Science of the Total Environment 324(2004) 91–103

0048-9697/04/$ - see front matter� 2003 Elsevier B.V. All rights reserved.doi:10.1016/j.scitotenv.2003.10.020

Biomarker signature in tropical wetland: lignin phenol vegetationindex (LPVI) and its implications for reconstructing the

paleoenvironment

Shafi M. Tareq *, Noriyuki Tanaka , Keiichi Ohtaa,b, c d,e

Division of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Furo-cho,a

Chikusa-ku, Nagoya 464-8601, JapanDepartment of Environmental Science, Jahangirnagar University, Dhaka 1342, Bangladeshb

Frontier Research System for Global Change, International Arctic Research Center, University of Alaska, Fairbanks, AK, USAc

Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japand

School of Environmental Science, The University of Shiga Prefecture, 2500 Hassaka-cho, Hikone, Shiga 522-8533, Japane

Accepted 16 October 2003

Abstract

Organic matter of a peat core(3.60 m, 7428 years BP) collected from Rawa Danau, west Java, Indonesia, wasanalyzed to evaluate the early diagenetic fates of lignin in a tropical wetland and to reconstruct past vegetation andclimate changes. Vertical profiles of(AdyAl)v, (AdyAl)s, andl show that the lignin composition is well preserved8

in a sub-aqueous environment under reducing conditions. The sedimentary terrigenous plant material at Rawa Danauis comprised predominantly of angiosperm wood. For this kind of tropical, diverse, and dynamic ecosystem, a newvegetation change index called lignin phenol vegetation index(LPVI): LPVI is defined using the lignin phenolcomposition. This index can sensitively detect terrestrial vegetation changes as well as environmental conditionsforcing such changes. The LPVI of the Rawa Danau peat core provides better resolution than other lignin parametersused previously, and reveals four major vegetation change events since the mid–late Holocene. In comparison toother geochemical data(i.e. elemental carbon, isotopes, and hydrocarbons), the LPVI is more sensitive and is able totrace even minor vegetation and climate changes and thus could improve biogeochemical interpretations of peatrecords.� 2003 Elsevier B.V. All rights reserved.

Keywords: Biomarker; Lignin; LPVI; Vegetation; Paleoenvironment; Tropical area

1. Introduction

The interest in identify past environmental var-iations is increasing, thus enhancing the prospectof developing more reliable and accurate methods

*Corresponding author. Tel.:q81-52-789-3475; fax:q81-52-789-3436.

E-mail address: smtareq@juniv.edu, smtareq@yahoo.com(S.M. Tareq).

for identifying past environment changes(Aaby,1976; Meyers, 1997; Kuder and Kruge, 1998;Pendall et al., 2001). The study of pollen, diatoms,isotopes or biomarkers in lake sediments hasbecome the standard means of investigating localpaleovegetation and paleoclimates(Ertel et al.,1984; Prahl et al., 1994; Meyers, 1994; Orem etal., 1997; Kuder and Kruge, 1998; Hu et al., 1999;Filley et al., 2001; Kaars et al., 2001; Anshari et

92 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 1. Vegetation types and chemical structure of lignin mon-omers (*nonwoody gymnosperm does not contain syringylphenols except Douglas fir).

al., 2001). However, pollen analysis faces somedifficulty in separating the local sources fromregional sources of plants and in determining thesize of local plant populations due to production,migration and early reworking pollen of differentspecies at different rates(Leopold et al., 1982,references therein). Large vegetation heterogeneitywith small-scale excursions of isotope valuesmakes isotopic variation less effective in identify-ing vegetation changes in tropical wetlands(Tareqet al., in preparation). Lignin is an abundant andstable phenolic macromolecule found in vascularplants, and is essentially absent in all other livingorganisms(Sarkaner and Ludwing, 1971; Hedgesand Mann, 1979; Ertel and Hedges, 1984; Goniand Hedges, 1995) and is unique to the source. Inlight of these characteristics, lignin oxidation prod-ucts (LOP) have already been used as potentialbiomarkers (Leopold et al., 1982). However,small-scale degradation of lignin had been reportedunder specific environmental conditions(e.g. Fun-gal degradation; Hedges et al., 1988a,b).

The isotopic compositions and molecular prop-erties of organic matter(OM) and the products oftheir transformation are largely dependent uponthe sources and the prevailing environmental con-ditions during the time of deposition(Meyers,1997; Filley et al., 2001). Therefore, any changesin environmental conditions and vegetation can bededuced from the composition of the organiccompounds. Alkaline CuO oxidation of ligninyields a suite of phenols that are grouped basedon plant taxonomy as shown in Fig. 1, and thatare used to identify woody and nonwoody tissuesof flowering (angiosperm) and nonflowering(gymnosperm) vascular plants(Hedges and Mann,1979; Goni and Hedges, 1990). Studies of theconcentrations and vertical distribution of thesecompounds in peat core can provide informationon gross taxonomic changes in the terrestrial veg-etation and amount of precipitation in response tochanges in vegetation. However, presently, veryfew studies in the literature, address the verticalevolution of lignin through the peat core to identifyvariations of its inputs through time(Leopold etal., 1982; Prahl et al., 1994; Louchouarn et al.,1997), or its fate during early diagenesis(Hamiltonand Hedges, 1988; Cowie et al., 1992), although

lignin phenols have successfully been used to studyquantitative input and lateral transport of land plantcarbon in transitional environments(land to sea)during the last three decades(Goni et al., 1997).

