Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet

The Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km−2 year−1) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km−2 year−1). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year−1), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year−1). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming

Characterization of microbial communities in raw and homogenized bentonite samples

World-wide appreciated strategy for the management and treatment of high level and long lived radioactive waste is to dispose it in a deep and stable geological formation. Microbial community present in the host or buffer material may compromise the effective performance and safety of waste disposal system. In the Czech Republic, bentonite from Černý vrch locality is planned to be used as a buffer material. Therefore, microbial community was analysed in two bentonite samples (homogenized and raw bentonite) from this source.16S rRNA gene was amplified targeting the variable V4 region and sequencing was performed using Ion Torrent platform. Both bentonite samples were inhabited by relatively similar bacteria. Beta and Alpha-proteobacteria dominated both samples. Moreover, chemolithotrophs including Thiobacillus, Gallionella and Nitrosomonas capable of oxidising NH3, Mn2+, Fe2+ and S2- were also present

Hydrogeology of the deepest underwater cave in the world: Hranice Abyss, Czechia

Little is known about water mixing in deep underwater cave shafts of hypogene karst. The Hranice Abyss (HA) in Czechia is currently the deepest underwater cave in the world. It shares a thermal and CO2-rich water source with an adjacent spa. Based on chemical and isotope composition, water in the HA is a mixture of shallow and thermal groundwaters. The shallow local groundwater is distinctly different from the adjacent Bečva River water in its elemental chemistry and sulfate δ34S values. The thermal water is mixed with 5–10% of modern water, based on tritium content and chlorofluorocarbons. Vertical profiling and deep sampling in the HA showed distinct changes with depth in temperature and TDS. Density-driven flow controls the mixing. In winter, the shallow water of the open HA lake is efficiently cooled; the denser surface water sinks to greater depths, which mixes the water column in the HA. During the summer the shallow water stagnates at the depth of 0–15 m. Periods of stagnation and of accelerated water flow and mixing in the HA perfectly fit with the periodic occurrence of CO2 evasion in the lake and the overall characteristics of the microbial communities, which showed the absence of any functional stratification. Ferric oxyhydroxide precipitation is the major cause for turbidity in the HA. Elevation-specific hydraulic responses of the HA groundwater, caused by the adjacent river’s level pulses, enabled a determination of the points along the river course at which the river is connected to groundwater by karst conduits