Sains Malaysiana 31: 49-56 (2002)                                                                                                                Sains bumi /

Earth Science

The Determination of ²³⁰Th in the Sediments: Sediment Accretion

in the Mangrove Forests of Tanjung Piai, Johore, Malaysia

Kamaruzzaman B. Y., Leong H. F., Moho Lokman H.,

Sulong I. & Chong K. Y.

Mangrove Research Unit (MARU)

Institute of Oceanography (INOS)

Kolej Universiti Sains & Teknologi Malaysia

21030 Kuala Terengganu, Malaysia

ABSTRACT

Accumulation of element Th with depth was determined in a 150 em core sediment obtained from the mangrove forest of Tanjung Piai, Johore, Malay­sia. In this study, a ²³⁰Th_excess method was used where the element relies on a constant production rate of ²³⁰Th from the radioactive decay of dissolved ²³⁴U in the water column. Applying the ²³⁰Th_excess and ²³⁰Th_excess/²³²Th method, average sedimentation rates of 0.84 cmyr^-1 and 0.88 cmyr^l were obtained, respectively. If this sedimentation rate is applicable to the core, the mangrove forest in the study sites was probably in immature stage with an estimated age of about 120 years. This finding suggests that the mangrove forests are not just passive colonizers of mud banks, but actively capture mud to create their own environments. Mangroves are thus an important sink for the fine sediment from rivers and coastal waters.

ABSTRAK

Akumulasi elemen Th terhadap kedalaman telah ditentukan ke atas 150 cm teras sedimen yang diperolehi di hutan bakau Tanjung Piai, Johor, Malaysia. Dalam kajian ini, kaedah ²³⁰Th _excess digunakan di mana elemen ini banyak bergantung kepada kadar penghasilan malar ²³⁰Th daripada pereputan bahan radioaktif ²³⁴U terlarut di dalam air laut. Dengan menggunakan kaedah ²³⁰Th_excess and ²³⁰Th_excess/²³²Th, purata sedimentasi masing-masing diperolehi sebanyak 0.84 cmyr^-1 and 0.88 cmyr^-l. Sekiranya kadar sedimentasi melalui sampel teras diambil kira, hutan paya bakau di Tanjung Piai, Johor berkemungkinan berada dalam peringkat tidak matang dengan anggaran usia lebih kurang 120 tahun. Penemuan ini mensyorkan bahawa persekitaran hutan bakau bukan sahaja dilihat sebagai penghuni pasif dataran lumpur, tetapi bertindak sebagai perangkap sedimen yang aktif. Oleh itu hutan bakau adalah penting dan berperanan bagi memerangkap sedimen halus daripada air sungai dan laut.

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