The present study examines the vertical distri-butions of lignin phenols in a 3.60 m peat corecollected from the tropical wetland at Rawa Danau,west Java, Indonesia, to determine whether thelignin analysis of peat can be utilized to reconstructthe past environment and vegetation changes in atropical wetland. The peat core represents anapparently continuous sedimentary sequence datedback to the Holocene(Cal. 7428 years BP). Wealso investigated the early diagenetic fate of ligninin a sub-aqueous tropical environment. Finally, wedefined and evaluated a new vegetation changeindex utilizing lignin phenol compositions that cansensitively characterize terrestrial vegetationchanges, as well as environmental conditions forc-ing such changes.

2. Materials and methods

2.1. Study area

The study area of Rawa Danau is located at thewestern tip of Java Island, Indonesia, at an eleva-

93S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 2. Map of the coring site.

tion of 100 m above sea level(asl) and near(f5km) the southern edge of the Sunda shelf(Fig.2). This is one of the few lowland sites in thisregion that records both aquatic and high altitudeterrestrial signatures and may clarify the precipi-tation history of the tropical lowland environments(Kaars et al., 2001). The geological setting, cli-mate and vegetation have been explained in detailelsewhere(Stuijts, 1993; Kaars et al., 2001). Brief-ly, Rawa Danau is located in the caldera of theDanau volcanic complex surrounded by high vol-canic terrain(400–700 m asl). Reliable informa-tion on the possible Holocene eruptions in theDanau complex is not available(Kaars et al.,2001). The main river is Ci Danau, which origi-nates in the northern lower slopes of Karangvolcano, and its catchment covers major portions(70 km ) of the caldera. The main vegetation2

types of the wetland are mixed swamp forest,Ficus retusa swamp forest and open herbaceousswamp, whereas dry land and upper mountainousareas are largely covered by deciduous plants withconifers, depending on altitude. The originalswamp forest of the caldera has been partly

replaced by rice fields. At present, the climate inthe region is dominated by monsoonal circulation,the migration of ITCZ, as well as land–sea distri-bution in the Malay Archipelago(Verstappen,1975; Monk et al., 1997).

2.2. Sampling

The peat core was collected by piston coring. Afield survey was carried out in October 2000 andthree short test cores were collected for site selec-tion before taking the main core. The main corewas taken from the northwestern corner of theRawa Danau caldera(Fig. 2) where the greatestthickness of peat deposits was found. The topsection of the core was disturbed and one gravitysub-core of 32 cm was taken to maintain thesedimentary sequence. For geochemical analysis,the core was cut into 2-cm sections, packed intoclean plastic bags and transferred to the laboratory.Visual observation during sample processing gavea rough identification of the core lithology. Her-baceous and grass-woody peats were found in theupper 50 cm and a few layers at different depthscontained silt–clay–sand.

94 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

2.3. Analyses

2.3.1. Bulk analysisTotal content of organic carbon(OC) and nitro-

gen were determined by a Thermo Quest elementalanalyzer, model NA 2500 NCS. The deviation isless than"5% for both OC and nitrogen. Stablecarbon isotope compositions were determined byan elemental analyzerymass spectrometer system(Thermo Quest NA 2500 NCSyFinnigan MAT252). Half the samples were analyzed at least induplicate with a maximum difference of"0.20‰.The performance of the system was evaluated byrunning the working standard alanined C (y13

21.56‰) and the accepted value(y21.56"0.07‰) was obtained within a sample size rangeof 7–100mg carbon.

2.3.2. Lignin analysisLignin analysis was carried out according to the

method developed by Hedges and Ertel(1982)and Goni and Hedges(1992) with minor modifi-cations. Briefly, the procedure involved the addi-tion of 25–40 mg of ground lipid-free peat, CuO(1 g) and Fe(NH ) (SO ) Ø6H O (100 mg) to 54 2 4 2 2

ml of 2 N nitrogen-purged NaOH solution in astainless steel bomb. The bomb was heated at 1708C for 3 h on a digital shaker(KS501, IKALabortechnik). A reaction mixture was acidifiedto pH 1, and lignin phenols were extracted withperoxide-free diethyl ether. The ether extract wasdried over anhydrous Na SO overnight and then2 4

concentrated under reduced pressure.Lignin phenols were converted to trimethylsilyl

derivatives with BSTFA and pyridine. Quantitativeanalyses of lignin phenols were performed using aJ&W Scientific capillary column (DB1, 60m=0.25 mm i.d.) installed in a Shimadzu 14Bgas chromatograph(GC). The GC conditions wereas follows; injector temperature: 2708C, flameionization detector temperature: 3008C, and oventemperature programmed from 120 to 2908C at 28Cymin with a final hold at 2908C for 10 min.Ethylvanillin was used as the GC internal stan-dards. The reproducibility of the analytical proce-dure for all lignin phenols was better than 95%except for thep-hydroxy phenols(90%).

