Acid rain is the common name for precipitation containing acidic oxides (usually sulphur or nitrogen). And it may not necessarily be a liquid, but also fog, snow, hail, dust or gases – in the latter case the term ‘dry deposition’ is used.
The main culprits of acid rain are sulphuric acid, nitric acid and ammonia, which are released into the atmosphere as a result of various human activities.
Sulphuric acid is formed in the atmosphere when water vapour reacts with sulphur dioxide. The latter is the result of burning fossil fuels. Industry, power stations and road traffic are the main culprits.
Very high combustion temperatures release another substance: nitrogen dioxide. When this substance combines with atmospheric water vapour, it forms nitric acid.
Organic fertilizers such as manure and slurry contain ammonia. When landowners apply these fertilisers to their fields, they release large quantities of ammonia into the atmosphere. Ammonia is not an acid, but a base. In the soil it is converted to nitric acid by bacteria.
When acid rain falls on the soil, sulphuric acid, nitric acid and ammonia are absorbed by the soil. Their effects depend on the nature of the soil. Because limestone neutralises acid, limestone soils tolerate acid rain better. As a rule, sandy soils contain little limestone. In addition, these soils are highly leached (leached). Under the influence of acids, nutrients are dissolved even faster into the soil. This leaching is intensified.
Acid rain increases impoverishment of sandy soils. Therefore, it is not surprising that the effects of acid rain are most visible on sandy areas. And since trees and other plants receive little nutrients, they become more susceptible to the disease. Tree foliage also suffers from acid rain. The protective layer of the leaves is dissolved by the acids. Losing a lot of moisture, the tree dies. Conifers are more sensitive to acid rain than deciduous trees, as they retain their needles throughout the year.
The metals in the soil, such as aluminium, lead and copper, dissolve in the acidic water of the groundwater table. When these substances end up in surface water, they pose a threat to fauna. Aluminium, for example, affects the gills of fish, disrupting their breathing. In acidified water, the eggs of frogs, toads and salamanders become mouldy. The larvae that do manage to hatch are marked by anomalies.
Controlling soil conditions
The legal regulations in force in Russia, e.g. the Federal Act on the Sanitary and Epidemiological Welfare of the Population, sets limit values for the content of chemical elements in soils of various designations.
For example, a chemical soil analysis is carried out to monitor soil conditions, which is mandatory for agricultural enterprises and companies in the construction sector during site planning, reconstruction and new construction of facilities.