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Reevaluation of Calcite Supersaturation in Soils
Author(s) -
Suarez D. L.,
Wood J. D.,
Ibrahim I.
Publication year - 1992
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/sssaj1992.03615995005600060020x
Subject(s) - alkalinity , calcite , chemistry , environmental chemistry , supersaturation , soil water , saturation (graph theory) , titration , inorganic chemistry , mineralogy , soil science , geology , mathematics , organic chemistry , combinatorics
The calcite saturation status of soil‐water systems in semiarid regions was reexamined taking into consideration organic ligand alkalinity and Ca‐organic complexation. These factors have been forwarded as the reason for earlier reports of calcite supersaturation in soil‐water systems. We examined groundwaters beneath irrigated lands, soil‐water suspensions in the laboratory using four soils and two levels of CO 2 , and soil water extracted from the root zone of an irrigated, cropped field. Total alkalinity and net inorganic C alkalinity were determined by titration. Calcium activity values calculated from total concentrations using the speciation program WATEQ4F were compared with Ca 2+ activity values measured with an ion‐specific electrode. In all our systems, total alkalinity and inorganic C alkalinity were almost equivalent and thus organic C alkalinity was negligible. Calculated Ca 2+ activity was generally 5 to 25% greater than Ca 2+ activity determined with an ion‐specific electrode. Although these data suggest the presence of additional Ca complexes not included in the speciation routines, the determined dissolved organic C values are too low for Ca‐organic complexes to be the cause of these differences in Ca 2+ activity. Ion activity products based on either measured Ca 2+ activity values or calculated Ca 2+ activities indicated that all systems were supersaturated, with saturation ratios of two to three.