Suspended sediment causes annual acute fish mortality in the Pilcomayo River (Bolivia)

Authors

  • L. H. Swinkels,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Nijmegen, The Netherlands
    2. Foundation ‘Los Amigos del Pilcomayo’, Villa Montes - Dep. Tarija, Bolivia
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  • M. W. P. M. Van de Ven,

    1. Foundation ‘Los Amigos del Pilcomayo’, Villa Montes - Dep. Tarija, Bolivia
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    • M.W.P.M van de Ven and M.J.M. Stassen contributed equally to this work.

  • M. J. M. Stassen,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Nijmegen, The Netherlands
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    • M.W.P.M van de Ven and M.J.M. Stassen contributed equally to this work.

  • G. Van der Velde,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Animal Ecology and Ecophysiology, Nijmegen, The Netherlands
    2. Naturalis Biodiversity Centre, Leiden, The Netherlands
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  • H. J. R. Lenders,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Nijmegen, The Netherlands
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  • A. J. P. Smolders

    Corresponding author
    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Nijmegen, The Netherlands
    2. B-WARE Research Centre, Nijmegen, the Netherlands
    • Correspondence to: A. J. P. Smolders, Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.

      E-mail: A.Smolders@science.ru.nl

      L. H. Swinkels, Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.

      E-mail: lennartswinkels@yahoo.com

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Abstract

Fish mortality in the middle reaches of the Pilcomayo River (Bolivia), locally called ‘borrachera’, can be observed almost every year at the onset of the rainy season. In order to study the potential causes of the ‘borrachera’, suspended sediment (SS) and selected water quality parameters have been monitored from mid-September until mid-December 2010. Gill samples were taken and analysed, before and during the ‘borrachera’ event on December 7th 2010. Data on river discharge were obtained from a database.

During the sampling period, the river hydrology changed dramatically. At the day of the ‘borrachera’, heavy rains in upstream reaches of the river catchment changed the river from a quiet stream into a turbulent river with extremely high concentrations of SS (> 100 g l−1). This may be caused by the inundation of the entire riverbed, which causes easily erodible material, left on the riverbanks at the end of the former rainy season, to be transported by the river during the first peak discharges.

As concentrations of heavy metals in filtered water samples did not show higher values during the ‘borrachera’, it is concluded that the ‘borrachera’ is unlikely to be caused by heavy metal toxicity. Results showed a strong association between the SS concentration and the ‘borrachera’. Gills of fish collected during the ‘borrachera’ were clogged with sediment to such an extent that oxygen uptake became virtually impossible. High SS concentrations are therefore considered to be the cause of this typical fish mortality phenomenon. Copyright © 2012 John Wiley & Sons, Ltd.

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