A Numerical Model for Determining Integral Primary Production and its Application to Lake Michigan

Abstract

A computer-based model for determining production by phytoplankton, integrated over depth and over an arbitrary time interval, is described. The solution incorporates light inhibition and uses the actual distribution of surface irradiance for the time interval of interest, since it is not possible to predict the detailed nature of cloudiness. Statistical procedures for estimating the model parameters from experimental data relating the rate of carbon uptake to irradiance are described. The model is applied to data collected from May 27, 1970 through February 3, 1971 from Lake Michigan.Integral primary production was bimodal at inshore and offshore stations with minimum production in midsummer and winter. There was great daily variability of integral production, due solely to variation of light. From this it is inferred that occasional in situ measurements would give a very poor knowledge of true seasonal trends.The model output was verified by performing two in situ experiments. The agreement was better than 95% on both dates. The model makes it possible to estimate integral primary production on a routine basis in large water bodies with well-mixed photic zones.