A lake, as a body of water, is in continuous interaction with the rocks and soils in its drainage basin, the atmosphere, and surface and groundwaters. Human industrial and agricultural activities introduce new inputs and processes into lake systems. This volume is a selection of ten contributions dealing with diverse aspects of lake systems, including such subjects as the geological controls of lake basins and their histories, mixing and circulation patterns in lakes, gaseous exchange between the water and atmosphere, and human input to lakes through atmospheric precipitation and surficial runoff. This work was written with a dual goal in mind: to serve as a textbook and to provide professionals with in-depth expositions and discussions of the more important aspects of lake systems.

A 20-winter computerized ice concentration data base was established for the Great Lakes. This report describes the computerized data set and an ice concentration climatology developed from it. Data reduction and analysis procedures, computer file structure and record format, and availability of the data are given.