forsuring

Forsuring, or acidification, is the process by which ecosystems become more acidic through the accumulation of hydrogen ions in soils, water bodies, and the atmosphere. In environmental contexts, forsuring is most often discussed in relation to soils and freshwater, driven by anthropogenic emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from fossil fuel combustion and industrial activity.

The mechanism begins with the atmospheric formation of acids from SO2 and NOx, which are returned to surface environments via rain, snow, and dry deposition. The resulting increase in hydrogen ion concentration lowers pH and reduces the soil’s acid-neutralizing capacity (ANC). Base cations such as calcium, magnesium, and potassium are leached from the soil, and dissolved aluminum ions (Al3+) can be mobilized, potentially harming plant roots and aquatic life.

Impacts vary by system but commonly include nutrient imbalances in soils, altered microbial activity, and reduced forest vigor. In freshwater ecosystems, lower pH can shift metal speciation, degrade water quality, and cause losses of sensitive fish and invertebrate species. Infrastructure, agriculture, and natural stone can also suffer from increased corrosion. A related phenomenon is ocean acidification, where rising atmospheric CO2 lowers seawater pH and affects calcifying organisms; this is related conceptually to forsuring but is driven primarily by CO2 rather than deposition of sulfur and nitrogen compounds.

Monitoring typically involves measuring pH, ANC, sulfate and nitrate deposition, base saturation, and long-term lake and soil surveys. Mitigation focuses on reducing emissions of SO2 and NOx; many regions have observed declines in acid deposition and gradual signs of recovery in affected ecosystems, though recovery is slow and uneven.