Equilibrium modeling of U(VI) speciation in high carbonate groundwaters: Model error and propagation of uncertainty

Remediation of U-contaminated sites relies upon thermodynamic speciation calculations to predict U(VI) movement in the subsurface. However, reliability and applicability of geochemical speciation and reactive transport models may be limited by determinate (model) errors and random (uncertainty) errors in the equilibrium speciation calculations. This study examines propagated uncertainty in two types of subsurface calculations: I. Dissolved U(VI) speciation based on measured analytical constraints and solution phase equilibria and II. Overall U(VI) speciation which combined the dissolved phase equilibria with previously published adsorption reactions. Three levels of uncertainty, instrumental uncertainty, temporal variation and spatial variation across a site, were investigated using first-derivative sensitivity calculations and Monte Carlo simulations. Dissolved speciation calculations were robust, with minimal amplification of uncertainty and normal output distributions. The most critical analytical constraints in the dissolved system are pH, DIC, total U and total Ca, with some effect from dissolved . When considering adsorption equilibria, calculations were robust with respect to adsorbed U(VI) concentration prediction, but bimodal distributions of dissolved U(VI) concentrations were observed in simulations with background levels of total U(VI) and higher (spatial and temporal variability) estimates of input uncertainty. Consequently, sorption model predictions of dissolved U(VI) may not be robust with respect these higher levels of uncertainty.     

Strengthening conceptual foundations: Analysing frameworks for ecosystem services and poverty alleviation research

A research agenda is currently developing around the linkages between ecosystem services and poverty alleviation. It is therefore timely to consider which conceptual frameworks can best support research at this nexus. Our review of frameworks synthesises existing research on poverty/environment linkages that should not be overlooked with the adoption of the topical language of ecosystem services. A total of nine conceptual frameworks were selected on the basis of relevance. These were reviewed and compared to assess their ability to illuminate the provision of ecosystem services, the condition, determinants and dynamics of poverty, and political economy factors that mediate the relationship between poverty and ecosystem services. The paper synthesises the key contributions of each of these frameworks, and the gaps they expose in one another, drawing out lessons that can inform emerging research. Research on poverty alleviation must recognize social differentiation, and be able to distinguish between constraints of access and constraints of aggregate availability of ecosystem services. Different frameworks also highlight important differences between categories of services, their pathways of production, and their contribution to poverty alleviation. Furthermore, we highlight that it is important to acknowledge the limits of ecosystem services for poverty alleviation, given evidence that ecosystem services tend to be more associated with poverty prevention than reduction. We conclude by reflecting on the relative merits of dynamic Social–Ecological Systems frameworks versus more static checklists, and suggest that research on ecosystem services and poverty alleviation would be well served by a new framework distilling insights from the frameworks we review.     

Spectroscopic constraints on outflows from BN-type objects

New high-quality high spectral resolution observations of the HI line emission from massive young stellar objects are described and discussed. It is proposed that two distinct physical components contribute to the observed emission. One of these is an optically-thick high-velocity stellar wind, the other a more slowly moving optically-thin volume of gas that may, in the case of S106IR at least, be caused by mass loading of the stellar wind. This decomposition is shown to resolve a long-standing problem regarding the relative widths of high and low opacity lines.     

De Draconis: Spectroscopic orbit,rotation effect and physical model

New spectroscopic observations are used for the determination of orbital elements and for a study of the rotation effect of DE Draconis. The primary component is found to rotate much faster than the synchronous rate and with its axis of rotation possibly inclined with respect to the perpendicular to the orbital plane. The system is fully detached and the stars are relatively young and unevolved.     

Inundation of a low-lying urban atoll island: Majuro,Marshall Islands

Natural Hazards - Majuro is a low-lying island perched on a coral atoll in the central Pacific Ocean and is home to nearly 28,000 people. Considered highly vulnerable to the impacts of marine...     

Proposal for applying a component-based mixture approach for ecotoxicological assessment of fracturing fluids

Hydraulic fracturing is increasingly being used to produce gas from unconventional resource sites for energy supply. Therefore, concerns about risks of this technology related to human health and the environment have to be addressed. Among the major issues is the potential contamination of surrounding water systems by chemical additives used in fracturing fluids. In this study, the ecotoxicological hazards of fracturing fluids, both, their individual components (chemicals) as well as their mixtures (product) were assessed using a component-based mixture approach. For five exemplary fracturing fluids, 40–90 wt% of the contained substances could unambiguously be defined in their chemical identity. The concentrations used in the applied fluid mixture were considered as (maximum) exposure concentrations. For components with mass fractions between 10 and 74 wt%, the effect concentrations for acute and chronic toxicity of fish, daphnia and algae were retrieved from experimental databases and through predictive modeling. The hazard indices calculated from the ratio of exposure to effect concentration were >1 for all fracturing fluids, using different scenarios. This indicated a hazard from the undiluted fracturing fluids. The assessment framework presented in this study allows for dealing with data gaps and uncertainties in a tiered fashion and in particular accommodates for combined effects resulting from chemical mixtures. It might be employed for ecotoxicological risk assessment of products containing chemical mixtures and optimization of their environmental performance.     

‘I’ve got my Sat Nav,it’s alright’: Users’ Attitudes towards,and Engagements with,Technologies of Navigation

The use of qualitative research techniques in a largely quantitative cartographic domain is opening up myriad ways to explore users’ engagements technologies of navigation. This study draws on young UK-based students’ real words and life experiences as they engage with Satellite Navigation and other wayfinding technologies during first-time visits to new places to reflect on the nature of the changing relationships between self, navigational object, space and place.