Physical characteristics of water column

Physical characteristics of the water column include parameters such as the temperature, salinity and turbidity of the water, but also the amount of oxygen and nutrients. These characteristics are mainly determined by the different water bodies in the Belgian part of the North Sea (BNS) (Belgian State, 2012).

Models show that a sample of seawater in the BNS can contain up to 95% Atlantic ocean water. Near the coast, however, there is also a large supply of freshwater from rivers such as the Scheldt, Rhine, Meuse and Seine (Lacroix et al., 2004). Due to the limited depth and strong currents, the water column in the BNS is continuously mixed. This makes it difficult or impossible to distinguish the water masses as different vertical layers in the water column, with the exception of the estuaries.

The seawater temperature in the BNS shows a seasonal cycle with a difference of about 15° C between winter and summer (Belgian State, 2012). In winter, the influx of warmer waters from the English Channel creates a temperature difference with the colder coastal zone. In summer, a reversal is visible, with warmer water in the coastal zone as a result of faster warming of the shallower coastal waters.

The deeper sea also has a different salinity than the coastal zone, where there is a greater supply of fresh water from rivers (Belgian State, 2012). These rivers also have an important effect on the amount of suspended sediment in the water, which determines the turbidity of the water. This is higher in the coastal zone and comes from French rivers, erosion of French chalk cliffs or erosion of the Holocene sediment off the Belgian coast (Fettweis & Van den Eynde, 2003).

In order to be able to monitor the status and changes in the state of the sea, it is important to monitor its physical characteristics. For example, the impact of climate change on the physical characteristics of the BNS is dealt with in the CLIMAR project. In addition, information on the nutrients and the oxygen content of seawater has been collected within the framework of the AMORE, AMORE II and AMORE III projects, as well as the monitoring obligations for OSPAR, the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD), among other things. Finally, various physical parameters are also measured on a monthly basis during the LifeWatch campaigns on the RV Simon Stevin, the data of which are available on the LifeWatch data explorer.