carbon cycle

Carbon cycle

Carbon dioxide is used by plants for photosynthesis. The carbon is then built up into carbon compounds in the plants.
These carbon compounds either:
a) decay into peat, then over millions of years, coal (under very high pressures and worked on by microbes in the absence of oxygen). The coal is then burned by factories to produce electricity, and thus the carbon is returned to carbon dioxide in the air; or

b) are eaten by animals (or remain in the plant, no difference). The carbon compounds in both the plants and animals are returned to the air as carbon dioxide via respiration and also when they die and decay, as microbes digest their biomass.
Thus the cycle is complete.

Nitrogen in the air is built up into nitrates by nitrogen fixing bacteria. These nitrates are then absorbed by plants and turned into plant proteins. Leguminous plants can simply take the nitrogen in the air, and then build it up into plant proteins. The plant protein is then eaten by animals, who then excrete the protein as ammonia. Both the plant and animals proteins can be broken down and digested by microbes once the plant or animal dies into ammonia.
This ammonia is then oxidized by nitrifying bacteria into nitrites, which are then oxidized again by other nitrifying bacteria into nitrates.
Denitrifying bacteria can reduce nitrates to nitrogen in the air, nitrites or ammonia.


Carbon Cycle

The movement of carbon, in its many forms, between the biosphere, atmosphere, oceans, and geosphere is described by the carbon cycle, illustrated in the adjacent diagram. The carbon cycle is one of the biogeochemical cycles. In the cycle there are various sinks, or stores, of carbon (represented by the boxes) and processes by which the various sinks exchange carbon (the arrows). We are all familiar with how the atmosphere and vegetation exchange carbon. Plants absorb CO2 from the atmosphere during photosynthesis, also called primary production, and release CO2 back in to the atmosphere during respiration. Another major exchange of CO2 occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis.
Two other important processes are fossil fuel burning and changing land use. In fossil fuel burning, coal, oil, natural gas, and gasoline are consumed by industry, power plants, and automobiles. Notice that the arrow goes only one way: from industry to the atmosphere. Changing land use is a broad term which encompasses a host of essentially human activities. They include agriculture, deforestation, and reforestation.
The adjacent diagram shows the carbon cycle with the mass of carbon, in gigatons of carbon (Gt C), in each sink and for each process, if known. The amount of carbon being exchanged in each process determines whether the specific sink is growing or shrinking. For instance, the ocean absorbs 2.5 Gt C more from the atmosphere than it gives off to the atmosphere. All other things being equal, the ocean sink is growing at a rate of 2.5 Gt C per year and the atmospheric sink is decreasing at an equal rate. But other things are not equal. Fossil fuel burning is increasing the atmosphere's store of carbon by 6.1 Gt C each year, and the atmosphere is also interacting with vegetation and soil. Furthermore, there is changing land use.
The carbon cycle is obviously very complex, and each process has an impact on the other processes. If primary production drops, then decay to the soil drops. But does this mean that decay from the soil to the atmosphere will also drop and thus balance out the cycle so that the store of carbon in the atmosphere will remain constant? Not necessarily; it could continue at its current rate for a number of years, and thus the atmosphere would have to absorb the excess carbon being released from the soil. But this increase of atmospheric carbon (in the form of CO2) may stimulate the ocean to increase its uptake of CO2 .
What is known is that the carbon cycle must be a closed system; in other words, there is a fixed amount of carbon in the world and it must be somewhere. Scientists are actively investigating the carbon cycle to see if their data does indeed indicate a balancing of the cycle. These types of investigations have led many scientists to believe that the forests of the Northern Hemisphere are, in fact, absorbing 3.5 Gt C per year, and so changing land use is actually removing carbon from the atmosphere (~2 Gt C/year), not increasing it as the diagram shows. Experiments are ongoing to confirm this information.
Balancing the Carbon Cycle
Using the data given in the carbon cycle diagram, attempt to balance the carbon cycle. By balance, we mean--given the amount of carbon moving between the various sinks, as listed on the process arrows--what must be the rate at which the various sinks are changing. Are they increasing, decreasing, or remaining constant? Be sure to include the uncertainties in your calculations. Remember, the carbon cycle is a closed system, so all the carbon must be accounted for. It cannot disappear.
If scientists can figure out where the carbon from anthropogenic sources is going, then it may be possible to devise programs to enhance the uptake of carbon in these sinks. This would reduce the rate of increase of carbon in the atmosphere and perhaps slow global warming. Hints: When scientists balance the carbon cycle, they consider only those processes and sinks which interact directly with the atmosphere, since increasing levels of CO2 in the atmosphere may cause global warming.
For decay from soil to atmosphere, use 60 GtC. This number is hotly contested, however, with many scientists believing that the soil is a significant sink for atmospheric carbon (2-3 GtC/year). Research is ongoing in this area.Consider whether sinks are growing or shrinking. For instance, from the Mauna Loa CO2 data (You will need Excel 5.0 or higher.) or the text version we can calculate the increase in carbon in the atmosphere with a high degree of certainty. What about the other sinks? What evidence do we have that they may be growing or shrinking?

Biogeochemical Cycles

While humans cannot control the weather on a daily basis, the influence of human life on the environment plays a significant role in global climate.
How often have you wished for a rainy day to go away, or for the warm weather of summer during wintertime? Unfortunately, these wishes rarely come true, and it seems as though humans have little control over the weather. While humans cannot control the weather on a daily basis, the influence of human life on the environment plays a significant role in global climate. Deforestation and fossil fuel burning are just a couple of examples of human activities that seriously disrupt the equilibrium of the global ecosystem and alter the biogeochemical cycles that play a role in determining the Earth’s climate.

Biogeochemical cycles are essentially the continuous transport and transformation of materials in the environment. Materials are transported through life, air, sea and land in a series of cycles. These cycles include the circulation of elements and nutrients upon which life and the earth’s climate depend. The most important biogeochemical cycles are those of water, carbon, nitrogen and certain other trace gases. In this text, however, we will discuss the carbon and nitrogen cycles, as they are closely intertwined with living things on Earth.
The carbon cycle is particularly influential when it comes to global climate. Much of the carbon in the carbon cycle is in the form of carbon dioxide, a gas that has a strong greenhouse effect because it absorbs infrared radiation. Carbon is one of the most common elements on Earth and it is the basis of all living things. Below is a graphical depiction of the carbon cycle: Nitrogen is another element that plays important roles in both biological and non-biological systems. Nitrogen gas makes up 80% of the Earth’s atmosphere and nitrogen exists in proteins of living organisms. The nitrogen cycle is depicted below:
Global climate change, temperature, precipitation and the stability of ecosystems are all dependent upon biogeochemical cycles. When humans inadvertently disrupt these cycles by, for example, polluting, disastrous consequences can result. A healthy understanding of these cycles are critical in order to ensure the health and safety of future generations of living things on Earth. From climate changes to atmospheric composition, biogeochemical cycles are an integral component of planetary biology.

Biography
http://www.cotf.edu/ete/modules/carbon/efremote4.html
http://www.cotf.edu/ete/modules/carbon/efcarbon.html
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