Observation of anoxic water mass in a tropical reservoir: the Cirata Reservoir in Java,Indonesia |
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Authors: | Yuichi Hayami Koji Ohmori Kenji Yoshino Yudhi S Garno |
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Institution: | (1) Faculty of Engineering, Ehime University, Matsuyama 790-8577, Japan;(2) Center for Marine Environmental Studies, Ehime University, Matsuyama 790-8577, Japan;(3) The Environmental Technology Center, BPPT, Jakarta, Indonesia;(4) Present address: Ariake Sea Research Project, Saga University, 1 Honjo-cho, Saga 840-8502, Japan |
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Abstract: | We conducted a transect survey of water quality and bottom sediments in a large tropical reservoir, the Cirata Reservoir,
located on the Citarum River, West Java, Indonesia. In the main basin of this reservoir, the surface water contained high
concentrations of chlorophyll a, up to 48 μg l−1, and most of the water body was occupied by thick anoxic water. The thickness of the surface oxygenated water was only 5–7 m,
whereas that of the anoxic water mass was more than 70 m. The concentrations of phosphate and ammonia were quite high in the
anoxic hypolimnion. The reasons for the formation of the huge anoxic water mass include the oligomictic status of circulation,
a relatively weak mixing caused by topography, high hypolimnion temperature, and high loads of organic matter. The carbon/nitrogen
(C/N) ratios and the carbon stable isotope ratios of sediments indicated that the major source of organic carbon in the sediments
was algal production in the reservoir and fish culture activity. The mechanism of eutrophication in the reservoir is also
discussed. |
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Keywords: | Cirata Reservoir Tropical reservoir Anoxic Stable isotopes Sediment |
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