The Siak, a tropical black water river in central Sumatra on the verge of anoxia |
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Authors: | Tim Rixen Antje Baum Thomas Pohlmann Wolfgang Balzer Joko Samiaji Christine Jose |
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Institution: | 1. Zentrum für Marine Tropen?kologie, Fahrenheitstr. 6, 28359, Bremen, Germany 2. Zentrum für Meeres- und Klimaforschung, Institut für Meereskunde, Universit?t Hamburg, Bundesstr. 53, 20146, Hamburg, Germany 3. Universit?t Bremen, FB2 Meereschemie (UBMCh), Postfach 330440, 28334, Bremen, Germany 4. University of Riau, Jl. Simpang Panam Km 12.5, Pekanbaru, Riau, Indonesia
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Abstract: | The Siak is a black water river in central Sumatra, Indonesia, which owes its brown color to dissolved organic matter (DOM)
leached from surrounding, heavily disturbed peat soils. The dissolved organic carbon (DOC) concentrations measured during
five expeditions in the Siak between 2004 and 2006 are among the highest reported world wide. The DOM decomposition appeared
to be a main factor influencing the oxygen concentration in the Siak which showed values down to 12 μmol l−1. Results derived from a box-diffusion model indicated that in addition to the DOC concentration and the associated DOM decomposition
the water-depth also plays a crucial role in regulating the oxygen levels in the river because of its impact on the turbulence
in the aquatic boundary layer and the surface/volume ratio of water in the river. Model results imply furthermore that a reduced
water-depth could counteract an increased oxygen consumption caused by an enhanced DOM leaching during the transition from
dry to wet periods. This buffer mechanism seems to be close to its limits as indicated by sensitivity studies which showed
in line with measured data that an increase of the DOC concentrations by ~15% could already lead to anoxic conditions in the
Siak. This emphasizes the sensitivity of the Siak against further peat soil degradation, which is assumed to increase DOC
concentrations in the rivers. |
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Keywords: | Anoxia Black water river Peat Sumatra |
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