Andre presfaktorer end næringsstoffer og klimaforandringer – sammenfatning

The Danish Environmental Protection Agency has funded a project “Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change” with the aim to identify a number of environmental pressure factors other than excess nutrient loading and climate change that potentially can affect the quality elements of the WFD. The project has resulted in 8 independent reports that are summarized in this study:

1. Petersen et al. 2018: DTU Aqua rapport nr. 336-2018 (1),
2. Høgslund et al. 2019: Videnskabelig rapport fra DCE nr. 323 (2),
3. Stæhr et al. 2019: DTU Aqua rapport nr. 353-2019 (3),
4. Petersen et al. 2020: DTU Aqua rapport nr. 358-2020 (4),
5. Petersen et al. 2020: DTU Aqua r rapport nr. 361-2020 (5),
6. Petersen et al. 2020: DTU Aqua rapport nr. 359-2020 (6),
7. Helmig et al. 2020: DTU Aqua rapport nr. 360-2020 (7),
8. Petersen et al. 2020: DTU Aqua rapport nr. 365-2020 (8),

where (1) is a review of potential effects of a number of pre-defined pressure factors - sand and gravel extraction, dredging of shipping lanes and harbours and clipping of the dredged material, physical constructions, fishery, shipping, plastic waste incl. micro plastics, hazardous substances and invasive species – was carried out. Based on the results of the review (1), more specific analyses were carried out for effects of fishery and other localized pressure factors (4, 5), sediment chemistry (2), 3 invasive species (3, 8) and exploitation of boulder reefs (7). All the specific analyses were carried out based on existing data sets primarily extracted from the Danish environmental monitoring programme NOVANA. Finally, methods of cumulation of effects of different types of pressure factors were assessed (6).

Overall, the screening of the scientific research literature and the performed data analyses that have been possible show that primarily fishing and secondary - and to a much lesser extent - invasive species are currently the most significant other pressure factors on the WFD quality elements in the WFD water bodies besides nutrient loading and climate change. However, for some of the pressure factors, this conclusion is based on a deficient data base. Thus, in general, no analyses have been performed for a number of invasive species and for the best monitored species – i.e. Japanese wireweed - effects on the quality element macroalgae could be detected. It can thus not be ruled out that an improved data set will lead to documentation of additional effects of e.g. other invasive species. On the other hand, for a number of other potential pressure factors, such as plastics and environmentally hazardous substances, it is unlikely that an improved data base will lead to documentation of potentially significant impacts at the water body level. Finally, there are a number of pressure factors – e.g. raw material extraction and excavation, etc. - where there is a sufficient data base to assess that these do not have significant effects on the quality elements at the water body level, as long as they are maintained and managed at the current level.

With regard to fisheries, use of bottom affecting gear like bottom trawl, mussel dredge etc. take place in almost half of the WFD water bodies. In the vast majority (68%) of the fisheries affected areas, the cumulative impact over 5 years constitutes <10% of the total area of the water body (some of which may be repeated impacts of the same area), but for some areas it is a very massive fishing impact. This applies in particular to the areas along Jutland's west coast, but there is also a significant area impact in several areas in and around the Kattegat. It can be readily assumed that fishing with bottom trawls can have a very significant effect on eelgrass (5), not least because the expected regeneration time for eelgrass is very long, whereas it was not possible to detect effects on benthic infauna using the WFD indicator DKI (4). A model study on impact of mussel dredging on Chlorophyll a concentrations did not reveal effects (5). A literature review of cascade effects of finfish fishing on the quality element phytoplankton likewise could not demonstrate expected significant effects in Danish WFD water bodies.