Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210 Pb and 137 Cs radioisotopes

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1 Geosciences Journal DOI /s c The Association of Korean Geoscience Societies and Springer 2013 Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210 Pb and 137 Cs radioisotopes Mohammadreza Gharibreza* John Kuna Raj Ismail Yusoff Zainudin Othman Wan Zakaria Wan Muhamad Tahir Mohammad Aqeel Ashraf } Department of Geology, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Soil Conservation and Watershed Management Research Institute, Tehran, PO Box , Iran Department of Geology, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Department of Geography and Environment, Sultan Idris University of Education, Tanjung Malim, Perak, Malaysia Isotope & Tracer Application Group (e-tag), Division of Environment and Waste Management, Malaysian Nuclear Agency (Nuclear Malaysia), Bangi, Kajang, Selangor, Malaysia Department of Geology, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia ABSTRACT: The evolutionary environmental history of Bera Lake was studied using the fallout radioisotopes 137 Cs and 210 Pb. 317 Cs horizons in the all ten studied cores showed a constant rate of 210 Pb supply along all distinctive layers in each core. The lithology of layers significantly affected the variation of 210 Pb value with depth. The chronology of Bera Lake sediment was conducted using the Constant Rate of Supply (CRS) model. The 1963 fallout maximum 137 Cs from atmospheric testing of nuclear weapons found in all selected master cores at the depth of 40 cm. The mean pre-1950 sediment accumulation rate was ranged between 0.06 ± 0.02 and 0.16 ± 0.2 g cm 2 y 1. Environmental impacts of five deforestation projects performed from 1972 to 1995 at the catchment area, contributed significantly toward increasing the sedimentation rate within Bera Lake. Besides the 137 Cs horizons, the charcoal horizon at the lower contact of white sandy mud revealed the datum of maximum deforestation in the study area. 210 Pb dates using the CRS model correlated historical sediment fluxes to anthropogenic changes in Bera Lake catchment area. Organicrich sediments deposited mostly at the top of the Bera Lake sediment columns with a mean rate of 0.2 ± 0.1 g cm 2 y 1 since High biomass productivity of mature oil palm plantations, which were developed in the catchment area, dictated organic-rich deposit distribution. This study highlighted capability of radioisotopes to reconstruct long-term ( years) history of a natural lake at a tropical area where surrounding catchment has extensively deforested over the recent decades. Key words: Bera Lake, CRS model, deforestation, 210 Pb and 137 Cs radioisotopes, sedimentation rate 1. INTRODUCTION Natural events and anthropogenic activities during the recent decades could be detected in the lake sediments. Fresh water lakes are the most sensitive sedimentary basins, *Corresponding author: Gharibreza@siswa.um.edu.my; gharibreza@scwmri.ac.ir which clearly show variations in the sedimentary regime. Sedimentation rates are measurable by traditional and new methods as hydrographic maps, in-situ surveying and physical measurements, and using isotopes tracer (Routh et al., 2007). Isotopes tracers and their relevant models were selected as the main tools in order to achieve research aims. Goldberg (1963) and Krishnaswami (1971) introduced a method for long-term ( years) chronology of lake sediments using radioisotopes. Dating of sediment profiles using 210 Pb is the more acceptable method in lakes where the accretion rate is relatively constant throughout the given period of time. 210 Pb values decrease exponentially with depth at a rate inversely proportional to the sedimentation rate. Therefore, the Constant Flux: Constant Sedimentation (CF:CS) and the Constant Initial Concentration (CIC) models are the recommended methods. On the other hand, sediment supply faces variation because of natural and anthropogenic impacts. Therefore, it shows a non-exponential decrease of 210 Pb concentration with depth. The Constant Rate of Supply (CRS) model was developed to study sedimentation rates in lakes that show deviations from the normal decline of 210 Pb concentration with depth (Appleby and Oldfield, 1978; Robbins et al., 1978). Pennington et al. (1973) and Appleby et al. (1991) introduced 137 Cs and 241 Am as artificial radioisotopes that serve as independent time markers. These fallout radioisotopes are widely used to verify 210 Pb dating using CIC and CRS models. These fallout radionuclides were emitted from nuclear bombs testing and from the 1986 Chernobyl reactor accident. The basic models were also improved to evaluate 210 Pb data and to interpret of sediment chronology (Appleby and Oldfield, 1983; Oldfield et al., 1984). This method has been adopted and applied in several case studies around the world based on the local situation. For instance, Flower et al. (2009) has highlighted applica-

