An estimate of the suspended particulate matter (SPM) transport in the southern North Sea using SeaWiFS images, in situ measurements and numerical model results

A study is presented where satellite images (SeaWiFS), in situ measurements (tidal cycle and snapshot) and a 2D hydrodynamic numerical model have been combined to calculate the long term SPM (Suspended Particulate Matter) transport through the Dover Strait and in the southern North Sea. The total amount of SPM supplied to the North Sea through the Dover Strait is estimated to be 31.74 x 106 t. The satellite images provide synoptic views of SPM concentration distribution but do not take away the uncertainty of SPM transport calculation. This is due to the fact that SPM concentration varies as a function of tide, wind, spring-neap tidal cycles and seasons. The short term variations (tidal, spring-neap tidal cycle) have not been found in the satellite images, however seasonal variations are clearly visible. Furthermore the SPM concentration in the satellite images is generally lower than in the in situ measurements. The representativness of SPM concentration maps derived from satellites for calculating long term transports has therefore been investigated by comparing the SPM concentration variability from the in situ measurements with those of the remote sensing data. The most important constraints of satellite images are related to the fact that satellite data is evidence of clear sky conditions, whereas in situ measurements from a vessel can be carried out also during rougher meteorological conditions and that due to the too low time resolution of the satellite images the SPM concentration peaks are often missed. It is underlined that SPM concentration measurements should be carried out during at least one tidal cycle in high turbidity areas to obtain representative values of SPM concentration

Spatio-temporal variation of surface suspended particulate matter concentration in the Belgian-Dutch coastal zone

sensing (MODIS-Aqua) data, were evaluated for their use in the assessment of coastal turbidity maximum (CTM) dynamics in Belgian coastal waters. The CTM is a dynamic coastal feature of which the geographic position and extent varies under different meteorological, astronomical and climatological conditions. Analyses were based on grouping-averaging of SPM concentration maps, using different classification schemes. To better spatially depict the CTM, entropy grouping was introduced. This technique analyses, per pixel, the total information contained within the probability distribution of SPM concentration. Results revealed wind-induced variations in position and extent of the CTM, with southwesterly winds inducing a largest CTM extent, in contrast to a strong reduction under northeasterly winds. Climate-induced variations were assessed contrasting 2 winters with opposing indices of the North Atlantic Oscillation (NAO). In a winter with a positive NAO index, hence stronger-than-average southwesterly winds, the CTM was extended to the Dutch waters, whereas the opposite occurred in winters with a negative NAO index, hence less-than-average southwesterly winds. To evaluate astronomical forcing (tides) grouping-averaging was performed of SPM concentration maps over a tidal cycle, and spring-neap conditions. Although, only part of the tidal cycle can be analysed, due to the sun-synchronicity of the MODIS-Aqua satellite, comparison of the results with in-situ data from a single observatory station showed good resemblance. It is concluded that MODIS-Aqua satellite data can be used to assess SPM concentration variability related to tides, neap-spring cycles, meteorological and climatological events

Kyste synovial intraosseux du scaphoïde carpien bilatéral révélé par une fracture pathologique: à propos d’un cas et revu de la littérature

Nous rapportons l'observation d'un jeune patient qui présente un kyste synovial intraosseux (KSIO) du scaphoïde révélé par une fracture pathologique. Le kyste synovial intraosseux du scaphoïde constitue une étiologie très rare des douleurs du poignet encore plus des fractures et la forme bilatérale associe à une fracture demeure une entité exceptionnelle, non décrite dans la littérature

MOnitoring en MOdellering van het cohesieve sedimenttransport en evaluatie van de effecten op het mariene ecosysteem ten gevolge van bagger- en stortoperatie (MOMO): activiteitsrapport 4 (1 oktober 2007 - 31 maart 2008)

The "MOMO" project is part of the general and permanent duties of monitoring and evaluation of the effects of all human activities on the marine ecosystem to which Belgium is committed following the OSPAR convention (1992). The goal of the project is to study the cohesive sediments on the BCP using numerical models as well as by carrying out of measurements. Through this data will be provided on the transport processes, which are essential in order to answer questions on the composition, origin and residence of these sediments on the BCP, the alterations of sediment characteristics due to dredging and dumping operations, the effects of the natural variability, the impact on the marine ecosystem, the estimation of the net input of hazardous substances and the possibilities to decrease this impact as well as this in-put

Optical remote sensing in support of eutrophication monitoring in the southern North Sea

Spring mean and maximum chlorophyll a (chla) concentrations are main factors to determine the eutrophication status of the Belgian waters as agreed within OSPAR in 2002. Other important assessment parameters to measure the degree of nutrient enrichment - the amounts of inorganic phosphate and nitrogen in winter - appeared to be above thresholds for most measurements performed in the period 1974-2002. As the standard in situ monitoring programme does not give a clear picture of the temporal and spatial distribution of chl a, it is logical to complement these measurements with optical remote sensing. However, chlorophyll concentrations derived from sensors such as SeaWiFS are unreliable in the Case 2 waters of this region because of high particulate and dissolved yellow substance absorption. Another important limitation of ocean colour sensors is the amount of useful images due to cloud cover. The combination of data from different ocean colour sensors in order to enable a better temporal coverage might be hampered by the different chlorophyll retrieval algorithms used. This study compares different global chl a algorithms (MODIS, SeaWiFS, MERIS) as well as a turbid water algorithm for the Southern North Sea. This is done by running the different algorithms on in situ reflectance spectra collected at 107 stations in the period 2001-2002 over the Southern North Sea and comparing them with in situ chl a concentrations, as well as by running the algorithms on a MERIS image of the 29th of July 2002. Based on this validation the accuracy of these products and their suitability for eutrophication monitoring in the Southern North Sea are assessed

