What is it called when a warm layer of water overlies a cold layer in lakes and reservoirs?

The phenomenon where a warm layer of water overlies a cold layer in lakes and reservoirs is called stratification. This process occurs due to differences in water temperature and density. Warm water is less dense than cold water, causing it to rise to the surface while the colder, denser water remains below.

During stratification, the warmer upper layer is often referred to as the epilimnion, while the colder layer is known as the hypolimnion. This separation affects the physical and biological conditions of the water, influencing factors such as nutrient distribution and oxygen levels. Stratification can play a critical role in the ecosystem of the water body, affecting aquatic life and the overall health of the lake or reservoir.

The other options refer to different concepts. Thermal inversion typically relates to atmospheric conditions rather than aquatic environments, mixing refers to the thorough blending of water layers, and upwelling is a process where deep, nutrient-rich water rises to the surface, typically found in oceanic contexts. Understanding stratification is essential for water quality management and ecological assessments in lakes and reservoirs.