Pollution of the Outer Oslofjord

Abstract

The Outer Oslofjord has recently been subject to concern. 1. The Inner Oslofjord. Covers an area of 193 km2, is 160 m deep and is separated from the Outer Oslofjord by the narrow Drøbak sound with a sill depth of less than 20 metres. This part of the Oslofjord constitutes an enclosed body of sea water, sensitive to pollution, receiving sewage from approximately 650,000 inhabitants. In spite of modern sewage treatment, the fjord still suffers torn eutrophication problems resulting in reduced oxygen in the deep water, and areas of anoxic bottom water. The fjord is an important recreation area. 2. The Outer Oslofjord. Recent findings indicate that eutrophication is slowly increasing. An increasing eutrophication of the Outer Oslofjord wil also increase the need (and cost) of better sewage treatment in the Inner Oslofjord. 3. The North Sea. The quality of the water in the Oslofjord area is also dependent on the water it receives from the Skagerrak. The Skagerrak water will periodically receive polluted water from the southern North Sea and Kattegat. When these episodes coincide with water renewals between the Oslofjord and the Skagerrak, the fjord will receive polluted water from other countries. The Oslofjord water will in turn discharge into the Skagerrak, but due to the general circulation pattern, this will mainly influence the Norwegian south-east coast.