Acid rain is detrimental for plants, animals, building, and objects alike. It reduces soil fertility and causes long-term damage to aquatic ecosystems, forests, crops, and all other vegetation. Acid rain contributes to stunted plant growth. In leaves, it causes photosynthesis suppression and tissue damage. It even inhibits seed germination.
What is Acid Rain?
Acid rain refers to any precipitation that has a lower pH value than normal rain water. All rain is naturally acidic to some extent because of the formation of carbonic acid by the combination of carbon dioxide with water. Any rain water with a pH of less than 4.6 is considered acidic. Acid can also occur naturally in the form of snow, sleet, hail, dew, frost or fog. The main contributors for this acidity are fossil fuels such as coal or petroleum that create sulphur dioxide and nitrogen oxides when burnt. They form sulphuric and nitric acid that dissolve in water droplets,and later fall as acid rain.
Inhibition of Seed Germination
In an experiment conducted by John G. McColl and Robert Johnson, it was found that at pH levels of 2.0 and less, the percentage of successful germination of plants like Douglas fir and Ponderosa pine was reduced by 30 per cent, and those that managed to germinate eventually died after fungal attacks. Additionally, sulphuric and nitric acid at pH levels of 2.0 were sprayed for 12 weeks at seedlings that were less than two years old and planted in native granitic soil. In such plants, the needles developed acid burns and brown tips, and over time, the seedlings wilted and died.
Reduction of Nutrients
Acid rain leads to the leeching of plant nutrients like calcium, magnesium and potassium from the soil because of the hydrogen ions present in it. This is a setback for the health and growth of plant life. It also mobilises the aluminium ions present in aluminium hydroxide, which directly affects the growth of roots and reduces the uptake of calcium. Low pH levels in plant moisture can harm the microbe populace essential for the decomposition of organic matter in the soil. It is the source of plant nutrients like phosphates and nitrates.
Increase in Toxins
Acid rain enhances the solubility of various toxic metals in the air and soil, such as mercury, cadmium, zinc, copper, chromium, and aluminium ions. These toxins in the environment lead to stunted plant development and the decrease in the number of bacteria needed to complete the nitrogen cycle.
Photosynthesis Suppression and Tissue Damage
Rain water with a low pH value weakens the plants by damaging the surface of the leaves. They strip the leaves of the protective coating, which results in excessive moisture loss and dehydration. This allows the acid to enter the system, displacing the water and reducing carbon dioxide uptake. As a result, the photosynthetic process suffers greatly. Plants with damaged leaves are unable to draw enough nutrients and become susceptible to toxins. Acid rain often works in conjunction with air pollutants, insects, diseases, drought, and cold weather. It makes the plant weak enough to succumb to one of these external factors.