- The constant movement of water between the atmosphere, the land surface and the subsurface is called the hydrologic or water cycle.
- The main force that moves water between the surface and the atmosphere is energy from the sun.
- Water at the surface is converted by this energy from liquid to gas (evaporation), and returns to the atmosphere in the form of water vapor.
- Some of the water returns to the atmosphere through transpiration, a process by which water is taken up by trees and plants through their roots, and is released back into the air through their leaves.
- The vapor then condenses into clouds and eventually returns to the surface as rain, snow or hail.
- Water that doesn’t evaporate and isn’t used by plants may run off the land into surface waters such as lakes and streams.
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- Some of the precipitation and melt water soaks into the land surface by the process of infiltration and moves downward to the water table to become groundwater. This process is referred to as recharge.
- Groundwater can also be recharged under special circumstances, by leakage from surface water bodies such as streams and lakes.
- Eventually, groundwater returns to the surface as it flows into a surface water body at a point of discharge (wetland, stream, lake or ocean).
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