MAP Technical Reports Series No. 106 UNEP

9.6 Environmental capacity
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According to the definition given by GESAMP Reports and Studies No. 30, the use of
the marine environment for waste disposal should be based on an assessment of the local
capacity to accommodate a rate of waste discharge, without unacceptable impacts on the
environment. The acceptability of the impact is a subjective judgement which should be reflected
in environmental standards set nationally or internationally. From a purely scientific point of view,
following again the GESAMP definition of marine pollution, any discharge which has no
deleterious effects on the important components of the ecosystem or on the various uses of the
marine environment., is acceptable.
Assessment of this capacity must take into account such physical processes as
dilution, dispersion, sedimentation and upwelling, as well as chemical, biological and
biochemical processes which lead to the degradation or removal from the impacted area of
eutrophicants, until they lose their potential for unacceptable impact.
The environmental capacity of an area for eutrophicants may be calculated, appropriate
models providing a preliminary assessment that can be progressively refined by the inclusion
of more parameters and variables and by experimentation.
9.7 Mathematical models
Mathematical models provide a means for synthesising available knowledge and for
testing control hypotheses.
The models should elucidate the most important factors affecting the ecosystem, and
the principle of parsimony should be advocated in order to reduce the large number of physical,
chemical and biological state variables to an essential and sufficient number compatible with the
questions to be answered.
A careful choice of space and time scales, boundaries and boundary conditions, should
be made in relation to the morphology and stratification of the area and the nature of the problem.
Models of eutrophication may be based on the following principles:
- conservation of mass, momentum and energy,
- process kinetics,
- stoichiometry.
See for example O'Kane et al. (1990), Betello and Bergamasco (1991), Rajar and
Certina (1991), Bragadin et al. (1992), Giovanardi and Tromellini (1992a), Guidorzi et al. (1992)
and O'Kane et al. (1992).
From these, a set of simultaneous non-linear differential equations is derived in terms
of the chosen state variables. "Process kinetics" provide some of the terms of the right hand
sides of the chemical and biological equations, for example, specific growth and death rates of
populations of plankton and bacteria. Laboratory and field experimentation is essential for the
precise specification of their dependence on forcing functions such as temperature and light.
When the model contains several subsystems interconnected by mass flows due, for example,
to ingestion and excretion, the stoichiometric conversion factors must also be determined.