3. Results and discussion

3.1. Chronology

The C ages were determined for nine layers14

in the core RD-1 sequence by conventional meth-ods. The ages were calibrated using CALIB rev.4.3 (Stuiver et al., 1998) in both BP and ADyBCyears and expressed at one sigma(65.3% confi-dence) and two sigma(95.4% confidence) ranges.Where multiple intersections of the calibrationcurve occurred, the largest relative area of theprobability distribution in each case was chosen torepresent the most probable age range. Unlessotherwise stated, ages discussed in this paper areexpressed as the median ages of the two-sigmaranges, which were taken as the most probable ageof the sample. The ageydepth relationship(r s2

0.93) indicated a coherent sequence of increasingage with depth and relatively stable sedimentationrates through the sequences. However, closeinspection of the age and depth relationshipshowed two different sedimentation rates: a highsedimentation rate(0.079 cmyyear) down to adepth of 127 cm, and comparatively low sedimen-tation rate(0.031 cmyyear) at depths between 127and 210 cm. The upper 50 cm showed a changein deposition from woody to nonwoody peat.Unfortunately, we have no radiocarbon data forthe bottom of the core. For this reason, we extrap-olated our available data down to the bottom depthusing simple linear regression and mathematicallycalculated the bottom age(Fig. 3). The C age14

data, as a function of depth, is described by thefollowing relationship.

14C Age (ky)s0.019=Depth (cm)

2q0.311 r s0.93Ž .

Extrapolation of the C age to the bottom of14

the core(360 cm) gives an age of almost 6529C years BP. Calibrating the extrapolated date of14

6529 C years BP yields a calendar year of 742814

BP (BC 5479 years). The two distinct sedimenta-tion rates give quite different ages for the bottomof the core, but we assume that the real age of thecore is between the two ages as calculated from

95S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 3. Depth-radiocarbon age relation for Rawa Danau core(RD-1). Solid and hollow triangles show two different sedi-mentation rates. The bottom age(7428 years BP) of the coreis an extrapolated value.

Table 1Definition of different lignin parameters

Parameter Definition

TLP 811 lignin phenols of vanillyl, syringyl,cinnamyl andp-hydroxybenzoic groups(mgyg dry peat)

l8 88 lignin phenols of vanillyl, syringyl, cinnamyl(mgy100 mg OC)V 83 Vanillyl phenols(mgy100 mg OC)S 83 Syringyl phenols(mgy100 mg OC)C 82 Cinnamyl phenols(mgy100 mg OC)(AdyAl)v Molar ratio of vanillic acid to vanillin(AdyAl)s Molar ratio of syringic acid to syringaldehyde(AdyAl)p Molar ratio ofp-hydroxybenzoic acid top-hydroxybenzaldehydeSyV Molar ratio of total syringyl to total vanillylCyV Molar ratio of total cinnamyl to total vanillyl

the linear relationship. The average sedimentationrate of the core is 0.048 cmyyear depending onthe calibrated bottom age of the core, which iscomparable to other tropical wetlands(Ledru,2001).

3.2. Vertical distributions of lignin phenols

Twenty-four sections of the Rawa Danau core(3.60 m) were selected for lignin phenol analysison the basis of the OC content andd C values.13

Eleven lignin phenols(p-hydroxyphenyl, vanillyl,syringyl and cinnamyl) were measured among theCuO oxidation products of all samples. All phenolsare regarded as lignin-derived components,although the p-hydroxyphenyl group has othersources (Hedges et al., 1988a,b). Hedges andParker(1976), Hedges and Mann(1979), Hedgeset al. (1982, 1988a,b) and other investigators(Ishiwatari and Uzaki, 1987; Orem et al., 1997;Dittmar and Lara, 2001) have used several ligninparameters to characterize the composition andbehavior of lignin in sediments. We used similarparameters after minor changes of the definitionsas summarized in Table 1.

Chronological changes of vanillyl, syringyl andcinnamyl phenols with depth(Fig. 4) reflect veg-etation changes, although recent studies(Opsahland Benner, 1995; Louchouarn et al., 1997) showthat syringyl and cinnamyl groups are more sen-sitive to early diagenesis than vanillyl compounds.The high concentrations of vanillyl and syringylphenols indicate woody plant contribution hasdominated in peat deposition rather than nonwoodyplants. Both vanillyl and syringyl phenols exhibitvertical profiles similar to that ofl (r s0.8).2

8

The strong correlation between vanillyl and syrin-gyl phenols(r s0.9; except four outlier) suggests2

that angiosperm tissues were an important com-ponent of lignin throughout the accumulation per-iods. The vertical profile of cinnamyl phenols isdifferent from those of the vanillyl and syringylgroups, and its concentration is comparatively low.During the periods of lower values of lignin

96 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 4. Vertical profiles of lignin phenols in the Rawa Danau core(RD-1).

parameters(S, V and l ), which commenced at8

353, 1310, 3287 and 4250 BP, there are significantexcursions ind C values, suggesting a change in13

OM input either through the changes in vegetationor hydrology.

