Sains Malaysiana 45(2)(2016): 157–166

Physicochemical Parameters of Bakun Reservoir in Belaga, Sarawak, Malaysia,

13 Months after Reaching Full Supply Level

(Parameter Fizikokimia Takungan Bakun di Belaga, Sarawak, Malaysia,

13 Bulan selepas Mencapai Tahap Bekalan Penuh)

Teck-Yee Ling*¹, Lee Nyanti², Theresa Muan², Jongkar Grinang³, Siong-Fong Sim¹ & Aazani Mujahid²

¹Department of Chemistry, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak Bumi Kenyalang, Malaysia

²Department of Aquatic Science, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak Bumi Kenyalang, Malaysia

³Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak Bumi Kenyalang, Malaysia

Received: 18 March 2015/Accepted: 5 July 2015

ABSTRACT

Determining the water quality of Bakun Reservoir 13 months after it operates at full supply level is crucial for better understanding of changes in the physicochemical parameters, which may enable the prediction of its effects on the survival of aquatic life in the reservoir. This study determined 13 physicochemical parameters at six stations within the reservoir at fixed depths. The results showed that the minimum 5 mg/L of dissolved oxygen (DO) required for sensitive aquatic organisms was recorded at 6 m depth. However, DO was not detectable at depths exceeding 7 m. The water was acidic at depths of more than 10 m. Turbidity and total suspended solids increased corresponding with depth. Inorganic nitrogen were predominantly in the form of ammonia-nitrogen, creating an unhealthy environment for aquatic life. Concentration of Chl-a was significantly higher at the subsurface water than 30 m depth in four out of six stations. The present study shows changes in water quality as compared to the pre-impounded period and 15 months after the filling phase, in particular, stratification of dissolved oxygen, thermocline conditions and alkalinity. The changes varied according to the distance from the dam and may have been influenced by existing land developments within the area such as the construction of the Murum Hydroelectric Dam, oil palm plantations and timber concessionares. Though the water quality might have deteriorated, further study is needed to determine if this condition will prolong.

Keywords: Impoundment; Murum; new reservoir; stratification; tropical reservoir

ABSTRAK

Menentukan kualiti air Empangan Bakun 13 bulan selepas ia beroperasi pada tahap bekalan penuh adalah penting untuk lebih memahami perubahan dalam parameter fizikokimia, yang membolehkan ramalan tentang kesannya terhadap kewujudan hidupan akuatik dalam takungan. Kajian ini menentukan 13 parameter fizikokimia di enam stesen dalam takungan pada kedalaman yang tetap. Keputusan menunjukkan bahawa minimum 5 mg/L bagi oksigen terlarut (DO) diperlukan oleh organisme akuatik sensitif dicatatkan pada kedalaman 6 m. Walau bagaimanapun, DO ini tidak dikesan pada kedalaman melebihi 7 m. Air adalah berasid pada kedalaman lebih daripada 10 m. Kekeruhan dan jumlah pepejal terampai meningkat sejajar dengan kedalaman. Nitrogen bukan organik yang kebanyakannya dalam bentuk ammonia-nitrogen, mewujudkan persekitaran yang tidak sihat untuk hidupan akuatik. Kepekatan Chl-a adalah lebih tinggi pada air subpermukaan daripada kedalaman 30 m di empat daripada enam stesen. Kajian ini menunjukkan perubahan dalam kualiti air berbanding dengan tempoh prapembendungan dan 15 bulan selepas fasa mengisi, khususnya, penstratuman oksigen terampai, keadaan termoklin dan alkalin. Perubahan ini berbeza mengikut jarak dari empangan dan mungkin dipengaruhi oleh pembangunan tanah sedia ada dalam kawasan seperti pembinaan Empangan Hidroelektrik Murum, ladang kelapa sawit dan konsesi perkayuan. Walaupun kualiti air mungkin semakin merosot, kajian tambahan diperlukan untuk menentukan jika keadaan ini akan berpanjangan.

Kata kunci: Murum; pembendungan; stratifikasi; takungan baru; takungan tropika

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*Corresponding author; email: tyling@frst.unimas.my