Toward a better understanding and quantification of methane emissions from shale gas development

The identification and quantification of methane emissions from natural gas production has become increasingly important owing to the increase in the natural gas component of the energy sector. An instrumented aircraft platform was used to identify large sources of methane and quantify emission rates in southwestern PA in June 2012. A large regional flux, 2.0–14 g CH₄ s⁻¹ km⁻², was quantified for a ∼2,800-km² area, which did not differ statistically from a bottom-up inventory, 2.3–4.6 g CH₄ s⁻¹ km⁻². Large emissions averaging 34 g CH₄/s per well were observed from seven well pads determined to be in the drilling phase, 2 to 3 orders of magnitude greater than US Environmental Protection Agency estimates for this operational phase. The emissions from these well pads, representing ∼1% of the total number of wells, account for 4–30% of the observed regional flux. More work is needed to determine all of the sources of methane emissions from natural gas production, to ascertain why these emissions occur and to evaluate their climate and atmospheric chemistry impacts.Methane is a very important component of the Earth’s atmosphere: it represents a significant component of the natural and anthropogenically forced greenhouse effect, with a global warming potential 28–34 times greater than CO₂ using a 100-y horizon and even greater on shorter time scales (1, 2). It also is an important sink for the hydroxyl radical, the dominant agent that defines the atmosphere’s cleansing capacity (3), has a significant impact on tropospheric ozone, and is one of the important sources of water vapor in the stratosphere, which in turn impacts stratospheric ozone and climate (4). The recent observation that global methane concentrations have begun increasing (5), after a decade of static or decreasing emissions in the late 1990s to ∼2007, has renewed interest in pinpointing the causes of global methane trends. Recently natural gas has been explored as a potential bridge to renewable energy, owing in part to the reduction in carbon emissions produced from electricity generation by natural gas compared with coal (6–9). Advances in drilling and well stimulation techniques have allowed access to previously locked reservoirs of natural gas, such as the Marcellus shale formation in Pennsylvania, which has led to a boom in natural gas production in the last decade (10). This has led to estimations of the carbon footprint of natural gas to examine the impact of increasing our reliance on natural gas for various energy needs (11–16). An important unresolved issue is the contribution of well-to-burner tip CH₄ emission to the greenhouse gas footprint of natural gas use. Given that CH₄ is a much more potent greenhouse gas than CO₂, quantifying CH₄ emissions has become critical in estimating the long- and short-term environmental and economic impacts of increased natural gas use. According to a recent study, if total CH₄ emissions are greater than approximately 3.2% of production, the immediate net radiative forcing for natural gas use is worse than for coal when used to generate electricity (8).The first estimates for CH₄ emissions from shale gas development were reported in late 2010 and are based on uncertain emission factors for various steps in obtaining the gas and getting it to market (17, 18). In the short time since these first estimates, many others have published CH₄ emission estimates for unconventional gas (including tight-sand formations in addition to shales), giving a range of 0.6–7.7% of the lifetime production of a well emitted “upstream” at the well site and “midstream” during processing and 0.07–10% emitted during “downstream” transmission, storage, and distribution to consumers (reviewed in refs. 18 and 19). The highest published estimates for combined upstream and midstream methane emissions (2.3–11.7%) are based on actual top-down field-scale measurements at specific regions (20, 21). Whereas a recent shale gas study (22) based on field sites across the United States to which the authors were given access scaled actual measurements up to the national level and found lower emissions than US Environmental Protection Agency (EPA) estimates, an equally recent study (23) used atmospheric measurements of greenhouse gases across the United States to inform a model and found CH₄ emissions, cumulatively and specifically from fossil fuel production activities, to be underestimated by the EPA.The current range of observed CH₄ emissions from US natural gas systems (2.3–11.7%), if it were representative of the national scale, applied to the reported 2011 unassociated gas production number yields a range of CH₄ emissions between 5.6 and 28.4 Tg CH₄, whereas the EPA reports 6.7 Tg CH₄ from natural gas systems in 2011 and only 28 Tg CH₄ total anthropogenic emissions (24). Natural gas systems are currently estimated to be the top source of anthropogenic CH₄ emission in the United States, followed closely by enteric fermentation, but the top-down observations suggest that natural gas may play a more substantial role than previously thought (24). Inadequate accounting of greenhouse gas emissions hampers efforts to identify and pursue effective greenhouse gas reduction policies.Although it is clear that analysis of the effect of natural gas use would benefit from better measurements of emissions from unconventional gas wells, the inaccessible and transient nature of these leaks makes them difficult to identify and quantify, particularly at a scale at which they are useful for bottom-up inventories or mitigation strategies (i.e., leak rates of individual components or activities). Previous techniques have used either bottom-up inventories of the smallest scale of contributions or top-down apportionment of observed large-scale regional enhancements over a complex area to identify the source of the enhancements (11, 17, 20–23, 25). Although the latter suggest that the leak rate may be higher than what bottom-up inventories have allocated, they give little to no information about where in the upstream production process these leaks occur, thus hampering the interpretation of these data for bottom-up inventories or mitigation purposes.Here we use an aircraft-based approach that enables sampling of methane emissions between the regional and component level scales and can identify plumes from single well pads, groups of well pads, and larger regional scales, giving more information as to the specific CH₄ emission sources. We implemented three types of flights over 2 d in June 2012: investigative (I), mass-balance flux (MB), and regional flux (RF). Details of each flight are presented in

