Monitoring of the outer Oslofjord - inputs and surveys in the water masses in 2013. Technical report

Summary

Monitoring of the water column in the outer Oslofjord is done in order to obtain information about the environment and inputs, focusing on nutrients (eutrophication). The report describes the inputs to the fjord and the performed investigations and results for phytoplankton, hydrophysical and hydrochemical conditions in 2013. Agriculture is the largest single source for the supply of both anthropogenic phosphorus and nitrogen. The picture does not change much from year to year. It may appear that amount of phosphorus from agriculture has declined somewhat in recent years. There was a moderate replacement of bottom water in several of the side fjords during winter and spring. This led to better oxygen conditions in some of the fjords. The summer/ all showed shorter periods of increasing nitrogen concentration associated with periods of runoff and reduced salinity in the surface at some stations. In 2013 it was recorded slightly higher phosphate concentrations in winter compared to previous years. Phytoplankton biomass was similar to previous years. A number of blooms occurred during the summer, after major runoff periods.