Acid Rain - Effects Of Acid Rain On Our Environment
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In nature, the combination of rain and oxides is part of a natural balance that nourishes plants and aquatic life. However, when the balance is upset, the results to the environment can be harmful and destructive. (See Table 7.1.)
|Human health and ecosystem||Effects||Recovery benefits|
|Human health||In the atmosphere, sulfur dioxide and nitrogen oxides become sulfate and nitrate aerosols, which increase morbidity and mortality from lung disorders, such as asthma and bronchitis, and impacts to the cardiovascular system.||Decrease emergency room visits, hospital admissions, and deaths.|
|Surface waters||Acidic surface waters decrease the survivability of animal life in lakes and streams and in the more severe instances eliminate some or all types of fish and other organisms.||Reduce the acidic levels of surface waters and restore animal life to the more severely damaged lakes and streams.|
|Forests||Acid deposition contributes to forest degradation by impairing trees' growth and increasing their susceptibility to winter injury, insect infestation, and drought. It also causes leaching and depletion of natural nutrients in forest soil.||Reduce stress on trees, thereby reducing the effects of winter injury, insect infestation, and drought, and reduce the leaching of soil nutrients, thereby improving overall forest health.|
|Materials||Acid deposition contributes to the corrosion and deterioration of buildings, cultural objects, and cars, which decreases their value and increases costs of correcting and repairing damage.||Reduce the damage to buildings, cultural objects, and cars, and reduce the costs of correcting and repairing future damage.|
|Visibility||In the atmosphere, sulfur dioxide and nitrogen oxides form sulfate and nitrate particles, which impair visibility and affect the enjoyment of national parks and other scenic views.||Extend the distance and increase the clarity at which scenery can be viewed, thus reducing limited and hazy scenes and increasing the enjoyment of national parks and other vistas.|
|SOURCE: "Appendix I: Effect of Acid Rain on Human Health and Selected Ecosystems and Anticipated Recovery Benefits," in Acid Rain: Emissions Trends and Effects in the Eastern United States, U.S. General Accounting Office, Washington, DC, March 2000|
Although pH levels vary considerably from one body of water to another, a typical pH range for the lakes and rivers in the United States is six to eight.
Low pH levels kill fish eggs, frog eggs, and fish food organisms. The degree of damage depends on several factors, one of which is the buffering capacity of the watershed soil—the higher the alkalinity, the more slowly the lakes and streams acidify. The exposure of fish to acidified freshwater lakes and streams has been intensely studied since the 1970s. Scientists distinguish between sudden shocks and chronic (long-term) exposure to low pH levels.
Sudden, short-term shifts in pH levels result from snowmelts, which release acidic materials accumulated during the winter, or sudden rainstorms that can wash residual acid into streams and lakes. The resulting acid shock can be devastating to fish and their ecosystems. At pH levels below 4.9, damage occurs to fish eggs. At acid levels below 4.5, some species of fish die. Below pH 3.5, most fish die within hours. (See Table 7.2.)
Mountainous streams in New York, North Carolina, Pennsylvania, Tennessee, and Arkansas have shown an acidity during rainstorms and snowmelts of three to 20 times that experienced during the rest of the year. Because many species of fish hatch in the spring, even mild increases in acidity can harm or kill the new life. Temporary increases in acidity also affect insects and other invertebrates, such as snails and crayfish, on which the fish feed.
Gradual decreases of pH levels over time affect fish reproduction and spawning. Moderate levels of acidity in water can confuse a salmon's sense of smell, which it uses to find the stream from which it came. Atlantic salmon are unable to find their home streams and rivers because of acid rain. In addition, excessive acid levels in female fish cause low amounts of calcium, thereby preventing the production of eggs. Even if eggs are produced, their development is often abnormal. Over time the fish population decreases while the remaining fish population becomes older and larger.
