SEDIMENTATION RATE AT SETIU LAGOON USING NATURAL
RADIOTRACER 210
Pb TECHNIQUE
NURLYANA BINTI OMAR
UNIVERSITI TEKNOLOGI MALAYSIA
ii
SEDIMENTATION RATE AT SETIU LAGOON USING NATURAL
RADIOTRACER 210
Pb TECHNIQUE
NURLYANA BINTI OMAR
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Master of Science (Physics)
Faculty of Science
Universiti Teknologi Malaysia
DECEMBER 2012
iv
For the nation
v
ACKNOWLEDGEMENTS
Alhamdulillah. First and foremost, I would like to express my gratitude to Prof.
Dr. Noorddin bin Ibrahim for his guidance, discussion, kind and useful advice
throughout this project.
I also would like to take this chance to express my deepest appreciation to my
parents, En. Omar Osman and Pn. Norhayati Jelani and also my siblings for their
constant believe and support to me.
Special thanks to En. Joseph from Institut Osenografi (INOS) Universiti
Malaysia Terengganu and also staff of INOS for helping me in the sampling process in
Setiu Lagoon.
I am also indebt especially to Afifah, Aezal, Nabilah Solehah, Nurul Farah Ain,
Zati Hani and to all my friend who helped me continuously along the way.
Not to forget, the staff of Perpustakaan Sultanah Zanariah (PSZ) for helping me
in locating many of journals and references that I needed in the process of completing
this project.
Lastly, to the entire individual that contributed their help, directly or indirectly in
this project, thank you for your influence and help.
vi
ABSTRACT
This study was conducted to determine the sedimentation rate of soil at Setiu
Lagoon by using natural radiotracer 210
Pb. The area covers a 10 km length lagoon
involving 5 sampling stations of approximately 2 km apart. The sediment samples were
collected using a corer box comprising of a meter long transparent PVC plastic pipe
inserted manually into the sediment bed 2 m below the water surface. The sediment core
extracted were then cut into several 5 cm interval, labeled and stored in a close beaker.
A total of 24 samples were collected from the 5 sampling stations. The measurement of
210Pb activity was made using Hyper Purity Germanium (HPGe). The total activity of
210Pb was measured from gamma ray peak of energy 46.5 keV and supported
210Pb by the
weighted average decay of 226
Ra daughters at 295, 351 and 609 keV. Unsupported 210
Pb
was calculated as the difference between the total and the supported 210
Pb activity. Two
models were used in this study to calculate the sedimentation rate; the Constant Initial
Concentration (CIC) and Advection-Diffusion Equation (ADE) model. The results show
that, there are differences in sedimentation rate values of each model for each station.
The sedimentation rates obtained using CIC model varies from 0.08 to 0.37 cm/yr
whereas ADE model varies from 0.43 to 0.93 cm/yr.
vii
ABSTRAK
Kajian ini dijalankan untuk menentukan kadar pemendapan tanah di Setiu Lagun
menggunakan radionuklid 210
Pb semulajadi. Kawasan ini meliputi 10 km panjang lagun
yang melibatkan 5 stesen persampelan yang jarak antara satu sama lain adalah
dianggarkan 2 km. Sampel sedimen telah diambil dengan menggunakan corer box yang
terdiri daripada paip PVC plastik lutsinar sepanjang satu meter yang telah yang
dimasukkan ke dalam sedimen yang jaraknya 2 m di bawah permukaan air. Teras
sedimen yang diekstrak kemudian dipotong 5 cm, dilabel dan disimpan dalam sebuah
bikar ditutp rapat. Sebanyak 24 sampel diperolehi dari 5 stesen persampelan. Ukuran
aktiviti 210
Pb telah dibuat dengan menggunakan alat pengesan Germanium Hiper Tulen
(HPGe). Jumlah keaktifan 210
Pb ditentukan dengan mengukur aras tenaga gamma 46.5
keV dan keaktifan 210
Pb lebihan yang turun dari udara boleh diukur pada aras tenaga
295, 351 dan 609 keV. Perbezaan jumlah keaktifan antara 210
Pb keseluruhan dan 210
Pb
lebihan yang turun dari udara akan memberikan nilai sebenar keaktifan 210
Pb yang
terhasil dalam tanah. Terdapat dua model yang telah digunakan dalam kajian ini, iaitu
Constant Initial Concentration (CIC), dan Advection-Diffusion Equation (ADE). Hasil
kajian menunjukkan bahawa terdapat perbezaan dalam kadar pemendapan di setiap
stesen bagi setiap jenis model. Nilai yang diperolehi bagi CIC berubah dari 0.08 ke 0.37
cm / thn dan ADE berbeza dari 0.43 kepada 0.93 cm / thn.
