Page 212 - DCAP601_SIMULATION_AND_MODELING

Simulation and Modelling

Notes
Figure 12.3: Two versions of Anderson’ model of the eutrophication of a lake
(Anderson 1973); left: a model of a lake subject to simulation experiments, right:
a model of the lake and its (agri-) cultural environment

The difference between the two approaches is twofold:
1. In the original approach Anderson took a formal model of the physical, chemical and
biological processes running in a lake to simulate what could happen if these processes
were disturbed by external influences imposed on the model by the simulating
experimenter — whereas the extended model embeds the model of a lake into its social,
political and economic environment and models influences external to the lake as internal
to the model, thus taking into account that the lake and its socioeconomic environment
interact and are interdependent.
2. The original approach starts from physical, chemical and biological theory providing the
equations between the main variables describing the lake and generates quantitative
simulation results (predictions) which might be compared to further observation data and
help improve (fine tune) the theory of the biochemical processes occurring in a lake —
whereas the extended model takes the behaviour of the lake for granted and adds a
number of assumptions about the behaviour and actions of a number of human actors
which are (or at least could have been) based on everyday observation and discussions
with stakeholders, and these assumptions are not aimed at generating quantitative
predictions about the effect of the tax rate imposed on artificial fertilisers on the oxygen
concentration in the lake, but only in qualitative predictions answering the question
under which tax regime and under which additional measures taken by government and
other neighbours of the lake its eutrophication could or could not be avoided.
Both approaches would serve as explanatory models: the restricted model would explain how
and why under certain external or internal circumstances a lake would be eutrophicated and
suffocate and what was the physical and biochemical mechanism behind the processes leading
to total consumption of oxygen at the ground of the lake —and it would at the same time
recommend countermeasures and allow for an estimation for their potential success; and the
extended model would explain under which conditions such countermeasures would be taken
by the population living around the lake and what incentives one part of the population would
have to promise another part of the population to take the necessary countermeasures.

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