Soils

Soil is the basis of wealth upon which all land-based life depends. Acid deposition is known to wash essential nutrients from soils, and aluminium which is normally bound in the soil may be released into ground water. Soil acidification may affect the health of trees and other vegetation.

Soils containing calcium and limestone are more able to neutralise sulphuric and nitric acid depositions than a thin layer of sand or gravel with a granite base. If the soil is rich in limestone or if the underlying bedrock is either composed of limestone or marble, then the acid rain may be neutralised. This is because limestone and marble are more alkaline (basic) and produce a higher pH when dissolved in water. The higher pH of these materials dissolved in water offsets or buffers the acidity of the rainwater producing a more neutral pH.

In regions where the soil is not rich in limestone or if the bedrock is not composed of limestone or marble, then no neutralising effect takes place, and the acid rainwater accumulates in the bodies of water in the area. This applies to much of the northeastern United States where the bedrock is typically composed of granite. Granite has no neutralising effect on acid rainwater. Therefore, over time, more and more acid precipitation accumulates in lakes and ponds. Such areas or catchments are termed acid-sensitive (poorly buffered), and can suffer serious ecological damage due to acid rain.

To grow, trees and other vegetation need healthy soil to develop in. Long-term changes in the chemistry of some sensitive soils occur as a result of acid rain. As acid rain moves through the soils, it can strip away vital plant nutrients such as calcium, potassium and magnesium through chemical reactions, thus posing a potential threat to future forest productivity. Furthermore, the number of microorganisms present in the soil also decreases as the soil becomes more acidic. This further depletes the amount of nutrients available to plant life because the microorganisms play an important role in releasing nutrients from decaying organic material. Trees growing in acidified soil are more susceptible to viruses, fungi and insect pests. Other plant life may grow more slowly or die as a result of soil acidification.

Poisonous metals such as aluminium, cadmium and mercury are leached from soils through reacting with acids. This happens because these metals are bound to the soil under normal conditions, but the added dissolving action of acids causes rocks and small-bound soil particles to break down. In addition, the roots of plants trying to survive in acidic soil may be damaged directly by the acids present. Finally, if the plant life does not die from these effects, then it may be weakened enough so that it will be more susceptible to other harsh environmental influences like cold winters or high winds.