How Does Acid Rain Affect Plants & Trees?

Written by alicia rudnicki
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How Does Acid Rain Affect Plants & Trees?
Acid rain pollutes water as well as forest foliage and soil. (forest image by Einar Bog from

Acid rain can kill forests, by weakening their trees and plants. It does this by injuring foliage and affecting the chemical composition of the soil so that trees and plants can't obtain the nutrients they need. Further damage occurs when acid rain increases the levels of substances in the soil that are toxic to trees and plants, such as aluminium.

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Composition of Acid Rain

Acid rain is defined as precipitation --- including rain, fog and snow --- that has high levels of nitric and sulphuric acids. The term also encompasses dry particulate that lands on the ground and which contains these pollutants. National Geographic notes that rotting vegetation and volcanic eruptions release some chemicals that cause the problem, but the biggest contribution comes from human activities involving the burning of fossil fuels. Auto exhaust and emissions from coal power plants and factories release nitrogen oxide and sulphur dioxide into the air, which turn into acids when they combine with water. Wind can carry acid rain for hundreds of miles.

Damage to Soil

Soil that is polluted by acid rain loses nutrients, such as calcium, potassium and magnesium. This is further worsened by the acids causing aluminium to move more freely through the soil, damaging roots and limiting the uptake of nutrients.

Increased soil acidity also makes it more difficult for seeds to germinate and for beneficial soil microorganisms to survive. The result is stunted growth of existing trees and plants as well as inhibition of new growth, according to the Physical Geography website. It adds that trees and plants then become "more vulnerable to diseases, insects, droughts and frosts."

Buffering and Acid Fog

The U.S. Environmental Protection Agency (EPA) says that some forests are less damaged by acid rain, because they possess "buffered" soil that resists changes in pH and other chemical problems caused by acid rain. Elements of buffering include soil composition and thickness as well as the underlying type of bedrock. EPA notes that while the Midwest has well-buffered soil, the Northeast does not. But even if a high altitude forest has well-buffered soil, the EPA says, it suffers if exposed to acid fog or cloud water, which damages foliage.

Physical Geography says that acid fog and acid clouds are 10 times worse for forests than acid rainfall. It also notes that "95 per cent of the elevated levels of nitrogen oxides in the atmosphere are the result of human activities."

Prevention Through Conservation

Conservation of energy is one of the main ways in which individuals can decrease acid rain, according to National Geographic. When less electricity is used at home, power plants emit less pollutants. Also, by cutting back on auto travel, consumers can decrease emissions of nitrogen oxide and sulphur dioxide.

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