Geochemical and Microbiological Controls on Mercury Methylation in Natural Waters

Mercury (Hg) is a global pollutant toxic to humans and wildlife. Monomethylmercury (MMHg) is a bioavailable compound that bioaccumulates and biomagnifies in food webs. Humans are primarily exposed to MMHg from seafood consumption (Sunderland 2007), and high quantities of the neurotoxin lead to reduced neurocognitive functioning in adults and the children of exposed mothers (Cohen et al. 2005, Yokoo et al. 2003). Negative effects from MMHg accumulation on the health of humans and wildlife requires a more complete understanding of the chemistry and microbiology driving Hg methylation in both marine and freshwater systems. This work focuses on water column distribution, speciation, and methylation of Hg. The aims of this dissertation are three-fold: (1) characterize the speciation and distribution of Hg in the western Arctic Ocean; (2) examine seasonal variations in Hg speciation, methylation, and demethylation, and the microbial communities of Hg methylators in Crystal Lake, Ohio; and (3) quantify Hg methylation rates and characterize methylating microbial communities in waters on the continental shelf of the northwest Atlantic Ocean. While Hg methylation has been studied for decades, this work is built upon recent improvements in Hg detection limits, and newly discovered genes responsible for Hg methylation. In conjunction with U.S. Arctic GEOTRACES (GN01), the western Arctic Ocean was sampled in the summer of 2015. Although Hg concentrations in the Canada and Eurasian Basins were low relative to the Atlantic and Pacific Oceans, higher MMHg concentrations were observed in Arctic seawater that recently interacted with continental margins. We estimate that the Arctic Ocean receives 4-71 kmol Hg yr−1 from the Bering Strait, which is likely to interact with sediments of the shallow continental shelves before entering into the Arctic Ocean. This is potentially important, because while the estimated atmospheric input to the Arctic Ocean is ~400 kmol Hg yr−1, inflowing Hg from the Bering Strait may still be an important source of Hg that can be methylated on the Chukchi Shelf. Mercury methylation potentials were measured in a stratified freshwater system, Crystal Lake, in Dayton, Ohio (objective #2). Mercury methylation occurred in both oxic and anoxic portions of the water column, but methylation potentials were greatest at the oxic/anoxic boundary layer. Mercury methylating genes were found throughout the water column and had the greatest copy number in the hypolimnion. Similarly, previous marine work showed that sediments and the microbial communities therein are large sources of MMHg to near shore marine systems (Fitzgerald et al. 2007), which led to methylation and demethylation studies along the northwest Atlantic shelf (objective #3). Greater abundance of Hg methylating microbes were observed in water overlying sediment as opposed to shallower waters, but methylation potentials did not significantly differ. Together, these results suggested that (1) Archaea may be responsible for Hg methylation in oxic waters; and (2) redox transition zones in the water column and the sediment-water interface are important sources of bioavailable MMHg. These studies improve our understanding of Hg cycling in natural waters and suggest possible conditions and organisms that stimulate Hg methylation

Contemporary Mobilization of Legacy Pb Stores by DOM in a Boreal Peatland

We examined how different landscape areas in a catchment containing a northern ombrotrophic peatland and upland mineral soils responded to dramatic decreases in atmospheric deposition of lead (Pb). Pb concentrations in the outflow stream from the peatland measured from 2009–2015 indicated continued mobilization and export of Pb derived from historic inputs to the bog. In contrast, Pb concentrations in surface peat and runoff from upland mineral soils have declined in response to reductions in atmospheric deposition. Relative to the early 1980s, Pb concentrations in the streamflow decreased only ∼50%, while Pb in surface peat and upland subsurface runoff decreased by more than 90%. Water level fluctuations in the slow-accumulating peat have allowed dissolved organic matter (DOM) to continue mobilizing Pb deposited in the peatland decades earlier. Strong correlations between dissolved organic carbon (DOC) and Pb concentrations in outflow from the peatland and in bog porewaters demonstrate Pb mobility related to DOM production. Peat stores of Pb in 2016 were less than or equal to those reported in the early 1980s despite the dry mass inventory increasing by 60–80%. Much of the loss in Pb stored in peat can be accounted for by stream runoff from the peatland

Starlikeness of Libera transformation (II) (Applications of Complex Function Theory to Differential Equations)

The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González

The GEOTRACES Intermediate Data Product 2017

Unidad de excelencia María de Maeztu MdM-2015-0552The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González