International audienceno abstrac

We measure the dispersion coefficient through homogeneous bead or sand packings at different flow rates from direct magnetic resonance imaging (MRI) visualizations of the transport characteristics of a pulse of paramagnetic nanoparticles. Through two-dimensional imaging we observe homogeneous dispersion inside the sample, but we show that entrance effects may induce significant radial heterogeneities, which would affect the interpretation of the breakthrough curve. Another MRI approach then provides quantitative measurements of the evolution in time of the longitudinal particle distribution in the sample. These data can be analyzed to deduce the coefficient of dispersion independently of entrance effects. The values obtained for this “effective” dispersion coefficient are almost ten times lower than the commonly accepted values.

Purpose: Since the 1960s, pollution of the marine environment has been observed around the world, and a general awareness of the potential environmental hazards from contaminants arose. This general awareness was followed by implementation of environmental regulations at the national and international levels regarding industrial discharges, and forcing the development of management programs to improve the environmental quality. This overview focuses on the status of assessments, regulations, and remediation actions of contaminated marine sediments in four North European countries: Sweden, Norway, Finland, and Denmark. Results and discussion: We found that the extent of assessment surveys and the implementation of sediment remediation actions vary between the countries, with Norway the most advanced. Norway has initiated national pilot remediation tests, followed by full-scale site remediation by dredging and in situ capping in several projects along the coast. Sweden is following Norway’s example, although with fewer completed projects. In Finland, the tradition of maintenance dredging is still very strong although the main purpose has not been cleanup actions. Accordingly, in Denmark, dredging is primarily used to maintain sailing depths. All four countries have implemented the Water Framework Directive in addition to national regulations that provide the authority for imposing and implementing sediment remediation measures. However, only Norway has implemented a national strategy on remediation of contaminated sediments. Conclusions: This overview highlights the need for enhanced communication and exchange of experiences between the four Nordic countries of concern with regard to sediment remediation strategy and management.