Acidification

Acidification is the process by which a substance or environment becomes more acidic, typically indicated by a lowering of pH and an increase in hydrogen ions. In environmental contexts, acidification refers to long-term decreases in pH of soils, rivers, lakes, or oceans, often driven by anthropogenic emissions of acids and weak bases, or by changes in the carbonate buffering system.

Oceans absorb about a quarter of human-caused CO2 each year. The dissolved CO2 forms carbonic acid, which lowers pH and reduces the availability of carbonate ions needed to form calcium carbonate minerals. This lowers the saturation state of aragonite and calcite, affecting calcifying organisms such as corals, mollusks, and some plankton. Ecosystem structure, food webs, and biogeochemical cycles can be altered as a result.

Soil acidification arises from acid deposition from burning fossil fuels, ammonia from agriculture, and high input of ammonium and nitrate. It can lead to leaching of base cations, aluminum release, decreased fertility, and altered microbial communities. Freshwater systems can experience pH declines from acid rain or runoff, affecting fish and invertebrates and changing nutrient cycling.

Acidification is monitored by measuring pH, alkalinity, dissolved inorganic carbon, and CO2 partial pressure. Buffering capacity and the carbonate system determine sensitivity. Main drivers are emissions of CO2, sulfur dioxide, and nitrogen oxides; natural processes modulate the rate.

Mitigation focuses on reducing emissions of CO2, SO2, and NOx; management practices to maintain buffering capacity; liming of soils and waters as a remediation in some cases; preserving sensitive habitats and supporting resilient ecosystems.