Effects of redox processes on soil acidity.

Abstract

Redox processes due to alternating aerobic and anaerobic conditions may give rise to strongly acidic or alkaline soils and waters. First, oxidized chemical components tend to be more acidic or less alkaline than their reduced counterparts. Second, and more important, redox processes often lead to the simultaneous formation of acidic (or potentially acidic) and alkaline substances with different mobility (dissolved or gaseous versus adsorbed or solid), so that one of the two substances can be exported, leaving a more acidic or more alkaline residue. Examples of acidification or alkalinization processes in wetlands based on these principles are: (1) formation of acid sulfate soils (transformation of seawater sulfate and sedimentary iron to immobile potential acidity (FeS₂) and mobile alkalinity (HCO₃^-), followed by oxidation of FeS₂ after the alkalinity has disappeared), (2) alkalinization of periodically flooded acid sulfate soils (formation of dissolved ferrous sulfate during reduction, and oxidation of the ferrous sulfate to ferric oxide and sulfuric acid at the soil surface, followed by drainage of the acid floodwater), (3) ferrolysis (immobilization of seasonally reduced ferric iron as exchangeable Fe²⁺, and removal of replaced bases by drainage, followed by oxidation of Fe²⁺ -clay to H⁺ -clay), and (4) soil alkalinization in closed depressions (reduction of sodium sulfate to sodium (hydrogen) carbonate and volatile H₂S). (Abstract retrieved from CAB Abstracts by CABI’s permission)