2 Mohammadreza Gharibreza, John Kuna Raj, Ismail Yusoff, Zainudin Othman, Wan Zakaria Wan Muhamad Tahir, and Mohammad Aqeel Ashraf tion of radioisotopes in study of environmental changes effects on the sedimentation rates, where the mean rate was 0.21 and 1.5 g cm 2 y 1 before and after anthropogenic activities in the Southern Mediterranean Lakes. Begy et al. (2009), in addition, has stated capability of CRS model in accumulation rate in Red Lake (Romania). Therefore, the mean sedimentation rate was ranged between 0.18 ± 0.04 and 1.85 ± 0.5 g cm 2 y 1 prior and post environmental changes. Moungsrijun et al. (2010) has reported a similar range of 210 Pb and 137 Cs activities in a lake in Thailand to the present research results. Furthermore, the accumulation rate has been ranged between 0.24 and 1.02 g cm 2 y 1 using CIC model. Such research also carried out by Kumar et al. (2007) to estimate sedimentation rates in North Indian Lakes by using 210 Pb and 137 Cs radionuclides, where capability of this technique was tested and approved in the mountainous Himalayan lakes. The 210 Pb chronology of Bera Lake sediment is recognized as a perfect method for the present study. This study is pioneer in testing the capability of radioisotopes to reconstruct history of a natural lake using radioisotopes in Malaysia. The main objective of this research is, therefore, to determine the history of environmental changes based on variations in sedimentation rates using 210 Pb and 137 Cs radioisotopes at Bera Lake. Current research might be a useful example for the application of radioisotopes to study historical changes in the lakes and reservoirs, especially that area that has experienced extensive land use changes Study Area Bera Lake is the largest natural lake which is known as the first RAMSAR site (Protected area) in Peninsular Malaysia. Severe sedimentation is recognized as an important issue in Bera Lake caused by extensive deforestation. Palynological evidences show that Bera Lake Basin originated some 5,300 years ago as poorly drained isolated area (Morley, 1981). Widespread deposits of humic matter and peat collection in this area started about 4,500 before present. This was followed by 150 to 200 years of heavy rainfall and intense storms that led to a persistently high water table (Wüst and Bustin, 2004). The Bera Lake catchment has experienced the most extensive land use changes over recent decades. The Federal Land Development Authority (FELDA) is the main executive agency for land use change in Malaysia (Henson, 1994). Between 1970 and 1995 five FELDA land development programs were performed in the study area (MPOC, 2007). These resulted in a changeover of km 2 of original forest to oil palm and rubber plantations. Bera Lake was proposed under the Convention of Wetlands as the first RAMSAR site in Malaysia in 1994 with the FELDA districts known as the Buffer Zone. Aerial photos (flown in 1966, 1:25,000 scale) of the Bera Lake catchment area were also studied as well as the West Malaysia land use map (1:500,000). The new land use map of Bera Lake Catchment area was developed based on a satellite image (Spot 5, 2009) of spatial resolution 10 m. A geographical information system (GIS) and an on-screen digitizing method were applied for mapping. Results highlighted the fact that land use change is continuing and encroaching into the Bera Lake RAMSAR site area. Oil palm and rubber plantations as well as cleared land distribution reached a maximum of 340 km 2 in 2009, representing an increase of km 2 since MATERIALS AND METHODS 2.1. Sampling and Sample Preparation In this study, two core sampler apparatus, types A and B, were developed (Gharibreza et al., 2012). A core sampler is a hand held corer, which is designed for 2-m undisturbed core sampling with high recovery rate and non compacted sediment column. A total of ten core samples were collected from Bera Lake (Fig. 1) under a deterministic strategy. Cores were preserved in a