Eutrophying substances: inflow to the North Sea, 1980-2001
The inflow of phosphorus and nitrogen to the North Sea was lower in the 1990s than in the 1980s. The inflow of phosphorus has fallen faster than the inflow of nitrogen.
Fall in inflow of phosphorus and nitrogen to the North Sea
The inflow of phosphorus and nitrogen to the North Sea was lower in the 1990s than in the 1980s. The exceptions were 1994 and 1995 because of large flows of water through the rivers.
The inflow of phosphorus has fallen faster than the inflow of nitrogen. As a result, the ratio of nitrogen to phosphorus in the water flowing to the sea is now higher. This has an adverse effect on the species composition of phytoplankton (algae). This imbalance also increases the risk of blooms of toxic species of algae.
The figure shows only the inflow to the North Sea from rivers. The inflow from other sources such as direct discharges into the North Sea and the precipitation of substances from the air (atmospheric deposition) makes only a relatively small contribution to the burden imposed by eutrophying substances. Farther out to sea, however, the atmospheric deposition of nitrogen is significant.
The variation in the inflow of nutrients is relatively high due to large variations in water flow rates.
Policy for the flow of nutrients into the North Sea
The aim of government policy was to reduce the flow of nutrients to the North Sea in 1995 by 50% compared to 1985 (V&W, 1990). This objective has now been achieved for phosphate but not for nitrogen.
