Demonstrating the Stratification of Dimictic and Meromictic Lakes in a Fish Tank

Abstract

The demonstration described in this paper attempts to illustrate the main controls on the vertical circulation of lake water. This phenomenon integrates the effects of annual air temperature cycles, fetch, and possible groundwater sources to a lake. Because the nature of a lake's circulation pattern has an effect on the “quality” of the sediment record preserved, it is among the most important limnological processes for students to understand.This demonstration involves a fish tank, colored water, salty water, and artificial sun and wind. The water in the tank “evolves” through the seasons of a typical meromictic lake, beginning with Spring turnover and ending with Fall turnover. The demonstration requires several hours to complete, and students measure water temperature and conductivity through the model year. I have found this demonstration to be a helpful illustration of dimictic and meromictic lakes; it is especially helpful to illustrate the seasonal evolution of lake water, which is not apparent during winter field studies of local northeastern US lakes.