Hjorth, M. & Josefson, A.B. (red.) 2010: Marine områder 2008. NOVANA. Tilstand og udvikling i miljø- og naturkvaliteten. Danmarks Miljøundersøgelser, Aarhus Universitet. 136 s. - Faglig rapport fra DMU nr. 760.
The overall status of the marine environment in Denmark in 2008 in terms of the status of algae, benthic animals and other important parameters has not improved. The decreased nutrient concentrations in water achieved by the considerable reductions in the loadings of nutrients to open waters and coastal areas have not lead to improvements. Similar trends were observed in 2006 and 2007. Air and sea temperatures were generally above average during 2008, without any extremely hot months and consequently, the year was one of the 3 hottest years registered at all. Average sea water temperature in the inner Danish waters has increased more than 1° C during the last 40 years. There was no improvement in the oxygen conditions probably as a result of the increased water temperatures, which lead to increased respiration and less oxygen content in the water. The nationwide status of the Danish marine environment can be summarised in the following points:
· Temperatures were higher than average in all months, but at the end of the year, sea water temperatures were relatively lower compared to recent years, only 0-0.5º C above average.
· Sea temperatures have increased more than 1º C during the last 40 years.
· Freshwater run-off varies considerably between years and in 2008, it was close to the average of 1997-2007.
· When corrected for variation in freshwater run-off, the total nitrogen and phosphorus loads in Denmark have dropped 47% and 69%, respectively from 1990 to 2008.
· The reduction in phosphorus loads happened especially during the first part of the 1990s mainly due to improved wastewater treatment (VMP I). It has lead to decreasing and stagnating phosphor concentrations in the marine environment.
· The reduction in nitrogen loads is primarily caused by reduced loadings of nitrogen from agricultural areas (VMP I and II) and improved wastewater treatment. The reduction has lead to a decreasing trend in nitrogen concentrations in the marine areas since 2002.
· The year 2008 was generally a normal year in terms of nutrient concentrations, although the all-time lowest nitrogen concentrations were observed during summer.
· There were clear indications of incoming water masses with high nutrient concentrations to Kattegat and the Great Belt from the Jutland coastal current during spring.
· Inorganic phosphorus and silicate concentrations have increased in bottom water in the inner Danish waters.
· The modelled transport of fresh water from the Baltic Sea out through the inner Danish waters is 47% above the climatological value and was the highest in the modelled period 2004-2008.
· In contrast to the fresh water transport, the modelled concentrations of phosphorous and nitrogen out through the inner Danish waters were close to mean averages for the period 2004-2008.
· Water clarity (Secchi depth) in open waters reached the lowest average in 2008 since the implementation of the national water quality directives. At the same time, the average chlorophyll concentration in the fjords was 3 µg l-1, which is the lowest recorded level so far and the total yearly production was average in both open water and in the fjords.
· The coinciding low water clarity and very low chlorophyll concentrations in the fjords are unusual. Water clarity must now be to a greater extent connected to factors other than chlorophyll containing autotrophic organisms. Resuspended material can play a role, but this parameter is not included in the monitoring program.
· The biomass of diatoms in 2008 was on average with 2007 and equal to the long-term average of 1989-2008 in open waters, while it was slightly lower than the long-term average in the fjords.
· Potentially toxic algae were only registered a few times in high concentrations.
· The dinoflagellate Alexandrium psudogonyaulax was observed for the first time in Limfjorden in concentrations up to 18,000 cells l-1.
· Oxygen deficiency in the inner Danish waters generally began later in the year compared to previous years. It had a shorter duration and was less widespread than in the period 2003-2006, partly because of regular events with heavy winds.
· The area impacted by severe oxygen deficiency in 2008 was larger than in 2007.
· Intense impacted areas in 2008 included the Southern Belt Sea, Aabenraa Fjord and Flensborg Fjord, where there were consistent critically low oxygen concentrations for 3 months and toxic hydrogen sulphide in the bottom water.
· The upper border of oxygen deficiency in the Bornholm deep was the highest (55 m) in the latest 5 years.
