisms show variable compositions irrespective of depth (Fig. 5), suggesting mixtures of different sources. This two-dimensional separation of source
OM indicates that both the autochthonous and
allochthonous productions could contribute to the tropical wetland SOM, and there were changes between terrestrial and aquatic sources as the major contributor. The
signature of microorganism sources was not exclusively
demonstrated but cannot be ruled out due to the rapid
10
S. M. Tareq and K. Ohta
diagenetic alteration of storage polysaccharides (compared to structural polysaccharides of vascular plants)
from their sources.
The PC2 offers valuable information about the sources
of organisms and depositional environments. PC2 values
of the peat core in the Rawa Danau as a function of depth
with distinct boundary lines between aquatic and terrestrial sources are presented in Fig. 9. The PC2 of carbohydrate compositions of the Rawa Danau peat deposits
records information about the changes in sources of the
SOM as well as the depositional environment of the tropical wetland during peat accumulation periods. These
changes likely resulted in an increased proportion of
aquatic production in the lake, which should lead to positive PC2 values. One possible explanation for positive
PC2 values is the higher contribution of aquatic as well
as microorganism sources compared to terrestrial sources.
A comparison of the vertical distribution patterns of
the PC2 and LPVI (Tareq et al., 2004) showed that they
were inversely synchronized with one another (Fig. 9)
and gymnosperm dominating events have relatively high
aquatic contribution. The result of the LPVI cannot simply be transposed to the present one, because the theoretical background and the type of biomolecules investigated are different in the two cases. However, the PC2
and LPVI indicate that the major sources of SOM at the
Rawa Danau might have been changing based on same
environmental factors (e.g., local climate and hydrology).
These changes might be directly related to the lake water
level or indirectly to lake catchment runoff (i.e.,
precipitations). High terrestrial runoff was also documented in core lithology as well as total organic carbon
content and total lignin profiles. The catchment runoff
increased the nutrient fluxes to the lake that enhanced
the aquatic productivity. The δ15N data (Tareq et al., 2007)
and diatom data (Kaars et al., 2001) also suggested
changes in lake water level and aquatic productivity. The
hydrological changes inferred from PC2 were also supported by other geochemical data such as lignin distribution. Therefore, from the PC2 values of sedimentary monosaccharide compositions, one can easily infer periodic
cycles of local climate and hydrology associated with dry
and wet microenvironments around a tropical wetland
such as the Rawa Danau during the periods accumulated
organic matter.
CONCLUSIONS
Carbohydrates are important material of sedimentary
organic matter, and their behavior in a subaqueous tropical aquatic ecosystem is complex. The multiplicity of biological sources, the initial loss of the more labile portions, and the dynamic or hydrological changes in continental aquatic ecosystems, may alter the signature origi-
nally contained in the neutral monosaccharide distribution. The relative abundances of individual monomers
inferred the changes in broad ranges of organic matter
sources such as all terrestrial plant sources from that of
aquatic sources. Subtle changes in monosaccharide composition and carbohydrate diagnostic parameters of RD1 core related to changes in sources and/or early
diagenesis. Although diagenesis was not the dominating
factors during accumulation periods, the monosaccharide
composition differed from that of living organisms. These
differences attributed to the initial loss of the more labile
portions, and to a considerable level of biotic/abiotic alternation of original carbohydrates macromolecular structure without depolymerization. The ratios between total
glucose and noncellulosic glucose (from mild hydrolysis
only) suggest that a significant amount of cellulose
(mostly derived from terrestrial plants) is present throughout the core, and the variations of cellulose concentrations might be related to variations of terrestrial source
input.
Principal component analysis on monosaccharide
compositional data of different source organisms and core
RD-1 core samples showed few transitions of the predominating source of SOM between terrestrial plants and
aquatic organism during the mid to late Holocene. PC2
values of sedimentary monosaccharide compositions are
the most important parameters that can easily infer
changes in carbohydrate sources associated with periodic
cycles of local climate and hydrology around a tropical
wetland. However, the interpretation of monosaccharide
data is highly complex and is useful as a qualitative proxy
rather than a quantitative proxy and should be used cautiously. The combination of monosaccharide composition
with other biomarkers such as lignin and wax hydrocarbon in addition to stable isotope ratios proved to be a
useful tool for understanding the variations of sources of
SOM at the Rawa Danau.
Acknowledgments—Shafi M. Tareq is grateful to Japan Society for the Promotion of Science (JSPS) for postdoctoral fellowship for foreign researcher. We are also grateful to Dr. Ken
Sawada and two anonymous reviewers for the constructive comments.
