The influence of dunes on mixing in a migrating salt‐wedge: Fraser River estuary,Canada

Dune bedforms and salt‐wedge intrusions are common features in many estuaries with sand beds, and yet little is known about the interactions between the two. Flow visualization with an echosounder and velocity measurements with an acoustic Doppler current profiler over areas of flat‐bed and sand dunes in the highly‐stratified Fraser River estuary, Canada, were used to examine the effect of dunes on interfacial mixing. As the salt‐wedge migrates upstream over the flat‐bed, mixing is restricted to the lower portion of the water column. However, as the salt‐wedge migrates into the dune field from the flat bed, there is a dramatic change in the flow, and large internal in‐phase waves develop over each of the larger dunes, with water from the salt‐wedge reaching the surface of the estuary. The friction Richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat‐bed, and a plot of internal Froude Number versus obstacle (dune) height shows that the salt‐wedge flow over the dunes is mainly supercritical. Such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment‐laden density currents, and may thus be influential in fluid mixing and sediment transport. Copyright © 2010 John Wiley & Sons, Ltd.     

High Purge Volume Sampling—A New Paradigm for Subslab Soil Gas Monitoring

Subslab soil gas sampling and analysis is a common line of evidence for assessing human health risks associated with subsurface vapor intrusion to indoor air for volatile organic compounds; however, conventional subslab sampling methods have generated data that show substantial spatial and temporal variability, which often makes the interpretation difficult. A new method of monitoring has been developed and tested that is based on a concept of integrating samples over a large volume of soil gas extracted from beneath the floor slab of a building to provide a spatially averaged subslab concentration. Regular field screening is also conducted to assess the trend of concentration as a function of the volume removed to provide insight into the spatial distribution of vapors at progressive distances away from the point of extraction. This approach minimizes the risk of failing to identify the areas of elevated soil vapor concentrations that may exist between discrete sample locations, and can provide information covering large buildings with fewer holes drilled through the floor. The new method also involves monitoring the extraction flow rate and transient vacuum response for mathematical analysis to help interpret the vapor concentration data and to support an optimal design for any subslab venting system that may be needed.     

Monitoring In Situ Biodegradation of MTBE Using Multiple Rounds of Compound‐Specific Stable Carbon Isotope Analysis

At a large industrial facility, methyl tert‐butyl ether (MTBE) was released to the subsurface and dispersed into the light, non‐aqueous phase liquids (LNAPL), in the first aquifer, with the LNAPL serving as a continuous source of MTBE in groundwater. Compound‐specific isotope analysis was conducted on both MTBE and tert‐butyl alcohol (TBA) in groundwater samples collected in 2008, 2011, and 2013 from wells located along and off the center line of the MTBE plume. The study demonstrated the onset and progress of biodegradation of MTBE between 2008 and 2013. The TBA observed in 2008 appears to be derived only in part from MTBE transformation while a significant portion of TBA might be contributed directly from LNAPL sources. In 2011 to 2013, the dominant source of TBA in the mid‐gradient plume was MTBE transformation. A contribution of an offsite LNAPL source, in particular to the down‐gradient area of the plume, is possible but could not be unequivocally confirmed. The time series provided direct evidence for MTBE biodegradation, but also a valuable insight on the sources of TBA.     

Confirming geomorphological interpretations based on portable OSL reader data

Portable optically stimulated luminescence (OSL) readers are increasingly being used in geomorphological and archaeological investigations, but information regarding data reproducibility and the reliability of interpretations based on portable OSL reader data has not yet been presented to the wider geomorphological community. This Letter addresses these two issues by returning to Grabben Gullen Creek in the southeastern Australian Tablelands where we remeasure a sediment profile that was first measured by other researchers 3 years earlier. We also compare portable OSL reader data measured on sediment interpreted to have been deposited in swampy meadow wetlands and flood alluvium settings with data measured on known swampy meadow and flood deposits. Our data show that portable OSL reader data are reproducible. Moreover, we confirm the earlier interpretation that stratigraphies commonly exposed in southeastern Australian Tablelands valley bottoms reflect pre‐European swampy meadow wetlands and flood alluvium. Copyright © 2015 John Wiley & Sons, Ltd.     

新疆准噶尔盆地北部中——新生代地层与古生物

新疆准噶尔盆地北部中-新生代地层分布广,化石类型多样,成为古生物、古气候、古环境研究理想地区.乌伦古河组和依希白拉组分别发现恐龙与哺乳动物等脊椎动物化石,证实它们不存在混生现象,对恐龙是否延续至新生代提出初步意见.     

Potential evidence of fossilised Neoproterozoic deep life: SEM observations on calcite veins from Oppaminda Creek,Arkaroola, South Australia

Scanning electron microscopy revealed micron-sized globular and coccoid objects, associated with filaments and mucus-like patches in antitaxial fibrous calcite veins from Oppaminda Creek, Northern Flinders Ranges, South Australia. Chemically the objects only differ from their calcite (CaCO₃) matrix by a higher sulphur content. The ∼585 Ma veins formed at about 3–6 km below the surface. Fluid inclusions indicate a temperature of formation of about 60–80°C, and not exceeding 100°C. A non-biogenic origin of the objects is discussed, but considered unlikely. Instead, morphology, chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation.     

Darkness on the Edge of Town: Mapping Urban and Peri-Urban Australia Using Nighttime Satellite Imagery

This article explores the use of nighttime satellite imagery for mapping urban and peri-urban areas of Australia. A population-weighted measure of urban sprawl is used to characterize relative levels of sprawl for Australia's urban areas. In addition, the expansive areas of low light surrounding most major metropolitan areas are used to map the urban–bush interface of exurban land use. Our findings suggest that 82 percent of the Australian population lives in urban areas, 15 percent live in peri-urban or exurban areas, and 3 percent live in rural areas. This represents a significantly more concentrated human settlement pattern than presently exists in the United States.     

Developing the Commons: The Contradictions of Growth in Exurban Montana

Property development in exurban areas has the capacity to undermine the amenity values that undergird that development. Predicated on that contradiction, this research seeks to explain the emergence of local, informal, planning-based regulations in the traditionally antiregulatory context of rural Montana. Adopting both the insights of institutional common property theory and those of critical materialist analysis of economic growth, the work reconciles accounts of development as inherently ecologically self-destructive with those stressing creative development and adoption of rules for collective self-governance. Using a detailed case analysis of a Montana county undergoing rapid growth, it examines what drives localized land use regulation, what controls are enacted, and whether such controls are resisted or facilitated by development capital. Findings suggest that informal regulations seek to control externalities of development on valuable amenity commons and that they are adopted with the acceptance, if not encouragement, of the development community. These fragile instruments are vulnerable to opposition, however, highlighting problems of more general relevance: Growth depends on a deregulated development regime, which produces externalities that undermine the valorization of property. Localized regulatory planning regimes are therefore both a solution to contradictions inherent in growth and a potential source of future planning problems.