GEOLOGY

Detailed explanation-1: -lakes occur, lakes exhibit a dimictic thermal pattern (two periods of mixing-in spring and autumn-per year) caused by seasonal differences in temperature and the mixing effects of wind (Figure 2).

Detailed explanation-2: -Dimictic lakes turn over twice a year, during the spring and the fall. This remixes dissolved oxygen and nutrients, needed by plants and animals in the lake. In the fall, the surface water becomes cooler and denser than the bottom waters. This cooler water sinks to the bottom, mixing the lake water.

Detailed explanation-3: -The most important actions causing lake mixing are wind, inflowing water, and outflowing water. While wind influences the surface waters of all lakes, its ability to mix the entire water volume in summer-stratified lakes is greatly reduced.

Detailed explanation-4: -Lakes are called dimictic if they circulate freely twice a year in the spring and fall and are directly stratified in summer and inversely stratified under ice cover in winter. Dimictic lakes represent the most common type of thermal stratification observed in most lakes of the cool temperate regions of the world.

Detailed explanation-5: -This destratification process often is called fall overturn. Fall overturn in lakes occurs when the summer-warmed surface layer cools to the same temperature as the hypolimnetic (lower) waters, allowing the lake water to mix from top to bottom.