Major pools of s are in rocks sediments and oceans as

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amino acids, DNA, and RNA, but is probably never limiting to growth.Major pools of S are in rocks, sediments, and oceans as dissolved sulfate (SO 4 2– ). Weathering of S- containing minerals, such as pyrite, releases soluble forms of S.Volcanic eruptions emit substantial amounts of sulfur dioxide (SO 2 ) into the atmosphere. Bacteria and archaea in anaerobic soils emit sulfur-containing gases such as H 2 S (biogenic emissions). In the atmosphere, S compounds are transformed to SO 4 2– and H 2 SO 4 (sulfuric acid), which are removed quickly by precipitation.Anthropogenic emissions have quadrupled since the Industrial Revolution. Most comes from burning sulfur- containing coal and oil and from smelting. Emissions of N and S have resulted in two related issues: Acid precipitation N deposition .Sites affected by these problems now include national parks and wilderness areas. Sulfuric acid (H 2 SO 4 ) originates from SO 2 , and nitric acid (HNO 3 ) from NO x . These acids fall to Earth with precipitation (wet deposition) or with dust and aerosols (dry deposition).Natural precipitation pH range: 5.0–5.6 Acid precipitation pH range: 5.0–2.0 As H + percolates through soil, it replaces Ca 2+ ,Mg 2+ , and K + at cation exchange sites on clay particles. These cations then leach out of the root zone, and the soil becomes acidic. This decreases nutrient supplies and increases toxic metals. Aluminum (Al 3+ ) is also released to the soil from cation exchange sites.Al is toxic to plants, soil invertebrates, and aquatic organisms. The combination of acid precipitation and Al in runoff has been linked to fish die-offs in in northern Europe and eastern North America. Restrictions on S emissions in North America and Europe have resulted in significant reductions in the acidity of precipitation, and forests are beginning to recover. Acid precipitation remains a problem in some countries with rapid industrial development, such as China and India. Changes in the global C cycle are influencing Earth’s climate.C in the atmosphere occurs primarily as carbon dioxide (CO 2 ) and methane (CH 4 ).Both are greenhouse gases that affect the global
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  • Spring '11
  • DALEGAWLIK

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