Selenium in soils of western Colorado

Abstract

Seleniferous soils are host to a diverse and unique community of plants, animals, and microorganisms. Often, studies of these organisms, if they report selenium at all, only report the total selenium content of the soil. We conducted a field survey of soils to determine a) whether total selenium is a reliable proxy for bioavailable selenium, and b) the general characteristics of typical seleniferous soils. We analyzed soils from 32 seleniferous and nearby non-seleniferous habitats across western Colorado. In normal, low-selenium soils, the relationship between total and bioavailable selenium is roughly linear. In seleniferous soils however (total Se > 2 mg/kg), there is no relationship between total and bioavailable selenium. Also, these soils can be broadly characterized by two principal axes: a metals-rich axis likely explained by the mineralogy and depositional environment of the parent rock, and a soluble, salt-rich axis likely explained by soil weathering and hydrology. There is considerably more variation along the former axis, which also appears to predict primary productivity, but selenium content, particularly bioavailable selenium, is influenced by the latter. Researchers in seleniferous environments must recognize that seleniferous soils are heterogeneous, and may be shaped by current environmental factors as much as by the geological past.