Birgit Hagedorn

Molecular and biogeochemical evidence for methane cycling beneath the western margin of the Greenland Ice Sheet

Microbial processes that mineralize organic carbon and enhance solute production at the bed of polar ice sheets could be of a magnitude sufficient to affect global elemental cycles. To investigate the biogeochemistry of a polar subglacial microbial ecosystem, we analyzed water discharged during the summer of 2012 and 2013 from Russell Glacier, a land-terminating outlet glacier at the western margin of the Greenland Ice Sheet. The molecular data implied that the most abundant and active component of the subglacial microbial community at these marginal locations were bacteria within the order Methylococcales (59–100% of reverse transcribed (RT)-rRNA sequences). mRNA transcripts of the particulate methane monooxygenase (pmoA) from these taxa were also detected, confirming that methanotrophic bacteria were functional members of this subglacial ecosystem. Dissolved methane ranged between 2.7 and 83 μM in the subglacial waters analyzed, and the concentration was inversely correlated with dissolved oxygen while positively correlated with electrical conductivity. Subglacial microbial methane production was supported by δ13C-CH4 values between −64‰ and −62‰ together with the recovery of RT-rRNA sequences that classified within the Methanosarcinales and Methanomicrobiales. Under aerobic conditions, >98% of the methane in the subglacial water was consumed over ∼30 days incubation at ∼4 °C and rates of methane oxidation were estimated at 0.32 μM per day. Our results support the occurrence of active methane cycling beneath this region of the Greenland Ice Sheet, where microbial communities poised in oxygenated subglacial drainage channels could serve as significant methane sinks.

Diversity and potential sources of microbiota associated with snow on western portions of the Greenland Ice Sheet

Snow overlays the majority of the Greenland Ice Sheet (GrIS). However, there is very little information available on the microbiological assemblages that are associated with this vast and climate-sensitive landscape. In this study, the structure and diversity of snow microbial assemblages from two regions of the western GrIS ice margin were investigated through the sequencing of small subunit ribosomal RNA genes. The origins of the microbiota were investigated by examining correlations to molecular data obtained from marine, soil, freshwater and atmospheric environments and geochemical analytes measured in the snow. Snow was found to contain a diverse assemblage of bacteria (Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria) and eukarya (Alveolata, Fungi, Stramenopiles and Chloroplastida). Phylotypes related to archaeal Thaumarchaeota and Euryarchaeota phyla were also identified. The snow microbial assemblages were more similar to communities characterized in soil than to those documented in marine ecosystems. Despite this, the chemical composition of snow samples was consistent with a marine contribution, and strong correlations existed between bacterial beta diversity and the concentration of Na(+) and Cl(-) . These results suggest that surface snow from western regions of Greenland contains exogenous microbiota that were likely aerosolized from more distant soil sources, transported in the atmosphere and co-precipitated with the snow.

Spatial and temporal distribution of soil organic carbon in nonsorted striped patterned ground of the High Arctic

[1] The role of periglacial processes on soil carbon distribution is examined at a High Arctic site in northwest Greenland. A 16-m trench dug across a series of nonsorted stripes at Thule Air Base revealed sand-rich wedges underlying striped, vegetated troughs, and organic-rich soil horizons buried at depth. The site has sparse prostrate vegetation and is estimated to contain 9.4 kg/m 2 of soil organic carbon (SOC) in the active layer. The distribution of carbon is variable with nearly half (49%) stored in the sand wedges, which only account for 10% of the trench area. Additionally, 62% of the total SOC was found below 25 cm, highlighting the significant role of cryoturbation and physical redistribution of carbon in permafrost-affected soils. Carbon in the active sand-rich wedges dates from modem at the surface (65 ± 35 radiocarbon years) to 2695 ± 40 radiocarbon years at depth, and carbon turnover time appears to be ∼450 years. Buried organic horizons found at 50-70 cm depth have radiocarbon ages of 27,480-31,900 BP. A conceptual model is proposed in which the active sand wedges have developed in an approximately 30 ka surface containing buried soils preserved in permafrost or under a cold-based glacier. As the ice retreated and soils warmed, soil development and active cryoturbation resumed forming nonsorted stripes in the modern surface.