Natural gas of radiolytic origin: An overlooked component of shale gas

Natural gas is an important fossil energy source that has historically been produced from conventional hydrocarbon reservoirs. It has been interpreted to be of microbial, thermogenic, or, in specific contexts, abiotic origin. Since the beginning of the 21^st century, natural gas has been increasingly produced from unconventional hydrocarbon reservoirs including organic-rich shales. Here, we show, based on a careful interpretation of natural gas samples from numerous unconventional hydrocarbon reservoirs and results from recent irradiation experiments, that there is a previously overlooked source of natural gas that is generated by radiolysis of organic matter in shales. We demonstrate that radiolytic gas containing methane, ethane, and propane constitutes a significant end-member that can account for >25% of natural gas mixtures in major shale gas plays worldwide that have high organic matter and uranium contents. The consideration of radiolytic gas in natural gas mixtures provides alternative explanations for so-called carbon isotope reversals and suggests revised interpretations of some natural gas origins. We submit that considering natural gas of radiolytic origin as an additional component in uranium-bearing shale gas formations will lead to a more accurate determination of the origins of natural gas.

Natural gas is extracted from conventional and unconventional hydrocarbon reservoirs to satisfy current energy demands. Three different origins of natural gas have been distinguished in previous literature including microbial, thermogenic, and abiotic (1). Some researchers also advocate for a low-temperature geocatalytic origin of some natural gases (ref. 2 and references therein). Microbial, thermogenic, and geocatalytic gases are derived from organic matter either by the action of microorganisms or due to elevated temperatures during burial of organic-rich sediments or through geocatalytic generation of nonmicrobial gases at low temperatures. Abiotic processes (3) do not involve organic matter but produce gases through gas–water–mineral interactions in the subsurface by reaction of native H₂ with CO₂ (4). The composition and isotopic signatures of natural gas components are frequently used to determine the origin and maturity of the natural gas (Fig. 1). Natural gases of microbial origin consist mostly of methane that is depleted in ¹³C (δ¹³C ranging between less than −90 and −50‰) (5). In contrast, thermogenic gases from shale gas reservoirs typically contain methane, ethane, propane, and higher n-alkanes with δ¹³C of methane varying between −75 and −20‰ (5) dependent on maturity. Geocatalytic gases mostly consist of methane with δ¹³C between −58 and −41‰ (14). Abiotic gases have a wide range of molecular compositions, and their methane is frequently enriched in ¹³C (δ¹³C ranging between −50 and +10‰) (5).Open in a separate windowFig. 1.Revised Bernard plot after Milkov and Etiope (5). Dark blue line indicates a thermogenic maturation line according to ref. 6 with % R_o increasing from 0.6 to 3. Black dashed lines indicate mixing of radiolytic (R) and thermogenic (T) gas components; the green dashed line indicates the mixing of radiolytic gas with a mixture of primary biogenic gas (e.g., methyl type fermentation) and/or secondary microbial gas (both marked as B in the legend). The brown dashed line indicates mixing of radiogenic (R) and microbial gas derived by CO₂ reduction. CR, CO₂ reduction; F, methyl-type fermentation; SM, secondary microbial; OA, oil-associated (midmature) thermogenic gas; LMT, late mature thermogenic gas after Milkov et al. (1). (Inset) Data points from the Woodford Shale with maturities (7) increasing toward lower dryness values. Data are from radiolytic gases (8) and Barnett and Fayetteville (9), Antrim (10), New Albany (11), Woodford (7), Colorado Group (12), and Alum (13) shales.With the onset of the shale gas revolution early in the 21st century facilitated by horizontal drilling technologies combined with high-volume hydraulic fracturing, natural gas has been increasingly produced in recent years from unconventional hydrocarbon reservoirs such as shales with high organic matter content. Such shales are often associated with high contents of radioactive elements (15–17), and hence, the organic matter they contain is exposed to significant radiation doses over geologic time spans. Naturally occurring radioactive isotopes such as ²³⁸U, ²³⁵U, ²³²Th, ²³⁰Th, and ⁴⁰K and their radioactive daughter products emit α- and β-particles and γ-rays that have penetration depths into the organic matter ranging from <100 µm for α-particles (18) and 1 to 5 mm for β-particles to >50 m for γ-rays (19). Potassium (K) and thorium (Th) are usually associated with detrital minerals. The concentration of radioactive ⁴⁰K is too low in shales to produce significant irradiation of surrounding matter since ⁴⁰K constitutes only 0.012% of all K isotopes (20), while concentrations of radioactive thorium can reach 20 ppm (e.g., refs. 21–23) and uranium (U) up to 2,600 ppm (24). Uranium is typically directly associated with organic matter in black shales (25–28), which will absorb most of the energy released during the U decay. For example, organic carbon in the Alum Shale in Europe with, on average, 100 ppm of U absorbed a 10⁸- to 10⁹-Gy radiation dose over the 500 Ma since its deposition (18, 29, 30).High radiation doses can cause changes in the structure and properties of organic matter (31–35). For the fossil organic matter, kerogen, the most notable changes are an increase of aromaticity, of degree of condensation, and of vitrinite reflectance and a decrease in bitumen content (29, 36–42). Ionizing radiation causes polymerization, cross-linking, dealkylation, and aromatization of organic matter (29, 30, 43, 44) and has been shown to produce short-chain alkanes such as methane, ethane, and propane (8). Additionally, experimental irradiation of organic matter showed the importance of mineral surface area and a presence of clay minerals (44) in disintegration of organic matter and formation of radiolytic products including gases. Furthermore, during irradiation, ⁻H^· radicals form in large quantities (45), which might facilitate radiolytic formation of alkanes.Laboratory-based irradiation experiments (8, 18) with organic matter and crude oils have revealed the formation of radiolytic gas that is mainly composed of H₂ (56 to 96 vol. %), while around 2% of the newly formed gas is composed of methane, ethane, and propane with a linear positive relationship between the radiation dosage and the amount of radiolytic H₂ and alkanes produced (19). These radiolytic hydrocarbons are derived from organic matter but neither through microbial nor through temperature-driven reactions, and they have been found to be depleted in ¹³C (δ¹³C of methane less than −65‰, δ¹³C of ethane less than −45‰, and δ¹³C of propane less than −37‰) (8).We note that previous laboratory-based irradiation experiments using shales and fossil organic matter have not used α-particle irradiation, which mostly occurs in U-rich rocks. Thus, the findings and conclusions presented in this paper are based on the assumption that isotopic signatures of radiolytic gases produced during gamma-ray irradiation in laboratory experiments are equivalent to those resulting from alpha radiation in the geosphere. This is supported by similarities observed between irradiated organic matter in laboratory experiments and in nature. Experiments that used gamma rays from a ⁶⁰Co source (18) demonstrated that irradiated organic matter in shales became slightly enriched in ¹³C requiring that the radiolytic gaseous products are depleted in ¹³C. The slight ¹³C enrichment of irradiated organic matter is also observed in natural U-rich rocks (37, 46–48), and thus, radiolytic hydrocarbons formed in such rocks are also expected to be depleted in ¹³C. This indirectly supports the notion that α-radiation in nature causes formation of ¹³C-depleted radiolytic gases in a very similar fashion to that of gamma radiation in laboratory experiments. However, laboratory data are currently scarce, and future experiments with α-particle irradiation of organic shales as well as controlled temperature parameters within the reaction chamber are needed.This study investigates whether radiolytic methane, ethane, and propane (also referred to as “light alkanes” in the subsequent text) constitute a previously overlooked component of natural gas, especially in organic-rich shale gas plays. We demonstrate that light alkanes derived from the irradiation of kerogen and oil make a nonnegligible contribution to natural gas mixtures from unconventional hydrocarbon reservoirs. By using an isotopic maturation-mixing model on a large set of natural gas data, we quantify the effect of the admixture of light alkanes of radiolytic origin to gases of thermogenic and microbial origin. We also demonstrate that the resulting isotope signatures can lead to misinterpretation of gas origin and maturation levels, and we provide an alternative explanation of the so-called isotope reversals in natural gas from unconventional hydrocarbon reservoirs. We conclude that radiolytic gas derived from organic matter constitutes a previously not recognized type of natural gas that needs to be considered especially in organic-rich unconventional hydrocarbon reservoirs that frequently contain uranium (U) in substantial quantities (15, 16).     

Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction

Horizontal drilling and hydraulic fracturing are transforming energy production, but their potential environmental effects remain controversial. We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of drinking water samples, with average concentrations six times higher for homes <1 km from natural gas wells (P = 0.0006). Ethane was 23 times higher in homes <1 km from gas wells (P = 0.0013); propane was detected in 10 water wells, all within approximately 1 km distance (P = 0.01). Of three factors previously proposed to influence gas concentrations in shallow groundwater (distances to gas wells, valley bottoms, and the Appalachian Structural Front, a proxy for tectonic deformation), distance to gas wells was highly significant for methane concentrations (P = 0.007; multiple regression), whereas distances to valley bottoms and the Appalachian Structural Front were not significant (P = 0.27 and P = 0.11, respectively). Distance to gas wells was also the most significant factor for Pearson and Spearman correlation analyses (P < 0.01). For ethane concentrations, distance to gas wells was the only statistically significant factor (P < 0.005). Isotopic signatures (δ¹³C-CH₄, δ¹³C-C₂H₆, and δ²H-CH₄), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas ⁴He to CH₄ in groundwater were characteristic of a thermally postmature Marcellus-like source in some cases. Overall, our data suggest that some homeowners living <1 km from gas wells have drinking water contaminated with stray gases.     

Forecasting potential global environmental costs of livestock production 2000-2050

Food systems--in particular, livestock production--are key drivers of environmental change. Here, we compare the contributions of the global livestock sector in 2000 with estimated contributions of this sector in 2050 to three important environmental concerns: climate change, reactive nitrogen mobilization, and appropriation of plant biomass at planetary scales. Because environmental sustainability ultimately requires that human activities as a whole respect critical thresholds in each of these domains, we quantify the extent to which current and future livestock production contributes to published estimates of sustainability thresholds at projected production levels and under several alternative endpoint scenarios intended to illustrate the potential range of impacts associated with dietary choice. We suggest that, by 2050, the livestock sector alone may either occupy the majority of, or significantly overshoot, recently published estimates of humanity's "safe operating space" in each of these domains. In light of the magnitude of estimated impacts relative to these proposed (albeit uncertain) sustainability boundary conditions, we suggest that reining in growth of this sector should be prioritized in environmental governance.     

