Macrobenthos characteristics and distribution, following intensive sand extraction from a subtidal sandbank

Macrobenthic fauna are investigated, to establish the nature and vulnerability of benthic communities to aggregate mining on a subtidal sandbank, the Kwinte Bank, in the Southern Bight of the North Sea. Within the central part of this sandbank, a depression (5 m deep) has been created, as a result of 20 years of dredging over the same small area (1 km long and 700 m wide). Three stations were sampled within this central depression; two on the western border; and two to the east of the depression. Another station was sampled in a “non-exploited” area to the north of the depression. Four stations were sampled outside of the concession area, on the adjacent Middelkerke Bank. The hypothesis is tested as to whether or not the density, species richness, taxon and community composition do not differ, between the depression and the adjacent sites (with similar sediment composition) on top of the sandbank. In addition, it is examined whether these parameters differ between the depression and reference sites, at the adjacent undisturbed sandbank. Differences in density and species richness could not be detected, between the different locations. Compared to the reference stations at the Middelkerke Bank and locations next to the depression, crustaceans (amphipods and in particular Bathyporeia spp.) and echinoderms (Ophiura spp. and Echinocardium cordatum) were more abundant in the area of the depression, suggesting a higher similarity to the swale environment, than was the case previously. The observed trends were similar, for both of the sampling periods, February and November 2004. However, the species composition difference has been observed within the context of the wide range of species assemblages described earlier for the Kwinte Bank, together with other Belgian subtidal sandbanks. Sand extraction has created small-scale habitat differences on the Kwinte Bank, to which the benthic fauna have adjusted; however, this is not significant on a true larger scale of the sandbank system, one year after cessation of the intensive disturbance

The influence of marine sand extraction on benthic copepod communities

More than 95% of the sand extraction on the Belgian Continental Shelf occurs on the Kwintebank and is concentrated at the north-western tip and in the centre of the bank. The extraction activities impact bottom habitat structure and diversity by coarsening and homogenising the sediment and cause a strong erosion process. Density, diversity and community structure of harpacticoid copepods on the Kwintebank were determined and related to sediment characteristics and sand extraction intensity. Samples were taken in 1997 with a Reineck box corer and included 10 stations on the bank and 2 in the channels next to the bank. Eighty copepod species were recorded, of which 38% were new to science. Three maior copepod communities were distinguished on the bank. Their occurrence was related to a linear gradient from fine sands in the south to coarser sands in the north. This gradient is a result of local tidal current patterns. A fourth community was found in the gullies next to the bank and in one station positioned in the centre of the bank. The sediment composition of this station however was comparable to the other bank stations. Analogies could be found in the occurrence of erosion and extraction areas and the occurrence of communities on the sandbank. The results of 1997 were compared with copepod species distribution data collected in 1978 prior to intensive sand extraction. The harpacticoid community structure of the southern part of the bank was still comparable after 20 years and hence stable in time. In the northern part the species composition altered in favour of interstitial species. In the centre of the bank a community shift was recorded due to changes in sediment characteristics, adjacent to an area with very low density and diversity. The harpacticoid cammuhities of areas with a high amount of exposure, like on the Kwintebank, are adapted to continuously changing conditions. Nevertheless human-induced physical disturbances may decrease community complexity in the centre of the bank, where the extension of a present depression can become quite problematic. This depression may grow due to sand extraction. The presence of some harpacticoids that are adapted to physical stress and the significantly higher density of juveniles in the most intensively exploited stations, suggest the existence of a frequently disturbed environment. Spreading the extraction activities over the different sandbanks in the concession zone will help decreasing the disturbance frequency and intensity

The impact of primary production in the water column on benthic copepods

A phytoplankton bloom was followed from 9 March till 12 July 1999 at a subtidal station in the Southern Bight of the North Sea. Chla (in surface-, bottom- and interstitial water) and nutrient concentrations (interstitial water) as well as diatom biomass were measured in order to detect any deposition of organic material originating from the bloom on the bottom. The response of the benthic copepods to the sedimentation of the spring phytoplankton bloom was described in terms of changes in density, diversity and community structure. In March the bottom was already organically enriched, probably due to lateral transport. May and June were characterised by organic enrichment derived from the diatom and Phaeocystis spring bloom. In April and July no organic enrichment was observed. The changes in copepod density, diversity and community structure have been attributed to organic enrichment. Over the whole time series copepods were most abundant in the upper two centimetres of the sediment. Nevertheless, a migration of the copepods to the surface was observed during the organic enrichment. Individual species reacted differently to the spring bloom. Some species disappeared, others took advantage of the situation for reproduction. Most pronounced was the reaction of Apodopsyllus n. sp. 1 which was defined as an opportunistic species. The species composition along the sediment depth profile was very diverse in the months devoid of organic enrichment, in contrast with the months with organic enrichment, the community structure over the depth layers then being homogeneous

Reliability analysis of semi-automatic train door systems in service on today's rolling stock of the SNCB

This article analyses the reliability of semi-automatic train door systems that are in use on today’s rolling stock of the SNCB. For the analysis several databases of the SNCB concerning both operation and maintenance were thoroughly screened. These databases are briefly explained and scaling factors are applied to compare the performance of different series of rolling stock relative to each other. Conclusions are made out of the available data