Derivation of daily phytoplankton production estimates from short-term experiments in some shallow, eutrophic Australian saline lakes

Abstract

Measurements of phytoplankton production typically involve short-term (3-6 hr) experiments; some means of conversion is then applied to the results to yield estimates of daily production. Several means of making such conversions are compared on the basis of carbon-14 experiments performed on three shallow, saline, eutrophic lakes. Day-long (12 hr) exposures tended grossly to underestimate the "true" daily production as measured by the cumulative results of consecutive short-term experiments. On the other hand, conversions based on half-day exposures and on radiation data were about equally effective, although both may involve uncertainties of at least 25 %. Conversion factors derived from short-term v. cumulative results varied seasonally and over even short periods of time, apparently in accord with variable biological and meteorological conditions. The accuracies of extrapolations based on these factors are fairly comparable, but to minimize errors short-term experiments should include the midday period when possible. An alternative would be to construct predictive models applicable to each lake as a separate entity, encompassing a wide range of conditions. For small lakes at least, general formulae and models are not likely to be effective.