Are nutrient concentrations in European transitional, coastal and marine waters decreasing?

Policy Question

Indicator codes: CSI 021 , MAR 005

(18 Oct 2018)

Examples of successful implementation of nutrient management strategies can be found in, for example, the Baltic Sea and the North Sea regions, where decreasing trends are observed.
The highest nitrogen and phosphorus concentrations are generally observed in transitional and coastal waters of the marine (sub)regions, which reflects the influence of direct and diffuse inputs of nutrients in the upstream catchments.
In the southwestern Baltic Sea, decreasing nitrogen and phosphorus concentrations were observed between 1990 and 2017. These trends illustrate the effects of reductions in nutrient inputs. Phosphorus concentrations in this period increased in other parts of the Baltic Sea, because of phosphorus release from sediment under anoxic conditions (HELCOM 2018).
In the Greater North Sea, nitrogen and phosphorus concentrations decreased between 1990 and 2017 at a large number of stations in transitional and coastal waters, with the exception of total phosphorous concentrations in parts of the Kattegat. Again, these trends reflect the effect of reductions in nutrient inputs (OSPAR 2017).
In the Celtic Seas, some offshore stations showed decreasing nutrient concentrations between 1990 and 2017.
In the Black Sea, time series of phosphorus concentrations showed significant decreases in the northwest shelf area, while nitrogen concentrations showed a more variable pattern.