Recent Sedimentation Rate and Sediment Ages Determination of Kemaman-Chukai Mangrove Forest, Terengganu, Malaysia

B.Y. Kamaruzzaman and M.C. Ong Institute of Oceanography and Maritime Studies, International Islamic University Malaysia (IIUM), Jalan Istana, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia

Abstract: Two 20 cm sediment cores were collected with a D-section corer in the Kemaman-Chukai 210 210 mangrove forest and analyzed for Pbex (excess Pb) in order to understand the sedimentation pattern. The activities of 210Pb along with the 208Po tracer were measured by Alpha Spectrometry on a silicon surface barrier detector connected to a multi channel analyzer. Sedimentation rates were determined applying 210Pb dating method and found to vary between 0.94-1.11 cm year−1. The highest accumulation rates were recorded near the river mouth and the lowest rates at the downstream. Assuming that the sedimentation rate values are accurate, this implies that the sediments in the upper 100 cm at Kemaman-Chukai mangrove forest were deposited during the past 90 years ago.

Key words: mangrove forest, sedimentation rate, sediment age, 210Pb

INTRODUCTION term accretion rates using radionuclides have been well documented[6-8] but use of this approach has been not Mangrove forests are a buffer zone between the many published[5,9] and limited in the mangrove coast and the ocean. One of their presumed important ecosystems. In the present study, we use 210Pb to functions is to provide a mechanism for trapping estimate sediment accretion rates. sediment. In terms of their biological and chemical The concentration of 210Pb within sediment is aspects, mangrove forests are highly productive source governed by processes such as source input from of organic matter, from which there is a net outwelling overlying waters through sedimentation, in situ of energy that supports the complex estuarine and production and radioactive decay. Many scientists have nearshore food web. Geologists, on the other hand, successfully demonstrated 210Pb as a sensitive tracer for view mangroves as sediment sinks, characterized by understanding the geochemical changes which have long-term import of sediments as indicated by the occurred during the century in different ecosystems, substantial accretion of recent sediments, which including coastal marine sediment, due to underlie mangrove forests and adjacent coastal plains[1]. industrialization. 210Pb has proved to be a valuable Physically, by virture of being in the intertidal areas, tracer of sediment mixing and accumulation in a variety they can act as a recorder of environmental changes via of environments[3,6,7,10,11]. 210Pb are naturally occurring sedimentological characteristics and in the preservation radionuclides of the 238U decay series with a 22.3 year. of spores and pollens. 210Pb is used to examine sediment mprocesses on a 100 Despite the acceptance that mangrove ecosystems year time scale. 210Pb is supplied by its effective parent are important sinks for sediments, few studies have 226Ra in seawater and from 222Rn in the atmosphere. addressed sediment accretion in this environment. The atmospheric source is produced as 222Rn, a short- Several authors[2,3] have studied some aspects of the lived (3.8 days) intermediate daughter of 226Ra, escapes sedimentology of mangroves and quote different from the earth’s crust, decay to 210Pb and is deposited sedimentation rates, which is probably a reflection of back to the ground. In most shallow water environment the non-representative sampling techniques employed. such as mangrove ecosystem, atmospheric input is the Spencely[4] and Shahbuddin et al.[5] have introduced a major source. In Malaysia, studies relating to simple method for measuring accretion by simulating mangroves are not well documented and only little pneumatophores using rods and stakes and an artificial information is known concerning the sedimentation of horizon marker method, respectively. Meanwhile, long- the mangrove forest[9,12]. Furthermore, geochemical

Corresponding Author: B.Y. Kamaruzzaman, Institute of Oceanography and Maritime Studies, International Islamic University Malaysia (IIUM), Jalan Istana, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia 522 Am. J. Agri. & Biol. Sci., 3 (3): 522-525, 2008 studies of sediments from the Malaysian mangrove Carpenter et al.[10] and Carpenter et al.[13]. Activities of forests have received little attention and only limited 210Po along with the 208Po tracer were measured by studies have been done regarding their role in the Alpha Spectrometry on a silicon surface barrier detector process of sedimentation[9]. In view of the importance connected to a multi channel analyzer. of the mangrove to various aspects of the environment, research on the sediment accretion as well as the Data analysis: Total 210Pb activity was determined sediment age were carried out. indirectly by the measurement of its alpha-emitting grand daughter nuclide, 210Po[14]. Measurement of ratio 210 209 MATERIALS AND METHOD Po and Po activity will provide an adequate figure of supported 210Pb, as these two elements are assumed [15] 210 Sampling sites: The Kemaman-Chukai mangrove is to be in equilibrium . Subtracting of supported Pb located in the Kemaman district, inside one of the most from total 210Pb will determine unsupported 210Pb. The extensive mangrove area (298.2 ha) on the east coast of activity of 210Pb is obtained by the formula below: Peninsular Malaysia (Fig. 1). The dominant species of mangrove tree found are Rhizopora sp., Avicennia sp. Activity 210Po(210Pb) = A(dpm/g) and Xylocarpus sp. The mangroves which are relatively Actual 210Po(210Pb) tracer weight 209Pb(g) = × 209Po(24.74dpm/g) × undisturbed have been gazetted as a mangrove reserve Actual 209Po sampleweight(g) forest by the Terengganu Forestry Department. The mangrove area lies on the southern bank of the Where: Kemaman estuary, where both the Kemaman and −λt A = Ao e (equal to the accumulative residual Chukai rivers flow into. The tide floods the area twice unsupported 210Pb below the sediment age of t) daily as it is semi-diurnal with a mean range of 1.8 m. −λt Ao = A/e (equal to the total unsupported Pb in the In this study, a 20 cm sediment core from bothe sediment column) Kemaman and Chukai mangrove were collected with a λ = Ln2/t = 0.639 (decay constant of 210Pb) D-section core sampler from this area (Fig. 1) and was 1/2 T1/2 = Half-life (22.3 years) cut into segments of approximately 5 cm interval, t = Depth (cm)/sedimentation rate in years labelled and stored in acid cleaned bottle for analysis. 210 210 Inventories (I) of Pb (unsupported) are expressed Analytical methods for Pb: The samples were cut in dpm-2 and were calculated according to Turekian[16]: into segment approximately 2 cm interval using plastic knife and was transferred to petri disc. The samples I = ΣAIρihi were dried in an oven at 60°C to constants weights. To facilitate geochemical analysis the sample were ground Where: 210 -1 into a fine powder using a pestle and mortar. The Ai = The Pbxs (dpm g ) 210 −3 process of Pb excess dating method is divided into i = The bulk density interval i (g cm ) two process, digestion process and Po platting h = The thickness of the interval (cm) process[10,13]. The excess 210Pb in a different core was measured by the same procedure describes by And finally the sedimentation rate can be calculated using the formula: 10°27’ E 10°28’ E 10°29’ E −λt CK A = Aoe Study area −λ(x/S) A = Aoe Chukai River 04°15’ N ln A = -(λ/S)x+ln Ao

