, Volume 90, Issue 2, pp 129–140 | Cite as

The Siak, a tropical black water river in central Sumatra on the verge of anoxia

  • Tim Rixen
  • Antje Baum
  • Thomas Pohlmann
  • Wolfgang Balzer
  • Joko Samiaji
  • Christine Jose


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.


Anoxia Black water river Peat Sumatra 



Diffusion coefficient




Oxygen consumption rate

C/O ratio

Ratio between organic carbon and oxygen


Dissolved organic carbon


Dissolved organic matter


El Niño Southern Oscillation


Oxygen flux rate across the air–water interface


Piston velocity


Oxygen concentration


Oxygen saturation concentration


Oxygen concentration in the river water


Oxygen partial pressure


Partial pressure of oxygen in the atmosphere


Partial pressure of oxygen in the river water


Terra gram


Oxygen flux through the sea surface into the surface layer


Southern Oscillation Index


Sungai (river)


Diffusion velocity


Ultra violet


Solubility coefficient of oxygen


Thickness of the layers in the model



We would like to thank all scientists and students from the University of Pekanbaru who helped us during our field work, the rector of the University of Riau, the captain of the research vessel R/V Senangin and his crew for their support. For helpful discussion we would like to thank the anonymous reviewer, V. Ittekkot, P. Damm our colleagues from the ZMT and Rena Kerr. We are also grateful to the Federal German Ministry for Education, Science, Research and Technology (BMBF, Bonn grant number 03F0392C-ZMT) for financial support and to R. Schlitzer as well as to P. Wessels and W.·H. F. Smith for providing Ocean Data View (ODV) and the generic mapping tools (GMT).


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Tim Rixen
    • 1
  • Antje Baum
    • 1
  • Thomas Pohlmann
    • 2
  • Wolfgang Balzer
    • 3
  • Joko Samiaji
    • 4
  • Christine Jose
    • 4
  1. 1.Zentrum für Marine TropenökologieBremenGermany
  2. 2.Zentrum für Meeres- und Klimaforschung, Institut für MeereskundeUniversität HamburgHamburgGermany
  3. 3.Universität Bremen, FB2 Meereschemie (UBMCh)BremenGermany
  4. 4.University of RiauPekanbaru, RiauIndonesia

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