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Nutrient_Cycles - Nutrient Cycles The elements required for...

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Nutrient Cycles The elements required for living systems are mostly stable. Radioisotopes play a minor role, and even the half-value period of 5770 years of 14 C is much higher than the life of the average organism. As a consequence, all elements of a biosphere are preserved. All that changes is their distribution within the biosphere, some are taken to new places, others are chemically integrated into different molecular components. All changes can be described by cycles. Cycles can be drawn up for any element, but in biology, that of oxygen , carbon , nitrogen , phosphor, sulphur , as well as water are of interest. Water is no element, but a largely stable molecule that is essential for all processes of life. Cycles can be described as systems just like the generalized ecosystem that we just got to know. Often, large pools of elements like the earth's crust, the ocean or the atmosphere are the system elements. Only a minute part of the material mills around and even less participates in the development of living systems. The Water Cycle The water cycle is the first to be introduced as the water supply of the earth's surface is besides the sun and the amount of energy provided by it the most important precondition of vegetation and thus also of the colonization of the earth. This known fact becomes especially impressive through satellite takings made of partially irrigated dry areas . Water can exist in three different states: solid (ice), fluid, and gaseous (vapor). It is in its fluid state at temperatures that are optimal for physiological processes. Water has a high heat storage capacity. It is moreover an ideal solvent for numerous ions. The pH-value of underground water fluctuates between pH 3 and pH 10. It is high in the coastal areas of the oceans and still higher in the open ocean. The high alkalinity is one of the main courses of the water's high capacity for carbon dioxide that becomes carbonate/bicarbonate in the water. Only a fraction of the existing water is altered chemically. The photolysis taking part during photosynthesis makes up the main part of this fraction. The earth surface is 510 million square kilometers, 362 million of it are covered by water and 325 million square kilometers of it are open oceans. The total amount of water is 1.5 billion square kilometers. 97 percent of it is ocean water. Only three percent is freshwater, and three quarters of it is immobile ice that makes up polar icecaps and glaciers. Its atmospheric part is lower than 0.001 percent. The amount that is available for plants has roughly the same magnitude.
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Atmospheric water has a fluctuating geographic distribution. It occurs mainly in the equator region. Water remains an average 9-10 days in the atmosphere, though it can return to earth after a few hours or after weeks. The atmospheric differences in temperature and pressure are the main cause of air circulation.
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