(8
themselves be expressed in simple mathematical equations.
The consideration of biological processes in dispersion models have
also caused great problems, Almost every substance, after its 1ntro-
duction into the sea, becomes a constituent part of the complicated
food chain. Hereby, they are adsorbed to a different extent by the
different. flora and fauna within the food chain, retained in the or-
ganism, and again execreted. This cycle, to date, has not been eclari-
fied for every substance and for every species. For that reason, a
description of these processes in dispersion models can take place
quantitatively only approximately and only for few substances and
marine organisms.
Moreover, it must be taken into account that all processes can in-
teract. An example therefor are salinity differences in the sea,
which can change the circulation (density driven currents) and si-
multaneously the physical environment of the organisms.
Dispersion models require, as input parameter, quantitative data
concerning the quantities of substances which are Introduced via the
rivers and the atmosphere, The discharge of a certain substance can
be subject to strong varilations (daily, moönthly, yearly, irregular,
etc,)-.
For the transport via the rivers, there are a multiplicity of data,
however these are avallable only sporadically or only for individual
pollutants., In part, the data are faulty owing to the great varia-
tion of the input or because of the inaccuracy of measurement of the
monitoring equipment (especially in the case of low concentrations),
For the burden from the atmosphere (with regard to some heavy met-
als, a very important pollutant source for the shelf seas}) only in-
sufficient data are available, For that reason, unrealistic simu-
lations of concrete spreading processes are frequently caused by in-
correct "preliminary concentrations”.
The numerical simulation of spreading processes {is & relatively new
field in oceanography, Hitherto, only the physical processes, 1nso-
far as these were mathematically realizable, were taken into account
in numerical models. The representation of chemical and biological
processes in dispersion models, however, are still in the develop-
ment stage. The advantage of models is that, for better understand-
ing of the entire system, one can investigate processes independent
of one another. The results shown here are also founded upon such a
“part study”, in order to gain, in this manner, statements which are
important for a interpretation and for the understanding of the en-
tire system.
In the transport and dispersion models of the IfMH and the DHI, at
present, only the eirculation and its fluctuatiöons resp. the current
field and a simulation of the turbulent mixzxing are taken into con-
eideration. Additional physical processes, such as sedimentation and
resuspension or spreading (as, for example, in the case of oil), the
effect of chemical reactions of the substances with the surroun-
ding water, and bilological processes are not considered. Exclusi-
vely, substances soluble in water were modelled which do not have an
