Adaptive split-operator methods for modeling transport phenomena in porous medium systems

Split-operator methods are commonly used to approximate environmental models. These methods facilitate the tailoring of different approximation approaches to different portions of the differential operator and provide a means to split large coupled problems into pieces that are more amenable to parallel computation than the original fully-coupled problem. However, split-operator methods introduce an additional source of approximation error into the solution, which is typically either ignored or controlled heuristically. In this work, we develop two methods to estimate and control the error in split-operator methods, which lead to a dynamic adjustment of the temporal splitting step based upon the error estimators. The proposed methods are shown to yield robust solutions that provide the desired control of error. In addition, for a typical nonlinear reaction problem, the new methods are shown to reduce the solution error by more than two orders of magnitude compared to standard methods for an identical level of computational effort. The algorithms introduced and evaluated have widespread applicability in environmental modeling.     

Application of a New Vertical Profiling Tool (ESASS) for Sampling Groundwater Quality During Hollow‐Stem Auger Drilling

A new tool called ESASS (Enhanced Screen Auger Sampling System) was developed by the U.S. Geological Survey. The use of ESASS, because of its unique U.S. patent design (U.S. patent no. 7,631,705 B1), allows for the collection of representative, depth‐specific groundwater samples (vertical profiling) in a quick and efficient manner using a 0.305‐m long screen auger during hollow‐stem auger drilling. With ESASS, the water column in the flights above the screen auger is separated from the water in the screen auger by a specially designed removable plug and collar. The tool fits inside an auger of standard inner diameter (82.55 mm). The novel design of the system constituted by the plug, collar, and A‐rod allows the plug to be retrieved using conventional drilling A‐rods. After retrieval, standard‐diameter (50.8 mm) observation wells can be installed within the hollow‐stem augers. Testing of ESASS was conducted at one waste‐disposal site with tetrachloroethylene (PCE) contamination and at two reference sites with no known waste‐disposal history. All three sites have similar geology and are underlain by glacial, stratified‐drift deposits. For the applications tested, ESASS proved to be a useful tool in vertical profiling of groundwater quality. At the waste site, PCE concentrations measured with ESASS profiling at several depths were comparable (relative percent difference <25%) to PCE concentrations sampled from wells. Vertical profiling with ESASS at the reference sites illustrated the vertical resolution achievable in the profile system; shallow groundwater quality varied by a factor of five in concentration of some constituents (nitrate and nitrite) over short (0.61 m) distances.     

Numerical Modeling of the Near‐Field Hydraulics of Water Wells

Numerical flow models can be a useful tool for dimensioning water wells and to investigate the hydraulics in their near‐field. Fully laminar flow can be assumed for all models calculated up to the screen. Therefore models can be used to predict—at least qualitatively, neglecting turbulent losses inside the well—the spatial distribution of inflow into the well and the overall hydraulic performance of different combinations of aquifer parameters and technical installations. Models for both horizontal (plan view) and vertical flow (cross section) to wells were calculated for a variety of setups. For the latter, this included variations of hydraulic conductivity of the screen, pump position, and aquifer heterogeneity. Models of suction flow control devices showed that they indeed can homogenize inflow, albeit at the cost of elevated entrance losses.     

Exploring the ‘ethical everyday’: An ethnography of the ethics of family consumption

Using ethnographic research with six families in the North West of England (2007–2009), this paper opens up the ‘black box’ of everyday ethical consumption by adding colour and form to these everyday experiences. While recent geographical literature has recognised the ethical considerations that are implicit in everyday consumption practices, there is a noticeable void of research that explores and fleshes out the everyday ethical actions of individuals and families as consumers. By exploring the everyday ethics of money, waste and health choices in family consumption practices, this paper makes the case for recognising the ethical nature of everyday practices and choices of consumption. It is argued that rather than consumers subscribing to a given set of ethics in consumption, there are multiple ways of recognising consumption as an ethically-embedded process.     

Privacy, reconsidered: New representations, data practices, and the geoweb

Blogging, social networking, and other Web 2.0 practices have sparked widespread debate about the status and future of privacy. This paper examines an explicitly geographical aspect of Web 2.0 with respect to these debates: the geospatial web, or ‘geoweb’. As part of fundamental shifts in the kinds of geographic information available, its circulation, and representative forms it assumes, the geoweb implies new objects of privacy concern and subsequent privacy-related negotiations over the aggregate of its component information, technologies, and data praxes. Thus we argue that privacy must not only be revisited, but indeed re-conceptualized. Whereas prior research on privacy vis-à-vis geographic information technologies has tended to question what privacy ‘is’, we focus instead on the constitutive outcomes of societal struggles over privacy. We examine how privacy is being negotiated around two geoweb services - Google Street View and the Twitter GeoAPI - to illustrate that these contestations produce privacy as a social object in particular ways. We show that public discourse around actual or anticipated privacy harms stemming from geoweb services and their uses, as well as the preventatives and remedies proposed or implemented to address such harms, reconstitute the objects and practices of privacy concern, and alter the roles and relationships of state, civil and corporate actors in the construction of privacy. Finally we suggest that the geoweb raises new privacy concerns because some of its representational forms - namely geo-tagged images and self-authored texts - facilitate identification and disclosure with more immediacy and less abstraction.     

