Nitrogen lithosphere

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

E. L. Shock (1990) provides a different interpretation of these results he criticizes that the redox state of the reaction mixture was not checked in the Miller/Bada experiments. Shock also states that simple thermodynamic calculations show that the Miller/Bada theory does not stand up. To use terms like instability and decomposition is not correct when chemical compounds (here amino acids) are present in aqueous solution under extreme conditions and are aiming at a metastable equilibrium. Shock considers that oxidized and metastable carbon and nitrogen compounds are of greater importance in hydrothermal systems than are reduced compounds. In the interior of the Earth, CO2 and N2 are in stable redox equilibrium with substances such as amino acids and carboxylic acids, while reduced compounds such as CH4 and NH3 are not. The explanation lies in the oxidation state of the lithosphere. Shock considers the two mineral systems FMQ and PPM discussed above as particularly important for the system seawater/basalt rock. The FMQ system acts as a buffer in the oceanic crust. At depths of around 1.3 km, the PPM system probably becomes active, i.e., N2 and CO2 are the dominant species in stable equilibrium conditions at temperatures above 548 K. When the temperature of hydrothermal solutions falls (below about 548 K), they probably pass through a stability field in which CH4 and NII3 predominate. If kinetic factors block the achievement of equilibrium, metastable compounds such as alkanes, carboxylic acids, alkyl benzenes and amino acids are formed between 423 and 293 K. 

The nitrogen cycle is the complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere (earth) and hydrosphere (water). Atmospheric nitrogen is made accessible to us and other life-forms in mainly two ways. 

The elements whose isotopes are routinely measured with gas inlet mass spectrometers are carbon (12C and 13C, but not 14C), oxygen (160, 170, l80), hydrogen ( H, 2H, but not 3H), nitrogen (14N and 1SN) and sulphur (32S, 33S, 34). Stable isotopes of H, C, N, O, and S occur naturally throughout atmosphere, hydrosphere, lithosphere, and biosphere. They are atoms of the same elements with a different mass. Each element has a dominant light isotope with the nominal atomic weight (I2C, 160,14N, 32S, and H) and one or two heavy isotopes (l3C, nO, 180, 15N, 33S, 34S, and, 2H) with a natural abundance of a few percent or less Table 1). 

Analysis of the model schemes of the flux diagrams of nitrogen compounds in nature proposed by various experts means we can construct a block diagram like that in Figure 4.6. Here the atmosphere, soil, lithosphere, and hydrosphere are considered as nitrogen reservoirs. The first three reservoirs are described by 2-D models, and the hydrosphere is described by a 3-D multi-layer model. The characteristics of nitrogen fluxes between these reservoirs are given in Table 4.5. The equations of the model are written as... 

The complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere and hydrosphere. 

There are 5 major reservoirs in the Earth system atmosphere, biosphere (vegetation, animals), soils, hydrosphere (oceans, lakes, rivers, groundwater), and the lithosphere (Earth crust). Elemental cycles of carbon, oxygen, nitrogen, sulfur, phosphorus, and other elements interact with the different reservoirs of the Earth system. The carbon cycle has important aspects in tropical forests due to the large amount of carbon stored in the tropical forests and the high rate of tropical deforestation 0acob 1999)-... 

Deines P., Harris J. W., and Gurney J. J. (1991a) The carbon isotopic composition and nitrogen content of lithospheric and asthenospheric diamonds from the Jagersfontein and Koffiefontein Kimberlite, South Africa. Geochim. Cosmochim. Acta 55, 2615-2625. 

Oxygen is by far the most abundant element in cmstal rocks, composing 46.6% of the lithosphere (4). In rock mineral stmctures, the predominant anion is 0, and water (H2O) itself is almost 90% oxygen by weight. The nonmetaUic elements fluorine, sulfur, carbon, nitrogen, chlorine, and phosphoms are present in lesser amounts in the lithosphere. These elements aU play essential roles in hfe processes of plants and animals, and except for phosphoms and fluorine, they commonly occur in earth surface environments in gaseous form or as dissolved anions. 

Thinking Criticaiiy Nitrogen makes up 0.002% of Earth s lithosphere but 78% of the atmosphere. How can you explain this difference ... 

The cycling of the element Ccirbon depends primarily on its chemical properties. Like nitrogen and sulfur, but unlike phosphorus, silica, and iron, carbon forms volatile, soluble, and insoluble compounds and can thus circulate through the atmosphere, hydrosphere and lithosphere. Since carbon is the basic element of life its circulation through the biosphere is of particular importance. 

Nitrogen in the Archaean mantle The initial nitrogen isotopic composition of the Earth is not well known. However, nitrogen isotope measurements on 2.9-3.3 Ga diamonds from the subcontinental lithosphere have a mean S15N value of -5, and a similar C/N ratio to that of the modern mantle (Fig. 5.4), suggesting that there has been very little change since about 3.0 Ga (Marty Dauphas, 2003). 

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