Biogeomorphology in the field: bedforms and species, a mystic relationship

Fine-scale seabed mapping (Owenia fusiformis, and the razor clam Ensis directus) occur near bedload convergence zones resulting from a mutually evasive flood- and ebb-dominant channel system. Such zones are at the end of the channels, hence also fine grained sediments, food and larvae are trapped. The combination of the coarser-grained bedload with thedeposition of fines is indeed the optimum for a lot of suspension and detritus feeders. Still, highest abundances occur at the fringes of such a system where stress levels are intermediate. Hypotheses were successfully tested along the Dutch coastal zone. Those insights are important to assess changes in seafloor integrity and hydrographic conditions

Sensitivity of tidal sand wave characteristics to environmental parameters: A combined data analysis and modelling approach

An integrated field data-modelling approach is employed to investigate relationships between the wavelength of tidal sand waves and four environmental parameters: tidal current amplitude, water depth, tidal ellipticity and median grain size. From echo sounder data at 23 locations on the Dutch continental shelf, the average wavelengths of observed sand waves are determined and compared with the wavelengths obtained with a process-based model. The latter describes the initial formation of these bedforms due to feedbacks between the tidal current and the erodible bed and uses environmental parameters for the 23 locations as input. Good agreement between observed and modelled wavelengths is found if the bottom stress experienced by tidal currents is adequately quantified. Model results show that the wavelength of sand waves increases with increasing water depth, tidal ellipticity and grain size (coarse sand), whilst it decreases with increasing tidal current amplitude and grain size (fine sand). Due to the limited number of stations and the fact that all four parameters change from location to location, the modelled relationships are only partly supported by the field observations

Management of massive point cloud data: Wet and dry

OTB onderzoekOTB Research Institut

Benthic Habitat Variations Over Tidal Ridges, North Sea, The Netherlands

Marine ecosystems on continental shelves endure an increasing burden of human activity offshore, and the impacts on benthic habitats are not well known. An improved understanding of how benthic habitats vary in relation to substrate types and seabed features is therefore essential to both scientists and offshore developers. This case study shows that marine habitats over two tidal ridges in the North Sea vary from low-density/low-diversity communities on the well-sorted sandy crests of ridges to high-density/high-diversity communities in the poorly sorted muddy, gravelly sediments in the adjacent troughs. On sandy continental shelves, including the Netherlands Continental Shelf (NCS) in the North Sea, tidal bedforms occur of different spatial scales, such as sand banks (tidal ridges), sand waves, and megaripples. Marine habitat maps reveal that benthic habitats vary spatially on continental shelves in relation to seabed morphology, water depth, and sediment composition. The different morphological elements of tidal ridges are expected to accommodate different benthic habitats. Some tidal ridge areas in the North Sea are nominated to become marine protected areas, but are also attractive for their marine aggregates and may be designated in part as mining areas. Due to their composition and shallow water depths, tidal ridges are also suitable locations for the construction of offshore wind farms. To date, the characteristics of relatively inaccessible seabeds are too poorly understood to explain the effects of physical parameters on benthic communities. Therefore, it is important to expand our understanding of benthic habitat variations associated with tidal ridges, for the benefit of both science and offshore development. © 2012 Elsevier Inc. All rights reserved

Air services on thin routes : Regional versus low-cost airlines

An examination of the impact in the US and EU markets of two major innovations in the provision of air services on thin routes - regional jet technology and the low-cost business model - reveals significant differences. In the US, regional airlines monopolize a high proportion of thin routes, whereas low-cost carriers are dominant on these routes in Europe. Our results have different implications for business and leisure travelers, given that regional services provide a higher frequency of flights (at the expense of higher fares), while low-cost services offer lower fares (at the expense of lower flight frequencies)