Application of carbon isotopes to detect seepage out of coalbed natural gas produced water impoundments

Coalbed natural gas (CBNG) production from coal bed aquifers requires large volumes of produced water to be pumped from the subsurface. The produced water ranges from high quality that meets state and federal drinking water standards to low quality due to increased salinity and/or sodicity. The Powder River Basin of northeastern Wyoming is a major coalbed natural gas producing region, where water quality generally decreases moving from the southeastern portion of the basin towards the center. Most produced water in Wyoming is disposed into impoundments and other surface drainages, where it may infiltrate into shallow groundwater. Groundwater degradation caused by infiltration of CBNG produced water holding impoundments into arid, soluble salt-rich soils is an issue of immense importance because groundwater is a major source for stock water, irrigation, and drinking water for many small communities in these areas. This study examines the potential of using stable C isotope signatures of dissolved inorganic C (δ¹³C_DIC) to track the fate of CBNG produced water after it is discharged into the impoundments. Other geochemical proxies like the major cations and major anions were used in conjunction with field water quality measurements to understand the geochemical differences between CBNG produced waters and ambient waters in the study area. Samples were collected from the CBNG discharge outfalls, produced water holding impoundments, and monitoring wells from different parts of the Powder River Basin and analyzed for δ¹³C_DIC. The CBNG produced waters from outfalls and impoundments have positive δ¹³C_DIC values that fall within the range of +12‰ to +22‰, distinct from the ambient regional surface and groundwaters with δ¹³C_DIC values ranging from −10‰ to −14‰. The results from the study demonstrate that these contrasting δ¹³C_DIC signatures can be used to trace seepage out of CBNG produced water impoundments into shallow groundwaters.     

Block-preconditioned Newton–Krylov solvers for fully coupled flow and geomechanics

The focus of this work is efficient solution methods for mixed finite element models of variably saturated fluid flow through deformable porous media. In particular, we examine preconditioning techniques to accelerate the convergence of implicit Newton–Krylov solvers. We highlight an approach in which preconditioners are built from block-factorizations of the coupled system. The key result of the work is the identification of effective preconditioners for the various sub-problems that appear within the block decomposition. We use numerical examples drawn from both linear and nonlinear hydromechanical models to test the robustness and scalability of the proposed methods. Results demonstrate that an algebraic multigrid variant of the block preconditioner leads to mesh-independent convergence, good parallel efficiency, and insensitivity to the material parameters of the medium.     

The time and place for political ecology: An introduction to the articles honoring the life-work of Piers Blaikie

Political ecology (PE) is experiencing a renaissance and embrace similar to that of Geography itself. Just as there is a rediscovery of the importance of place and thus Geography, Geographers and others are discovering that this critical approach to the human-environment dialectic provides unique theoretical, methodological, and practical insights for unravelling the complexities of this contentious nexus. The host of new volumes that introduce students and the larger academic community to PE each emphasize different theoretical and thematic confluences. This volume is organized around the life-long work and intellectual history of a leading political ecologist, Piers Blaikie, and as such it is both a tribute to that work, and an alternative means to discover what PE is today. Piers Blaikie’s life-work also encompasses research and writing on natural disasters and risk, development policy and practice, international environmental policy, conservation and biodiversity, AIDS in Africa, livelihoods, and books on India and Nepal. By assessing Blaikie’s long and productive career, from pioneering foundational texts, through transdisciplinary exchanges in the fields of Geography, Development Studies, and policy, to constructive and critical engagement with the post-modern turn, and questions of epistemology and methodology, the contributions to this themed issue provide a diverse yet coherent set of insights. The three sessions of the Association of American Geographers (AAG) Conference in Denver in 2005 and group of articles that emerged from them to form this collection serve to clarify the major convergences and dissonances in the field and its ongoing vitality. In Piers Blaikie’s case, as a central actor in both the theory and practice of PE, a collection based upon a critical overview of his contributions to PE provides a new window into seeing and understanding the past, present, and future of the field.     

Coarse sediment supply sets the slope of bedrock channels in rapidly uplifting terrain: Field and topographic evidence from eastern Taiwan

The incision rate and steepness of bedrock channels depend on water discharge, uplift rate, substrate lithology, sediment flux, and bedload size. However, the relative role of these factors and the sensitivity of channel steepness to rapid (>1 mm yr⁻¹) uplift rates remain unclear. We conducted field and topographic analyses of fluvial bedrock channels with varying channel bed lithology and sediment source rock along the Coastal Range in eastern Taiwan, where uplift rates vary from 1.8 to 11.8 mm yr⁻¹ and precipitation is relatively consistent (1.5–2.7 m yr⁻¹), to evaluate the controls on bedrock channel steepness. We find that channel steepness is independent of rock uplift rate and annual precipitation but increases monotonically with sediment size and substrate strength. Furthermore, in reaches with uniform substrate lithology (mudstone and flysch), channel steepness systematically varies with sediment source rock but not with channel width. When applied to our data, a mechanistic incision model (saltation-abrasion model) suggests that the steepness of Coastal Range channels is set primarily by coarse-sediment supply. We also observe that larger particles are mainly composed of resistant lithologies derived from volcanic rocks and conglomerates. This result implies that hillslope bedrock properties in the source area exert a dominant control on the steepness of proximal channels through coarse-sediment production in this setting. We propose that channel steepness may be insensitive to uplift rate and flow discharge in fast-uplifting landscapes where incision processes are set by coarse sediment size and supply. Models assuming a proportionality between incision rate and basal shear stress (stream power) may not fully capture controls on fluvial channel profiles in landslide-dominated landscapes. Processes other than channel steepening, such as enhanced bedload impacts and debris-flow scour, may be required to balance rock uplift and incision in these transport-limited systems.     

