Aarhus University Seal / Aarhus Universitets segl

No. 308: Marine areas 2017. NOVANA

Hansen, J.W. (red.) 2019: Marine områder 2017. NOVANA. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 128 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 308. http://dce2.au.dk/pub/SR308.pdf

Summary

In 2017, some of the parameters were status quo compared to the positive development in the marine environment in recent years whereas degradation was registered for other parameters. The year was characterised by a relatively low run-off during the first six months, a very high run-off in the autumn and a similar seasonal distribution of input of nutrients from land to the sea. The year was also characterised by relatively high temperatures in spite of a chilly summer with relatively windy weather in June and at the beginning of August. The concentrations of the dissolved inorganic nutrients were relatively low during the first six months of the year, and in a few cases the lowest since 1989. However, the increased run-off in the autumn lead to a relatively high increase in the concentration of nitrogen in fjords and coastal areas. Oxygen depletion began very early in some areas and became extensive and severe during the summer, but it ended in the autumn as usual.

The growth of phytoplankton and especially the concentration of chlorophyll were increased compared to the levels in 2012-2013, whereas the water clarity was on average level for the period since the mid-90s. The status of the water bodies was thus overall worse in 2014-2017 than in 2012-2013.

The general positive development of eelgrass during the last ten years has stagnated. The coverage of macroalgae in coastal waters and outer fjords in 2017 has increased during the last ten years while the development has stagnated in the inner fjords, Limfjorden and on stone reefs.

The biodiversity of the bottom fauna indicates that the environmental conditions for the bottom fauna in general were worse in the more open waters (the North Sea/Skagerrak) than in the inner waters where the bottom fauna has developed positively in recent years in most areas. The population of harbour seals has multiplied several times since the end of the 70s, but the growth has decreased in recent years. The number of grey seals has increased significantly since 2005 and the grey seal breeds again in the Danish waters. The abundance of harbour porpoises varies both between areas, seasons and years but overall the populations in the North Sea and the inner Danish waters seem to be stable.

In spite of the improved status of the environment in recent years, the development during the latest years has showed that the Danish waters are still very vulnerable to stress and still far from the goal of a stable, good environmental status. In addition to the load of nutrients (eutrophication), the environmental status is also affected negatively by other conditions such as fishery, climate change and hazardous substances.

In summary, the data from the national monitoring programme showed that the effort to secure an improved, marine environment has a positive effect. But the marine environment is still under pressure and responds slowly to the improving initiatives.