Cycles biosphere

One of the things that environmental scientists do IS to keep track of important elements in the biosphere—in what form do these ele ments normally occur to what are they transformed and how are they returned to their normal state Careful studies have given clear although compli cated pictures of the nitrogen cycle the sulfur cy cle and the phosphorus cycle for example The carbon cycle begins and ends with atmospheric carbon dioxide It can be represented in an abbrevi ated form as... 

Carbon. Most of the Earth s supply of carbon is stored in carbonate rocks in the Hthosphere. Normally the circulation rate for Hthospheric carbon is slow compared with that of carbon between the atmosphere and biosphere. The carbon cycle has received much attention in recent years as a result of research into the possible relation between increased atmospheric carbon dioxide concentration, most of which is produced by combustion of fossil fuel, and the "greenhouse effect," or global warming. Extensive research has been done on the rate at which carbon dioxide might be converted to cellulose and other photosyntheticaHy produced organic compounds by various forms of natural and cultivated plants. Estimates also have been made of the rate at which carbon dioxide is released to soil under optimum conditions by various kinds of plant cover, such as temperature-zone deciduous forests, cultivated farm crops, prairie grassland, and desert vegetation. 

Natural water systems contain numerous minerals and often a gas phase (Fig. 1). They include a portion of the biosphere and organisms, and their abiotic environments are interrelated and interact with each other. The distribution of chemical species in waters is strongly influenced by an interaction of mixing cycles and biological cycles. 

The Flow of Energy in the Biosphere and the Carbon and Oxygen Cycles Are Intimately Related... 

FIGURE 18.3 The flow of energy in the biosphere is coupled primarily to the carbon and oxygen cycles. 

If 3 X kg of CO9 are cycled through the biosphere annually, how many human equivalents (70-kg persons composed of 18% carbon by weight) could be produced each year from this amount of CO9 ... 

The continuous interchange of nitrogen between the atmosphere and the biosphere is called the nitrogen cycle. Global estimates are difficult to obtain and there are frequently regional and local impacts which vary greatly from the mean. However, some indication of the size of the various reservoirs of nitrogen in the atmosphere, on land, and in the seas is... 

The global carbon cycle is the continuous movement of carbon between the living and nonliving portions of the biosphere, driven in part by biological processes and resulting in a constant supply of carbon to life (Figure 1). The... 

Olson, J. S. Pfoderer, H. A. Chan, Y. H. Changes in the Global Carbon Cycle and the Biosphere ORNL/EIS-109, Oak Ridge National Laboratory Oak Ridge, TN, 1978. 

Ear from being just the processing of water on Earth, this cycle is the basis for a wide range of meteorologic, geochemical, and biological systems. Water is the transport medium for all nutrients in the biosphere. Water vapor condensed into clouds is the chief control on planetary albedo. The cycling of water is also one of the major mechanisms for the transportation of sensible heat (e.g. in oceanic circulation) and latent heat that is released when water falls from the air. 

The consequences of the massive "loss" of energy accompanying passage from one trophic level to another also include the fact that organisms low in the trophic ladder tend to dominate the cycling of elements through the biosphere. This is especially true on land where vascular plants dominate both the physical structure and... 

One of the most important functions of the pedosphere is the cycling of elements that occurs within soils and the transfers that occur between the atmosphere, lithosphere, biosphere, and hydrosphere through soils. Soil is an interface between the atmosphere and lithosphere, between the biosphere and lithosphere, and between roots and soil organisms and the atmosphere. In many ways, soil acts as a membrane" covering the continents and regulating the flow of elements between these other systems of the Earth. 

The soil may represent a thin film on the surface of the Earth, but the importance of soils in global biogeochemical cycles arises from their role as the interface between the Earth, its atmosphere, and the biosphere. All terrestrial biological activity is founded upon soil productivity, and the weathering of rocks that helps to maintain atmospheric equilibrium occurs within soils. Soils provide the foundation for key aspects of global biogeochemical cycles. 

This treatment of the carbon cycle is intended to give an account of the fundamental aspects of the carbon cycle from a global perspective. After a presentation of the main characteristics of carbon on Earth (Section 11.2), four sections follow 11.3, about the carbon reservoirs within the atmosphere, the hydrosphere, the biosphere... 

Although the largest reservoirs of carbon are found in the lithosphere, the fluxes between it and the atmosphere, hydrosphere, and biosphere are small. It follows that the turnover time of carbon in the lithosphere is many orders of magnitude longer than the turnover times in any of the other reservoirs. Many of the current modeling efforts studying the partitioning of fossil fuel carbon between different reservoirs only include the three "fast" spheres the lithosphere s role in the carbon cycle has received less attention. 

Fig. 11-15 Variation in the vertical distribution of carbon dioxide in the air around a forest with time of day. (Reprinted with permission from B, Bolin (1970). The carbon cycle. In The Biosphere," p. 51, W. H. Freeman, NY.)...

Fig. 11-18 A four-box model of the global carbon cycle. Reservoir inventories are given in moles and fluxes in mol/yr. The turnover time of CO2 in each reservoir with respect to the outgoing flux is shown in brackets. (Reprinted with permission from L. Machta, The role of the oceans and biosphere in the carbon dioxide cycle, in D. Dryssen and D. Jagner (1972). "The Changing Chemistry of the Oceans," pp. 121-146, John Wiley.)...

Pollard, D., Sitch, S. and Haxeltine, A. (1996). An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics. Global Biogeochem. Cycles 10, 603-628. 

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