· During the period 1989-2008 the depth limit of eelgrass retreated to lower depths in the inner fjords. Generally, eelgrass covered a smaller part of the shallow areas (1-4 m) in the fjords.
· The total algal cover in deeper parts of selected stone reefs in Kattegat was significantly lower than the average for the period 1994-2001, which is in line with the low water clarity observed in open waters.
· The grazing of macroalgae by sea urchins is still a problem on many reefs in the Great Belt and it is possibly spreading to parts of Store Middelgrund in Kattegat.
· There is a continued deterioration of bottom fauna diversity in open sea areas and inner Danish waters since the mid 1990s and it is not caused by oxygen deficiency since species tolerant to oxygen deficiency are not dominating. Other reasons may include general less access to suitable food
· The dominating species of diving ducks in the inner Danish waters in 2008 were eider, common scooter and tufted duck.
· Long-tailed duck was primarily observed on Rønne Banke.
· Red-throated diver is the most common diver and it was registered mostly in Kattegat, especially between Læsø and Anholt and Ålborg Bugt.
· Eider is abundant in Danish waters all year, but most are found in winter in the western parts of the inner Danish waters. A decline in numbers which started in 2000 is apparently still continuing.
· Razorbill and common murre were primarily observed in Kattegat, north of Zealand, and in the deep northern parts and in the southern end of the Danish North Sea.
· Monitoring of marine mammals in the Danish waters focuses on harbour seal, grey seal and harbour porpoise.
· Harbour seal is the most common seal in Denmark and it has increased from 2,000 individuals in 1976 to 13,300 individuals in 2008 due to a hunting ban in 1977 and a formation of a series of no access reserves. A declining growth rate has been observed which may indicate the species is reaching its carrying capacity in Denmark.
· In February and March 2008, 76 and 65 grey seals were observed in Kattegat and Rødsand. Close to Christiansø near Bornholm up to 8 grey seals were observed daily in April-May. The grey seal is breeding in Denmark again after a hundred year break.
· Harbour porpoises in Danish waters have been counted in July 1994 and in July 2005. An alarming decline of 40% has been observed, probably due to several reasons among them by-catches.
· White-beaked dolphin, bottle-nosed dolphin and minke whale are regular visitors in Danish water, but very little is known on population sizes and development.
· Contamination of metals was found in 20-40% of sediment samples in 2008, where concentrations were found to be above background levels according to the OSPAR assessment criteria in regard to As, Ni, Zn, Pb, Cu and Cr.
· Contamination of heavy metals was comprised of Cd and Hg where 70% of the sediment samples had contents above background levels, particularly in the samples from the inner Danish waters.
· Contamination of Hg was present in almost all fish samples (85-95%) and 40% of mussel samples did not comply with the EU Hg environmental quality criteria, but values were within the food quality criteria.
· The amount of Cu in mussels led to several areas being assessed as markedly polluted according to international assessment criteria and in Karrebæk Fjord the food quality criterion for Pb was exceeded in sand mussels.
· Apart from metals, TBT and PAHs still present the biggest contamination problems.
· Despite the ban of TBT it is still ubiquitous in concentrations causing imposex and intersex in whelks in all Danish waters. Based on environmental criteria set by OSPAR, a general good status was only achieved in the North Sea and Skagerrak. In the inner Danish waters, levels were either ‘not satisfactory’ or ‘bad’ around certain polluted harbours and piers. However, a decreasing trend in concentrations has been observed, which indicates that conditions are improving.
· Certain PAHs were above ERL- and EAC-values in 22-30% of sediment samples and 10% of mussel samples.
· The brominated flame deterrent BDE-47 was measured in all mussels, and in close to 50% of sediment samples, but in all cases, values were close to the detection limit.
· Dioxins were present in almost all samples in very low amounts, which are not expected to be harmful.
Mussels were affected by biological effects from hazardous substances in approximately half of the investigated coastal areas, where eelpout and its fry also were worst impacted. There are indications of widespread endocrine disruptions in eelpout in Danish waters, but the causing substances are unknown.
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