Examination of mercury contamination from a recent coal ash spill into the Dan River, North Carolina, United States.

Coal ash spills occasionally occur due to the accidental failure of surface impoundments, and toxic metal-laden ash can pose a serious health threat to adjacent aquatic ecosystems. Here, we performed an investigation into longitudinal variations of mercury (Hg) contamination in the Dan River (North Carolina, United States) about 17 and 29 months after a February 2014 coal ash spill incident, in which the reported Hg concentrations in the spilled coal ash (210 ng/g) were 1-2 orders of magnitude higher than the river sediments (2-61 ng/g). We examined total Hg (THg) and methyl Hg (MeHg) in sediments from 0 to 65 km downstream of the spill, and found that most of the variations of THg and MeHg in surface sediments (0-16 cm) could be well accounted by the organic matter content and appeared to be not contaminated by Hg derived from coal ash. In examining MeHg bioaccumulation in invertebrates (aquatic and riparian) and fish in the Dan River and fish in a reservoir downstream of Dan River, we found no evidence of elevated MeHg bioaccumulation due to the 2014 coal ash spill. Thus, we concluded that Hg contamination from the coal ash spill is largely absent in the Dan River for both surface sediments and biota within the first three years of spill (until 2017), even though the majority of coal ash may be buried deeper in the sediment in the river channel and/or the downstream reservoir. Alternatively, the Hg associated with the coal ash is largely not bioavailable for extensive microbial Hg methylation. The findings provide useful insights into remediation strategies for this incident and other coal ash spills.

The seasonal distribution and concentration of antibiotics in rural streams and drinking wells in the piedmont of North Carolina.

The present study investigated 16 residential, rural well sites and respective nearby streams in the Piedmont of North Carolina over three different seasons to determine antibiotic presence and concentration. Fifteen antibiotics were detected in stream surface water, groundwater, and stream sediment compartments. Antibiotics detected representing penicillin, sulfonamide, macrolide, aminoglycoside, lincosamide, and quinolone groups. Sulfamethoxazole (SMX), sulfamerazine (SMR), danofloxacin (DAN), and erythromycin (ETM) were the most commonly detected among samples throughout the sampling period. Concentrations reported in the study ranged from 0 to 1740 ng/L in surface water and groundwater, and 0t378 µg/kg in stream sediment. There was a seasonal influence on antibiotic concentrations in each environmental compartment. Fall had the highest antibiotic concentrations for surface water and stream sediments overall, and groundwater concentrations were highest in the winter. Principal component analysis (PCA) was used to assess the correlation between environmental variables. Antibiotic concentrations correlated with groundwater pH, surface water pH, and surface water temperature. Non-metric multidimensional scaling (NMDS), used to display seasonal and environmental compartment data, demonstrated no discernible trend in the distribution of antibiotics over time. Human health risk assessments based on risk quotients (RQs). RQs from groundwater assessment shown no risk to children 6-11 years old, or adults 18 years old or older. Results from this study illustrate that the occurrence of antibiotics in streams and groundwater in the Piedmont of North Carolina is widespread and provide a basis for future studies investigating the occurrence of antibiotics in rural areas, especially where animal density is high. This work is important because it contributes to the paucity of information on antibiotic pollution in rural areas, and because it illustrates the importance of using a combined targeted and non-targeted approach to antibiotic pollution in streams and groundwater.

Linking permafrost thaw to shifting biogeochemistry and food web resources in an arctic river.

Rapidly, increasing air temperatures across the Arctic are thawing permafrost and exposing vast quantities of organic carbon, nitrogen, and phosphorus to microbial processing. Shifts in the absolute and relative supplies of these elements will likely alter patterns of ecosystem productivity and change the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. The ultra-oligotrophic nature of surface waters across the Arctic renders these ecosystems particularly susceptible to changes in productivity and food web dynamics as permafrost thaw alters terrestrial-aquatic linkages. The objectives of this study were to evaluate decadal-scale patterns in surface water chemistry and assess potential implications of changing water chemistry to benthic organic matter and aquatic food webs. Data were collected from the upper Kuparuk River on the North Slope of Alaska by the U.S. National Science Foundation's Long-Term Ecological Research program during 1978-2014. Analyses of these data show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for discharge-corrected nitrate concentrations (+), discharge-corrected dissolved organic carbon concentrations (-), total phosphorus concentrations (-), and δ13 C isotope values of aquatic invertebrate consumers (-). These changes show that warming temperatures and thawing permafrost in the upland environment are leading to shifts in the supply of carbon and nutrients available to surface waters and consequently changing resources that support aquatic food webs. This demonstrates that physical, geochemical, and biological changes associated with warming permafrost are fundamentally altering linkages between upland and aquatic ecosystems in rapidly changing arctic environments.

Snail populations in arctic lakes: competition mediated by predation?

For 2 species of snails in arctic Alaskan lakes, I studied the patterns of snail distribution with respect to habitat, distribution of predatory fish, and the potential for interspecific competition. The snails Lymnaea elodes and Valvata lewisi co-exist in these arctic lakes, either in the presence of lake trout, Salvelinus namaycush, or in the absence of predation. Intensive sediment core sampling of Toolik Lake and Lake N-2, with trout and lacking trout, respectively, showed that the smaller snail, Valvata, was abundant in Toolik but ocurred at very low densities in Lake N-2. On the open sediments of lakes containing trout, diver surveys revealed very low densities of adult Lymnaea (0.12±0.12/m2), but similar surveys in lakes without trout revealed much higher densities of adult Lymnaea (7.1±1.8/m2). A survey of 14 lakes indicated that adult Lymnaea grew to a smaller mean size in lakes with trout than in lakes which lacked trout.In laboratory and field experiments, the presence of Lymnaea lowered the fecundity of Valvata. Laboratory experiments also showed that Lymnaea fecundity was enhanced by the presence of Valvata. Enhancement was not due to predation by Lymnaea on Valvata eggs or young. The observed patterns of distribution and abundance in the absence of trout, combined with results from laboratory experiments, are consistent with the hypothesis that competitive and facilitative interactions control the population dynamics of the two snails. The distribution and abundance patterns of snails where trout are present suggest that trout predation rather than competition controls snail population dynamics in lakes containing trout.