Characterising thermal water circulation in fractured bedrock using a multidisciplinary approach: a case study of St. Gorman’s Well,Ireland

A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring in a fractured limestone setting is derived from a multidisciplinary approach. St. Gorman’s Well is a thermal spring in east-central Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a three-dimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system. Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies; and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled hydrothermal circulation system.

     

Preparing The National Map for the 3D Elevation Program – products,process and research

The 3D Elevation Program (3DEP) is a collaborative effort among government entities, academia, and the private sector to collect high-resolution 3-dimensional data over the United States. The United States Geological Survey (USGS) is making preparations for managing, processing, and delivering petabytes of 3DEP elevation products for the Nation. In addition to the existing 1/3, 1, and 2 arc-second seamless elevation data layers of The National Map, new 3DEP products include lidar point cloud data; a standard 1-meter DEM layer; additional source datasets; and, in Alaska, 5-meter digital elevation models. A new product generation system improves the construction and publication of the seamless elevation datasets, prepares the additional 3DEP products for distribution, and automates the data management functions required to accommodate the high-volume 3DEP data collection. Major changes in geospatial data acquisition, such as high resolution lidar data, volunteered geographic information, data processing using parallel and grid computer systems, and user needs for semantic access to geospatial data and products, are driving USGS research associated with the 3DEP. To address the research requirements, a set of inter-related projects including spatiotemporal data models, data integration, geospatial semantics and ontology, high performance computing, multi-scale representation, and hydrological modeling using lidar and other 3DEP data has been developed.     

Cleaved clasts in Dalradian conglomerates: possible evidence for Neoproterozoic compressional tectonism in Scotland and Ireland?

Cleaved metasedimentary clasts are present in stratigraphically and geographically distinct conglomerates in the Argyll and Southern Highland Groups of the Neoproterozoic Dalradian succession in the SW Scottish Highlands and NW Ireland. The significance and relationships of these clasts are that: (1) they were unequivocally reworked and deposited by sedimentary processes; (2) their internal foliation is probably due to contractional deformation that pre‐dates regional Caledonian fabrics; and (3) most of the cleaved clasts are only moderately deformed psammites and pelites and thus cannot be construed as having been derived from extensional mylonites. These conclusions, coupled with the generally accepted inferences that the Dalradian succession post‐dates Grenville deformation (c. 1100–1000 Ma) and pre‐dates early Palaeozoic Caledonian deformation (c. 470 Ma) and that the lowermost exposed Dalradian rocks, the Grampian Group, are truncated by a c. 806 Ma shear zone, imply that the clasts must have been foliated during an episode of mid‐Neoproterozoic contractional deformation. The clasts may thus represent further evidence in support of the contentious c. 870–800 Ma Knoydartian orogeny and thereby further render as equivocal interpretations that the Neoproterozoic tectonostratigraphic evolution of the Scottish Highlands and NW Ireland is a record of long‐lived ‘episodic’ extensional tectonism. Copyright © 2000 John Wiley & Sons, Ltd.     

Humic Substances as a Mediator for Microbially Catalyzed Metal Reduction

The potential for humic substances to serve as a terminal electron acceptor in microbial respiration and to function as an electron shuttle between Fe(III)-reducing microorganisms and insoluble Fe(III) oxides was investigated. The Fe(III)-reducing microorganism Geobacter metallireducens conserved energy to support growth from electron transport to humics as evidenced by continued oxidation of acetate to carbon dioxide after as many as nine transfers in a medium with acetate as the electron donor and soil humic acids as the electron acceptor. Growth of G. metallireducens with poorly crystalline Fe(III) oxide as the electron acceptor was greatly stimulated by the addition of as little as 100 μM of the humics analog, anthraquinone-2,6-disulfonate. Other quinones investigated, including lawsone, menadione, and anthraquinone-2-sulfonate, also stimulated Fe(III) oxide reduction. A wide phylogenetic diversity of microorganisms capable of Fe(III) reduction were also able to transfer electrons to humics. Microorganisms which can not reduce Fe(III) could not reduce humics. Humics stimulated the reduction of structural Fe(III) in clay and the crystalline Fe(III) forms, goethite and hematite. These results demonstrate that electron shuttling between Fe(III)-reducing microorganisms and Fe(III) via humics not only accelerates the microbial reduction of poorly crystalline Fe(III) oxide, but also can facilitate the reduction of Fe(III) forms that are not typically reduced by microorganisms in the absence of humics. Addition of humic substances to enhance electron shuttling between Fe(III)-reducing microorganisms and Fe(III) oxides may be a useful strategy to stimulate the remediation of soils and sediments contaminated with organic or metal pollutants.     