Increased acidity can also cause the release of aluminum and manganese particles stored in a lake or river bottom. High concentrations of these metals are toxic to fish.
In 1988 the Environmental Defense Fund (EDF), an environmental watch group, sounded one of the first alarms that the coastal waters of the eastern United States were receiving large inputs of nitrogen. The nitrogen led to an excessive growth of algae on the surface of the water. This in turn resulted in the loss of oxygen and light to the water and the long-term decline of marine life. The EDF concluded that the major sources of the nitrogen were human activities—the runoff of fertilizer, animal waste from farms, and discharge from sewage treatment plants and industrial facilities. Researchers noted that the significant decline of the Chesapeake Bay and other estuaries could also be attributed to the increase in NO5 from automobiles and electric power plants, along with toxic chemicals, pesticides, and wetland destruction.
|6.0–6.4||Unlikely to be harmful except when carbon dioxide levels are very high (1000 mg I 1)|
|5.0–5.9||Not especially harmful except when carbon dioxide levels are high (20 mg I 1) or ferric ions are present|
|4.5–4.9||Harmful to the eggs of salmon and trout species (salmonids) and to adult fish when levels of Ca2, Na and Cl are low|
|4.0–4.4||Harmful to adult fish of many types which have not been progressively acclimated to low pH|
|3.5–3.9||Lethal to salmonids, although acclimated roach can survive for longer|
|3.0–3.4||Most fish are killed within hours at these levels|
|SOURCE: "Generalized Short-Term Effects of Acidity on Fish," in National Water Quality Inventory: 1998 Report to Congress, U.S. Environmental Protection Agency, Washington, DC, June 2000|
During the 1990s acidic and polluted waters caused the disappearance of many aquatic species, leaving gaping holes in the food chain and diminishing the biological balance and diversity that keeps Earth genetically healthy. According to the American Fisheries Society and the Environmental Protection Agency (EPA), many species of freshwater fish have become extinct since the late 1970s, and additional species have become endangered, threatened, or listed as "of special concern" for their ultimate survival.
Soil and Vegetation
Acid rain is believed to harm vegetation by changing soil chemistry. Soils exposed to acid rain can gradually lose valuable nutrients, such as calcium, magnesium, and potassium, and become too concentrated with dissolved inorganic aluminum, which is toxic to vegetation. Long-term changes in soil chemistry may have already affected sensitive soils, particularly in forests. Forest soils saturated in nitrogen cannot retain other nutrients required for healthy vegetation. Subsequently, these nutrients are washed away. The EPA reports that nitrogen saturation has already been found in a number of regions, including northeastern forests, the Colorado Front Range, and mountain ranges near Los Angeles, California. The same effects have been reported in Canada and Europe. Nutrient-poor trees are more vulnerable to climatic extremes, pest invasion, and the effects of other air pollutants, such as ozone.
Some researchers believe that acid rain disrupts soil regeneration, which is the recycling of chemical and mineral nutrients through plants and animals back to the Earth. They also believe acids suppress decay of organic matter, a natural process needed to enrich the soils. Valuable nutrients like calcium and magnesium are normally bound to soil particles and are, therefore, protected from being rapidly washed into groundwater. Acid rain, however, may accelerate the process of breaking these bonds to rob the soil of these nutrients. This, in turn, decreases plant uptake of vital nutrients. (See Figure 7.4.)
Acid deposition can cause leafy plants such as lettuce to hold increased amounts of potentially toxic substances like the mineral cadmium. Research has also found a decrease in carbohydrate production in the photosynthesis process of some plants exposed to acid conditions. Research is underway to determine whether acid rain could ultimately lead to a permanent reduction in tree growth, food crop production, and soil quality. Effects on soils, forests, and crops are difficult to measure because of the numerous species of plants and animals, the slow rate at which ecological changes occur, and the complex interrelationships between plants and their environment.
