The Sulfur Cycle

The

sulfur cycle

is the collection of processes by which sulfur moves to and from minerals (including the waterways) and living systems.

Sulfur

     In nature: it can be found as the pure element, and as sulfide and sulfate minerals.

Commercial uses: fertilizers, gunpowder, matches, insecticides, fungicides, vitamins, proteins and hormones. It is critical in the environment, climate and the health of ecosystems. Its the 10 th most abundant element in the universe and 7 th most abundant element in our body.

Amino acids: Cystein and methionine

Biological importance

 Amino acids: Methionine and Cysteine   Therefore important part of proteins, enzymes etc. Vitamins

WHERE is sulfur found?

   The majority of Earth's sulfur is stored: In rocks underground!

In sulfur salts at the bottom of the ocean!

Sulfur Cycle

 In ground: most found in rocks, or salt in earth, or as sediment at bottom of ocean    Found as S, H 2 S, SO 4 -2 , (NH 4 ) 2 SO 4 Enter ground: Plants absorb, or left by acid deposition (fog or precipitation) As SO 4 -2 , (NH 4 ) 2 SO 4 , and then turn H 2 S by bacteria, decay, and plant use  Stored: Ground, rock, ocean, somewhat in air

Sulfur Cycle

 Sulfur is transferred into biosphere then back into ground, or from ground to atmosphere   Microorganisms turn it into H 2 S (gas) Oxidized in atmosphere to SO 2 , and then to H 2 SO 4 with water contact (an acid)   Mined ores released to atmosphere in factories as H 2 S and SO 2 Volcanoes and hot springs

Sulfur Cycle

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Deposited next in water

 Through precipitation, dry deposition, leaching  Rainfall= deposited 73E12 grams sulfur in 1960      SO 4 -2 H 2 SO 4 leaches from soil into ocean as sediment falls into ocean Dimethyl Sulfide, carbonyl sulfide (biogenic gases), released by plankton returns back into atmosphere (turns into SO 2 ) Either re-evaporated, left as sediment for long time, or deposited on land 20E12 grams of sulfur a year deposited on land by sea  When back on land, cycle repeats

The Atmospheric Portion

 Volcanic eruptions, breakdown of organic matter in swamps and tidal flats, and the evaporation of water, especially seawater, release sulfur directly into the atmosphere.

 Sulfur eventually settles to earth or comes down with rainfall.

Driving Force

 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 (incl. Biological, hydrological, due to sun energy) Plant uptake, microbes (Desulfovibrio sp. or Desulfotomaculum sp.)

Biochemicaltransformations

 Physical Weathering release of sulfides (HS-) or sulfates (SO4-3) from minerals  Biological transformations:  Aerobic sulfur-oxidizing bacteria ; sulfides are converted to sulfate (SO4-2) sulfate is assimilated by plants and microbes  Anaerobic sulfate-reducing bacteria; sulfate converted to sulfides   Aerobic or anaerobic Mineralization of organic S, release as either HS- or SO4-2

Human Activities

 The burning of fossil fuels and processing of metals releases huge quantities of sulfur into the atmosphere.

 Human activities are responsible for one-third of all sulfur emissions and 90% of all sulfur dioxide emissions.

 Sulfur dioxide emissions lead to acid rain as sulfur dioxide reacts with water to form H 2 SO 4 and sulfur trioxide reacts with water to form H 2 SO 4 .

Human Effect

 

When mine ores, sulfur/sulfides released into soil Combustion of fossil fuels

 Release of SO 2 , causes acid rain, increases amount already present    28% of sulfur in rivers from pollution, mining, erosion, etc.

Help move cycle but also upset balance- too much S means acid rain Hydrodesulphurization (refine hydrocarbons)- surplus of S

Conclusion

 Sulfur Cycle is important to biological and natural processes although human’s role impacts nature in a negative way