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Acidification and Deacidification of Coastal Plain Soils as a Result of Periodic Flooding
Author(s) -
Breemen N.
Publication year - 1975
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1975.03615995003900060035x
Subject(s) - alkalinity , soil water , chemistry , sulfuric acid , soil acidification , sulfate , ferric , environmental chemistry , soil ph , waterlogging (archaeology) , solubility , inorganic chemistry , soil science , geology , ecology , wetland , organic chemistry , biology
Periodic flooding of recent coastal plain soils causes either acidification or deacidification of the surface horizons. Acidification of sulfate‐bearing “nonacid” soils (pH > 5) involves formation of FeS and partial loss of alkalinity (HCO 3 ‐ ) in the flood water during the wet season, followed by oxidation of FeS to ferric oxide and sulfuric acid in the dry season. Deacidification of acid soils (pH < 4.5) takes place during flooding. This involves reduction of ferric oxides to Fe 2+ , the simultaneous release of adsorbed SO 4 2‐ or hydrolysis of basic sulfates (that function as proton donor during iron reduction at low pH), followed by oxidation of dissolved FeSO 4 to ferric oxide and sulfuric acid at the soil‐water interface, and removal of H 2 SO 4 by lateral surface drainage. During soil reduction the actual pH increases and a shift from one process to the other takes place if the pH becomes high enough (4.5 to 5) for the weak acids CO 2 and H 2 S to function as proton donors. Therefore, deacidification beyond pH 4.5 to 5 automatically invokes the release of alkalinity. Conversely, acidification to a pH below 4.5 to 5 during a dry season will be undone by deacidification in the following wet season. This explains why the surface horizons of periodically flooded acid sulfate soils and nonacid marine soils eventually attain the same pH under dry conditions. This pH is fundamentally related to the dissociation constant, the solubility and the partial pressure of CO 2 .