The analysis of liquid storage tanks on deep elastic foundations

The behaviour of a cylindrical liquid storage tank resting on a deep homogeneous elastic layer is examined. The analysis employs a substructure approach and proceeds by examining the behaviour of the tank base, the tank walls and the soil separately and developing flexibility matrices for each of these components. These flexibility matrices are then assembled and the complete soil structure system analysed.     

Sensitivity of estuarine phytoplankton to hexavalent chromium

Experiments were conducted in which we tested the effects of hexavalent chromium on both natural assemblages of phytoplankton and cultures of Thalassiosira pseudonana clone 3H. Water was collected from various locations in Yaquina Bay, Oregon, with salinities ranging from 32·5‰ to 0·03‰. A variety of nutrient regimes were tested by adding major nutrients and micro-nutrients, and/or stripping micro-nutrients with activated carbon. In one high salinity experiment, chromium was stimulatory, as were micro-nutrient additions. In other high and medium salinity experiments, chromium was neither stimulatory nor inhibitory, at levels up to 1·9 μ mole l^?1 Cr. There was, however, slight inhibition of growth at 19·0 μ mole l^?1 Cr, due specifically to inhibition of Skeletonema costatum. In our freshwater experiments, chromium was very inhibitory at 1·9 μ mole l^?1 Cr, and slightly inhibitory at 0·19 μ mole l^?1 Cr. Species inhibited by chromium were Surirella ovata, Detonula confervacea, and Cyclotella sp. Experiments were conducted with T. pseudonana grown over a wide range of salinities. Chromium was found to be very inhibitory in freshwater and became progressively less toxic as the salinity increased. Most inhibition was neutralized by a salinity of 2·1‰.     

The Goodlett-Denny mound: a glimpse at 45 years of Pennsylvania treethrow mound evolution with implications for mass wasting

A rootplate/mound formed by the uprooting of a black cherry tree (Prunus serotina) in Potter County, Pennsylvania, was photographed in 1950 near the time of formation and again in 1952 and 1963 by J.C. Goodlett and C.S. Denny. The mound was located and photographed by the author in 1989 with the aid of background trees with identifying peculiarities and using the earlier consistent perspectives. Between 1950 and 1963 most of the rootmass had decomposed, leaving a mound with an estimated volume of 5.28 m³ in 1963. By 1989 the mound had lost 60% of its 1963 height and its volume had diminished to 2.09 m³. Mean annual erosion on the mound from 1989 to 1995 was much less than during the 1963–1989 period indicating a diminishing sediment contribution to the forest floor commensurate with lowering of the mound surface.     

Primary production, plant and detrital biomass, and particle transport in the Columbia River Estuary

The dynamics of primary production and particulate detritus cycling in the Columbia River Estuary are described, with particular reference to mechanisms that account for patterns within the water column, on the tidal flats, and in the adjacent wetlands. Analysis of patterns in phytoplankton flora and biomass and in distribution of detrital particulate organic matter (DPOC) in the water column indicated that salinities of 1–5 delineated an essentially freshwater flora from a marine or euryhaline flora, and that living phytoplankton was converted to DPOC at the freshwater-brackishwater interface. Similarly, the benthic diatom assemblages on tidal flats reflected either the fresh or the brackish nature of the water inundating the flats. Emergent vascular plants were grouped into six associations by cluster analysis, the associations being separated mainly on the bases of different relative abundances of freshwater, euryhaline or brackishwater species, and on whether samples occurred in high or low marsh areas.Annual rates of net areal 24-hr production averaged 55, 16, and 403gC m⁻²y⁻¹ for phytoplankton, benthic algae, and emergent vascular vegetation, respectively. Total production over the whole estuary was 17,667 metric tons C y⁻¹ for phytoplankton, 1,545mt C y⁻¹ for benthic algae, and 11,325mt C y⁻¹ for emergent vascular plants, for a grand total to 30,537mt C y⁻¹. Phytoplankton biomass turned over approximately 39 times per year on average, while benthic algae turned over about twice and emergent plants once per year.Budgets for phytoplankton carbon (PPOC) and DPOC were developed based on PPOC and DPOC import and export, grazing loss, and in situ production and conversion of PPOC to DPOC. It is suggested that 36,205mt y⁻¹ of PPOC is converted to DPOC in the estuary, principally at the freshwater-brackishwater interface. About 40,560mt y⁻¹ of PPOC is exported to the ocean, and 159,185mt y⁻¹ of DPOC is transported into the marine zone of the estuary (no data are available on DPOC export to the ocean). Thus, the estuary acts principally as a conduit for the transport of particles to the sea, and only secondarily as a converter of viable phytoplankton cells to detrital carbon and as a trap for DPOC.     

