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