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Use of 234U and 238U isotopes to identify fertilizer-derived uranium in the Florida Everglades

Applied Geochemistry

By:
, , and
DOI: 10.1016/S0883-2927(99)00053-0

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Abstract

Surface water and peat in the northern Everglades have very low natural concentrations of U and are therefore sensitive to the addition of small amounts of U from anthropogenic sources such as fertilizer. Peat samples collected along a nutrient gradient in the northern Everglades have unusually high concentrations of U (> 1 ??g/g, dry basis) and also have a distinctive 234U/238U activity ratio (AR). AR values for U-enriched peat fall in the narrow range of AR values for commercial phosphate fertilizer (1.00 ??0.05) In contrast, AR values for low-U peat from background sites exceed 1.05. The spatial distribution of anomalous U concentration, and of fertilizer-like AR values in peat, parallel a previously documented pattern of P enrichment These results strongly suggest that some of the U in nutrient-impacted peatlands is fertilizer-derived. Agricultural drainage water sampled in the northern Everglades has high concentrations of dissolved U (0.3-2.4 ??g/1) compared to surface water from background sites (<0 1 ??g/1) Measured AR values in drainage water (0.949-0.990) are also permissive of a fertilizer origin for the U and are different from AR values in surface water or peat at background sites (AR > 1.05). Synoptic sampling of surface water along drainage canals indicate that Lake Okeechobee, and some drainage from agricultural fields, are sources of dissolved U, whereas wetlands farther downstream act as sinks for U. Historically cultivated agricultural soft has only a marginally elevated (+0.2 ??g/g) average concentration of U compared to nearby uncultivated soil and incorporates only 20% of the U from an aqueous solution that was slurried with the soil. In contrast, a similar experiment with fresh Everglades peat indicated uptake of 90% of the added U. These experiments support the proposed removal of U from agricultural fields and concentration of U in downstream peatlands. The methodology of this study can be used to describe the behavior of fertilizer-derived U in other low-U environments.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Use of 234U and 238U isotopes to identify fertilizer-derived uranium in the Florida Everglades
Series title:
Applied Geochemistry
DOI:
10.1016/S0883-2927(99)00053-0
Volume
15
Issue:
3
Year Published:
2000
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Applied Geochemistry
First page:
369
Last page:
383
Number of Pages:
15