Cross-shelf circulation and phytoplankton distribution at the summertime New England shelfbreak front

We investigate aspects of the secondary (cross-shelf) circulation at the Middle Atlantic Bight shelfbreak front using high-resolution data collected on the New England Shelf in August 2002. The alongshore shelfbreak jet coincides with the front at the seaward edge of the cold pool (remnant winter shelf water) and there is a suggestion of a cross-stream convergence centered at the jet core. Despite indications of convergence we found no evidence of a surface subduction on the seaward side of the front. At depth 70 m near the shelfbreak there was a patch of chlorophyll, located within a local temperature–salinity maximum which, though significantly below the euphotic zone, appeared to be photo-acclimated and viable. The chlorophyll feature could be the result of a local subduction by a larger scale eddy circulation seaward of the front.Dye tracer experiments directly observed the convergence at the foot of the shelfbreak front and subsequent upwelling of bottom boundary layer water along the shoreward side of the shelfbreak front. But, we found no evidence that this upwelling influenced productivity at the front. Further, since there was no cross-shelf maximum in subsurface chlorophyll at the front, we conclude that this productivity is in general, sustained by a broadly distributed local vertical nutrient flux from an underlying nutrient reservoir.     

A conceptual model of the strongly tidal Columbia River plume

The Columbia River plume is typical of large-scale, high discharge, mid-latitude plumes. In the absence of strong upwelling winds, freshwater from the river executes a rightward turn and forms an anticyclonic bulge before moving north along the Washington coast. In addition to the above dynamics, however, the river plume outflow is subject to large tides, which modify the structure of the plume in the region near the river mouth. Observations based on data acquired during a summer 2005 cruise indicate that the plume consists of four distinct water masses; source water at the lift-off point, and the tidal, re-circulating and far-field plumes. In contrast to most plume models that describe the discharge of low-salinity estuary water into ambient high-salinity coastal water, we describe the Columbia plume as the superposition of these four plume types.We focus primarily on a conceptual summary of the dynamics and mutual interaction of the tidal and re-circulating plumes. The new tidal plume flows over top of the re-circulating plume and is typically bounded by strong fronts. Soon after the end of ebb tide, it covers roughly 50–100% of the re-circulating plume surface area. The fronts may penetrate well below the re-circulating plume water and eventually spawn internal waves that mix the re-circulating plume further. The re-circulating plume persists throughout the tidal cycle and corresponds to a freshwater volume equivalent to 3–4 days of river discharge. Finally, the plume water masses are distinguished from one another in term of surface chlorophyll concentration, suggesting that the above classification may also describe different biological growth regimes. The low-salinity re-circulating plume serves as an extension of the estuary into the coastal ocean, or an “estuary at sea”, because residence times during periods of high river flow are greater than those in the estuary.     

Experiments on the survival of six brackish macro-invertebrates from the Baltic Sea after dredged spoil coverage and its implications for the field

Physical disturbance by disposal of dredged materials in estuarine and coastal waters may result in burial of benthic fauna. Survival rates depend on a variety of factors including the type and amount of disposed materials and the lifestyle of the organisms. Laboratory burial experiments using six common macrobenthic invertebrates from a brackish habitat of the western Baltic Sea were performed to test the organisms' escape reaction to dredged material disposal. Experimental lab-results were then extrapolated to a field situation with corresponding bottom topography and covering layer thicknesses at experimental field disposal study sites. Resulted survival rates were then verified by comparison with results of an earlier field study at the same disposal sites.Our experimental design in the lab included the disposal of two types of dredged material (i.e. ‘till’ and ‘sand/till mixture’) and two covering layer depths (i.e. 10–20 cm and 14–40 cm). All three bivalves Arctica islandica (Linnaeus), Macoma balthica (Linnaeus), Mya arenaria (Linnaeus) and the polychaete Nephtys hombergii (Savigny) successfully burrowed to the surface of a 32–41 cm deposited sediment layer of till or sand/till mixture and restored contact with the overlying water. These high escape potentials could partly be explained by the heterogeneous texture of the till and sand/till mixture with ‘voids’. The polychaete Bylgides (Harmothoe) sarsi (Malmgren) successfully burrowed through a 16 cm covering layer whereas the polychaete Lagis koreni (Malmgren) showed almost no escaping reaction. No general differences in escape behaviour after burial were detected between our test species from the brackish habitat and those reported in the literature for the same species in marine environments. However, a size-dependence in mobility of motile polychaetes and M. arenaria was apparent within our study. In comparison to a thick coverage, thin covering layers (i.e. 15–16 cm and 20 cm) increased the chance of the organisms (N. hombergii and M. arenaria) to reach the sediment surface after burial. This was not observed for the other test species. While crawling upward to the new sediment surfaces burrowing velocities of up to 8 cm d^− 1 were observed for the bivalves and up to 20 cm d^− 1 for N. hombergii. Between 17 and 79% of the test organisms showed burrowing activity after experimental burial. The survival rate (defined as the ability to regained contact with the sediment surface) ranged from 0 to 33%, depending on species and on burial depth. The organisms reached the sediment surface by burrowing (polychaetes and bivalves) and/or by extending their siphons to the new sediment surface (bivalves). The extrapolation of laboratory survival rates to the two disposal sites was obtained based on the in situ thicknesses of the dredged spoil layers measured by multi-beam echo sounder. This resulted in total average survival rate estimates for the test species of 45 and 43% for the two disposal sites. The results obtained during the laboratory tests and the following extrapolation to the field were verified by the range of results from a previous field study, using grab sampling shortly before and after a disposal event in June 2001. The effect of dredged material disposal on the tested Baltic Sea benthic macrofauna was assessed by extrapolating the verified laboratory results to the field.     

