Dahl, K. & Josefson, A.B. (Eds.) 2009: Marine områder 2007 – Tilstand og udvikling i miljø- og naturkvaliteten. NOVANA. Danmarks Miljøundersøgelser, Aarhus Universitet. 113 s. - Faglig rapport fra DMU nr. 707.

Summary

Despite notable reductions in the supply of nutrients to Danish coastal waters in recent years, the environmental condition in these waters in 2007 has not improved. Weather conditions resulted in a large supply of nutrients from land during winter 2006 to spring 2007, in comparison to previous years. This resulted in higher nutrient concentrations and consequently also higher chlorophyll concentrations during spring. Bottom water oxygen conditions have not improved in general, despite the fact that there were only a limited number of severe oxygen depletion events as a result of strong winds during summer. A possible explanation for the limited improvement in oxygen conditions may be that the water temperatures are increasing as a result of global warming, leading to increased respiration and decreased solubility of oxygen in sea water.

The following points summarise the environmental conditions for 2007.

Meteorology and hydrography

• The annual mean water temperature has increased by approximately 1º C during the last 40 years and both surface and bottom water temperatures in 2007 were the warmest on record. Bottom water temperatures off-shore were 2º C higher than normal (1961 - 1990) throughout the year.
• Freshwater discharge to the inner Danish waterswas considerably above average between November 2006 and March 2007 as well as in July 2007. As a result, the freshwater nitrogen loading was high.

Nutrient loading and concentrations

• The flow corrected freshwater nutrient dischargehas decreased by approximately 40 % and 75 % for nitrogen and phosphorus, respectively, from 1989 to 2000. From 2000 and onwards the levels have remained stable. 
• Sea water nutrient concentrations have gradually decreased since 1989. Phosphorus concentrations have now remained stable since 1997 while nitrogen concentrations continue to decrease slightly since 2002. This is mainly due to the effects of the national water quality directives (Vandmiljøplan I and II).

Phytoplankton and water clarity

• The large supply of nutrients in the winter months of 2006 and early 2007 resulted in an exceptionally large spring phytoplankton bloom in March. Additionally, the increased run-off in July resulted in a new bloom. Chlorophyll concentrations in the off shore waters were among the highest recorded since the start of the monitoring program in 1989. Concentrations in the fjords were also in the high end.
• Water clarity (Secchi depth) was exceptionally poor for the whole year in all waters, representing the worst conditions since the start of the monitoring program.
• High concentrations of the flagellate Chattonella sp., which is toxic for fish, were recorded in the <st1:place w:st="on">Kattegat</st1:place> and Little Belt in March 2007. However, no effects on fish were observed. Additionally high concentrations of potentially toxic Dinophysis and Pseudo-nitzschia were measured in some areas.

Oxygen depletion

• Oxygen conditions in 2007 were better than previousyears for the coastal waters and enclosed fjords, and better than expected due to the large phytoplankton blooms in spring and July. This is most likely due to the frequent strong winds in summer which were capable of mixing the water column and hereby supplying oxygen to bottom waters. The offshore bottom waters experienced widespread low oxygen concentrations for a longer period; however concentrations were only below the critical level of 2mg O2 l-1 in isolated places.

Benthic vegetation and fauna

• No significant changes for benthic vegetation were recorded, compared to last year, and the general lack of improvement since the 90s is consistent with the lack of change in water clarity. 
• Local species richness of benthic fauna in the off-shorewaters of the Kattegat and Belt Sea region has gradually decreased since the start of the 1990s and for the last four years has been at a level which is half that from 1990. Richness in 2007 was the second poorest on record, and the fauna density has fallen by 50 %.Benthic fauna status measured using the DKI index for ecological status with respect to the Water Framework Directive, has changed from "good" to "moderate" in 2007.

Environmentally hazardous substances

• TBT, PCB and the PAH anthracene are still the only substances that exceed OSPAR's Ecotoxicological Assessment Criteria (EAC)(2008). For the localities where there are enough data for a time series analysis, the concentrations of some organic contaminants are decreasing. All regions can still be classified as "very polluted" with respect to TBT. Levels of dioxin, furans and co-planar-PCBs are all below the thresholds for food quality, and PAH concentrations in fish and mussels are generally acceptable with regard to OSPAR’s EACs. However, compared to the Norwegian criteria some localities can be classified as markedly contaminated with respect to PAH criteria.
• Investigations of lysosomal membrane stability in blue mussels indicate that mussels from ~40 % of the coastal sites are affected by environmentally hazardous substances. The observed effects are mainly correlated to elevated concentrations of organic contaminants such as PCBs and PAHs.
• Measurements on the fish viviparous blenny (Zoarces viviparus) show differences in effect levels between sites, with regard to CYP1A enzyme activity and larvae deformities. The greatest effects on CYP1A are in coastal waters where there is generally a greater loading of organic contaminants such as PAH and PCBs.

Full report in Danish pdf (6.2 MB)