On the discrepancies between a colorimetric and isotopic method for measuring nitrate utilization in nutrient-depleted waters: implications for the design of experimental protocols in new production studies
✍ Scribed by Gerd Slawyk; Patrick Raimbault; Valérie Gentilhomme
- Publisher
- Springer
- Year
- 1990
- Tongue
- English
- Weight
- 624 KB
- Volume
- 207
- Category
- Article
- ISSN
- 1573-5141
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✦ Synopsis
Calorimetric analyses of nitrate disappearance from seawater have been compared with isotopic analyses of "N-1abelled nitrate incorporation into particulate matter. The slope (1.41) of a regression line calculated from 19 sample pairs gathered during 6 time-series experiments and 2 single end-point incubations showed that nitrate incorporation is positively related to changes in nitrate concentration but that it accounts only for 71% of nitrate disappearance.
"N-isotope dilution as a consequence of nitrilication, if any, would not fully explain discrepancies between the two analytical procedures. A further possible mechanism responsible for the imbalance between nitrate-incorporation and -disappearance rates suggests losses of "N label from plankton biomass to an unanalyzed pool (dissolved organic nitrogen?) which increase (up to 65 %) with incubation time. The lack of "N-mass balance calls for the need to consider additional nitrogen pools in "N budgets of isotope experiments and not only substrate and biomass pools as has been done so far.