Important Factors for Estimating Annual Phytoplankton Production in the Experimental Lakes Area

Abstract

Annual phytoplankton growth rates from 21 lakes in the Experimental Lakes Area (ELA) for the 4-yr period 1973–76 are reported. The coefficient of variation of production in most lakes over this period was about 20%. This variability was the same for both control and experimental lakes. Subthermocline populations were quantitatively unimportant in eutrophied basins but up to 50% of annual production occurred in hypolimnion chlorophyll peaks in some transparent control lakes. The exact details of chlorophyll distribution as monitored with an in vivo fluorometer are unnecessary for accurate measurements of production, even in lakes having hypolimnion chlorophyll peaks. Annual production rates were about 80% of the rates predicted with simulated cloudless weather. The common practice of not correcting production estimates for basin morphometry when reporting areal production rates resulted in overestimation of productivity by roughly 20%. The results indicate several ways for simplifying the numerical primary production model.Key words: production, morphometry, models, limnology, Experimental Lakes Area, incubator