Deep lakes only mix in spring and fall, and the bottom of deep lakes stays cold and dark because light cannot reach the bottom. Shallow lakes, in contrast, mix all summer because light reaches the bottom of the lake and warms the whole water column.
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During the summer the lake absorbs energy, but the land reradiates energy to the atmosphere. Therefore, air over land is warmer than that over the water. In the winter the energy absorbed by the lake water is gradually released to the atmosphere, making the air over the water warmer than that over the land.
In sharp contrast to deep lakes, shallow lakes (typically mean depths less than 8 feet) can remain well-mixed and oxygenated from surface to bottom over the summer months. Thus, the depletion of dissolved oxygen is typically not a problem in many shallow lakes.
But, in winter some lake surfaces can get very cold. When this happens, the surface water becomes more dense than the deeper water with a more constant year-round temperature (which is now warmer than the surface), and the lake turns, when the colder surface water sinks to the lake bottom.
We now have a micro (small) scale circulation — the lake breeze. This lake breeze that develops in the spring can cause a 30 degree difference in temperature over a few miles. It can oscillate back and forth, where you a warm one minute, but cold the next. We see this on a grand scale as well around the globe.
When the upper water layers warm in the summer months, they become separated from deep water by a transition zone known as a thermocline. In a thermocline, the temperature decreases rapidly with small increases in depth. This phenomenon linking temperature change with depth is called temperature stratification.
Sunlight warms the entire water column in a shallow lake, therefore the water can mix with the bottom sediments all summer long. Waves caused by wind can also turn to the bottom of shallow lakes and stir up sediments.
Lake Erie. The fourth largest out of the five Great lakes, Erie is also the shallowest and the smallest in volume. In terms of surface area, Erie takes thirteenth place in the world. Niagara River is its biggest natural outflow, providing a huge amount of hydroelectric power to both the United States and Canada.
Deep lakes only mix in spring and fall, and the bottom of deep lakes stays cold and dark because light cannot reach the bottom. Shallow lakes, in contrast, mix all summer because light reaches the bottom of the lake and warms the whole water column.
Rain may have a cooling effect on the lake surface by lowering the near-surface air temperature, by the direct rain heat flux into the lake, by mixing the lake surface layer through the flux of kinetic energy and by convective mixing of the lake surface layer.