Contribution of Calcite to the Particle-Size Spectrum of Lake Michigan Seston and Its Interactions with the Plankton

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Abstract
We determined the contribution of calcite to the total particle-size spectrum of Lake Michigan seston during different seasons in 1978–83 and 1985, employing a novel Coulter counter method, to examine the intensity and ecological effects of calcite whitings that result from autogenic precipitation of calcite. The whitings were most intense during September, when 12–56% of the total particle volume was calcite. Overall, food web dynamics were more controlling of than controlled by whitings. Year-to-year variation in calcite concentration was probably caused by predation-controlled variation in primary production, which drives calcite precipitation through CO2 uptake. Feeding rate of cladocerans in Lake Michigan is slightly reduced (16%) by calcite, but that of copepods is not. Light extinction is only slightly increased. Coprecipitation and sinking of P with calcite is probably a minor factor in regulating P concentration in the epilimnion of Lake Michigan. Removal of nutrients is enhanced by increased sinking rates caused by inclusion of calcite in fecal pellets and matter. Although all of the effects of calcite on plankton dynamics appear to be subtle in Lake Michigan, large effects can be expected for lakes of greater calcium hardness and eutrophy.