Microbial ecology of Keane Wonder Spring, Death Valley National Park

This research is focused on developing a better understanding of he physiological and phylogenetic diversity as well as environmental abundance of bacteria of the genus: Shewanella in selected desert ecosystems. Prior research from this laboratory has revealed that these bacteria are very abundant in sulfurand organic-rich aquatics habitats. We have selected a number of habitats for detailed investigation (cultivation, molecular ecology and relevant environmental chemistry) including the Tropicana Wash, spring in Death Valley, the lower Virgin River and possibly Big Soda Lame, Nevada

Biogeochemical and historical drivers of microbial community composition and structure in sediments from Mercer Subglacial Lake, West Antarctica

Ice streams that flow into Ross Ice Shelf are underlain by water-saturated sediments, a dynamic hydrological system, and subglacial lakes that intermittently discharge water downstream across grounding zones of West Antarctic Ice Sheet (WAIS). A 2.06 m composite sediment profile was recently recovered from Mercer Subglacial Lake, a 15 m deep water cavity beneath a 1087 m thick portion of the Mercer Ice Stream. We examined microbial abundances, used 16S rRNA gene amplicon sequencing to assess community structures, and characterized extracellular polymeric substances (EPS) associated with distinct lithologic units in the sediments. Bacterial and archaeal communities in the surficial sediments are more abundant and diverse, with significantly different compositions from those found deeper in the sediment column. The most abundant taxa are related to chemolithoautotrophs capable of oxidizing reduced nitrogen, sulfur, and iron compounds with oxygen, nitrate, or iron. Concentrations of dissolved methane and total organic carbon together with water content in the sediments are the strongest predictors of taxon and community composition. δ¹³C values for EPS (−25 to −30‰) are consistent with the primary source of carbon for biosynthesis originating from legacy marine organic matter. Comparison of communities to those in lake sediments under an adjacent ice stream (Whillans Subglacial Lake) and near its grounding zone provide seminal evidence for a subglacial metacommunity that is biogeochemically and evolutionarily linked through ice sheet dynamics and the transport of microbes, water, and sediments beneath WAIS

On the linear fractional self-attracting diffusion

In this paper, we introduce the linear fractional self-attracting diffusion driven by a fractional Brownian motion with Hurst index 1/2<H<1, which is analogous to the linear self-attracting diffusion. For 1-dimensional process we study its convergence and the corresponding weighted local time. For 2-dimensional process, as a related problem, we show that the renormalized self-intersection local time exists in L^2 if $\frac12<H<\frac3{4}$.Comment: 14 Pages. To appear in Journal of Theoretical Probabilit

Solute sources and geochemical processes in Subglacial Lake Whillans, West Antarctica

Subglacial Lake Whillans (SLW), West Antarctica, is an active component of the subglacial hydrological network located beneath 800 m of ice. The fill and drain behavior of SLW leads to long (years to decades) water residence times relative to those in mountain glacier systems. Here, we present the aqueous geochemistry of the SLW water column and pore waters from a 38-cm-long sediment core. Stable isotopes indicate that the water is primarily sourced from basal-ice melt with a minor contribution from seawater that reaches a maximum of ~6% in pore water at the bottom of the sediment core. Silicate weathering products dominate the crustal (non-seawater) component of lake- and pore-water solutes, and there is evidence for cation exchange processes within the clay-rich lake sediments. The crustal solute component ranges from 6 meq L -1 in lake waters to 17 meq L -1 in the deepest pore waters. The porewater profiles of the major dissolved ions indicate a more concentrated solute source at depth (&gt;38 cm). The combination of significant seawater and crustal components to SLW lake and sediment pore waters in concert with ion exchange processes result in a weathering regime that contrasts with other subglacial systems. The results also indicate cycling of marine water sourced from the sediments back to the ocean during lake drainage events

Glacial controls on redox-sensitive trace element cycling in Arctic fjord sediments (Spitsbergen, Svalbard)

