Toxic effects of selenium (Se) contamination in freshwaters have been well documented. However, study of Se contamination has focused on lentic and larger order lotic systems, whereas headwater streams have received little scrutiny. In central Appalachia, surface coal mining is a common Se source to headwater streams, thus providing a useful system to investigate Se bioaccumulation in headwater food chains and possible longitudinal patterns in Se concentrations. Toward that end, we assessed Se bioaccumulation in 2 reference and 4 mining‐influenced headwater streams. At each stream, we sampled ecosystem media, including streamwater, particulate matter (sediment, biofilm, leaf detritus), benthic macroinvertebrates, salamanders, and fish, every 400 m along 1.2‐ and 1.6‐km reaches. We compared media Se concentrations within and among streams and evaluated longitudinal trends in media Se concentrations. Selenium concentrations in sampled media were higher in mining‐influenced streams compared with reference streams. We found the highest Se concentrations in benthic macroinvertebrates; however, salamanders and fish bioaccumulated Se to potentially harmful levels in mining‐influenced streams. Only one stream demonstrated dilution of streamwater Se with distance downstream, and few longitudinal patterns in Se bioaccumulation occurred along our study reaches. Collectively, our results provide a field‐based assessment of Se bioaccumulation in headwater food chains, from streamwater to fish, and highlight the need for future assessments of Se effects in headwater streams and receiving downstream waters. Environ Toxicol Chem 2020;39:692–704. © 2020 SETAC

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Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non-forested

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