Page 187 - Fundamentals of Air Pollution

References 153

northeastern United States and eastern Canada is quite varied, but much
of the area is covered with thin soils with a relatively limited neutralizing
capacity. In watersheds with this type of soil, lakes and streams are suscepti-
ble to low pH and elevated levels of aluminum. This combination has been
found to be very toxic to some species of fish. When the pH drops to ~5,
many species of fish are no longer to reproduce and survive. In Sweden,
thousands of lakes are no longer able to support fish. In the United States
the number of polluted lakes is much smaller, but many more may be
pushed into that condition by continued acidic deposition. In Canada,
damage to aquatic systems and forest ecosystems is a matter of considerable
concern.
Aquatic systems in areas of large snowfall accumulation are subjected to
a pH surge during the spring thaw. Acidic deposition is immobilized in
the snowpack, and when warm springtime temperatures cause melting,
the melted snow flows into streams and lakes, potentially overloading the
buffering capacity of the aquatic system.
A second area of concern is reduced tree growth in forests. As acidic
deposition moves through forest soil, the leaching process removes nutri-
ents. If the soil base is thin or contains barely adequate amounts of nutrients
to support a particular mix of species, the continued loss of a portion of
the soil minerals may cause a reduction in future tree growth rates or a
change in the types of trees able to survive in a given location.

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8. Charlson, R. J., Waggoner, A. P., and Thielke, H. F., "Visibility Protection for Class I
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