Thursday, June 26, 2014

Biogeochemical cycles: Sulphur cycle

Biogeochemical cycles: Sulphur cycle


  • Sulfur- S, it is an element
  • Naturally found in earth
  • At room temperature it is a solid
  • Present in proteins, amino acids, vitamins, and enzymes, necessary for plants and animals
  • Often reacts with hydrogen creating hydrogen sulfide (H2S)
  • Can dissolve in water
  • With metals in water, forms metal sulfides and sulfates in air


Presence:
  • In ground: most found in rocks, or salt in earth, or as sediment at bottom of ocean
  • Found as S, H2S, SO4-2, (NH4)2SO4
  • Underground: Plants absorb, or left by acid deposition (fog or precipitation)
  • Found as SO4-2, (NH4)2SO4, converted to H2S by bacteria, decay, and plant use
  • Stored: Ground, rock, ocean, some quantities in air

Cycle:
  • Sulfur is transferred into biosphere then back into ground, or from ground to atmosphere
  • Microorganisms turn it into H2S (gas) 
  • Oxidized in atmosphere to SO2, and then to H2SO4 (an acid) with water contact
  • Mined ores released to atmosphere in factories as H2S and SO2
  • Volcanoes and hot springs
  • Deposited next in water
  • Through precipitation, dry deposition, leaching
  • SO4-2 leaches from soil into ocean as sediment
  • H2SO4 falls into ocean
  • Dimethyl Sulfide, carbonyl sulfide (biogenic gases), released by plankton returns back into atmosphere (turns into SO2)
  • Either re-evaporated, left as sediment for long time, or deposited on land 
  • When back on land, cycle repeats
Sulphur cycle driven by:
  • constant addition of sulfur to environment by earths interior (Geosphere)
  • Human disturbance, addition of sulfur to atmosphere, (also dug up from environment)
  • Natural processes (Biological, Hydrological and due to Sun’s energy)
  • Plant uptake, microbes (Desulfovibrio sp. or Desulfotomaculum sp.)
Presence:
  • Most sulfur in particulate form
  • Therefore it is a sedimentary cycle
  • Very short residence time in atmosphere (1-2 days)
  • Even in atmosphere, found as aerosols (<1 micrometer), not gas usually
  • In atmosphere, very much less than 1%
  • 90-95% SO2 from power plants and factories
Sources:
  • In the process of mining ores, sulfur/sulfides released into soil
  • Combustion of fossil fuels
  • Release of SO2, causes acid rain, increases amount already present
  • Almost 30% of sulfur in rivers from pollution, mining, erosion, etc.
  • Sulfur cycle but also upset balance- too much Sulfur induces acid rain
  • Hydrodesulphurization (refining hydrocarbons)
Sulfur Cycle is important to biological and natural processes although human’s role impacts nature in a negative way
Driving force for life



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