Aquatic Primary Productivity and the 14C-CO2 Method: A History of the Productivity Problem

Recent appraisals of the primary productivity of the biosphere have concluded that in spite of their vast area, the total annual net production of lakes and oceans is only about one half of the annual production of terrestrial ecosystems (122). The bulk of this production (75%) occurs in the open ocean at a rate of approximately 50 g C m-2 yr-1. The only standard method sufficiently sensitive to measure such low rates of carbon uptake is the radiocarbon (14C-CO2) tracer method first introduced by Steemann Nielsen in 1952. This method has proven so useful that nearly all aquatic ecology laboratories now include it among their standard techniques. However, too few of us who use the method are fully aware of either the vast literature on the 14C method or the implications of this literature for our work. Over the past decade I have used the method extensively and have compared the results with other measures of the carbon budget of natural plankton assemblages. I frequently discovered that different methods did not agree and that the literature was a source of contradiction. Schools of aquatic scientists rarely agree on the use of the method or the interpretation of the results. The frequent suggestion that a standardized procedure at least yields values for primary production valid for comparisons encounters two objections: (a) An absolute value for primary production would be preferable to a relative one, and (b) even the results from a standardized procedure are not compa-