Glacial meltwater is an important source of bioessential trace elements to high latitude oceans. Upon delivery to coastal waters, glacially sourced particulate trace elements are processed during early diagenesis in sediments and may be sequestered or recycled back to the water column depending on local biogeochemical conditions. In the glaciated fjords of Svalbard, large amounts of reactive Fe and Mn (oxyhydr)oxides are delivered to the sediment by glacial discharge, resulting in pronounced Fe and Mn cycling concurrent with microbial sulfate reduction. In order to investigate the diagenetic cycling of selected trace elements (As, Co, Cu, Mo, Ni, and U) in this system, we collected sediment cores from two Svalbard fjords, Van Keulenfjorden and Van Mijenfjorden, in a transect along the head-to-mouth fjord axis and analyzed aqueous and solid phase geochemistry with respect to trace elements, sulfur, and carbon along with sulfate reduction rates. We found that Co and Ni associate with Fe and Mn (oxyhydr)oxides and enter the pore water upon reductive metal oxide dissolution. Copper is enriched in the solid phase where sulfate reduction rates are high, likely due to reactions with H2S and the formation of sulfide minerals. Uranium accumulates in the solid phase likely following reduction by both Fe- and sulfate-reducing bacteria, while Mo adsorbs to Fe and Mn (oxyhydr)oxides in the surface sediment and is removed from the pore water at depth where sulfidization makes it particle-reactive. Arsenic is tightly coupled to Fe redox cycling and its partitioning between solid and dissolved phases is influenced by competition with FeS for adsorption sites on crystalline Fe oxides. Differences in trace element cycling between the two fjords suggest delivery of varying amount and composition of tidewater glacier (Van Keulenfjorden) and meltwater stream (Van Mijenfjorden) material, likely related to oxidative processes occurring in meltwater streams. This processing produces a partially weathered, more reactive sediment that is subject to stronger redox cycling of Fe, Mn, S, and associated trace elements upon delivery to Van Mijenfjorden. With climate warming, the patterns of trace element cycling observed in Van Mijenfjorden may also become more prevalent in other Svalbard fjords as tidewater glaciers retreat into meltwater stream valleys

Biogeochemical and historical drivers of microbial community composition and structure in sediments from Mercer Subglacial Lake, West Antarctica

Ice streams that flow into Ross Ice Shelf are underlain by water-saturated sediments, a dynamic hydrological system, and subglacial lakes that intermittently discharge water downstream across grounding zones of West Antarctic Ice Sheet (WAIS). A 2.06 m composite sediment profile was recently recovered from Mercer Subglacial Lake, a 15 m deep water cavity beneath a 1087 m thick portion of the Mercer Ice Stream. We examined microbial abundances, used 16S rRNA gene amplicon sequencing to assess community structures, and characterized extracellular polymeric substances (EPS) associated with distinct lithologic units in the sediments. Bacterial and archaeal communities in the surficial sediments are more abundant and diverse, with significantly different compositions from those found deeper in the sediment column. The most abundant taxa are related to chemolithoautotrophs capable of oxidizing reduced nitrogen, sulfur, and iron compounds with oxygen, nitrate, or iron. Concentrations of dissolved methane and total organic carbon together with water content in the sediments are the strongest predictors of taxon and community composition. δ¹³C values for EPS (−25 to −30‰) are consistent with the primary source of carbon for biosynthesis originating from legacy marine organic matter. Comparison of communities to those in lake sediments under an adjacent ice stream (Whillans Subglacial Lake) and near its grounding zone provide seminal evidence for a subglacial metacommunity that is biogeochemically and evolutionarily linked through ice sheet dynamics and the transport of microbes, water, and sediments beneath WAIS

Microbial sulfur transformations in sediments from Subglacial Lake Whillans

Diverse microbial assemblages inhabit subglacial aquatic environments. While few of these environments have been sampled, data reveal that subglacial organisms gain energy for growth from reduced minerals containing nitrogen, iron, and sulfur. Here we investigate the role of microbially mediated sulfur transformations in sediments from Subglacial Lake Whillans (SLW), Antarctica, by examining key genes involved in dissimilatory sulfur oxidation and reduction. The presence of sulfur transformation genes throughout the top 34 cm of SLW sediments changes with depth. SLW surficial sediments were dominated by genes related to known sulfur-oxidizing chemoautotrophs. Sequences encoding the adenosine-5’-phosphosulfate (APS) reductase gene, involved in both dissimilatory sulfate reduction and sulfur oxidation, were present in all samples and clustered into 16 distinct OTUs. The majority of APS reductase sequences (74%) clustered with known sulfur oxidizers including those within the Sideroxydans and Thiobacillus genera. Reverse-acting dissimilatory sulfite reductase (rDSR) and 16S rRNA gene sequences further support dominance of Sideroxydans and Thiobacillus phylotypes in the top 2 cm of SLW sediments. The SLW microbial community has the genetic potential for sulfate reduction which is supported by experimentally measured low rates (1.4 pmol cm-3d-1) of biologically mediated sulfate reduction and the presence of APS reductase and DSR gene sequences related to Desulfobacteraceae and Desulfotomaculum. Our results also infer the presence of sulfur oxidation, which can be a significant energetic pathway for chemosynthetic biosynthesis in SLW sediments. The water in SLW ultimately flows into the Ross Sea where intermediates from subglacial sulfur transformations can influence the flux of solutes to the Southern Ocean