Marine områder - Status over miljøtilstanden i 1998 - Faglig rapport ...

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long-lasting and intense oxygen depletion due to persistent stratification.
The biomass of phytoplankton in 1998 was generally low. The relatively
higher rainfall observed in 1998, especially compared with
1996 and 1997, did not give an increase in phytoplankton biomass.
The windy summer, providing the energy needed for mixing of the
water column, probably resulted in a greater grazing activity from
bottom living filtrators in shallow waters.
Macroalgae depth limits in the Kattegat were smaller in 1998 than in
the two preceding dry years, and the depth limits for eelgrass followed
a similar pattern. Attached vegetation is the most sensitive
parameter for monitoring light conditions for the benthic vegetation.
Bottom fauna biomass was generally low during 1998. To a large degree
this has occurred due to a low food level in the dry years of
1996-1997, or the natural oscillations of populations. Populations in
the open waters peaked in the beginning of the 1980s and again in
the mid 90s, however, the reasons cannot be determined. It is expected
that the production relationship predicted for bottom fauna
will be reflected in an increase in biomass in 1999.
This is the first time that heavy metals and contaminants are reported
as part of the national monitoring. It is therefore not possible to talk
about developments in time, but only about concentrations and effects.
The concentration of PAH's and heavy metals in most areas are
at levels that are typically found in the marine environment, although
locally higher concentrations can be observed. PCB occurs in
concentrations where one cannot rule out that there will be environmental
effects as there are a few areas with high concentrations. TBT
is found at high concentrations at all stations and there is a decided
ecological effect. Hormone disturbances in the form of imposex and
intersex were widespread in females of different snail species and
can be related to the TBT-concentration.
The tendency of a general positive development for the marine environment
should be seen in the background of the very serious situation
in the 1980s that resulted in formation of the Action Plan on the
Aquatic Environment. In 1998 there are still serious problems with
oxygen depletion, macrovegetation coverage is still smaller than expected,
and there is too high concentration of nutrients and chlorophyll.
Rainfall in 1998 was over normal, but the negative effects of
this was compensated for by a windy summer. In years with normal
or higher than average rainfall and warm, quiet summer weather,
one may still expect serious environmental problems in the Danish
open waters as the load of N, both from land and the atmosphere is
too high. We can conclude the goals outlined for the Aquatic Environment
have not been fulfilled.