Potential impacts of long-term subsidence on the wetlands and evacuation routes in coastal Louisiana

A steady-state subsidence forecast model was developed as a proof of concept to estimate changes in surface elevations of the wetlands and evacuation routes across coastal Louisiana for the years 2015, 2025, 2050, and 2100. Subsidence estimates were derived from an empirical study published by the National Geodetic Survey. Forecasted vertical change was subtracted from current surface elevations. Land and evacuation routes estimated to have surfaces at or below 0 m in elevation, NAVD88, were quantified and classified as vulnerable to inundation hazards. The extent of the coastal zone susceptible to hurricane induced storm surge was also evaluated relative to surge models published by the National Weather Service. The results indicate spatially heterogeneous rates of subsidence that are forecasted to consume nearly 50 % of the existing coastal margin wetlands by 2100. The most significant rate increases are anticipated between 2015 and 2050. Relative to the impact on evacuation routes, subsidence occurring between the 2015 and 2025 forecast years expanded at slower rates when compared to the latter half of the century. Subsidence adjusted storm surge forecasts reveal similar patterns. The methods employed and findings produced demonstrate forecasting capabilities that provide emergency managers and transportation engineers with resources applicable to evacuation modeling, hazard mitigation, environmental sustainability research, costal restoration efforts, and more.     

Ground motion characteristics and shaking damage of the 11th March 2011 M w9.0 Great East Japan earthquake

A catastrophic M _w9.0 earthquake and subsequent giant tsunami struck the Tōhoku and Kanto regions of Japan on 11th March 2011, causing tremendous casualties, massive damage to structures and infrastructure, and huge economic loss. This event has revealed weakness and vulnerability of urban cities and modern society in Japan, which were thought to be one of the most earthquake-prepared nations in the world. Nevertheless, recorded ground motion data from this event offer invaluable information and opportunity; their unique features include very strong short-period spectral content, long duration, and effects due to local asperities as well as direction of rupture/wave propagation. Aiming at gaining useful experience from this tragic event, Earthquake Engineering Field Investigation Team (EEFIT) organised and dispatched a team to the Tōhoku region of Japan. During the EEFIT mission, ground shaking damage surveys were conducted in Sendai, Shirakawa, and Sukagawa, where the Japan Meteorological Agency intensity of 6+ was observed and instrumentally recorded ground motion data were available. The damage survey results identify the key factors for severe shaking damage, such as insufficient lateral reinforcement and detailing in structural columns from structural capacity viewpoint and rich spectral content of ground shaking in the intermediate vibration period range from seismic demand viewpoint. Importantly, inclusion of several ground motion parameters, such as nonlinear structural response, in shaking damage surveys, can improve the correlation of observed ground motion with shaking damage and therefore enhance existing indicators of potential damage.     

Studies of ionospheric variations during geomagnetic activities at the low-latitude station, Ile-Ife, Nigeria

The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S ₄ index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from ?40 to 0 nT) and during geomagnetic storm events (with Dst about ?100 nT). Seasonal variations of the TEC and S ₄ index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.     

Subjectivity,Power, and the IRB

A substantial literature in social sciences, including law and society, examines the intersections of research ethics and institutional review board (IRB) frameworks. Although geographers have engaged this literature, we argue that further involvement in ethical and regulatory discussions will advance opportunities for better understanding and negotiating the complex subjectivities produced in the IRB structure. Drawing on illustrative experiences of researchers, we focus specifically on the institutions convening IRBs, the researchers, and the human “subjects” produced in the IRB process. We conclude with a call for greater open discussion of the power dynamics, subjectivities, and challenges of formal ethical research structures.     

Making Markets: Think Tank Legislation and Private Property in Detroit

The growing literature on shrinking and declining cities portrays the problems of vacancy and abandonment as symptoms of the absence of capital, while the policy transfer literature views declining cities as unlikely sites for the incubation of neoliberal urban policy. This study examines how declining cities have become key sites for tailored market intervention, focusing on the collapse of Detroit's land market. Long-term decline has been exacerbated by legislative changes orchestrated by think tanks seeking to reinvigorate the market for private property while using homeownership for neighborhood stabilization. Analysis of legislative proceedings, tax foreclosure auction data, and interviews with developers, officials, and activists document the trajectory of these policies of market fundamentalism and indicate that the primary “stabilization” has involved a revitalization of the conditions for predatory capital accumulation in a declining city.