Liming as a countermeasure

If finely ground limestone (CaCO3) is added to water it raises the pH and increases resistance to acidification. The liming of lakes and waterways is carried out on a large scale in Sweden and Norway. In Sweden around 7500 lakes and 11,000 kilometres of waterways are now limed each year.

The goal of liming is partly to restore acidified lakes and waterways, and partly to increase the resistance of the lakes and waterways that are at risk but not yet affected.

Because the water in a lake is constantly being replaced, liming must be repeated every few years. In running water, lime dosing equipment is used to continuously add lime to the water.

In order to raise the pH in small waterways, and to increase the duration of the effect when lakes are limed, part of the lime is often spread on wetlands in the catchment area. This causes damage to plants, including killing off bog moss, but the area is limited and the benefits are generally considered to outweigh the harm.

Liming of soils

The acidification process in soils can be countered by liming. This raises the pH level and tops up reserves of exchangeable cations (increases the base saturation), while also reducing the concentration of free aluminium ions. Lime acts like a filter in the upper layer of the forest soil, where it can capture and neutralize future acid deposition before it has time to leach out base cations and/or dissolve toxic aluminium.

The effect of the added lime penetrates slowly into the soil, at roughly one centimetre per year, but on the other hand persists for a long time in the future. The liming of soil can therefore help counter the acidification of surface water in the long term. A dosage of 3-5 tonnes of lime per hectare has been estimated to protect soil from acidification for 20-30 years with levels of acid deposition in southern Sweden as they were in the late 1990s.

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