MAP Technical Reports Series No. 106 UNEP

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It is to be noted that aspects regarding the balance and breaking point between
beneficial and deleterious effects of eutrophication have not been well studied and documented
yet. Also, there is a lack of what could be termed a kind of benefit/damage scale that would
permit to evaluate in more objective terms the results of eutrophication.
2.7 Adriatic eutrophication in context of marine eutrophication worldwide
While the process of eutrophication in fresh waters has a history dating back to at least
the last century, widespread phenomena of eutrophication in the marine environment are more
recent, though both, fresh and marine eutrophication has been accelerated in the aftermath of
growing urbanization, intensification of agriculture, and industrial development generally following
World War II. Estuaries and Inland Seas and marine basins of but limited hydraulic exchange
have been first affected; yet, as has been reported by many authors (Gray and Paasche, 1984;
Rosenberg, 1985; Okaichi et al., 1987; GESAMP, 1988; Forsberg, 1991; Dederen, 1992;
Vollenweider, 1992, a.o.), coastal marine eutrophication has increased in many parts of the
world. Eutrophication in the Mediterranean (UNESCO, 1988; Stirn, 1993) makes part of this
worldwide evolution of the problem.
3. CAUSES AND MECHANISMS OF EUTROPHICATION
Causes and mechanisms of eutrophication have to be evaluated within the context of
our scientific knowledge about the structural and dynamic properties of aquatic ecosystems, and
the metabolic processes that govern them. Indeed, the process of eutrophication (as well as the
reverse process of oligotrophication) represents merely a particular aspect of the aquatic
ecosystem dynamics. To set the frame work about marine eutrophication, some of the relevant
facts about aquatic ecosystems are summarized in the following sections. Appendix I deals with
the methodological questions concerning the measurement of biomass in the aquatic
environment.
3.1 Structure and compartments of aquatic ecosystems
Aquatic ecosystems do not differ essentially from terrestrial ones as to structure. The
main difference between the two kinds of systems lies in the difficulty to allocate single aquatic
ecosystems to major geographic complexes, such as biomes, which is practically impossible.
This does not mean there is no geographic differentiation between aquatic ecosystems, but their
distinctive properties refer to the compositional make-up of secondary producers, rather than
to that of the primary producers. Many primary producer species, particularly phytoplankton, exist
over large geographic areas, while the natural area of many secondary producers is confined.
Simplifying the actual structural complexity of aquatic ecosystems, their components
belong, in principle, to one of the four interrelated main compartments:
a. Primary producers
b. Secondary producers
c. Mineralizer / Detritus
d. Nutrient pool
3.1.1 Primary producers
This compartment encompasses all those species called autotrophic that build their
biomass from inorganic nutrients and utilize for the synthesis of organic matter either radiant