Biogeochemistry of Isotopically-distinct Sources of Lead in a Former WWII Aerial Gunnery Range

Isotopic composition and concentrations of Pb are used to identify sources of anthropogenic and natural Pb and to assess Pb bioavailability in soils and native plants at a former military installation that served as a WWII era aerial gunnery range. Surficial soil and plant samples are obtained both in target practice areas where copious amounts of bullets persist and areas unaffected by target practice that are devoid of bullets. A selective sequential extraction procedure is used to determine the distribution of Pb amongst different soil components: soil carbonates and ion-exchangeable minerals, organics, oxide and hydroxide minerals, and leachate of residual silicate clays. Plants samples are obtained by sampling multiple species within 1 m square area for each soil sample location. Isotopic compositions of samples directly reflect the presence or absence of bullets in the sample area. Anthropogenic Pb in sample locations with abundant bullets display a wide range of ^(206)Pb/^(207)Pb values (1.140–1.234), but relatively less variation in ^(206)Pb/^(208)Pb values (0.473–0.488), which is hypothesized to be reflective of ore-mixing in the manufacture of bullets. Plant samples exhibit a distinction between anthropogenic and natural Pb similar to soil samples, but consistently display lighter ^(206)Pb/^(207)Pb values than soil samples, which is inferred to be representative of the influence of regional atmospheric deposition of contaminant Pb

Hydrocarbon seepage in the deep seabed links subsurface and seafloor biospheres

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chakraborty, A., Ruff, S. E., Dong, X., Ellefson, E. D., Li, C., Brooks, J. M., McBee, J., Bernard, B. B., & Hubert, C. R. J. Hydrocarbon seepage in the deep seabed links subsurface and seafloor biospheres. Proceedings of the National Academy of Sciences of the United States of America, 117(20), (2020): 11029-11037, doi: 10.1073/pnas.2002289117.Marine cold seeps transmit fluids between the subseafloor and seafloor biospheres through upward migration of hydrocarbons that originate in deep sediment layers. It remains unclear how geofluids influence the composition of the seabed microbiome and if they transport deep subsurface life up to the surface. Here we analyzed 172 marine surficial sediments from the deep-water Eastern Gulf of Mexico to assess whether hydrocarbon fluid migration is a mechanism for upward microbial dispersal. While 132 of these sediments contained migrated liquid hydrocarbons, evidence of continuous advective transport of thermogenic alkane gases was observed in 11 sediments. Gas seeps harbored distinct microbial communities featuring bacteria and archaea that are well-known inhabitants of deep biosphere sediments. Specifically, 25 distinct sequence variants within the uncultivated bacterial phyla Atribacteria and Aminicenantes and the archaeal order Thermoprofundales occurred in significantly greater relative sequence abundance along with well-known seep-colonizing members of the bacterial genus Sulfurovum, in the gas-positive sediments. Metabolic predictions guided by metagenome-assembled genomes suggested these organisms are anaerobic heterotrophs capable of nonrespiratory breakdown of organic matter, likely enabling them to inhabit energy-limited deep subseafloor ecosystems. These results point to petroleum geofluids as a vector for the advection-assisted upward dispersal of deep biosphere microbes from subsurface to surface environments, shaping the microbiome of cold seep sediments and providing a general mechanism for the maintenance of microbial diversity in the deep sea.We wish to thank Jody Sandel as well as the crew of R/V GeoExplorer for collection of piston cores, onboard core processing, sample preservation, and shipment. Cynthia Kwan and Oliver Horanszky are thanked for assistance with amplicon library preparation. We also wish to thank Jayne Rattray, Daniel Gittins, and Marc Strous for valuable discussions and suggestions, and Rhonda Clark for research support. Collaborations with Andy Mort from the Geological Survey of Canada, and Richard Hatton from Geoscience Wales are also gratefully acknowledged. This work was financially supported by a Mitacs Elevate Postdoctoral Fellowship awarded to A.C.; an Alberta Innovates-Technology Futures/Eyes High Postdoctoral Fellowship to S.E.R.; and a Natural Sciences and Engineering Research Council Strategic Project Grant, a Genome Canada Genomics Applications Partnership Program grant, a Canada Foundation for Innovation grant (CFI-JELF 33752) for instrumentation, and Campus Alberta Innovates Program Chair funding to C.R.J.H