KM Where: A = Activity of excess 210Pb in the sediment at any 04°14’ N depth Kemaman 210 River Ao = Activity of excess Pb in the freshly deposited South China Sea sediment at depth = 0(the sediment-water interface) Fig. 1: Sampling location where 2 cores were collected S = Sedimentation rate in cm year−1 at Kemaman (KM) and Chukai (CK) mangrove λ = Radioactive decay constant (0.0311/year) forest, Terengganu, Malaysia t = Time in year 523 Am. J. Agri. & Biol. Sci., 3 (3): 522-525, 2008

RESULTS AND DISCUSSION be the dominant source of sediment to the Kemaman- Chukai mangrove forest. 210 Figure 2 shows the activities of Pbxs were In Kemaman mangrove forest, the sedimentation generally decreasing exponentially with depth. Some rate obtained is consistent with the result obtained by 210 higher value of Pb activity on the surface might be Shabuddin et al.[5], ranging from 0.64-1.46 cm year−1 caused by the settling particles which were basically with artificial horizontal marker method but is slightly derived from the atmosphere and land or from the older higher compared with Kamaruzzaman et al.[19] and sediment issued from the resuspension process[17]. It is [20] −1 230 Kamaruzzaman et al. , 0.68 cm year with Thex clear that 210Pb increases monotonically with depth, 230 232 [18] and Thex/ Th method. In comparison with other suggesting of the particulate scavenging . The studies in Malaysia, sedimentation rate at Kemaman- determination of average sedimentation rate is based on 210 Chukai mangrove is slightly higher than Pahang the assumption that the Pbxs is incorporated into the −1[21] [18] mangrove, 0.65 cm year and Johor mangrove, sediments with a constant rate . As shown in Fig. 2, 0.84 cm year−1[22] but lower compared to Matang applying the formula as above, the sedimentation rate [23] −1 230 mangrove, Perak , 1.08 cm year using Th of Kemaman and Chukai mangrove forest were excess −1 method. estimated to 1.11 and 0.94 cm year , respectively. The 210 From the sedimentation rates, Pb dating sedimentation rate was estimated by selecting the ‘best- technique was used to determine the sediments age for curve’ from the establishment 210Pb (dpm g−1) the major estuarine mangrove forest in Terengganu distribution with depth. The p>0.01 calculated from the region. Sediment age can be determined by dividing the statistical test, ANOVA two factor prove that the sediment depth with sedimentation rate. The lower the sedimentation rate among the study area are not sedimentation rate indicates the older age of sediment. significantly different. In this study, Chukai mangrove Assuming that the sedimentation rate values are which is situated about 2 km from river mouth had the accurate, this implies that the sediments in the upper lowest accumulation rate while the highest sediment 100 cm at Kemaman-Chukai mangrove forest were accumulation rate occurs at Kemaman mangrove which deposited during the past 90 years. From the ANOVA is situated near the river mouth. Rivers are believed to test, the sediment age does not differ significantly

among the study areas with p<0.05. Briefly, Chukai 3.0 Kemaman mangrove mangrove which had the lowest sedimentation rate had the oldest mangrove with 106.6 years while the .

m youngest mangrove, 90.2 years, occurred at Kemaman p d (

mangrove which had the highest sedimentation rate. b P 2.0

0 1 2

s CONCLUSION s e ) c

1 x − E g The sedimentation rates of Kemaman-Chukai mangrove forest, based on the 210Pb dating techniques 1.0 0 2 4 6 8 10 12 14 16 18 20 were shown to be similar to the known local sea-level Depth (cm) rise rate. The immobility of Pb in sediments was confirmed with stable 210Pb at the mangrove. It is 3.0 Chukai mangrove suggested that the stable 210Pb is a powerful tracer in mangrove sediment studies on the determination of

. changing sedimentation rates, postdepositional m p d

( mobilization and historical Pb sources.

b P

0 2.0 1 2

ACKNOWLEDGEMENT s s e

) c 1 x −

E g This research was conducted with joint funding from the Malaysia Ministry of Science and Technology 1.0 under Fundamental Research Grant project number 0 2 4 6 8 10 12 14 16 18 20 Depth (cm) 57008. The authors wish to express their gratitude to Oceanography Laboratory, INOS and INOCEM teams 210 Fig. 2: Pbexcess distribution with depth in Terengganu for their invaluable assistance and hospitality mangrove forest throughout the sampling period. 524 Am. J. Agri. & Biol. Sci., 3 (3): 522-525, 2008

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