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Mobility and Uptake by Plants of Elements Placed Near a Shallow Water Table Interface¹

ABSTRACT

The water table interface is the transition between unsaturated, usually aerated, soil and water-saturated, often anaerobic soil. Plant roots may approach this transition zone and absorb elements soluble in and below the transition zone. To examine this possibility, we studied elements that differ in solubility as a function of oxidation-reduction potential. Barley (Hordeum vulgare cv. Conquest) was grown in field lysimeters, and treatments included various elements (iron, technetium and uranium plus phosphorus), element placement depths, and water table regimes. Measurements included plant uptake of each element, plant root distribution, and soil profiles of total and extractable amounts of each study element and related elements. The transition from aerobic to anaerobic conditions occurred –10 cm above the water table interface. The mobility of the elements decreased in the order Tc > U > P Fe. The redox gradient markedly modified the mobility of Tc and U. The Fe was more soluble in the reducing environment than in the oxidizing environment, but no migration of Fe was detected. The plant roots were almost entirely confined to the oxidized layers of soil. The plants absorbed no treatment Fe, very little treatment P and U (from the shallow placement only), but substantial amounts of Tc. A fluctuating water table further restricted plant uptake. The water table interface markedly changed the mobility of some of the study elements but the effect on rooting depth was more profound. Thus, the water table interface did not present a unique condition for plant roots to absorb elements as the elements diffused upward from the reducing environment.

Key Words: iron • technetium • uranium • phosphorus

¹ Contribution from Atomic Energy if Canada Limited, Pinawa, MB, Canada, R0E 1L0, Issued as AECL-8428.

² Assistant research officer and technologist, respectively. Environmental Research Branch, Whiteshell Nuclear Research Establishment, Pinawa, MB, Canada, R0E 1L0.

Received for publication June 19, 1984.

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