Trace metal enrichments in Lake Tanganyika sediments: Controls on trace metal burial in lacustrine systems

We investigate the distributions of several key diagenetic reactants (C, S, Fe) and redox-sensitive trace metals (Mo, Cd, Re, U) in sediments from Lake Tanganyika, East Africa. This study includes modern sediments from a chemocline transect, which spans oxygenated shallow waters to sulfidic conditions at depth, as well as ancient sediments from a longer core (∼2 m) taken at ∼900 m water depth. Modern sediments from depths spanning ∼70-335 m are generally characterized by increasing enrichments of C, S, Mo, Cd, and U with increasing water depth but static Fe distributions. It appears that the sedimentary enrichments of these elements are, to varying degrees, influenced by a combination of organic carbon cycling and sulfur cycling. These modern lake characteristics contrast with a period of high total organic carbon (C_org), total sulfur (S_Tot), and trace metal concentrations observed in the 900 m core, a period which follows the most recent deglaciation (∼18-11 ky). This interval is followed abruptly by an interval (∼11-6 ky) that is characterized by lower C, S, U, and Mo. Consistent with other work we suspect that the low concentrations of S, Mo, and U may indicate a period of intense lake mixing, during which time the lake may have been less productive and less reducing as compared to the present. An alternative, but not mutually exclusive, hypothesis is that changes in the lake’s chemical inventory, driven by significant hydrological changes, could be influencing the distribution of sedimentary trace elements through time.     

Introducing new feminist political ecologies

Political Ecology is firmly established as an important area of enquiry within Geography that attends to many of the most important questions of our age, including the politics of environmental degradation and conservation, the neoliberalisation of nature and ongoing rounds of accumulation, enclosure and dispossession, focusing on access and control of resources, and environmental struggles around knowledge and power, justice and governance. This short introductory paper considers how feminists working in this field of enquiry consider the gender dimension to such issues, and how political ecologies might intersect with a feminist objectives, strategies and practices: a focus for early iterations of a promising sub-field, labelled Feminist Political Ecology. It considers a number of epistemological, political and practical challenges that together may account for the relatively limited number of works that self-identify as feminist political ecology. Whilst this has made it difficult for Feminist Political Ecology to gain purchase as a sub-field within the political ecology cannon, this introductory piece highlights fruitful new ways that developments in feminist thinking enrich work in this field, evident in a flowering of recent publications.     

Decision support for climate change adaptation planning in the US: why it needs a coordinated internet-based practitioners’ network

Decision support resources are emerging across the United States to address the adaptation and mitigation challenges associated with climate variability and change. In theory, climate-related decision support identifies the need to move beyond the linear dissemination of information from experts to decision-makers. Interviews with researchers and federal program managers, however, show that in practice there are still wide gaps between the development of climate science and its application. Lessons learned in two example cases of decision support experiments are discussed to highlight some of the on-going challenges in applying climate science, e.g. defining decision support, involving decision-makers, and determining effectiveness. The published literature also shows these reoccurring challenges but emphasizes more collaboration between science and decision-makers as this improves the relevance, compatibility, and accessibility of climate science information and can increase users’ receptiveness. This article proposes that the US Global Change Research Program (USGCRP) can help the development of decision support resources, in one way, by coordinating an Internet-based practitioners’ network. A coordinated network could provide opportunities for climate-related decision support practitioners to build collaborative partnerships, share lessons-learned, provide feedback to the USGCRP, and thereby assist the transition of science into decision-making processes to better address adaptation planning.     

Measurement of advective soil gas flux: results of field and laboratory experiments with CO2

A multi-channel, steady-state flow-through (SSFT), soil-CO₂ flux monitoring system was modified to include a larger-diameter vent tube and an array of inexpensive pyroelectric non-dispersive infrared detectors for full-range (0–100 %) coverage of CO₂ concentrations without dilution. Field testing of this system was then conducted from late July to mid-September 2010 at the Zero Emissions Research and Technology project site located in Bozeman, Montana, USA. Subsequently, laboratory testing was conducted at the Pacific Northwest National Laboratory in Richland, WA, USA using a flux bucket filled with dry sand. In the field, an array of 25 SSFT and 3 non-steady-state (NSS) flux chambers was installed in a 10 × 4 m area, the long boundary of which was directly above a shallow (2-m depth) horizontal injection well located 0.5 m below the water table. Two additional chambers (one SSFT and one NSS) were installed 10 m from the well for background measurements. Volumetric soil moisture sensors were installed at each SSFT chamber to measure mean moisture levels in the top 0.15 m of soil. A total flux of 52 kg CO₂ day^?1 was injected into the well for 27 days and the efflux from the soil was monitored by the chambers before, during, and for 27 days after the injection. Overall, the results were consistent with those from previous years, showing a radial efflux pattern centered on a known “hot spot”, rapid responses to changes in injection rate and wind power, evidence for movement of the CO₂ plume during the injection, and nominal flux levels from the SSFT chambers that were up to sevenfold higher than those measured by adjacent NSS chambers. Soil moisture levels varied during the experiment from moderate to near saturation with the highest levels occurring consistently at the hot spot. The effects of wind on measured flux were complex and decreased as soil moisture content increased. In the laboratory, flux-bucket testing with the SSFT chamber showed large measured-flux enhancement due to the Venturi effect on the chamber vent, but an overall decrease in measured flux when wind also reached the sand surface. Flux-bucket tests at a high flux (comparable to that at the hot spot) also showed that the measured flux levels increase linearly with the chamber-flushing rate until the actual level is reached. At the SSFT chamber-flushing rate used in the field experiment, the measured flux in the laboratory was only about a third of the actual flux. The ratio of measured to actual flux increased logarithmically as flux decreased, and reached parity at low levels typical of diffusive-flux systems. Taken together, the results suggest that values for advective CO₂ flux measured by SSFT and NSS chamber systems are likely to be significantly lower than the actual values due to back pressure developed in the chamber that diverts flux from entering the chamber. Chamber designs that counteract the back pressure and also avoid large Venturi effects associated with vent tubes, such as the SSFT with a narrow vent tube operated at a high chamber-flushing rate, are likely to yield flux measurements closer to the true values.     

