This paper discusses several physical processes that are relevant to water quality and sustainable management of small and large lakes. Knowledge of water movements is important because circulation influences the distribution of dissolved substances, nutrients, microorganisms and plankton. Although there is a tremendous amount of variability in the origins of a lake (natural) and a reservoir or impoundment (artificial), they share several common physical, chemical and biological characteristics. In particular, reservoirs have controlled outflow, whereas the lakes are uncontrolled. In addition to these aspects, the physical limnology of these water bodies is governed by the shape and size of the basin. Two aspects of size that have a strong bearing on water quality are residence time and depth. Shallow lakes (<10 m) are generally well-mixed, and deeper lakes (>10 m) are often subject to thermal stratification during certain times of the year. Therefore, the water balance of a lake or reservoir   generally depends on the inflow, outflow, groundwater flow, precipitation, and evaporation over the water shed region of the lake. Discussion of large-scale water motions includes water levels, seiches, currents, waves and turbulence. Wind, solar radiation, stratification, and earth's rotation are important forces causing water movements of lakes.

National Water Research Institute, Burlington, Ontario, Canada
Email: Ram.Yerubandi@ec.gc.ca