Modelling of Water Circulation and the Dynamics of Phytoplankton for the Analysis of Eutrophication
Environmental Impact Assessment Center of Finland (EIA ltd.)
Tekniikantie 21 B, 02150 Espoo, Finland
Systems Analysis Laboratory Research Reports A82 October 2001
The eutrophication and algal blooms are problems in many Finnish lakes and
sea areas. One possible way to approach the problem is mathematical
modelling. If the most important processes have been successfully modelled,
it is easy to calculate the effects of nutrient load changes. This thesis
presents experiences on developing and applying eutrophication models.
The pre-calculated flow fields are the most important input to the water
quality model, so the applications of the flow model are examined in two
papers. The results indicate that the flow model can produce typical flows
caused by wind. The simulations of the timing of upwelling were also
successful. The excessive vertical diffusion can cause problems in
eutrophication model applications.
The results of simulations indicate that the greenhouse effect will advance
and enlarge the spring bloom of phytoplankton. However, the average
phytoplankton biomass in the Gulf of Finland will be near current level,
defined in these scenarios by the available amount of nutrients almost
unchanged due to the insignificant changes in the external nutrient inputs.
The more significant nutrient load reductions from the major loading points
have a clearly decreasing effect on the total algal biomasses even in one
year long simulations. When the nitrogen fixing cyanobacteria was taken
into account in the simulation, the results indicated that the phosphorus
removal from St. Petersburg would decrease both average cyanobacteria and
other algae biomasses. The biomass of other algae might increase in the zone
where additional nitrogen is transported from the east. The Finnish national
agenda, which is nitrogen dominated, does not seem to be an effective way
to fight against accumulations of cyanobacteria. However, the total
phytoplankton biomass will decrease near the Finnish coast.
phytoplankton dynamics, hydrodynamics, load reductions, eutrophication,
nutrients, Gulf of Finland