In the preceding posts important principles and some orders of magnitude regarding energy flow within ecosystems were discussed. As already emphasized, the movement of materials in the ecosystem is an equally important consideration. The more or less circular paths of the chemical elements passing back and forth between organisms and environment are known as biogeochemical energy cycles. ‘’bio’’ refers to living organisms and ‘’geo’’ to the rocks, soil, air, and water of the earth. Geochemistry is an important physical science, concerned with the chemical composition of the earth and the exchange of elements between different parts of the earth’s crust energy and its oceans rivers, and so on. Biogeochemistry energy is thus the study of the exchange (that is, back and forth movement) of chemical materials between living and nonliving components of the biosphere.  plified  energy – flow diagdram to show the interrelation of the two basic processes, and to reemphasize the point already made, namely that energy is required to drive the cycling of materials. Vital elements in nature are never, or almost never, homogeneously distributed or present in the same chemical form throughout an ecosystem. Rather, materials exist in compartments or pools, with varying rates of exchange between them. From the ecological standpoint it is advantageous to distinguish between a large, slow – moving nonbiological pool and a smaller but more active pool that is exchanging rapidly with organisms. In figure 4 -1 the large reservoir is the box labeled ‘’pool’’; and the rapidly cycling material is represented by the stippled circle going from autotrophs to heterotrophs and back again. Sometimes the reservoir portion is called the unavailable pool and the cycling portion the available pool; such a designation is permissible provided it is clearly understood that the terms are relative. An atom in the reservoir pool is not necessarily permanently unavailable to organisms but only relatively so; in comparison, an atom in the cycling pool is instantly available. Almost always there is a slow movement of atoms between the unavailable and the available pools.
biogeochemical   Decomposition

       Decomposition not only releases nutrients energy but the organic energy by products may also increase the availability of minerals energy for uptake by autotrophs. On way this occurs is by a process known as chelation in which organic molecules ‘’grasp’’ or form complexes with, calcium, magnesium, iron, copper, zinc, and other ions. Such chelated minerals are more soluble and less toxic than some of the inorganic salts of the element, especially in the case of metals. Chelators are nearly added to cultures and microcosms to enhance the availability of nutrients.