The effect of acid rain on trees is influenced by many factors. Some trees adapt to environmental stress better than others; the type of tree, its height, and its leaf structure (deciduous or evergreen) influence how well it will adapt to acid rain. Acid rain may affect trees in at least two ways: in areas with high evaporation rates, acids will concentrate on leaf surfaces; in regions where a dense leaf canopy does not exist, more acid may seep into the Earth to affect the soil around the tree's roots.
Scientists believe that acid rain directly harms trees by leaching calcium from their foliage and indirectly harms them by lowering their tolerance to other stresses. Trees are exposed to many natural threats, including drought, ice storms, invasive species, and forest fires. These stresses, combined with increased air and water pollution, can prove too much for sensitive tree species.
A 1994 joint report of the European Commission and the UNECE surveyed 102,300 trees at 26,000 sampling plots in 35 European countries and found that almost one-quarter of the trees in Europe were defoliated by more than 25 percent. The report showed that forest damage is a problem in virtually all European countries. The most severely affected country was the Czech Republic, where 53 percent of all trees had suffered moderate or severe defoliation or died. The least affected was Portugal, where 7.3 percent of trees were damaged.
In 1998 the National Acid Precipitation Assessment Program (NAPAP) identified forest ecosystems in the United States that are most at risk to acid rain damage due to natural sensitivity and high acid deposition rates. (See Figure 7.5.) The EPA blames acid deposition, along with other pollutants and natural stress factors, for increased death and decline of northeastern red spruce at high elevations (for example, in the Adirondacks) and decreased growth of red spruce in the southern Appalachians. Acid rain is also closely linked to the decline of sugar maple trees in Pennsylvania.
In Soil Calcium Depletion Linked to Acid Rain and Forest Growth in the Eastern United States, the USGS reported in March 1999 that calcium levels in forest soils had declined at locations in ten states in the eastern United States. Calcium is necessary to neutralize acid rain and is an essential nutrient for tree growth. Sugar maple and red spruce trees, in particular, showed reduced resistance to stresses such as insect defoliation and low winter temperatures. Although the specific relationships among calcium availability, acid rain, and forest growth are uncertain, Gregory Lawrence, a scientist and coauthor of the report, speculated: "Acid rain releases aluminum from the underlying mineral soil layer.… The result is that aluminum replaces calcium, and the trees have a harder time trying to get the needed calcium from the soil layer."
In 2001 the Hubbard Brook Research Foundation reported that more than half of large-canopy red spruce trees in the Adirondack Mountains and the Green Mountains had died since the 1960s. Acid rain was considered the primary cause.
According to the EPA, acid rain has also been implicated in impairing the winter hardening process of some trees, making them more susceptible to cold-weather damage. In some trees, the roots are prone to damage because the movement of acidic rain through the soil releases aluminum ions, which are toxic to plants.
One area in which acid rain has been linked to direct effects on trees is from moist deposition via acidic fogs and clouds. The concentrations of acid and SO5 in fog droplets are much greater than in rainfall. In areas of frequent fog, such as London, significant damage has occurred to trees and other vegetation because the fog condenses directly on the leaves.
The Forest Health Monitoring Program is a joint effort supported by the U.S. Department of Agriculture (USDA) and private and academic entities. The program monitored precipitation pH and the deposition of SO5, nitrate, ammonium, and total nitrogen in U.S. forests from 1979 to 1995. It estimates that nearly half of forest area in the North and just over 20 percent of forest area in the South are covered by relatively high SO5 deposition. Northern forests were much more exposed to nitrate deposition (40 percent) than were southern forests (less than 1 percent). High ammonium deposition was a problem for more than 62 percent of forests in the North, but less than 20 percent of forests in the South.
Increased freshwater acidity harms some species of migratory birds. Experts believe the dramatic decline of the North American black duck population since the 1950s is due to decreased food supplies in the acidified wetlands. The U.S. Fish and Wildlife Service reports that ducklings in wetlands created by humans in Maryland are three times more likely to die before adulthood if raised in acidic waters.