viii
TABLE OF CONTENTS
CHAPTER ITEMS PAGE
DECLARATION iii
DEDICATION iv
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENT viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xiv
LIST OF ABBREVATIONS xv
LIST OF APPENDIXS xvi
I INTRODUCTION
1.1 Background of Study 1
1.2 Research Problem 2
1.3 Objectives 3
1.4 Research Scope 3
1.5 Significant 3
ix
II LITERATURE REVIEW
2.1 Introduction to Sedimentation 4
2.2 Method on Sedimentation Rate Study 5
2.2.1 Artificial Horizon Marker 5
2.2.2 Natural Occurring Radiotracer 6
2.3 210
Pb Radiotracer in Sedimentation Rate Study 8
2.4 Previous Study 9
2.5 Sampling Area 12
2.6 Mathematical Models 13
2.6.1 Constant Initial Concentration (CIC) 13
2.6.2 Advection-Diffusion Equation (ADE) 15
III RESEARCH METHODOLOGY
3.1 Introduction 17
3.2 Sample Collection 17
3.3 Sample Preparation 22
3.4 Detecting System 23
3.4.1 Spectrometer Calibration 26
3.4.1.1 Detector Calibration 26
3.4.1.2 Detector Efficiency Calibration 28
3.4.1.3 Minimum Detection Limit (MDL) 28
3.5 Data Calculation 29
3.5.1 210
Pb Activity 29
IV RESULTS AND DISCUSSION
4.1 Background Radiation 30
4.2 Detector Efficiency 32
4.3 Minimum Detection Limit (MDL) 33
4.4 210
Pbex Vertical Profile 34
x
4.5 Mathematical Models 40
4.5.1 Constant Initial Concentration (CIC) 40
4.5.2 Advection-Diffusion Equation (ADE) 44
4.6 Result and Discussion 48
V CONCLUSION
5.1 Conclusion 51
5.2 Recommendations 52
REFERENCES 53
APPENDIXS 58
xi
LIST OF TABLES
NO TITLE PAGE
2.1 Uranium Decay Scheme 7
3.1 Coordinate of the Five Setiu Station 18
3.2 Energy for Each Isotope 27
4.1 Background Counts 31
4.2 Efficiency Data 32
4.3 Minimum Detection Limit 34
4.4 Activity of 210
Pb for Setiu 1 35
4.5 Activity of 210
Pb for Setiu 2 36
4.6 Activity of 210
Pb for Setiu 3 37
4.7 Activity of 210
Pb for Setiu 4 38
4.8 Activity of 210
Pb for Setiu 5 39
4.9 ln (210
Pbex) Activity for CIC Model 41
4.10 Sedimentation Rate Using CIC Model 44
4.11 Sedimentation Rate for Setiu 1 Station 45
4.12 Sedimentation Rate for Setiu 2 Station 45
4.13 Sedimentation Rate for Setiu 3 Station 46
4.14 Sedimentation Rate for Setiu 4 Station 46
4.15 Sedimentation Rate for Setiu 5 Station 47
4.16 Overall Sedimentation Rate by Using ADE Model 47
4.17 Sedimentation Rate for CIC and ADE Model 48
xii
LIST OF FIGURES
NO TITLE PAGE
2.1 210
Pb Decay Chain 8
2.2 Maps of Terengganu and Setiu 12
3.1 Map of Setiu 17
3.2 Transparent Corer Box and Cylindrical Container 19
3.3 PVC “holder” 19
3.4 Setting Up Transparent Corer Box 20
3.5 Inserting Corer Box 20
3.6 Sediment is Placed in Cylindrical Container 21
3.7 Sediment Sample 21
3.8 250 micron Sieve 22
3.9 Marinelli Beaker 23
3.10 Hyper Purity Germanium (HPGe) Detector 24
3.11 Dewar Tank 24
3.12 Generalized MCA Block Diagram 25
3.13 Sample Reference Material IAEA-314-Ra226,Th and U in
Stream
26
3.14 Energy Calibration Spectrum 27
4.1 Net Peak Area and Continuum in Gamma Spectrum 31
4.2 Efficiency Calibration Curve 33
4.3 Vertical Distribution of 210
Pbex in Setiu 1 35
4.4 Vertical Distribution of 210
Pbex in Setiu 2 36
4.5 Vertical Distribution of 210
Pbex in Setiu 3 37
xiii
NO TITTLE PAGE
4.6 Vertical Distribution of 210
Pbex in Setiu 4 38
4.7 Vertical Distribution of 210
Pbex in Setiu 5 39
4.8 ln 210
Pbex (bq/kg) versus Depth (cm) for Setiu 1 41
4.9 ln 210
Pbex (bq/kg) versus Depth (cm) for Setiu 2 42
4.10 ln 210
Pbex (bq/kg) versus Depth (cm) for Setiu 3 42
4.11 ln 210
Pbex (bq/kg) versus Depth (cm) for Setiu 4 43
4.12 ln 210
Pbex (bq/kg) versus Depth (cm) for Setiu 5 43
xiv
LIST OF SYMBOLS
SYMBOL TITLE PAGE
α Slope of the line ln Ax versus x (depth) 14
λ 210
Pb Decay Constant 15
x Depth of Sediment 14
t Time (year) 14
xv
LIST OF ABBREVATIONS
ABBREVATIONS TITLE PAGE
Pb Plumbum 1
Th Thorium 2
Be Beryllium 2
Cs Cesium 2
Si Silicon 2
Fe Iron 2
Po Polonium 2
Bi Bismuth 3
Pa Protactinium 7
U Uranium 7
Ra Radium 7
Rn Radon 7
HPGe Hyper Purity Germanium 3
keV Kiloelectron Volt 3
PVC Polyvinyl Chloride 18
MCA Multi Channel Analyzer 25
xvi
LIST OF APPENDIXS
APPENDIX TITLE PAGE
A Peak Locate Report 57
1
CHAPTER 1
INTRODUCTION
1.1 Background Study
In tracing the history of the effect of mankind on the environment, it is evident
that in many places, the period of the greatest impact has been within the last 150 years.