The vanillyl, syringyl and cinnamyl groupsstrongly correlate(r s0.85, r s0.96 and r s2 2 2

v s c

0.89) to the total lignin phenols(TLP) except fora few sections(four sections as shown in Fig. 5).Such outlier sections indicate that changes in therelative abundance of higher plants sources tookplace during the accumulation periods. The rela-tively weak correlation(r s0.62) between p-2

p

hydroxyphenyl groups and TLP may be attributedto the non-lignin source signature ofp-hydroxy-phenyl group(Wilson et al., 1985; Hedges et al.,1988a,b). The four outlier points in Fig. 5 indicatechanges in the terrestrial vegetation andyor localhydrology as discussed later.

The vertical distribution ofl shows no down-8

core trend with depth, and fluctuates irregularly(6.2–26.1) with an average value of 13.3. Thisfluctuation could reflect source variations, post-depositional degradation andyor other factors. Thel values of Rawa Danau are higher than those8

from other lake sediments(Wien Lake: 0.66–2.09,

Hu et al., 1999; Lake Washington: 0.9–1.91,Hedges et al., 1982) and coastal lacustrine sedi-ments, and are comparable to the value observedin other tropical wetlands(Bourdon et al., 2000).The highl values reflect the high carbon contents8

and the dominance of terrestrial plant sources inthe OM, as is also suggested by the highCyNratio (Table 2). The variation ofl is large in the8

upper part of the core(50 cm; covering 1000years BP). The high concentration peaks observedin a few sections probably reflect increasing inputsof lignin due to lower dilution by non-ligneousmaterials, in agreement withCyN ratio values.The decreasing trends observed at depth of 10, 25,110 and 160 cm probably originate from theprogress of in situ lignin degradation and also fromincreased dilution by algal materials.

Both OC and total lignin content are lowest atthe depth of high silt–clay content, which is apossible time of erosion of high-mountainous are-as. Both OC and TLP sharply increase immediatelyafter the signature of mountainous erosion, indi-cating increasing primary biomass production. Thesubtle changes between the two time periods is asignature of precipitation and the consequent run-off changes that caused land-sliding or erosion of

97S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 5. Relationships between TLP and vanillyl(a), syringyl (b), cinammyl(c) andp-hydroxyphenyl(d) groups of core RD-1.

mountainous slopes. After the periods of possiblehydrological change, biomass productivity, espe-cially flowering and nonwoody plants(herbs, grassand sedge), increased as reflected in the TLPconcentration(Table 2). Vertical profiles of ligninat Rawa Danau represent the changes in terrestrialbiomass production that depend on precipitation.Similarly, the concentration of lignin in the wet-lands may be a useful direct indicator of precipi-tation and an indirect indicator of climate changein tropical areas.

3.3. Lignin phenol ratio: diagenesis and sourcesignature

It is necessary to consider the diagenesis oflignin before discussing its origin. The acidyalde-hyde ratios of three lignin phenol groups(asdefined in Table 1) have been used to characterizediagenetic alteration in a variety of geochemicalsamples (Hedges et al., 1982; Ishiwatari andUzaki, 1987; Orem et al., 1997; Dittmar and Lara,2001). From the values of AdyAl ratios, the

occurrence of considerable degradation of ligninafter deposition is clear for all samples becausethe Rawa Danau samples yields more acid andless aldehyde than fresh plant tissues in each group(AdyAl for fresh plants: 0.10–0.50; Opsahl andBenner, 1995; Hu et al., 1999). The reason for theelevated acid in LOP is the partial oxidation ofthe lignin phenol side-chain in its way to furtherdecay(Hedges et al., 1988a,b). However, the hugevalues of AdyAl may not be directly related todiagenesis. Instead, they may reflect the presenceof ester-bound vanillic andyor syringic acid in thematrix of the peat, which may include humic-typesubstances. This type of bonding has beenobserved in certain plants(Opsahl and Benner,1995) and also in humic substances(Ertel andHedges, 1984).

A plot of the AdyAl ratios against depth showsthat (AdyAl)p is highly variable with no relation-ship to the other two parameters(Fig. 6). However,(AdyAl)p is not related to lignin diagenesis or todiagenesis in general(Hedges et al., 1988a,b). The(AdyAl)v and (AdyAl)s closely parallel each

98 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Table 2Total organic carbon(TOC), CyN, d C and abundances of lignin phenols produced by CuO oxidation of Rawa Danau core(RD-13

1) samples, West Java, Indonesia

Sample Depth TOC CyN d C13 p-Hg Vg Sg Cg TLPNo. (cm) (%) (PDB ‰) (mgygdwt.) (mgygdwt.) (mgygdwt.) (mgygdwt.) (mgygdwt.)

