Biogeochemical cycles

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10 Jun 2019

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Biogeochemical cycles

  1. BiogeochemicalBiogeochemical CycleCycle Presented by, Md. Galib Ishraq Emran. Department of Environmental Sciences. 2015-16 Sessions. Registration No: 41778. Class Roll: 219. Jahangirnagar University, Savar, Dhaka-1342. Email:
  2. Biogeochemical Cycle “A biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.” Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through the biogeochemical cycles All chemical elements occurring in organisms are part of biogeochemical cycles.
  3. Important Biogeochemical Cycle The most well-known and important biogeochemical cycles include the followings:-  The Carbon cycle,  The Nitrogen cycle,  The Sulfur cycle,  The Oxygen cycle,  The Phosphorus cycle.
  4. Importance of Biogeochemical Cycle  Biogeochemical cycles are the processes where in different elements on earth surface are interconverted such that autotrophs can best utilize them.  The flow of energy takes place from primary producers to consumers.  The process involves transfer of energy in terms of food and also involves chemical conversion.  All of the biogeochemical cycles are mainly involved proper maintenance of ecosystem with proper energy flow across primary producers and consumers at tertiary stage.
  5.  Carbon is the building block of life. It is the element that anchors all organic substances, from coal and oil to DNA (deoxyribonucleic acid, the compound that carries genetic information).  Carbon is one of the elements that have a gaseous phase as part of its cycle, occurring in the Earth’s atmosphere as carbon dioxide (CO2) and methane (CH4), both greenhouse gases.  Carbon enters the atmosphere through the respiration of living things, through fires and by diffusion from the ocean. It is removed from the atmosphere by photosynthesis of green plants, algae, and photosynthetic bacteria. The Carbon
  6. “The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.” It is one of the most important cycles of the earth and allows for carbon to be recycled and reused throughout the biosphere and all of its organisms. The carbon cycle was initially discovered by Joseph Priestley and Antoine Lavoisier, and popularized by Humphry Davy The Carbon Cycle
  7. The major reservoirs of Carbon The following major reservoirs of carbon interconnected by pathways of exchange: The Atmosphere The Terrestrial biosphere The Oceans The Sediments including fossil fuels The Earth's interior (carbon from the Earth's mantle and crust is released to the atmosphere and hydrosphere by volcanoes and geothermal systems)
  8. The simplified Diagram of the Carbon Cycle
  9. Carbon in the Atmosphere  Carbon exists in the Earth's atmosphere primarily as the gas carbon dioxide (CO2). Although it is a small percentage of the atmosphere (0.03%), it plays a vital role in supporting life.  Other gases containing carbon in the atmosphere are methane and chlorofluorocarbons.  Trees and other green plants convert carbon dioxide into carbohydrates during photosynthesis, releasing oxygen in the process.  The phytoplankton, get their carbon from atmospheric carbon dioxide that has dissolved in ocean water.
  10. Carbon in the Biosphere  About half the dry weight of most living organisms is carbon. It plays an important role in the structure, biochemistry, and nutrition of all living cells.  Living biomass holds about 575 gigatonnes of carbon, most of which is wood. Soils hold upwards of 2700 gigatonnes, mostly in the form of organic carbon, with perhaps a third of that inorganic forms of carbon such as calcium carbonate.  Autotrophs are organisms that produce their own organic compounds using carbon dioxide from the air or water in which they live. The most important autotrophs for the carbon cycle are trees in forests on land and phytoplankton in the Earth's oceans.
  11. Carbon in the Hydrosphere  The oceans contain around 36,000 gigatonnes of carbon.  Carbon is readily exchanged between the atmosphere and ocean. In regions of oceanic upwelling, carbon is released to the atmosphere. Conversely, regions of down welling transfer carbon (CO2) from the atmosphere to the ocean. When CO2 enters the ocean, it participates in a series of reactions which are locally in equilibrium.  In the oceans, dissolved carbonate can combine with dissolved calcium to precipitate solid calcium carbonate. When these organisms die, their shells sink and accumulate on the ocean floor.
  12. Continue…………………  Carbon is transferred within the biosphere as heterotrophs feed on other organisms or their parts (e.g., fruits).  Most carbon leaves the biosphere through respiration. When oxygen is present, aerobic respiration occurs, which releases carbon dioxide into the surrounding air or water. Otherwise, anaerobic respiration occurs.  Burning of biomass can also transfer substantial amounts of carbon to the atmosphere.  Carbon may also be circulated within the biosphere when dead organic matter (such as peat) becomes incorporated in the geosphere.
  13. The Importance of the Carbon Cycle  Carbon is a key element for life, composing almost half of the dry mass of the earth’s plants (that is, the mass when all water is removed).  The carbon budget is the balance of carbon among the three reservoirs. The carbon cycle is vitally important to life on earth.  Through photosynthesis and respiration it is the way the earth produces food and other renewable resources. Through decomposition, it serves as the earth’s waste disposal system.
  14.  In addition, the carbon cycle is important because carbon- containing gases in the atmosphere affect the earth’s climate. Increased carbon dioxide (CO2) in the atmosphere has been responsible for more than half of the climate warming observed in recent decades.  The carbon cycle is inextricably linked to other chemical cycles, including those of nitrogen, phosphorus, and sulfur, as well as to the global hydrological cycle.  Carbon is an element found in all living substances as well as in many inorganic materials. Both diamond and coal are nearly pure carbon, but with different structures. Continue…………………
