Why is Australia not affected by acid rain?

Forest dieback and acid rain are not really history

The term "acid rain" is a little reminiscent of the sometimes not so "good old days" when sulfur oxides still gushed from the chimneys of industry in abundance Earth fell. This also made the soil more acidic over time. That, in turn, did not always benefit the forests there, and the term »Waldsterben« appeared more frequently in the media, which even made it into French as a loan word »le Waldsterben«. In order to save their forests on particularly sensitive soils, some federal states began to neutralize the acid there by applying lime.

Nicole Wellbrock from the Thünen Institute for Forest Ecosystems in Eberswalde and her colleagues are investigating how successful this measure is. Even if effective filter systems have been reliably preventing the chain of effects sulfur exhaust gases - acid rain - soil acidification at the source since the 1980s in western Germany and after the reunification since the 1990s in eastern Germany, these investigations remain not only for theorists, but also for Forest owners more than interesting. After all, manure from factory farming has long been a new source of further acidification of the soil in agriculture, and road traffic also plays an important role in this.

This article is contained in Spectrum Compact, Temperate Forests - The green lungs of our latitudes

Every 15 years, federal state officials, planning offices and researchers flock out to examine the forest soils. The second and so far last soil condition survey took place from 2006 to 2008; The scientists have just proposed the three years from 2022 to 2024 for a third inventory of forest soils. The most important hand tool for soil scientists is first of all a spade, which is often replaced by an excavator if the terrain allows it. They use it to dig a pit almost a meter deep and half a meter wide. The color and the type of rooting usually quickly reveal the type of soil. At the same time, such a soil profile provides initial indications of the ecological status.

The soil scientists then hammer eight drill sticks into the ground ten meters away from this profile wall. One of them in the north, the next in the northwest, then in the west and so on, until finally the eighth of these gouge bits is driven into the depths in the northeast. The scientists then lever the device out of the ground again, thus also recovering the soil enclosed within it. "We normally examine five layers in it at different depths and the humus layer on top," explains Nicole Wellbrock.

Normal rain is slightly acidic

The researchers are looking for answers to a whole series of questions: How many stones are there in a layer, how dense is the soil there? And of course: how acidic is the soil? Chemists specify this degree of acidity as the pH value, which sounds rather complicated as the »negative decadic logarithm of the hydrogen ion concentration«, but works relatively simply: a pH value of 7.0 indicates neutral water. If the liquid is ten times more acidic, the pH value drops by one notch to 6.0. A rise to pH 8.0, on the other hand, makes the liquid ten times less acidic.

On this scale, normal rain with a pH value of 5.6 turns out to be slightly acidic because it absorbs carbon dioxide from the air, which creates a little carbonic acid. Tea with a pH of 5.5 is similarly acidic, whereas coffee already has a pH of 5.0. In earlier decades, the sulfuric acid produced from the exhaust gases from heating systems and industrial chimneys suppressed the pH value of acid rain to values ​​below 4.5. For comparison: apple juice has a pH of 3.5, while lemon juice only has a pH of 2.4.