The Water Cycle

Nutrients are elements essential for life on Earth. The most important of these nutrients are water, carbon (and oxygen), nitrogen, and phosphorous. These nutrients are recycled throughout the ecosystems to provide for the living organisms. Water takes up more than two-thirds of the Earths surface and makes up almost 70 percent of living matter. Such abundance of water on Earth makes it also the most valuable among the nutrients.

Water cycle recycles water with the use of processes such as evaporation, condensation and precipitation. Evaporation occurs when liquid water is transformed to water vapor with the use of atmospheric temperature. Water vapor then rises up into the atmosphere. Evaporation occurs not only on surface waters, but also on animals and plants body surfaces. 

Transpiration is evaporation that occurs in plants. Plants absorb water through their roots, leaves and branches and release water through specialized openings that regulate water in the plant body. The combination of evaporation and transpiration is called evapotranspiration.

Condensation is the opposite of evaporation. The water vapor in the atmosphere is turned into liquid water droplets. This process is also affected by low atmospheric temperature. With very low atmospheric temperature, water vapor condenses to form ice crystals. Accumulation of condensed water vapor forms clouds. Clouds that are heavy enough release these water droplets in the process of precipitation in the form of rain. Ice crystals that fall from the atmosphere are called snow or hail.

Water reservoirs are where water is stored after they fall from the atmosphere. Such reservoirs are the bodies of water, biosphere and groundwater. Groundwater moves into soil and rock in the process of infiltration. Such movement is affected by gravity because of the downward movement of groundwater. The water that did not become groundwater is called runoff. Large amounts of runoff can form large bodies of water. Runoff and groundwater also provide water into oceans and lakes to replace evaporated water. 

The water cycle works as a closed cycle on the Earth. Water molecules from land and plants form into water vapor in the process of evaporation and transpiration, respectively. Together, the process is called evapotranspiration. Water vapor ascends into the atmosphere and forms clouds. Condensation then occurs when water vapor is transformed into water droplets. Clouds full of condensed water vapor then releases water droplets in the process of precipitation in the form of rain, snow or hail. The processes of evapotranspiration and condensation are largely affected by temperature. Water reservoirs provide storage of rain water. Water moves into the soil through infiltration and is stored as groundwater. Excess water not used as groundwater is called runoff. Runoff is then added to oceans and lakes. Plants absorb water through the roots and then released through transpiration. Water reservoirs also start to evaporate water into the atmosphere thus completing the cycle. Water cycle is an important process that largely affects life on Earth, whether it may be living or non-living. 


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