A thermocline is a distinct layer in a body of water, typically a lake or reservoir, where the temperature changes rapidly with depth. This transition layer is characterized by a steep temperature gradient, and separates the warmer upper layer from the colder deeper layer. In this essay, we will explore the factors that contribute to the development of a thermocline in a reservoir.

Reservoirs are man-made bodies of water created by impounding a river or stream. They serve many purposes, such as providing a source of drinking water, generating hydroelectric power, and regulating the flow of rivers. The creation of a reservoir alters the natural water cycle and can have significant impacts on the local ecosystem. The formation of a thermocline is one of these impacts and can have both positive and negative effects on the reservoir and the surrounding environment.

The development of a thermocline is a complex process influenced by a variety of factors, including solar radiation, wind, water depth, and the surrounding topography. The primary driver of thermocline formation is solar radiation, which heats the surface layer of the water and creates a temperature gradient with depth. As the sun heats the surface layer, the warmer water becomes less dense and rises, while the cooler water sinks, creating a circulation pattern known as convection. This circulation pattern helps to mix the water column and distribute heat throughout the reservoir.

As the summer months progress and solar radiation becomes more intense, the surface layer of the reservoir continues to warm, while the deeper layers remain relatively cool. The warmer surface layer acts as an insulating barrier, preventing heat from penetrating deeper into the water column. This creates a stable temperature gradient, with the warm surface layer gradually transitioning to the colder deeper layer. This transition layer is the thermocline and is typically located between 20- 40 feet deep, depending on the size and shape of the reservoir.

The depth of the thermocline is influenced by several factors, including the size and shape of the reservoir, the depth of the water, and the intensity of solar radiation. In smaller reservoirs, the thermocline may be located closer to the surface, while in larger reservoirs, it may be deeper. Similarly, deeper bodies of water tend to have deeper thermoclines, while shallow bodies of water have shallower thermoclines. The intensity of solar radiation also plays a role, with more intense radiation leading to a deeper thermocline.

Wind also plays a role in thermocline formation, particularly in larger reservoirs. As wind blows across the surface of the water, it creates turbulence that can help to mix the water column and disrupt the stable temperature gradient. This can lead to the formation of a shallow thermocline or prevent the formation of a thermocline altogether. However, if the wind is strong enough, it can create a deeper thermocline by increasing the rate of mixing and distributing heat throughout the water column.

The surrounding topography also influences the formation of a thermocline, particularly in reservoirs that are located in hilly or mountainous regions such as Bull Shoals Lake. As water flows into the reservoir from the surrounding hills and tributary creeks, it can bring cooler water with it, which can deepen the thermocline. Additionally, the shape of the reservoir can affect the intensity and direction of solar radiation, which can also influence the depth and location of the thermocline.

The formation of a thermocline has significant implications for the ecology of a reservoir. The thermocline acts as a physical barrier, preventing the mixing of water between the warmer upper layer and the colder deeper layer. This can lead to the stratification of nutrients, with the majority of nutrients being located in the deeper layer where they are inaccessible to surface-dwelling organisms.