REFERENCES
Amon, R. M. W. and Benner, R. (2003) Combined neutral
monosaccharides as indicators of the diagenetic state of
dissolved organic matter in the Arctic Ocean. Deep-Sea Res.
I 50, 151–169.
Aspinall, G. O. (1970) Pectins, plant gums and other plant
polysaccharides, The carbohydrates. Chemistry and Biochemistry (Pigman, W. and Horton, D., eds.), 515–536,
Academic Press, London.
Benner, R. and Opsahl, S. (2001) Molecular indicators of the
sources and transformations of dissolved organic matter in
the Mississippi River plume. Org. Geochem. 32, 597–611.
Bourdon, S., Laggoun-Défarge, F., Disnar, J. R., Maman, O.,
Guillet, B., Derenne, S. and Largeau, C. (2000) Early
diagenesis of organic matter from higher plants in a
malagasy peaty marsh. Application to environmental reconstruction during the Sub-Atlantic. Org. Geochem. 31, 421–
438.
Cowie, G. L. and Hedges, J. I. (1984a) Carbohydrate sources
in a coastal marine environment. Geochim. Cosmochim.
Acta 48, 2075–2088.
Cowie, G. L. and Hedges, J. I. (1984b) Determination of neutral sugars in plankton, sediments, and wood by capillary
gas chromatography of equilibrated isomeric mixtures. Anal.
Chem. 56, 497–504.
Cowie, G. L. and Hedges, J. I. (1994) Biochemical indicators
of diagenetic alteration in natural organic mixtures. Nature
369, 304–307.
Crawford, R. L. (1981) Lignin Biodegradation and Transformation. Willey, New York, 154 pp.
da Cunha, L. C., Serve, L. and Blazi, J.-L. (2002) Neutral sugars as biomarkers in the particulate organic matter of a
French Mediterranean river. Org. Geochem. 33, 953–964.
Davis, J. C. (1987) Statistics and Data Analysis in Geology.
John Wiley & Sons, New York, 656 pp.
de Leeuw, J. and Largeau, C. (1993) A review of
macromolecular organic compounds that comprise living
organisms and their role in kerogen, coal and petroleum
formation. Org. Geochem.: Principals and Applications
(Engel, M. H. and Macko, S. A., eds.), 23–72, Plenum Press,
New York.
Degens, E. T. and Mopper, K. (1975) Decay mechanism of organic matter in marine soils. Soil Sci. 119, 65–72.
Guggenberger, G., Zech, W. and Thomas, R. J. (1996) Lignin
and carbohydrate alteration in particle-size separates of an
oxisol under tropical pastures following native savanna. Soil
Biol. Biochem. 27, 1629–1638.
Hamilton, S. E. and Hedges, J. I. (1988) The comparative
geochemistries of lignins and carbohydrates in a anoxic
fjord. Geochim. Cosmochim. Acta 52, 129–142.
Hedges, J. I. (1990) The chemistry of archaeological wood.
Archaeological Wood: Properties, Chemistry, and Preservation (Rowell, R. M. and Barbour, R. J., eds.), 111–140,
American Chemical Society, Washington, D.C.
Hedges, J. I., Cowie, G. L., Ertel, J. R., BarBour, R. J. and
Hatcher, P. G. (1985) Degradation of carbohydrates and
lignins in buried woods. Geochim. Cosmochim. Acta 49,
701–711.
Hedges, J. I., Cowie, G. L., Richey, J. E., Quay, P. D., Benner,
R., Strom, M. and Forsberg, B. R. (1994) Origins and
processing of organic matter in the Amazon River as indicated by carbohydrates and amino acids. Limnol. Oceanogr.
39, 743–761.
Ittekkot, V. and Arian, R. (1986) Nature of particulate organic
matter in the river Indus, Pakistan. Geochim. Cosmochim.
Acta 50, 1643–1653.
Jia, G., Dungait, J. A. J., Bingham, E. M., Valiranta, M.,
Korhola, A. and Evershed, R. P. (2008) Neutral
monosaccharides as biomarker proxies for bog-forming
Distribution of combined monosaccharides in sediments
11
plants for application to palaeovegetation reconstruction in
ombrotrophic peat deposits. Org. Geochem. 39, 1790–1799.
Kaars, S. V. D., Penny, D., Tibby, J., Fluin, J., Dam, R. A. C.
and Suparan, P. (2001) Late quaternary paleoecology,
palynology and palaeoliminology of a tropical lowland
swamp, Rawa Danau, West Java, Indonesia. Palaeogeograp.
