Forests, acid rain

In actual "damage to forest" ("acid rain"- probiems) investigations, the main matrices which must be anaiyzed are needles, leaves, pieces of wood, roots and soil. The elements Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V, and Zn can be determined routinely in such samples by ICP/DCP-spectrometry (Table 9). The concentrations of the heavy metals Cd, Pb, Hg, As and others are in most cases too low (exception soil, for these analytical techniques). A similar picture can be obtained for the field of bioindicators for environmental influences (plants, animals, organs of man) (Schramel et al., 1984 Wolf et al., 1984) (Table 10). In case of soils and sludges, in most the samples one can obtain all relevant elements, such as the legally regulated heavy metals Cd, Pb, Zn, Cu, Ni, and Cr (Table 11,12) (Schramel et al., 1982). 

Acid deposition occurs when sulfur dioxide and nitrogen oxide emissions are transformed in the atmosphere and return to the earth in rain, fog or snow. Approximately 20 million tons of SOj are emitted annually in the United States, mostly from the burning of fossil fuels by electric utilities. Acid rain damages lakes, harms forests and buildings, contributes to reduced visibility, and is suspected of damaging health. 

Acid precipitation, or acid rain, can causes significant impacts on freshwater, coastal, and forested ecosystems (e.g.. Likens et ai, 1996). Both NOi", from NO emissions, and SO from SO2 emissions contribute significantly to acid rain. The relative ratio of SO /NOf in precipitation will be substantially determined by the regional emissions of SO2/NO3. In developed countries, uncontrolled combustion of coal and high-sulfur fuel oil led to significant emissions of SO2, relative to NO Due to strict control of smokestack SO2 emissions in some regions and increasing NO emissions from automobiles, the relative contribution of NOi is expected to increase (Sirois, 1993 Mayewski et ai, 1990). 

Likens, G.E., Driscoll, C. T. and Buso, D. C. (1996). Long-term effects of acid rain response and recovery of a forest ecosystem. Science 272, 244—246. 

The low pH of acid precipitation can destroy forests and kill fish. Some lakes and streams lie in soil that has the natural ability to buffer the increased acidity of acid rain, usually because the soil contains a high amount of lime. Other lakes and streams, however, have no such buffering capacity. The pH of the water is not the main problem—at least not directly. The problem lies in the amount of aluminum compounds that are leached out of the soil surrounding the lake or stream at lower pHs. Aluminum is toxic to many aquatic species. 

At one point it was assumed that the earth, its oceans and rivers, and its atmosphere were so vast or self-cleansing that we could discharge anything into them without damage to our planet. We now know this is not true. Currently, we must deal with toxic waste dumps, with smog, with acid rain that kills forests, and with pollution of rivers and the ocean by chemical discharges. How did this happen ... 

Small amounts of some contaminants can be serious. When we burn coal, not only do we produce carbon dioxide, the major product, but we can liberate small amounts of mercury and larger amounts of sulfur dioxide. The mercury can form toxins that harm fish as well as humans, while sulfur dioxide can produce acid rain that destroys forests and water supplies. How can these contaminants be most effectively removed or dealt with And how can we generate the energy that we need without releasing such by-products ... 

Prolonged exposure to acid rain causes forest soils to lose valuable nutrients. It also increases the concentration of aluminum in the soil, which interferes with the uptake of nutrients by the trees. Lack of nutrients causes trees to grow more slowly or to stop growing altogether. More visible damage, such as defoliation, may show up later. Trees exposed to acid rain may also have more difficulty withstanding other stresses, such as drought, disease, insect pests and cold weather. 

In addition to the damage acid rain causes to structures, acid rain also affects natural environments. Significant loss of spruce forests due to the burning of spruce needles by acid rain has occurred in Scandinavia. Acid rain also extracts a heavy toll on aquatic systems and associated organisms. Most adult fish cannot tolerate pHs much lower than 5.0, and even the most tolerant species will not survive below a pH of 4.0. Fish larvae are even more susceptible to low pH levels. Insects and their larvae also perish when pH approaches 4.0 in aquatic systems. Numerous lakes in upstate New... 

The effects of acid rain can be seen in lakes and streams, in forests, and on all kinds of structures. The lowered pH kills fish eggs, fish, and many other organisms that live in lakes and streams. In forests, the acid can kill the leaves and needles of trees. It damages the soil by depleting it of nutrients, which stunts plant growth. Acid rain also eats away at the surfaces of buildings and other structures. Structures made of marble and other calcium-containing stone are particularly sensitive to acid rain. 

Beneficial and Harmful Effects. At low levels, sulfur dioxide in the atmosphere is not harmful to crops, but damage can occur at excessive levels (305—309). Crops differ gready in their sensitivity. Forest damage attributed to acid rain is often cited but the observed symptoms seem to have multiple causes and the contribution of sulfur acids is unspecified. The sulfur in precipitation is, up to a point, beneficial to plant growth because sulfur is an essential nutrient. Lessening the sulfur content of the atmosphere requires that supplementary sulfur be provided in fertilizer to some crops some crops already require supplementary sulfur. Sulfur dioxide itself has been found useful in drip irrigation systems (310,311) and in calcareous soils (308). Small field generators have been developed for this purpose. 

Acid rain threatens lakes and forests throughout the world. Monitoring the pH of rainwater is a critical component of programs to measure and reduce the production of acid rain. 

The two photographs in (a) show the same obelisk before and after the effects of acid rain, (b) Many forests downwind from heavily industrialized areas, such as in the northeastern United States and in Europe, have been noticeably hard-hit by acid rain. 

The toxicity of aluminum has been recognized most clearly by the development of bone disease caused by deposition of A1 in bones of patients on hemodialysis and in infants on intravenous therapy/ 6 Excessive A1 in the water used for dialysis may also cause brain damage. Dietary aluminum may be one cause of Alzheimer s disease/ h but this is controversial as is a possible role of aluminum in vaccines in causing inflammation in muscle.1) Solubilization of soil aluminum by acid rain has been blamed for the decline of forests in Europe and North America,) for the death of fish in acid waters,k and for very large reductions in yield for many crops/ An aluminum-resistant strain of buckwheat makes and secretes from its roots large amounts of oxalate which binds and detoxifies the Al3+ ions. ... 

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