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Response of coastal phytoplankton to ammonium and nitrate pulses: seasonal variations of nitrogen uptake and regeneration
Collos, Y.; Vaquer, A.; Bibent, B.; Souchu, P.; Slawyk, G.; Garcia, N. (2003). Response of coastal phytoplankton to ammonium and nitrate pulses: seasonal variations of nitrogen uptake and regeneration. Aquat. Ecol. 37(3): 227-236. dx.doi.org/10.1023/a:1025881323812
In: Aquatic Ecology. Springer: Dordrecht; London; Boston. ISSN 1386-2588, more
Peer reviewed article  

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Keywords
    Ammonium compounds; Coastal lagoons; Nitrates; Nitrification; Particulate organic matter; Particulate organic nitrogen; Phytoplankton; Regeneration; Seasonal variations; Uptake; MED, France, Languedoc-Roussillon, Thau Lagoon [Marine Regions]; Marine

Authors  Top 
  • Collos, Y.
  • Vaquer, A.
  • Bibent, B.
  • Souchu, P.
  • Slawyk, G.
  • Garcia, N.

Abstract
    Seasonal variation in uptake and regeneration of ammonium and nitrate in a coastal lagoon was studied using 15N incorporation in particulate matter and by measuring changes in particulate nitrogen. Uptake and regeneration rates were two orders of magnitude lower in winter than in summer. Summer uptake values were 2.8 and 2.2 μmol N.l-1.d-1 for ammonium and nitrate, respectively. Regeneration rates were 2.9 and 2.1 μmol N.lsup>-1.d-1 for ammonium and nitrate respectively. Regeneration/uptake ratios were often below one, indicating that water column processes were not sufficient to satisfy the phytoplankton nitrogen demand. This implies a role of other sources of nitrogen, such as macrofauna (oysters and epibionts) and sediment. Phytoplankton was well adapted to the seasonal variations in resources, with mixotrophic dinoflagellates dominant in winter, and fast growing diatoms in summer. In winter and spring, ammonium was clearly preferred to nitrate as a nitrogen source, but nitrate was an important nitrogen source in summer because of high nitrification rates. Despite low nutrient levels, the high rates of nitrogen regeneration in summer as well as the simultaneous uptake of nitrate and ammonium allow high phytoplankton growth rates which in turn enable high oyster production.

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