Sains Malaysiana 38(6)(2009): 805–812

Evolution of Groundwater Chemistry in the Shallow Aquifer of a

Small Tropical Island in Sabah, Malaysia

(Evolusi Kimia Air Bawah Tanah Akuifer Cetek Pulau Tropika Bersaiz Kecil di Sabah, Malaysia)

Ahmad Zaharin Aris*

Department of Environmental Sciences

Faculty of Environmental Studies

Universiti Putra Malaysia, Selangor, Malaysia

Mohd Harun Abdullah & Sarva Mangala Praveena

Environmental Science Programme

School of Science and Technology

Universiti Malaysia Sabah, Sabah, Malaysia

Diserahkan: 10 Disember 2008 / Diterima: 27 Mac 2009

ABSTRACT

Groundwater is the prime source of freshwater in most small islands. A detailed groundwater and seawater chemistry study was undertaken from March 2006 to January 2007 to examine the evolution of groundwater in the shallow aquifer of Manukan Island, Sabah, Malaysia. Coastal groundwater aquifers especially for small islands are often exposed to heavy pumping and consequently to risks of seawater intrusion. Major ion chemistry analysis showed that the groundwater quality of the island experienced changes attributed to seawater intrusion. The groundwater has undergone a compositional change from Ca-rich to Na-rich which can be explained mostly by simple mixing process and cation exchange process. From the PHREEQC simulation model, calcite, dolomite and aragonite solubility showed positive mean values (0.65; 1.11; 0.51, respectively) of the saturation indices (SI) indicating supersaturation which attributed from the simple mixing and eventually cation exchange process. This information is important in protecting and remediating the disturbed aquifer situation.

Keywords: Groundwater chemistry evolution; PHREEQC; small island aquifer; seawater intrusion

ABSTRAK

Air bawah tanah merupakan sumber utama air tawar di kebanyakan pulau-pulau bersaiz kecil. Kajian terperinci kimia air bawah tanah dan air laut dilakukan dari Mac 2006 hingga Januari 2007 bagi mengetahui proses evolusi air bawah tanah akuifer cetek di Pulau Manukan, Sabah, Malaysia. Akuifer air bawah tanah di kawasan pantai selalunya terdedah kepada pengepaman berlebihan dan seterusnya mengakibatkan risiko penerobosan air laut. Analisis kimia ion-ion utama menunjukkan bahawa kualiti air bawah tanah di pulau tersebut mengalami proses perubahan yang disebabkan oleh penerobosan air laut. Air bawah tanah mengalami perubahan komposisi daripada kaya-Ca kepada kaya-Na yang boleh diterangkan secara jelas oleh proses percampuran dan juga proses penukargantian kation. Daripada simulasi model PHREEQC, keterlarutan kalsit, dolomit dan aragonit menunjukkan nilai purataSI (0.65; 1.11; 0.51 masing-masing) adalah positif yang diakibatkan oleh percampuran air dan seterusnya membawa kepada proses penukargantian kation. Maklumat ini adalah berguna bagi menjaga dan memelihara akuifer yang telah terganggu.

Kata kunci: Akuifer pulau kecil; evolusi air bawah tanah; penerobosan air laut; PHREEQC

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*Pengarang untuk surat-menyurat; e-mail: zaharin@env.upm.edu.my