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Phytoplankton functional groups for ecological assessment in young sub-tropical reservoirs: case study of the Nam-Theun 2 Reservoir, Laos, South-East Asia

Joanna Martinet, Stéphane Descloux, Pierre Guédant, Frederic Rimet
  • Joanna Martinet
    Nam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality and Biodiversity Dept.– Aquatic Environment Lab, Lao People's Democratic Republic
  • Stéphane Descloux
    EDF, Hydro Engineering Centre – Savoie Technolac, France
  • Pierre Guédant
    Nam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality and Biodiversity Dept.– AE Lab, Lao People's Democratic Republic


The early stages following the creation of reservoirs are typically physical and biological unstable periods due to the conversion from a lotic to a lentic ecosystem. The sub-tropical Nam Theun 2 Reservoir (Laos) was impounded in 2008. Several limnological parameters were monitored from March 2009 to December 2011 in order to understand the evolution of the phytoplankton community. A strong inter annual variability of hydrodynamic pattern was observed. Rainfall and hydraulic balance were the main physical factors driving the community structure. Periods of highest hydraulic stability led to a phytoplankton biomasses increase. The first assemblages were dominated by the S-C-strategists reaching high biomasses but low diversity. Over the three years, phytoplankton became more diverse due to a diversification of ecological niches, mostly explained by a greater water transparency and a more stable thermal stratification. The applicability of functional groups for biomonitoring in this young sub-tropical reservoir was investigated and compared to a classical taxonomical approach. The dominant functional groups (Lo, A, E, F, N and P) characterized the NT2 Reservoir as meso-oligotrophic with a tolerance to low nutrients supply. Our results support the hypothesis that a functional group approach is more informative than a species-based approach to assess trophic level and dissolved organic carbon concentrations in such reservoirs.


phytoplankton biomass, functional groups succession, young sub-tropical reservoir, trophic level.

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Submitted: 2014-01-24 14:23:41
Published: 2014-05-15 09:22:27
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Copyright (c) 2014 Joanna Martinet, Stéphane Descloux, Pierre Guédant, Frederic Rimet

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