Nutrient Loading to Norwegian Coastal Waters and Its Contribution to the Pollution of the North Sea

Abstract

The North Sea Declaration aims at reducing the load of nutrients to the North Sea by the order of 50 per cent between 1985 and 1995. This paper gives an overview of the nutrient loading to the Norwegian coastal waters, and an estimate of how much of this loading reaches the local Skagerrak coast and the North Sea. The average annual nutrient load to coastal waters from land-based sources along the Norwegian North Sea coastline (from the Swedish border to 62°N) is approximately 3,600 tons of phosphorus and 70,000 tons of nitrogen. Municipal wastewater is the main source of phosphorus (44 per cent), while agriculture contributes with 20 per cent of the total load. Background runoff, i.e. runoff from forested areas and uplands, including effects of acid precipitation, is the main source of nitrogen inputs (40 per cent). Agriculture is the second major source (32 per cent). Our calculations indicate that deposits of airborne nitrogen via precipitation contribute approximately 15-20,000 tons of nitrogen inputs on the coastal watersheds draining to this coast. The Norwegian loading amounts to 3-4 % of the total nutrient inputs to the North Sea from the surrounding countries. Taking into consideration the dominating current systems in the North Sea and along the Norwegian coast, only a small part of this load reaches the middle and southern parts of the North Sea susceptible to eutrophication. This implies that the Norwegian nutrient input has minimal effects on the eutrophication of the North Sea. There is a considerable need for developing standard methods for estimating nutrient inputs to the North Sea. Emphasis should be put on preparing guidelines for assessing comparable nutrient input data from all North Sea countries.