Effects of acid rain. Acids can affect receiving systems in a variety of ways, some good, others bad. Addition of nitrate to ecosystems deficient in nitrogen can lead to enhanced biologic productivity. Toxic effects associated with the release of aluminum and magnesium from clay minerals if the pH of soils falls below about 5.5, however, may offset the benefits. Leaching of metals from soils and sediments also can have adverse effects on aquatic systems. Fish may be killed by aluminum even under conditions where the pH is considered otherwise benign. Given the current rates of acid deposition, the pH of a number of lakes in the northeastern United States and in southeastern Canada is expected to average 4.2 to 4.8, with occasional depressions to near 3.8 during periods of snowmelt or heavy rain. Most fish species and almost all mollusks perish if the pH falls below 4.8; plank tonic communities are simplified in this case, dominated by a few acid-tolerant taxa.
Adverse effects of acid precipitation are most obvious for lakes, and it is not surprising that this aspect of the issue has received the most attention in the press. The effects on the terrestrial biosphere are more ambiguous. It appears that elevated levels of ozone in the troposphere may pose a more serious hazard for plant life even at locations removed from major industrial sites. Effects in this case, for a variety of agronomic and forest species, include foliar injury and significant reduction in growth and yield. In summary, there are deficiencies in current scientific understanding of acid rain, both ...
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Adverse effects of acid precipitation are most obvious for lakes, and it is not surprising that this aspect of the issue has received the most attention in the press. The effects on the terrestrial biosphere are more ambiguous. It appears that elevated levels of ozone in the troposphere may pose a more serious hazard for plant life even at locations removed from major industrial sites. Effects in this case, for a variety of agronomic and forest species, include foliar injury and significant reduction in growth and yield. In summary, there are deficiencies in current scientific understanding of acid rain, both in its atmospheric and biospheric dimensions. Uncertainties can be removed or reduced by a suitably directed research program. It is clear that the chemistry of the troposphere, both polluted and clean, should receive attention in these Climatic effects of polluted air. Less obvious than local concentrations of pollution but potentially more important are the climatic effects of air pollutants. Thus, as a result of the growing worldwide consumption of fossil fuels, atmospheric carbon dioxide levels have increased steadily since 1900, and the rate of increase is accelerating. The output of carbon dioxide is believed by some to have reached a point such that it may exceed both the capacity of plant life to remove it from the atmosphere and the rate at which it goes into solution in the oceans. In the atmosphere carbon dioxide creates a "greenhouse effect." Like glass in a greenhouse, it allows light rays from the Sun to pass through, but it does not allow the escape of the heat rays generated when sunlight is absorbed by the surface of the ground. An increase in carbon dioxide, therefore, can cause an increase in the temperature of the lower atmosphere. If allowed to continue, this could cause melting of the polar ice caps, raising of the sea level, and flooding of the coastal areas of the world. There is every reason to fear that such a climatic change may take place. Counterbalancing the effect of carbon dioxide is the increase of particulate matter in the air, a result of the output of smoke, dust, and other solids associated with human activity. Such an increase might, in turn, increase the reflectance, or albedo, of the atmosphere, causing a higher percentage of solar radiation to be reflected back into space. This, in time, could cause a lowering of the Earth's surface temperature and, potentially, a new ice age. At present, however, the greater danger appears to lie in the steady increase in carbon dioxide, with its associated atmospheric warming. Scientists also fear that the ozonosphere (or ozone layer of the atmosphere) is being depleted by the chemical action of chlorofluorocarbons emitted from aerosol cans and refrigerators and by pollutants from rockets and supersonic aircraft. Depletion of the ozone layer, which absorbs ultraviolet radiation from the Sun, would have serious effects on living organisms on the Earth's surface, including increasing frequency of skin cancer among humans. Another climatic effect of pollution is acid rain. The phenomenon occurs when sulfur dioxide and nitrogen oxides from the burning of fossil fuels combine with water vapour in the atmosphere. The resulting precipitation is damaging to water, forest, and soil resources. It is blamed for the disappearance of fish from many lakes in the Adirondacks, for the widespread death of forests in European mountains, and for damaging tree growth in the United States and Canada. Reports also indicate that it can corrode buildings and be hazardous to human health. Because the contaminants are carried long distances, the sources of acid rain are difficult to pinpoint and hence difficult to control. Acid rain has been reported in areas as far apart as Sweden and Canada, and in parts of the United States from New England to Texas. The drifting of pollutants causing acid rain across international boundaries has created disagreements between Canada and the United States and among European countries over the causes and solutions of the precipitation. The international scope of the problem has led to the signing of international agreements on the limitation of sulfur and nitrogen oxide emissions.effort.