An evaluation of the effect of degassing on the oxidation state of hydrous andesite and dacite magmas: a comparison of pre- and post-eruptive Fe2+ concentrations

The bulk (post-eruptive) wt% FeO concentration in each of 11 phenocryst-poor (<5%) andesite and dacite (60–69 wt% SiO₂) lavas from different monogenetic vents in the Mexican arc has been measured by titration, in duplicate. The results match, within analytical error, the wt% FeO content of the magmas during phenocryst growth (pre-euptive), which were calculated on the basis of oxygen fugacity and temperature results from Fe–Ti two-oxide oxygen barometry. The average deviation between the pre- and post-eruptive FeO concentrations is ±0.15 wt%. Application of the plagioclase-liquid hygrometer shows that at the time of phenocryst growth, these 11 magmas contained from ~3–8 wt% H₂O, which was extensively degassed upon eruption. There is no evidence that degassing of ≤8 wt% H₂O changed the oxidation state of these magmas. Calculations of pre-eruptive and post-eruptive oxygen fugacity values relative to the Ni-NiO buffer (in terms of log₁₀ units) for the 11 samples span a similar range; pre-eruptive ∆NNO = −0.9 to +0.7 and post-eruptive ∆NNO = −0.4 to +0.8. The data further show that extensive groundmass (closed-system) crystallization had no affect on bulk Fe³⁺/Fe²⁺ ratios. Finally, there is no systematic variation in the range of pre-eruptive Fe³⁺/Fe^T values of the samples as a function of SiO₂ concentration (i.e., differentiation). Therefore, the results of this study indicate that the elevated Fe³⁺/Fe^T ratios of arc andesites and dacites, compared with magmas erupted in other tectonic settings, cannot be attributed to the effects of (1) degassing of H₂O, (2) closed-system crystallization, and/or (3) differentiation effects, but instead must be inherited from their parental source rocks (i.e., mantle-derived arc basalts).     

Obsessive–compulsive disorder (OCD): Gendered metaphors,blogs and online forums

In order to understand social recovery from mental illness, it is important to examine the role played by social space, including virtual space. This article examined blogs and online forums for people with obsessive–compulsive disorder (OCD). In particular, it addressed gender differences in the metaphors used by men and women in these virtual spaces. Empirical data illustrated that, in general, women are more likely to frame their experiences of OCD as a journey, whereas men are more likely to frame them as a battle. Use of these different metaphors has potential implications for social recovery.     

Late Wisconsin periglacial environments of the southern margin of the Laurentide Ice Sheet reconstructed from pollen analyses

Full‐glacial pollen assemblages from four radiocarbon‐dated interstadial deposits in southwestern Ohio and southeastern Indiana imply the presence of herbaceous vegetation (tundra or muskeg with subarctic indicator Selaginella selaginoides) on the southern margin of the Miami lobe of the Laurentide Ice Sheet ca. 20 000 ¹⁴C yr BP. Scattered Picea (spruce) and possibly Pinus (pine) may have developed regionally ca. 19 000 ¹⁴C yr BP, and ca. 18 000 ¹⁴C yr BP, respectively. Spruce stumps in growth position support a local source of pollen. Prior to the ca. 14 000 ¹⁴C yr BP glacial advance, small amounts of Quercus (oak) and other deciduous pollen suggest development of regional boreal (conifer–hardwood) forests. Copyright © 2002 John Wiley & Sons, Ltd.     

Exploring Agroecological Sustainability: Unearthing Innovators and Documenting a Community of Practice in Southeast Australia

In this article we describe a movement to regenerate and sustainably use native grasslands using innovative grazing and cropping strategies. We find that this movement has the essential characteristics of a “community of practice” (COP) and is a strong example of a bottom-up transition toward a sustainable agroecological farming system. This COP was identified and described using participatory rural appraisals followed by biophysical and sociocultural studies with active COP members. Using these multiple mixed-method approaches helped characterize the COP’s many layers, revealing how and why it is driven and fashioned by innovators who collaborate via joint enterprise, mutual engagement, and shared repertoire. Holistic Management, Grazing for Profit, and Stipa Native Grasses Association were the key enabling programs/associations for the COP, which, like other agroecological movements, exists on the margins of conventional agri-innovation systems and endures with little public acknowledgment or support. It is a potent grass-roots example of adaptive farm management that generates optimism in the farming families involved, and challenges existing research and extension paradigms regarding both innovation and practice change.