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CausesThe essential nutrients causing eutrophication are nitrogen in the form of nitrate or ammonium and phosphorus in the form of phosphate. In addition, inputs of bioavailable organic phosphorus and nitrogen can cause eutrophication, as bacteria can mineralise the organic phosphorus to phosphate and the organic nitrogen to ammonium, which is further oxidised to nitrite and nitrate. Marine waters receive dissolved and particulate nutrients and organic matter from land via rivers and direct discharges, from the atmosphere and from adjacent seas (see Figure 1.1). In Denmark the most important sources are:
Discharges from point sources, losses from agriculture and atmospheric deposition are monitored as an integrated part of the National Aquatic Monitoring and Assessment Programme and reported annually (Conley et al. 2002). The inputs from adjacent seas are also monitored within the national monitoring programme. There are three major avenues of advective transport of nutrients that must also be considered:
All three sources have influence on the marine environment by supplying
additional nutrients. The waters from the German Bight and the Baltic
Sea have already received high inputs of nutrients. The input from the
Baltic Sea differs from the two firsts because it actually dilutes bioavailable
nitrogen concentrations in the Danish Straits and the Kattegat. The median
winter surface concentrations of nitrate (1986–1993) in the water
from the Baltic is 4.6 µM compared to the median concentrations
in the waters in the Danish Straits and Kattegat, which are 7.3 (6.5–8.8)
µM and 7.4 (6.0–9.7) µM, respectively.
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Danish Environmental Protection Agency & National Environmental Research Institute • updated: |