Canine long-term bone marrow culture neutrophil production and functionality

This in vitro study has been conducted to determine the optimal experimental conditions under which to produce canine neutrophils in long-term bone marrow cultures (LTBMC), establish functional parameters of neutrophils obtained from LTBMC and peripheral blood and to ascertain whether these cells display physiological similarities. Our aim is to provide an experimental model, enabling a correlation between hemopoietic injury and neutrophil functionality. The authors demonstrate for the first time that canine neutrophils grown in cultures are able to produce oxyradicals capable of killing bacterial products. Moreover, culture-grown neutrophils contain gelatinase granules, a marker of terminal neutrophil differentiation, and express a specific surface antigen. The results described in this article illustrate the development of a dynamic system that mimics physiological hemopoiesis.     

Biomass use,production, feed efficiencies,and greenhouse gas emissions from global livestock systems

We present a unique, biologically consistent, spatially disaggregated global livestock dataset containing information on biomass use, production, feed efficiency, excretion, and greenhouse gas emissions for 28 regions, 8 livestock production systems, 4 animal species (cattle, small ruminants, pigs, and poultry), and 3 livestock products (milk, meat, and eggs). The dataset contains over 50 new global maps containing high-resolution information for understanding the multiple roles (biophysical, economic, social) that livestock can play in different parts of the world. The dataset highlights: (i) feed efficiency as a key driver of productivity, resource use, and greenhouse gas emission intensities, with vast differences between production systems and animal products; (ii) the importance of grasslands as a global resource, supplying almost 50% of biomass for animals while continuing to be at the epicentre of land conversion processes; and (iii) the importance of mixed crop–livestock systems, producing the greater part of animal production (over 60%) in both the developed and the developing world. These data provide critical information for developing targeted, sustainable solutions for the livestock sector and its widely ranging contribution to the global food system.The importance of the livestock sector as a user of natural resources, as a source of livelihoods, and as an engine of economic growth has been the focus of significant attention in the last decade (1–5). As the largest land-use system on Earth, the livestock sector occupies 30% of the world’s ice-free surface, contributes 40% of global agricultural gross domestic product, and provides income for more than 1.3 billion people and nourishment for at least 800 million food-insecure people, all the while using vast areas of rangelands, one-third of the freshwater, and one-third of global cropland as feed. In the process, livestock can both contribute valuable nutrients for crops and be responsible for nutrient pollution and land degradation, and they can both provide critically important protein and micronutrients to human diets and contribute to obesity. The sector has many dualities, and the roles played by livestock change depending on location and circumstances. However, there is growing recognition that improving the environmental performance of livestock systems as well as establishing sustainable levels of consumption of animal-sourced foods, are essential for the sustainability of the global food system (5–7).Insufficient attention has been paid to the generation of livestock data at the level of detail required for elucidating their future role in attaining key global sustainability goals. Some of these goals are poverty reduction, food and nutritional security, ecosystem protection, mitigation of greenhouse gases (GHG), and adaptation to climate change, for example. To date, global integrated assessments have included incomplete representations, at best, of the livestock sector (8–11). Some global analyses exist (1, 12–16); although these have focused on specific topics, such as biomass use, GHG emissions, and water footprints, they have required methodological simplifications to achieve global coverage. Such analyses fail to do justice to the considerable heterogeneity that exists in livestock production systems, management practices, resource-use efficiencies, and mitigation potentials. Detailed, disaggregated global livestock data are essential for informing policy analyses of the choices facing humanity in feeding the world, managing ecosystems, promoting economic growth, and sustaining the livelihoods of the poor. If the problems are global, the solutions are generally local and highly situation-specific: high-resolution spatially explicit data are critical if targeting of technology and policy to achieve sustainability is to be efficient and effective.Here we take one step toward filling a critical data gap for global change and sustainability research of the world’s food and ecosystems. We are unique in developing and describing a global, biologically consistent, spatially disaggregated dataset on biomass use, productivity, GHG emissions, and key resource-use efficiencies for the livestock sector, broken down into 28 geographical regions, 8 production systems, 4 animal species (cattle, small ruminants, pigs, and poultry), and 3 animal products (milk, meat, and eggs). We analyze the biological consistency of the data and discuss the main drivers of resource-use efficiency in the global livestock sector. We discuss how these data can contribute to the unraveling of key sustainability issues for the sector and conclude with further data and research needs.     

