Acidification

What is acidification?

All compounds, which have the capability to release hydrogen ions (H+) are acids. Hydrogen ions can attack man-made and natural  materials as well as living tissues and cause damage to health, human capital and natural values. Acidifying compounds emitted into the atmosphere are transported by wind and deposited as acidic particles or acid rain or snow hundreds or thousands of kilometers from the source.

 

Some compounds which contribute to acidification:    

Hydrochloric acid: HCl H+ +  Cl-
Sulfuric acid: H2SO4 H+ + HSO4-
Sulfur dioxide: SO2+ H2O (vapor in air) H2SO3, H2SO3 H+ + HSO3-
Nitric oxide: NO + O3 (atmospheric ozone) NO2 + O2 
Nitrogen dioxide: NO2 + ½ H2O + ¼O2  HNO3
Nitric acid: HNO3 H+ + NO3-
 Ammonia: NH3 + 2O2   HNO3 + H2O
Phosphoric acid: H3PO4   H+ + H2PO4-

What are the possible effects of acidification?

Damage to constructions and monuments 

 

Materials such as limestone, cement and concrete are sensitive to acid because the acid may  react with their content of chalk and disintegrate the material structure. Constructions such as houses, bridges, roads and sculptures are made of these materials and may be damaged due to  the acid deposition. Acids can also cause considerable corrosion of metal surfaces.

 

 

Statue damaged by acid deposition 

Stone building damaged by acid deposition

 

Damage to terrestrial systems

Acidification releases nutrients and toxic substances from the soil. This stresses plants and  trees and increases their susceptibility to other environmental pressures such as exposure to   sulfur dioxide and ozone as well as wind and drought. Acidification may lead to reduced health of trees and eventually death of whole forests. Some soils contain chalk which neutralizes the acid and hence keep the effects of acidification invisible for a period. However, as the chalk disappears, there may come a day when the neutralization capacity of the soil is used up and effects on vegetation appear.
Various stages of forest-death in mountainous areas of Central Europe. The trees are dead or dying because of acidification and other environmental stress factors. The acidification is a result of sulfur oxides emissions from lignite and coal combustion in nearby industrial areas.
 


Damage to aquatic systems 

Acid deposition in lakes and rivers affects the whole ecosystem and may change the composition of living organisms in the water and in worst cases, eliminate almost all life.

One direct effect of acidification is reduced activity and reproduction of photosynthetic algae, which serve as the food base for all living organisms in the water. With reduced primary production of algae, the base of the food chain is weakened and all higher animals have to find new food sources or die. Some more indirect effects are washout of nutrients and metal ions (e.g. Ca2+) and release of toxins (e.g. aluminum-ions, Al3+) from the terrestrial environment and from the bottom sediment. Calcium, for instance, is a major component of fish bones and lack of this component in the water may lead to fish deformities and death. Too high concentrations of aluminum-irons in the water irritate the gills of fish. Excretions of mucus as a response to the irritation may cover the gills of the fish to such extend that it cannot absorb sufficient oxygen.

Acidified lakes and rivers may look blue due to the lack of algae. The blue color of acidified  waters can be misinterpreted as healthiness due to lack of nutrient enrichment but instead may be a sign of complete collapse of the ecosystem.

Oceans are too vast to be affected by acidification.

Carbon dioxide, which is released to the atmosphere as a result of acid’s reaction with chalk contributes to global warming, 2H+ + CaCO3 Ca2+ + CO2 + H2O.

 

Direct damage to plants    

In addition to the above indirect effects on plants, the acid deposition can also cause direct damage to plant tissues such as leaves and flowers.