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Ambiguous climate impacts on competition between submerged macrophytes and phytoplankton in shallow lakes

Authors

  • SARIAN KOSTEN,

    1. Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands
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  • ERIK JEPPESEN,

    1. Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark
    2. Greenland Climate Research Centre (GCRC), Greenland Institute of Natural Resources, Nuuk, Greenland
    3. Sino-Danish Centre for Education and Research (SDC), Beijing, China
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  • VERA L.M. HUSZAR,

    1. Departamento de Botânica, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil
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  • NÉSTOR MAZZEO,

    1. Departamento de Ecología y Evolución, CURE-Facultad de Ciencias, UdelaR. Maldonado, Uruguay
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  • EGBERT H. Van NES,

    1. Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands
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  • EDWIN T.H.M. PEETERS,

    1. Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands
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  • MARTEN SCHEFFER

    1. Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands
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Sarian Kosten, Department of Aquatic Ecology and Water Quality Management, Wageningen University, 6700 DD Wageningen, The Netherlands. E-mail: sarian.kosten@wur.nl

Summary

1. Shallow lakes may switch from a state dominated by submerged macrophytes to a phytoplankton-dominated state when a critical nutrient concentration is exceeded. We explore how climate change may affect this critical nutrient concentration by linking a graphical model to data from 83 lakes along a large climate gradient in South America.

2. The data indicate that in warmer climates, submerged macrophytes may tolerate more underwater shade than in cooler lakes. By contrast, the relationship between phytoplankton biomass [approximated by chlorophyll-a (chl-a) or biovolume] and nutrient concentrations did not change consistently along the climate gradient. In warmer climates, the correlation between phytoplankton biomass and nutrient concentrations was overall weak, especially at low total phosphorus (TP) concentrations where the chl-a/ TP ratio could be either low or high.

3. Although the enhanced shade tolerance of submerged plants in warmer lakes might promote the stability of their dominance, the potentially high phytoplankton biomass at low nutrient concentrations suggests an overall low predictability of climate effects.

4. We found that near-bottom oxygen concentrations are lower in warm lakes than in cooler lakes, implying that anoxic P release from eutrophic sediment in warm lakes likely causes higher TP concentrations in the water column. Subsequently, this may lead to a higher phytoplankton biomass in warmer lakes than in cooler lakes with similar external nutrient loadings.

5. Our results indicate that climate effects on the competitive balance between submerged macrophytes and phytoplankton are not straightforward.

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