Aarhus University Seal / Aarhus Universitets segl

No. 208: Marine areas in 2015

Hansen, J.W. (red.) 2016: Marine områder 2015. NOVANA. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 148 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 208

Summary

In 2015, 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 and the end of the year, relatively high temperatures and a windy summer. 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 growth (primary production) and the amount (chlorophyll) of phytoplankton were generally at a low level, whereas the water clarity was on average level for the period since 1989. The status of the water bodies were thus relatively good, however, slightly worse than in 2013 and 2014.

In accordance with the relatively good status of the water bodies, the depth distribution of macro algae on stone reefs had increased significantly compared to the earliest registrations and on level with the distribution in recent years.

The development of oxygen depletion was on the same level as in 2014 despite an expectation of improved conditions due to lower temperatures and more windy conditions.

The bottom fauna in the fjords has reduced in abundance, biomass and biodiversity during the period 1998-2015, whereas there has been no significant trend for bottom fauna along the coasts within the same period. In recent years, the bottom fauna in the open inner waters has increased in abundance, biomass and biodiversity after many years of decline.

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 without any clear trend.

In spite of improved status of the environment in recent years, the changes in 2015 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 mercury, TBT, a few tar compounds (PAH) 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 of the marine environment to reduced stress is very complex, impressionable and takes a long time.