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Cesium in Soils and Plants in the Sagebrush Steppe Ecosystem

Investigators and Affiliations

Lawrence L. Cook, Graduate Student, Graduate Student, Department of Biological Sciences, Idaho State University, Pocatello, ID
Richard S. Inouye, Professor, Department of Biological Sciences, Idaho State University, Pocatello, ID
Terence P. McGonigle, Associate Professor, Department of Botany, Brandon University, Brandon, Manitoba, Canada

Funding Sources

The Idaho State University Department of Biological Sciences
The Idaho State University Center for Ecological Research and Education
The Inland Northwest Research Alliance
The Idaho State University Graduate Student Research and Scholarship Committee
A Bechtel Educational Outreach Program grant awarded to Richard Inouye
Sigma Xi

Accomplishments


This research was conducted as part of a doctoral program and has been completed.

Dissertation Abstract

Cesium (Cs) movement in ecosystems is important due to Cs radioisotopes introduced via nuclear technologies. Stable Cs uptake by plants is comparable to Cs radioisotopes. Three lines of investigation were used to determine stable Cs movement in the sagebrush steppe ecosystem of the eastern Snake River Plain. First, 27 sites were surveyed to determine Cs concentrations in 28 soil and 330 plant samples. Titanium (Ti) was used to indicate soil contamination on plant samples. Cesium in soils correlated with quartz and cation exchange capacity. Cesium in plants correlated with Ti. Transfer factors, i.e., the concentration ratio of plant Cs to soil Cs, were on the order of 10-3.

Second, the validity of Ti to indicate soil contamination was assessed. Milling inert filter paper indicated that background Ti levels account for concentrations to 10 mg Ti•kg plant-1. Concentrations of Ti and Cs associated with seedlings grown in a dust-free environment increased significantly with moderate dusting. Washing dust-laden plants with seven washing agents revealed none as superior in removing soil from seven species and none was effective in removing all soil from any one species. Energy dispersive spectrometry showed plant surface elemental signatures consistent with soil coatings.

Third, four grasses were evaluated as phytoremediation candidates via greenhouse experiments. The species were Agropyron spicata (bluebunch wheatgrass), A. cristatum (crested wheatgrass), Leymus cinerus (Great Basin wildrye), and Bromus tectorum (cheatgrass). Plant Cs concentrations were higher in Cs-spiked soil. Total Cs per seedling was greatest in the high Cs, high fertility, and high moisture soil treatment combination.

These studies indicated: (1) the uptake of Cs by regional plants is low and much of the Cs is in soil adhering to plant surfaces, (2) Ti is a reliable indicator of soil contamination for plant samples slated for trace element analysis and should be used when assessing trace element composition of field samples, and (3) Great Basin wildrye, bluebunch wheatgrass, crested wheatgrass, and cheatgrass are viable phytoremediation agents when used in a strategy combining soil fertilization and irrigation and possibly stable Cs addition. Preference should be given to the native bluebunch wheatgrass and Great Basin wildrye because they do not negatively impact regional biodiversity.
 

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