The Sulfur Cycle

The Sulfur CycleThesulfur cycleis the collection of processes by which sulfur moves to and from minerals (including the waterways) and living systems.1SulfurIn 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 10th most abundant element in the universe and 7th most abundant element in our body.Amino acids: Cystein and methionine

2Biological importanceAmino 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!

4Sulfur CycleIn ground: most found in rocks, or salt in earth, or as sediment at bottom of oceanFound as S, H2S, SO4-2, (NH4)2SO4Enter ground: Plants absorb, or left by acid deposition (fog or precipitation)As SO4-2, (NH4)2SO4, and then turn H2S by bacteria, decay, and plant useStored: Ground, rock, ocean, somewhat in airSulfur CycleSulfur is transferred into biosphere then back into ground, or from ground to atmosphereMicroorganisms turn it into H2S (gas) Oxidized in atmosphere to SO2, and then to H2SO4 (an acid) with water contactMined ores released to atmosphere in factories as H2S and SO2Volcanoes and hot springsSulfur CycleDeposited next in waterThrough precipitation, dry deposition, leachingRainfall= deposited 73E12 grams sulfur in 1960SO4-2 leaches from soil into ocean as sedimentH2SO4 falls into oceanDimethyl 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 20E12 grams of sulfur a year deposited on land by seaWhen back on land, cycle repeats

8The Atmospheric PortionVolcanic 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.

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Driving ForceDriven 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.)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 anaerobicMineralization of organic S, release as either HS- or SO4-2

BiochemicaltransformationsHuman ActivitiesThe 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 H2SO4 and sulfur trioxide reacts with water to form H2SO4.13Human EffectWhen mine ores, sulfur/sulfides released into soilCombustion of fossil fuelsRelease of SO2, causes acid rain, increases amount already present28% of sulfur in rivers from pollution, mining, erosion, etc.Help move cycle but also upset balance- too much S means acid rainHydrodesulphurization (refine hydrocarbons)- surplus of SConclusionSulfur Cycle is important to biological and natural processes although humans role impacts nature in a negative way