Hydrology and Geochemistry of River-borne Material in a High Arctic Drainage System, Zackenberg, Northeast Greenland

The roles of chemical and mechanical weathering in permafrost regions were assessed, by measuring stream discharge and major, trace, and rare earth elements (REE) of suspended matter (SPM), river-bed sediments (RBS), and water in two lithologically different catchments in the High Arctic at Zackenberg, Northeast Greenland. The drainage basin contains sedimentary and crystalline rocks. In streams draining the sedimentary rock area, SPM and total dissolved solutes (TDS) are high with maximum values of 2500 mg L−1 and 105 μS cm−1, respectively. Variation of both relates to changes in vegetation and morphology. Mineral fractionation during transport and soil-forming processes in the sedimentary portion of the study area lead to characteristic chemical profiles for the SPM and RBS. Streams draining the crystalline rock area have low SPM (18 mg L−1) and TDS (14 μS cm−1) as a result of poor soil development and a lack of vegetation. Mechanical denudation exceeds chemical denudation by an order of magnitude for the entire catchment. Because the REE distributions of the crystalline differ from those in the sedimentary SPM differ, it is possible to quantify source rock contributions to the main outflow using a mixing calculation. A mass balance comparing the SPM in the main outflow with the tributaries, using the REEs as “fingerprints,” indicates that about 90% of the sedimentary basin suspended matter is redeposited before reaching the outflow, at least over the period of observation. Taking this redeposition into account, the rate of chemical denudation (100 kg km−2 d−1) exceeds mechanical denudation (70 kg km−2 d−1) in the sedimentary drainage basin.

Di(2-ethylhexyl) phthalate inhibits B cell proliferation and reduces the abundance of IgM-secreting cells in cultured immune tissues of the rainbow trout.

Plasticizer di(2-ethylhexyl) phthalate (DEHP) and its active metabolite MEHP have important immunotoxic effects in mammalian species, including inhibition of cell proliferation, inflammation inhibition, lowering of the antibody response, and apoptosis. Virtually nothing is known about the potential detrimental effects of DEHP/MEHP on the teleost immune system, although phthalates are a likely threat to fish health. Here we investigated whether short-term in vitro DEHP exposure would affect B lineage cells in the rainbow trout, using cultured immune tissues. Cell culture conditions, evidence of cellular incorporation of DEHP, and possible effects of DEHP on immune genes were first established using the mouse pre-B cell line PD31 and data confirmed a dose-dependent cellular uptake of DEHP using liquid chromatography-coupled ion trap mass spectrometry. Effects of in vitro DEHP exposure on trout B cell proliferation were tested by flow cytometry. Significant, dose-dependent inhibition was evident in both anterior and posterior kidney cultures after 24 h exposure to ≥4 μM DEHP. DEHP-induced cell death was not significant for the range of DEHP tested. Further, the abundance of IgM-secreting plasmablasts and plasma cells was significantly reduced after in vitro exposure of ≥16 μM DEHP for 2 or 7 days. Finally, in vitro DEHP exposure significantly lowered the levels of secreted HCmu transcripts in a dose-dependent manner. B lineage cells from posterior kidney were more sensitive to effects of in vitro DEHP exposure than those from anterior kidney. Together, the data support a model where DEHP modifies the normal B cell activation pathways in rainbow trout, promoting B cell differentiation while suppressing plasmablast expansion, resulting in fewer IgM-secreting plasma cells. Insufficient production of protective antibody make fish more susceptible to infection, and increases their risk for disease and mortality in polluted waters.

An enhanced model of the contemporary and long‐term (200 ka) sublimation of the massive subsurface ice in Beacon Valley, Antarctica

A massive ice body buried under several decimeters of dry regolith in Beacon Valley, Antarctica, is believed to be more than 1 Ma old and perhaps over 8.1 Ma; however, vapor diffusion models suggest that subsurface ice in this region is not stable under current climate conditions. To better understand the controls on sublimation rates and stability of this massive ice, we have modeled vapor diffusion using 12 years of climate and soil temperature data from 1999 to 2011, including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of ground ice sublimation. The model is then extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures estimated from ice core data from nearby Taylor Dome and a relationship between atmospheric temperature and humidity derived from our meteorological records. The model quantifies the impact of episodic snow events; they account for a nearly 30% reduction in the massive ice loss. The sublimation rate of ground ice averages 0.11 mm a−1 between 1999 and 2011 in Beacon Valley. Parameterized with past environmental conditions and assuming the same regolith thickness, the modeled sublimation rate of ground ice in Beacon Valley averages 0.09 mm a−1 for the last 200 ka, comparable to the long-term average rate estimated independently from various studies based on cosmogenic isotopes. This study provides a realistic estimate of the long-term sublimation history and supports the inference that the buried ice in Beacon Valley is older than 1 Ma.

