Evaluation of selenium in terrestrial and wetland soils, plants and waters at Fort Carson, Colorado

Selenium (Se) is essential for adequate nutrition in animals and humans, yet there is only a small order of magnitude between necessary levels and concentrations that can become toxic or even lethal. Fort Carson Military Reservation covers over 56,000 ha (138,000 acres) just east of the Rocky Mountains in southeastern Colorado, where Se occurs naturally in geologic formations. The objective of this research was to identify areas in Fort Carson with the greatest potential for environmental Se distribution, transport and bioavailability.; A geographic information system (GIS) was constructed by consolidating detailed coverages for geology, soils and vegetation into 43 “descriptive mapping units,” with 92 sampling sites representing about 99% of the described area. Sample data for phosphate-extractable Se concentrations were used to characterize Se trends in descriptive units (e.g., >0.5 mg Se/kg dry weight for soils, >5 mg Se/kg dry weight for plants, and >5 μg Se/L in water).; Seleniferous soils were primarily calcareous clays, silts and shales, or sediments derived from shales and eolian deposits, formed on parent materials of Cretaceous aged shales or Quaternary aged alluvium underlain by Cretaceous age shale. The eastern half of Fort Carson exhibited the greatest potential for containing seleniferous soils.; Seleniferous plants followed the order forbs > shrubs > grasses > trees; no sampled tree material (including needles, cones and leaves) exceeded the plant Se suitability limit. Plant Se uptake was not necessarily dependent upon land disturbance or soil Se concentration. Areas having the highest plant and soil Se concentrations were coincident with areas of high plant productivity (e.g., >1,000 kg/ha), plentiful water supply, and soils derived from or overlying Cretaceous Pierre shales.; The majority of wetland-riparian sediment samples were seleniferous, with those from an ephemeral pond increasing in Se concentration with depth. Emergent plants common between sampled sites tended to have greater Se uptake when sediment Se concentrations were higher, with Se levels in aquatic plants being some of the highest. Nearly all water samples exceeded the 5 μg/L critical Se level for protection of aquatic life, with two near the 50 μg/L critical concentration regulated for the protection of livestock drinking waters.