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Acids from atmospheric pollution may be deposited to the environment through dry deposition (by acidic aerosols or gas-phase acids) or by wet deposition. Wet deposition includes acid rain, acid sleet, acid fog, and acid snow. In poorly buffered watersheds acid precipitation causes acidification. In many areas of the U.S. and Europe, year-round or chronic acidification has eradicated native fish species in lakes and streams (1, 2). Some streams that are not chronically acid may become acidic during the spring spawning season. This acute or episodic acidification (spring shock) can result in a decreased rate of sport fish hatching and reduced viability of the fry that do manage to hatch (3). One reason for the toxicity of acidification is the increased solubility of metals, especially aluminum, at low pH.
Acute acidification during snowmelt or storms is a complex process and may be due to a number of factors. One of these may be early or preferential release of acid impurities during the initial stages of snowmelt. The fact that the first liquid formed is more acidic is related to two-component phase equilibria often studied in introductory chemistry classes and can be demonstrated by a simple experiment using frozen vinegar.
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