Lake, ocean and lagoon can provide a basis for reconstructing the many aspects of this
impact such as, for estimating rate of change, and for establishing a baseline in
environmental monitoring program (Walling and He, 1993).
The establishment of accurate chronologies of sedimentation rates based on
palynological or stratigraphy methods often provides only historical averages involving
many meters of sediment. Furthermore, such measurements not only lack the necessary
accuracy and details but may not adequately reflects the rates within the upper 20 cm or
so of the sediment where significant sediment-water exchanges are occurring at the
present time (Robbin and Edgington, 1975).
Nowadays, natural radionuclides have become powerful tracer that can provide
basic insights into a variety of marine processes, such as processes in the water column
and in biological and sedimentary system. Radioisotope 210
Pb (half-life 22.2 years) for
instance has become the important tool for determining accumulation rates in sediments
2
on about 100-year time scale. Shorter-lived natural radioisotopes such as 234
Th and 7Be
(half-life of 24 and 53 days) have proved useful in determining deposition and mixing
rates on time scales of a few month (Dibb and Rice, 1989). Similarly the basis of using
137Cs to derive chronologies for sediments during the past 30-40 years is based on the
fact that weapon released atmospheric radio-cesium is washed away by precipitation and
is rapidly and strongly bound to fine particulates of the land surface. Through run-off it
gets washed away from land surface and settles on the lake or ocean bottom.
Since then, application of radiometric methods to sedimentary geochronology
has enjoyed considerable success (Durham and Joshi, 1980). Krishnawami (1971)
evaluated the use of 210
Pb as well as three other radionuclides (32
Si, 55
Fe, 137
Cs) for
dating recent freshwater lake sediments and concluded that 210
Pb is ideal for dating lake
sediments as old as a century. Subsequently, Koide (1972) further validated the utility of
the method and determined sedimentation rates in a series of lakes. Edgington (1991)
used the anthropogenic 137
Cs and natural radionuclide 210
Pb to estimate the recent
sedimentation rates in Lake Baikal. Their results were used for the development of
mass-balance models for sediments and contaminants.
1.2 Research Problem
Most studies on sedimentation rate such as Maria (2009) used 210
Po, an alpha
emitter as proxy to 210
Pb radiotracer. This is due to the gamma decay energy that was
released by 210
Pb (46.5 keV) lies in the low energy region. With high background, the
detection of 210
Pb will be difficult. This study is to prove that 210
Pb can be use in
studying sedimentation rate process without using 210
Po as proxy.
3
1.3 Objectives
The objectives of this research are;
1.3.1 To determine the efficiency of Hyper Purity Germanium (HPGe) for low
energy gamma of less than 100 keV.
1.3.2 To determine the total activity of 210
Pb in sediment samples based on the
46.5 keV gamma energy.
1.3.3 To determine the supported 210
Pb activity based on the average of 295.2
keV (214
Pb), 351.6 keV (214
Pb) and 609.3 keV (214
Bi) gamma energies.
1.3.4 To estimate sedimentation rate at Setiu Lagoon, Terengganu by using
two different mathematical models; Constant Initial Concentration (CIC)
and Advection-Diffusion Equation (ADE) model.
1.4 Research Scope
This study will cover 22 km long of Setiu Lagoon, Terengganu (Setiu Mangroves
forest) which is located on the East Coast of Peninsular Malaysia.
This study is based on the use of natural 210
Pb radioisotope gamma ray of 46.5
keV. Two mathematical models, Constant Initial Concentration (CIC) Advection-
Diffusion Equation (ADE) will be used in this study.
1.5 Significance
This study will help in profiling the sedimentation process within the last 20
years. Apart from that, it can trace back the history of humankind. This method is more
accurate, easy and time saving.
53
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