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Reevaluation of Calcite Supersaturation in Soils

“Reevaluation of Calcite Supersaturation in Soils” Soil Science Society of American Journal 56 (1992): 1776-1784.

D.L. Suarez, J.D. Wood, and I. Ibrahim

ABSTRACT

The calcite saturation os soil-water systems in semiarid regions was reexamined taking into consideration organic ligand alkalinity and Ca-organic complexation.Theses 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 CO2, and soil water 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 compared with Ca2+, 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 Ca2+ activity was generally 5 to 25% greater than Ca2+ 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 Ca2+ activity values or calculated Ca2+ activities indicated that all systems were supersaturated, with saturation ratios of two to three.