‘Acid rain’ changes the chemistry of soils and waters, causes damage to materials, and threatens wildlife and human health. Most important anthropogenic sources of acidifying compounds emitted to the air are fuel combustion and agriculture. Sulfur dioxide and nitrogen oxides in the atmosphere act as strong acids increasing the natural acidity of rainwater. Ammonia emissions from agriculture and the subsequent deposition of reduced nitrogen compounds trigger acidification processes in soils. Besides those external hydrogen ion (H+) sources, ecosystem internal turnover processes linked to nutrient cation uptake by vegetation, the nitrogen cycle, and biomass export from ecosystems are also of major importance. Several H+ sinks in soil, bedrock, and waters can compensate for H+ release (e.g., carbonate dissolution or silicate weathering). Land-use changes and fossil fuel use have led to dramatically increasing atmospheric carbon dioxide (CO2) concentrations worldwide. CO2 is absorbed by oceans and reacts with seawater to form carbonic acid. Acidification of oceans could have adverse effects on marine organisms using calcium carbonate in seawater to construct their shells and skeletons. Acidification is the result of a sensitive (un-)balance between ecosystem internal and external H+ sources and internal H+ sinks of different capacities and reaction rates.
Lükewille A. & Alewell C., 2026. Acidification. In: Fath B. D. (Eds.), Encyclopedia of Ecology (Third Edition), pp. 458-468. Elsevier. Chapter.
