Inputs of nutrients to coastal waters

Inputs of nutrients to coastal waters are steadily rising in most parts of Norway, whereas inputs along the Skagerrak coast have been reduced since 1985. Measurements show that water quality is generally good in more open areas along the Skagerrak coast, but poorer in certain fjords.

Fish farming the largest source of nutrients

Nutrients from fish farming are largely discharged along the North Sea and Norwegian Sea coast of Norway and all the way north and east to the Russian border, with the largest discharges in the river basin districts from Møre og Romsdal and northwards. However, nutrient concentrations do not build up in this area in the same way as they do further south, from Rogaland to Sogn og Fjordane. In 2012, total phosphorus discharges from fish farming in Norway were about 9 000 tonnes, and this sector is by far the largest source of phosphorus discharges.

Both fish farming and agriculture are large sources of nitrogen, each accounting for 30–50 per cent of Norway’s total anthropogenic releases. Calculations show that inputs from agriculture were unchanged from 1990 to 2012, while discharges from fish farming rose.

Agriculture important source along the Skagerrak coast

The impacts of nutrient inputs are more marked along the Skagerrak coast than anywhere else in Norway. Agriculture and municipal waste water treatment are the main anthropogenic sources of nitrogen and phosphorus inputs in this area.

Lower inputs from waste water, agriculture and industry

Norwegian discharges of phosphorus and nitrogen from municipal waste water, agriculture and industry have been reduced since 1985. In all, discharges of nitrogen to the Skagerrak coast have been reduced by about 40 per cent, and discharges from agriculture have been cut by about 25 per cent.

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Inputs of nutrients are estimated

Inputs of nutrients are estimated on the basis of figures reported to Norway’s Pollutant Release and Transfer Register and other national registers for point sources such as municipal waste water, industry and fish farming. Discharges from non-point sources such as agriculture and the natural environment are estimated using factors for different types of areas and forms of land use. These estimates can be compared with measurements made in the larger river systems.

Large waste water treatment plants monitor their residual discharges, but discharges from smaller plants have to be estimated. In many parts of Norway, it also of interest to include nutrient discharges with waste water from rural areas with a scattered population. The proportion of these discharges that reaches local water bodies depends on the type of discharge, how the water is treated and the distance to the water body. These discharges are estimated.

Not all industrial plants are required to monitor releases of pollutants, and a certain proportion of industrial discharges must therefore be estimated. Deposition of nitrogen after long-range atmospheric transport is estimated using modelling and measurements of precipitation.

Discharges from fish farms are estimated on the basis of feed consumption, feed quality and fish production.

Water quality is measured

Measurements of coastal water quality are made at the same time as the annual measurements for the monitoring programme for nutrients in coastal waters.

Differences between calculated inputs and measured water quality

Differences may arise between calculated inputs of nutrients and actual measurements of water quality because inputs are calculated for specific sources. They do not take into account factors such as climate change or long-range transboundary transport of nutrients with ocean currents and in the atmosphere.

For example, Norway has recently experienced milder winters and more intense rainfall. This may well have resulted in more leaching of nutrients from soils, so that background runoff has risen.