Acid Rain - Atmospheric Deposition, Chemistry Of Precipitation, Spatial Patterns Of Acidic Precipitation, Dry Deposition Of Acidifying Substances
environmental causes reductions
"Acid rain" is a popularly used phrase that refers to the deposition of acidifying substances from the atmosphere and the environmental damage that this causes. Acid rain became a prominent issue around 1970, and since then research has demonstrated that the deposition of atmospheric chemicals is causing widespread acidification of lakes and streams, and possibly soil. The resulting biological effects include the extirpation (or local extinction) of many populations of fish. Scientific understanding of the causes and consequences of acid rain, in conjunction with lobbying of government by environmental organizations, has resulted in large reductions in the atmospheric emissions of pollutants in North America and parts of Europe. If these reductions prove to be large enough, acid rain will be less of an environmental problem in those regions.
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Strictly speaking, the term "acid rain" should only refer to rainfall, or so-called wet precipitation. However, the proper meaning of acid rain is "the deposition of acidifying substances from the atmosphere." This is because acidification is not just caused by acidic rain, but also by chemicals in snow and fog, and by inputs of gases and particulates when precipitation…
Large regions are affected by acidic precipitation in North America, Europe, and elsewhere. A relatively small region of eastern North America is known to have experienced acidic precipitation before 1955, but this has since expanded so that most of the eastern United States and southeastern Canada is now affected. …
Because they have such a large surface area of foliage and bark, forests are especially effective at absorbing atmospheric gases and particles. Consequently, dry inputs accounted for about 33% of the total sulfur deposition to a hardwood forest in New Hampshire, 56-63% of the inputs of S and N to a hardwood forest in Tennessee, and 55% of their inputs to a conifer forest in Sweden. …
Soil acidification can occur naturally. This fact can be illustrated by studies of ecological succession on newly exposed parent materials of soil. At Glacier Bay, Alaska, the melting of glaciers exposes a mineral substrate with a pH of about 8.0, with up to 7-10% carbonate minerals. As this material is colonized and modified by vegetation and climate, its acidity increases, reaching about pH 4.8 …
Compared with the water of precipitation, that of lakes, ponds, streams, and rivers is relatively concentrated in ions, especially in calcium, magnesium, potassium, sodium, sulfate, and chloride. These chemicals have been mobilized from the terrestrial part of the watersheds of the surface waters. In addition, some surface waters are brown-colored because of their high concentrations of dissolved …
Few studies have demonstrated injury to terrestrial plants caused by an exposure to ambient acid rain. Although many experiments have demonstrated injury to plants after treatment with artificial "acid rain" solutions, the toxic thresholds are usually at substantially more acidic pHs than normally occur in nature. For example, some Norwegian experiments involved the treating of young…
The community of microscopic algae (or phytoplankton) of lakes is quite diverse in species. Non-acidic, oligotrophic (i.e., unproductive) lakes in a temperate climate are usually dominated by golden-brown algae and diatoms, while acidic lakes are typically dominated by dinoflagellates, cryptomonads, and green algae. An important experiment was performed in a remote lake in Ontario, in which sulfur…
Although liming rapidly decreases the acidity of a lake, the water later re-acidifies at a rate determined by size of the drainage basin, the rate of flushing of the lake, and continued atmospheric inputs. Therefore, small headwater lakes have to be re-limed more frequently. In addition, liming initially stresses the acid-adapted biota of the lake, causing changes in species dominance until a new,…
In spite of many uncertainties about the causes and magnitudes of the damage associated with acid rain and related atmospheric depositions, it is intuitively clear that what goes up (that is, the acid-precursor gases) must come down (as acidifying depositions). This common-sense notion is supported by a great deal of scientific evidence, and because of public awareness and concerns about acid rain…
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