freezer at a temperature of 4 C before being sliced at 2 ± 0.2-cm intervals. The sliced samples dried at 60 C and were ground for further analytical procedures. Prepared samples were packed in a cylindrical containers with screw caps with 4.7 cm height, and cm 3 volume for three weeks before counting to allow the 226 Ra to secularly equilibrate with 222 Rn and its' shorter half-life daughters Analytical method Well-calibrated gamma-spectrometry based on hyper-pure germanium (HpGe) detectors at Nuclear Malaysia (NM) were applied to measure specific 210 Pb and 137 Cs activities in prepared samples. The gamma-spectrometer model GCW2523 detector at Nuclear Malaysia calibrated a relative efficiency of 25% and full width at half maximum (FWHM) of 2.04 kev for 60 Co gamma-energy line at 1332 kev. Lead shielding dimension is 1 mm (0.040 in) tin and 1.6 mm (0.062 in) copper graded liner. These materials are used to prevent interference by lead x rays or scattered external sources. The gamma-spectrometer was calibrated using multinuclides standard (NIST) solutions in the same sample detector geometry. The lower limit of detection, with 95% confidence, was 0.3 Bq for 24 hours measuring time. International Atomic Energy Agency (IAEA) reference samples QA2 = IAEA-326; QA6 = IAEA-385 were used for quality control of the gammaspectrometer and its calibration. Reference and repeated samples showed 210 Pb and 226 Ra values in an acceptable range of activity Chronology models The Bera Lake sediment chronology was performed using the CRS model. The assumptions for application of CIC model was not meet the criteria for this study. The CRS model

3 Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210Pb and 137Cs radioisotopes Fig. 1. Bera Lake morphology and core sampling positions. assumes a constant 210Pb flux but allows the sediment supply to vary. Therefore, this model is applied to most sedimentary basins where the sediment supply may vary in response to climatic or anthropogenic changes. The CRS dating model (1) is expressed as follows (Appleby and Old- field, 1978b): At = A0 e λ t Where At is the cumulative (1) 210 Pbex below the level repre-

4 Mohammadreza Gharibreza, John Kuna Raj, Ismail Yusoff, Zainudin Othman, Wan Zakaria Wan Muhamad Tahir, and Mohammad Aqeel Ashraf senting time t, λ represents the 210 Pb decay constant of 210 Pb ( y 1 ) and A 0 is the total cumulative 210 Pb ex inventory (Bq m 2 ) at the point where the 210 Pb tot activity reaches radioactive equilibrium with the supporting 226 Ra (2). A 0 Where ρ i = dry bulk density (kg m 3 ) of the i th depth interval, h i = thickness of the i th depth interval (m) and A i = 210 Pb ex (Bq kg 1 ). Besides, 210 Pb flux (Bq m 2 y 1 ) can be calculated by the following Equation (3): 210 P = ( ρ i h i A i ) b flux = A 0 λ the sediment ages (4) at any depth arecalculated by: 1 t --In A 0 = ---- λ A Sedimentation rate (cm y 1 ) is calculated by dividing mass flux (g cm 2 y 1 ) by dry bulk density (g cm 3 ). A mean sedimentation rate in the CRS model is obtainable by using a slope regression method. Plotting the In 210 Pb ex versus depth represents a linear profile, where 210 Pb ex decreases exponentially. The mean sedimentation rate (cm y 1 ) for a (2) (3) (4) given sediment column can be found by dividing of constant decay by the slope ( λ/slope). The accuracy of 210 Pb dates, using the CRS model is vertified by referencing to the well-resolved peaks of 137 Cs at distinctive horizons. 137 Cs horizons include the first appearance in sediment columns (i.e., ) and the fallout maximum (i.e., ) from atmospheric testing of atomic bombs. Besides, stratigraphic charcoal horizon which settled during and after the maximum deforestation procedures in 1973 at Bera Lake are also used to verify 210 Pb dates. 3. RESULTS Pb and 137 Cs Inventories and 210 Pb Flux Inventory and flux of fallout radionuclide 210 Pb are calculated based on Equations (2) and (3). The maximum and minimum 210 Pb inventories at Bera Lake were calculated to be 5112 ± 70 and 1440 ± 41 Bq m 2, respectively. The estimated value of the 210 Pb flux along the mainstream of Bera Lake is 90 ± 5 Bq m 2 y 1. An increase occurred to 159 ± 2 Bq m 2 y 1 towards the corners of the lake due to the divergent current releasing sediments in a semi closed area. In other words, the morphological shape and stream pattern control Fig. 2. Fallout radionuclides concentration vs. depth at Core 2 and 210 Pb dates using the CRS chronology model.

