Acid Rain And The Aquatic Environment

The earliest concerns over the impact of acid rain on the environment were expressed by Robert Smith, in England, as long ago as 1852 (Park 1987), but modern interest in the problem dates only from the 1960s. Initial attention concentrated on the impact of acid rain on the aquatic environment, which can be particularly sensitive to even moderate increases in acidity, and it was in the lakes and streams on both sides of the Atlantic that the effects were first apparent. Both LaBastille (1981) and Park (1987) credit Svente Oden, a Swedish soil scientist, with bringing the problem to the attention of the scientific community, in a campaign which began in 1963. Both also mention the work of Eville Gorham in the late 1950s, in the English Lake District, and the studies of Gene Likens and Herbert Bormann in New Hampshire, dating back to 1963. Gorham was also one of the first to become involved in the study of acid lakes in Canada, in the area polluted by smelter emissions around Sudbury, Ontario (Gorham and Gordon 1960). From these limited beginnings, the scientific investigation of the problem has grown rapidly. By the mid-1980s, a majority of scientists accepted that a link existed between the emissions of SO2 and NO X and the acidification of lakes. A minority remained unconvinced. Along with politicians in the United States and Britain, they continued to counter requests for emission reductions with calls for more studies (Park 1987), despite an estimate that research over a quarter of a century had resulted in more than 3000 studies in North America alone (Israelson 1987).

There is a tendency for all lakes to become more acidic with time, as a result of natural ageing processes, but studies of acid-sensitive lakes suggest that observed rates of change in pH values since the middle of the nineteenth century have exceeded the expected natural rates. The analysis of acid sensitive diatom species in lake sediments has allowed pH-age profiles to be constructed for some 800 lakes in North America and Europe (Charles et al. 1990). Most of these profiles indicate that lake acidification is a relatively recent phenomenon, with little change in pH values indicated prior to 1850. In almost a century and a half since then, pH values in the lakes studied have decreased by between 0.5 and 1.5 units (see Figure 4.7). In contrast, less sensitive lakes—those with adequate buffering for example—showed little change.

Some of the increased acidity could be explained by changing land use. In the Netherlands, for example, agricultural practices such as sheep washing and the foddering of ducks kept levels of acidity artificially low in the past, but as these activities declined, the acidity of the lakes began to rise again (Charles et al. 1990). In south-west Scotland, reforestation has been accompanied by increasing acidity because the trees have a greater ability than the vegetation they replaced to scavenge acid aerosols from passing air streams (Mason 1990). Such situations seem to be the exception, however, and the general consensus is that declining pH values are the result of increased acidic deposition since the Industrial Revolution. Rising levels of copper, zinc and lead in the lake deposits, plus the

The Basic Survival Guide

The Basic Survival Guide

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