Today, water pollution is considered to be one of the major ecological problems. In Slovenia and
the Mediterranean, mercury, among other pollutants, is present in high concentrations. One
of the ways to tackle the problem of water pollution is to use mathematical models that can
help in determining the level of pollution and the possible ways of sanitation. The PCFLOW3D
model is a 3D baroclinic mathematical model, which enables us to model hydrodynamic and
some environmental variables in real time. In the dissertation, the PCFLOW3D model was upgraded
with two conceptual pelagic models for the lower trophic level, with a conceptual benthic
model of organic matter mineralization in sediments, with an empirical wave model for the Gulf
of Trieste and with empirical models for scalar fields of certain environmental variables and of
the concentrations of mercury species in the Mediterranean region. The two lower trophic level
models were based primarily on Crispi et al. (2002) and Fennel et al. (2006). The empirical
models were generated using two artificial intelligence tools, namely model trees (Weka software)
and the ANFIS combination of fuzzy systems and neural networks (Matlab Fuzzy Logic Toolbox
software).
With the upgraded PCFLOW3D model it is possible to quantitatively model the concentration
of phosphates, nitrates, ammonium, dissolved oxygen, zooplankton, chlorophyll-a and two size
classes of phytoplankton and detritus. Among the processes in the water column it takes into
account the mineralization of detritus, nitrification, aggregation of smaller organic particles into
larger ones and the exchange of oxygen between water and atmosphere. The benthic model is
designed to determine the impact of aerobic mineralization, nitrification, and denitrification in
sediments on the concentration of environmental variables in the water column. The combined
benthic-pelagic model enables us to simulate the biogeochemical cycling of the listed variables in
open oceans, on continental margins and in continental waters, and, with only little additional
upgrade, it can be used to model the carbon cycle or the cycle of other important elements or
complexes.
The empirical wave model for the Gulf of Trieste forecasts average and peak wave period, average
and maximum wave height, mean direction of wave propagation and spread at peak period.
The input variables are: past values of wind speed and direction, fetch, speed, and direction of
currents in the top water layer; from the meteorological forecast of the input variables waves
can be forecasted even 72 hours ahead. The results of modelling are comparable with those of
physical wind-wave models, if used in near shore sites with complex hydrodynamic and meteorological
conditions; above all the forecast of wave height can be used well with r t 0.95. In
future, the model can be used to quantify the impact of waves on the resuspension of sediments
and the consecutive change in concentration of mercury species in the water column of the Gulf
of Trieste.
Empirical models for scalar fields of conductivity, transmission and dissolved oxygen concentration
in the Mediterranean Sea are very well correlated with measurements (r t 1.0). These
models can be used for a more accurate determination of concentrations of mercury species in the
water column which depends on them. The empirical models for scalar fields of total, elementary,
reactive, monomethyl and dimethyl mercury in the Mediterranean Sea are estimated as worse,
but from the structure of the model trees it can be concluded that the concentration of mercury
species in the Mediterranean Sea is most influenced by the concentration of dissolved oxygen,
the concentration of organic matter and light intensity. In future, similar empirical models for
the determination of mercury species concentration in water compartments can be generated
with other artificial intelligence tools, among which the methods which combine induction and
deduction seem most suitable. The combination of such models and the benthic-pelagic conceptual
PCFLOW3D model can be used to determine the scalar fields of mercury species in the
Mediterranean Sea or in other water compartments with similar pollution problems.
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