Effects of N: P loading ratios on phytoplankton community composition, primary production and N fixation in a eutrophic lake

Tobias Vrede, Ashley Ballantyne, Cecilia Mille-Lindblom, Grete Algesten, Cristian Gudasz, Sandra Lindahl, Anna Kristina Brunberg

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112 Scopus citations

Abstract

1. The aim of this study was to assess the effects of different nitrogen (N) to phosphorus (P) loading ratios on phytoplankton community composition and primary production in a naturally eutrophic lake. Furthermore, the sources of N fuelling primary production were estimated using 15N stable isotope tracers. 2. A mesocosm experiment was performed with the same amount of P added to all mesocosms (similar to internal loading rates) but with a range of N additions (0-86 μm N), resulting in a gradient of N : P supply ratios. 3. Low N : P supply ratios resulted in a significant shift in the phytoplankton assemblage to a community dominated by N-fixing cyanobacteria and a supply of atmospheric N2 estimated to be up to 60% of total supply. 4. The N : P loading ratio had no significant effect on primary production, total nitrogen (TN) concentration or particulate N concentration. 5. Our results imply that a reduced N : P ratio of the nutrient load does not necessarily result in a lower TN concentration and downstream N export due to compensation by N-fixing cyanobacteria.

Original languageEnglish
Pages (from-to)331-344
Number of pages14
JournalFreshwater Biology
Volume54
Issue number2
DOIs
StatePublished - Feb 2009

Keywords

  • Eutrophication
  • N stable isotopes
  • Nitrogen
  • Phosphorus
  • Stoichiometry

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