Pulse oximetry versus arterial blood gas specimens in long-term oxygen therapy

Portable pulse oximeters are now widely available for the assessment of arterial oxygenation, and the U.S. Medicare program considers saturation readings to be acceptable substitutes for arterial PO₂ in selecting patients for long-term oxygen therapy (LTOT). Current oximeters are reasonably accurate (plus or minus 4 or 5 percent of the co-oximetry value), but the clinician should be aware of several potential problems. Readings may be inaccurate in the presence of hemodynamic instability, carboxyhemoglobinemia, jaundice, or dark skin pigmentation, and also during exercise. Indicated saturation may substantially overestimate arterial PO₂ if the patient is alkalemic. Pulse oximetry cannot detect hypercapnia or acidosis. For these and other reasons, pulse oximetry should not be used in initial selection of patients for LTOT, as a substitute for arterial blood gas analysis in the evaluation of patients with undiagnosed respiratory disease, during formal cardiopulmonary exercise testing, or in the presence of an acute exacerbation. Pulse oximetry is an important addition to the clinician’s armamentarium, however, for titrating the oxygen dose in stable patients, in assessing patients for desaturation during exercise, for sleep studies, and for in-home monitoring.     

Weaning from long-term mechanical ventilation

As many as 5% of patients who need mechanical ventilation will require prolonged mechanical ventilation (PMV). The cost of their care and its associated morbidity is alarming; however, good outcomes can be achieved when their care is specialized and delivered in a programmatic manner. In this article, we review some of the common and potentially reversible reasons why patients fail successfully liberation from mechanical ventilation. We examine the outcomes of patients requiring PMV and present evidence that supports the development of specialized units where patients can be cohorted and may produce better outcomes than would be likely if these patients remained in the ICU.     

Intestinal gas production following ingestion of fruits and fruit juices

Human intestinal gas production was measured by breath hydrogen and rectal flatus analysis following ingestion of test meals of five fruit juices and two fruits. Of the juices fed, only orange juice and apricot nectar were without effect on one or more of these parameters. Apple juice caused an increase in hydrogen production in all subjects and an increase in rectal flatus in 4 of 5 subjects tested. Grape juice, raisins and bananas significantly elevated hydrogen production. Prune juice caused diarrhea and a very large increase in breath hydrogen. Possible relationships to carbohydrate composition are discussed.Supported in part of USDA Cooperative Agreement No. 12-14-100-10000 (74) and National Institutes of Health Grant AM 10202.     

Stromal growth factor production in irradiated lectin exposed long-term murine bone marrow cultures

