INTRODUCTION

Estuaries and rivers are often regions ofhigh sedimentation, serving as traps for mineralsfrom inland sources transported seaward by rivers,and materials from the coastal ocean transportedlandward. Determinations of the relativecontributions of inland and marine sources ofsediments in estuaries are necessary for predictingand controlling sedimentation in habours, andbecoming the sites of major discharges of urbanand industrial pollutants. Grain size analysis is aclassical sedimentological method which has beenwidely used in the studies of sedimentaryenvironment and sedimentary process. In therecent 20 years, many geologists tried to recovertransport directions and paths of sediments

Spatial and temporal bottom sediment characteristicsof Pahang River-Estuary, Pahang, Malaysia

A. SITI WAZNAH¹, B.Y. KAMARUZZAMAN¹*, M.C. ONG²,S.Z. RINA¹ and S. MOHD ZAHIR¹

¹Institute of Oceanography and Maritime Studies, International Islamic University Malaysia,Jalan Sultan Ahmad Shah, Bandar Indera Mahkota, 25200 Kuantan, Pahang, (Malaysia).

²Faculty of Maritime Studies and Marine Science Universiti MalaysiaTerengganu- 21030 Kuala Terengganu, Terengganu, (Malaysia).

(Received: January 01, 2010; Accepted: February 01, 2010)

ABSTRACT

Bottom sediment samples from Pahang river- estuary were analyzed for the sedimentcharacteristics in order to understand better sedimentation processes in the estuary. The mean, sorting,skewness and kurtosis values of each sample were determined by the Moment’s method. This studyshowed that the sediment characteristics were not significantly differ (p > 0.05) with the seasonalchanges, except for sorting (p < 0.05). The sediment mean size becomes finer towards the estuarinearea with the range of very coarse sand to fine silt. This indicates that the characteristics of depositedsediments at each station are much dependant upon the combination of physical forces such asfreshwater run-off, tidal currents and waves.

Key words: Pahang river-estuary, sediment characteristics, mean size,sorting, skewness, kurtosis, pre-monsoon, post-monsoon.

according to the spatial distributions of sedimentgrain size parameters (Shi Xuefa et al., 2002).McLaren (1981), McLaren and Bowles (1985)demonstrated that there is a relationship betweennet transport direction of sediments and certainspatial variation of grain size parameter, and fourgrain size parameters; average grain size (Xφ),sorting coefficient (σφ), skewness (Skφ), and kurtosis(Kφ) were commonly used to recover the transportdirection of sediments. Gradually, the method ofgrain size trend analysis has been set up (Gao andCollins, 1992; 1994). At present, this method hasbeen widely used in the study of coarse-grainedsedimentary environments such as estuary, coastalzone and tidal channel, but it is relatively seldomapplied to continental shelf (Gao and Collins, 1998;Cheng Peng and Gao, 2000).

Oriental Journal of Chemistry Vol. 26(1), 39-44 (2010)

40 Waznah et al., Orient. J. Chem., Vol. 26(1), 39-44 (2010)

In Malaysia, there is little research done regardingspatial and temporal variation of bottomsedimentation along the river. The information aboutsedimentation rate or erosion aspects is very limited.Nevertheless, detailed investigation concerning bothspatial and temporal variability are required in orderto better understand the sedimentation processesin the estuaries and along the Kuala Pahang river.In view of the importance of the bottomsedimentation data to various aspects of theenvironment, this study was carried out. The aim ofthis research is to determine the sedimentcharacteristics such as mean size, sor ting,skewness and kurtosis as well as their distributionpatterns.

MATERIAL AND METHODS

Sampling sitesThe study was carried out at Pahang river-

estuary (Fig. 1). Pahang river- estuary located atPekan, which is situated about 50km south ofKuantan. This area has a humid tropical climatewith two monsoon periods, characterized by bimodalpatterns: southwest and northeast monsoons.Pahang river- estuary is mostly influenced by thesemidiurnal tides with two high tides and two lowtides within a lunar day. A total of 62 bottomsediments which lies between longitude103o25’56.48" E to 103o29’10.55" E and latitude03o33’01.78" N to 03o30’50.38" N, were collectedduring pre-monsoon (August) and post-monsoon(April) seasons using Ponar grab.

