Biosphere main elements

Fig. 2.3 Distribution of elements in the four main environmental materials, lithosphere, hydrosphere, atmosphere and biosphere. The elements are shown in their actual form as compounds, ions or molecules as appropriate. The main components of each material are shown in boxes, other major constituents are shown outside the boxes.

Thus, the chemical reactivity of the elements in seawater is reflected by the residence time. It is important to note, however, that while residence times tell us something about the relative reactivities, they also tell us nothing about the nature of the reactions. The best source of clues for imderstanding these reactions is to study the shape of dissolved profiles of the different elements. When we do this we find that there are six main characteristic types of profiles as described in Table 10-8. Notice that most of these reactions occur at the phase discontinuities between the atmosphere, biosphere, hydrosphere, and lithosphere. 

The main introduction of arsenic into the biosphere is anthropogenic as result of industrial activity and the use of herbicides and biocides that contain the element. Arsenic is mainly released into the atmosphere as a consequence of its isolation, burning of fossil fuels and the smelting of ores (combustion). The oxides generated thermally are particulate in nature, which owing to their small size (in the nanometer scale) are held up in the exhaust gases and are easily vented into the local atmosphere and then distributed by the prevailing air currents. Models for the transport of arsenic predict that currently 285 tonnes are deposited annually on the Artie as a consequence of industrial activity in the northern hemisphere. 

The migration of chemical elements in a thermodynamically open system does by no means lead to chaos. The direction of mass transport is kept under control by a large variety of diverse equilibrium processes. On the other hand, the main feature of the migration cycles of the biosphere, i.e. their openness, depends on this equilibrium. 

In any given time the vast majority of S is in the lithosphere. However, the main transport of this element occurs in the atmosphere, hydrosphere, and biosphere. The role of the biosphere often involves reactions that result in the movement of sulfur from one reservoir to another. 

Of approximately 80 elements found in soils, 17 are used by plants to grow. These are called the essential elements and include H, C, O, N, P, S, K, Mg, Ca, B, Cl, Mn, Fe, Cu, Zn, Mo, and Co. Hydrogen and O are derived from the hydrosphere, C from the atmosphere, N from the biosphere, and the remaining 13 from the lithosphere or the mineral soil. Soil is mainly an O-Si-Al-Fe matrix containing relatively small amounts of the other essential... 

Nitrogen is an essential element for all forms of life and its biogeochemical cycle is one of the most important in the modem biosphere. It is a structural component of amino acids from which proteins are synthesized. Animal and human tissue (muscle, skin, hair, etc.), enzymes and many hormones are composed mainly of proteins. 

The cyclic transformation of nitrogenous compounds is of great importance in the total turnover of this element in the biosphere. The main features of the biological nitrogen cycle are illustrated schematically in Fig. 4.16. Plants and algae assimilate nitrogen as either nitrate or ammonia to form... 

Polysaccharides are the most abundant biomacromolecules in the biosphere. These complex carbohydrate comprising glycosidic bonds are one of the main stractural elements of plants and exoskeletal animals (cellulose, carrageenan, chitin, etc.). 

There is one major disadvantage, however the need to separate and recover the catalyst. This disadvantage has two aspects. Cost aside, the release into the biosphere of large amounts of the heavier transition metals would almost certainly have untoward effects. They are the very elements discussed in an earlier section. They are rare and have never occurred in appreciable amounts in living systems. But here, too, there is an encouraging lesson to be learned - the catalysts are compounds of very expensive metals - any significant loss would be prohibitively expensive. This very fact has forced the development of methods to prevent their loss. It is mainly a matter of the necessary incentive. 

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