5 Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210 Pb and 137 Cs radioisotopes Fig. 3. Fallout radionuclides concentration vs. depth at Core 8 and 210 Pb dates using the CRS chronology model. 210 Pb flux at Bera Lake. Previous studies performed in Malaysia, Thailand and Indonesia highlighted the low activity of 137 Cs (<400 Bq m 2 ), which are in accordance with 137 Cs activity in tropical Australia (Neergaard, 2008; Othman, 2003; Barokah, 2001; Moungsrijun, 2010). They also stressed the ability of 137 Cs to investigate soil redistribution in catchment area and as a confirmation time marker in sedimentation studies in tropical areas. The 137 Cs activities shown in Figures 2, 3, and 4 can be divided into two distinctive categories. The first group includes known 137 Cs horizons (1954, 1963) and the second category indicator of reworked and erosion-induced 137 Cs from the catchment area. Although 137 Cs showed peaks in 1986 in the selected master cores coinciding with the Chernobyl accident, scientific reports to verify its fallout in Malaysia are not available Sedimentation Rate at Bera Lake Sedimentation rate status in different parts of Bera Lake is presented in the master cores. Figures 2, 3, and 4 depict 210 Pb chronology using the CRS model and graphic variation of total 210 Pb, supported and unsupported 210 Pb values as well as 137 Cs horizons in master cores. Further details of sedimentation rates are explained in the three geographical parts of Bera Lake. Variation in sedimentation rates in different parts of Bera Lake is presented in Figure 5. A northward sedimentation rate found at the south part of the lake, ranged between 0.8 and 1.8 cm y 1. The mean sedimentation rate at the middle of the lake was varied between 1 and 1.4 cm y 1. A clear increase in sedimentation rate (1.4 to 2.6 cm y 1 ) was recorded at the north of the lake, where velocity of currents has been reduced and entered to the semi-closed areas. In other word, morphological shape and stream pattern are controlling sediment distribution at the Bera Lake Sedimentation rate at the south of Bera Lake Cores 2 and 7 are identified as master cores in order to describe unsupported 210 Pb inventory and its variation versus depth and sedimentation rate at the south of Bera Lake. The 226 Ra value gained a mean value of 38 ± 6.5 Bq kg 1 in the studied cores. The equilibrium of total 210 Pb value with the supporting 226 Ra was calculated at a depth of 60 cm. The maximum unsupported 210 Pb concentration varied between 60 ± 11, 40 ± 11, and 38 ± 16 Bq kg 1 in Cores 2, 3, and 7, respectively. The unsupported 210 Pb variation versus depth (Fig. 2) revealed a clear lithological dependence of 210 Pb value in Bera Lake sediment. The unsupported 210 Pb values decreased with a few minor irregularities in layers 4 and 3. A deeper

6 Mohammadreza Gharibreza, John Kuna Raj, Ismail Yusoff, Zainudin Othman, Wan Zakaria Wan Muhamad Tahir, and Mohammad Aqeel Ashraf Fig. 4. Fallout radionuclides concentration vs. depth at Core 5 and 210 Pb dates using the CRS chronology model. zone (layers 2 and 1) depicts an exponential variation of unsupported 210 Pb with depth. A northward increase in the mean sedimentation rate was recorded at the south of Bera Lake, where the accumulation rate was calculated to be 0.24 ± 0.32, 0.27 ± 0.25 and 0.47 ± 0.54 g cm 2 y 1 at Cores 2, 3 and 7, respectively. Further, the mean pre-1950 accumulation rate was 0.06 ± 0.02, 0.07 ± 0.07 and 0.21 ± 0.21 g cm 2 y 1 at Cores 2, 3 and 7, respectively. The South of Bera Lake experienced a remarkable accumulation of terrestrial sediments when Layer 3 was deposited at the mean rate of 0.48 ± 0.48, 0.39 ± 0.13, and 0.41 ± 0.29 g cm 2 yr 1 at Cores 2, 3, and 7, respectively. Five FELDA land development projects relicts were recorded at Core 7, where sediment fluxed at rates of 0.43, 0.12, 0.17, 0.34, 0.82 g cm 2 yr 1, respectively Sedimentation continued with a mean rate of 0.22 ± 0.1 g cm 2 y 1 at the uppermost layer of the Bera Lake sediment column. A sediment flux was recorded at the depths of 2 to 4 cm, remarks a huge flood occurred in 2007 signaled rates of 0.32 and 0.17 g cm 2 y 1 at Cores 2 and 7. The 137 