Chapt. 1a - Carbon Cycle
Information about Carbon in the earth's atmosphere.
1. Carbon dioxide ("oxidized" carbon) in earth's atmosphere escaped from molten rock when it erupted and cooled on the earth surface. Photosynthesis in plants and algae converts atmospheric carbon dioxide and water into living tissue (biomass is a form of "reduced" carbon) releasing oxygen. Microbes and other organisms decompose biomass, thereby producing humus (another "reduced" form of carbon). Soil humus accounts for three times more "reduced" carbon than biomass.
Each year, photosynthetic organisms convert 14% of the total atmospheric carbon dioxide into biomass totaling about 100 billion metric tons. Half of this, 50 billion metric tons, is immediately respired by the plants and algae that fixed it. The remaining 50 billion metric tons is respired by organisms in the soil that comprise the decomposition food chain.
2. Respiration, which releases the energy stored in biomass and humus by combining it with atmospheric oxygen to release carbon dioxide and water, is very sensitive to changes in temperature while the photosynthetic rate does not change much with temperature. This is important because scientists believe a rise in global temperature will stimulate respiration, which pumps carbon dioxide into the atmosphere, more than it will stimulate photosynthesis, which extracts H carbon dioxide from the atmosphere.
If this is so, a global rise in temperature triggered by elevated carbon dioxide levels will create a positive feedback which will further accelerate the rise in carbon dioxide levels and temperatures. However, some (James Lovelock - Gaia Hypothesis) propose that with more CO² in the atmosphere more will be absorbed by the oceans and more vegetation will grow on the planet and tie up more CO² and the levels will stabilize.
Anaerobic respiration in wetlands and waterlogged soils is the primary source of methane. Methane is 20 times as effective as carbon dioxide trapping long-wavelength radiation from the earth. Global temperature increases could also stimulate the release of methane from wetlands. Anaerobic respiration uses the oxygen in biomass, residue and humus for respiration and produces the oxygen-free product methane (CH4).
3. The oxidation of "reduced" forms of carbon (biomass, humus and fossil fuels) increase the atmospheric levels of carbon dioxide. This can occur by the burning of coal and petroleum, the destruction of forests and other natural ecosystems, and the expansion of agriculture to feed a growing population. The tilling of croplands stimulates biological activity that accelerates the oxidation of humus. The destruction of natural ecosystems releases the "reduced" carbon stored in biomass, residue and humus.
Boreal forests may figure prominently in global warming. Respiration by boreal forests in the upper latitudes releases as much carbon dioxide annually as the burning of fossil fuels and accounts for 20-30% of the global respiration. Scientists estimate that 43% of the global soil humus reserve resides in boreal forest ecosystems. All estimates of global warming predict greater warming in the upper latitudes than at the equator.
The role of carbon in biodiversity in Conservation Agriculture.
Clarence Lehman, Director Cedar Creek Nat. History Area, MN
1. Biodiversity increases stability of the system.
2. Biodiversity increases the productivity of the system.
3. Biodiversity increases carbon storage and Carbon sequestration.
4. Biodiversity reduces nutrient losses to groundwater and is more efficient in
nutrient capture.
5. Biodiversity decreases susceptibility to disease.
6. Biodiversity increases resistance to exotic species.
7. Biodiversity effects are more pronounced with increasing carbon dioxide and
nitrogen application.
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