Palaeoclimat. Palaeoecol. 171, 185–212.
Kaiser, H. F. (1958) The varimax criteria for analytical rotation in factor analysis. Psychometrika 23, 187–200.
Keil, R. G., Tsamakis, E., Giddings, J. C. and Hedges, J. I.
(1989) Biochemical distributions (amino acids, neutral sugars, and lignin phenols) among size-classes of modern marine sediments from the Washington coast. Geochim.
Cosmochim. Acta 62, 1347–1364.
Kögel-Knabner, I. (2002) The macromolecular organic composition of plant and microbial residues as inputs to soil
organic matter. Soil Biol. Biochem. 34, 139–162.
Kuder, T., Kruge, M. A., Shearer, J. C. and Miller, S. L. (1998)
Environmental and botanical controls on peatification—a
comparative study of two New Zealand restiad bogs using
Py-GC/MS, petrography and fungal analysis. Internat. J.
Coal Geol. 37, 3–27.
Lallier-Vergès, E., Marchand, C., Disnar, J.-R. and Lottier, N.
(2008) Origin and diagenesis of lignin and carbohydrates
in mangrove sediments of Guadeloupe (French West Indies):
Evidence for a two-step evolution of organic deposits. Chem.
Geol. 255, 388–398.
Moers, M. E. C., Jones, D. M., Eakin, P. A., Fallick, A. E.,
Griffiths, H. and Larter, S. R. (1993) Carbohydrate
diagenesis in hypersaline environments: application of GCIRMS to the stable isotope analysis of derivatized
saccharides from surficial and buried sediments. Org.
Geochem. 20, 927–933.
Moers, M. E. C., de Leeuw, J. W. and Baas, M. (1994) Origin
and diagenesis of carbohydrates in ancient sediments. Org.
Geochem. 21, 1093–1106.
Mopper, K. (1977) Sugars and uronic acids in sediment and
water from Black sea and North sea with emphasis on analytical techniques. Mar. Chem. 5, 585–603.
Murayama, S. (1984) Changes in the monosaccharide composition during the decomposition of straws under field conditions. Soil Sci. Plant Nutrit. 30, 367–381.
12
S. M. Tareq and K. Ohta
Nierop, K. G. J., Lagen, B. V. and Buurman, P. (2001) Composition of plant tissues and soil organic matter in the first
stages of a vegetation succession. Geoderma 100, 1–24.
Oades, J. M. (1984) Soil organic matter and structural stability: mechanisms and implications for management. Plant
Soil 76, 319–337.
Ogier, S., Disnar, J.-R., Albéric, P. and Bourdier, G. (2001)
Neutral carbohydrate geochemistry of particulate material
(trap and core sediments) in an eutrophic lake (Aydat,
France). Org. Geochem. 32, 151–162.
Opsahl, S. and Benner, R. (1999) Characterisation of carbohydrates during early diagenesis of five vascular plant tissues.
Org. Geochem. 30, 83–94.
Parsons, T. R., Takahashi, M. and Hargrave, B. (1984) Biological Oceanographic Processes. Pergamon Press, Oxford, 330
pp.
Reyment, R. A. and Joreskog, K. H. (1993) Applied Factor
Analysis in the Natural Sciences. Cambridge Univ. Press,
Cambridge, 371 pp.
Sjostrom, E. (1981) Wood Chemistry, Fundamentals and Applications. Academic Press, London, 293 pp.
Tareq, S. M., Tanaka, N. and Ohta, K. (2004) Biomarker signature in tropical wetland: lignin phenol vegetation index
(LPVI) and its implications for reconstructing the
paleoenvironment. Sci. Total Environ. 324, 91–103.
Tareq, S. M., Tanoue, E., Tsuji, H., Tanaka, N. and Ohta, K.
(2005) Hydrocarbon and elemental carbon signatures in a
tropical wetland: Biogeochemical evidence of forest fire and
vegetation changes. Chemosphere 59, 1655–1665.
Tareq, S. M., Tanaka, N. and Ohta, K. (2007) Isotopes and lignin
signature in tropical peat core: An approach to reconstruct
past vegetation and climate changes. TROPICS 16, 131–
140.
Wilson, M. A. and Hatcher, P. G. (1988) Detection of tannins
in modern and fossil barks and in plant residues by highresolution solid-state nuclear magnetic resonance. Org.
Geochem. 12, 539–546.
