Publication

Summary

Water column monitoring in the outer Oslo Fjord is performed to obtain information about the environmental condition and inputs to the area, focusing on nutrients (eutrophication). The report describes inputs to the fjord in 2015 and results from the monitoring regarding phytoplankton, hydrophysical and hydro-chemical conditions in 2016. The national reporting routines for source-specific data, and subsequent processing, of inputs to the outer Oslofjord mean that results from the individual year will not be available until the autumn of the year after the year reported. The figures for nutrient salts in this report therefore apply for the year 2015. There was no major replacement of bottom water in sidefjords during the winter and spring of 2016. In sidefjords with shallow sills or more pools (Iddefjorden, Frierfjord) no replacement of bottom waters has taken place since the winter of 2010. However, in November 2016 there were observed replacement of the bottom water in Hvaler all the way in to Iddefjorden. In 2015 was phytoplankton biomass moderate. The phytoplankton were dominated by dinoflagellates in in the open sidefjords, whereas diatoms dominated in the fjord influenced by freshwater. Concentration of nitrogen was similar or higher compared with 2015 for the winter period. During the summer period the concentration of nitrogen was lower in 2016 than in 2015. During the summer of 2016, fewer periods of runoff was recorded than in the previous years, result in lower silicate and nitrogen concentrations. The replacement of bottom water in November in Hvaler result in high concentration of phosphate in the surface.