Algal bloom. Photo: Jon Lasse Bratli (Climate and Pollution Agency)
Fish farming the largest source of nutrients in Norway
For Norway as a whole, fish farming is the largest source of input of both phosphorus and nitrogen. Fish farming is responsible for a growing proportion of discharges of nutrients to Norwegian coastal waters between Stavanger and Finnmark. However, the coastal waters from Stad to the Russian border are not classified as a problem area with regard to eutrophication. Neither has Norway any international obligations to reduce discharges in these areas.
Run-off from agriculture important along the Skagerrak coast
Run-off from agriculture is the most important human source of both nitrogen and phosphorus along the coast of Skagerrak and to coastal waters near the largest towns. The Skagerrak coast is defined as Norway's problem area.
Reduced discharges from municipal waste-water and industry
Norwegian discharges of phosphorus and nitrogen from municipal waste-water and industry have been reduced since 1985. Discharges of phosphorous to the Skagerrak have been reduced by around 60 per cent, whereas discharges of nitrogen have been reduced by around 40 per cent.
Inputs of nutrients are calculated theoretically
Inputs of nutrients to coastal waters are calculated theoretically using a model known as TEOTIL. The data used includes figures from national registers of discharges from point sources such as municipal waste-water, industry and fish farming. For diffuse sources such as agriculture and background runoff from non-cultivated areas, figures are calculated for different areas and land use. The calculated values can be compared with those actually measured in large rivers.
Large waste water treatment plants monitor the quantities of nutrients they discharge, while the quantities discharged from smaller plants are calculated theoretically. In many parts of Norway, there is a very scattered pattern of settlement. In such areas, the proportion of nutrient discharges that reaches local water bodies will depend on how waste water is treated, and the distance to the water body. The size of such discharges is calculated theoretically.
Not all industrial enterprises are required to monitor the quantities of nutrients they discharge, so a proportion of the industrial discharges must also be calculated theoretically. Deposition of nitrogen from long-range transport of nutrients is calculated using numerical models and measurements of the concentration in precipitation.
Discharges from fish farming are calculated on the basis of feed consumption, feed quality and fish production.