1 0 18 24 y27.78 8.68 11.9 12.99 1.43 352 4.3 19 18 y27.96 12.39 21.65 16.74 2.52 53.33 6.4 3 54 y28.19 1.83 6.23 1.8 0.65 10.524 25.6 34 16 y29.02 13.17 20.4 17.53 2.36 53.465 27.7 35 18 y27.62 11.07 11.34 15.71 2.03 40.156 30.3 56 29 y27.94 10.94 77.15 10.46 2.71 101.267 44 32 19 y28.31 9.97 72.26 9.48 2.24 93.958 55.5 30 20 y28.51 14.39 17.83 15.48 2.09 49.799 76.1 27 21 y28.64 14.82 22.57 21.61 3.23 62.2210 85.2 20 21 y28.01 5.73 9.93 7.39 1.01 24.0611 96.7 16 19 y28.88 5.7 7.71 5.3 0.71 19.4212 117.1 3 19 y28.29 2.44 1.88 1.91 0.31 6.5513 143.7 38 36 y27.15 5.89 48.35 44.56 2.14 100.9414 156 23 25 y28.97 4.68 13.42 7.17 1.01 26.2815 175.3 8 19 y26.97 2.62 2.92 3.04 0.5 9.0816 192.6 31 39 y29.91 4.71 35.7 17.75 3.24 61.417 207.7 13 24 y27.77 2.58 6.93 5.83 0.54 15.8918 220.6 11 27 y29.09 5.01 3.96 3.68 0.37 13.0219 240 28 32 y29.25 5.96 12.9 9.84 0.58 29.2820 278.1 35 34 y28.81 7.5 12.3 9.61 0.85 30.2621 295.8 23 38 y30.07 10.71 11.01 9.1 0.99 31.8122 306.8 22 35 y27.98 5.45 11.66 9.16 0.62 26.8823 348.7 23 29 y28.27 7.78 7.99 5.84 0.45 22.0524 359.7 36 35 y28.29 46.95 27.59 29.7 1.36 105.6

Abbreviations: p-Hg, p-hydroxyphenyl group; Vg, vanillyl group; Sg, syringyl group; Cg, cinnamyl group; TLP, total ligninphenol; mgygdwt., milligram per gram dry weight of the samples; PDB, Pee Dee Belemnite.

other with the vanillyl ratio always being greater,as similarly reported by Hedges et al.(1982) forLake Washington. The AdyAl ratios of all threegroups in the upper section of the core are extreme-ly high. These high AdyAl ratios might indicatethat a small fraction of sedimentary lignin poly-mers suffered oxidative degradation before theonset of reducing conditions due to changes in thehydrology of the lake. At present in Rawa Danauswamp, important seasonal variations of the watertable occur, and drying of surface peat wasobserved. During such dry periods, an efficientdegradation of lignin by white rot fungi may haveoccurred, essentially at the top of the profile. Forboth (AdyAl)v and(AdyAl)s, no general increas-ing or decreasing trend is observed with depthexcept extremely high values at the top of thecore. The lack of such a trend with depth supportsthe conclusion that lignin(after the initial degra-

dation in the oxic top layer of the recent past;1000 years BP) remains diagenetically unalteredin this sub-aqueous tropical wetland. However,(AdyAl)p rapidly increases from 150 cm to thebottom of the core. The abrupt increase in(AdyAl)p may be related to the history of the lakedepth and changes in aquatic productivity(fromdiatom records; Kaars et al., 2001) that can con-tribute to the non-lignin sources ofp-hydroxyben-zoic group and especiallyp-hydroxybenzoic acid.

Lignin phenol ratios(SyV and CyV), indicatethe relative contribution of terrestrial vegetation tothe total OM. Changes are particularly noticeablein the SyV ratio, which decreased at depths 3.4,30.3, 44, 156.0 and 192.6 cm. The changes ofSyV ratio with depth can be used to distinguishsources of OM derived from either gymnosperms(low SyV values,f0) or angiosperms(high SyVvalues, more than one). The vertical profiles ofSy

99S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Fig. 6. Vertical profiles of lignin phenol ratios(SyV andCyV)and acidyaldehyde ratios of vanillyl, syringyl andp-hydroxy-phenyl groups of Rawa Danau core(RD-1).

Fig. 7. A plot of SyV vs. CyV values of all 24 Rawa Danaupeat samples with means and ranges for gymnosperm(G),nonwoody gymnosperm(g), angiosperm(A) and nonwoodyangiosperm(a) (Hedges and Mann(1979)).

V and CyV indicate that vascular plant sources atthe Rawa Danau were mostly angiosperm tissues(SyV)0.5). These ratios are very similar to thosereported for other tropical wetlands and mangrovesediments(Bourdon et al., 2000; Dittmar and Lara,2001). The low SyV and CyV values at differentdepths are associated with highl , and the lignin8

phenol vegetation index(LPVI; discussed in Sec-tion 3.4) values indicate a high concentration oflignified material mostly comprised of gymno-sperm tissues. Using calibrated radiocarbon( C)14

ages for the core, we can date the observed changesin SyV and CyV from the mid to late Holocene.A plot of SyV vs. CyV ratios with ranges andmeans of woody and nonwoody tissues of gym-nosperm and angiosperm plants(Hedges andMann, 1979) shows a variable compositions(Fig.7), suggesting mixtures of different sources. Thistwo-dimensional separation of source OM indi-cates that at least three different types of planttissues occurred with in the peat core, such asangiosperm, gymnosperm and nonwoody gymno-sperm. It is also clear from the two-dimensionalseparation that the major contributor is angiospermplants and that there are periodic changes betweenangiosperm and gymnosperm contributions fromthe mid to late Holocene. The presence of non-

woody angiosperm tissues was not exclusivelydemonstrated but cannot be ruled out due to rapiddiagenetic alteration of cinnamyl phenols from itssources(Huang et al., 1999; Dittmar and Lara,2001).