Analytical MethodsGrain sizes of the sediments were

determined using the standard dry and wet sievingtechniques (Folk, 1974). Samples which consistsof more than 90% sand were analysed using thedry sieving method, while samples having more than90% fine sediments were analysed using the laserdiffraction method. The median grain size of thesediment was estimated by linear interpolation ofthe distribution curve. Both median and mean grainsize were used in the preliminary data analysis,although only the mean is presented in this studybecause both parameters show equivalent results.Sedimentological characteristics are reported in phi(ø) units using the conversion factor of Folk (1974)as below. By using the negative value, coarse grainsize will have a lower phi (Ø) value which tend toincrease when the particles size become finer.

Ø = -log2 D

where D is diameter of particle in mm.

The mean, standard deviation andskewness of each sample were calculated by themoments method using equations defined byMcBride (1971). The method of moments uses datafrom every grain plot data to obtain statisticalinformation concerning the sedimentary population.The formula proposed by McBride (1971) used tocalculate the sedimentological characteristics ofmean, skewness and sorting are as follows:

Fig. 1: Location of the study area along Pahang River- Estuary, Pahang

41Waznah et al., Orient. J. Chem., Vol. 26(1), 39-44 (2010)

...(1)

...(2)

...(3)

whereX ø = mean sizeσ ø = sortingSk ø = skewnessφ = weight % or volume % (frequency) of

each size classn = number of samplem = mid-point of each size class

Silt and clay content of the bottomsediment were analyzed using the laser diffractionmethod. The laser diffraction technique is based onthe principle of laser ensemble light scattering.Briefly, samples were prepared by first dissolvingall carbonates using 4M hydrochloric acid (HCl)solution. Then the organic components wereremoved by adding 20% hydrogen peroxide (H2O2)solution, and finally with calgon (dispersing agents)solution to break up the flocs that may have formedwith clays. The solution was stirred, and measuredusing the subjected ultrasonic bursts of 10 to 15seconds duration, before being poured into theParticle Size Analyzer (PSA) system.

RESULTS AND DISCUSSION

Figs. 2, 3, 4 and 5 showed the distributionpatterns of sediment mean size, sorting, skewnessand kurtosis for both pre- monsoon and post-monsoon seasons, respectively. Mean size usuallyserves a simple indication of the force applied tothe sediment to move the grains, or a very roughindicator of energy state. In this study, stations atthe upstream area were much coarser comparedto the downstream area for both seasons. Thisphenomenon was also proved by the spatialstatistical analysis (p < 0.05); where the sedimentwas dominantly coarsely type (Figure 2). The meansize indicate that the fine sand were deposited at amoderately low energy conditions and the coarse

sand were deposited at a high energy conditions.The variation in phi mean size, therefore, revealsthe differential energy conditions leads to thedeposition of these kinds of sediments in differentlocations.

In general, sorting identifies sediment interms of the variability in the size of its particles.Sorting commonly occurs throughout the processof weathering, erosion and deposition (Briggs, 1977;Dyer, 1985). This study shows that most of thestations were occupied by the poorly sortedsediment, with the ranges of 0.74 to 2.37Ø and0.74 to 1.70Ø for both pre- monsoon and post-monsoon seasons (Fig. 3). This indicates a widerange of particle size had been occurred. Theseranges of grain size typically result from fluctuationsin the velocity of the transporting agents, such aswater or wind. The greater the speed and energyinvolved, the larger or heavier are the particles thatcan be transported. These conditions also explainedthe reasons of the significant differences observedamong the stations and seasons (p < 0.05) for thesorting distribution.

Skewness is the measure of the degreeof symmetry to provide a measure of the tendencyof the data to spread preferentially to one side ofthe average value. The average of skewness valuesfor pre- monsoon and post- monsoon seasons are0.10 ± 0.45Ø and 0.13 ± 0.32Ø, respectively(Fig. 4). The symmetry of the samples varies fromstrongly fine skewed to strongly coarse skewednature for both seasons. The strongly fine skewedand fine skewed sediments (which are dominant inthis study) generally imply the introduction of finematerial or removal of coarser fraction (Friedman,1961) or winnowing of sediments (Duane, 1964).The predominant fine skewed nature of sedimentsindicates excessive riverine input. The positiveskewness of sediments also indicates theunidirectional transport or the deposition ofsediments in sheltered low energy environment(Brambati, 1969).