Challenges in the application of spatial computable general equilibrium models for transport appraisal

The use of spatial computable general equilibrium (SCGE) models for assessing the economic impacts of transport projects is one of the key items on the research agenda for project appraisal in the Netherlands. These models are particularly suitable for analysing indirect effects of transport projects through linkages between the transport sector and the wider economy. Potentially, according to the literature, indirect effects that are additional to first-order direct cost reductions can turn out to be up to almost 80% in magnitude of the direct impacts. Given the relevance of these models for policy appraisal, experiences with this new modelling approach are important to report. After two years of development and application of SCGE models for transport appraisal, we found that the translation of theory behind the spatial equilibrium models into practical model specifications and empirical applications is a challenging task, and may lead to problems in project appraisal in terms of inaccuracies in the assessment of impacts. This paper discusses some key challenges we encountered with the specification of the Dutch SCGE model RAEM. This chapter is especially useful for researchers developing SCGE applications for use in transport appraisal and those who want to get a better understanding of differences between theoretical and computable SCGE modelling.     

Probabilistic modelling of the ultimate strength of ship plates with non-uniform corrosion

This paper presents the results of a parametric study of probabilistic modelling of the ultimate strength of ship plates with non-uniform corrosion represented by random fields. The load-shortening behaviour of the plates with non-uniform reduction of thickness due to corrosion under longitudinal compression is obtained using a general-purpose nonlinear finite element analysis program. A nonlinear time-dependent corrosion model is used to define the probabilistic characteristics of the random fields based on corrosion data measured in plate elements at different locations of bulk carriers. Based on the probabilistic models derived by Monte Carlo simulation, equations to predict the mean and the 5 % characteristic value of the ultimate strength of plates with non-uniform corrosion are developed. Finally a regression equation is proposed to take into account the effect of non-uniform corrosion patterns in the predictions of the ultimate strength of plates with uniform corrosion.     

The Development of a Visualization Methodology for Integrated Coastal Management

Coastal management information is frequently communicated to stakeholders and the public through complicated management documents and engineering plans. With the recognition that public involvement in coastal decision-making processes should be widened have come calls to develop new techniques to communicate complicated coastal information. Using Virtual Reality Geographical Information Systems and visualization packages, such information may be presented using formats more suitable for public consultation and information dissemination exercises than those currently employed. Using a site on the north Norfolk coast of England, an integrated Geographical Information Systems based methodology is presented that allows the visualization of proposed coastal management interventions. Visualizations have been produced that can be published in traditional paper-based management documents, or electronically. The different visualizations are compared and the technical issues surrounding their use discussed. It is argued that the methodology has clear advantages over traditional communication methods, although further research is necessary to determine how it may be practically employed by coastal managers.     

An Overview of Spatial Management and Marine Protected Areas in the East China Sea

Marine ecosystems of the East China Sea are rich in biodiversity, with 12,933 species of which approximately 47.7% are endemic. As anthropogenic impacts are intensifying, fishery resources and biodiversity in the East China Sea are under threat from overfishing, habitat loss, pollution, and biological invasions. Marine protected areas (MPAs) and other spatial management measures are believed useful tools to protect and restore biological resources. Seventeen nature reserves, seven special marine reserves, and three fishery resource conservation zones covering a combined area of 102,156 km² have so far been established in the Chinese East China Sea in order to protect fishery resources, biodiversity, and marine landscapes. This article provides a review and inventory of MPAs in the Chinese East China Sea as implemented by the People's Republic of China.     

Fleet deployment optimization for liner shipping Part 2. Implementation and results

We use linear programming (LP) for solving the problem of the optimal deployment of an existing fleet of multipurpose or fully containerized ships, among a given set of routes, including information for lay-up time, if any, and type and number of extra ships to charter, based on a detailed and realistic model for the calculation of the operating costs of all the ship types in every route and on a suitable LP formulation developed in earlier work of the authors. The optimization model is also applicable to the problem of finding the best fleet compostion and deployment, in a given set of trade routes, which may be the case when a shipping company is considering new or modified services, or a renewal of the existing fleet. In addition, two promising mixed linear-integer programming formulations are suggested.