Fringes on the EVN MkIV data processor at JIVE

The highlight of the 4th EVN/JIVE Symposium was the inauguration of the new EVN MkIV data processor at JIVE. This paper deals with the state of the processor in October 1998 and how it was used for fringe detection experiments.     

Calibration of a Par-Tec 200 laser back-scatter probe FOR in situ sizing of fluvial suspended sediment

The in situ or effective particle size distribution of fluvial suspended sediment may differ considerably from that of the chemically dispersed mineral fraction owing to flocculation. Obtaining a meaningful measure of the effective particle size distribution ideally requires that measurements should be made in situ. A rigorous assessment of the associated degree of flocculation also requires that the same measurement technique is used subsequently to establish the absolute particle size composition of the suspended sediment by analysis of the chemically dispersed mineral fraction. While few in situ measurement devices currently exist, a Par-Tec 200 laser back-scatter probe has previously been shown to be capable of making both in situ and laboratory particle size measurements of fluvial sediment. The accuracy and precision of this device is assessed in this paper. While able to distinguish relative size differences with a high degree of precision, the Par-Tec 200 performed poorly in terms of accuracy when compared with measurements made using a laser diffraction device. A calibration algorithm has been devised for the Par-Tec 200 size data, using standard sediment samples sized by means of a laser diffraction device as the reference. Application of the calibration to Par-Tec 200 measurements of heterogeneous sediment samples significantly improved the representativeness of the particle size distribution, both in terms of overall form, and the median particle size. © 1998 John Wiley & Sons, Ltd.     

Further 2MASS mapping of hot dust in planetary nebulae

We have used 2 Micron All Sky Survey (2MASS) mapping results to investigate the distribution of hot dust continua in 12 planetary nebulae (PNe). The nature of this emission is unclear, but it is possible that where the continuum is extended, as is the case for M 1-12 and NGC 40, then the grains concerned may be very small indeed. The absorption of individual photons by such grains may lead to sharp spikes in temperature, as has previously discussed for several other such outflows. Other sources (such as MaC 1-4, He 2-25, B1 2-1 and K 3-15) appear to be relatively compact, and the high temperatures observed are understandable in terms of more normal heating processes. It is possible that the grains in these cases are experiencing high radiant flux levels.
Finally, it is noted that whilst the core of M 2-2 appears to show hot grain emission, this is less the case for its more extended envelope. The situation may, in this case, be similar to that of NGC 2346, in which much of the emission is located within an unresolved nucleus. Similarly, it is noted that in addition to hot dust and gas thermal continua, the emission in the interior of NGC 40 may be enhanced through rotational–vibrational transitions of H₂, and/or the 2p³P⁰–2s³S transition of He  i .     

Real-time hybrid simulation for structural control performance assessment

Real-time hybrid simulation is an attractive method to evaluate the response of structures under earthquake loads.The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time,thus allowing investigation of structural systems with rate-dependent components.Real-time hybrid simulation is challenging because it requires performance of all calculations,application of displacements,and acquisition of measured forces,within a very small increment of time.Furthe...     

Suspended sediment transport in a small Mediterranean agricultural catchment

The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km²) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004–2005 to 2006–2007). An annual average SSC of 17.3 mg l^?1, with a maximum of 2270 mg l^?1, was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd.     

Forest blowdown impacts of Hurricane Rita on fluvial systems

Hurricane Rita, a category three hurricane which struck the US Gulf Coast near the Louisiana/Texas border in 2005, did not cause extensive river flooding. However, the storm did result in extensive forest damage and tree blowdown. High‐resolution post‐storm aerial photography allowed an inventory of river bank trees blown into the channel along the lower Neches and Sabine Rivers of southeast Texas and southwest Louisiana. Blowdowns directly into the channel averaged 9·3 per kilometer in the lower Neches and 13·4 in the lower Sabine River, but individual reaches 10 to 20 km in length had rates of 20 to 44 blowdowns per kilometer. Though large woody debris (LWD) from Hurricane Rita was widely perceived to reduce the capacity of channels to convey flow, no strong evidence exists of increased flooding or significant reductions in channel conveyance capacity due to LWD from the storm. The Rita blowdown inventory also allowed an assessment of whether similar blowdown events could account for major logjams and rafts on Red, Atchafalaya, and Colorado Rivers on the Gulf Coast, which blocked navigation from tens to hundreds of kilometers in the 1800s. Results from Hurricane Rita suggest that blowdown into channels alone – not withstanding blowdown elsewhere in the river valleys or along tributaries which could deliver LWD to the river – is sufficient to completely block channels, thus providing a plausible mechanism for initiating such (pre)historic log rafts. Copyright © 2009 John Wiley & Sons, Ltd.