Kurtosis is a statistical value measuringthe degree of peakedness of a normal distributioncurve for mean size distribution and is associatedwith standard deviation (sorting) value. Accordingto this study, majority of the samples falls under

42 Waznah et al., Orient. J. Chem., Vol. 26(1), 39-44 (2010)

Fig. 2: Mean size distribution pattern during pre-monsoon and post-monsoon seasons

Fig. 3: Sorting distribution pattern during pre-monsoon and post-monsoon seasons

Fig. 4: Skewness distribution pattern during pre-monsoon and post-monsoon seasons

43Waznah et al., Orient. J. Chem., Vol. 26(1), 39-44 (2010)

leptokurtic to very leptokurtic nature of distributions,which varied from 1.83 to 5.77Ø and 1.75 to 5.32Øfor both pre- monsoon and post- monsoon seasons(Fig. 5). Friedman (1962) suggested that extremehigh or low values of kurtosis imply that part of thesediment achieved its sorting elsewhere in a highenergy environment. The variation in the kurtosisvalues is a reflection of the flow characteristics ofthe depositing medium (Seralathan and Padmalal,1994; Baruah et al., 1997). Finer in size anddominant leptokurtic nature of sediments typicallyreflect maturity of the sand and variation in thesorting values are likely due to continuous additionof finer or coarser materials in varying proportions(Prabhakara Rao et al., 2001).

Fig. 6 shows the correlations betweenmean size and sorting, skewness, and also kurtosisfor both seasons. Most researchers proposed thatthe employment of mean size & sorting value as atool of an indicator to the sediment distributionpattern. Therefore, this study indicates that thetransformation of sediment transport was mostprobably happen with the proportion of coarse sand& poorly sorted sediment. The correlation betweenmean size & skewness indicated that the symmetryof skewness tended to be positively skewed withthe increasing of mean size. Besides, the correlationamong mean size and kurtosis showed that theleptokurtic of sediment decreasing as the mean sizein phi increasing.

Fig. 5: Kurtosis distribution pattern during pre-monsoon and post-monsoon seasons

Fig. 6: Correlations between sediment characteristicsduring pre-monsoon and post-monsoon seasons

44 Waznah et al., Orient. J. Chem., Vol. 26(1), 39-44 (2010)

CONCLUSION

The statistical analyses for all foursediment parameters implied that there were nosignificant differences observed with the changesof seasons, except sorting. However, spatially therewere significant differences obtained for the all fourparameters; mean size, sorting, skewness and

kurtosis. Thus, it can be concluded that sedimentcharacteristics in the study area are not muchinfluenced by the monsoon seasons. Thecharacteristics of deposited sediments at eachstation are possibly dependant upon thecombination of physical forces such as freshwaterrun-off, tidal currents and waves, even thought thosecombinations were not discussed in this study.

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2. Brambati. A., Stratigraphy and sedimentationof Siwaliks of North Eastern India. Proc. Inter.Sem. Intermontane Basins: Geology andResources, Chiang Mai, Thailand. 427-439(1969).

3. Cheng Peng, Gao Shu, Characteristics ofgrain size parameters and net transport trendof seabed sediments in the North Yellow Sea,Oceanologia et Limnologia Sinica (inChinese), 31(6): 604 (2000).

4. Dixit, S.S. and Witcomb, D. Heavy MetalBurden in Water, Substrate andMicroinvertebrate Body Tissue of a PollutedRiver Irwell (England). EnvironmentalPollution (Series B). 6: 161-172 (1983).

5. Duane, D.B., Significance of skewness inrecent sediments, western Pamlico Sound,North Carolina; Jour. Sed. Pet., 34: 864-874(1964).

6. Friedman, G.M., distinction between (sic)dune, beach, and river sands from theirtextural characteristics: Jour. Sed. Pet., 31:514-529 (1961).

7. Friedman, G.M., On sor ting, sor tingcoefficients and the log normality of the grain-size distributions of sandstones. Jour. Geol.70: 737-753 (1962).

8. Gao Shu, Collins, M., Sediment grain sizetrend and marine sediment dynamics,Chinese Scientific Foundation (in Chinese),

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