3.4. Lignin phenols vegetation index (LPVI)

Lignin phenol ratios(SyV vs. CyV) do not givea fine resolution spectrum of past vegetationchanges of tropical dynamic ecosystems becauseof the large vegetation heterogeneity as well as thedifferent diagenetic reactivities of cinnamyl, syr-ingyl, and vanillyl groups(C)S)V) during trans-port through the environment before burial insediments. However, they have been used success-fully during the last three decades to distinguishangiosperm, gymnosperm and nonwoody terrestrialplant sources in OM of lakes, rivers, estuaries andoceans(Hedges and Mann 1979; Wilson et al.,1985; Hu et al., 1999; Dittmar and Lara, 2001).For such conditions, we developed a binary equa-tion to define a new index using lignin phenolcomposition to identify vegetation changes calledthe LPVI as shown in the following equation:

100 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

Table 3Means and ranges of LPVI

Plant types LPVI value rangesa

Low Mean High

Gymnosperm woods 1 1 1Nonwoody gymnosperm tissues 12 19 27Angiosperm woods 67 181 415Nonwoody angiosperm tissues 378 1090 2782

Lignin phenols data for specific plants were obtained froma

Hedges and Mann(1979).

Fig. 8. Vertical profile of LPVI for Rawa Danau core(RD-1).Also illustrated are ranges for: gymnosperm(G), nonwoodygymnosperm(g), angiosperm(A) and nonwoody angiosperm(a), which were calculated from plant–lignin phenol data forthe individual categories given by Hedges and Mann(1979).

w{ } {LPVIs S(Sq1)y(Vq1)q1 = C(Cq1)y(V

} xq1)q1

WhereV, S and C are expressed in % of thel .8

All vascular plants produce vanillyl phenols(V)0) upon oxidation with CuO and can be separatedfrom nonvascular plant sources. The gymnospermwood, angiosperm wood, and nonwoody gymno-sperm tissue samples are resolved into non-over-lapping boundary lines in the axis of LPVI.Gymnosperm and angiosperm woods have differ-ent boundary lines because the gymnosperm woodproduced neither syringyl nor cinnamyl phenolsand thus plots near the origin. However, angio-sperm wood contains significant amounts of syr-ingyl phenols and shows comparatively higherLPVI values(Table 3). The nonwoody angiospermtissues produce both syringyl and cinnamyl phe-nols, have the highest LPVI values and slightlyoverlap with the angiosperm wood. Nonwoodygymnosperm has narrow LPVI ranges because itdoes not contain syringyl phenols(except Douglasfir) but does contain a relatively small fraction ofcinnamyl phenols. We used data from the literatureand applied them to our theoretical calculation.Means and ranges of LPVI were calculated fromthe plant–lignin data available from Hedges andMann (1979).

3.4.1. Implications at Rawa DanauLignin studies have been used in templates for

understanding OM composition and depositionalenvironment. The LPVI offers valuable informa-tion about the paleoenvironment in a series. TheLPVI values of the peat core in Rawa Danau are

shown in Fig. 8 as a function of depth with distinctboundary lines for gymnosperm, angiosperm, non-woody gymnosperm and nonwoody angiospermplants. The LPVI of the Rawa Danau peat depositsrecords information about vegetation changes aswell as depositional and burial conditions. Fig. 8reflects changes in the terrestrial vegetation com-position of the wetland during peat accumulationperiods. The vegetation change likely resulted inan increased proportion of gymnosperm(woodyand nonwoody) plants on the landscape, whichshould lead to low LPVI values, since gymno-sperm wood produces only vanillyl phenols where-as cinnamyl phenols are derivatives of nonwoodytissues. One possible explanation for the elevatedLPVI values at four depths(27.7, 76.1, 117.1 and

101S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

175.3 cm) is the higher contribution of angio-sperms relative to gymnosperms(as explainedabove). This is consistent with the results fromother lignin phenol parameters(SyV and CyV).Therefore, from the LPVI values, one can easilyinfer periodic cycles of vegetation changes asso-ciated with dry and wet microenvironments inRawa Danau during the peat accumulation periods.Vegetation heterogeneity due to non-hydrologicfactors(e.g. forest fire) may also occur.

In Rawa Danau, the vegetation changes arerelated to forest fire events as concluded fromelemental carbon(soot carbon) analysis(e.g. Dur-ing vegetation change events the elemental carbonis significantly high; 0.01–0.24%, Tareq et al., inpreparation). Forest fires may occur naturally andyor artificially during clearance of tropical lowlandfor agricultural uses. During forest fire events, thelow values of LPVI at different depths indicatethe presence of a higher gymnosperm composition(woody and nonwoody). This is a silent signatureof the impact of a forest fire on the compositionof tropical vegetation, which is also supported bypollen data of the core(H. Tsuji, personnel com-munication). Under tropical wet and warm climaticconditions, forest fires might have first affectedangiosperms(at low altitudes) rather than gym-nosperms(at high altitudes) whereas regenerationof angiosperm and nonwoody plants(grass, herbsand sedges) could be faster than woody gymno-sperms. In comparing elemental carbon, the carbonpreferences index(CPI (n-alkanes C –C): 2.2–23 33

10.2, and changes these values during vegetationchange events; Tareq et al., in preparation) valuesof the same core, and the LPVI provide strongevidence for a direct linkage between lignin bio-marker and forest fire records. Both forest fire andvegetation changes relate to climate changes, andtherefore, the LPVI is useful to identify paleocli-matic events(e.g. precipitation, long-term oscilla-tion, land-sliding).