Hematopoietic regulatory factors produced by adherent (stromal) cells in long-term murine bone marrow cultures have been investigated. Using an in situ double layer agar overlay system, we demonstrated that exposure of the stromal cells to 1,100-rad irradiation increased their activities in stimulating colony formation of FDC-P1, an interleukin 3 (IL 3)-responsive cell line. The colony-stimulating activities (CSAs) of the irradiated stroma also stimulated normal marrow cells to form granulocyte-macrophage, megakaryocyte, and mixed lineage colonies. Addition of the lectin pokeweed mitogen to the irradiated stroma increased the level of CSAs. The FDC-P1 CSA of the irradiated stroma was inhibited by antibodies directed against murine granulocyte- macrophage colony stimulating factor (GM-CSF) but not by those against murine IL 3. Stromal-derived CSA for marrow cells was also partially blocked by anti-GM-CSF antibodies, probably reflecting the presence of other CSAs such as CSF-1. This latter growth factor has been found to be present in conditioned media from Dexter stroma, but levels are not increased after irradiation or lectin exposure. Partially purified GM- CSF, like IL 3, stimulated FDC-P1 proliferation and granulocyte, macrophage, and megakaryocyte colony formation. These results indicate that the major terminal differentiating hormone elicited by irradiation or lectin exposure of murine marrow stromal cells is GM-CSF. This growth factor, along with CSF-1, can account for the differentiated progeny produced in this system: macrophages, granulocytes, and megakaryocytes.     

Extracellular matrix production by the adherent cells of long-term murine bone marrow cultures

We have studied the deposition of extracellular matrix proteins in the adherent stroma of long-term murine bone marrow cultures. Stable hematopoiesis was maintained for greater than 12 wk. At selected intervals, culture dishes were sacrificed by removing all nonadherent cells and air drying the dishes. The adherent stromal layer was analyzed for the presence of intracellular and extracellular collagen, fibronectin, and laminin using double immunofluorescent staining with specific antisera against these matrix components. In cultures examined during the first 2 wk, large numbers of stromal cells contained collagen, fibronectin, and laminin. Over the next 2 wk, an extensive extracellular network of fibronectin, laminin, and collagen was deposited on the dishes, which persisted throughout the life of the cultures. In contrast to a previous report, we detected substantial numbers of endothelial cells by means of immunofluorescent staining of stromal cells with antisera to type IV collagen, laminin, and factor VIII antigen. Although deposition of these extracellular matrix proteins coincides with onset of active hematopoietic cell production, the relative roles of the stromal cells and the extracellular matrix in supporting hematopoiesis in murine bone marrow cell cultures remain to be determined.     

The effect of lithium on growth factor production in long-term bone marrow cultures

We have previously reported that lithium chloride (LiCl) stimulates the production of granulocyte-macrophage colony-forming cells (GM-CFC), pluripotent stem cells (CFU-S), and differentiated granulocytes, macrophages and megakaryocytes in murine Dexter marrow cultures and that this effect appears to be mediated indirectly by a radioresistant adherent marrow cell. In this study we have established that exposure of murine Dexter cultures to LiCl (4 mEq/L) causes an increase of colony-forming cell megakaryocytes (CFU-meg) over 1 to 6 weeks of culture in both supernatant (188% to 611%) and stromal phases (123% to 246%). Moreover, we have shown that lithium treatment of either irradiated (1,100 rad) or unirradiated stromal cells increased production of activities stimulating formation of megakaryocyte, granulocyte, macrophage, and mixed lineage colonies and proliferation of the factor-dependent cell line, FDC-P1. This FDC-P1 stimulatory activity was completely blocked by an antibody to purified recombinant granulocyte-macrophage colony stimulating factor (rGM-CSF). The baseline or lithium-induced--stromal-derived bone marrow colony stimulating activity was partially blocked by the antibody to rGM-CSF and by an antibody to purified colony stimulating factor I (CSF-1); the two antibodies combined resulted in greater than 90% inhibition of the lithium-induced marrow stimulatory activity. In addition, radioimmunoassay (RIA) showed that although CSF-1 was detectable in supernatants of these cultures, exposure to lithium did not increase CSF-1 levels. These data indicate that Dexter stromal cells produce CSF- 1 and GM-CSF and that lithium appears to exert its stimulatory effects on in vitro myelopoiesis by inducing production of GM-CSF.     

Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production

Carbon release due to permafrost thaw represents a potentially major positive climate change feedback. The magnitude of carbon loss and the proportion lost as methane (CH₄) vs. carbon dioxide (CO₂) depend on factors including temperature, mobilization of previously frozen carbon, hydrology, and changes in organic matter chemistry associated with environmental responses to thaw. While the first three of these effects are relatively well understood, the effect of organic matter chemistry remains largely unstudied. To address this gap, we examined the biogeochemistry of peat and dissolved organic matter (DOM) along a ∼40-y permafrost thaw progression from recently- to fully thawed sites in Stordalen Mire (68.35°N, 19.05°E), a thawing peat plateau in northern Sweden. Thaw-induced subsidence and the resulting inundation along this progression led to succession in vegetation types accompanied by an evolution in organic matter chemistry. Peat C/N ratios decreased whereas humification rates increased, and DOM shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH₄ and CO₂ production potentials, higher relative CH₄/CO₂ ratios, and a shift in CH₄ production pathway from CO₂ reduction to acetate cleavage. These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH₄. This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.High-latitude soils in the Northern Hemisphere contain an estimated 1,400–1,850 petagrams (Pg) of carbon, of which ∼277 Pg is in peatlands within the permafrost zone (1, 2). This quantity of 277 Pg represents over one-third of the carbon stock in the atmosphere (ca. 800 Pg) (3). The fate of this carbon in a warming climate—i.e., the responses of net carbon balance and CH₄ emissions—is important in predicting climate feedbacks of permafrost thaw. Although northern peatlands are currently a net carbon sink, and have been since the end of the last glaciation, they are a net source of CH₄ (4, 5), emitting 0.046–0.09 Pg of carbon as CH₄ per year (4, 6, 7). Due to CH₄’s disproportionate global warming potential (33× CO₂ for 1 kg CH₄ vs. 1 kg CO₂ at a 100-y timescale) (8), this is equivalent to 6–12% of annual fossil fuel emissions of CO₂ (8.7 Pg of C) (9). The thaw of permafrost peatlands may alter their CH₄ and CO₂ emissions due to mobilization of formerly frozen carbon, higher temperatures, altered redox conditions, and evolving organic matter chemistry. Changes in carbon emissions, and in CH₄ emission in particular, could have potentially significant climate impacts.CH₄ is produced by two primary mechanisms (10–12), distinguishable by δ¹³C values. The reduction of CO₂ with H₂ (hydrogenotrophic production) generally produces CH₄ more depleted in ¹³C (δ¹³C = −110 to −60‰) than CH₄ produced by the cleavage of acetate into CH₄ and CO₂ (δ¹³C = −70 to −30‰) (10, 11, 13–15). Due to the coproduction or utilization of CO₂ during CH₄ production (10–12, 16, 17), δ¹³C_CH4 also depends on δ¹³C_CO2, so we use the more robust parameter α_C (10) to represent the isotopic separation between CH₄ and CO₂. Despite the two production pathways’ stoichiometric equivalence (17), they are governed by different environmental controls (18). Distinguishing these controls and further mapping them is therefore essential for predicting future changes in CH₄ formation under changing environmental conditions. Several studies have suggested that the proportion of CH₄ produced by acetate cleavage relative to CO₂ reduction is likely to increase with increasing pH (19, 20) and organic matter reactivity (12, 14, 15), but direct evidence of the latter is lacking.In this study, we tested the hypotheses that (i) organic matter reactivity increases with permafrost thaw due to thaw-induced subsidence and associated shifts in hydrology and plant community (21), and (ii) CH₄ production shifts from hydrogenotrophic to acetoclastic due to this increase in organic matter reactivity. We assessed organic matter reactivity along a distinct chronosequence of permafrost thaw stages with differing plant community and hydrology by performing anaerobic incubations of peat collected along this sequence. We then compared the results to peat and dissolved organic matter (DOM) chemical structure, as described by C/N ratios and Fourier transform infrared (FTIR) spectroscopy of peat and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) of DOM. Our study specifically addresses the effect of thawing permafrost, and its attendant shifts in hydrology and plant communities, on CH₄ and CO₂ production potentials and mechanisms, via changes in organic matter chemical composition (commonly referred to as organic matter “quality”) in a thawing peatland complex.