||Acidification of Aquatic and Terrestrial Systems: Chemical Weathering.
Schnoor, J. L.;
||Iowa Univ., Iowa City. ;Eidgenoessische Technische Hochschule, Zurich (Switzerland).;Environmental Research Lab.-Duluth, MN.
Oxidation reduction reactions;
Air water interfaces;
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||The pH and p(epsilon) of the terrestrial and aquatic environment is determined by coupled reactions of oxidation-reduction and acid-base. If disturbances are created in elemental cycles of the environment (whereby oxidation of C, S, and N exceeds reduction reactions), a net production of H(+1) ions is a necessary consequence. The authors have shown that aggrading biomass and humus and oxidation reactions (nitrification, sulfur oxidation) serve to add protons to aqueous systems, while chemical weathering, ion exchange, and reduction reactions (denitrification, H2S production) serve to consume protons (add ANC to the water). Bar diagrams are a convenient means to examine changes in ANC or BNC in water and soils. Atmospheric acid deposition creates an additional input of hydrogen and sulfate ions (H2SO4) to the terrestrial and aquatic ecosystem which is partly neutralized by increased weathering and cation export. It is balanced, in part, by aluminum dissolution and causes the negative effects in aquatic ecosystems on fish and possibly on forests. The lakes which have been acidified by acid precipitation are those with extremely sensitive hydrologic settings and with watersheds lacking carbonate minerals. They tend to be small lakes. They respond relatively rapidly to changes in acid loading (on the order of a few hydraulic detention times). The soils of these watersheds have not been greatly acidified by acid precipitation nor has podzolization occurred due to anthropogenic acid deposition. However, this does not imply that more subtle changes in nutrient cycling or forest production could not have occurred. Soil solution pH could be reduced by the anthropogenic input of acids. The authors have proposed a quantitative framework with which to examine these questions.
||Prepared in cooperation with Eidgenoessische Technische Hochschule, Zurich (Switzerland).
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||6F; 7D; 8H; 68A; 68D; 57H; 99F; 48G
||PC A03/MF A01