Cs showed well-resolved peaks at depths of 39 and 37 cm which are in agreement with 210 Pb dates using the CRS model. An activity of 8.38 Bq m 2 appeared as the first appearance of 137 Cs in 1954 at the south of Bera Lake sediment column (Fig. 2). Another remarkable 137 Cs peak with an activity of Bq m 2 found at depths of 39 cm which agrees with the maximum 137 Cs fallout in Once again, a northward increase in the sedimentation rate at the south of Bera Lake has revealed in the 137 Cs value. The first appearance and maximum fallout of the 317 Cs were and Bq m 2, respectively, in Core 7. A 137 Cs peak (13.34 Bq m 2 ) appeared at the depth of 30 cm (Fig. 2), probably a signal of 137 Cs fallout in 1986 due to the Chernobyl accident. In addition, 137 Cs peaks have significantly depicted natural events in study area. Such peaks in Layer 5 indicates a huge flood that occurred in 2007, displayed properly by a peak at depth of 6 cm and 137 Cs activity of Bq m 2. As a result, 137 Cs horizons highlighted the ability of the CRS model to depict the chronology of Bera Lake sediments. A mean sedimentation rate based on depths of 137 Cs horizons in the Bera Lake sediment column were calculated to be 0.7 and 1.12 cm y 1 in Cores 2 and 7, respectively. Results agreed with the mean sedimentation rate calculated by a slope regression model in which In 210 Pb unsupported were plotted versus cumulative mass depth Sedimentation rate at the middle of Bera Lake Sedimentation status at the middle of Bera Lake was investigated in Cores 6, 4, and 8. Detailed unsupported 210 Pb and

7 Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210 Pb and 137 Cs radioisotopes Fig. 5. Sediment distribution and sedimentation rate map of Bera Lake. 137 Cs inventories and their variation with depth and sedimentation rate were described in the master Core 8. The 226 Ra activity gained a mean value of 40 ± 7 Bq kg 1 in the studied cores. The equilibrium of total 210 Pb activity with the supporting 226 Ra was obtained at a depth of 70 cm. The unsupported 210 Pb concentration at the north and east of Bera Lake main open water ranged between 19 ± 18 and 1 ± 8 Bq kg 1, while at the deepest part is varying between 95 ± 19 and 1 ± 10 Bq kg 1 in Core 6. Once again, results highlighted the effects of lithology on unsupported 210 Pb distribution with depth at the middle of Bera Lake (Fig. 3). The unsupported 210 Pb values decreased steeply with a few irregularities until layers contacts. An exponential variation of unsupported 210 Pb with depth appeared at the uppermost layer of Core 6. The unsupported 210 Pb activity showed a peak slightly below the sediment surface at Core 8. Seemingly, this peak may have been caused by steep redox gradients across the uppermost few centimeters of sediment. A margin ward increase in the mean sedimentation rate was recognized at the middle of Bera Lake, where the deposition rate was calculated to be 0.4 ± 0.59, 0.35 ± 0.75, and 0.13 ± 0.16 g cm 2 y 1 at cores 6, 8, and 4, respectively. Besides, the mean pre-1950 accumulation rate was calculated to be 0.05 ± 0.01 and 0.14 ± 0.16 g cm 2 y 1 at Cores 6 and 8, respectively. White sandy mud (Layer 3) an indicator of terrestrial sediment fluxes, accumulated at the middle of Bera Lake with a mean rate of 0.78 ± 0.75 g cm 2 yr 1 in Core 6, and 0.54 ± 1.2 g cm 2 y 1 in Core 8. Five FELDA land development projects have contributed to sediment flux along the main axes of Bera Lake at Core 6 rates of 0.69, 0.52, 1.01, 1.53, and 2.16 g cm 2 y 1, respectively. A different trend in the deposition of organic-rich sediments dominated the uppermost Layer 4 of the middle of Bera Lake. The highest accumulation rate was observed at Core 8 with a mean rate of 0.35 ± 0.3 g cm 2 y 1, while organicrich deposits settled at a mean rate of 0.08 ± 0.02 g cm 2 y 1 at the deepest part of Bera Lake. The deforestation projects were prohibited in 1994 was coincided with land clearing by locals; sediment was fluxed into the north margin of the middle of Bera Lake with a rate of 0.47 g cm 2 y 1. The sedimentation rate was continued and promoted to 1.35 g cm 2 y 1 in The first appearance of 137 Cs at the middle of the Bera Lake sediment