Chapter 22, Problem 1RQ

Summary Introduction

To review:

The major sources and sinks of carbon, nitrogen, and sulfur and to identify the sources that recycle rapidly.

Introduction:

The biogeochemical cycle refers to a pathway through which essential elements of living matter get circulated. The elements in these pathways flow in various forms from the non-living to the living components of the biosphere. Reservoirs are the regions of the biosphere that possess a significant amount of the element required for life. They acts as a source for living organisms, as well as a sink, to which the element returns.

Explanation of Solution

The cycling of a particular nutrient does not take place efficiently on the surface of the Earth. The cycling of a nutrient takes place efficiently below the crust of the Earth. The dead and decayed organisms form fossils and enable the rapid conversion of organic carbon into its inorganic form. Thus, the cycling of carbon can most rapidly take place. The major sources and sinks of the above-mentioned nutrients are listed below:

Major source and sink of carbon:

Source: The major sources of carbon are emissions from forest fires, burning of fossil fuels, and respiration. The largest reservoir of carbon is comprised of the carbonate rock. The biospheric carbon can be found as methane produced by methanogens, as carbon dioxide produced by respiration, and fermentation.

Sink: The main carbon sink is the plants, the ocean, and soil. The atmosphere acts like a sink for carbon dioxide that is generated by heterotrophy and by geological outgassing from volcanoes.

Major source and sink of nitrogen:

Source: The major source of nitrogen is in the atmosphere where dinitrogen constitutes approx 70% of air. Its sources may also include agricultural land, livestock and poultry, and agricultural emissions because of the increased use of fertilizers in agricultural soils.

Sink- The primary sink of nitrogen is the nitrogen gas present in the atmosphere. Nitrogen is fixed into ammonia by bacteria and Archaea. The denitrifying bacteria reduce the nitrate back into nitrogen to return it to the atmosphere.

Major source and sink of sulfur:

Source- The major source of sulfur is the volcanoes that release a large amount of sulfur dioxide into the air and human combustion of fossil fuels such as coal, oil and natural gas.

Sink- Sulfur is not present in huge quantities in the atmosphere. It is present within the oceans and other water bodies, which act as the major sink of sulfur.