  15. The Nitrogen  Nitrogen is essential to life because nitrogen is necessary for proteins including DNA, the carrier of genetic information.  Free nitrogen makes up approximately 80% of the Earth’s atmosphere. However, organisms cannot use nitrogen directly.  Some, like animals, require nitrogen in an organic compound. Others, including plants, algae, and bacteria, can take up nitrogen either as the nitrate ion (NO3 - ) or the ammonium ion (NH4 + ).  In contrast to hydrogen, oxygen, and carbon, nitrogen is a relatively non-reactive element.
  16. The Nitrogen Cycle “The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out via both biological and non-biological processes.” Important processes in the nitrogen cycle include: 1. Nitrogen fixation 2. Nitrification 3. Denitrification
  17. The Nitrogen Cycle The simplified Diagram of the Nitrogen cycle
  18. Nitrogen fixation “Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3).” This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and amino acids for proteins. Nitrogen fixation is accomplished by 1.Soil bacteria 2.Rhizobiumbacteria 3.Blue green algae in waterand soil 4.Lighting
  19. Denitrification “Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products.”
  20. Harmful effects of Nitrogen Oxides  Nitric oxide (NO) is less toxic than nitrogen peroxide (NO2 ). NO attaches to hemoglobin and reduces oxygen transport efficiency. It’s effect is much less than carbon monoxide due to lower concentration in the atmosphere.  Acute exposure to nitrogen peroxide can be quite harmful to human health. For exposures ranges from several minutes to one hour, a level of 50 – 100 ppm of nitrogen peroxide causes inflammation of lung tissue for period of 6 – 8 weeks, after which time the subject normally recovers.
  21. Continue………………… Exposure of the subject to 150 – 200 ppm of nitrogen peroxide causes bro nchio litis fibro sa o blite rans , a condition fatal within 3 –5 weeks after exposure. Death generally results within 2 – 10 days after exposure to 500 ppm or more of nitrogen peroxide.Exposure of plants to several ppm of nitrogen peroxide causes leaf spotting and break-down of plant tissue.  Exposure to 10 ppm of nitric oxide causes a reversible decrease in the rate of photosynthesis.  Nitrogen oxides are known to cause fading of dyes and inks used in some textiles.  Much of the damage to materials caused by NOx comes from secondary nitrates and nitric acid.
  22. Control of Nitrogen Oxides Low excess air firing is effective in reducing NOx emissions during the combustion of fossils. Incomplete fuel burnout with the emission of hydrocarbon, soot, and carbon monoxide (CO) is an obvious problem with low-excess-air firing. This may be overcome by a two-stage combustion process.
  23. The Sulfur  Sulfur is one of the components that make up proteins and vitamins.  Sulfur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulphur.  Plants absorb sulfur when it is dissolved in water. Animals consume these plants, so that they take up enough sulfur to maintain their health.  Approximately 100 million metric tons of sulfur per year enters the global atmosphere through anthropogenic activities, primarily as sulfur dioxide (SO2) from the combustion of coal and residual fuel oil.
  24. The Sulfur Cycle “The sulfur cycle are the collection of processes by which sulfur moves to and from minerals (including the waterways) and living systems.”  Among the significant species involved in the sulfur cycle are gaseous hydrogen sulfide (H2S); mineral sulfides, such as lead sulfide (PbS), sulfuric acid (H2SO4), the main constituent of acid rain; and biologically bound sulfur in sulfur-containing proteins.  The essential steps of the sulfur cycle are: • Mineralization of organic sulfur • Oxidation of sulfide and elemental sulfur (S) • Reduction of sulfate to sulfide • Microbial immobilization of the sulfur compounds
  25. The simplified Diagram of the Sulfur cycle
  26. Effects of atmospheric Sulfur dioxide  Its primary effect is upon the respiratory tract, producing irritation and increasing airway resistance, especially to people with respiratory weakness and sensitized asthmatics. Sulfur dioxide causes death in humans at 500 ppm.  Atmospheric sulfur dioxide is harmful to plants, some species of which are affected more than others.  Acute exposure to high levels of the gas kills leaf tissue, a condition called leaf necrosis. The edges of the leaves and the areas between the leaf veins show characteristics damage.
  27. Continue……………  Chronic exposure of plants to sulfur dioxide causes chlorosis, a bleaching or yellowing of the normally green portion of the leaf.  Long-term, low-level exposure to sulfur dioxide can reduce the yields of grain crops such as wheat or barely. Sulfur dioxide in the atmosphere is converted to sulfuric acid, so that in areas with high levels of sulfur dioxide pollution, plants may be damaged by sulfuric acid aerosols.  One of the more costly effects of sulfur dioxide pollution is deterioration of building materials. Limestone, marble and dolomite are attacked by atmospheric sulfur dioxide.
  28. Sulfur dioxide Removal  A number of processes are being used to remove sulfur and sulfur oxides from fuel before combustion and from stack gas after combustion.  Most of these efforts concentrate on coal, since it is the major source of sulfur oxides pollution.  Physical separation techniques may be used to remove discrete particles of pyretic sulfur from coal.  Chemical methods may also be employed for removal of sulfur from coal.
  29. Phosphorus Cycle (Review)
  30. 1) Manahan, Stanley E. 2000 “Environmental Chemistry”, Lewis Publishers, Boca Raton: CRC Press LLC, New York. 7th Edition. 2) Miller, G. T, 2004 “Environmental Sciences”, Thomson Asia Pte. Ltd., Singapore. 10th Edition. 3) Textbook of Environmental Studies by Erach Bharucha, Universities Press, India, 2005. 4) Some References