Selenium is highly elevated in Appalachian streams and stream organisms that receive alkaline mine drainage from mountaintop removal coal mining compared to unimpacted streams in the region. Adult aquatic insects can be important vectors of waterborne contaminants to riparian food webs, yet pathways of Se transport and exposure of riparian organisms are poorly characterized. We investigated Se concentrations in stream and riparian organisms to determine whether mining extent increased Se uptake in stream biofilms and insects and if these insects were effective Se biovectors to riparian spiders. Biofilm Se concentration increased (p = 0.006) with mining extent, reaching a maximum value of 16.5 μg/g of dw. Insect and spider Se increased with biofilm Se (p = 0.004, p = 0.003), reaching 95 and 26 μg/g of dw, respectively, in mining-impacted streams. Adult insect biomass was not related to mining extent or Se concentrations in biofilm. Even though Se concentrations in aquatic insects were significantly and positively related to mining extent, aquatic insect Se flux was not associated with mining extent because the mass of emerging insects did not change appreciably over the mining gradient. Insect and spider Se concentrations were among the highest reported in the literature, regularly exceeding the bird Se dietary risk threshold of 5 μg/g of dw. Risks of Se exposure and toxicity related to mining are thus not constrained to aquatic systems but extend to terrestrial habitats and food webs.

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Mountaintop removal coal mining is the predominant form of surface mining in the Appalachian Region of the United States and leads to elevated levels of chemical constituents in streams draining mined watersheds. This data set contains measurements of water chemistry in the mountaintop mined landscape of Central Appalachia. These data were collected to determine the accumulation and transport of mercury (Hg) and selenium (Se) across environmental compartments in mountaintop mining‐impacted waters as well as the impact of mountaintop mining on the aquatic‐terrestrial subsidy. Samples were collected in summer 2017 and spring/summer 2018. Data predominantly include Se, THg, and methylmercury (MeHg) in the following environmental compartments at sites impacted and unimpacted by mountaintop removal coal mining: water, sediment, biofilm, larval cranefly, adult aquatic insects, and spiders. Additional water parameters that have been found to vary across a gradient of mountaintop mining impact (total organic carbon [TOC], total nitrogen [TN], sulfate [SO4], nitrate [NO3], chloride [Cl], pH, sodium [Na], potassium [K], magnesium [Mg], calcium [Ca], manganese [Mn], sulfur [S], specific conductance) were also measured. The majority of sites represented are headwater streams, although some settling ponds below valley fills are included. This data set also includes taxonomic characterization of the adult aquatic insect community as well as measurements of spider density at a subset of sites. There are no copyright restrictions; please cite this data paper when the data are used in publications.