Aarhus University Seal / Aarhus Universitets segl

No. 253: Marine areas 2016. NOVANA

Hansen, J.W. (red.) 2018: Marine områder 2016. NOVANA. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 140 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 253
http://dce2.au.dk/pub/SR253.pdf 

Summary

In 2016, the positive development from previous years was maintained for some parameters while there was a small decline for other parameters. The year was characterised by a high run-off and accordingly high input of nutrients from land during the beginning of the year (and at the end of 2015), relatively high temperatures and wind varying between short windy periods and longer periods with weak winds. Despite the relatively large run-off at the beginning of the year, the nutrient concentrations were mainly low, and in a few cases the lowest since 1989. The development of oxygen depletion was worse than expected from the weather conditions and the run-off from land.

The growth (primary production) and the amount (chlorophyll) of phytoplankton were increased compared to the level of recent years, whereas the water clarity was on average level for the period since the mid-1990s. The status of the water bodies were thus overall worse than in period 2012-2015.

The general positive development of eelgrass in recent years stagnated in some areas, while there was a small decline in other areas. The coverage (total) of macro algae in coastal waters and on stone reefs was increased compared to 10 years earlier, while this trend had stagnated in the fjords.

The bottom fauna indicated that the conditions in general were worse in the more open waters (North Sea/ Skagerrak) than in the coastal waters. The population of harbour seal has multiplied several times since 1970s but has been reasonably stable the last couple of years and grey seal has increased significantly in numbers. The abundance of harbour porpoise varies a lot from year to year, but overall the population in the North Sea and the inner Danish waters seems to be stable, whereas the population in the Baltic Sea is seriously threatened.

In spite of improved status of the environment in recent years, the changes in 2016 demonstrated that the Danish waters are still very vulnerable to stress and still far away from the objective of a stable, good environmental status. In addition to the load of nutrients (eutrophication), the environmental status is also affected negatively by many other conditions such as fishery, climate change and hazardous substances.

The concentrations of most of the hazardous substances were at the same levels or lower, as in previous years, but especially the concentrations of a few heavy metals (mercury, lead, and cadmium) and brominated flame retardants (PBDE) were so high at several locations that adverse biological effects might occur.

In summary, the data from the national monitoring programme showed that the effort to secure an improved marine environment has succeeded. The marine environment is, however, still vulnerable to stress and the response to reduced stress takes a long time.