Voie antérieure transversale dans l’ostéosynthèse d’une fracture type III du processus coronoïde chez un adolescent: à propos d’un cas et revue de literature

Les auteurs rapportent une observation rare d'un jeune adolescent de 17 ans qui a présenté une fracture du processus coronoïde du coude survenue suite à un accident de sport. Il s'agit d'une observation décrivant un abord particulier par voie antérieure transversale permettant un contrôle direct et vissage en compression du fragment déplacé; l'évolution radio clinique était  satisfaisante. Nous discuterons à la lumière de la littérature, notre attitude thérapeutique, et l'évolution de ce cadre nosologique à travers l'analyse de cette observation

Calibration and validation of an algorithm for remote sensing of turbidity over La Plata river estuary, Argentina

The La Plata River, located at 35°S on the Atlantic coast, is one of the largest waterways of South America. It carries a large amount of suspended particulate and dissolved organic matter, and is considered among the most turbid waters of the world. Very high values of total suspended matter have been reported in this region, with mean values ranging from 100 to 300 g m-3 and extreme concentrations up to 400 g m-3. Satellite sensors have shown to be the best tools available to map river plumes and to study their influence on the adjacent ocean. However, global algorithms for remotely estimating sediment concentration are not currently available. Moreover, such high sediment loads represent a challenge to atmospheric correction algorithms which usually rely on the assumption of zero water-leaving reflectance in the near infrared or short wave infrared part of the spectrum (black pixel assumption). In the extremely turbid waters of La Plata Estuary such assumptions are not valid. A two band algorithm to estimate turbidity using near infrared and the short wave infrared bands (858 nm and 1240 nm) of the MODIS-Aqua sensor is presented. The model is calibrated using in situ reflectance and turbidity measurements from turbid waters of the Southern North Sea and Scheldt River (Belgium) and then applied to MODIS imagery of La Plata River estuary (Argentina). A good correlation was found between modelled and in situ turbidity values when the algorithm was applied to concurrent MODIS imagery. Moreover, satellite-derived turbidity maps show a spatial distribution of sediment consistent with patterns and characteristic features of the estuary

Mud Origin, Characterisation and Human Activities (MOCHA): Final report

The cohesive sediments, which are frequently found in the Belgian nearshore zone (southern North Sea), are of different age such as tertiary clays and Holocene, modern and recently deposited muds. The area is characterised by a turbidity maximum. The source areas of the recently deposited muds and the effect of human impact vs. natural processes on the distribution and/or erosion of these sediments have been investigated using historic and recent bottom samples, in situ and remote sensing (satellite images) SPM concentration measurements, numerical modelling, GIS and clay mineral and microfossil analysis. The Schelde estuary, the potential erosion areas of cohesive sediments on the BCS and adjacent areas and the SPM transport through the Dover Strait have been considered as possible source areas.The historic bottom samples have been collected in the beginning of the 20th century, the quality of these samples and the meta-information is very high and they have proven to be a major reference to understand the evolution of the cohesive sediment distribution. The recent bottom samples consist of box core, Reineck core and Van Veen grab samples collected during the last 10 years. The processing of the historic and recent data on cohesive sediments was mainly based on field descriptions of the samples (consolidation, thickness) and morphological evolution. On some of the recent samples radioactive and gamma densitometric measurements have been carried out. During the processing the emphasis was put on the occurrence of thick layers (>30 cm) of freshly deposited to very soft consolidated mud and of clay and mud pebbles, because these sediments are witnesses of changes.Satellite images, in situ measurements and a 2D hydrodynamic numerical model have been combined to calculate the long term SPM transport through the Dover Strait and in the southern North Sea. The satellite images (SeaWiFS) provide synoptic views of SPM concentration. The representativness of SPM concentration maps derived from satellites for calculating long term transports has been investigated by comparing the SPM concentration variability from the in situ measurements with those of the satellite data. It is underlined that SPM concentration measurements should be carried out during at least one tidal cycle in high turbidity areas to obtain representative values of SPM concentration.Areas where the thickness of the Quaternary cover is less than 2.5 m were defined as potential erosion areas of Palaeogene clay containing deposits. In the framework of this project, the geological data related to the BCS have been reviewed and the relevant information was compiled into a GIS. This also included a small part of the French continental shelf. Additionally information was added from vibrocores analysis and Dutch geological data. Approximately 20 % of the BCS, 6 % of the small part of the French area and only 3% of the Dutch study area could possibly serve as a source for fine suspended sediments. Quaternary muds are mostly presented in the 2 eastern nearshore area; on the Dutch part they occur more offshore. Their occurrence represents 11% of the BCS and approximately 35% of the Rabsbank area Cretaceous microfossils are present in all samples and have been transported into the area with the residual water transport. Material from the east, in particular from the Eocene-Oligocene transitional strata, has been found in the eastern nearshore area up to about Oostende. This zone coincides with the extension of the Holocene mud and could indicate an erosion of these sediments and/or a transport of clay minerals from the Schelde estuary.Clay mineral analysis has been carried by two approaches in order to determine source areas. The results of the second approach show that no systematic differences in the clay mineralogy depending on geographic location could have been found within the samples. The results clearly prove the necessity of using more elaborate sample preparation procedures in examining the provenance of the mud deposits.Thick layers of fresh mud were deposited in the beginning of the 20th century mainly in a narrow band along the coast from about Nieuwpoort up to the mouth of the Westerschelde. These deposits were mainly the result of natural morphological changes. Today, most of the depositions of thick layers of fresh mud have been induced by anthropogenic operations, such as dumping, deepening of the navigation channels and construction and extension of the port of Zeebrugge. Comparing the actual situation with the situation 100 years ago reveals that the area around Zeebrugge where fresh mud is deposited extends more offshore today