|For the past few decades, acid rain has become one of many ecological concerns. Little was known about acid rain until recent. Many studies have been made to determine the chemistry of this ecological problem. The effects of acid rain can be seen in many areas. Below are an examples of just a few.|
Over the years, scientists, foresters, and others have
watched some forests grow more slowly without knowing why. The
trees in these forests do not grow as quickly as usual. Leaves
and needles turn brown and fall off when they should be green
Acid Rain on the Forest Floor
A spring shower in the forest washes leaves and falls through the trees to the forest floor below. Some of the water soaks into the soil. Some trickles over the ground and runs into a stream, river or lake. That soil may neutralize some or all of the acidity of the acid rainwater. This ability of the soil to resist some pH change is called buffering capacity. A buffer resists changes in pH. Without buffering capacity, soil pH would change rapidly. Midwestern states like Nebraska and Indiana have soils that are well buffered. Places in the mountainous northeast, like New York's Adirondack Mountains, have soils that are less able to buffer acids. Since there are many natural sources of acid in forest soils, soils in these areas are more susceptible to effects from acid rain.
How Acid Rain Harms Trees
Acid rain does not usually kill trees directly. Instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. Scientists believe that acidic water dissolves the nutrients and helpful minerals in the soil and then washes them away before the trees and other plants can use them to grow. At the same time, the acid rain causes the release of toxic substances such as aluminum into the soil. These are very harmful to trees and plants, even if contact is limited. Toxic substances also wash away in the runoff that carries the substances into streams, rivers, and lakes. Less of these toxic substances are released when the rainfall is cleaner. Even if the soil is well buffered, there can be damage from acid rain. Forests in high mountain regions receive additional acid from the acidic clouds and fog that often surround them. These clouds and fog are often more acidic than rainfall. When leaves are frequently bathed in this acid fog, their protective waxy coating can wear away. The loss of the coating damages the leaves and creates brown spots. Leaves turn the energy in sunlight into food for growth. This process is called photosynthesis. When leaves are damaged, they cannot produce enough food energy for the tree to remain healthy. Once trees are weak, they can be more easily attacked by diseases or insects that ultimately kill them. Weakened trees may also become injured more easily by cold weather.Acid rain can harm other plants in the same way it harms trees. Food crops are not usually seriously affected, however, because farmers frequently add fertilizers to the soil to replace nutrients washed away. They may also add crushed limestone to the soil. Limestone is a basic material and increases the ability of the soil to act as a buffer against acidity.