column in 1954 gained 10.5 Bq m 2. A wellresolved peak appeared at the depths of 40 cm with Bq m 2 activities. This represents maximum 137 Cs fallout in 1963, which agrees with 210 Pb dates using the CRS model. A clear similarity was recorded between the depths of this peak in the south and the middle of Bera Lake. A 137 Cs peak with a 19 Bq m 2 concentration at a depth of 30 cm (Fig. 3), likely indicates 137 Cs fallout in 1986 due to the Chernobyl accident. Other 137 Cs peaks between the depths of 0 to 30 cm inferred reworked and erosion-induced 137 Cs sources because of deforestation projects. As a result, the ability of the CRS model to portray the chronology of Bera Lake sediments is verified significantly by 137 Cs horizons. A mean sedimentation rate based on the stratigraphic depths of 137 Cs horizons was calculated to be 0.78 and 1.01 cm y 1 in Cores 8 and 6, respectively. The 137 Cs based sedimentation rate in master core 8 agrees with the mean sedimentation rate, which is calculated by a slope regression model in which In 210 Pb unsupported is plotted versus accumulative mass depth Sedimentation rate at the North of Bera Lake Sedimentation rates at the north of Bera Lake were evaluated in Cores 1, 5, and 9. Detailed unsupported 210 Pb and 137 Cs inventories as well as their variation with depth and sedimentation rate were described by the master Core 5. The 226 Ra activity gained a mean concentration of 36 ± 8 Bq kg 1 at the north of Bera Lake. The total 210 Pb activity approached equilibrium with the supporting 226 Ra at a depth of 65 cm. The unsupported 210 Pb values at the north of Bera Lake varying between 76 ± 25 and 1.25 ± 12 Bq kg 1 (Fig. 4). A clear, steep decline in unsupported 210 Pb values was found

8 Mohammadreza Gharibreza, John Kuna Raj, Ismail Yusoff, Zainudin Othman, Wan Zakaria Wan Muhamad Tahir, and Mohammad Aqeel Ashraf at layer contacts, which revealed the effects of lithology and sedimentary condition changes on the radionuclide concentration. An exponential variation of unsupported 210 Pb versus depth with some minor irregularities appeared along layers 3 and 4, separately (Fig. 4). The mean sedimentation rate at the north of Bera Lake was promoted in semi-closed open water (Core 9), where the highest deposition rate (2.58 ± 2.1 cm y 1 ) was recorded. Additionally, the maximum 210 Pb flux in Bera Lake reached to 159 ± 2 Bq m 2 at the position of this core. Besides, the mean sedimentation rate settled 0.17 ± 0.23 and 0.34 ± 0.5 g cm 2 y 1 at Cores 1 and 5, respectively. 210 Pb dating by CRS model revealed that Layer 1 was deposited pre-1950 with a mean sedimentation rate of 0.06 ± 0.01, 0.05 ± 0.02, 0.14 ± 0.26 g cm 2 y 1 at Cores 1, 9, and 5, respectively. Terrestrial sediments signal intensive erosion induced deposits, observed at the north of Bera Lake with a mean rate of 0.55 ± 0.43, 0.17 ± 0.12 and 0.2 ± 0.08 g cm 2 y 1 in cores 1, 5 and Core 9, respectively. Five FELDA land development projects were clearly manifested in Layer 3 in which sediment were fluxed into the north of Bera Lake at rate of 0.43, 0.34, 0.18, 0.12, and 0.17 g cm 2 y 1, separately. Sedimentation continued at the uppermost layer of the north Bera Lake sediment profile with organic-rich sediments since The highest dry accumulation rate of this layer was identified at the position of Core 9 with a mean rate of 0.28 g cm 2 y 1 (1.35 cm y 1 ). Organic-rich deposits settled with the mean rate of 0.13 ± 0.04 and 0.1 ± 0.07 g cm 2 y 1 at Cores 5 and 1, respectively. The CRS model dating has placed an organic-rich sediment flux at Cores 1 and 5 in 1996 at rates of 0.17 and 0.2 g cm 2 y 1. The 2007 flood event in the north of the lake was recorded at the depths of 2 and 4 cm at Core 5 at a rate of 0.1 g cm 2 y 1. The first appearance of 137 Cs in 1954 at the north of Bera Lake sediment column was calculated to be 7.93 Bq m 2. A well-resolved peak appeared at depths of 39 cm with Bq m 2 activities. This depicts the 1963 fallout maximum from the atmospheric testing of nuclear weapons, which is supported with 210 Pb dates using the CRS model. A vivid similarity was recorded between the depths of this peak at all the parts of Bera Lake sediment column. Other 137 Cs peaks between the depths of 0 and 38 cm inferred reworked and erosion-induced 137 Cs sources because of land clearance projects. Once again, 137 Cs confirmation horizons affirmed that the CRS model is an applicable method for the chronology of Bera Lake sediments. 