Acidic deposition and internal proton sources in acidification of soils and waters

Enough is now known of the sources of hydrogen ions (protons) in natural ecosystems for the relative importance of external and internal sources to be compared. In acidic soils in the northeastern United States and western Europe, external often exceeds internal proton loading, resulting in soil acidification by aluminium dissolution and sulphate retention. One consequence is the export of ecologically significant quantities of hydrogen ion and aluminium in drainage water.