Oslo (formerly Christiania until 1900 and Kristiania in 1900-1925) is located at the end of the Oslofjord which is about 100 km long, stretching from the Skagerrak in the south to the city of Oslo in the north.

Oslo, administrative area in grey shading.

The inner Oslofjord is a long, narrow and deep basin (maximum depth 164 meters). It is separated from the outer fjord by the Drøbak Sound (depth 27 m), which effectively prevents good water exchange between the inner and outer fjord. The inner fjord consists of two deep basins, the Vestfjorden (160 metres deep) and the Bunnefjord (160 metres deep), and three shallower basins, the Lysakerfjord, the harbour area of Oslo and the Bekkelaget basin. Due to the limited water exchange and great depths, the Oslofjord is vulnerable to nutrient loading: the deeper water layers easily become anoxic i.e. suffer from lack of oxygen.

Of the several rather small rivers flowing through Oslo, the Akerselva is the biggest. It flows from Maridalsvannet (a small lake), which is Oslo's main water supply source, through the city and out into the harbour. Other rivers are the Lysakerelva and the Alna River.

Research history

The first studies on the Oslofjord were carried out in the 19th century. The studies by G. O. Sars (1865), H. H. Gran (1897), Simmons (1898), Hjort (1900) and Petersen (1915) showed that the condition of the fjord was good at that time. In 1898 hydrographic and biological studies of the fjord were carried out by J. Hjort and H.H. Gran. They found that the plankton population in the fjord chiefly originated from Skagerrak. Hydrograpical and meteorological circumstances were responsible for bringing plankton to the inner Oslofjord.

In 1900 Axel Holst, professor of medicine at the University of Kristiania, was engaged by the municipal water closet committee to investigate the pollution of the Akerselva River and the harbour basin area.

Angling in the city centre in 1931, The City Museum of Oslo.

Holst found both to be heavily polluted. The main pollution source was the city's sewage and especially the sewage content of the organic matter. The organic matter settled on the bottom and developed into sludge, which for its part caused hydrogen sulphide to rise to the surface. The gas was poisonous and the smell was awful. Holst's prime concern was the effect that pollution had on public health. The bacteria content also was alarmingly high and was believed to cause health hazards. Holst's studies supported the arguments of those who wanted introduction of water closets and the reconstruction of Kristiania`s sewerage system. Salicath, a sanitary engineer and member of the municipal board of health, was named to plan a new sewerage system.

In the 1930s several water quality studies were carried out by researchers of the Marine Institute of the University of Oslo, including professors J. Ruud and T. Braarud. A general aim was to examine the effects that pollution had on marine life. Discharge of sewage water was found to increase phytoplankton production in the fjords. Nutrient salts containing phosphorous and nitrogen were considered to be responsible for this effect, which was, in general, thought to have a positive effect on marine life in the fjords. But in some ways it could cause danger to marine life. The final effect of pollution on marine life could not be determined by these studies.

In 1946-1950 Fredrik Beyer and Ernst Føyn of the biological laboratory of the University of Oslo conducted studies on the fjord and concluded that marine life in all parts of the fjord was being adversely affected. Their investigation showed that the oxygen levels in all parts of the inner Oslofjord were becoming progressively lower. The situation was especially critical in the so-called Bunnefjorden.

In the 1950s a number researchers including Braarud, Beyer and Føyn, stated that the fjord could not sustain normal marine life, as the discharge of sewage water was causing enormous plankton production increases. This, in turn, resulted in the deficiency of oxygen caused by the decomposition of increased amount of organic matter. As a result, in some parts of the fjord the marine life of the bottoms disappeared. People asked whether pollution was caused by organic matter or by nutrients. Pollution had ruined the recreational value of the fjord: it looked dirty and smelled bad. The media and private citizens directed several complaints about the pollution to the municipality.

The first monitoring programme on the Inner Oslofjord was launched by NIVA (Norwegian Water Research Institute) in 1962-1965. The main goal was to gather basic information on the state of the fjord which could guide the application of future technical solutions. The main task was to determine what was causing the wastewater pollution, to understand how pollution and its effects were linked, and to obtain quantitative data on water renewal processes, marine life, and chemical processes affected by pollution. The main result was the conclusion that the pollution was being caused by nutrients in the wastewater. In 1977 a national monitoring programme on water pollution was launched.

In 1991 studies in the Oslo harbour basin showed high concentrations of toxic compounds containing quicksilver, lead, copper and zinc. In 1992 another study on toxic wastes estimated total amount of quicksilver discharged into the fjord to be 40 kg a year, along with high amounts of lead (8400 kg), copper (12200 kg), and zinc (24700 kg). Especially the outlet areas of water courses were very polluted by toxic wastes.

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