Chalcophile and platinum-group element (PGE) concentrations in the sulfide minerals from the McCreedy East deposit,Sudbury, Canada,and the origin of PGE in pyrite

Magmatic sulfide deposits consist of pyrrhotite, pentlandite, chalcopyrite (± pyrite), and platinum-group minerals (PGM). Understanding the distribution of the chalcophile and platinum-group element (PGE) concentrations among the base metal sulfide phases and PGM is important both for the petrogenetic models of the ores and for the efficient extraction of the PGE. Typically, pyrrhotite and pentlandite host much of the PGE, except Pt which forms Pt minerals. Chalcopyrite does not host PGE and the role of pyrite has not been closely investigated. The Ni–Cu–PGE ores from the South Range of Sudbury are unusual in that sulfarsenide PGM, rather than pyrrhotite and pentlandite, are the main carrier of PGE, probably as the result of arsenic contribution to the sulfide liquid by the As-bearing metasedimentary footwall rocks. In comparison, the North Range deposits of Sudbury, such as the McCreedy East deposit, have As-poor granites in the footwall, and the ores commonly contain pyrite. Our results show that in the pyrrhotite-rich ores of the McCreedy East deposit Os, Ir, Ru, Rh (IPGE), and Re are concentrated in pyrrhotite, pentlandite, and surprisingly in pyrite. This indicates that sulfarsenides, which are not present in the ores, were not important in concentrating PGE in the North Range of Sudbury. Palladium is present in pentlandite and, together with Pt, form PGM such as (PtPd)(TeBi)₂. Platinum is also found in pyrite. Two generations of pyrite are present. One pyrite is primary and locally exsolved from monosulfide solid solution (MSS) in small amounts (<2 wt.%) together with pyrrhotite and pentlandite. This pyrite is unexpectedly enriched in IPGE, As (± Pt) and the concentrations of these elements are oscillatory zoned. The other pyrite is secondary and formed by alteration of the MSS cumulates by late magmatic/hydrothermal fluids. This pyrite is unzoned and has inherited the low concentrations of IPGE and Re from the pyrrhotite and pentlandite that it has replaced.     

Spatial gradients in plant leaf wax D/H across a coastal salt marsh in southern California

Coastal salt marsh ecosystems contain strong environmental gradients that are anticipated to influence the D/H ratios recorded in the leaf waxes of salt-tolerant plants. We characterized the molecular and hydrogen isotopic composition of alkanes in plant and sediment samples as well as the D/H ratios of environmental and plant waters across an elevation and inundation gradient in a southern Californian, coastal salt marsh. We sampled the dominant salt marsh plant species: Salicornia virginica, Arthrocnemum subterminale and Jamuea carnosa (all succulents), as well as Monanthochloe littoralis and Limonium californicum (nonsucculents). Plant xylem water hydrogen isotopic compositions indicate a shift in source waters from meteoric influences at upland sites (δD value −20‰) to seawater dominated values (0‰) at lowland areas. We found leaf water D enrichment relative to xylem water ranging from mean δD values of +54‰ (upland) to +28‰ (lowland), interpreted as a reduction of transpiration with increasing inundation time. This has the effect of increasing the net fractionation between source water and leaf wax product across the environmental gradient from mean values of −101‰ (upland) to −134‰ (lowland), with an attenuated signal recorded in the δD values of plant leaf wax n-alkanes (−122‰ to −136‰). These results constrain the hydrogen isotopic composition of salt marsh organic matter that may contribute to marine carbon budgets of the Santa Barbara Basin, and further indicate the potential for plant leaf waxes to resolve paleoenvironmental change, including sea level change, in sediment cores from salt marsh ecosystems.     

A spatially explicit degree-day model of Rift Valley fever transmission risk in the continental United States

A spatially explicit degree-day model was used to evaluate the risk of Rift Valley fever virus (RVFV) transmission by mosquitoes to humans and livestock within five target states in the continental United States: California, Minnesota, Nebraska, New York, and Texas. A geographic information system was used to model potential virus transmission based on a 12-day moving window assessment of the extrinsic incubation period theorized for RVFV in the United States. Risk of potential virus transmission in each state was spatially evaluated on a 10-km grid using average historical daily temperature data from 1994 to 2003. The highest levels of transmission risk occur in California and Texas, with parts of these states at risk of RVFV transmission for up to 8 months per year. Northern Minnesota, central New York, and most of coastal and high-elevation California are at low to null risk. Risk of impact to the livestock industry is greatest in California, Texas, and Nebraska. A standard global climate model was used to evaluate future risk in the year 2030 in Nebraska, and showed an increase of transmission risk days from approximately 3 to 4 months per year.