Water and carbon cycle

The already mentioned feedback between the water and carbon cycle (see also Fig. 2.31) is not only given by the essential role of water in sustaining all forms of life. Observational evidence indicates that transpiration rates of plants are high at the same time as CO2 fixing by the plants, and hence CO2 flux from the atmosphere to the plant canopy is large. When an environment is humid, plants grow more rapidly, draw more CO2 from the atmosphere, and release more water to the atmosphere. 

With high-hardness waters, the carbonate-cycle form of precipitation treatment is often preferred to the phosphate-cycle because it forms a less bulky and less dense sludge. The disadvantages of hard-water carbonate-cycle precipitation treatments include ... 

Water and carbon play critical roles in many of the Earth s chemical and physical cycles and yet their origin on the Earth is somewhat mysterious. Carbon and water could easily form solid compounds in the outer regions of the solar nebula, and accordingly the outer planets and many of their satellites contain abundant water and carbon. The type I carbonaceous chondrites, meteorites that presumably formed in the asteroid belt between the terrestrial and outer planets, contain up to 5% (m/m) carbon and up to 20% (m/m) water of hydration. Comets may contain up to 50% water ice and 25% carbon. The terrestrial planets are comparatively depleted in carbon and water by orders of magnitude. The concentration of water for the whole Earth is less that 0.1 wt% and carbon is less than 500 ppm. Actually, it is remarkable that the Earth contains any of these compounds at all. As an example of how depleted in carbon and water the Earth could have been, consider the moon, where indigenous carbon and water are undetectable. Looking at Fig. 2-4 it can be seen that no water- or carbon-bearing solids should have condensed by equilibrium processes at the temperatures and pressures that probably were typical in the zone of fhe solar... 

Measurements of S cycling in Little Rock Lake, Wisconsin, and Lake Sempach, Switzerland, are used together with literature data to show the major factors regulating S retention and speciation in sediments. Retention of S in sediments is controlled by rates of seston (planktonic S) deposition, sulfate diffusion, and S recycling. Data from 80 lakes suggest that seston deposition is the major source of sedimentary S for approximately 50% of the lakes sulfate diffusion and subsequent reduction dominate in the remainder. Concentrations of sulfate in lake water and carbon deposition rates are important controls on diffusive fluxes. Diffusive fluxes are much lower than rates of sulfate reduction, however. Rates of sulfate reduction in many lakes appear to be limited by rates of sulfide oxidation. Much sulfide oxidation occurs anaerobically, but the pathways and electron acceptors remain unknown. The intrasediment cycle of sulfate reduction and sulfide oxidation is rapid relative to rates of S accumulation in sediments. Concentrations and speciation of sulfur in sediments are shown to be sensitive indicators of paleolimnological conditions of salinity, aeration, and eutrophication. 

Water and carbon dioxide provide the most attractive and abundant source materials for the fuel products of an artificial photosynthetic device, as seen in Fig. 11. These two compounds are the outcome of the heterotrophic cycle providing the energy sources of the living organism, and the result of consumption of fossil fuels by mankind. Not surprisingly, both of the materials exhibit high chemical... 

Lomstein, B.A., Jensen, A.G.U., Hansen, J.W., Andreasen, J.B., Hansen, L.S., Bemtsen, J., and Kunzendorf, H. (1998) Budgets of sediment nitrogen and carbon cycling in the shallow water of Knebel Vig. Denmark. Aquat. Microb. Ecol. 14, 69-80. 

Wollast, R., and Vanderborght, J. P. (1994) Aquatic Carbonate Systems Chemical Processes in Natural Waters and Global Cycles. In Chemistry of Aquatic Systems Local and Global Perspectives, S. Bidoglio and W. Stumm, Eds., Kluwer, Dordrecht. 

It was also mentioned in Section 3.2 that tropospheric H2 formed by the above process reacts with OH to form water. The CO formed from the carbon atoms of methane is transformed into C02 by appropriate chemical processes (see Subsection 3.3.2). Both water and carbon dioxide are used by the plants during their photosynthetic activity. Thus, a major part of hydrogen and carbon of CH4 returns to the plants, thus closing the atmospheric methane cycle. 

The natural cycles in the atmosphere are able to transport only a few compounds namely oxygen, nitrogen, water and carbon dioxide. Many more gases could of course be transported however, they would significantly affect life on Earth. 

If items made of PHAs are composted, they are completely degraded to water and carbon dioxide as the final products of their oxidative breakdown. Here it has to be emphasized that these final oxidation products are the basic materials for the photosynthetic regeneration of carbohydrates by green plants. This demonstrates that, in contrast to petrol-based plastics, PHAs are embedded into the natural closed cycle of carbon. The range of applications for PHAs is not limited to simple packaging materials, but encompasses commodity items, materials for agro-industrial purposes and pharmaceutical and medical applications. The major advantageous characteristics of PHAs can be summarized as follows ... 

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