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<blurb target="industry" width="550">
<short><![CDATA[Numerous industrial processes involve mining sulfur compounds from the Earth's crust and /or releasing sulfur compounds into the atmosphere. The single largest human input to the atmosphere is sulfur dioxide (SO2) from power plants that burn sulfur-containing coal. Human inputs to the atmosphere exceed all natural inputs combined.]]></short> </blurb>

<blurb target="atm" width="550"><short><![CDATA[Natural sources of sulfur in the atmosphere include volcanoes, evaporation, and bacterial processes of decay. Unlike carbon and nitrogen, atmospheric sulfur does not have to be “fixed” or transformed by bacteria in order to be useful to other organisms.]]></short></blurb>

<blurb target="deposition" width="420"><short><![CDATA[In the atmosphere, sulfur dioxide reacts with oxygen and water vapor to form sulfuric acid (H2SO4), which falls back to Earth as acid precipitation. Acid precipitation can lower the pH of soils, lakes, and streams, harming their inhabitants. It also increases the rate of weathering of rocks and human structures.]]></short></blurb>

<blurb target="waste" width="420"><short><![CDATA[Runoff from sewage treatment and industrial sites may contain a variety of sulfur compounds. Organic molecules containing sulfur can be “desulfurated” by many kinds of bacteria, producing hydrogen sulfide gas (H2S). The presence of organic matter in aquatic environments also speeds up sulfate reduction, another bacteria-mediated reaction with H2S as an end product.]]></short></blurb>

<blurb target="ocean" width="420"><short><![CDATA[The oceans constitute the biggest reservoir of sulfur available to organisms. The most common form is sulfate (SO42-). Sulfur oxidizing bacteria produce sulfate from sulfide (HS-) or elemental sulfur (S) in the presence of oxygen. In the deep ocean environment around hydrothermal vents, some specialized bacteria and archaea use elemental sulfur or sulfate in a form of respiration that doesn’t require oxygen.]]></short></blurb>

<blurb target="sediment" width="460"><short><![CDATA[Sulfur in aquatic environments eventually makes its way to the sediments, where dead organisms, organic wastes, and minerals eroded from land are deposited. In anaerobic sediments (without oxygen), bacteria reduce sulfate to sulfide, which is toxic to many organisms. When such sediments are stirred up by activities such as dredging, the released sulfide can kill fish and other aquatic life.]]></short></blurb>

<blurb target="fertilizer" width="420"><short><![CDATA[Many amino acids, the building blocks of proteins, contain small amounts of sulfur. Thus sulfur is a component of animal wastes that result from the breakdown of proteins and is also found in manure-based fertilizers. Plants take up only some of the sulfur in fertilizers. The rest is washed away in runoff or enters the atmosphere through gasification.]]></short></blurb>

<blurb target="gas" width="420"><short><![CDATA[Many microorganisms produce hydrogen sulfide gas (H2S) as the end product of their sulfur use. Whether this occurs in water-logged soils, spoiled food, hot springs, or your intestines, you can recognize this end product by its unpleasant odor. To other microbes, H2S is not an end product, but a starting point for sulfur oxidation to sulfate.]]></short></blurb>

<blurb target="erosion" width="420"><short><![CDATA[Most sulfur on Earth is bound up in minerals, primarily gypsum (CaSO4) and pyrite (FeS2). Over vast geological time scales, aquatic sediments become rocks which are lifted into landforms and eroded away again by the processes of weathering and erosion. Human activities may affect the latter steps: acid precipitation can increase the rate of weathering, while deforestation, development, and other land use practices can increase erosion.]]></short></blurb>

<blurb target="bird" width="420"><short><![CDATA[Sulfur that is incorporated into the bodies of animals and plants becomes available to the environment again either through the waste products deposited by the organism or through microbial decay processes after its death.]]></short></blurb>



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