Small-scale spatial variation of selenium concentrations in Chironomid larvae.

Abstract

Selenium is an important contaminant of many freshwater wetlands receiving agricultural drainage water (Ohlendorf et al. 1986) or natural runoff from seleniferous soils (Maier and Knight 1994). One such wetland is the Benton Lake basin at Benton Lake National Wildlife Refuge in central Montana. Selenium-contaminated water originating from agricultural drainage and selenium-containing natural runoff enters the refuge primarily by way of its main tributary. After entry into the lake, water moves through the diked wetland units as water flow is manipulated for management purposes within this closed basin (Nimick 1997). We have been monitoring selenium concentrations in aquatic invertebrates at Benton Lake since 1988. At least some samples of all invertebrate taxa collected exceeded the 5 μg/g selenium dry wt concentration which, in the diets of migratory birds, has been associated with embryo teratogenesis under some field and laboratory conditions (Skorupa and Ohlendorf 1991). Selenium concentrations were consistently higher in the sediment-dwelling larvae of the family Chironomidae (Order: Diptera) than in any other taxon sampled. Chironomids are an important food for many species of migratory birds breeding at Benton Lake (Bartonek and Hickey 1969, Sugden 1973).