Environmental Problems, Their Causes, and Sustainability 1

Potential problem areasbecause of sensitive soilsPotential problem areas because of air pollution:emissions leading to acid depositionCurrent problem areas(including lakes and rivers)Figure 20-10 Natural capital degradation: regions where acid deposition is now a problem (red) and regionswith the potential to develop this problem (yellow and green). Such regions have large inputs of air pollution(mostly from power plants, industrial plants, and ore smelters) or are sensitive areas with soils and bedrock thatcannot neutralize (buffer) inputs of acidic compounds (green areas and most red areas). (World ResourcesInstitute and U.S. Environmental Protection Agency)are especially susceptible because they dissolve evenin weak acid solutions. Large amounts of money arespent each year to clean and repair monuments andbuildings that have been attacked by acid deposition.Acid deposition also decreases atmospheric visibility,mostly because of the sulfate particles it contains.For most aquatic systems, acid deposition hasharmful effects when the pH falls below 6 and especiallybelow 4.5, which kills most fish. Another effect isthe release into lakes of aluminum ions (Al 3 ) attachedto minerals in nearby soil. These ions asphyxiate manykinds of fish by stimulating excessive mucus formation,which clogs their gills.Lakes vary in their sensitivity to inputs of acids.Those on sand or igneous rocks, such as granite, generallyhave little buffering capacity to neutralize acidsand thus are more susceptible to acidification. Much ofthe damage to aquatic life in such sensitive areas is aresult of acid shock. This is caused by the sudden runoffof large amounts of highly acidic water and aluminumions into lakes and streams when snow melts in thespring or after unusually heavy rains.Because of excess acidity, several thousand lakes inNorway and Sweden contain no fish, and many morelakes there have lost most of their acid-neutralizing capacity.In Canada, at least 1,200 acidified lakes containfew if any fish, and some fish populations in manythousands of other lakes are declining because of increasedacidity. In the United States, several hundredlakes (most in the Northeast) are threatened with excessacidity.Acid deposition is not always the main culprit.Some lakes are acidic because they are surrounded bynaturally acidic soils.What Are the Effects of Acid Depositionon Plants and Soils? Depleting Nutrientsand Damaging and Weakening PlantsAcid deposition can deplete some soil nutrients,release toxic ions into the soil, and weaken plantsso they become more susceptible to other stresses.Acid deposition (often along with other air pollutantssuch as ozone) can harm forests and crops, especially446 CHAPTER 20 Air Pollution