Epilimnetic and Metalimnetic Primary Production in an Indiana Hardwater Lake

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Abstract
Primary productivity in an Indiana lake, which contained a metalimnetic layer of cyanobacteria, was calculated for the summers of 1979–81 by using a numerical model. Production estimates of 183 and 187 g C∙m−2 were obtained for 1979 and 1980; the estimate for 1981 was 50% higher. These values were two- to four-fold higher than estimates made in 1963 and 1964. Production in the metalimnion accounted for 29, 44, and 34% of the total during the three summers. Changes in the vertical distribution of biomass in the water column appeared to have had a greater effect upon metalimnetic production than differences in water transparency or incident solar radiation. The average values measured for the latter two variables were reasonably similar during the 3 yr, whereas the depth at which the metalimnetic layer of cyanobacteria stratified decreased from 9 m in 1979 to 5 m in 1981.