Tissue Phthalate Levels Correlate With Changes in Immune Gene Expression in a Population of Juvenile Wild Salmon.

Phthalates have detrimental effects on health and have been shown to dysregulate the immune system of mammals, birds, and fish. We recently reported that di(2-ethylhexyl) phthalate exposure reduces the abundance and inhibits the proliferation of rainbow trout (Oncorhynchus mykiss) IgM+ B lymphocytes and expression of secreted immunoglobulin heavy-chain mu transcripts in an in vitro culture system. We proposed that phthalates act as immunomodulators by modifying the normal B cell-activation pathways by accelerating B cell differentiation while suppressing plasmablast expansion, thus resulting in fewer IgM-secreting plasma cells. This hypothesis was tested here in an in vivo field study of juvenile Dolly Varden (Salvelinus malma) from a plastic-polluted lake in the Gulf of Alaska. Fish tissues were analyzed for both phthalate levels using liquid chromatography-coupled tandem mass spectrometry and for changes in immune gene expression using reverse transcriptase-real time polymerase chain reaction. Results showed that fish with higher tissue levels of di(2-ethylhexyl) phthalate, di(n-butyl) phthalate, and/or dimethyl phthalate expressed significantly fewer secreted and membrane-bound immunoglobulin heavy-chain mu and Blimp1 transcripts in their hematopoietic tissue. This suggests that in vivo uptake of phthalates in fish changes the expression of B cell-specific genes. Chronic exposure to phthalates likely dysregulates normal B-lymphoid development and antibody responses in salmonids and may increase susceptibility to infection. Given the conserved nature of B-lineage cells in vertebrate animals, other marine species may be similarly affected by chronic phthalate exposure.

Characterization of water dynamics in frozen soils by solid-state deuteron NMR

The presence of unfrozen water in soils at sub-freezing temperatures is important for biogeochemical processes as well as for the genesis of landscapes and survival of life. While several mechanisms can lead to the existence of liquid water at sub-freezing temperatures, this work focuses on the dynamical (entropic) contribution stemming from motions of water molecules at water-soil or water-ice interfaces. We demonstrate the utility of solid-state (2)H NMR methods for characterization of water dynamics in soils on various time scales. Using a sample from McMurdo Dry Valleys, Antarctica, we show the existence of dynamics spanning a milliseconds to picoseconds time scale range. Computational modeling allows for a quantitative description of the dynamics, which involves models such as an exchange between bound and free water, and changes in effective viscosity of water in the soil matrix.

Predicting risk of trace element pollution from municipal roads using site-specific soil samples and remotely sensed data

Studies of environmental processes exhibit spatial variation within data sets. The ability to derive predictions of risk from field data is a critical path forward in understanding the data and applying the information to land and resource management. Thanks to recent advances in predictive modeling, open source software, and computing, the power to do this is within grasp. This article provides an example of how we predicted relative trace element pollution risk from roads across a region by combining site specific trace element data in soils with regional land cover and planning information in a predictive model framework. In the Kenai Peninsula of Alaska, we sampled 36 sites (191 soil samples) adjacent to roads for trace elements. We then combined this site specific data with freely-available land cover and urban planning data to derive a predictive model of landscape scale environmental risk. We used six different model algorithms to analyze the dataset, comparing these in terms of their predictive abilities and the variables identified as important. Based on comparable predictive abilities (mean R2 from 30 to 35% and mean root mean square error from 65 to 68%), we averaged all six model outputs to predict relative levels of trace element deposition in soils-given the road surface, traffic volume, sample distance from the road, land cover category, and impervious surface percentage. Mapped predictions of environmental risk from toxic trace element pollution can show land managers and transportation planners where to prioritize road renewal or maintenance by each road segments relative environmental and human health risk.