JOURNAL OF PLANKTON RESEARCH | VOLUME 9 | NUMBER 2 | PAGES 317-325 | 1987
© Oxford University Press
research-article |
Inter-comparison of 14C-labelled bicarbonate solutions prepared by different institutes for measurement of primary productivity in natural waters and monoalgal cultures
Carbon 14 Centralen (C14C), The International Agency for 14C Determination 15, Agent Allé, DK-2970 Hørsholm 1The Danish Isotope Centre 2, Skelbaekgade, DK-1717 Copenhagen V, Denmark
Received on January 1, 1986; accepted on December 1, 1986
An intercomparative study was carried out to investigate possible effects on primary productivity measurements when using NaH14C03 solutions prepared by different methods. Five different ampoule batches coded A, B, C, D and E were tested. Three of the batches (A, B and D) had been produced by direct dilution of industrially produced NaH14CO3, of high specific activity. A and D were diluted with distilled water added carrier, whereas no information on how batch B was diluted could be obtained. Batch E was prepared by trapping 14CO2, gas — released by strong HCl from Ba14CO3 — in sodium hydroxide. In the case of batch C, the process of manufacture was not known. The tests were carried out on different phytoplankton material with low algal density. Two batches (B and C) showed significant inhibitory effects on Pcalc (–5–44%), on the slope of the ascending part of the light adaptation curve (
), and on Pmax. Batch A showed minor, but still significant effects. The four batches A, B, C and D carried rather high amounts of non-volatile rest activity (between 13 and 194 d.p.m./µCi), which made measurements of the release of extracellular dissolved organic carbon (EOC) almost impossible. This phenomenon,per se, would if uncor-rected produce considerably higher per cent EOC release in low-productive waters, as has been reported by many authors. As to the standardization of the working solutions, two batches (C and D) showed a poor accuracy (16 and 18% deviation, respectively) when tested at the C14C, and two batches (A and B) showed unacceptably high variability between ampoules of the same batch. The study indicates that it is not recom-mendable to use working solutions prepared by direct dilution of industrially produced NaH14CO3 of high specific activity without prior testing of possible effects on algal photosynthesis. It is recommended that the specific activity of the working solution be measured if it is not exactly specified by the manufacturer by a ‘Certificate of Quality’.