Food chain transfer of selenium in lentic and lotic habitats of a western Canadian watershed

Selenium (Se) is an essential micronutrient, exhibiting a narrow margin between nutritionally optimal and potentially toxic concentrations. Egg-laying vertebrates at the top of aquatic food chains are most at risk in environments with elevated aqueous Se concentrations. The Elk River watershed in British Columbia, Canada receives effluents containing Se from five coal mine operations. This study tested three hypotheses that might account for higher Se concentrations in fish from lentic compared to lotic habitats in the watershed: (1) enhanced uptake by aquatic primary producers, (2) longer food chain length, or (3) greater food web accumulation through sediment–detrital pathways. Stable isotope and Se concentration data demonstrated that Se concentrations in aquatic primary producers and food chain lengths were comparable in lentic and lotic habitats. Enhanced formation of organoselenium and subsequent uptake and cycling via sediment–detrital pathways likely account for higher fish tissue Se concentrations in lentic than in lotic areas.