GRID-Arendal : State of the Environment Norway - Acid rain

Direct effects of SO2 and NOx

SO2 and NOx have adverse effects on human health. Investigations show that the effects may reduce the function of the lungs in astmathics, increase the resistance of the respiratory passages ( healthy and astmathics) and increase the receptiveness for infection of the respiratory passages. Population groups in heavily affected areas have a larger number of acute- and chronic respiratory diseases.

SO2 and NOx have adverse effects on vegetation. Heavy concentrations of NOx has proven to inhibit vegetation growth, especially when ozone is present (synergistic effects).

SO2 inhibits photosynthesis in green plants, leading to reduced plant growth.

The chemistry of acid in the soil. Indirect effects.

The effects of acid rain are substantial. However, soil and water have a natural buffer capacity. This means that nature has a natural ability to cope with acid rain up to a certain level: the critical load.

The problems are most severe where the soil contains only a small amount of Calcium, Potassium and Magnesium. These elements constitute the basic buffer capacity of the soil. When the critical load has been exceeded, the metal cations and other plant nutrients are washed out. This explains why there is often a significant amount of aluminium in water coming from areas damaged by acid precipitation.

The acid in acid rain is due to Hydrogen ions (H+). The buffer capacity of soil implicates that the soil absorbs the H+ ions, while other positive ions are liberated. In other words; the H+ ions replace the other ions bound in the soil structure (colloids).
The problem become apparent when there are more H+ ions absorbed than can be neutralised. The positive ions “washed out” by H+ ions are called cations. The most common cations are: Calsium (Ca++), Magnesium (Mg++), Potassium (K+), Aluminium (Al+++), Manganese (Mn++) and Ammonium (NH4+).

How long it would take for an ecosystem to regain its normal chemical and biological status if emissions were to cease is uncertain. The chemistry of the soil and its capacity for recovery will be decisive. The soils store of base cations would gradually be built up through the inflow from weathering and from the atmosphere: a process that may be assumed to need several decades, in some cases centuries.

Effects of the washing out of metal ions

• Aluminium
  The washing out of metal ions has lead to damages of forests, lakes, watercourses and fish. Sources for potable water may become poisoned by high concentrations of copper, lead and aluminium. Aluminium causes the most severe problems to the water in southern Norway.

• Death of fish
  Death of fish is the best known effect of acidification, and is therefore a reliable and frequently used indicator. There are two reasons for the death of fish. When the acidification reaches a certain level, the fry die. Different species of fish have different tolerance levels to acidic water. The most sensitive species are trout and salmon. The presence of aluminium in the water is another common cause of fish death. Aluminium is toxic to fish, because it prevents a fish from absorbing salts and destroys the gills. Increased concentrations of aluminium is the major cause of fish death in the southern part of Norway.

  From 1960 to 1990, areas with damages to fish stock were quintupled. Of the 13,000 investigated stocks of fish in the Southern part of Norway during this period, 19 per cent were lost, while a reduction in the number of fish was registered in 21 per cent of the stocks.

• Damage to vegetation
  Damage to vegetation and the dying of forests have long been associated with acid rain. The washing out of metal ions results in limited plant nutrients. (Nitrogen, Phosphorus, Potassium, Magnesium etc) In many cases, a plant’s ability to absorb these nutrients depends on the level of acidification in the soil. Vegetation exposed to acid rain will therefore absorb less of these essential nutrients. The result is poorer quality of a plant’s proteins, stunted growth and exposure to diseases.

  Green plants are the foundation of the food chain, and a reduction in plant production will have consequences higher up in the food chain. Animals and human beings may experience less valuable nutrition.

  Compared to other countries, the situation in Norway is better than in Central Europe. In e.g. the Czech Republic, 71 per cent of the forest has been damaged due to acid rain. The situation is also severe where the supply of potable water is concerned. (Source: Dr. Josef Krecek, Inst. of Applied Ecology, Agricultural University of Prague).