Seasonal calcite precipitation was observed and analyzed in a calcareous, ultra-oligotrophic lake, Torch Lake, Michigan (USA). A mass-balance model of the lake’s epilimnion was developed to synthesize the observations and investigate the interactions of the various processes that generate calcite, which appears to be the predominant contributor to seasonal variations in water clarity during summer stratification. This mass balance model provides a representation of calcite precipitation with particulate surface area changing over time, and demonstrates that the change in water clarity could be explained by calcite using standard optical models.

Phytoplankton growth is the most often cited driver of calcite precipitation in lakes. Given the ultra-oligotrophic conditions of Torch Lake, it was hypothesized that the seasonal temperature change of the lake water may have more of an effect on calcite precipitation than primary production.

Using the mass balance model to quantify the roles of the various chemical, biological and physical processes interacting in the lake, it was shown that the seasonal temperature change does drive calcite precipitation more than primary production in Torch Lake. In addition, the discovery was made that in Torch Lake air-water exchange of CO2 affects the calcite precipitation rate more than primary production.

Time variable mass balance models of calcite precipitation can be used both to support scientific research as well as to provide a tool to assess how management options such as load reductions or land use changes might impact future water quality and clarity.