A comparison of weakly and fully non-linear models of the shoaling of a solitary internal wave

This study investigates the behaviour of internal solitary waves crossing a continental slope in the presence of a seasonal thermocline. Comparisons are made between a fully non-linear computational fluid dynamics (CFD) model, and weakly non-linear theory. Previous observations suggested that the amplitudes of solitary waves are capped as they pass across the continental slope, which may be due to laminar dynamics, or due to the effect of turbulence. Across the continental slope, CFD and second order variable depth KdV (vEKdV) predictions agree well with observations of a limited change in solitary wave amplitude. First order variable depth KdV theory overpredicts the final amplitude significantly. In terms of the wave shape, the CFD modeled wave changes from a KdV shape in deep water towards an EkdV solution in shallow water, as observations suggest. The phase speed of the CFD and vEKdV waves are similar to that observed in waters of 400–500 m deep, but are slightly lower than observed in 140 m depth. CFD predictions using a standard k, turbulence model showed that turbulence had little effect on the amplitude. These preliminary results indicate that in this situation wave capping is due to laminar, large amplitude solitary wave dynamics and is independent of turbulent mixing.     

Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum

The BRITICE-CHRONO Project has generated a suite of recently published radiocarbon ages from deglacial sequences offshore in the Celtic and Irish seas and terrestrial cosmogenic nuclide and optically stimulated luminescence ages from adjacent onshore sites. All published data are integrated here with new geochronological data from Wales in a revised Bayesian analysis that enables reconstruction of ice retreat dynamics across the basin. Patterns and changes in the pace of deglaciation are conditioned more by topographic constraints and internal ice dynamics than by external controls. The data indicate a major but rapid and very short-lived extensive thin ice advance of the Irish Sea Ice Stream (ISIS) more than 300 km south of St George's Channel to a marine calving margin at the shelf break at 25.5 ka; this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel. The release event between 25 and 26 ka is interpreted to have stimulated fast ice streaming and diverted ice to the west in the northern Irish Sea into the main axis of the marine ISIS away from terrestrial ice terminating in the English Midlands, a process initiating ice stagnation and the formation of an extensive dead ice landscape in the Midlands.     

Exceptionally Long MTBE Plumes of the Past Have Greatly Diminished

Studies published in the late 1990s and early 2000s identified the presence of exceptionally long methyl tert‐butyl ether (MTBE) plumes (more than 600 m or 2000 feet) in groundwater and have been cited in technical literature as characteristic of MTBE plumes. However, the scientific literature is incomplete in regard to the subsequent behavior and fate of these MTBE plumes over the past decade. To address this gap, this issue paper compiles recent groundwater monitoring records for nine exceptional plumes that were identified in prior studies. These nine sites exhibited maximum historical MTBE groundwater plume lengths ranging from 820 m (2700 feet) to 3200 m (10,500 feet) in length, exceeding the lengths of 99% of MTBE plumes, as characterized in multiple surveys at underground storage tank sites across the United States. Groundwater monitoring data compiled in our review demonstrate that these MTBE plumes have decreased in length over the past decade, with five of the nine plumes exhibiting decreases of 75% or more compared to their historical maximum lengths. MTBE concentrations within these plumes have decreased by 93% to 100%, with two of the nine sites showing significant decreases (98% and 99%) such that the regulatory authority has subsequently designated the site as requiring no further action.     

Bayesian hierarchical models for soil CO<Subscript>2</Subscript> flux and leak detection at geologic sequestration sites

Proper characterizations of background soil CO₂ respiration rates are critical for interpreting CO₂ leakage monitoring results at geologic sequestration sites. In this paper, a method is developed for determining temperature-dependent critical values of soil CO₂ flux for preliminary leak detection inference. The method is illustrated using surface CO₂ flux measurements obtained from the AmeriFlux network fit with alternative models for the soil CO₂ flux versus soil temperature relationship. The models are fit first to determine pooled parameter estimates across the sites, then using a Bayesian hierarchical method to obtain both global and site-specific parameter estimates. Model comparisons are made using the deviance information criterion (DIC), which considers both goodness of fit and model complexity. The hierarchical models consistently outperform the corresponding pooled models, demonstrating the need for site-specific data and estimates when determining relationships for background soil respiration. A hierarchical model that relates the square root of the CO₂ flux to a quadratic function of soil temperature is found to provide the best fit for the AmeriFlux sites among the models tested. This model also yields effective prediction intervals, consistent with the upper envelope of the flux data across the modeled sites and temperature ranges. Calculation of upper prediction intervals using the proposed method can provide a basis for setting critical values in CO₂ leak detection monitoring at sequestration sites.     

Finding Science with Science: Evaluating a Domain and Scientific Ontology User Interface for the Discovery of Scientific Resources

Current approaches to the discovery of scientific resources (publications, data sets and web services) are dominated by keyword search. These approaches do not allow scientists to search on the deeper semantics of scientific resources, or to discover resources on the basis of the scientific approaches taken. This article evaluates a user interface that allows users to discover scientific resources through structured knowledge in the form of ontologies describing the domain and the scientific knowledge inherent within the scientific resource, and also through informal user tags. These combined capabilities provide scientists with new and powerful options for resource discovery. A qualitative user evaluation explored how scientists felt about the approach for resource discovery in the context of their scientific work. The study showed that marine scientists were enthusiastic about the capabilities of such an approach and appreciated the ability to browse the visual structure of the knowledge and query on scientific method but, overall, preferred the use of tags over ontologies. The exploratory nature of the user study was used to identify future directions for such improvements.