4. Conclusions

Lignin signatures in peat land are well preservedafter the onset of reducing conditions and can beused as a potential indicator of past vegetationchanges. Concentrations of TLP and ratios of

lignin phenols(SyV andCyV) provide informationabout paleovegetation. A qualitative estimate ofthe vascular plant contribution to the Rawa Danaushows that the sedimentary terrigenous plant mate-rial was comprised predominantly of angiospermwood. However, this estimate cannot resolve veg-etation types very well. The new molecular tracermethod introduced in this paper is useful for theidentification of past vegetation and analysis oforganic mixtures in a wetland. In such application,climate change events(e.g. precipitation, droughtand forest fire) can be identified. The LPVI pro-vides better resolution of different plant sources inOM than the lignin parameters used previously(Hedges and Mann, 1979; Orem et al., 1997;Dittmar and Lara, 2001), and was applicable to atropical diverse ecosystem. In comparison to theother geochemical data(e.g. elemental carbon,isotopes and hydrocarbon), the LPVI is moresensitive and able to trace back even minor vege-tation and climate change events. However, theinterpretation of lignin phenol data is highly com-plex and useful as a qualitative proxy not forquantitative proxy and should be used cautiously.One of the potential problems is the compositionalchanges in lignin resulting from biodegradation(especially ester-bound cinnamyl groups) duringtransport and after burial in sediments(Kuder andKruge, 1998; Orem et al., 1997; Dittmar and Lara,2001). Despite these limitations, the new LPVI,together with the other geochemical data, canimprove the biogeochemical interpretations of peatrecords.

Acknowledgments

Shafi M. Tareq is grateful to Japanese Ministryof Education, Culture, Sports, Science and Tech-nology (Monbu-kagaku-sho) for financial supportfor this study. He also wish to thanks NagoyaUniversity for providing travel award to presentpart of the result of this paper in 39th IUPACCongress and 86th conference of the Canadiansociety for chemistry at Ottawa, Canada. Thismanuscript benefited from some useful suggestionsby anonymous reviewer.

102 S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

References

Aaby B. Cyclic climatic variations in climate over the past5500 yr reflected in raised bogs. Nature 1976;263:281–284.

Anshari G, Kershaw PA, Kaars SVD, et al. A late Pleistoceneand Holocene pollen and charcoal record from peat swampforest, Lake Sentarum Wildlife Reserve, West Kalimantan,Indonesia. Palaeogeogr Palaeoclimatol Palaeoecol2001;171:213–228.

Bourdon S, Laggoun-Defarge F, Disnar JR, Maman O, GuilletB, Derenne S, Largeau C. Organic matter sources and earlydiagenetic degradation in tropical peaty marsh(Tritrivakely,Madagascar): implication for environmental reconstructionduring the sub-Altantic. Org Geochem 2000;31:421–438.

Cowie GL, Hedges JI, Calvert SE. Sources and relativereactivities of amino acids, neutral sugars and lignin in anintermittently anoxic marine environment. Geochim Cos-mochim Acta 1992;56:1963–1978.

Dittmar T, Lara RJ. Molecular evidence for lignin degradationin sulphate-reducing mangrove sediments(Amazonia, Bra-zil). Geochim Cosmochim Acta 2001;65(9):1417–1428.

Ertel JR, Hedges JI. The lignin component of humic sub-stances: distribution among soil and sedimentary humic,fulvic and base-insoluble fractions. Geochim CosmochimActa 1984;48:2065–2074.

Ertel JR, Hedges JI, Perdue EM. Lignin signature of aquatichumic substances. Science 1984;223(4635):485–487.

Filley TR, Freeman KH, Bianchi TS, Baskaran M, ColarussoLA, Hatcher PG. An isotopic biogeochemical assessment ofshift in organic matter input to Holocene sediments fromMud lake, Florida. Org Geochem 2001;32:1153–1167.

Goni MA, Hedges JI. Potential applications of cutin-derivedCuO reaction products for discriminating vascular plantsources in natural environments. Geochim Cosmochim Acta1990;54:3073–3083.

Goni MA, Hedges JI. Lignin dimmers: structures, distributionand potential geochemical application. Geochim CosmochimActa 1992;56:4025–4043.

Goni MA, Hedges JI. Sources and reactivities of marine-derived organic matter in coastal sediments as determinedby alkaline CuO oxidation. Geochim Cosmochim Acta1995;59(14):2965–2981.

Goni MA, Ruttenberg KC, Eglinton TI. Sources and contri-bution of terrigenous organic carbon to surface sedimentsin the Gulf of Mexico. Nature 1997;389:275–278.

Hamilton SE, Hedges JI. The comparative geochemistries oflignin and carbohydrates in an anoxic fjord. GeochimCosmochim Acta 1988;52:129–142.

Hedges JI, Ertel JR. Characterization of lignin by capillarygas chromatography of CuO products. Anal Chem1982;54:174–178.

