JOURNAL OF PLANKTON RESEARCH | VOLUME 6 | NUMBER 3 | PAGES 457-474 | 1984
© Oxford University Press
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Verification of 14C and O2 derived primary organic production measurements using an enclosed ecosystem
1DAFS Marine Laboratory Victoria Road, Aberdeen 2Department of Oceanography, University of Southampton Southampton, UK
Received on May 1, 1983; accepted on November 1, 1983
The stimulus for these experiments came from a recent series of papers which have suggested that the 14C technique may underestimate primary production by as much as 10-fold. We evolved the following strategy to attempt to verify the 14C technique in nearshore waters: (i) to examine the validity of in vitro (i.e., bottle incubation) measurements by comparing observed in situ oxygen changes in a large enclosed natural ecosystem against those determined in vitro and if no evidence of containment effects were indicated, (ii) compare 14C and oxygen measurements in simultaneous in vitro incubations. The first step essentially tests the containment problem, the second the physiological and calibration problems of the 14C technique. The first experiment was run with nitrate as the main source of inorganic nitrogen, the second with ammonia. PQs for converting the 14C measurements to oxygen values were calculated from the equation PQ = PQc + 2/(C/NO3) where PQc is the ‘carbon PQ’ (taken as 1.25) and (C/NO3) is the molar carbon to nitrate assimilation ratio. Although there appear to be some minor residual problems in the interpretation of the data when nitrate was the dominant nitrogen source, the overriding conclusions were: first, that the close agreement between the changes in in situ and in vitro dissolved oxygen concentration during the photoperiod gave no evidence for any notable containment effect upon photosynthesis. Secondly, the in vitro rates of 14CO2-determined photosynthetic production and gross photosynthetic oxygen production agreed, within the precision of the two techniques. The experiment further demonstrated the need to determine soluble as well as particulate organic production and to pay attention to the potential effect of the nitrogen nutrient upon the PQ. Thus it was concluded that our data give no evidence for marked errors in the 14C-technique of measuring primary organic production for coastal waters.
Present address: Department of Marine Microbiology, Institute of Botany, University of Gothenburg, Carl Skottsbergs Gata 22, S-413 19 Gothenburg, Sweden.
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