AME 46:95-106 (2007)  -  doi:10.3354/ame046095

Planktonic primary production in estuaries: comparison of 14C, O2 and 18O methods

F. Gazeau1,2,3,6,*, J. J. Middelburg4, M. Loijens5, J.-P. Vanderborght5, M.-D. Pizay1, J.-P. Gattuso1,2

1CNRS, Laboratoire d’Océanographie de Villefranche, BP 28, 06234 Villefranche-sur-Mer Cedex, France
2Université Pierre et Marie Curie–Paris 6, Laboratoire d’Océanographie de Villefranche, 06234 Villefranche-sur-Mer Cedex, France
3Unité d’Océanographie Chimique (B5), MARE, Université de Liège, 4000 Sart Tilman, Belgium
4Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, Postbus 140, 4400 AC Yerseke, The Netherlands
5Laboratoire d’Océanographie Chimique et Géochimie des Eaux, Université Libre de Bruxelles, Campus de la Plaine, CP 208, Boulevard du Triomphe, 1050 Brussels, Belgium
6Present address: Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, Postbus 140, 4400 AC Yerseke, The Netherlands

ABSTRACT: Rates of primary production were measured in 2 estuaries (Randers Fjord, Denmark, and the Scheldt estuary, Belgium/The Netherlands) using 3 different incubation methods: (1) the oxygen light-dark method (O2-LD), (2) 14C incorporation and (3) 18O labeling. Estimates based on the 14C incorporation technique were not significantly different from those obtained using the O2-LD technique. The 18O approach provided rates significantly lower than the 2 other techniques. Ratios of O2-LD to 18O-based rates (range: 0.99 to 3.54) were often statistically significantly higher than 1 and increased with decreasing salinities and/or lower oxygen concentrations. The underestimation of gross primary production by the 18O method may be due to an intracellular recycling of labeled oxygen which increased in magnitude with decreasing external oxygen conditions. These results suggest that the 18O method must be used with extreme care in nutrient-rich, low oxygen systems.


KEY WORDS: Primary production · Phytoplankton · Estuaries · Incubation method · Oxygen · Carbon-14 · Oxygen-18


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