A PPENDIX
(see p. 13)
Distribution of combined monosaccharides in sediments
13
17.91
19.42
3.36
33.56
34.59
55.53
32.21
29.98
27.28
20.13
15.77
3.18
37.97
22.97
7.94
31.44
12.91
10.80
27.75
34.93
23.00
21.59
23.12
35.61
0
4.3
6.4
25.6
27.7
30.3
44
55.5
76.1
85.2
96.7
117.1
143.7
156
175.3
192.6
207.7
220.6
240
278.1
295.8
306.8
348.7
359.7
24
18
54
16
18
29
19
20
21
21
19
19
36
25
19
39
24
27
32
34
38
35
29
35
C/N
Ly
1.20
1.83
9.96
2.18
5.56
1.40
1.26
2.42
1.33
4.93
5.84
9.32
1.13
8.33
7.89
1.79
7.60
10.94
7.52
5.46
8.80
6.28
7.93
6.94
5.80
5.84
3.94
4.59
5.07
8.12
8.99
4.90
4.64
5.92
3.59
4.37
8.72
6.02
3.78
4.77
3.85
4.16
4.53
4.42
3.85
4.05
3.01
5.41
Ar
3.13
1.66
5.32
1.38
3.06
0.71
0.56
1.30
0.86
1.50
1.92
1.98
0.64
1.33
2.03
0.79
0.90
1.04
0.88
0.96
0.59
1.28
0.65
0.54
Ri
5-C sugar
Xy
14.86
11.76
6.67
13.02
14.07
15.44
16.32
18.63
17.90
12.91
12.37
8.15
18.89
10.31
8.95
11.70
8.46
8.50
13.63
11.80
12.15
12.05
12.62
14.63
3.23
2.21
8.28
2.54
3.77
1.74
2.35
2.50
2.11
4.46
8.32
9.95
3.00
5.65
8.72
2.38
6.70
11.11
5.71
4.79
7.38
6.97
7.74
4.54
Rh
4.55
1.98
8.56
1.85
3.11
1.06
0.76
2.03
1.93
3.52
5.40
4.34
1.71
3.70
4.24
2.44
5.06
7.14
4.04
5.05
4.64
4.83
5.18
3.14
Fu
Deoxy sugar
Ma
8.00
7.17
6.99
10.87
6.92
15.65
19.39
16.14
10.92
11.04
10.56
5.23
9.22
11.68
6.95
14.03
8.11
9.12
9.52
12.60
10.54
9.55
8.83
9.65
2.63
2.87
7.25
3.26
5.76
1.37
1.29
3.35
2.49
6.29
9.78
7.69
0.95
7.76
6.50
3.15
7.93
11.94
7.51
7.73
7.40
6.27
9.04
5.73
Ga
6-C sugar
Neutral sugar composition (as mol%), mild hydrolysis
Gl
22.99
23.28
18.66
20.77
13.98
14.18
11.11
15.98
19.33
24.84
13.47
31.45
12.19
12.17
31.05
16.11
26.84
11.14
12.08
17.36
11.02
12.54
18.27
7.61
5.33
5.90
5.19
4.11
3.88
8.63
9.01
4.49
3.74
3.64
4.03
3.30
6.22
6.10
2.44
7.64
2.18
1.86
3.71
2.32
3.60
2.42
2.57
4.95
Ma2
28.27
35.48
19.19
35.43
34.79
31.69
28.99
28.28
34.77
20.96
24.72
14.20
37.35
26.95
17.46
35.20
22.37
23.04
30.88
27.51
30.03
33.75
24.17
36.86
Gl2
Strong hydrolysis
113.88
136.08
33.57
122.54
86.92
154.71
159.89
120.97
137.12
79.52
49.53
27.54
155.82
67.09
31.50
124.37
44.67
27.38
53.95
61.86
50.54
46.56
42.50
74.80
TNS
(mg/g)
2.23
2.52
2.03
2.71
3.49
3.23
3.61
2.77
2.80
1.84
2.84
1.45
4.06
3.22
1.56
3.19
1.83
3.07
3.56
2.59
3.73
3.69
2.32
5.85
(Gl+Gl2)/Gl
*Organic carbon (OC), and C/N data obtained from Tareq et al. (2004). Abbreviations: Ly, lyxose; Ri, ribose; Ar, arabinose; Xy, xylose; Fu, fucose; Rh, rhamnose;
Ma, mannose; Ga, galactose; Gl, glucose; TNS, concentrations of total neutral sugars; (Gl+Gl2)/Gl, ratio of total glucose yield and noncellulosic glucose (mild
hydrolysis).
OC
(%)
Depth
(cm)
Appendix 1. Neutral monosaccharide compositions of Rawa Danau core (RD-1) as mol% of total monosaccharides*