Monitoring of the outer Oslofjord. Investigations in 2013

Summary

The hydrographic conditions were studied at 16 stations on seven occasions. Three stations in the Hvaler area were sampled 10 times. Stations located in the outer part of the border zone and on the west and the outer part of the Oslofjord had better conditions in the water masses than those located further into the side fjords, with longer distance from the central parts of the fjord. The Drammensfjord and Mossesundet both have elevated nitrogen concentrations. Drammensfjorden also has poor oxygen conditions in bottom waters. The Larviksfjord and Sandefjords fjord have "good" or "very good" conditions, except for secchi-depth. Vestfjorden near Tønsberg differs slightly from the other western stations in the Oslofjord by having "moderate" state of nitrogen parameters. The Frierfjord has experienced slightly elevated nitrogen concentrations over several years. This was also true in 2013. It also has a challenge in terms of oxygen concentration in the bottom water. There is a gradient in environmental conditions in the Hvaler area with the best conditions in the outer part. Bottom water in the Iddefjord was still in the condition class "very poor".