4. DISCUSSION Long-term variation in the rate of sediment supply into Bera Lake and the lithology of the deposited sediments were studied through 210 Pb dating using the CRS model. The chronology of sediment columns correlated to the phases of land use changes in the catchment area. According to Henson (1994), five FELDA projects were carried out in the Pahang State between 1970 and Land development phases were conducted between 1970 and 1975, 1976 and 1980, 1981 and 1985, 1986 and 1990, and between 1991 and 1995, respectively. A sixth phase of land development was also carried out by the locals between 1995 and Tan et al. (2009) reported that a typical oil palm land development project is comprised of six main stages, the most important of which is land clearing. The duration of such clear lands for 2,000 hectares of oil palm farm usually takes 14 months. Severe and continuous exposure of Permian- Triassic continental sediments and igneous rocks during the FELDA projects has thus led to several tons of sediments being transported to Bera Lake wetlands and open waters. Deposition of eroded sediments in the Bera Lake basin started with the settlement of a white sandy mud Layer 3. A clear accordance between the historical environmental impacts of FELDA projects in the catchment area and the increased sediment supply was affirmed by 210 Pb dating and 137 Cs horizons (Figs. 2, 3, and 4). A dilution of the atmospheric 210 Pb fallout by increased sedimentation coincided with FELDA projects in the Bera Lake sediment column. Additionally, the normal process of sediment accumulation of the pre-1970 term was interrupted. The pre-1970 mean sedimentation rate at the south of Bera Lake was 0.06 ± 0.02 g cm 2 y 1, while the dramatic increase of the rate to 1.13 g cm 2 y 1 was occurred after the implementation of the first and second FELDA projects (from 1972 to 1980). Besides, the fifth FELDA land development phases, was recognized as main projects in terms of contribution in the deposition of white sandy mud layer. An influx of sediment at the top of sediment column was correlated with a huge flood in December, 2007, when 1,200 mm of rain precipitated in 11 days and the water level rose to drown the whole Bera Lake lowland area. This natural event was also verified remarkably by the highest reworked 137 Cs activity at the top of the sediment column of master cores. The 137 Cs value was 5 times greater than the value of the maximum artificial fallout of 137 Cs in 1963 in the master Core 2. The 210 Pb dating of core samples, however, points out that the environmental impact was not recorded uniformly in all parts of Bera Lake. For example, the impacts of the first FELDA project in the sediment profile at the north end of Bera Lake appeared two years later than those at the south end. Maximum sedimentation rates in the south, middle and north of Bera Lake were recorded in 1987, 1980 and 1974 with the mean of 3.3, 1.3, and 0.43 g cm 2 y 1, respectively. These influxes of sediments occurred during the first, second, and fourth FELDA development projects. Figure 6 depicts the meaningful association between deforestation phases and the rate of sedimentation at master Core 2. Clear differences observed between sediment fluxes prior and post FELDA land development projects (Fig. 6). Sedimen-

