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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