Acid rain leaches calcium out of the soil and robs snails of the calcium they need to form shells. Because tit-mice and other species of songbirds get most of their calcium from the shells of snails, the birds are also perishing. The eggs they lay are defective—thin and fragile. The chicks either do not hatch or have bone malformations and die.
In 2002 researchers at Cornell University released the results of a large-scale study showing a clear link between acid rain and widespread population declines in a song-bird called the wood thrush. The scientists believe that calcium depletion has had a negative impact on the birds' food source, mainly snails, earthworms, and centipedes. The birds may also be ingesting high levels of metals that are more likely to leach out of overly acidic soils. Declining wood thrush populations were most pronounced in the higher elevations of the Adirondack, Great Smoky, and Appalachian mountains. The researchers warned that acid rain may also be contributing to population declines in other songbird species.
Investigations into the effects of acid rain on objects such as stone buildings, marble statues, metals, and paints only began in the 1990s. A joint study conducted by the EPA, the Brookhaven National Laboratory, and the Army Corps of Engineers in 1993 found that acid rain was causing $5 billion worth of damage annually in a 17-state region. Two-thirds of the damage was created by pollution whose source was less than 30 miles away. Many of the country's historical monuments and buildings are located in eastern states that have been most hard-hit by acid rain.
Acid rain is suspected, in part, of damaging the Statue of Liberty and the Egyptian pyramids. Examination of the 700-year-old, 37-foot-tall bronze Great Buddha of Kamakura, an important symbol of Japanese culture, shows pock marks and rust stains, the result of acid rain.
New kinds of protective chemicals that adhere to limestone and marble are helping to save some of the world's decomposing monuments from acid rain and other pollutants. These chemicals, called consolidants, were developed in the 1960s in response to widespread water damage to stone buildings in Venice. Among the monuments getting close attention are the Taj Mahal in India; the Parthenon in Athens, Greece; the Lincoln Memorial in Washington, D.C.; and the Alamo in Texas. Experts report, however, that these chemicals have many limitations. They are toxic and difficult to apply, and their effects are only temporary, yet they permanently alter the nature of the stone. Most important is that their long-term effects are uncertain. For those reasons their use was banned on the Acropolis in Athens, Greece.
Reports of damage to automotive coverings have been increasing. The general consensus within the automobile industry is that the damage is caused by some form of "environmental fallout"—the term used in the automobile industry. Automakers suspect acid rain damage to automobile paint, especially to many newer models that have clear protective overcoats. Chemical analyses of the damaged areas of some car finishes have showed elevated levels of SO5, implicating acid rain.
The auto industry began using clear-coat finishes in the mid-1980s. Although the new high-gloss paints look better, complaints are mounting over marred surfaces, especially on dark-or metallic-colored cars in the northeastern and southeastern United States. Automakers believe that when acid rain falls on autos the moisture evaporates, leaving a permanent blemish caused by sulfuric acid and nitric acid—the composition of acid rain. Some car dealers now offer optional protective sealants at added expense to buyers. Higher-priced cars often include protective sealants in the purchase price.
Acid rain has several direct and indirect effects on human health. Particulates are extremely small pollutant particles that can threaten human health. Particulates related to acid rain include fine particles of SO5 and nitrates. These particles can travel long distances and, when inhaled, penetrate deep into the lungs. Studies of death rates across the United States, such as that reported in "Lung Cancer, Cardiopulmonary Mortality, and Long-Term Exposure to Fine Particulate Air Pollution" (Journal of the American Medical Association, March 6, 2002), have found some correlation between elevated mortality levels and high SO5 levels. Acid rain and the pollutants that cause it can lead to the development of bronchitis and asthma in children. Acid rain is also believed to be responsible for increasing health risks to those over the age of 65; those with asthma, chronic bronchitis, and emphysema; pregnant women; and those with histories of heart disease.