9 Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210 Pb and 137 Cs radioisotopes Fig. 6. Sedimentation rates at Bera Lake, in contrast with land development distribution in catchment area. tation dramatically increased 22 times by the first and second phases when white sandy mud was deposited at Bera Lake. Land preparation in the Bera Lake catchment continued by burning felled trees. A remarkable charcoal horizon was detected at the lower contact of Layer 3 when terrestrial sediment was started to deposit in all sectors of Bera Lake. Plotting of 210 Pb dating using the CRS model with deforestation phases revealed that significant sediment delivery from the catchment area into Bera Lake was delayed 1 to 2 years. A clear organic-rich to peat deposits at the top of Bera Lake sediment column were settled mainly since 1994 when highly organic waste production was associated with the oil palm plantations. Available data shows that oil palm plantations amass 8.3 tons of biomass per year; a value that is 2.5 tons more per year than a rain forest produces (MPOC, 2007). In addition, the dry matter productivity per year of an oil palm plantation is about 36 tons, as compared with about 26 tons for a rain forest. According to the distribution of oil palm plantations and rainforest areas in Bera Lake, annual bio mass productivity was calculated to be 1.5 million cubic meters. This amount of biomass could potentially cover Bera Lake catchment at a rate of 0.4 cm yr 1. Such situation, runoff is mainly limited to organic matter and organic-rich sediments became the main deposited sediments in Bera Lake. The mean sediment supply after the fifth FELDA development project gradually decreased to 0.2 ± 0.1, 0.21 ± 0.1, ± 0.34, 0.29 ± 0.007, 0.11 ± 0.04, 0.08 ± 0.02, 0.13 ± 0.24, 0.24 ± 0.38, and 0.17 ± 0.14 g cm 2 y 1 in Cores 1, 2, 3, 4, 5, 6, 7, 8, and 9, respectively. The results provide decision makers with useful guidelines for management practice within the catchment area. 5. CONCLUSION A general constant rate of 210 Pb supply trends settled into Bera Lake. The lowest 210 Pb values were observed with maximum dilution by increased sedimentation and coarser sediments deposition. The well-resolved 137 Cs peaks affirmed that the CRS model can be applicable providing a chronology of Bera Lake sediments. A noticeable relationship was achieved between depths of the 1963 maximum 137 Cs fallout in the master Cores 2, 8 and 5. This proved that a slightly uniform sediment distribution regime was existed throughout all of Bera Lake prior to deforestation projects and has confirmed the accuracy of 210 Pb dating using the CRS model in the present study. The overall evidence clearly shows the important role of environmental changes by FELDA since 1971 in the Bera Lake catchment in terms of the rate of sediment supply and lithology of the sediment profiles. In Bera Lake, the sediment distribution was controlled significantly by the morphological shape and stream pattern. As a result, maximum 210 Pb inventory and flux were recorded in the semi-closed area of Bera Lake. A northward increment in sediment accumulation trend settled along the main axes of Bera Lake prior to Maximum terrestrial sedimentation started with a massive white sandy mud (Layer 3) at mean rates of 0.48 ± 0.48, 0.54 ± 1.2 and 0.17 ± 0.12 g cm 2 y 1 in the south, middle and north ends of Bera Lake since Different contributions of FELDA project, in terms of sediment supply were recorded at different divisions of Bera Lake. Official prohibition of land development projects by 1994 and the maturing of oil palm plantations have decreased remarkably the imported terrestrial sediments at Bera Lake; however, the high biomass productiv-

10 Mohammadreza Gharibreza, John Kuna Raj, Ismail Yusoff, Zainudin Othman, Wan Zakaria Wan Muhamad Tahir, and Mohammad Aqeel Ashraf ity of oil palm plantations has significantly changed the sediment supply to organic-rich sediments. Sedimentation of organic-rich sediments (Layer 4) in all parts of Bera Lake has involved an average rate of supply of 0.2 ± 0.1 g cm 2 y 1. The organic-rich layer is playing an important role at Bera Lake in preserving 210 Pb and 137 Cs radionuclides, especially those that came from natural and anthropogenic events after ACKNOWLEDGMENTS: The authors are grateful to the Institute of Research Management and Monitoring (IPPP), University of Malaya for funding this research. We are also grateful to Dr. Zal U un Wan Mahmood for her help explaining the calculation models. The authors deeply thank the technicians of Gama-Spectrometer Lab, Mr. Yii Mee Wo, Mr. Ishak Kamarozaman, and Mr. Johari Abd Latif for their analysiss of samples for radioisotope activity. 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