Hedges JI, Mann DC. The characterization of plant tissues bytheir lignin oxidation products. Geochim Cosmochim Acta1979;43:1803–1807.

Hedges JI, Parker PL. Land derived organic matter in surfacesediments from the Gulf of Mexico. Geochim CosmochimActa 1976;40:1019–1029.

Hedges JI, Ertel J, Leopold EB. Lignin geochemistry of latequaternary sediment core from lake Washington. GeochimCosmochim Acta 1982;46:1869–1877.

Hedge JI, Clark WA, Cowie GL. Organic matter sources tothe water column and surficial sediments of marine bay.Limonl Oceanogr 1988;33:1116–1136.

Hedges JI, Blanchette RA, Weliky K, Devol AH. Effect offungal degradation on the CuO oxidation products of lignin:a controlled laboratory study. Geochim Cosmochim Acta1988;52:1803–1807.

Huang Y, Freeman KH, Eglinton TI.d C analyses of individ-13

ual lignin phenols in quaternary lake sediments: a novelproxy for deciphering past terrestrial vegetation changes.Geology 1999;27(5):471–474.

Hu FS, Hedges JI, Gordon ES, Brubaker LB. Lignin biomarkerand pollen in postglacial sediments of an Alaskan lake.Geochim Cosmochim Acta 1999;63(9):1421–1430.

Ishiwatari R, Uzaki M. Diagenetic changes of lignin com-pounds in a more than 0.6 million-year-old lacustrine sedi-ment (Lake Biwa, Japan). Geochim Cosmochim Acta1987;51:321–328.

Kaars SVD, Penny D, Tibby J, Fluin J, Dam RAC, SuparanP. Late quaternary paleoecology, palynology and palaeoli-minology of a tropical lowland swamp, Rawa Danau, WestJava, Indonesia. Palaeogeogr Palaeoclimatol Palaeoecol2001;171:185–212.

Kuder T, Kruge MA. Preservation of biomolecules in sub-fossil plants from raised peat bogs—a potential paleoenvi-ronmental proxy. Org Geochem 1998;29(5–7):1355–1368.

Leopold EB, Nickmann R, Hedges JI, Ertel JR. Pollen andlignin records of late quaternary vegetation, Lake Washing-ton. Science 1982;218(4579):1305–1307.

Louchouarn P, Lucotte M, Canuel R, Gangne J-P, Richard L-F. Sources and early diagenesis of lignin and bulk organicmatter in the sediments of lower St. Lawrence estuary andthe Saguenay fjord. Marine Chem 1997;58:3–26.

Ledru M-P. Late Holocene rainforest disturbance in FrenchGuiana. Rev Palaeobot Palyno 2001;115:161–176.

Meyers PA. Preservation of elemental and isotopic sourceidentification of organic matter. Chem Geol 1994;114:289–302.

Meyers PA. Organic geochemical proxies of paleoceanograph-ic, paleolimonologic and paleoclimatic processes. Org Geo-chem 1997;27(5–6):213–250.

Monk KA, de-Fretes Y, Reksodiharjo-Lilley G. The ecologyof Nusa Tenggara and Maluku. The Ecology of IndonesiaSeries, vol. 5, Periplus Editions, Hong Kong, 1997.

Opsahl S, Benner R. Early diagenesis of vascular plant tissues:lignin and cutin decomposition and biogeochemical impli-cations. Geochim Cosmochim Acta 1995;59(23):4889–4904.

Orem WH, Colman SM, Lerch HE. Lignin phenols in sedi-ments of lake Baikal, Siberia: application to paleoenviron-mental studies. Org Geochem 1997;27(3–4):153–172.

Pendall E, Markgraf V, White JWC, Dreier M, Kenny R.Multi-proxy records of late Pleistocene–Holocene climate

103S.M. Tareq et al. / Science of the Total Environment 324 (2004) 91–103

and vegetation changes from a peat bog in Patagonia. QuatRes 2001;55:168–178.

Prahl FG, Ertel JR, Goni MA, Sparrow MA, Eversmeyer B.Terrestrial organic carbon contributions to sediments on theWashington margin. Geochim Cosmochim Acta1994;58(14):3035–3048.

Sarkaner KV, Ludwing CH., Lignins Wiley Inter Sci; NewYork, 1971 p. 916.

Stuijts I-LM. Late Pleistocene and Holocene vegetation ofwest Java, Indonesia. A BalkemayRotterdamyBrook field,1993; 124–5.

Stuiver M, Reimer PJ, Bard E, Beck JW, Burr GS, HughenAK, Kromer B, McCormac G, Plicht JVD, Spurk M.

Intcal98 radiocarbon age calibration 24000-0 cal BP. Radi-ocarbon 1998;40(3):1041–1083.

Tareq SM, Ohta K, Tanaka N. Hydrocarbon and elementalcarbon signature in a Tropical wetland: Biogeochemicalevidence of forest fire and vegetation changes, Chemo-sphere, 2003(submitted).

Verstappen HT. On palaeoclimates and landform developmentin Malaysia. Mod Quat Res Southeast Asia 1975;1:3–35.

Wilson JO, Valiela I, Swain T. Sources and concentration ofvascular plant material in sediments of Buzzards bay, Mas-sachusetts, USA. Mar Biol 1985;90:129–137.